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AER1011 Flight Physics 1Week 7 Tutorial 7 Question Sheet
Answers should be given correct to 2 decimal places.
1. A turbojet is mounted on a stationary test stand at sea-level. The inlet and exit areas are
identical (0.45m2). If the velocity of the exhaust gas is 400m/s at a pressure of 101325Pa
and at a temperature of 750K, what is the static thrust of the engine?
Answer:
̇ (𝒗𝒆 − 𝒗∞ ) + (𝒑𝒆 − 𝒑∞ )𝑨𝒆
𝑻 = 𝒎𝒂𝒊𝒓
Evaluate the mass flow rate at the exit: density = 0.470731kg/m3, mass flow
rate=84.73kg/s
Exit pressure=ambient sea-level so this term will cancel.
Therefore T=84.73*400=33.89kN of static thrust generated.
2. A jet aircraft engine is assumed to provide a maximum of 250kN of static thrust at sea-level.
Assuming a lapse rate of 0.9, what would be the maximum of thrust expected at an altitude
of 4000 metres?
𝑻 = 𝑻𝑺𝑳 𝝈𝒎 = 𝟐𝟓𝟎𝒌 ∗ 𝟎. 𝟔𝟔𝟖𝟓𝟎.𝟗 = 𝟏𝟕𝟑. 𝟗𝟗𝒌𝑵 𝒐𝒇 𝒕𝒉𝒓𝒖𝒔𝒕 𝒂𝒕 𝟒𝒌𝒎
3. For the engine described in Question 2, the amount of thrust generated decreases linearly
with increasing speed. The manufacturer datasheet indicated that at 300 m/s, the amount
of thrust generated by the engine at sea-level will have reduced to 175kN. Using this
information, calculate the maximum amount of thrust you would expect the aircraft engine
to generate at M0.65 at an altitude of 5000 metres on a standard day.
M0.65 @ 5000 metres = 208.33m/s on a standard day. The lapse rate you should use is
given in Q2 (although you should always assume this is 0.96 unless explicitly told
otherwise)
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