Tail Stalls?

hammer

hammer

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I had a DE tell me recently that the reason the flaps in a 172 have a placard that says "avoid slips with flaps extended" is because you have an increased liklihood for a tail stall. First question, is this true? Second question, what is a tail stall? I feel kind of ignorant asking this but I did some looking and although I find mention of tail stalls, I can't find a good definition of one. Is it a stall that effects the entire tail (otherwise, would it be called an elevator stall)? What is recovery like?
 
Ya know how the tail makes that 'negative lift' to 'hold' the nose up and allow the airplane to have positive stability?

A tail stall is what happens when the horizontal stabilizer's critical angle of attack is exceeded. You no longer have that negative lift and the nose will drop rapidly (CG is fore of center of lift).

It could happen if you pull back rapidly and the tail stalls before the wing stalls, but airplanes are tested so this doesn't happen.

If you fly into icing conditions the tail is more likely to get ice than the wings, and any ice that is accumulated will be much greater on the tail than on the wings, which could lead to a tail stall.

The recovery procedure would be to decrese the AOA of the tail; i.e., push forward on the yoke. You also want to decrease power.
 
I've tried numerous times to get a tail stall (at altitude of course) in a 172 by slipping with flaps and have never been able to. Has anyone else?
 
Oh and for the 172 'avoid slips with flaps extended'... Gene Whitt mentions on his site very quickly that he has experienced this while slipping with full flaps. This is the only time I've heard this, and 99.9999999% of the time nothing will probably happen. Other people say it's because Cessna didn't want the buffett ('burbling' air over the tail) to freak out pilots while slipping and lead to a loss of control. Who knows... but I personally would rather follow Cessna's advice and plan my approaces so I don't need to slip, or just go around.

BTW is 'burbling' a word?
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I didnt even know a 172 could have a "tail stall"....ive heard of t-tails getting mushy at low airspeeds...but i think this is due to the decreased prop wash over the control surfaces. Hopefully i'll never have to learn first hand about a tail stall.

-seth
 
I've experienced the buffet in 172's with 40 degrees of flaps but I would consider it mild. The placard says avoid and not don't, so if you need to slip it, go ahead. It comes down like a rock with 40 degrees out and a slip.
 
SkyGuyEd..

I cant even really make the C-172 stall in a slipped config. As I attempt to approach the stall, the airspeed gets so slow that I cant maintain the rudder authority to maintain the slip. So, usually, if I DO stall, I am nearly wings level and unslipped when it occurs.
 
Good call. In a light aircraft like a 172, by the time you get slow enough to stall the tail, even with flaps in, you are probablly really close to stalling the wing anyway. And if it DOES happen, its pretty easy to catch. Now the T-tail is a horse of a different color. That was one of the REAL fears of F-104 Starfighter pilots. That airplane needed EXTREME angle of attack in order to manuver, however if you got the AOA too high, the turbulant air coming off the wings would "blank out" the tail, and cause the nose to violently pitch up, or drop. It was unpredictable as to which one would occur. Definately an interesting topic, but not really something to fear in little airplanes. Just respect the buffet.
 
[ QUOTE ]
I had a DE tell me recently that the reason the flaps in a 172 have a placard that says "avoid slips with flaps extended" is because you have an increased likelihood for a tail stall. First question, is this true?

[/ QUOTE ]If you go to your POH or PIM and look at the expanded normal procedures (the part after the checklists that no one reads
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), you will find Cessna's reason for the advisory.
 
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The recovery procedure would be to decrese the AOA of the tail; i.e., push forward on the yoke. You also want to decrease power.

[/ QUOTE ]

I'm sure what you meant o to say is that to get out of a tail stall, you pull back on the yoke and decrease power. It is the opposite recovery to a wing stall.

Ray
 
Actually, the recovery isn't quite that cut and dry. As I am sure you are aware, an airfoil can stall in either an extremely positive AOA situation, OR in an extremely negative AOA situation. This includes the horizontal stab. So the correct action is to UNDO what you just DID. If youre pulling too hard, and the tail stalls, stop pulling. Same with pushing. Like I said, this can happen to ANY airfoil. Even the rudder. Its possible to stall it and swap ends. This is quite an interesting topic, but it seems to me that it boils down to a simple piece of advice to all pilots. Listen to what your airplane is telling you.
 
Putting the airplane configuration back the way you had it was usually the best option. Tail plane stalls can also happen if tail plane icing is encountered. The recovery (at least on the twin otter flown by NASA) was to pull the nose up, and raise the flaps depending on the situation.
 
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