VOL.7,NO.1,JAN.-FEB.1970 J.AIRCRAFT 3 32nd Wright Brothers Lecture Supersonic Air Transport-True Problems and Misconceptions P.SATRE Sud Aviation,Paris,France The transition from subsonie to supersonic transports will be the last opportunity of achiev- ing major time savings on long range fights for some time to come,as hypersonie transport will probably not be flying before a few decades.The state of the art has progressed far enough to enable designers to match supersonic airplane stage fuel and reserves requirements with acceptable operating weight empty and economic payload.A supersonic transport design program faces several major technical problems.Design features and solutions incorporated in the CONCORDE are discussed,in particular,the aerodynamic design compromise between high-speed and low-speed requirements.Kinetie heat problems and choice of materials are also reviewed.As far as reliability and safety are concerned,in trying to move forward,a more rational approach has been used as compared to subsonic airplanes, especially when it comes to certification regulations.Finally,in the area of operations,prob- lem matters are now well defined and the outlook is optimistic.Supersonic transports will cause new problems but they also have inherent advantages.In this area,certain problems have been somewhat exaggerated.On the whole,the supersonic transport looks promising. Introduction problems specific to the SST.First of all,however,it might be appropriate to consider these problems in relation to the HIS 14th of July is a double celebration as I have been invited by the AIAA to deliver the Wright Brothers general evolution of aeronauties or perhaps I should say of air transport. Memorial Lecture on the very day of our Bastille day.For One of the most practical yardsticks for measuring this me,this invitation is at once a great honor and a great plea- progress is the decrease in Direct Operating Costs (DOC). sure. I will refrain from going into the finer points of DOC defini- What tremendous changes have been wrought since 1903. tions.for we all know what is involved in broad terms.How, when Orville Wright made the first controlled flight!Aero- then,have the engineers managed to sbrink DOC's over the nautics,then a realm surrounded with an aura of mystery in years?They had two ways of doing this:to increase which moved only pioneers like the Wright Brothers,has capacity-and with it the gross weight-and to increase since spawned two of the world's most flourishing industries: flight speeds.In fact,we find that they have consistently the aviation industry and air transport.And for something applied both approaches concurrently. over ten years now,it has an equally prosperous junior: Figure I shows the evolution in transport aireraft speeds. astronautics. The gain in speed brings an attendant reduction in DOC's The intervening few decades have been marked with ad- as technological advances gradually allow this gain to be vances now taken for granted but which a little thought will show to be truly extraordinary.I do not propose to achieved at not too great a cost. This condition has indeed been fulfilled and we see from the relate these at length,but rather to talk to you about what I curve that flight speeds have steadily increased while,at the have been concerned with daily these last few years,namely same time,as shown in Fig.2,DOC's have tapered off- though how much of this is due to greater speed and how much to greater capacity is not readily apparent.(In B.2707 Fig.2,for comparison,DOC are re-estimated taking into account U.S.consumer prices variation). 1500 It would be a mistake to infer that the same trend in Concorde speed can be maintained for long.In fact,I am convinced Tu.144 that it cannot,and that the switch to supersonic transports 100 500 747 8 Dc 7c 8707120 60 0C8-30 940 195019601.97019801990 870x320 0c8:63877 Fig.I Cruise speed increase. Presented as Paper 69-759 at the AIAA Aircraft Design and 1950 1955 19601,9651970 Operations Meeting,July 14-16,1969,Los Angeles,Calif.;sub- mitted August 29,1969;revision received October 2,1969. Fig.2 Direct operating cost trend
VOL. 7, NO. 1, JAN.-FEB. 1970 J. AIRCRAFT 32nd Wright Brothers Lecture Supersonic Air Transport—True Problems and Misconceptions P. SATRE Sud Aviation, Paris, France The transition from subsonic to supersonic transports will be the last opportunity of achieving major time savings on long range flights for some time to come, as hypersonic transport will probably not be flying before a few decades. The state of the art has progressed far enough to enable designers to match supersonic airplane stage fuel and reserves requirements with acceptable operating weight empty and economic payload. A supersonic transport design program faces several major technical problems. Design features and solutions incorporated in the CONCORDE are discussed, in particular, the aerodynamic design compromise between high-speed and low-speed requirements. Kinetic heat problems and choice of materials are also reviewed. As far as reliability and safety are concerned, in trying to move forward, a more rational approach has been used as compared to subsonic airplanes, especially when it comes to certification regulations. Finally, in the area of operations, problem matters are now well defined and the outlook is optimistic. Supersonic transports will cause new problems but they also have inherent advantages. In this area, certain problems have been somewhat exaggerated. On the whole, the supersonic transport looks promising. Introduction T HIS 14th of July is a double celebration as I have been invited by the AIAA to deliver the Wright Brothers Memorial Lecture on the very day of our Bastille day. For me, this invitation is at once a great honor and a great pleasure. |fc What tremendous changes have been wrought since 1903, when Orville Wright made the first controlled flight! Aeronautics, then a realm surrounded with an aura of mystery in which moved only pioneers like the Wright Brothers, has since spawned two of the world's most flourishing industries: the aviation industry and air transport. And for something over ten years now, it has an equally prosperous junior: astronautics. The intervening few decades have been marked with advances now taken for granted but which a little thought will show to be truly extraordinary. I do not propose to relate these at length, but rather to talk to you about what I have been concerned with daily these last few years, namely Speed M.pH. 1,000 B-2707 ^mmm * Concorde Tu.144 1940 1950 1.960 1.970 1,980 Fig. 1 Cruise speed increase. 1,990 Presented as Paper 69-759 at the AIAA Aircraft Design and Operations Meeting, July 14-16, 1969, Los Angeles, Calif.; submitted August 29,1969; revision received October 2,1969. problems specific to the SST. First of all, however, it might be appropriate to consider these problems in relation to the general evolution of aeronautics or perhaps I should say of air transport. One of the most practical yardsticks for measuring this progress is the decrease in Direct Operating Costs (DOC). I will refrain from going into the finer points of DOC definitions, for we all know what is involved in broad terms. How, then, have the engineers managed to shrink DOC's over the years? They had two ways of doing this: to increase capacity—and with it the gross weight—and to increase flight speeds. In fact, we find that they have consistently applied both approaches concurrently. Figure 1 shows the evolution in transport aircraft speeds. The gain in speed brings an attendant reduction in DOC's as technological advances gradually allow this gain to be achieved at not too great a cost. This condition has indeed been fulfilled and we see from the curve that flight speeds have steadily increased while, at the same time, as shown in Fig. 2, DOC's have tapered off— though how much of this is due to greater speed and how much to greater capacity is not readily apparent. (In Fig. 2, for comparison, DOC are re-estimated taking into account U.S. consumer prices variation). It would be a mistake to infer that the same trend in speed can be maintained for long. In fact, I am convinced that it cannot, and that the switch to supersonic transports 1 60^5——— ———— \ 8-63 B 747 1,950 1955 1.960 1.965 1,970 Fig. 2 Direct operating cost trend
P.SATRE J.AIRCRAFT Table 1 Subsonic vs supersonic weight breakdown comparison Subsonic Pistons Subsonie Supersonic Fuel,including reserves, 38-40 47-49 Operating weight empty, 47-48 44-45 : Payload, 12-15 6-9 Subsonic Jets and the figure claims to be no more than a mere forecast for the 21st century Supersonic Jets It is still fairly easy to forecast flight speeds,but gross weight prediction is not so simple.Figure 5 shows their Hypersonic 01， history.In point of fact,any extrapolation must allow for 0 traffic trends and,as you know,much can depend on whether 0 6 Mach number the growth rate is taken as 8%or 15%(which are for all Fig.3 Transatlantie stage;block time vs cruise speed practical purposes the limit figures quoted in the forecasts). Summing up,then,the way seems fairly clear:increase the flight speed in step with technological progress and will prove to be the last big step forward in this respect for increase the gross weight as and when such inerease is war- ranted or demanded by traffic growth.These improvements many years to come. While we are about it,let us dispose of one misconception will be automatically reflected in the DOC figure.Two As shown in Fig.3,aireraft in the Mach 2 and Mach 2.7 things remain paramount,however,in any such evolution, namely:1)to improve safety and reliability and 2)to categories belong to the same family;the saving in time due take operational requirements into account,which is not to the increase in speed is 334 hr with the currently envi- sioned SST's,and these aircraft are no more different from to say that they can remain static and I say so most em- each other than two subsonic aircraft Aying at Mach 0.75 phatically. Given this fairly clear pattern,how do SST's shape up on and Mach 0.90,respectively.Only,by achieving Mach 5 or the eve of their entry into service?What are their true 6,may we expect to pass yet another truly significant mile- problems?And what are the misconceptions being en- stone.And to establish that this would be the ultimate tertained about them? stage,we need only remember that the average passenger must not be subjected to accelerations in excess of g,which sets a lower limit of approximately 1 hr for the transatlantic Performance crossing. Let us bear in mind that it is no doubt perfectly reasonable We might as well admit right away that,like all their to make a Mach 2-2.2 aircraft if it is built now,using light forerunners,SSTs will not give their best performance as alloy,or a Mach 2.5-2.7 aircraft if it is built a little later, soon as they go into service.Like all other aireraft,they using titanium.Yet the missions devolving upon these will begin in a modest way and improve with time.As you aireraft do not differ fundamentally.The stage times are were able to see from Fig.2 just now,the 707 had a DOC close to that of the DC 7.It has since diminished by 30%. about the same,and above all the thermal balance is con- trolled in the same way:by using fuel-conventional The pattern of evolution in SSTs can be expected to be fuel-as the heat sink,with no further precautions.This comparable,as we shall see presently. no longer applies in the case of a hypersonic aircraft,which How will the first SSTs compare,performancewise,with the current long-haul subsonic jets?Table I gives you some would have to use a different fuel or resort to some other idea of the payload vs takeoff weight eapability. cooling device,quite apart from the acceleration problem I just mentioned.In short,from Mach 3 upwards,the The figures given are no more than orders of magnitude difficulties add up very fast while the returns diminish.In but they speak for themselves:fuel consumed plus reserves fact,it appears that hypersonic aircraft will not be worthwhile are up by some 9%and this must be made good by a reduction until the day they can be justified by a sufficient traffic in empty weight and/or payload.But the payload cannot growth over stage lengths of 5000-10,000 miles.This would be allowed to drop below the indicated figures,for notwith- standing faster turnrounds and a greater potential (CON- produce the breakdown shown in Fig.4 (on which the log- CORDE,for example,is designed for some 14,000 trans- arithmic scale enables the respeetive traffic magnitudes to be more clearly portrayed).However,we are not there yet, atlantie flights as against 7000 for a subsonie aireraft),prof- itability would otherwise be impossible. We had therefore to gain 3%on the empty weight.You who are familiar with the problems involved in reducing AIR TRAFFIC aireraft empty weights,can appreciate the magnitude of this achievement. It must be realized that designing a supersonic airplane isn't quite like building a powered buggy. You all remember what the first automobiles looked like- -a motor mounted SUBSONIC JETS SUPERSONIC JETS Table 2 DOC breakdown Fuel Approx.30% Man-hours Crew HYPERSONIC Maintenance Approx.20% Depreciation Items affected by Insurance 100200 30010002000 50o05i688 aireraft and Financing Approx.50 Fig.4 Air traffic share breakdown including hypersonic spare prices Spares Tooling aireraft
