Gah...Spins...

[caliginousface]

Alright so I thought I had a hold of this earlier today but upon trying to teach myself again I have stumbled.

Why during a turning stall that is coordinated, we do not enter a spin?

This is because the wings stall at the same time because we are coordinated, and we get a wing drop because the dipped wing is not producing as much lift.

Does that make sense?

This is what I have written down, I hope this makes sense:

So if we were practicing stalls and didn't have enough rudder we'll say, the airplane begins to yaw, and as the stall approaches, it begins to turn. At this point one wing becomes more stalled than the other because the outside wing must travel faster, and is producing more lift than the inside wing.


THERE IS SOOOOOOOOOO MUCH to know for this CFI madness, eprops, kudos, chewy, to all you CFI's.

[meritflyer]

Remember the definition or relative wind - the wind perpindicular to the relative flight path of the aircraft.

Definition of angle of attack - angle formed by the chord line and the relative wind.

Okay, so while in a turn while coordinated, we have changed the direction of our relative wind. Instead of the relative wind being directed over the wings during straight and level flight, its now being directed in a similar fashion over the wings during the turning stall until CLmax is reached. So as long as the aircraft is coordinated during the stall there is no slip or skid to produce auto-yaw. Remember auto roll and yaw begin the spin.

So, if we were to turn 20 degrees to the left while stalling the aircraft, uncoordinated, we'd already have the auto roll from the outside wing traveling faster than the inside wing hence creating more lift and wanting to roll the airplane to the left. Now, add auto yaw by being uncoordinated and you have a recipe for a spin.

The direction of the spin during our turning stall to the left may go either way depending on a few factors such as aileron position, rudder position, and corrective actions taken during the incipient phase.

Your idea is right on track. Outside wing travels faster gives us roll. Uncoordinated rudder gives us a component of yaw = SPIN!

[saxman66]

Originally Posted by caliginousface

So if we were practicing stalls and didn't have enough rudder we'll say, the airplane begins to yaw, and as the stall approaches, it begins to turn. At this point one wing becomes more stalled than the other because the outside wing must travel faster, and is producing more lift than the inside wing.

I wouldn't say because the outside wing has more lift because its travelling faster. Remember, you're uncoordinated so this may not be the case.

You always stall at your critical angle of attack (AOA). The outside wing will be at a higher AOA, so thats why it will stall first and possibly cause a spin.

Hope that helps

[caliginousface]

Alright I think i've got it. Thanks guys.

[meritflyer]

Originally Posted by saxman66

A- I wouldn't say because the outside wing has more lift because its travelling faster. Remember, you're uncoordinated so this may not be the case.

B- You always stall at your critical angle of attack (AOA). The outside wing will be at a higher AOA, so thats why it will stall first and possibly cause a spin.

Hope that helps

A-Why not? Actually the inside wing has a greater AoA in a turn. Hard to picture, I know. Think of the dynamics of a turn. As the lowered wing in a turn has a greater AoA it produces a greater amount of lift. Drag is a bi-product of lift which results in the inside wing traveling a smaller radius as it acts as the pivot point for the turn. This increase in drag and decrease in velocity due to distance traveled results in the wing pivoting.

B- The outside wing does in fact have more lift due to an increase in velocity. This explains overbanking tendency. Think of it as a prop. Why does the inner portion of the blade have a reduced AoA when compared to the outter portion. Greater velocity produces greater lift.

The Pilots Handbook of Aeronautical Knowledge outlines this well. I suggest you read it.

[caliginousface]

Originally Posted by meritflyer

A-Why not? Actually the inside wing has a greater AoA in a turn. Hard to picture, I know. Think of the dynamics of a turn. As the lowered wing in a turn has a greater AoA it produces a greater amount of lift. Drag is a bi-product of lift which results in the inside wing traveling a smaller radius as it acts as the pivot point for the turn. This increase in drag and decrease in velocity due to distance traveled results in the wing pivoting.

So if the lowered wing is producing more lift, but not as much lift as the wing with the downward defleced aileron. Though like you said, the low wing is also now producing more drag. Is that reasoning ok?



Alright so one more time. As we approach a stall, uncoordinated with not enough right rudder, we start to get a yawing moment to the left. We also have a rolling moment because of the right wing producing more lift because it is traveling faster than the now dipped left wing. When we stall, the left wing is now more stalled than the right wing as it was not producing as much lift as the right wing.

