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. Mani￾festly, the administration's routine process of reapplying the former rule was out of question in this case. After exam￾ination 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 handling￾qualities : 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. 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 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, 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 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 recom￾mendations 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 oper￾ational criterion, namely optimal operation. Moreover, this framework varies with time. A case in point is the noise problem. In view of the perfor￾mance 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 CON￾CORDE 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 differ￾ent 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 CON￾CORDE, Fig. 18 shows you that we are keeping to our objectives, namely to remain substantially within the en￾velope 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 airworthi￾ness 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)