Alieons effect in Spins

C

Clipper5895h

New Member
I am going through spin training for my CFI spin endorsement and I had an awesome chance to fly in the flight school's decathlon. We proceeded to do all types of spins (right left,power on/off, stick forward/back and aileron in/out of spin direction). What I still can't wrap my head around is why does in turn aileron accelerate the rate of rotation. In my mind, by applying in turn aileron, you are lowering the chamber of that down going wing, and increasing the camber of the outer up going wing. By doing this, wouldn't you be increasing the drag on that outer wing and flatting the spin (more lift=more drag). If I hadn't seen it for myself, I wouldn't believe it...hopefully someone can straighten me out!
 
The spin is caused by a coupling of the yaw and roll axis during a stall. When in-spin aileron is applied more roll is introduced. Assuming an upright spin to the left: Applying left aileron in a spin just as normal flight will increase bank angle. When the more roll is introduced this causes the nose to pitch down. The acceleration of the rotational rate is caused by the nose pitching down and the masses of the airplane (engine) lining up closer to its rotational axis. Ever see a figure skater spin up in a tight pirouette? Their rotation rate increases as they bring their arms and legs inward, closer to their spin axis.

Aerodynamically speaking (still assuming a spin to the left) with in-spin aileron, the left aileron is deflected up, the right on is down. Where is some of the relative wind coming from on the left wing? If you guessed from behind you're correct.
 
TwoTwoLeft said:
The spin is caused by a coupling of the yaw and roll axis during a stall. When in-spin aileron is applied more roll is introduced. Assuming an upright spin to the left: Applying left aileron in a spin just as normal flight will increase bank angle. When the more roll is introduced this causes the nose to pitch down. The acceleration of the rotational rate is caused by the nose pitching down and the masses of the airplane (engine) lining up closer to its rotational axis. Ever see a figure skater spin up in a tight pirouette? Their rotation rate increases as they bring their arms and legs inward, closer to their spin axis.

Aerodynamically speaking (still assuming a spin to the left) with in-spin aileron, the left aileron is deflected up, the right on is down. Where is some of the relative wind coming from on the left wing? If you guessed from behind you're correct.
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Thanks a bunch...that makes a lot more sense. So, having the relative wind behind will do/cause/affect what exactly?
 
Clipper5895h said:
Thanks a bunch...that makes a lot more sense. So, having the relative wind behind will do/cause/affect what exactly?
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Lets say you're still stuck in that spin to the left. Now you apply out-spin aileron. Left aileron deflects down, right aileron deflects up. The left wing has a component of relative wind that comes from behind due to the rotation. The downward deflected aileron increases the camber of the outside portion of the wing, with the relative wind coming from behind just enough lift is produced for the control surface to have an effect, roll is reduced. Now the adverse yaw is also contributing to the other pro-spin yaw inputs. Less roll, more yaw, flatter spin.

The opposite is happening with in-spin aileron. Just the adverse yaw created is not strong enough to counter the other pro-spin yaw inputs. That's what the rudder is for.
 
Also, keep some perspective. What you guys are posting is true for most normal straight-wing GA aircraft.

In the T-38, you actually apply pro-spin aileron to start the recovery.
 
Hacker15e said:
Also, keep some perspective. What you guys are posting is true for most normal straight-wing GA aircraft.

In the T-38, you actually apply pro-spin aileron to start the recovery.
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All the dynamics still apply. With fuselage-heavy, short-winged aircraft introducing pro-spin aileron does a number of things to aid in recovery. From what I've seen & read (I've never spun a T-38) these types of airplanes tend to naturally spin at a flatter attitude. Introducing more roll component steepens the spin exposing more rudder surface. At the same time accelerating the rotational rate allows for a stronger impulse as recovery rudder is deflected. Also the density altitudes are much higher where pilots are usually spinning these aircraft. That also affects recovery time. I dont think spinning a T38 out of 3000agl would be much fun! What altitudes did you guys use?

I remember watching a video a few years back on spinning the Hawker Hunter. Apparently its the only jet aircraft known to consistently recover from an inverted spin.
 
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