Burt Rutan's White Knight and SpaceShip One, Photo Courtesy of Scaled Composites
Thermodynamics and Propulsion

11.5 Trends in thermal and propulsive efficiency

Trends in thermal efficiency are shown in Figure 11.8. The trends are driven by increasing compression ratios and corresponding increases in turbine inlet temperature as shown in Figures 11.9 and 11.10. Whereas trends in propulsive efficiency are due to generally higher bypass ratio engines, as shown in Figure 11.11.

Figure 11.8: Trends in aircraft engine efficiency (after Pratt & Whitney).
Image fig3EtaTrends_web

Figure 11.9: Pressure ratio trends for commercial transport engines (Epstein, 1998)
Image fig3PRTrends_web

Figure 11.10: Trends in turbine inlet temperature (Koff, 1991)
Image fig3TITTrends_web

Figure 11.11: Trends in engine bypass ratio (Epstein, 1998)
Image fig3BPRTrends_web