P. SATRE J. AIRCRAFT Block Time . Hours I Table 1 Subsonic vs supersonic weight breakdown comparison Subsonic Pistons Subsonic Jets Supersonic Jets Hypersonic ^-LL'UL/' 0 12345 6 Mach number Fig. 3 Transatlantic stage; block time vs cruise speed. will prove to be the last big step forward in this respect for many years to come. While we are about it, let us dispose of one misconception. As shown in Fig. 3, aircraft in the Mach 2 and Mach 2.7 categories belong to the same family; the saving in time due to the increase in speed is 3^-4 hr with the currently envisioned SST's, and these aircraft are no more different from each other than two subsonic aircraft flying at Mach 0.75 and Mach 0.90, respectively. Only, by achieving Mach 5 or 6, may we expect to pass yet another truly significant milestone. And to establish that this would be the ultimate stage, we need only remember that the average passenger must not be subjected to accelerations in excess of ^g, which sets a lower limit of approximately 1 hr for the transatlantic crossing. Let us bear in mind that it is no doubt perfectly reasonable to make a Mach 2-2.2 aircraft if it is built now, using light alloy, or a Mach 2.5-2.7 aircraft if it is built a little later, using titanium. Yet the missions devolving upon these aircraft do not differ fundamentally. The stage times are about the same, and above all the thermal balance is controlled in the same way: by using fuel—conventional fuel—as the heat sink, with no further precautions. This no longer applies in the case of a hypersonic aircraft, which would have to use a different fuel or resort to some other cooling device, quite apart from the acceleration problem I just mentioned. In short, from Mach 3 upwards, the difficulties add up very fast while the returns diminish. In fact, it appears that hypersonic aircraft will not be worthwhile until the day they can be justified by a sufficient traffic growth over stage lengths of 5000-10,000 miles. This would produce the breakdown shown in Fig. 4 (on which the logarithmic scale enables the respective traffic magnitudes to be more clearly portrayed). However, we are not there yet, 200 Stage Length N.M 500O 100OO Subsonic Supersonic Fuel, including reserves, % Operating weight empty, % Payload, % 38-40 47-48 12-15 47-49 44-45 6-9 and the figure claims to be no more than a mere forecast for the 21st century. It is still fairly easy to forecast flight speeds, but gross weight prediction is not so simple. Figure 5 shows their history. In point of fact, any extrapolation must allow for traffic trends and, as you know, much can depend on whether the growth rate is taken as 8% or 15% (which are for all practical purposes the limit figures quoted in the forecasts). Summing up, then, the way seems fairly clear: increase the flight speed in step with technological progress and increase the gross weight as and when such increase is warranted or demanded by traffic growth. These improvements will be automatically reflected in the DOC figure. Two things remain paramount, however, in any such evolution, namely: 1) to improve safety and reliability and 2) to take operational requirements into account, which is not to say that they can remain static and I say so most emphatically. Given this fairly clear pattern, how do SST's shape up on the eve of their entry into service? What are their true problems? And what are the misconceptions being entertained about them? Performance We might as w r ell admit right away that, like all their forerunners, SSTs will not give their best performance as soon as they go into service. Like all other aircraft, they will begin in a modest way and improve with time. As you were able to see from Fig. 2 just now, the 707 had a DOC close to that of the DC 7. It has since diminished by 30%. The pattern of evolution in SSTs can be expected to be comparable, as we shall see presently. How will the first SSTs compare, performancewise, with the current long-haul subsonic jets? Table 1 gives you some idea of the payload vs takeoff weight capability. The figures given are no more than orders of magnitude but they speak for themselves: fuel consumed plus reserves are up by some 9% and this must be made good by a reduction in empty weight and/or payload. But the payload cannot be allowed to drop below the indicated figures, for notwithstanding faster turnrounds and a greater potential (CONCORDE, for example, is designed for some 14,000 transatlantic flights as against 7000 for a subsonic aircraft), profitability would otherwise be impossible. We had therefore to gain 3% on the empty weight. You who are familiar with the problems involved in reducing aircraft empty weights, can appreciate the magnitude of this achievement. It must be realized that designing a supersonic airplane isn't quite like building a powered buggy. You all remember what the first automobiles looked like—a motor mounted Table 2 DOC breakdown Fig. 4 Air traffic share breakdown including hypersonic aircraft. Fuel Man-hours Items affected by aircraft and spare prices Crew Maintenance Depreciation Insurance Financing Spares Tooling Approx. 30% Approx. 20% Approx. 50%
JAN.-FEB.1970 SUPERSONIC AIR TRANSPORT Table 3 Safety reserves according to TSS-OPS 5.7 M668w 1 Standard mission plus: 001 8747 Missed approach Climb,diversion and 30 min alternate hold at 15,000 ft 600 Enroute reserves (to be determined for each route;might be 3%of block fuel on North Atlantic) 500 2 One-engine failure: L1011 Destination or alternate must be reached with fuel avail- 400 DC 10 able for 30 min hold at 15,000 ft ·CONCORDE 3 Two-engine failure or pressurisation failure: 300 8707320 Any airport appropriate for landing must be reached 8707.1200 No holding 200 100 8314pC4 DC6B on a buggy chassis.Our job is altogether different.Building a supersonic airplane means not only a change in engines and 1940 1950 1960 1970 1980 geometry but also a shift in the state of the art. Indeed, the compromise must be a little more advanced in all respects Fig.5 Maximum takeoff weight trend. than on subsonic aircraft:refinements in design to save from 7.5-10.35%of the takeoff weight.A simple calculation weight,and more automation to alleviate the crew's work- shows that the DOC then drops from 1.3 to 0.94. load since the same functions must be performed in a shorter Assuming the same gains,the subsonic transport's time.Yet thesc advances must be made without com- DOC drops from I down to only 0.83.Now subsonic aireraft promising safety.On the contrary,parallel efforts are are not going to make any weight savings without a corre- made to increase it.Many of the solutions adopted stom sponding increase in the buying price,and,as for fuel con- from these three joint requirements. sumption,there has been far more time to experiment,so that But it so happens that we nourish great hopes from the there is certainly less latitude.Ultimately,as SST technology very hurdles which we find we must clear from the perfor- becomes more commonplace,so the supersonie transport's mance standpoint.For the fact that the weight of fuel is DOC will tend toward that of its subsonic counterpart. 5-8 times the payload also means that 1 saved on fuel DOC will tend toward that of its subsonie counterpart.And consumption means a 5-8%gain in payload. as I was just saying,it is those present narrow margins of ours In other words,the improvement in propulsion efficieney precisely,which give us broad seope for the future. will be far more effective than on subsonic aircraft.On I would like to revert for a moment to the question of the whole,we think that there is every reason to believe that reserves.The over-all design does not depend on them a SSTs will offer a greater development potential than subsonic great deal,but the way the plane is to be operated does to a aireraft. great extent.The quantities of fuel quoted previously This can be established cursorily by reference to the fig- inciude reserves amounting to about 9%of the takeoff ures.Our current estimates are that,given substantially weight.This is a maximum and should be compared with the same weight,the SST will have a DOC of 1.3,if we take the FAA's projected figure of about 8.5%and with 7%or so that of the subsonie transport as 1. of the Anglo-French regulations (TSS-OPS 5.7). To see whether it can be dropped to 1 or even below,let Table 3 provides a very concise summary of the TSS-OPS, us take a look at Table 2,which gives a D0C breakdown per from which you ean see that the requirement provides ample types of cost.The purchase price of the SST may come safety,which,of course,is as it should be. down:the techniques involved,which seem very sophis- In fact even the figure of 7%is arguable,for it hardly ticated at present,will become more conventional,hence seems right to apply worldwide a rule that was formulated less costly.A 10%saving on the buying price would mean primarily with New York and a few other major airports in a 5%saving on the DOC. mind.In fact,TSS-OPS 5.7 does provide for a number of But it is the weight breakdown which will provide the special cases. most signifieant gain.Let us now turn to Fig.6 which Let us nevertheless assume a figure of 7%.This means reproduees the weight breakdown in Table 1. that,under the TSS-OPS 5.7 regulation,airlines are left Assuming coustant prices,highly likely gains of 1%on the with 2%of the takeoff weight with which to optimize the OWE and 5%on fuel consumption would raise the payload flight regularity-payload compromise as they see fit.We be- Pierre Satrc Pierre Satre,born May 4,1909 at Grenoble,France,was educated in Marseille.He is a graduate of Ecole Polytechniqne (Class of 1929)and Ecole Nationale Superieure de l'Acronautique (Class of 1934).He started his career as an Aeronautics Engineer in varioux ministerial offices. In March 1941,he was appointed Chief Engineer at SNCASE-Toulouse (later to be known as Sud Aviation).In this capacity,he was in charge of a number of military and commercial aircraft,among them the Armagnae,Grognard,and Durandal,a Mach-2 fighter plane,and finally the well known Caravelle with rear engines. Appointed Technical Director of Sud Aviation in 1959,he is,specifically,Technical Director of the Concorde projeet. Mr.Satre is an officer of the Legion d'Honneur and Commander of the National Order of Merit and a member of AIAA:he has been awarded the British Silver Medal,as well as numerous other French and foreign medals. He is married and has five children
