Physics of Rudder with regard to lifting a dropped wing.

[denverpilot]

And, taken to its logical extreme, you have a spin!



Kind of like a dog chasing its own tail.

It can be, but you're supposed to get off the rudder when back to level. If you stay on it, you're switching from slipping to skidding and that's gonna be a problem. Up until then, you're essentially trying to force an over the top spin entry and it's going to try not to do that in most Cessna's. I can't speak for other trainers. But Cessnas usually need a blast of power to go over the top and the scenario was a "falling leaf".

Of course what we are discussing here is an uncoordinated turn....or a skid that lifts a wing.

It's a slip until back to a level wing attitude, then it's a skid.

In the Robby 182 in a falling leaf, eventually it'll slow to the point where rudder won't lift the wing back to level at the slowest part of the nose proposing. If you hold it full aft elevator and full rudder (usually right rudder since the prop even at idle is exerting a small left turning tendency unless you really get the fuel balance out of whack), the nose will fall and both wings speed up and the rudder lifts the down wing. Let off and it'll probably drop the same wing again in the next slow porpoise.

There's never enough energy in the porpoise to flip it over the top into the spin in the direction of the rudder smashed all the way to the floor, unless you purposefully exaggerated the porpoise by entering fast and pulling to a very nose high attitude. If you enter it by slowing up normally it'll just go from slipping with the nose near the horizon to about ten degrees down and leveling itself and back.

And even in the non-Robby Cessnas unless you're loaded way way aft, it takes significant elevator pull to hold that falling leaf. If you release back pressure at any point, you're flying again. Most folk won't hold that much back pressure if they see it trying to do an over the top spin entry. Or not more than once anyway! Heh.

 

[dtuuri]

Uncle uncle! I cannot follow your circular incoherence. Now it sounds like you're saying stall is unrelated to AOA? I don't know...post after post I cannot identify any clear points because your writing style is inarticulate to the point of befuddlement. I do like aerodynamics discussions, though - just not this one. File this one away...I think everyone has long been groaning at this one.

I cannot let this go without trying to set you straight one more time. Here's a link that may befuddle you less: http://www.av8n.com/how/htm/snaps.html#sec-slip-stall-speed.

dtuuri

 

[RoscoeT]

I cannot let this go without trying to set you straight one more time. Here's a link that may befuddle you less: http://www.av8n.com/how/htm/snaps.html#sec-slip-stall-speed.

dtuuri

Man that clears up exactly what I need to be set straight on. This article is about as helpful with that as posting an article on underwater basket weaving. Not sure what you're even talking about anymore...not that I ever did, I think. I'd respond to something specific you said, and you'd come back each time with some nonsensical tangent, usually involving dihedral or something. Dihedral not even mentioned in this 'article'. I see there's a book out there titled, 'Ramblings of an incoherent mind'. Did you write that?

PS: And did you see that you received special mention at the end of post #1 of this thread? I guess this is too entertaining for me to put you on ignore.

http://www.pilotsofamerica.com/forum/showthread.php?t=79321

 

[dtuuri]

Not sure what you're even talking about anymore...not that I ever did, I think.

Review time:

Yawing a wing with dihedral presents the underside of the outside wing toward the relative wind such that it lifts (banks) in the direction of the rudder input.
...

Things reverse during a stall. ... You can pick up the dropping right wing with left rudder because during a stall, left rudder increases the AOA of the left wing. This causes the left wing to stall more deeply than the right wing.

I can't buy that. The advancing wing, even if stalled, should get more lift not less because of the area presented to the relative wind and, perhaps, even start to "fly" again because of the effective sweep of the wing. Meanwhile the other side loses lift for the reasons I stated above. IMO.

dtuuri

Sure, I hate math when it comes to explaining aerodynamics. It's a cop out.

One wing speeds up momentarily = momentary increase in lift.

The opposite wing slows down = momentary loss of lift.

The wing (not counting swept wing aircraft) has dihedral, so side slip increases AoA and lift on one side.

The other side decreases AoA and so does the lift.

Side slip causes interference from the fuselage which decreases lift on the lagging side.

You're welcome.

dtuuri

In other words, I challenged your statement that left rudder picks up a dropping right wing because the AoA of the left wing is increased.

PS: And did you see that you received special mention at the end of post #1 of this thread? I guess this is too entertaining for me to put you on ignore.

Consider the source. As for "ignore", if you want to lose the ability to rebut criticism, by all means use it. Makes my job easier.

dtuuri

 

[RoscoeT]

In other words, I challenged your statement that left rudder picks up a dropping right wing because the AoA of the left wing is increased.

Kudos for offering up a lucid statement here. If you are in a stall and kick left rudder, the left wing's AOA will increase (more deeply stalled), causing the left wing to drop. Increased AOA also causes a yaw to the left due to the increased drag of the left wing. What you have just created is a spin...this is how they happen. It has been shown that the inner wing has a higher AOA during a spin, though both wings are above critical AOA (stalled). The left rudder input caused the left wing drop. The same principle can be used to pick up a right wing drop with left rudder during a stall. We've already been through this, but before you just went into some nonsense about dihedral. What I describe is true in airplanes with zero dihedral, so I did not follow you there, or in most other places where the dartboard seemed to keep moving.

