stall speed

[salat]

Hello!
What is simple formula for estimating stall speed for small to average models? Say 1m ws.
Thank you,
Kostya

[vintage1]

It varies as the square root of wing loading, but I cannot remember the constant.Wing camber and thickness also affects it a bit.

[Brandano]

It's always an approximate anyway. If the model is climbing or turning the stall speed is higher, if it's diving it's lower.. better think in terms of stall angle, which can be measured for a specific wing profile experimentally.

[JetPlaneFlyer]

The formula (in SI units) is:

V = √( 2 W g / ρ S Clmax )


V = Stall speed M/s
ρ = air density (use 1.2 KG/M^3)
S = wing area M^2
Clmax = Coefficient of lift at stall
W = weight KG
g = acceleration due to gravity = 9.81 m s^-2


Clmax varies according to airfoil used, wing planform and Reynolds Number. Something around '1' should be in the right ballpark for rough estimate.

Bear in mind that this would be the stall speed in straight and level flight only. Stall speed will increase in turns or whenever the 'g' loading in increased.

[salat]

thank you!!!
is there any approximation exist to estimate dependence of stall speed from bank angle? Do both high wing and low wing loose lift at same speed in bank?

Kostya

[JetPlaneFlyer]

Yes;
Multiply 9.81 by 1/cosine bank angle and put this new figure into the above formula in place of 'g'

Or some typical figures:
30 Deg bank stall speed would increase by 7.5%
45 Deg bank stall speed would increase by 19%
60 Deg bank stall speed would increase by 41%

You can in the same way calculate stall speed at any 'g' factor... If you pull a '4g' manouvre than you would multiply 9.81 by 4 and input this as 'g' in the formula to get stall speed. Or perhaps more simply; stall speed increases as the square root of the 'g' factor.

Steve

[Brandano]

Hence the "snap roll", which is nothing more than a 1 turn spin through a high speed stall