D
Thrust Data for Performance Calculations TURBOJETS
Engine data, for several sample engines, are given for J-60, J52, JT9D3, JT8D-9, TF-30, TFE731-2, GE F404-400, FJ-44, Allison T-56 turboprop, and AVCO Lycoming I0-540 reciprocating engines. Although all these engines are somewhat dated and all have been superceded to give higher higher thrust thrust and better better fuel fuel consum consumpti ption, on, they they do repres represent ent typical typical perf perfor orma manc ncee tren trends ds.. As is clear clearly ly seen seen,, the the thru thrust st and and spec specifi ificc fuel fuel consumption (SFC) curves vary widely with speed and altitude. Thus, there are no general-duty expressions available that would permit carrying out easy and simple performance calculations. However, several approximate expressions, shown below, have been used with some engineering success. As a first-order rough approximation, engine thrust can be scaled linearly (for similar engines) and the fuel consumption can be decreased by at least 5 percent. The process consists of curve-fitting the thrust equation as a function of altitude, velocity, or both. Each engine may require its own special curve-fitting expression and may have to be accomplished in a piecewise fashion over the velocity and/or altitude range.
Jet Engines
For subsonic flight the simplest correlation is 267 Aircraft Performance. Maido Saarlas © 2007 John Wiley & Sons, Inc. ISBN: 978-0-470-04416-2
268
THRUST DATA FOR PERFORMANCE CALCULATIONS
Figure D.1
Pratt and Whitney J-60 Turbojet Engine
T T ref
where T ref may be taken as T , the sea level thrust value. A somewhat improved expression is o
Figure D.2
AVCO Lycoming IO-540 Reciprocating Engine
(D.1)
TURBOJETS
Figure D.3
269
AVCO Lycoming IO-540 Reciprocating Engine
T T ref
n
(D.2)
which is often written as T T
h 36,089 ft
h 36,089 ft
n
o
A better correlation, but more cumbersome to curve fit and to use, is T T
(A
BV 2)
(D.3)
o
The advantage of Eq. D.3 lies in taking into account the realistic thrust variation with velocity. Usually this is not very significant at higher altitudes and velocities but may be 10 percent or more during
270
THRUST DATA FOR PERFORMANCE CALCULATIONS
Figure D.4
Pratt and Whitney TF-30 Turbofan Engine
the take-off portion of flight (see TF-30 and JT9D data). At higher speeds, another correlation that has been used is T T
(1
cM )
(D.4)
o
where, typically, .25 c .5. Specific fuel consumption varies with both altitude and velocity and defies generalization with both of those parameters. It has been found that the velocity effect can be correlated for some engines, very approximately, by TSFC 1 TSFC ref
.5M
(D.5)
TURBOJETS
Figure D.5
271
Williams / Rolls FJ-44 Turbofan Engine
Reciprocating Engines
Reciprocating engines admit more generalizations:
•
•
BHP is independent of velocity V . SFC tends to be independent of both velocity and altitude.
For engine brake horsepower, the commonly accepted altitude variation is
272
THRUST DATA FOR PERFORMANCE CALCULATIONS
Figure D.6 Garrett TFE-731-2 Turbofan Engine
BHP BHPo
1.132 .132
(D.6)
where subscript o refers to the sea-level value. For supercharged engines, it is assumed that BHP remains constant to at least 25,000 ft altitude. Correlations used for higher altitude supercharged engines are: BHP BHPo
.765
h
36,089 ft
1.331 , h
36,089 ft
,
(D.7)
TURBOJETS
Figure D.7 GE F404-400 Installed Performance
273
274
THRUST DATA FOR PERFORMANCE CALCULATIONS
Figure D.8
Pratt and Whitney JT8D-9 Turbofan Engine
Figure D.9
Pratt and Whitney JT9D-3 Turbofan Engine
TURBOJETS
Figure D.10
Figure D.11
Pratt and Whitney J52 Turbojet Engine
Allison T-56-A Turboprop Engine, Horsepower
275
276
THRUST DATA FOR PERFORMANCE CALCULATIONS
Figure D.12
Figure D.13
Allison T-56-A Turboprop Engine, Thrust
Allison T-56-A Turboprop Engine, Specific Fuel Consumption
