atpl question
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atpl question
Can anyone tell me the effect that a change in altitude will have on an aeroplane's TAS? I have a question which is as follows:
An aeroplane performs a straight and level horizontal flight at the same angle of attack at two different altitudes: (all other factors of importance being constant, assume ISA conditions and no compressibility effects)
A – the TAS at the higher altitude is higher
B – the TAS at both altitudes is the same
C – the TAS at the higher altitude cannot be determined
D – the TAS at the higher altitude is lower
Ref: AIR: atpl, cpl;
Ans: A
Is the answer above correct? If so please elaborate.
An aeroplane performs a straight and level horizontal flight at the same angle of attack at two different altitudes: (all other factors of importance being constant, assume ISA conditions and no compressibility effects)
A – the TAS at the higher altitude is higher
B – the TAS at both altitudes is the same
C – the TAS at the higher altitude cannot be determined
D – the TAS at the higher altitude is lower
Ref: AIR: atpl, cpl;
Ans: A
Is the answer above correct? If so please elaborate.
will be higher ( Considering ISA conditions ).
Perhaps someone should explain to the poster why we are assuming constant IAS in the question.
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From the "ECTM" graph:
Constant EAS: CAS, TAS and MACH number increase with increasing altitude.
Constant CAS: EAS decreases with increasing altitude, TAS and MACH number increase with increasing altitude
Constant TAS: EAS and CAS decrease with increasing altitude, MACH number increases with incrasing altitude.
Constant MACH number: EAS, CAS and TAS decrease with increasing altitude.
Constant EAS: CAS, TAS and MACH number increase with increasing altitude.
Constant CAS: EAS decreases with increasing altitude, TAS and MACH number increase with increasing altitude
Constant TAS: EAS and CAS decrease with increasing altitude, MACH number increases with incrasing altitude.
Constant MACH number: EAS, CAS and TAS decrease with increasing altitude.
Last edited by slav4o1; 30th Dec 2010 at 16:24.
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Exactly, the answer comes from the lift equation:
L = CL * A * Rho/2 * V^2
Assuming weight is constant, the lift for straight and level flight must equal weight (L = W). The higher the altitude, the lower the density (Rho) of the air (mainly due to reduced air pressure). And if density decreases, you have to increase true airspeed (V) in order to create the same amount of lift and keep forces balanced.
L = CL * A * Rho/2 * V^2
Assuming weight is constant, the lift for straight and level flight must equal weight (L = W). The higher the altitude, the lower the density (Rho) of the air (mainly due to reduced air pressure). And if density decreases, you have to increase true airspeed (V) in order to create the same amount of lift and keep forces balanced.
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Nothing to do with IAS. All the question refers to is the fact that at a higher altitude with a constant AoA you require an increase in TAS. Look at the Lift equation, as density is decreasing, something must increase in order to produce the same lift.
Hope its clear
Hope its clear
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