AAWSAP DIRD, MHD Air Breathing Propulsion and Power for Aerospace Applications, November 2010

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UNCLASSIFIED//FAR OFFICI CIs. W&i e ..tv
thrust (Fth) is produced from each mass unit of propellant. The thrust efficiency
(ll ) is a measure of how much of the power/energy that is available results in
directed kinetic energy (thrust power) in the flow. The thrust density is a
measure of how much thrust is produced per unit cross-sectional area, Ac (area
perpendicular to the flow direction). Although the thrust density is a packaging
issue for spacecraft, it is critical for air vehicles where drag is present. The
thrust-to-power measures the acceleration efficiency. Traditionally a trade exists
between fuel/propellant efficiency and thrust-to-power (speed vs. economy). The
final parameter is the specific mass or weight (mass)-to-power ratio. In most
cases the efficiencies improve with the size of the system (economy of scale).
Measures of performance are fundamentally different between air-breathing and
rocket systems due to the inlet on the air-breathing system.
Rocket
Air-Breathing
FIB = m, ue - m(/ u
+ Ae (Pe - panil )
= ,,;J(l +f)u.-u] + A. (P. - P anti )
=
Thrust
I
= _
F....=lh'-­
Thrust
l sp - ----------
SP ­
fuel weight flow rate
propeJlant weight flo w rate
F,h
u cq
=
=
0
m, go
o o
fuel mass flow rate __ mJ
TSFC = -----­
Thrust
F111
.
p jel = 1/2 m, u;q = 1/2 F,1, ISP 8 0
.
p
1/2 ( ,,;, u;q _,,;au2)
1] =
½ ·er = F,h l sp 8 0 _ 112 m, u;q
1] =___!!!_ = ---'------'-­
P,,/ect
2 P,,,,cr
P ,/ec,
P e,ec/
P,,,c,
Above, m0 is the mass flow rate of the air, mI is the mass flow rate of the fuel,
m, is the exit flow rate, go is the acceleration of gravity (reference point, Earth),
Ue is the nozzle exit velocity, u is the flight/vehicle velocity, Ueq is the equivalent
exit velocity, Ae is the nozzle exit cross-sectional area, Pe is the nozzle exit
UNCLASSIFIED/Peft. err1e1111t ~9E 8,.L?/
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