JAN.-FEB. 1970 SUPERSONIC AIR TRANSPORT Table 3 Safety reserves according to TSS-OPS 5.7 . Standard mission plus: Missed approach Climb, diversion and 30 min alternate hold at 15,000 ft Enroute reserves (to be determined for each route; might be 3% of block fuel on North Atlantic) I One-engine failure: Destination or alternate must be reached with fuel available for 30 min hold at 15,000 ft > Two-engine failure or pressurization failure: Any airport appropriate for landing must be reached No holding on a buggy chassis. Our job is altogether different. Building a supersonic airplane means not only a change in engines and geometry but also a shift in the state of the art. Indeed, the compromise must be a little more advanced in all respects than on subsonic aircraft: refinements in design to save weight, and more automation to alleviate the crew's workload since the same functions must be performed in a shorter time. Yet these advances must be made without compromising safety. On the contrary, parallel efforts are made to increase it. Many of the solutions adopted stem from these three joint requirements. But it so happens that we nourish great hopes from the very hurdles which we find we must clear from the performance standpoint. For the fact that the weight of fuel is 5-8 times the payload also means that 1% saved on fuel consumption means a 5-8% gain in payload. In other words, the improvement in propulsion efficiency will be far more effective than on subsonic aircraft. On the whole, we think that there is every reason to believe that SSTs will offer a greater development potential than subsonic aircraft. This can be established cursorily by reference to the figures. Our current estimates are that, given substantially the same weight, the SST will have a DOC of 1.3, if we take that of the subsonic transport as 1. To see whether it can be dropped to 1 or even below, let us take a look at Table 2, which gives a DOC breakdown per types of cost. The purchase price of the SST may come down: the techniques involved, which seem very sophisticated at present, will become more conventional, hence less costly. A 10% saving on the buying price would mean a 5% saving on the DOC. But it is the weight breakdown which will provide the most significant gain. Let us now turn to Fig. 6 which reproduces the weight breakdown in Table 1. Assuming constant prices, highly likely gains of 1% on the OWE and 5% on fuel consumption would raise the payload L 1011 m DC 1 * CONCORDE Fig. 5 Maximum takeolf weight trend. from 7.5-10.35% of the takeoff weight. A simple calculation shows that the DOC then drops from 1.3 to 0.94. Assuming the same gains, the subsonic transport's DOC drops from 1 down to only 0.83. Now subsonic aircraft are not going to make any weight savings without a corresponding increase in the buying price, and, as for fuel consumption, there has been far more time to experiment, so that there is certainly less latitude. Ultimately, as SST technology becomes more commonplace, so the supersonic transport's DOC will tend toward that of its subsonic counterpart. DOC will tend toward that of its subsonic counterpart. And as I was just saying, it is those present narrow margins of ours, precisely, which give us broad scope for the future. I would like to revert for a moment to the question of reserves. The over-all design does not depend on them a great deal, but the way the plane is to be operated does to a great extent. The quantities of fuel quoted previously include reserves amounting to about 9% of the takeoff weight. This is a maximum and should be compared with the FAA's projected figure of about 8.5% and with 7% or so of the Anglo-French regulations (TSS-OPS 5.7). Table 3 provides a very concise summary of the TSS-OPS, from which you can see that the requirement provides ample safety, which, of course, is as it should be. In fact even the figure of 7% is arguable, for it hardly seems right to apply worldwide a rule that was formulated primarily with New York arid a few other major airports in mind. In fact, TSS-OPS 5.7 does provide for a number of special cases. Let us nevertheless assume a figure of 7%. This means that, under the TSS-OPS 5.7 regulation, airlines are left with 2% of the takeoff weight with which to optimize the flight regularity-pay load compromise as they see fit. We bePierre Satre Pierre Satre, born May 4, 1909 at Grenoble, France, was educated in Marseille. He is a graduate of Ecole Poly technique (Class of 1929) and Ecole Nationale Superieure de I'Aeronautique (Class of 1934). He started his career as an Aeronautics Engineer in various ministerial offices. In March 1941, he was appointed Chief Engineer at SNCASE-Toulouse (later to be known as Sud Aviation). In this capacity, he was in charge of a number of military and commercial aircraft, among them the Armagnac, Grognard, and Durandal, a Mach-2 fighter plane, and finally the well known Caravelle with rear engines. Appointed Technical Director of Sud Aviation in 1959, he is, specifically, Technical Director of the Concorde project. Mr. Satre is an officer of the Legion d'Honneur and Commander of the National Order of Merit and a member of AIAA; he has been awarded the British Silver Medal, as well as numerous other French and foreign medals. He is married and has five children
P.SATRE J.AIRCRAFT 00C VORTICES (d] 10 CL PREDICTED +38 IN FLIGHT.BETWEEN M O AND M.0.8 Fig.6 Anticipated improvements. lieve this would be by far preferable to imposing statutory reserves not strictly necessary for safety,for,like the empty weight,the fuel weight must be determined even more pre- cisely than on subsonic aireraft beeause of its economic (d implications. 10 15 OF ATAC In short,the performance problem with SSTs is a genuine one but let us not add to it through excessive conservation Fig.8 Concorde lift curve and lift increase due to vortices. on reserves based on a misconception.Presently,when I go on to examine operating problems,I shall show why ean be reduced.3)It must possess excellent flying qual- ities throughout the flight envelope. it is no exaggeration to speak of excessive conservation, especially when reserves equal to or greater than those on Now although the third requirement can be met by making subsonic aireraft are being contemplated even through the the necessary refinements,the first two are in direct conflict. contingencies likely to be met on the journey are far fewer. The subsonic regime is of considerable importance in the And while we are on the subjeet of performance,let me turn over-all economies of the SST,as portrayed diagramatically right away to another misconception. in Table 5. The takeoff and landing speeds associated with delta You will observe that the requirements imposed for holdings wing aircraft are higher than with other aircraft.Some and diversions have a determining effect.This being so,the have inferred from this that landings in particular would attractions of variable geometry as a means of resolving present difficulties.At no time was this view shared by this contradiction are manifest,and I am not surprised that the chief pilots of our customer Airlines,who from the outset Boeing attempted a breakthrough along these lines.Their has posed the problem in stark and simple fashion:speed design study,the only one to have been taken far enough. is important,but less important than flving qualities.The was necessary to establish that the variable geometry solution CONCORDE's flight tests have shown how right they were: is not yet ripe.This is not to say that we shall not see back thanks to excellent flying qualities,landings at 160 kt can with us some day.But so far the 3 SST design projects be controlled without any trouble,and you will find confir- feature near-fixed geometry,I say "near"because the droop mation of this in Table 4. nose and the air intakes do feature variable geometry,which This leads me straight on to the origin of these relatively makes my task simpler.I shall simplify it still further by high takeoff and landing speeds,namely the aerodynamic confining myself to what I know well:the solutions adopted for the CONCORDE. compromise between high and low speeds Starting with a pure delta wing with 63.5 of sweepback, we set about looking for improvemnents,with special emphasis High-Speed/Low-Speed Aerodynamic on low-speed qualitics. Compromise A sharply swept apex (about 76),as shown in Fig.7, produced a triple advantage:1)a reduction in the thick- There are at least three requirements to be met in de- ness ratio at the wing root,plus an arrow planform,both signing an SST:1)The airplane must be configured for favorable factors for supersonic flight,2)a forward supersonic cruise fight.2)It must adapt readily to shift in aerodynamic center location,which in turn shifted subsonie fight,notably for takeoff,for landing,and also, for holdings prior to lauding until such time these holdings Table 4 Concorde 001--first fandings Touch down WING TIP:55 Approach Air Vertical Bank No.of speed, speed, speed, angle BASIC DELTA:63,5 fight kt kt m/sec 167 T60 1 0.9 APEX:76 2 171 165 0. 0.6 3 175 165 0.6 0.7 4 171 166 0.4 5 179 171 0.2 6 175 16 0.5 0 7 176 0.s 0 174 16S 0.8 0.4 165 10 0.2 Mean values 172 165 0.7 0.4 Fig.7 Wing plan form. Cinetheodolite failure
P. SATRE J. AIRCRAFT 100 CL Fig. 6 Anticipated improvements. lieve this would be by far preferable to imposing statutory reserves not strictly necessary for safety, for, like the empty weight, the fuel weight must be determined even more precisely than on subsonic aircraft because of its economic implications. In short, the performance problem with SSTs is a genuine one but let us not add to it through excessive conservation on reserves based on a misconception. Presently, when I go on to examine operating problems, I shall show why it is no exaggeration to speak of excessive conservation, especially when reserves equal to or greater than those on subsonic aircraft are being contemplated even through the contingencies likely to be met on the journey are far fewer. And while we are on the subject of performance, let me turn right away to another misconception. The takeoff and landing speeds associated with delta wing aircraft are higher than with other aircraft. Some have inferred from this that landings in particular would present difficulties. At no time was this view shared by the chief pilots of our customer Airlines, who from the outset has posed the problem in stark and simple fashion: speed is important, but less important than flying qualities. The CONCORDE'S flight tests have shown how right they were: thanks to excellent flying qualities, landings at 160 kt can be controlled without any trouble; and you will find confirmation of this in Table 4. This leads me straight on to the origin of these relatively high takeoff and landing speeds, namely the aerodynamic compromise between high and low speeds. High- Speed/Low- Speed Aerodynamic Compromise There are at least three requirements to be met in designing an SST: 1) The airplane must be configured for supersonic cruise flight. 2) It must adapt readily to subsonic flight, notably for takeoff, for landing, and also, for holdings prior to landing until such time these holdings WING TIP:55° ACL DUE TO VORTICES (X (d*} i PREDICTED IN FLIGHT,BETWEEN M=OANDM = 0.8 <X (d") Fig. 8 Concorde lift curve and lift increase due to vortices. can be reduced. 3) It must possess excellent flying qualities throughout the flight envelope. Now although the third requirement can be met by making the necessary refinements, the first two are in direct conflict. The subsonic regime is of considerable importance in the over-all economics of the SST, as portrayed diagramaticallv in Table 5. You will observe that the requirements imposed for holdings and diversions have a determining effect. This being so, the attractions of variable geometry as a means of resolving this contradiction are manifest, and I am not surprised that Boeing attempted a breakthrough along these lines. Their design study, the only one to have been taken far enough, was necessary to establish that the variable geometry solution is not yet ripe. This is not to say that we shall not see back with us some day. But so far the 3 SST design projects feature near-fixed geometry, I say "near" because the droop nose and the air intakes do feature variable geometry, which makes my task simpler. I shall simplify it still further by confining myself to what I know well: the solutions adopted for the CONCORDE. Starting with a pure delta wing with 63.5° of sweepback, we set about looking for improvements, with special emphasis on lowr -speed qualities. A sharply swept apex (about 76°), as shown in Fig. 7, produced a triple advantage: 1) a reduction in the thickness ratio at the wing root, plus an arrow planform, both favorable factors for supersonic flight, 2) a forward shift in aerodynamic center location, which in turn shifted Table 4 Concorde 001—first landings Touch down Fig. 7 Wing plan form. No. of flight 1 2 3 4 5 6 7 8 9 Mean values Approach speed, kt 167 171 175 171 179 175 176 174 165 172 Aiispeed, kt 160 168 165 166 171 169 172 168 150 165 Vertical speed, m/sec 1.1 0.5 0.6 . . . a a 0.5 0.8 0.8 . . . a 0.7 Bank angle d° 0.9 0.6 0.7 0.4 0.2 0 0 0.4 0.2 0.4 1 Cinetheodolite failure