Yea, nay?

[fish314]

Originally Posted by caliginousface

So if the lowered wing is producing more lift, but not as much lift as the wing with the downward defleced aileron. Though like you said, the low wing is also now producing more drag. Is that reasoning ok?



Alright so one more time. As we approach a stall, uncoordinated with not enough right rudder, we start to get a yawing moment to the left. We also have a rolling moment because of the right wing producing more lift because it is traveling faster than the now dipped left wing. When we stall, the left wing is now more stalled than the right wing as it was not producing as much lift as the right wing.

Yea, nay?

Spins happen for one reason and one reason only. STALL + YAW = SPIN. If you get rid of either the stall or the yaw, the aircraft will recover from the spin.

To understand what happens in a spin you need to know what happens to lift and drag in a stall, but unfortunately most books only show you the coefficient of lift and drag with respect to angle of attack charts from zero angle of attack to just past the critical angle of attack. They don't show very well what happens AFTER the critical angle of attack.

Here's what happens: After the critical angle of attack, the wing still produces lift, but it produces MUCH less lift. Basically as angle of attack continues to increase past critical, coefficient of lift decreases dramatically. Also, coefficient of drag continues to increase.

In a coordinated stall (straight ahead or turning) both wings behave exactly the same. However, when you add yaw, the side opposite the yaw has a slight decrease in angle of attack, and the side with the yaw has a slight increase in angle of attack.

Therefore if you yaw to the left, the left wing will increase it's angle of attack and the right wing will decrease its angle of attack. This means that lift on the left wing will decrease and lift on the right wing will increase, which will cause that turn to the left that we associate with a left spin.

Also, a yaw to the left will cause drag on the left wing to increase and drag on the right wing to decrease, which will cause even MORE yaw to the left. For this reason, simply taking out the pro-spin rudder may not be enough to stop the spin in many airplanes. This is also why the spin is often refered to as "auto-rotation" or "auto-turning" or even "auto-yawing". Because once you introduce yaw to get into a spin, the act of spinning is enough to keep producing yaw to keep you in the spin.

Spin recovery procedures vary from airframe to airframe, but they all share this common trait. All of them have you either:

1. Remove the yaw. (Neutralize the rudder or add anti-spin rudder)
2. Remove the stall. (Forward elevator)
3. Remove both the yaw and the stall.

They may also have you change engine settings (either to prevent flameout of a jet engine, or just to reduce engine induced yaw), apply controls smoothly or abruptly depending on the type of aircraft, or do other things.

In general you will use the rudder and the elevator to recover from a spin, rather than the aileron, b/c if you tried to raise the low wing, you would simply be putting that wing's aileron down into the airstream. This would cause more drag on that wing than the other, and even MORE pro-spin yaw. In other words, ailerons are ineffective at recovering a spin in most airplanes, and usually hurt more than they help.

[caliginousface]

THANK YOU!!!!!

[fish314]

No probs.

[meritflyer]

Originally Posted by fish314

Also, a yaw to the left will cause drag on the left wing to increase and drag on the right wing to decrease, which will cause even MORE yaw to the left. For this reason, simply taking out the pro-spin rudder may not be enough to stop the spin in many airplanes. This is also why the spin is often refered to as "auto-rotation" or "auto-turning" or even "auto-yawing". Because once you introduce yaw to get into a spin, the act of spinning is enough to keep producing yaw to keep you in the spin.

Auto-rotation and auto yaw are not the same thing.

[fish314]

Originally Posted by meritflyer

Auto-rotation and auto yaw are not the same thing.

True. I wrote that paragraph slightly unclearly. The difference in lift causes the inside wing to drop or outside wing to rise (auto-rotation) and the difference in drag causes the pro-spin yaw (auto-yaw). I was just trying to show why when you get in to a spin, the airplane doesn't necessarily just come out by itself (although in some airplanes it can). Because of all of these "auto" factors.

[meritflyer]

Originally Posted by fish314

True. I wrote that paragraph slightly unclearly. The difference in lift causes the inside wing to drop or outside wing to rise (auto-rotation) and the difference in drag causes the pro-spin yaw (auto-yaw). I was just trying to show why when you get in to a spin, the airplane doesn't necessarily just come out by itself (although in some airplanes it can). Because of all of these "auto" factors.

Gotcha.