Page 222 - The Jet Engine

Thrust distribution

across the exit area of the propelling nozzle by combining the gas loads on the individual
(pressure thrust). Algebraically, this force is engine locations.
) A.
expressed as (P-P 0
21. On engines that operate with a non-choked
Where A = Area of propelling nozzle in sq.in. nozzle, the (P-P 0 ) A function does not apply and the
P = Pressure in lb. per sq.in. thrust results only from the gas stream momentum
= Atmospheric pressure in lb. per sq.in.
P 0 change.
Therefore, assuming values of mass flow, pressure Inclined combustion chambers
and area to be the same as in the previous calcula- 22. In the previous example (Para. 14) the flow
tions i.e. through the combustion chamber is axial, however, if
the combustion chamber is inclined towards the axis
Area of propelling nozzle (A) = 332 sq.in.
Pressure (P) = 6 lb. per sq.in. of the engine, then the axial thrust will be less than
(gauge) for an axial flow chamber. This thrust can be obtained
Atmospheric Pressure (P) = 0 lb. per sq.in. by multiplying the sum of the outlet thrust by the
(gauge) cosine of the angle (see fig. 20-2). The
Mass flow (W) = 153 lb. per sec. Base
Hypotenuse
Velocity (v J ) = 1,917 ft. per sec. cosine = and for a given angle
is obtained by consulting a table of cosines. It should
The thrust
be emphasized that if the inlet and outlet are at
= P ( − P0 )⋅ A + WV J − 0 different angles to the engine axis, it is necessary to
g multiply the inlet and outlet thrusts separately by the
153 X , 1 917 cosine of their respective angles.
= 6 ( − ) 0 ⋅ 332 + − 0
32
AFTERBURNING
= 1,992 + 9,166
23. When the engine is fitted with an afterburner
= 11,158 lb., the same as previously calculated (Part 16), the gases passing through the exhaust

Fig. 20-2 A hypothetical combustion chamber showing values required for calculating thrust.

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