Pushover from Pattern Altitude

[poadeleted20]

In a descending turn a slip decreases the difference in AOA between the two wings and therefore reduces the chances of a spin.

It may reduce it, but it does not eliminate it. You really can spin out of a crossed-controll stall whether the rudder is in the same direction as the bank or opposite it.

 

[gismo]

It may reduce it, but it does not eliminate it. You really can spin out of a crossed-controll stall whether the rudder is in the same direction as the bank or opposite it.

If you stall while you're turning left with right rudder (slipping turn), when the plane rolls off to the right it looks to me like the plane would then be skidding to the right as it starts to spin. I thing the same would be true if the plane was initially slipping with the left wing low while holding heading. That said, when I've tried to initiate a spin from a slip I've been unable to precipitate a stall, let alone a spin. It seems that the slip diminishes the elevator authority enough to preclude reaching the critical AoA. This is in the Porterfield, I'm a little reluctant to try any sort of uncoordinated stall in the Baron given their proven tendency to enter unrecoverable spins.

 

[COFlyBoy]

In a descending turn a slip decreases the difference in AOA between the two wings and therefore reduces the chances of a spin. A skid is much, much worse, increasing that difference. In level flight it doesn't make much difference.

I really need to post those pictures of my AOA demonstrator, but gotta take them first.

Dan

Gotta cry foul on there being a difference between level flight and descending. If you aren't accelerating down, then descending flight is the same as level flight (its just at an angle relative to the ground).

 

[jesse]

It may reduce it, but it does not eliminate it. You really can spin out of a crossed-controll stall whether the rudder is in the same direction as the bank or opposite it.

You won't spin from a slip. You can transition from a slip, to wings level, to a skid and then spin. That is no longer a slip and it's damn hard to get an airplane to do that and it's very obvious it's occurring - giving you plenty of time to prevent it.

I'm curious what light ga aircraft will spin from a slip? You must have experience doing it since you've made statements as if you've had. I'm damn curious because I've never got it to happen and I don't know someone that has. Slip to skid to spin is not a spin from a slip and is easy to prevent.

 

[timwinters]

What model of 172 tells you to fly the downwind at 61 KIAS????

Most POHs I've seen will give you a flaps up approach speed of 65-75 KIAS. 61 KIAS is for short field final approach with full flaps.

1957, C172 (no suffix), my 182 is a 1958 A model.

At any rate, I still don't understand the contention that the downwind should be flown flaps up at 61 as Tim mentioned.

I never trim with flaps up. I always have the first notch of flaps in.

By the way, the older 172s and 182s are far less nose heavy than the later models, especially the 182s. I trim my 182 on downwind and never have to touch the trim again. It will naturally slow as I continue to add flaps and it never gets nose heavy nor requires additional trim to relieve yoke pressure. It seems that some 182 models need small increments of additional nose up trim all the way to the flare.

 

[poadeleted20]

You won't spin from a slip. You can transition from a slip, to wings level, to a skid and then spin. That is no longer a slip

So your point is that as the airplane departs from controlled flight, you're no longer in a slipping turn, and thus the spin you enter was not entered from a slipping turn, but rather from some intermediate state? :groan:

The dynamics of that situation do mean that in the interim after the airplane departs from controlled flight the airplane will briefly be in something other than a slipping turn before the spin starts, but the point remains that you can enter a spin from a stall entered in a slipping turn.

 

[Dan Thomas]

Gotta cry foul on there being a difference between level flight and descending. If you aren't accelerating down, then descending flight is the same as level flight (its just at an angle relative to the ground).

Argue with the textbooks, then. I'll post the pics of the AOA demonstrator. Any downward turn is a spiral and the geometry involved with a helix changes the AOA between the wings.

Dan

 

[jesse]

The dynamics of that situation do mean that in the interim after the airplane departs from controlled flight the airplane will briefly be in something other than a slipping turn before the spin starts, but the point remains that you can enter a spin from a stall entered in a slipping turn.

The point is that it's generally harder to spin in a light ga aircraft by adding pro-slip rudder in the turn. If you're racking it around steep and you're concerned about a spin you can dump in pro-slip rudder and alleviate that concern while bringing yourself down faster.

