Warbirds and Tip Stalls

I agree Marty :)

Hi Marty,

On Mar 18, 7:46 am, "Ed Forsythe" wrote:

It's the helix angles in the turn that affect AOA. Next time you encounter a spirtal staircase, pay attention to the handrails. They're parallel, but they're not at the same angle with respect to the horizon. They both have to rise the same amount so that they follow the stairs, but the inside one is steeper because its radius is so much smaller that the outside one, and therefore much shorter. Now, if we have a board that we place across the handrails, we'll see that if that board is a wing travelling in a descending turn, it's AOA on the inside is much higher than it is on the outside. In a climbing turn, the outer wing is at a higher AOA. Dihedral doesn't affect the AOA, since it's an angle in a different dimension. So getting slow in a descending turn will stall the inside wing first and it'll drop. In an climbing turn the outside wing will fall first. if the airplane is well-designed, the stall pattern will start at the inboard trailing edge and work forward and outward, and if one wing's stall pattern is just a little more advanced than the other, that wing will be less able to carry its weight and will drop, even if the stall hasn't reached the tip. That's why the term "tip stall" is so misleading. It implies that everything's OK unless the tips stall. With those spiral staircase handrails, if you "skid" or "slip" your board you'll see the AOAs change drastically. A skid in a descending turn will increase the AOA on the inside wing (dangerous) and a slip will decrease it (safe). The spiral staircase is far tighter than any turn, but it serves to illustrate the AOA changes. AOA doesn't have to change a lot to create trouble. Like I say, I really need to post those photos of my AOA table.

Dan