JAN.-FEB.1970 SUPERSONIC AIR TRANSPORT 7 Table 5 Importance of subsonic regime SECONDARY AIR YALVE FIRE DOOR Route Paris-J.F.K.-3200 nm LAVER Block time Fnel consumption Subsonic AUXILIARY DOOR BAY COOLING Super- Sub- Super- Sub- DOOR sonic sonic sonie sonic Standard mission—lo RAMP ASSEMBLY PRIMARY NOZZLE holding (ideal case) 79% 21% 840 16% 15-min holding (average case) 74% 267% S1% 19% Supersonic 200-min diversion 30- SHOCK PATTERN FUSER NOZZLE min holding (eritical case under which Fig.9 Concorde power plant. requirements are set) 62% 38% 75元 25% the CONCORDE,the fact that the nacelles were grouped in pairs imposed a two-dimensional air intake.This is the heaviest loads into the most rigid structural area and schematized in Fig.9.I will spare you the deseription of facilitated accommodation of the landing gear,3)a these intakes and merely repeat that it is all very difficult more intense attached leading edge vortex resulting in greater to match up and optimize.I believe one of the hardest lift at low speeds. problems in designing a supersonic transport to be the con- Much work was also done on the shape of the wingtip, figuring of its propulsion system.This is indeed a thorny and the process of improving it aerodynamically has gone technical problem,for just now we saw the enormous economie on until just recently.It turned out that reducing the importance of fuel consumption. sweep to 559,by truncating the delta slightly,improved the On CONCORDE,so far,the system has functioned sat- lift drag ratio in subsonic flight against a very small tradeoff isfactorily in subsonic flight,and while it is difficult to dis- in the supersonic regime. sociate drag from thrust,we can say that the theoretical This ultimately led us to the ogee delta planfori shown figures have been borne out to within the measurement in the figure.It is more difficult to depict the wingtip error. As you know,I am not yet in a position to tell you camber and twist,though optimizing them is importaut. how the system will behave in supersonie flight. Finally,the dihedral must be chosen with due allowance for wing deformation in flight (which is significant despite the Thermal Problem and Choice of Materials small span:16 in.at the wingtip in cruise relative to static on the ground)and for the ground clearance. I am obviously still less in a position to talk to you about Optimally configured in this way,the wing has already fatigue in supersonic flight.In fact only the operational demonstrated its qualities in subsonie flight (Fig.8).This aircraft themselves will provide us with in flight fatigue confirmation fills us with confidence that our expectations data since our objective is a service life of 45-50,000 hr. for supersonic flight will be borne out and that the changes over half of which will be under high-temperature conditions. decided upon as between the prototype and the production The structural behavior will be investigated by fatigue aireraft will have the desired effect. tests on a full-scale structure which will be subjeeted to Studying the propulsion system on the ground is more mechanical and thermal loads,with suitable amplification difficult.First,the interactions between the intake,the coefficients to insure safety. engine and the nozzle are highly complex;second,none of Figure 10 represents the equivalent of a flight eyele:the our test facilities provided complete simulation of flight mechanical loads are applied twice,the thermal loads once, conditions.The margin of uncertainty is therefore greater. amplified by 15-20%.This procedure gives the speeimen Thus,making the final choice between major options is time to cool down. doubtless less simple.Although all 3 SST projects ulti- Our confidence in these tests is founded,in the main, mately settled for a fixed delta wing by the end of their firstly on the component tests and secondly on experiments design studies,the powerplants are of the direct flow type with the CARAVELLE,the results of which are summarized in two cases and of the bypass type in the third.The ad- in Table 6. vautages,from the drag and weight standpoint,offered by During these CARAVELLE fatigue tests,99 damages the direct-flow type made us decide in its favor,and we use were noted.Seven modifications were decided upon and a development of the British Olympus turbojet,the Olympus introduced,since which only 9 damages have been recorded 593. in service,even though many of the aireraft have now logged The problem of configuring the propulsion system for more than 20,000 hr (and some as many as 27,000-28,000 hr) supersonie/subsonic operation is not so much an engine problem as an air intake and nozzle problem.In the case of Thermal loads 1+151o202 Table 6 Caravelle structural fatigue test results (without landing gear) Number of cycles applied to specimen: 100.000 Number of damages during testing: 99 Number of modifications decided: Number of flight cycles completed: upt030,000 (0.5 cracks Same damages as during testing 0.3 fastener failures 9 (0.1 fretting corrosion New types of damage 0.2 cracks including one dne to stress corrosion Fig.10 Fatigue testing
JAN.-FEB. 1970 SUPERSONIC AIR TRANSPORT Table 5 Importance of subsonic regime SECONDARY AIR VALVE Route Paris-J.F.K.-3200 nm Fuel consumption SubBlock time Super- Sub- Supersonic sonic sonic sonic Standard mission—no holding (ideal case) 79% 15-min holding (average case) 74% 200-min diversion -f 30- min holding (critical case under which requirements are set) 62% 21% 84% 26% 81% 38% 75% 16% 19% the heaviest loads into the most rigid structural area and facilitated accommodation of the landing gear, 3) a more intense attached leading edge vortex resulting in greater lift at low speeds. Much work was also done on the shape of the wingtip, and the process of improving it aerodynamically has gone on until just recently. It turned out that reducing the sweep to 55°, by truncating the delta slightly, improved the lift drag ratio in subsonic flight against a very small tradeoff in the supersonic regime. This ultimately led us to the ogee delta planform shown in the figure. It is more difficult to depict the wingtip camber and twist, though optimizing them is important. Finally, the dihedral must be chosen with due allowance for wing deformation in flight (which is significant despite the small span: 16 in. at the wingtip in cruise relative to static on the ground) and for the ground clearance. Optimally configured in this way, the wing has already demonstrated its qualities in subsonic flight (Fig. 8). This confirmation fills us with confidence that our expectations for supersonic flight will be borne out and that the changes decided upon as between the prototype and the production aircraft will have the desired effect. Studying the propulsion system on the ground is more difficult. First, the interactions between the intake, the engine and the nozzle are highly complex; second, none of our test facilities provided complete simulation of flight conditions. The margin of uncertainty is therefore greater. Thus, making the final choice between major options is doubtless less simple. Although all 3 SST projects ultimately settled for a fixed delta wing by the end of their design studies, the powerplants are of the direct flow type in two cases and of the bypass type in the third. The advantages, from the drag and weight standpoint, offered by the direct-flow type made us decide in its favor, and we use a development of the British Olympus turbojet, the Olympus 593. The problem of configuring the propulsion system for supersonic/subsonic operation is not so much an engine problem as an air intake and nozzle problem. In the case of Table 6 Caravelle structural fatigue test results (without landing gear) Number of cycles applied to specimen: Number of damages during testing: Number of modifications decided: Number of flight cycles completed: Same damages as during testing New types of damage 100,000 99 7 up to 30,000 0.5 cracks "} 0.3 fastener failures /• 9 0.1 fretting corrosion/ 0.2 cracks including one due to stress corrosion 2 BOUNDARY^ LAYER BLEED Subsonic AUXILIARY DOOR BAY COOLING DOOR TERTIARY AIR DOORS RAMP ASSEMBLY PRIMARY NOZZLE A_____\ Supersonic SHOCK PATTERN DIFFUSER SECONDARY NOZZLE Fig. 9 Concorde power plant. the CONCORDE, the fact that the nacelles were grouped in pairs imposed a two-dimensional air intake. This is schematized in Fig. 9. I will spare you the description of these intakes and merely repeat that it is all very difficult to match up and optimize. I believe one of the hardest problems in designing a supersonic transport to be the configuring of its propulsion system. This is indeed a thorny technical problem, for just now we saw the enormous economic importance of fuel consumption. On CONCORDE, so far, the system has functioned satisfactorily in subsonic flight, and while it is difficult to dissociate drag from thrust, we can say that the theoretical figures have been borne out to within the measurement error. As you know, I am not yet in a position to tell you how the system will behave in supersonic flight. Thermal Problem and Choice of Materials I am obviously still less in a position to talk to you about fatigue in supersonic flight. In fact only the operational aircraft themselves will provide us with in flight fatigue data since our objective is a service life of 45-50,000 hr, over half of which will be under high-temperature conditions. The structural behavior will be investigated by fatigue tests on a full-scale structure which will be subjected to mechanical and thermal loads, with suitable amplification coefficients to insure safety. Figure 10 represents the equivalent of a flight cycle: the mechanical loads are applied twice, the thermal loads once, amplified by 15-20%. This procedure gives the specimen time to cool down. Our confidence in these tests is founded, in the main, firstly on the component tests and secondly on experiments with the CARAVELLE, the results of which are summarized in Table 6. During these CARAVELLE fatigue tests, 99 damages were noted. Seven modifications were decided upon and introduced, since which only 9 damages have been recorded in service, even though many of the aircraft have now logged more than 20,000 hr (and some as many as 27,000-28,000 hr) Fig. 10 Fatigue testing
