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Beginner's Guide
to Propulsion
Maximum Flight Time
Answers
- The Maximum Flight
Time for an aircraft depends on the specific fuel consumption, net thrust,
and the mass of the fuel load. If all other factors for
the following aircrafts remain the same, which of the 2 aircraft has
the longer maximum flight time? Place an "X" on the correct line.
A.
AIRCRAFT
A - The throttle setting is 58% _____X_____
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AIRCRAFT
B - The throttle setting is 75% ___________
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B.
AIRCRAFT
A - The engine is producing 1500 pounds of thrust
_____X______
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AIRCRAFT
B - The engine is producing 2000 pounds of thrust ________
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C.
AIRCRAFT
A - has a turbojet engine with an afterburner ________
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AIRCRAFT
B - has a plain turbojet engine
_____X_____
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D.
AIRCRAFT
A - has a turboprop engine ___X_______
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AIRCRAFT
B - has a rocket engine ___________
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E.
AIRCRAFT
A - has a L/D (lift to drag ratio) of .5 __________
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AIRCRAFT
B - has a L/D (lift to drag ratio) of .8 _____X_____
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F.
AIRCRAFT
A - has a fuel mass flow rate of 2500 lbm/hr_____X_____
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AIRCRAFT
B - has a fuel mass flow rate of 3500 lbm/hr__________
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- For a given
mission, the required flight time could replace the maximum flight time
in the required equation. This idea may be needed to solve the following:
A. For mission I, we need 4500 pounds of thrust for 3 hours.
If the Thrust Specific Fuel Consumption is .8, how much fuel
is needed for this mission?
M=
t x TSFC x F
M = 3 x .8 x 4500 = 10,800 lb mass of fuel
B. For
the second mission, the engines are being fed from a fuel tank that
delivers 3200 pounds mass per hour. If the aircraft is producing 2500
pounds of thrust, what is the TSFC?
TSFC
= mf /F
TSFC = 3200/2500 =1.28
C. If the
aircraft can carry 20,000 pounds mass of fuel plus the amount needed
for takeoff and landing, what is the limit for the time the
mission can take?
tmax
= M / (TSFC x F)
tmax = 20,000/(1.28 x 2500) or 20,000/3200 = 6.25
hours
D. The
aircraft plans to maintain a cruise speed of 120 mph. What is the
aircraft's maximum range?
R
= V x tmax
R = 120 x 6.25 = 750 miles
E. The
aircraft was forced to land unexpectedly. At that time, there were
only 15,000 pounds mass of fuel in excess of that needed for takeoff
and landing. All other conditions remain the same. If the final destination
of the mission is 630 miles away, what cruise speed should
be maintained?
Step 1: tmax
= 15,000/3200 = 4.6875 hrs,
Step 2: R
= V x tmax
630
miles = V x 4.6875 hours
V
= 135 mph
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Related Pages:
Standards
Activity
Worksheet
Propulsion Activity Index
Propulsion Index
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