But the article you posted doesn't delve into this specific issue. At the risk of further headbashing, what evidence are you presenting that shows left rudder during a stall does not cause the left wing's AOA to increase?

 

[dtuuri]

...what evidence are you presenting that shows left rudder during a stall does not cause the left wing's AOA to increase?

Same page: http://www.av8n.com/how/htm/roll.html#fig-dihedral

Coincidentally, the diagram shows a slip in the same direction as an application of left rudder would. Exaggerated, to be sure, but you can see the relative wind striking under the right wing and above the left. Prior to the sideslip both wings would be struck from beneath. "Stalled" is irrelevant. So, the left wing's AoA is decreased not increased.

dtuuri

 

[RoscoeT]

Same page: http://www.av8n.com/how/htm/roll.html#fig-dihedral

Are you back on this dihedral merry go round?? Please say yes so I can be done with you and this thread.

 

[dtuuri]

Are you back on this dihedral merry go round?? Please say yes so I can be done with you and this thread.

The planes you fly (are you a pilot?) have zero dihedral? What evidence are you presenting that proves the left wing in your scenario experiences an increase in AoA and not a loss of lift due to fuselage interference, as shown in the linked document?

dtuuri

 

[RoscoeT]

The planes you fly (are you a pilot?) have zero dihedral? What evidence are you presenting that proves the left wing in your scenario experiences an increase in AoA and not a loss of lift due to fuselage interference, as shown in the linked document?

I have done many stalls, falling leafs, spins, and snap rolls in airplanes with and without dihedral. Yes, I mean ZERO dihedral. Lots of aerobatic airplanes have zero dihedral. Guess what....there is NO DIFFERENCE in the rudder's ability to pick up dropped wings, and cause spins and snap rolls. The rudder still causes the wing to stall further on the same side....dihedral, or no dihedral. Go get some training in an airplane with no dihedral and see for yourself.

It ain't the dihedral dude. If you want to keep thinking spins are driven by dihedral and fuselage interference, that's fine with me. There is plenty of established and published spin dynamics out there by folks with aerospace degrees that indicate otherwise.

Adios to this thread.

 

[dtuuri]

Ok, one at a time:

Kudos for offering up a lucid statement here.

Somehow I don't feel complimented.

If you are in a stall and kick left rudder, the left wing's AOA will increase (more deeply stalled), causing the left wing to drop.

If the right wing dropped and left rudder causes the left wing to drop as far or even farther in order to pick it up--you'd experience negative 'g's by kicking rudder. But you don't.

Increased AOA also causes a yaw to the left due to the increased drag of the left wing.

Well, you just "kicked" left rudder. Don't you suppose that had something to do with causing "a yaw to the left"?

What you have just created is a spin...this is how they happen.

Not that fast. A lot goes on between horizontal flight and nose-straight-down vertical flight. The yaw (left rudder induced) creates fuselage interference which raises the stalling speed (lowers the stalling angle of attack) of the left wing causing a "departure" in that direction, i.e., an "over the top" stall. As the plane rolls and falls more nose-down to the left the rolling motion centers on the spin axis. At this point a vector analysis will indicate the inside wing (left one) is at the higher AoA. The outside (right) wing may not be stalled all.

It has been shown that the inner wing has a higher AOA during a spin, though both wings are above critical AOA (stalled).

Only partially agree for most kinds of spins.

The left rudder input caused the left wing drop. The same principle can be used to pick up a right wing drop with left rudder during a stall.

I don't see how you can have your cake and eat it too.

We've already been through this, but before you just went into some nonsense about dihedral. What I describe is true in airplanes with zero dihedral, so I did not follow you there, or in most other places where the dartboard seemed to keep moving.

Most GA planes have dihedral, but my explanation doesn't present the problems yours does above. Like I said though, you don't have to have a correct theory as long as it predicts what happens reliably enough to bet your life on it. It's what you believe the most.

But the article you posted doesn't delve into this specific issue.

Ah, but it did.

dtuuri

 

[dtuuri]

I have done many stalls, falling leafs, spins, and snap rolls in airplanes with and without dihedral. Yes, I mean ZERO dihedral. Lots of aerobatic airplanes have zero dihedral. Guess what....there is NO DIFFERENCE in the rudder's ability to pick up dropped wings, and cause spins and snap rolls. The rudder still causes the wing to stall further on the same side....dihedral, or no dihedral. Go get some training in an airplane with no dihedral and see for yourself.

I've done them too, but I've reached a different conclusion about the cause and effect. Mine agree more with the linked article.

It ain't the dihedral dude. If you want to keep thinking spins are driven by dihedral and fuselage interference, that's fine with me. There is plenty of established and published spin dynamics out there by folks with aerospace degrees that indicate otherwise.

That's a strawman argument. See my last post for my understanding.

Adios to this thread.

Don't let the door slap ya...

dtuuri

 

[denverpilot]

LOL. So it's all clear now, right Bryan? (Sorry you asked, yet? Haha.)