I still want to know what light ga aircraft you've flown that'll enter a spin from a turning slip? I'd sure like to know so that I can find one and try it.

 

[RMCN172RG]

In the C-172, the technique that I've been taught and strive for consistency with in the pattern to descend to land is:
Abeam the threshold, power to 1500, carb heat on, pull yoke to maintain traffic pattern altitude and slow to 80kts, 10 degrees of flaps, push over to maintain 80 until downwind to base turn point.

Slight variance mid field Carb heat and Gear down, trimmed for 80 knots, in your case down and welded so only two items. Abeam the numbers pull the power add a notch of flaps and hold level. She'll slow down and go down at about 75 knots. Smooth as a ....... you get the idea.

 

[nosehair]

I still want to know what light ga aircraft you've flown that'll enter a spin from a turning slip? I'd sure like to know so that I can find one and try it.

Hey, whassat on your face _ a prop strike? (j/k)

Anyway, any ol' 172 or whatever will roll right on over the top side into a spin in the other direction if you just set there and go into a slipping turn and cram full top rudder and yank it back and stall it and let it roll over and keep the rudder in and now your skiddin into the turn in the other direction and into the spin.

You both know thats what your sayin, don't you?

 

[whifferdill]

Hey, whassat on your face _ a prop strike? (j/k)

Anyway, any ol' 172 or whatever will roll right on over the top side into a spin in the other direction if you just set there and go into a slipping turn and cram full top rudder and yank it back and stall it and let it roll over and keep the rudder in and now your skiddin into the turn in the other direction and into the spin.

You both know thats what your sayin, don't you?

If any relatively pointless illumination has come from this thread drift, it seems to be that some planes will and and some planes won't. I will believe that some planes will, if you will believe that some won't.

For the non-believers, take your selection of RV, Pitts, Decathlon, Citabria, or Cub (those are all I can confirm...I'm sure there are many more), and set up a slip with full aileron and rudder deflection just as you would to lose altitude on a normal power-off approach...then pull the stick all the way back without removing any aileron or rudder. Be prepared for a dissapointing non-event.

If anyone CAN produce otherwise from the conditions I described, in the airplanes I mention, I'd like to know the secret...because I would sure like to figure out how to increase my chances of spinning out of my typical slipping approach when I'm on short final.

It seems others have produced a spin under these conditions in planes I have not attempted this in, and I have no reason to think they are mistaken.

So far we've heard of two "spinners" - Cherokee 140, and C-172...both metal trainers. If this is truly the case, it's further irony how airplanes that have been designed to be aerodynamically forgiving to the lowest-common denominator are just the opposite under certain conditions. I will take my aerodynamically neutral "unforgiving" Pitts any day. It'll easily recover from anything you ask it to, and also do anything you ask, except spin out of a full slip it seems.

 

[denverpilot]

So far we've heard of two "spinners" - Cherokee 140, and C-172...both metal trainers. If this is truly the case, it's further irony how airplanes that have been designed to be aerodynamically forgiving to the lowest-common denominator are just the opposite under certain conditions. I will take my aerodynamically neutral "unforgiving" Pitts any day. It'll easily recover from anything you ask it to, and also do anything you ask, except spin out of a full slip it seems.

I found it difficult to get C-172s to do this, if at all, power off. I keep noticing in the thread that the people who are arguing that most trainers "won't do it" are talking completely power-off, in a descent for a landing... and those saying "it will do it!" don't specify.

Add some power, usually all of it, and it'll whip right over.

I'll specify for my experience. It required power. All of it at my altitude up here, and power on, a C-172 will go right over the top and enter the spin toward the up-wing side. Someone else here alluded to it... they said their instructor set up for a "departure stall"... power all the way up, get the yoke back in your lap, slip like mad, and it'll break "over the top". Relatively slowly.

Most C-172s I did it in, liked going left more than they liked going right. Right would take a rediculously long time to develop.

One airplane (that was probably out of rig... it didn't particularly fly straight even after much screwing around with the rudder trim tab -- I hate junk rentals...) would be particularly snappy entering to the left, and it was the aircraft we shot video of.