P.SATRE J.AIRCRAFT E Table 7 Effeet of cold working on the creep strength of AU2GN 12 AU4G1￥2021 g:130c AU2GN兰2618 Drop in creep strength, Condition % Quenched and tempered 0 Quenched and stretched 1.5,tempered 16 0.4 AU2GN Quenched and stretched 6%,tempered 23 Quenched and stretched,tempered,stretched 1.5 40 0 10.000 20000 30.000 40.000 under 20 cyeles/hr approximately.This is schematized in Fig.15. Fig.1I Creep strain of AU4GI and AU2GN sheet metal I should like to add that,from the fatigue standpoint, specimen (ONERA results). testing of large structural clements bore out the structural solutions we adopted,in addition to the choice of the alloy out of the 30,000 hr of life,the test was designed to guarantee itself. initially.Based on the accumulated in-flight experience,the In short,we have developed satisfactory solutions with actual fatigue life will be much greater. AU2GN for most of the airframe,though it also includes Moreover,these damages occurred only on a limited steel-mainly for the landing gear-and titanium.I should mumber of aireraft (usually fewer than 10 and never more than like to repeat here that to put the question "titanium or no 20)out of more than 200 CARAVELLE in service,and titanium'is yet another misconception.Just what use is generally did so in the course of the first 10,000 flight hours. made of titanium depends primarily on the mission envisaged We consequently place great reliance on this over-all for the aireraft.I have already said that titanium was no test which enables appropriate preventive measures to be doubt necessary at Mach 2.5,but not at Mach 2.I would taken in the great majority of cases.Yet it is no more add that even it is not necessary,its use can be justified all than a check and an ultimate precaution,intended merely the same,though of course it would be introduced gradually. to bear out the struetural options we made.How did we Subsonic aircraft use titanium.So far the CONCORDE go about making these choices? has made seant use of it:about 1.5%of the struetural The fundamental criterion in the choice of a light alloy weight on the production aircraft,whose definition is in the was the resistance to creep.Figure 11 shows the good process of being frozen. strength characteristics of the selected alloy (AU2GN Yet in the prototype defined three years earlier,the figure similar to your 2618)and why a very well-known alloy like was only 0.5%,and there can be no doubt that it will rise AU4GI (similar to 2021)had to be discarded in spite of all further still.For instance,we are studying the possibility its qunhties:good mechanical properties and impervious- of introducing titanium rivets instead of the present monel ness to stress corrosion,and the fact that it is an alloy which rivets.If it is adopted,this modification alone will raise the is now fully mastered in the industrial sense proportion of titanium by 0.5%.If a somewhat higher speed Our studies have since led us to set a limit of 0.1%on were envisaged for a secoud-generation CONCORDE.the creep strain (Fig.12).It should be noted also that cold- leading edges could in turn be made of titanium.However working reduces the creep strength of AU2GN,as shown in I shall not dwell on this any louger as there are a few more Table 7.All conventional sheet-metal forming had therefore misconceptions I must dispel. to be ruled out on CONCORDE,which implied some revamp- ing of our workshops.In fact the CONCORDE was in- Improving Reliability and Safety strumental in bringing about another change as well:it was partly responsible for the advances made in numerically- Although we now think this problem has been fully mas- controlled machine-tools in Europe. tered,we must inelude it among what I have called the true Figure 13 shows a 20-ft panel being machined by such problems.For,I must say,to have applied existing rules methods,and Fig.14 a frame web machined from the solid, purely and simply would not have made any sense. where 335 lb are machined down to 25 lb. As I have already said,we are not building a powered Becuuse it is desigued for creep strength,the aireraft is buggy.Yet some of the things one reads or hears suggest over designed for creep/fatigue interaction at frequencies of that that is precisely the way the SST is thought of in some CREEP AT 150C X 1750c 0.05 CT88图CREEP AILURE车 15 0,01 WITHOUT CREE中CRACKS 90 TES 51 OUT PRIOR CREP 3 104 103 Fig.13 Numerically controlled machining of an upper Fig.12 Post-creep fatigue strength. wing skin panel
P. SATRE J. AIRCRAFT 0.8 30,000 40,000 TIME(HOURS) Fig. 11 Creep strain of AU4G1 and AU2GN sheet metal specimen (ONERA results). out of the 30,000 hr of life, the test was designed to guarantee initially. Based on the accumulated in-flight experience, the actual fatigue life will be much greater. Moreover, these damages occurred only on a limited number of aircraft (usually fewer than 10 and never more than 20) out of more than 200 CARAVELLE in service, and generally did so in the course of the first 10,000 flight hours. We consequently place great reliance on this over-all test which enables appropriate preventive measures to be taken in the great majority of cases. Yet it is no more than a check and an ultimate precaution, intended merely to bear out the structural options we made. How did we go about making these choices? The fundamental criterion in the choice of a light alloy was the resistance to creep. Figure 11 shows the good strength characteristics of the selected alloy (AU2GN, similar to your 2618) and why a very well-known alloy like AU4G1 (similar to 2021) had to be discarded in spite of all its qualities: good mechanical properties and imperviousness to stress corrosion, and the fact that it is an alloy which is now fully mastered in the industrial sense. Our studies have since led us to set a limit of 0.1% on creep strain (Fig. 12). It should be noted also that coldworking reduces the creep strength of AU2GN, as shown in Table 7. All conventional sheet-metal forming had therefore to be ruled out on CONCORDE, which implied some revamping of our workshops. In fact the CONCORDE was instrumental in bringing about another change as well: it was partly responsible for the advances made in numericallycontrolled machine-tools in Europe. Figure 13 shows a 20-ft panel being machined by such methods, and Fig. 14 a frame web machined from the solid, where 335 Ib are machined down to 25 Ib. Because it is designed for creep strength, the aircraft is over designed for creep/fatigue interaction at frequencies of Table 7 Effect of cold working on the creep strength of ____ AU2GN Drop in creep strength, Condition % Quenched and tempered 0 Quenched and stretched 1.5%, tempered 15 Quenched arid stretched 6%, tempered 23 Quenched and stretched, tempered, stretched 1.5% 40 under 20 cycles/hr approximately. This is schematized in Fig. 15. I should like to add that, from the fatigue standpoint, testing of large structural elements bore out the structural solutions we adopted, in addition to the choice of the alloy itself. In short, we have developed satisfactory solutions with AU2GN for most of the airframe, though it also includes steel—mainly for the landing gear—and titanium. I should like to repeat here that to put the question "titanium or no titanium" is yet another misconception. Just what use is made of titanium depends primarily on the mission envisaged for the aircraft. I have already said that titanium was no doubt necessary at Mach 2.5, but not at Mach 2. I would add that even it is not necessary, its use can be justified all the same, though of course it would be introduced gradually. Subsonic aircraft use titanium. So far the CONCORDE has made scant use of it: about 1.5% of the structural weight on the production aircraft, whose definition is in the process of being frozen. Yet in the prototype denned three years earlier, the figure was only 0.5%, and there can be no doubt that it will rise further still. For instance, we are studying the possibility of introducing titanium rivets instead of the present monel rivets. If it is adopted, this modification alone will raise the proportion of titanium by 0.5%. If a somewhat higher speed were envisaged for a second-generation CONCORDE, the leading edges could in turn be made of titanium. However, I shall not dwell on this any longer as there are a few more misconceptions I must dispel. Improving Reliability and Safety Although we now think this problem has been fully mastered, we must include it among what I have called the true problems. For, I must say, to have applied existing rules purely and simply would not have made any sense. As I have already said, we are not building a powered buggy. Yet some of the things one reads or hears suggest that that is precisely the way the SST is thought of in some 0,05 0,02 0,01, 0,05 EQUIVALENT HbURS AT 120°C CREEP AT 150°C X 17S°C « «- —— 4 —— 105 2. 10* ___ 1750C ___ 150 «»C O 4 _ ] CREEP AILURE! -* —— v 4 * ' > > WIT CREE •IOUT > CRACKS 9O TESTS WITHOUT PRIOR CREEP • Fig. 12 Post-creep fatigue strength. 2 OF CYCLES AT20°C Fig. 13 Numerically controlled machining of an upper wing skin panel
JAN.-FEB.1970 SUPERSONIC AIR TRANSPORT 9 Table 8 Systems safety assessment of number of channels Life of specimen System 1 (EG powered System 2 flight controls) (EG INS) MTBF 5000hr 2000hr Single failure prob- ability in 1 hr 2.104 5.10-4 10 Data Accident probability in pure fatigue the case of a total system failure Approx.1 10-5 Simplex system 2.10- 5.10-9 02101 10 606 Accident.probabilitics Duplex system 4.10-8 25.10-1 Fig.15 Fatigue-creep interaction at 150C. Triplex system 8.10-12 125.10-7 Preferred system Triplex system How can this be done in practice?Well,given a set of Duplex system 8.10 1 2.5.10-12 circumstances,one must determine what snags could arise and what their probability and consequences are going to be. Relatively harmless consequences can be accepted with a quarters.In other words,these people talk as if the solutions fairly high frequency.Serious consequences must have a used on current aircraft were adequate to resolve the prob- very low probability rating so as to remain consistent with lems of the supersonie transport.I must caution you against a loss probability of less than 1 in 10 million hr.In practice that notion. it is difficult,and usually outright impossible,to evaluate The CONCORDE projeet and the rules which were drawn probabilities of 10-8 with any accuracy.In point of fact, up for certification of the aireraft were reviewed concurrently the double failure coneept means that probabilities can be in order to achieve enhanced safety and reliability.From brought down to more manageable magnitudes:10-3 or the outset we set ourselves a goal,which emerges elearly 10-4per flight hour.Table 8 shows how. from Fig.16. Many systems have MTBFs of 1000-10,000 hr,and it is This graph,which is drawn from an ITA publication, precisely these MTBFs which must be checked.Having done gives a very clear idea of jet aireraft loss probabilitics and this and having approximately estimated the probability the way they evolve.In the casc of subsonic jets,it has of a disastrous accident linked to a failure in the system dropped from an initial 1 in 100,000 hr to 1 in 400,000 hr being checked (e.g.,1 or 10-2 or 10-),calculation will operation-a figure that has been maintained for several show whether the system must be duplicated or triplicated. years.With the CONCORDE,the objective we set our- Naturally the calculations in Table 8 are highly simplified. selves was one loss in 10 million hr.We shall not succeed But the figure does nevertheless illustrate my point well, from the very start,but we do hope to achieve a curve of the namely that,despite its relatively low MTBF,system 2 kind shown,cqualling from the start at least the current rate does not substantially improve safety unless something is for subsonic aircraft,and ultimately tending toward the done about system 1.Assuming only those two systems target rate. existed on the aireraft,the step to be taken would be to At this point,I would like to stress a fact which stands out improve the MTBF of system 1. in the figure,namely that absolute safety is a pipe dream In actual fact,sinee we cannot achieve better than 10- What is more,to reduce the hazards as much as possible on or 10-1 on many systems,it is quite illusory to seek values specific items is not the proper course cither,for the means beyond 10-or 10-12 on other systems,aud any efforts along at our disposal are limited,so that efforts must be direeted such lines will ncecssarily prove of no avail.It would be with discernment,where they are going to he most effective tantamount to digging valleys instcad of eropping the peaks For instance,many people consider that,for the price and in order to avoid colliding with mountains. Yet there are weight allowed for rafts on transoccanie fights,the aireraft pcople who still dig valleys.In my view,the inereasing could be equipped with more effective altimeter or anti- number and complexity of on-board systems,especially on collision warning systems,for example.In other words, SSTs,precludes this luxury there can be no question of eoncentrating on,for example In the case of the CONCORDE,the tests as a whole were the most reliable power flying control units or the most conducted along these lines:to obtain a degrec of safety con- reliable powerplant without bothering about the rest. The sistent with our goal.In the case of certification too,the aim is to have the safest and most reliable complete airplanc with the means at one's disposal.The development effort should therefore be directed to the less reliable systems,with H special emphasis on those affecting flight safety. 1/10000000 20 TOTAL NUMBER OF FLICHT HOURS MILLIONS Fig.14 Center web of frame 66. Fig.16 Trend in jet aireraft losses
