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How do you calculate take off/stall speed based on wing loading?

#1
Hi, I have a flying wing with a 25 degree wing sweep, and 0.7m of wing span. The wing loading is about 4.1Kg/m^2. The weight is about 320g. It has a flat bottom airfoil and no pitch (the bottom of the wing is exactly parallel to the direction of travel).

Is it possible to calculate the stall speed or minimum take off speed based on that information? I do not need a super accurate result, just a rough estimate will do.
 

quorneng

Well-known member
#4
Are you sure you are not over thinking this?
It is not at all easy to judge the airspeed of a model plane so calculating its theoretical stall speed is at best only a rough guide.
Assuming a plane is correctly set up it will take off when it has reached sufficient speed.
Trying to "haul it off" before it aerodynamically responds adequately is a recipe for disaster.
 

Bricks

Well-known member
#5
Also what I have found with wings is how much reflex that I put into the elevons will determine to a point at where she stalls at. Along with that the more sweep the faster she needs to fly tp keep from stalling especially in turns. I have one wing pushing 35 degrees sweep and if you do not use more throttle in turns she will stall and go into a death spiral unless I am high enough to recover..
 

Tench745

Active member
#6
Naturally, the estimated stall speed is just that, an estimate. Wing geometry, airfoil, etc will affect the true performance. Adding reflex changes the airfoil, thus changing your coefficient of lift (CL) and therefore changing stall speed. As far as needing more throttle in turns, that is a different set of factors than we're talking about here.
As your angle of bank increases the G-load increases. If I remember correctly, a 60 degree bank pulls 2Gs. So, your plane has effectively doubled in weight. Of course, the bank angle also affects the vertical lift vector.
Estimated stall speed is a rough guess at the minimum speed you can maintain level flight.