Va

[Unscheduled stopover]

Does anybody know how to calculate Va. Apparently there is a formulae that you can use starting with Vso and involving G limits. Ive never heard of it. Would anybody care to shed some light.

Cheers

[Oktas8]

VA = VS1 x sq.rt. (Max load factor)

where VA = manoeuvring speed
and VS1 = stalling speed in the configuration being examined (typically, nil flap, wheels up if applicable)
and max load factor is the limit (or maximum permitted) load factor in the configuration being examined.

This is not entirely accurate as VA is based on many variables not just positive load factor. However, it gives a good rule of thumb.

Note that a) it only addresses positive load factor, not negative and b) it does not guarantee protection in all circumstances. For example "rolling g" refers to the simultaneous application of full aileron and full up elevator - manufacturers are only required to protect to two thirds limit load factor in this case for many aircraft. Refer FAR or JAR Part 23.

Hope this helps as an intro to the subject,
Oktas8

[IRRenewal]

Rough air penetration speed is related to stall speed and G limit of your aircraft.

Suppose clean stall is 60, G limit is 4. Now, at this G limit the stall speed is 120.

So, if you fly in (really) rough air at 120 and you get a major jolt then the wing stalls when the G limit is reached. This might be unpleasant, but overstessing the wing would potentially be even more unpleasant.

So, Va = SQRT(G_limit) * Actual Stall Speed

Since stall speed goes up with weight, so does Va.

Cheers

Gerard

Funny that,

Nobody replies for 13 hours, and while I am writing my reply somebody else does the same.

Gerard

[Oktas8]

I've been the second person to reply in two minutes so many times - at last the shoe is on the other foot! ;)

I believe rough air penetration speed is a little less than Va, to allow for unexpected gusts simultaneously increasing airspeed and increasing angle of attack - wouldn't want to be already at Va when that happened! Vb is the term that comes to mind, but is usually ignored for light (piston) aircraft.

O8

[Unscheduled stopover]

Thanks for the replies. Got a tick for that one!