JAN.-FEB. 1970 SUPERSONIC AIR TRANSPORT Table 8 Systems safety assessment of number of channels , Data MTBF System 1 (EG powered flight controls) 5000 hr System 2 (EG INS) 2000 hr Single failure probability in 1 hr 2.10~4 5. 1C)-4 Accident probability in the case of a total system failure Accident probabilities Simplex system Duplex system Triplex system Preferred system Approx. 1 2.10-4 4.10-8 8.10~12 Triplex system 8.10-12 H)-5 5.10-9 25.10-" 125. 10 ~ 17 Duplex system 2.5.10-12 quarters. In other words, these people talk as if the solutions used on current aircraft were adequate to resolve the problems of the supersonic transport. I must caution you against that notion. The CONCORDE project and the rules which were drawn up for certification of the aircraft were reviewed concurrently in order to achieve enhanced safety and reliability. From the outset we set ourselves a goal, which emerges clearly from Fig. 16. This graph, which is drawn from an IT A publication, gives a very clear idea of jet aircraft loss probabilities and the way they evolve. In the case of subsonic jets, it has dropped from an initial 1 in 100,000 hr to 1 in 400,000 hr operation—a figure that has been maintained for several years. With the CONCORDE, the objective we set ourselves was one loss in 10 million hr. We shall not succeed from the very start, but we do hope to achieve a curve of the kind shown, equalling from the start at least the current rate for subsonic aircraft, and ultimately tending toward the target rate. At this point, I would like to stress a fact which stands out in the figure, namely that absolute safety is a pipe dream. What is more, to reduce the hazards as much as possible on specific items is not the proper course cither, for the means at our disposal are limited, so that efforts must be directed with discernment, where they are going to be most effective. For instance, many people consider that, for the price and weight allowed for rafts on transoceanic flights, the aircraft could be equipped with more effective altimeter or anticollision warning systems, for example. In other words, there can be no question of concentrating on, for example, the most reliable power flying control units or the most reliable powerplant without bothering about the rest. The aim is to have the safest and most reliable complete airplane with the means at one's disposal. The development effort should therefore be directed to the less reliable systems, with special emphasis on those affecting flight safety. Life of specimen (hours) 103 pu cree > fatigue creep interaction pure fatigu Frequency (cycles/hour) 10-2 10'1 1 10 102 103 104 105 106 107 Fig. 15 Fatigue-creep interaction at 150°C. How can this be done in practice? Well, given a set of circumstances, one must determine what snags could arise and what their probability and consequences are going to be. Relatively harmless consequences can be accepted with a fairly high frequency. Serious consequences must have a very low probability rating so as to remain consistent with a loss probability of less than 1 in 10 million hr. In practice it is difficult, and usually outright impossible, to evaluate probabilities of 10~8 with any accuracy. In point of fact, the double failure concept means that probabilities can be brought down to more manageable magnitudes: 10~3 or 10~4 per flight hour. Table 8 shows how. Many systems have MTRFs of 1000-10,000 hr, and it is precisely these MTBFs which must be checked. Having done this and having approximately estimated the probability of a disastrous accident linked to a failure in the system being checked (e.g., 1 or 10~2 or 10~4 ), calculation will show whether the system must be duplicated or triplicated. Naturally the calculations in Table 8 are highly simplified. But the figure does nevertheless illustrate my point well, namely that, despite its relatively low MTBF, system 2 does not substantially improve safety unless something is done about system 1. Assuming only those two systems existed on the aircraft, the step to be taken would be to improve the MTBF of system 1. In actual fact, since we cannot achieve better than 10~9 or 10 ~ 10 on many systems, it is quite illusory to seek values beyond 10~n or 10~12 on other systems, and any efforts alongsuch lines will necessarily prove of no avail. It would be tantamount to digging valleys instead of cropping the peaks in order to avoid colliding with mountains. Yet there are people who still dig valleys. In my view, the increasing number and complexity of on-board systems, especially on SSTs, precludes this luxury. In the case of the CONCORDE, the tests as a whole were conducted along these lines: to obtain a degree of safety consistent with our goal. In the case of certification too, the 60-, 20,, 10 15 20 TOTAL NUMBER OF FLIGHT HOURS (MILLIONS ) Fig. 14 Center web of frame 66. Fig. 16 Trend in jet aircraft losses
10 P.SATRE J.AIRCRAFT (Fig.17).We are convineed that this characteristic will allow traffie compatibility problems to be resolved at best. UODISTANCE As for the rest,we have abided by the ICAO's recom- mendations concerning safety,ground facilities used in common with the subsonie aircraft (especially aerodromes) DISTANCE a minimum of special services,a noise level not exeeeding that 40 of subsonie aireraft,and compatibility with the all-round economics of the subsonic services.Yet rumors of all kinds 1000 often ill-founded,concerning the operational problems of SSTs 20 keep cropping up periodically not to say continuously.Let us take stock of the situation. 100 In the first place,in contrast to what generally happens in the case of technical problems,the solutions,here,are beyond the constructor's control.He is confined within a Fig.17 Effect of subsonic leg during climb. frame-work imposed by rules and recommendations,by common usage,and by what constitutes the ultimate oper- authorities laid down similar requircments.In fact,these ational criterion,namely optimal operation.Moreover, requirements pose particularly tricky problems where flying this framework varies with time. qualities are concerned because these qualities are not easily A case in point is the noise problem.In view of the perfor- quantified.The underlying principle,however,which is to mance penalty,the natural tendency would be to accept a concentrate equally on all items and not to be content with high noise level for the SST.But because we did not wish simply applying ready-made rules,remains the same. ours to be the noisiest,the limit we stipulated for the CON- There are two good illustrations of this:the choice of a CORDE is based on the figures already recorded with other safe initial climb speed Va and the problem of speed stability aireraft (Fig.18). in transonic flight.On conventional aireraft Va is taken as In the meantime,more restrictive regulations on noise 1.3 times the stalling speed.But delta wing aireraft like the control have been formulated.Of course,the noise problem CONCORDE have no stalling speed,which meant revising is undoubtedly a true problem,but it is an altogether differ- the concept of safety associated with the choice of Va.Mani- ent matter for the manufacturer if the requirements are festly,the administration's routine process of reapplying the laid down after the design has been defined instead of before. former rule was out of question in this case.After exam- Ten years are needed to create a really new airplane,and to ination of the problem,the Anglo-French authorities decided modify its fundamental characteristics during the latter to adopt a new datum speed,namely Vzrc (zero rate of years requires acrobatic feats that are better avoided. climb),and to impose,inter alia,the following requirements: As regards the noise problem in the case of the CON- 1)V:1.25 Vagc,2)Va permitting a normal acceleration of CORDE,Fig.18 shows you that we are keeping to our 1.6 g,and 3)Vs enabling the aireraft to be controlled according objectives,namely to remain substantially within the en- to the criteria of 'TSS Standard 5,which I shall not go into velope of existing aircraft,with a slight increase in side-line here. noise that is offset by an improvement in overflying and What is important is that these requirements collectively approach noise levels.But we would consider it abnormal insure attainment of the required degree of safety,which was to apply requirements set forth 3 or 4 yr after the airworthi- implicit in the former 30%margin over the stalling speed. ness certificate had been applied for,provided of course As to speed stability,of what use is it in the transonic that safety was not involved.And the same applies to all phases since the aireraft is accelerating continuously?Of no manufacturers.By the same token,the time needed to use at all.The true aim here is to assure safety by reducing adapt the ground facilities must be counted in years,and we the crew's workload as far as possible during this phase. Yet know that whatever needs new aircraft may have must static stability does not necessarily mean good handling be stated fairly early.Iu this connection,one cannot over qualities:the Spitfire is an excellent example of an unstable emphasize the importance of the working group on SSTs set aircraft which was easy to fly.Moreover,to add more up by the ICAO.The scheme could be generalized,and the black boxes is to add more possible sources of failure,and if coordinated planning coneept recently propounded by the they serve no useful purpose then the level of safety is reduced. ICAO,which seems excellent to us,could be implemented Only the fight tests can show what must be done.These through those channels.All we ask is that the motto examples show that the rules must be revised as soon as a should be“evolution,”not“revolution."Additional time change of any siguificance occurs.And this is what was done limits or sufficient advance notification would save much to make the CONCORDE a safe airplane. unnecessary effort and insure that problems are dealt with correctly. Operational Problems The first question is,must the SST bring an upheaval in air operations?In everything we did,at any rate,the primary concern was to insure that it should not.Ad- mittedly,it is not possible to comply strictly with ICAO resolution A 14-7.A necessary exception,for instance,is flight through the subsonic levels at supersonic speeds.Thus, the CONCORDE initiates transonie acceleration at 25,000 ft and reaches 42,000 ft at Mach 1.6 after covering 120 naut miles in 10 min.Clearly,this flight phase is not exactly compatible with subsonic aireraft in that traffic lane,par- ticularly if the supersonic jets are to be fed into the lane at 10-min intervals. The SSTs have their compensations,however.A delta wing aireraft will accept a level flight leg at around Mach 0.9 against a slight increase in block consumption [about 1ng707/320 Concorde estimotes DC 8.60 300 Ib for 100 naut miles in the case of the CONCORDE Fig.18 Community noise comparison (ISA sea level)