And the video... of course... is long gone, lost in a move many years ago...

Didn't really try it, but I suppose you might get a Skyhawk to do it, set up for lower or no power, if you really yanked from fast level flight trying to force an accelerated stall, but you're just abusing a Skyhawk doing that...

And if anyone's doing that much yanking in the pattern, they probably deserve to end up in a pile of sheet metal off the end of the runway, anyway.

I'd love to go see what a older straight tail 150 would do... those are spinnin' little fools, and the non-swept tail had more rudder authority than the later swept tails.

But around here, two guys in a 150 or 152 with half tanks is barely going to get off the ground on a summer day anyway, so I had to move over to a 172 very early in flight training.

 

[Dan Thomas]

Here are the pictures of the AOA table as promised. The thing is built of 1/4" steel rails, bent to represent relative wind on each wing. The angles and radii are exaggerated so that the angles and changes are easily visible; in real life, they're much smaller but are still a factor in stall/spin stuff. A small model, made so that the wings are precisely aligned with each other and have no washout, is placed on the rails to demonstrate the AOA of different modes of flight. Before anyone challenges it: Those climbing/descending turn rails are parallel, as the relative wind would be in flight, but because the inside one has to drop more in a shorter distance its angle is steeper. This difference is what kills the base-to-final skidders or glide-stretchers. The same helical difference is the reason we have twist in propeller blades. Same distance travelled through the axis of the helix, different angles at different radii.

The first few show a descending turn; with coordinated flight, the AOA is higher on the inside wing. Skidding increases the AOA there, slipping decreases it. A climbing turn shows the AOA higher on the outside wing. A level steep turn shows that the AOA is the same on both wings, but in reality the usual overbanking tendency demands a bit of opposite aileron, which raises the AOA on the inside wing on the span occupied by the aileron. Next we have level cruise flight (low AOA), a normal glide (low/moderate AOA, and a stretched glide (high AOA, high drag, high sink rate. Might not stall but still can kill.) And last, we have the buzz job: The guy who flies level and does a sharp pullup, increasing AOA briefly before the flight path turns upward and reduces it. If the guy is aggressive enough he'll get an accelerated stall and kill himself, even if he's well above stall speed.

Hoping this helps

Dan

 

[dmccormack]

Hoping this helps

Dan

Wow! That's neat!!!

But -- where's Bernoulli?

 

[poadeleted20]

The point is that it's generally harder to spin in a light ga aircraft by adding pro-slip rudder in the turn.

I agree that it's harder to get yourself into a fully developed spin from a crossed-control stall with rudder opposite bank, but the point remains that it is possible.

If you're racking it around steep and you're concerned about a spin you can dump in pro-slip rudder and alleviate that concern while bringing yourself down faster.

While that's true, you can kick in bottom rudder, too, and there's no chance of spinning there, either, unless you stall the plane. But if you do stall the plane with controls crossed at TPA or below, you can still have a real "Bad Day at Black Rock" whether the turn out of which you stalled was skidded or slipped.

I still want to know what light ga aircraft you've flown that'll enter a spin from a turning slip?

Well, given your definition of the situation, where you consider the plane to be no longer in a turning slip when the nose starts over the top, and it won't be in a spin until after that happens, then by your definition, no plane will enter a spin directly from a turning slip. But that's a semantics issue, and doesn't change the fact that if you stall while in a slipped turn, you can end up in a spin if you don't fix things fairly quickly.

Yes, you have more time to fix things in that case than a skidded turn stall, and it's easier to prevent a spin from occurring. However, as I've found teaching crossed-control stalls, the "over the top" movement when you do that with top rudder can be significantly more disorienting than the more direct downward nose slice of a bottom rudder crossed-control stall, and that can delay the application of the correct control inputs.

All in all, it's best simply not to stall in the traffic pattern -- that will prevent all the spin problems arising from both slipped and skidded turns.

 

[Dan Thomas]

Wow! That's neat!!!

But -- where's Bernoulli?

Steel rails don't demonstrate pressure drop too well.

Dan

 

[dmccormack]

Steel rails don't demonstrate pressure drop too well.

Dan

Well, I'm not disappointed at all -- that's a very well done model!