Spin Help

ozziecat35

ozziecat35

4 out of 5 great lakes prefer Michigan.
Can someone dumb it down for me? I understand the principle of spins, but what I'm unclear on is how the lower wing is at a higher AOA versus the higher wing? I get that the lower wing is more stalled, and at a higher AOA, but what I don't get is how?

Thanks!
 
One simple way to visualize it is to think of the wing rotating, since it's rotating around a circle the outer wing is moving faster than the inner wing.

Compare it to a circle race track, the cars on the outer ring will need to drive faster than cars on the inner ring if they want to stay abeam each other, as the outer ring covers a greater distance.

Since the outer wing is going "faster" the relative wind is faster and striking the wing from a more direct head-on angle, therefore it's relative wind is at a lower angle of attack. Same reason your propeller has a twist in it (the outer portion moves faster than the inner portion).

This contributes to the continued rotation of the spin. As the inner wing is at a higher angle of attack there is more drag than the outer wing at a lower angle of attack... so the inner wing continues to be "pulled back" more than the outer wing, contributing to the continued rotation.
 
rframe said:
One simple way to visualize it is to think of the wing rotating, since it's rotating around a circle the outer wing is moving faster than the inner wing.

Compare it to a circle race track, the cars on the outer ring will need to drive faster than cars on the inner ring if they want to stay abeam each other, as the outer ring covers a greater distance.

Since the outer wing is going "faster" the relative wind is faster and striking the wing from a more direct head-on angle, therefore it's relative wind is at a lower angle of attack. Same reason your propeller has a twist in it (the outer portion moves faster than the inner portion).

This contributes to the continued rotation of the spin. As the inner wing is at a higher angle of attack there is more drag than the outer wing at a lower angle of attack... so the inner wing continues to be "pulled back" more than the outer wing, contributing to the continued rotation.
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Thanks, exactly what I was looking for.

Wouldn't the upper (outer) wing be creating more drag since it's going faster? Or in the case, the higher AOA has more drag then the faster TAS?
 
ozziecat35 said:
Thanks, exactly what I was looking for.

Wouldn't the upper (outer) wing be creating more drag since it's going faster? Or in the case, the higher AOA has more drag then the faster TAS?
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That was my hang up yesterday when I started digging into spins. I figured that the outer wing would have higher drag as it was probably generating more lift (as a result of being 'less' stalled than the inner wing). Great question.

It's really funny that you ask this now, because less than 24 hours ago, I got stuck on the exact same thing.
 
SteveCostello said:
That was my hang up yesterday when I started digging into spins. I figured that the outer wing would have higher drag as it was probably generating more lift (as a result of being 'less' stalled than the inner wing). Great question.

It's really funny that you ask this now, because less than 24 hours ago, I got stuck on the exact same thing.
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Exactly my thought!! I don't feel so bad now that someone else has the same question.
 
You have to realize that induced drag increases exponentially with angle of attack. Remember the concept of Max L/D... it exists where total drag is lowest. Total drag decreases with an increase of airspeed up until Max L/D...then total drag starts to rise again as airspeed increases above Max L/D because of the affects of parasite (skin friction drag).

Induced drag is a powerful monster.

Drag.jpg
 
rframe said:
You have to realize that induced drag increases exponentially with angle of attack. Remember the concept of Max L/D... it exists where total drag is lowest. Total drag decreases with an increase of airspeed up until Max L/D...then total drag starts to rise again as airspeed increases above Max L/D because of the affects of parasite (skin friction drag).

Induced drag is a powerful monster.

Drag.jpg
Click to expand...

ok so as long as the TAS of the higher wing is less then L/D Max, the drag from the less stalled wing is not really a factor?
 
ozziecat35 said:
ok so as long as the TAS of the higher wing is less then L/D Max, the drag from the less stalled wing is not really a factor?
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Well the drag is present, its just less than the other wing.

Another way to think of this... when you fly at MCA what happens as the airplane gets slower and slower and you want to maintain altitude? You have to add power, right? As the airplane gets slower and the angle of attack gets higher the drag becomes VERY high. In many light airplanes you can end up with cruise power settings just to maintain altitude at MCA. So it takes very small differences in angle of attack to generate large differences in drag loads (as you get near critical angle of attack it's reaaaaally high).

Quick experiment next time you are flying. See how much power you need to maintain altitude at best glide speed. Then slow the airplane until the stall horn is blaring and see how much power you need to maintain altitude.
 
Of course... induced drag. *ding* Perfect. Thanks for the great explanation. The ASA book I am pouring through doesn't mention induced drag at all in the spin section.

Actually, despite the positive reviews that book gets, I'm pretty disappointed in how the book is written. It's pretty disjointed, and the writing is not all that great. The organization of the topics and the discussion thereof leaves quite a bit to be desired.
 
SteveCostello said:
Of course... induced drag. *ding* Perfect. Thanks for the great explanation. The ASA book I am pouring through doesn't mention induced drag at all in the spin section.

Actually, despite the positive reviews that book gets, I'm pretty disappointed in how the book is written. It's pretty disjointed, and the writing is not all that great. The organization of the topics and the discussion thereof leaves quite a bit to be desired.
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I have the Jeppesen Private and Commercial manuals...extremely well written.
 
SteveCostello said:
Of course... induced drag. *ding* Perfect. Thanks for the great explanation. The ASA book I am pouring through doesn't mention induced drag at all in the spin section.

Actually, despite the positive reviews that book gets, I'm pretty disappointed in how the book is written. It's pretty disjointed, and the writing is not all that great. The organization of the topics and the discussion thereof leaves quite a bit to be desired.
Click to expand...