10 P. SATRE J. AIRCRAFT Aeioclc Fuel Ib Fig. 17 Effect of subsonic leg during climb. authorities laid down similar requirements. In fact, these requirements pose particularly tricky problems where flying qualities are concerned because these qualities are not easily quantified. The underlying principle, however, which is to concentrate equally on all items and not to be content with simply applying ready-made rules, remains the same. There are two good illustrations of this: the choice of a safe initial climb speed F3 and the problem of speed stability in transonic flight. On conventional aircraft ¥3 is taken as 1.3 times the stalling speed. But delta wing aircraft like the CONCORDE have no stalling speed, which meant revising the concept of safety associated with the choice of F3. Manifestly, the administration's routine process of reapplying the former rule was out of question in this case. After examination of the problem, the Anglo-French authorities decided to adopt a new datum speed, namely VZRC (zero rate of climb), and to impose, inter alia, the following requirements: 1) V3 > 1.25 VZRC, 2) V3 permitting a normal acceleration of 1.6 g, and 3) F3 enabling the aircraft to be controlled according to the criteria of TSS Standard 5, which I shall not go into here. What is important is that these requirements collectively insure attainment of the required degree of safety, which was implicit in the former 30% margin over the stalling speed. As to speed stability, of what use is it in the transonic phases since the aircraft is accelerating continuously? Of no use at all. The true aim here is to assure safety by reducing the crew's workload as far as possible during this phase. Yet static stability does not necessarily mean good handlingqualities : the Spitfire is an excellent example of an unstable aircraft which was easy to fly. Moreover, to add more black boxes is to add more possible sources of failure, and if they serve no useful purpose then the level of safety is reduced. Only the flight tests can show what must be done. These examples show that the rules must be revised as soon as a change of any significance occurs. And this is what was done to make the CONCORDE a safe airplane. Operational Problems The first question is, must the SST bring an upheaval in air operations? In everything we did, at any rate, the primary concern was to insure that it should not. Admittedly, it is not possible to comply strictly with ICAO resolution A 14-7. A necessary exception, for instance, is flight through the subsonic levels at supersonic speeds. Thus, the CONCORDE initiates transonic acceleration at 25,000 ft and reaches 42,000 ft at Mach 1.6 after covering 120 naut miles in 10 min. Clearly, this flight phase is not exactly compatible with subsonic aircraft in that traffic lane, particularly if the supersonic jets are to be fed into the lane at 10-min intervals. The SSTs have their compensations, however. A delta wing aircraft will accept a level flight leg at around Mach 0.9 against a slight increase in block consumption [about 300 Ib for 100 naut miles in the case of the CONCORDE (Fig. 17)]. We are convinced that this characteristic will allow traffic compatibility problems to be resolved at best. As for the rest, we have abided by the ICAO's recommendations concerning safety, ground facilities used in common with the subsonic aircraft (especially aerodromes), a minimum of special services, a noise level not exceeding that of subsonic aircraft, and compatibility with the all-round economics of the subsonic services. Yet rumors of all kinds, often ill-founded, concerning the operational problems of SSTs keep cropping up periodically not to say continuously. Let us take stock of the situation. In the first place, in contrast to what generally happens in the case of technical problems, the solutions, here, are beyond the constructor's control. He is confined within a frame-work imposed by rules and recommendations, by common usage, and by what constitutes the ultimate operational criterion, namely optimal operation. Moreover, this framework varies with time. A case in point is the noise problem. In view of the performance penalty, the natural tendency would be to accept a high noise level for the SST. But because we did not wish ours to be the noisiest, the limit we stipulated for the CONCORDE is based on the figures already recorded with other aircraft (Fig. 18). In the meantime, more restrictive regulations on noise control have been formulated. Of course, the noise problem is undoubtedly a true problem, but it is an altogether different matter for the manufacturer if the requirements are laid down after the design has been defined instead of before. Ten years are needed to create a really new airplane, and to modify its fundamental characteristics during the latter years requires acrobatic feats that are better avoided. As regards the noise problem in the case of the CONCORDE, Fig. 18 shows you that we are keeping to our objectives, namely to remain substantially within the envelope of existing aircraft, with a slight increase in side-line noise that is offset by an improvement in overflying and approach noise levels. But we would consider it abnormal to apply requirements set forth 3 or 4 yr after the airworthiness certificate had been applied for, provided of course that safety was not involved. And the same applies to all manufacturers. By the same token, the time needed to adapt the ground facilities must be counted in years, and we know that whatever needs new aircraft may have must be stated fairly early. In this connection, one cannot over emphasize the importance of the working group on SSTs set up by the ICAO. The scheme could be generalized, and the coordinated planning concept recently propounded by the ICAO, which seems excellent to us, could be implemented through those channels. All we ask is that the motto should be "evolution," not "revolution." Additional time limits or sufficient advance notification would save much unnecessary effort and insure that problems are dealt with correctly. ^^H^^BKM^Hii^M^-^ Fig. 18 Community noise comparison (ISA sea level)
JAN.-FEB.1970 SUPERSONIC AIR TRANSPORT Or.at any rate,most of them,for there is one exception to the rule.I refer to the sonie boom,about which reliable information will not become available until very late. At the moment we know that the general public is usually up in arms if it is exposed to sonie booms producing over- pressures of 10-20 psf,but that it does not seem to be put out even if it is exposed daily to a few bangs of about 2 psf level.SSTs will produce overpressures in the order of 2 psf.And knowing that overpressure is not the only factor which governs the effeets of sonic boom,what must the conclusion be?Frankly,we are surprised to find some people being quite emphatic already. Anyway,with a little patience we shall all be in a position to judge from factual evidence.Suffice it to say at this stage that studies like the joint NASA-FAA study,which seek to place the focusing zones in predetermined areas Fig.19 Sonie boom. where they will be the least nuisance.seem to us of great interest.For as Fig.19 shows.the limit could well lie within this zone,at any rate from the overpressure standpoint. fuel to be the really useful figure,i.e.,for covering 98-999 But we are seeking to minimize focusing effect by selection of contingeneies without encroaching on the other reserves. of an appropriate climb and acceleration profile. If you compare this figure with those put forward in the Fortunately,the other problems are easier to grasp if not draft regulations-which contemplate plate as much as to actually solve.Let us begin by disposing of 2 misconcep- 7% -you will understand why I was talking about excessive tions concerning ozone and radiation.Ozone is almost conservatism just now.2)Cruise climb is an interesting completely dissociated at the temperatures encouutered in proposition economically and could have proved a source of the air-conditioning circuit,and it is quite simple to install difficulty for interseetions.But a geographically fixed additional means if necessary.As for radiation,it could network of routes considerably simplifies the problem of be dangerous anywhere between twice and twenty times in intersections,and solutions compatible with cruise climb an 11-yr solar eycle,depending on estimates.During these are being studied.3)As for the question of separation, very rare emergencics,the SST would descend to a safe it is now an established fact based on millions of fight hours level,which would of course have to be higher than the that separations in cruise flight are extremely safe.There level uscd by subsouie aircraft,since flight times are shorter. was still some hesitation about reducing them;however, Or could it be that subsonic planes have a problem which new techniques,and inertial navigation in particular,should has been completely neglected so far.. bring about this reduction.But a fundamental parameter Let us climinate another problem which,though a verv in inertial navigation is the duration of the flight.Hence, real one,is not peculiar to the SST:that of transporting because of the shorter flight times,SSTs will enjoy even more the passengers from the aireraft to the center of the city. accurate navigation than subsonic aircraft.In point of Figure 20 shows why the supersonic passenger will be more fact,the NATSPG's experts and we manufaeturers have sensitive to loss of time.In any ease,any gains made here reached the same conclusion,namely that lateral separation will be beneficial to all.A reasonable target would be for for SSTs can certainly be 60 NA,possibly less.4)In sug- the times involved here not to exceed half the block time. gesting that uniformity in the matter of safety is a must, We are then left with the problems connected with accom- I shall be restating a concept already put forward here.Now, plishment of the mission:waiting for the departure,the the terminal areas of large airports are far less safe than the strict observance of timetables,air traffic control in the international routes.Consequently,that is where efforts departure zone,choice of the route and scparation in eruise must be concentrated.In addition,congestion of these fight,air traffie control in the arrival zonc,holdings,diver- zones is a cause of considerable financial losses for the oper- sions and the determination of reserves ators. And the problem will become cven more acute for I cannot dwell here at length on all these problems,which supersonic transports because the fight-hour costs more in have yet to be cleared up.I should merely like to make their case.It is well known and the caleulations presented a few points which relate to them in varying degrees,for a at the IATA conference in Lucerne,for example,have borne few serious and interesting indications are beginning to this out that the margin between complete saturation and emerge from studies which have been undertaken.1)The SST roughly normal traffic flow (with,say,an average holding is far less sensitive to weather conditions than subsonic time of a few minutes)is no more than 20% It must be aircraft.This means that it can be allocated a set gco- agreed to spread traffie so as to limit it to 20%below satura- graphical route without being penalizcd,namely the great tion and thus,preserve normal operating conditions.This circle path between the point of exit from the departure does not prevent progress by any means:if uew methods zone and the point of entry into the arrival zonc. This also can set back the suturation poiut,traffie can become denser, means that there is far less uncertainty about en route con- but in our view air transport is not suffieiently organized. sumption than with subsonic aireraft.The same safety The irrational situation existing in today's Air Transport is level can be maintained with a lower pcreentage of reserves to unique,and cannot be found in any other organized transport cover the route. Some airlines have cstimated 3%of block- system.There is much left to be done in this area for the benefit of all concerned.5)In the case of the SST,gains will be more substantial,as shown in Table 9.It has been Table 9 Protracted hold fuel penalty suggested in some quarters that priority be granted to the supersonie jets.In our view,an all embracing solution Boeing 707 Concorde would be by far preferable,and at the same time it would 30-min hold at (lb fuel 6000 15,500 alleviate the problem of reserves,which we manufacturers 10,000ft cannot resolve.In spite of our cfforts to improve their 200kt block fuel 5% 10% ocrformance in subsonic flight,SSTs will have reserves 30-min hold at (Ib fuel representing over 20%of their block fuel. 10,000ft 10,200 300kt block fuel 6.5% As for the unfortunate passenger,the less said the better. I have personally already done Montreal-New York in
