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AER1011 Flight Physics 1Week 8 Tutorial 8 Question Sheet
Answers should be given correct to 2 decimal places.
You may assume ISA conditions unless otherwise stated.
1. An aircraft has a mass of 10,000kg, wing area of 56m2, Cd,0=0.015 and k=0.056. The aircraft
experiences a block in the fuel line preventing fuel from getting to the engines at an altitude
of 9500m and enters into a gliding flight from its cruise altitude to an altitude of 3500
metres, at which point the fuel line is unblocked.
(a) What are the true airspeeds of the aircraft at the start and end of the glide descent
phase, assuming that pilot has selected the glide angle to maximise the range of the
aircraft.
Maximum range equates to minimum glide angle. Therefore we are looking for L/D
max. This occurs when 𝑪𝑫,𝒐 = 𝑪𝑫,𝒊
We assume that there are small angles involved, so
𝟐𝑾 𝟐∗𝟏𝟎𝟎𝟎𝟎∗𝟗.𝟖𝟏
𝒗 = √𝝆𝑺𝑪 = √𝟎.𝟑𝟓𝟖𝟏∗𝟏.𝟐𝟐𝟓𝟔∗𝟓𝟔∗𝟎.𝟓𝟏𝟕𝟓 =124.2m/s at 9500 metres, and 88.55m/s at
𝑳
3500 metres.
(b) What is the glide angle for maximum range?
𝟏
Maximum range, minimum glide angle =𝐬𝐢𝐧−𝟏 𝑳 = 𝟑. 𝟑𝟐𝟑𝒐
( )
𝑫 𝒎𝒂𝒙
(c) What are the rates of descent recorded at 9500 metres, 7000 metres and 4000 metres?
𝒉̇ = 𝒗𝒔𝒊𝒏(𝜸)
At 9500 metres, v=124.2 m/s, 𝒉̇ = 𝟕. 𝟏𝟗𝟗m/s
At 7000 metres, v=107.16m/s, 𝒉̇ =6.2115m/s
At 4000 metres, v=90.9m/s, 𝒉̇ =5.269m/s
(d) What is the time interval between the start of the glide and the fuel line finally being
unblocked?
Halfway point is 6500 metres, v=104.17m/s, 𝒉̇ =6.038m/s
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