Page 146 - Aeronautical Engineer Data Book

Principles of propulsion 121

λ 1.6
Dimensionless specific thrust parameter 1.2 λ = f(P /P ) η = f(P /P ) 0.3 Overall efficiency η 0

2
3
for α = 5
0
3
2
for α = 5
0.8
0.2
0.4
η = f(α)
0
for P /P = 10
3 2 0.1
1 3 7 11 15
Compressor pressure ratio P /P
3 2
2 4 6 8
/t
Cycle temperature ratio α = T 4 0
Fig. 8.5 Turbojet performance indicative design points
Table 8.1 Turbojet performance parameter groupings
Non-dimensional Uncorrected Corrected
group

Flight speed V 0 / t 0 V 0

Rpm N/ T N/
·
·
2
Air flow rate W a / T/D P W a / /
2
Thrust F/D P F/
·
·
2
Fuel flow rate W f J∆H c /D P T W f /
= T/T std = T/519 (T/288) = corrected temperature
= P/p std = P/14.7 (P/1.013
10 ) = corrected pressure
5
·
W f = fuel flow
8.2.2 Turbofan
Most large airliners and high subsonic trans­
port aircraft are powered by turbofan
engines. Typical commercial engine thrust
ratings range from 7000 lb (31 kN) to
90 000 lb (400 kN+) suitable for large aircraft
such as the Boeing 747. The turbofan is