Stall AOA and ground effect

[Old Geek]

This week's Aviation Week had an article about the Gulfstream G650 prototype that crashed while performing a single-engine takeoff. Part of the cause was determined to be the fact that in ground effect, the wings would stall at an A0A of three degrees less than in free air and that the stick shaker was not programmed to take that into account.

How does this apply to little airplanes? Does a 150 also stall at a lower AOA in ground effect than in free air?

 

[poadeleted20]

Yes, but in a 150, the difference isn't significant.

 

[denverpilot]

The effect is there but as Ron says, you can't possibly fly accurately enough to notice it.

 

[Threefingeredjack]

Plus a 150's wing is slightly higher to begin with, and with the shorter wing quickly moves out of ground effect.

 

[Dan Thomas]

This week's Aviation Week had an article about the Gulfstream G650 prototype that crashed while performing a single-engine takeoff. Part of the cause was determined to be the fact that in ground effect, the wings would stall at an A0A of three degrees less than in free air and that the stick shaker was not programmed to take that into account.

How does this apply to little airplanes? Does a 150 also stall at a lower AOA in ground effect than in free air?

I don't think the stall AoA changes in ground effect, but the deck angle might. The ground not only interferes with tip vortices and downwash, but with the usual slight upflow ahead of the wing. This reduces AOA and caused float on landing, but can also enable an early liftoff with the nose high. If that high nose attitude is held as the airplane rises out of ground effect, the wing might achieve stall angle.

I think.

Dan

 

[Threefingeredjack]

I don't think the stall AoA changes in ground effect, but the deck angle might. The ground not only interferes with tip vortices and downwash, but with the usual slight upflow ahead of the wing. This reduces AOA and caused float on landing, but can also enable an early liftoff with the nose high. If that high nose attitude is held as the airplane rises out of ground effect, the wing might achieve stall angle.

I think.

Dan

Actually it does. I've already tossed the magazine, but if I remember the article correctly the IGE critical AOA was 2 or 3 degrees less tan the OGE and consequently the stick shaker setting was too low. If you need the exact numbers I can cut and paste from the online issue.