Hi,

810935:

Q. Assuming no compressibility effects, the correct relationship between stall speed, limit load factor (n) and VA is:

A. VA >= VS * SQRT (n)

Explanation:

...At lower masses, VS will be lower so published VA may be greater than VS times the square root of 2.5

[this suggests VA is fixed regardless of mass].

810937:

Q. How does VA (EAS) alter when the aeroplane's mass decreases by 19%?

A. 10% reduction.

(Wrong answer: No change)

Explanation:

VA is the stalling speed of an aircraft at its maximum load factor (g). We know that ANY stalling speed changes with the square root of the change in mass.

A 19% reduction in mass is a change of mass by a factor of 0.81. So the stalling speed will reduce by a factor of (√0.81), which = 0.90

For example, if VA was 100kts, the new VA at the lower mass will be:

100kts x 0.90 = 90kts. This is a reduction of 10%.

[i.e. VA varies with mass, just like VS does. I put 'no change' and was wrong...]

I am struggling to see these answers as consistent. Please will someone point me to what I'm missing?

Many thanks.

Edit, addition:

Q 810939 adds to the mix:

Q. The manoeuvring speed VA, expressed as indicated airspeed, of a transport aeroplane:

A. Depends on aeroplane mass and pressure altitude.

[I thought that VA was a fixed speed set by the manufacturer assuming MAUM (and maybe PA 1013mb?), then looking at the max speed where full back stick would give 2.5g, as per Q 810935. I didn't realise it changed as a function of the mass at a given time (or indeed altitude, PA or otherwise). Either way, I started thinking I understood VA, now I'm confused. Please help!]

810935:

Q. Assuming no compressibility effects, the correct relationship between stall speed, limit load factor (n) and VA is:

A. VA >= VS * SQRT (n)

Explanation:

...At lower masses, VS will be lower so published VA may be greater than VS times the square root of 2.5

[this suggests VA is fixed regardless of mass].

810937:

Q. How does VA (EAS) alter when the aeroplane's mass decreases by 19%?

A. 10% reduction.

(Wrong answer: No change)

Explanation:

VA is the stalling speed of an aircraft at its maximum load factor (g). We know that ANY stalling speed changes with the square root of the change in mass.

A 19% reduction in mass is a change of mass by a factor of 0.81. So the stalling speed will reduce by a factor of (√0.81), which = 0.90

For example, if VA was 100kts, the new VA at the lower mass will be:

100kts x 0.90 = 90kts. This is a reduction of 10%.

[i.e. VA varies with mass, just like VS does. I put 'no change' and was wrong...]

I am struggling to see these answers as consistent. Please will someone point me to what I'm missing?

Many thanks.

Edit, addition:

Q 810939 adds to the mix:

Q. The manoeuvring speed VA, expressed as indicated airspeed, of a transport aeroplane:

A. Depends on aeroplane mass and pressure altitude.

[I thought that VA was a fixed speed set by the manufacturer assuming MAUM (and maybe PA 1013mb?), then looking at the max speed where full back stick would give 2.5g, as per Q 810935. I didn't realise it changed as a function of the mass at a given time (or indeed altitude, PA or otherwise). Either way, I started thinking I understood VA, now I'm confused. Please help!]

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