ROLLS-ROYCe LyMPUS total air flow as turbofan B since both ERGN MACH-2.O DERNATIVE ENGNES engines would have almost the same weight x/O of intake,nozzles etc and drag and,poten- tially the same take-off noise. Figure 11 shows thrust and sfc of engine D compared with engine B as datum.Both engines have nearly the same thrust and sfc.If mixing is deleted from engine D the thrust will fall and sfc rise by some 210 g 4 as shown.Engine D,unmixed,is now scaled down to the same flow as engine B, and,as shown,the thrust falls by the same amount (at constant sfc).Duct burning is now added to the scaled down engine D,to restore the thrust,If the duct burner MACH 2.0 SA+5℃ STRATOSPHERE Fig 9.Gross Weight Community Noise,Fixed Mission Range/Variations in Payload 2驰 8 SFC RELATIVE e TO ENGINE ' DESISN MACH.2O 绿 XICOO o SDEKT BHRNINS EFFICIENCY Z· O5RBAD【MwhM2s -BHRN TO RESTORE THRLEST FOR WEIGHT 1地 9 4500 NM 饼 00%DIET BHRNING EPFICIENCY 3 SL正7 SAME FLOW AS P上2xW6 u2e@创 3a THRUST RELATIVE TO ENGINE 'B' r Fig 1l. Comparison of Duct Burning Turbofan with Dry Mixed Turbofan at Same SMMATED NOISE IO EPNdg ITERVALS Total Airflow efficiency,including profile losses,is 100%the sfc will fall slightly and rise Fig 10. Gross Weight Community Noise again,When the thrust of engine B is Fixed Payload/Variations in Mission reached it will be seen that the sfc is 8 Range above engine B.If a typical current duct burner efficiency of 85%is achieved the Reference 5 also shows a linear vari- sfc at datum thrust is shown to be nearly ation of DOC and TOC with design gross 16%above the engine B datum. weight,for a given range and payload. Cost estimation is the subject of a further The 2/3 scaled engine D with duct burn- ICAO study,and this subject will not be ing and the dry mixed turbofan B may,at pursued further in this paper,except to the same thrust level,be scaled up or down note that the viability of the aircraft is equally to meet a given thrust level. reflected by the take-off gross weight for a given mission. The same aircraft model used to compare the dry engine family,may be used to com- Included in Reference 5 is a list of the pare the duct burning engine with the dry sensitivities of gross weight,noise and turbofan.Table 5 compares the duct burn- costs to changes in component assumptions, ing engine sfc at the four flight conditions from which the risks involved in not meet- used for the mission fuel evaluation with ing design targets can be assessed. the dry turbofan for 100%and 85%duct burner efficiency,It will be noted that Duct Burning whilst the supersonic cruise and transonic acceleration sfc are higher for the duct The studies described so far have burning engine,the subsonic diversion and assumed no afterburning or duct burning at hold sfc are lower,due to the smaller core cruise,Duct burning will now be examined size and higher bypass ratio. as applied to turbofan D whose take-off bypass'ratio is 1.31,and a comparison will Table 6 gives the breakdown of the power- be made with turbofan B (take-off bypass plant plus fuel weight comparison. The ratio 0,46).The most instructive com- duct burning engine at 100%burner parison is between turbofan B and turbo- efficiency is shown to have a powerplant fan D scaled down (by 2/3)to give the same plus fuel weight penalty of only 1.1%TOGW >.total air flow as turbofan B since both engines would have almost the same weight of intake, nozzles etc and drag and, poten￾tially the same take-off noise. Figure I1 shows thrust and sfc of engine D compared with engine B as datum. Both engines have nearly the same thrust and sfc. If mixing is deleted from engine D the thrust will fall and sfc rise by some 4% as shown. Engine D, unmixed, is now scaled down to the same flow as engine B, and, as shown, the thrust falls by the Same amount (at constant sfc). Duct burning is now added to the scaleddownengine D, to restore the thrust, If the duct burner Fig 9. Gross Weight - Community Noise,Fixed Mission Range/Variations in Payload SUMMATED NUS5 IO tP@,dB A'rEWAL5 Fig 10. Gross Weight - Community Noise * Fixed Payload/Variations in Mission Range Reference 5 also shows a linear vari￾ation of DOC and TCC with design gross weight, for a given range and payload. Cost estimation is the subj6ct of a further ICAO study, and this subject will not be pursued further in this paper, except to note that the viability of the aircraft is reflected by the take-off gross weight for a given mission. sensitivities of gross weight, noise and costs to changes in component assumptions, from which the risks involved in not meet￾ing design targets can be assessed. Included in Reference 5 is a list of the Duct Burning * The studies described so far have assumed no afterburning or duct burning at cruise. Duct burning will now be examined as applied to turbofan D whose take-off bypass'ratio is 1.31, and a comparison will be made with turbofan B (take-off bypass ratio 0.46). The most instructive com- parison is between turbofan B and turbo￾fan D scaled down (by 2/3) to give the same Fig 11. Comparison of Duct Burning Turbofan with Dry Mixed Turbofan at Same Total Airflow efficiency, including profile losses, is 100% the sfc will fall slightly and rise again. When the thrust of engine B is reached it will be seen that the sfc is 8% above engine B. If a typical current duct burner efficiency of 85% is achieved the sfc at datum thrust is shown to be nearly 16% above the engine B datum. The 2/3 scaled engine D with duct burn￾ing and the dry mixed turbofan B may, at the same thrust leve1,be scaled up or down equally to meet a given thrust level. The same aircraft model used to compare the dry engine family, may be used to com￾pare the duct burning engine with the dry turbofan. Table 5 compares the duct burn￾ing engine sfc at the four flight conditions used for the mission fuel evaluation with the dry turbofan for 100% and 85% duct burner efficiency. It will be noted that whilst the 'supersonic cruise and transonic acceleration sfc are higher for the'duct burning engine, the subsonic diversion and hold sfc are lower, due to the smaller core size and higher bypass ratio. Table 6 gives the breakdown of the power￾plant plus fuel weight comparison. The duct burning engine at 100% burner .' efficiency is shown to have a powerplant plus fuel weight penalty of~only 1.1% TCGW 7