The FAA publications are the ones I found that were the best. After spending money on ASA and Jeppesen crap, I always came right back to the AFH, PHAK, and other FAA publications.

The inside wing has a higher AOA in relation to the relative wind. The induced drag on the inside wing exceeds the total drag on the outside wing. Plus as the outside wing accelerates it wants to produce even more lift which will also tend to roll the plane towards the inside wing. So there are several factors in play when it comes to spins. My advice is if you are going to be a CFI, get yourself real comfortable with them and let your students scare the crap out of themselves so they know its no joke. That is my approach anyways. others will disagree because scared students sometimes quit. I'm more about keeping them alive and making them proficient than selling them on the idea.
 
desertdog71 said:
The FAA publications are the ones I found that were the best. After spending money on ASA and Jeppesen crap, I always came right back to the AFH, PHAK, and other FAA publications.

The inside wing has a higher AOA in relation to the relative wind. The induced drag on the inside wing exceeds the total drag on the outside wing. Plus as the outside wing accelerates it wants to produce even more lift which will also tend to roll the plane towards the inside wing. So there are several factors in play when it comes to spins. My advice is if you are going to be a CFI, get yourself real comfortable with them and let your students scare the crap out of themselves so they know its no joke. That is my approach anyways. others will disagree because scared students sometimes quit. I'm more about keeping them alive and making them proficient than selling them on the idea.
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That's probably a good case by case scenario...especially with an over-confident or cocky student. Hey look, my FOI studying is working!!!
 
My approach is a good ground lesson explaining stall concepts beating in the idea of angle of attack not airspeed, recovery in power off (landing config) and power on (departure config), and explaining spin concepts and PARE recovery.

I really like to emphasize the problems with stalls in maneuvering flight, as I think the way stall recovery is often taught limits the student's perception of stalls being a problem on takeoff and landing... that's not where most stall accidents occur. I demonstrate accelerated stalls and explain why this is a big problem when people start to gain more confidence than skill and start doing stupid crap like buzzing or flying too close to terrain. I also give most of my students a primer on mountain flying and talk about maneuvering in slow flight, in canyons, without horizon reference... which can be very disorienting and cause over-reactions that could induce a stall/spin.

I usually introduce power off stalls on the second lesson and power on stalls on the third lesson (giving a demonstration of yaw/roll instability and the importance of rudder to level wings. Then after they've practiced for a bit and understand the concepts I will ask them to explain spin recovery to me in flight and then I'll demonstrate spins. I think they are very disorienting for new students the first time so I like them to see that and absorb the process rather than fumble through it... they can read a book and watch youtube all they want, but there's nothing like that first sensation of whirling trees in the windscreen. Then if they want (I dont require it) I let them enter and recover from spins under my supervision. Of course, if they inadvertently spin due to a sloppy power on stall demonstration...well then that's just a free bonus.
 
rframe said:
My approach is a good ground lesson explaining stall concepts beating in the idea of angle of attack not airspeed, recovery in power off (landing config) and power on (departure config), and explaining spin concepts and PARE recovery.

I really like to emphasize the problems with stalls in maneuvering flight, as I think the way stall recovery is often taught limits the student's perception of stalls being a problem on takeoff and landing... that's not where most stall accidents occur. I demonstrate accelerated stalls and explain why this is a big problem when people start to gain more confidence than skill and start doing stupid crap like buzzing or flying too close to terrain. I also give most of my students a primer on mountain flying and talk about maneuvering in slow flight, in canyons, without horizon reference... which can be very disorienting and cause over-reactions that could induce a stall/spin.

I usually introduce power off stalls on the second lesson and power on stalls on the third lesson (giving a demonstration of yaw/roll instability and the importance of rudder to level wings. Then after they've practiced for a bit and understand the concepts I will ask them to explain spin recovery to me in flight and then I'll demonstrate spins. I think they are very disorienting for new students the first time so I like them to see that and absorb the process rather than fumble through it... they can read a book and watch youtube all they want, but there's nothing like that first sensation of whirling trees in the windscreen. Then if they want (I dont require it) I let them enter and recover from spins under my supervision. Of course, if they inadvertently spin due to a sloppy power on stall demonstration...well then that's just a free bonus.
Click to expand...
:D
 
Can I ask a serious question? Setting aside the principal of intensity, why do we want to 'scare' students about spins? I don't inherently disagree with the notion, but the reality of the situation is that spins are just another thing that airplanes can do, not a wholly separate flight regime.

What I mean to say is that I'm concerned by the concept of 'scaring pilots away' from the edges. The edges, in this case, are soft and squishy ... and there's a whole lot to learn there that's not "Don't do that!"

Now I have zero experience instructing. With any luck, I'll have my CFI in a week and change ... but I'm not speaking from instructional experience. I definitely appreciate the concept of letting a student stall uncoordinated and showing them how it feels, don't get me wrong. But as a soon-to-be (I hope!) instructor, I do wonder if cultivating 'fear' based on unexpected outcomes of an event that they may already be worried about is the right way to approach it for most students.

Thoughts? Am I off-base?

~Fox
 
I believe is flying the edges as much as possible. Allowing a student to get sloppy on a power on stall and do the inadvertent wing over is just a good way to drive that point home about being sloppy. The outcome is never unexpected because its made clear before airborn what the lesson is going to be, and what the possible outcomes are. I never had anybody quit over getting shook up a little doing a maneuver. I'd much rather they do it with me rather than on their solo cross country on takeoff.
 
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