JAN.-FEB. 1970 SUPERSONIC AIR TRANSPORT 11 Or, at any rate, most of them, for there is one exception to the rule. I refer to the sonic boom, about which reliable information will not become available until very late. At the moment we know that the general public is usually up in arms if it is exposed to sonic booms producing overpressures of 10-20 psf, but that it does not seem to be put out even if it is exposed daily to a few bangs of about 2 psf level. SSTs will produce overpressures in the order of 2 psf. And knowing that overpressure is not the only factor which governs the effects of sonic boom, what must the conclusion be? Frankly, we are surprised to find some people being quite emphatic already. Anyway, with a little patience we shall all be in a position to judge from factual evidence. Suffice it to say at this stage that studies like the joint NASA-FAA study, which seek to place the focusing zones in predetermined areas where they will be the least nuisance, seem to us of great interest. For as Fig. 19 shows, the limit could well lie within this zone, at any rate from the overpressure standpoint. But we are seeking to minimize focusing effect by selection of an appropriate climb and acceleration profile. Fortunately, the other problems are easier to grasp if not to actually solve. Let us begin by disposing of 2 misconceptions concerning ozone and radiation. Ozone is almost completely dissociated at the temperatures encountered in the air-conditioriing circuit, and it is quite simple to install additional means if necessary. As for radiation, it could be dangerous anywhere between twice and twenty times in an 11-yr solar cycle, depending on estimates. During these very rare emergencies, the SST would descend to a safe level, which would of course have to be higher than the level used by subsonic aircraft, since flight times are shorter. Or could it be that subsonic planes have a problem which has been completely neglected so far. . . ? Let us eliminate another problem which, though a very real one, is not peculiar to the SST: that of transporting the passengers from the aircraft to the center of the city. Figure 20 shows why the supersonic passenger will be more sensitive to loss of time. In any case, any gains made here will be beneficial to all. A reasonable target would be for the times involved here not to exceed half the block time. We are then left with the problems connected with accomplishment of the mission: waiting for the departure, the strict observance of timetables, air traffic control in the departure zone, choice of the route and separation in cruise flight, air traffic control in the arrival zone, holdings, diversions and the determination of reserves. I cannot dwell here at length on all these problems, which have yet to be cleared up. I should merely like to make a few points which relate to them in varying degrees, for a few serious and interesting indications are beginning to emerge from studies which have been undertaken. l)The SST is far less sensitive to weather conditions than subsonic aircraft. This means that it can be allocated a set geographical route without being penalized, namely the great circle path between the point of exit from the departure zone and the point of entry into the arrival zone. This also means that there is far less uncertainty about en route consumption than with subsonic aircraft. The same safety level can be maintained with a lower percentage of reserves to cover the route. Some airlines have estimated 3% of blockTable 9 Protracted hold fuel penalty Boeing 707 Concorde 30-min hold 10,000 ft 200 kt 30-min hold 10,000 ft 300 kt at fib fuel <? 1% block fuel at fib fuel < (% block fuel 6000 15,500 5% 10% 10,200 6.5% Fig. 19 Sonic boom. fuel to be the really useful figure, i.e., for covering 98-99% of contingencies without encroaching on the other reserves. If you compare this figure with those put forward in the draft regulations—which contemplate plate as much as 7%—you will understand why I was talking about excessive conservatism just now. 2) Cruise climb is an interesting proposition economically and could have proved a source of difficulty for intersections. But a geographically fixed network of routes considerably simplifies the problem of intersections, and solutions compatible with cruise climb are being studied. 3) As for the question of separation, it is now an established fact based on millions of flight hours that separations in cruise flight are extremely safe. There was still some hesitation about reducing them; however, new techniques, and inertia! navigation in particular, should bring about this reduction. But a fundamental parameter in inertial navigation is the duration of the flight. Hence, because of the shorter flight times, SSTs will enjoy even more accurate navigation than subsonic aircraft. In point of fact, the NATSPG's experts and we manufacturers have reached the same conclusion, namely that lateral separation for SSTs can certainly be 60 NM, possibly less. 4) In suggesting that uniformity in the matter of safety is a must, I shall be restating a concept already put forward here. NOWT , the terminal areas of large airports are far less safe than the international routes. Consequently, that is where efforts must be concentrated. In addition, congestion of these zones is a cause of considerable financial losses for the operators. And the problem will become even more acute for supersonic transports because the flight-hour costs more in their case. It is well known and the calculations presented at the I AT A conference in Lucerne, for example, have borne this out that the margin between complete saturation and roughly normal traffic flow (with, say, an average holdingtime of a few minutes) is no more than 20%. It must be agreed to spread traffic so as to limit it to 20% below saturation and thus, preserve normal operating conditions. This does not prevent progress by any means: if new methods can set back the saturation point, traffic can become denser, but in our view air transport is not sufficiently organized. The irrational situation existing in today's Air Transport is unique, and cannot be found in any other organized transport system. There is much left to be done in this area for the benefit of all concerned. 5) In the case of the SST, gains will be more substantial, as shown in Table 9. It has been suggested in some quarters that priority be granted to the supersonic jets. In our view^, an all embracing solution would be by far preferable, and at the same time it would alleviate the problem of reserves, which we manufacturers cannot resolve. In spite of our efforts to improve their performance in subsonic flight, SSTs will have reserves representing over 20% of their block fuel. As for the unfortunate passenger, the less said the better. I have personally already done Montreal-New York in
12 P.SATRE J.AIRCRAFT 为txtro journey time to the CONCORDE effort.The collaboration between the United States and Europe is already widespread in the field of engines and equipment;I hope it will soon exteud to the aircraft as well. 100 But it is not enough to keep building more advanced aireraft.Ground facilities,and airports in particular,must also keep pace.There can be no question of accepting as Supersonic permanent the holding constraints currently being imposed on aircraft at certain airports. 50 objective This is no easy problem,as we are well aware,but it must Subsonic absolutely be solved at all costs.We find it difficult not to compare the stringency of the noise level reduction proj- ects with the looseness of many of the projeets for dealing 0 Extra journey time(hours) with ground facilities and air traffic control.The former 0 2 are too severe,the latter not sufficiently so. Fig.20 Effect of extra journey time (transatlantic My personal conviction is that neither of these problems journey). can be resolved by a stroke of magic-no more the noise problem than the congestion problem.Both are going to require patient effort and a start has been made by all con- 3 hr and 45 min,i.e.,at a block speed of 80 mph,on an air- cerned.What are needed simply are directives and reason- craft which was supposed to fly at 500 mph. able time limits.The trait specific to SSTs in both eases is their marked sensitivity,which heightens the disadvantages Conclusion of whatever constraints are imposed. However,I feel confident that the efforts of aireraft manu- What must we conclude from this review of the SST's facturers and the authorities will converge toward reason- problems?In the first place,much still remains to be done able compromises that will result in a gradual improvement by the aireraft constructors.Our task is all the more fas of the present situation,yet remain compatible with poten- cinating because we are very far from having solved all our tial technical advances. problems.And in any event,the era of supersonic aviation And while we hesitate to become involved in problems is close at hand.As I have said,our current difficulties are which either siniply do not exist or have beeu incorreetly precisely those in which we also place greatest hope:if stated,we are ready to cooperate to the best of our ability to a loss of 1%fuel consumption means a 5%loss in payload, solve the two problems I just mentioned,or any real problem then a 1%gain on fuel consumption must mean a 5%gain for that matter. in payload. In the last few years,the misconceptions entertained about About the progress of aircraft,I gladly note,which my the SS'T have often been highlighted at the expense of its presence here today shows once more,the atmosphere of true problems.I thank you for the opportunity you offered cooperation existing in the western world.And I wish to me to review all these problems,and to express my confidence convey my thanks to the U.S.industry for its contribution in the brilliant future of supersonic transport
12 P. SATRE J. AIRCRAFT Fig. 20 Effect of extra journey time (transatlantic journey). 3 hr and 45 min, i.e., at a block speed of 80 mph, on an aircraft which was supposed to fly at 500 mph. Conclusion What must we conclude from this review of the SST's problems? In the first place, much still remains to be done by the aircraft constructors. Our task is all the more fascinating because we are very far from having solved all our problems. And in any event, the era of supersonic aviation is close at hand. As I have said, our current difficulties are precisely those in which we also place greatest hope: if a loss of 1% fuel consumption means a 5% loss in payload, then a 1% gain on fuel consumption must mean a 5% gain in payload. About the progress of aircraft, I gladly note, which my presence here today shows once more, the atmosphere of cooperation existing in the western world. And I wish to convey my thanks to the U.S. industry for its contribution to the CONCORDE effort, The collaboration between the United States and Europe is already widespread in the field of engines and equipment; I hope it will soon extend to the aircraft as well. But it is not enough to keep building more advanced aircraft. Ground facilities, and airports in particular, must also keep pace. There can be no question of accepting as permanent the holding constraints currently being imposed on aircraft at certain airports. This is no easy problem, as we are well aware, but it must absolutely be solved at all costs. We find it difficult not to compare the stringency of the noise level reduction projects with the looseness of many of the projects for dealing with ground facilities and air traffic control. The former are too severe, the latter not sufficiently so. My personal conviction is that neither of these problems can be resolved by a stroke of magic—no more the noise problem than the congestion problem. Both are going to require patient effort and a start has been made by all concerned. What are needed simply are directives and reasonable time limits. The trait specific to SSTs in both cases is their marked sensitivity, which heightens the disadvantages of whatever constraints are imposed. However, I feel confident that the efforts of aircraft manufacturers and the authorities will converge toward reasonable compromises that will result in a gradual improvement of the present situation, yet remain compatible with potential technical advances. And while we hesitate to become involved in problems which either simply do not exist or have been incorrectly stated, we are ready to cooperate to the best of our ability to solve the two problems I just mentioned, or any real problem for that matter. In the last few years, the misconceptions entertained about the SST have often been highlighted at the expense of its true problems. I thank you for the opportunity you offered me to review all these problems, and to express my confidence in the brilliant future of supersonic transport