Tail Icing

[luvflyin]

Whats the answer? This was asked in newsletter that's about dinky bug smashers. Big iron guys, chime in to. Maybe it's all the same, big or little planes. I dunno.

* You suspect ice on your tail (Horizontal Stabilizer) and you detect a potential stall on approach to landing. What do you do?
Pitch back (nose up), raise flaps
Pitch forward (nose down), raise flaps
Pitch back (nose up), lower flaps
Pitch forward (nose down), lower flaps

 

[Grum.Man]

Pitch rearward, raise flaps

 

[MauleSkinner]

Raise flaps.

 

[Stewartb]

On approach to landing? Raising flaps will increase stall speed. I'd leave flaps alone and lower the nose and/or add power.

 

[jordane93]

https://www.faasafety.gov/gslac/ALC/course_content.aspx?cID=33&sID=160&preview=true

 

[luvflyin]

https://www.faasafety.gov/gslac/ALC/course_content.aspx?cID=33&sID=160&preview=true

Hmm. It doesn't differentiate between Horizontal Stabilizers with Elevators and a Stabilator. Based on the picture showing flow, ice, separation bubble, separated region and angle of attack it seems there would be a big difference in what you should do.

EDIT: Just dawned on me that with a Stabilator, a tailplane stall wouldn't even occur.

MORE EDIT: Stabilators can stall, read on

 

[steingar]

If you're approaching a stall you speed up. Could mean pitching the nose down, could mean adding power.

 

[MauleSkinner]

On approach to landing? Raising flaps will increase stall speed. I'd leave flaps alone and lower the nose and/or add power.

If you're approaching a stall you speed up. Could mean pitching the nose down, could mean adding power.

The question was about tail stall, not wing stall. Speeding up can make things worse. Retracting flaps resolves the AOA issue with the tail.

 

[steingar]

I think tailplane stalls are a much bigger threat to turbines than smaller GA aircraft. Part of that is exposure, another in power delivery.

 

[luvflyin]

On approach to landing? Raising flaps will increase stall speed. I'd leave flaps alone and lower the nose and/or add power.

Yeah. The stall speed of the wing. You certainly have to stay above that while you are dealing with tail plane stall.

 

[MauleSkinner]

Please explain how increased velocity makes a tailplane stall worse. They actually aren't that big a worry in most GA, I think tailplane icing and tailplane stalls are a much bigger worry with turbines.

Increased speed (or power if the propwash goes over the flaps) increases the downward flow of air off the back of the wing, increasing the AOA of the horizontal stabilizer.

Edit: I’ve only ever had one tail deice failure in a light GA airplane, and I landed with flaps up on that.

Any other time I had ice on the tail of a light GA airplane, I’ve also had ice on the wings, so the whole system was screwed up, not just the tail...which is probably one reason tail stall isn’t much of a factor.

 

[Stewartb]

On typical GA planes the tail exerts a down force in flight, right? What happens when it ices up?

 

[Tantalum]

Could mean pitching the nose down, could mean adding power.

Raising flaps will increase stall speed. I'd leave flaps alone and lower the nose and/or add power.

These are literally the exact opposites of how to handle a tail stall.. the flaps increase the angle of attack on the tail, so raising the flaps will reduce that tail AoA.. you're also supposed to maintain or reduce thrust (similar reason)..

This is taught quite thoroughly.. jordane's post above has a visual and some good explanations

 

[Doc Holliday]

I think tailplane stalls are a much bigger threat to turbines than smaller GA aircraft. Part of that is exposure, another in power delivery.

Large jets typically don’t have tail anti ice or deice capabilities. It’s not an issue.

 

[Stewartb]

On typical GA planes the tail exerts a down force in flight, right? What happens when it ices up?

Tail ice is a big problem in Caravans according to guys I've talked to. I don't think Caravan procedures apply to my 180 or Cub. I guess the topic needs to be aircraft specific.

 

[Tantalum]

Just dawned on me that with a Stabilator, a tailplane stall wouldn't even occur.

Curious.. I know the shape is different, I wonder in real world testing what the airflow differences would look like. I imagine that even if you were to stall the tailplane the subsequent recovery would be easier

 

[MauleSkinner]

Tail ice is a big problem in Caravans according to guys I've talked to. I don't think Caravan procedures apply to my 180 or Cub. I guess the topic needs to be aircraft specific.

...and if tail ice is a problem on those airplanes, you’ve got bigger problems to worry about.

Like most things, it’s context-sensitive, and unless the full context is given, you have to be familiar with the topic in order to know if it applies to you or not.

 

[Kenny Phillips]

Hmm. It doesn't differentiate between Horizontal Stabilizers with Elevators and a Stabilator. Based on the picture showing flow, ice, separation bubble, separated region and angle of attack it seems there would be a big difference in what you should do.

EDIT: Just dawned on me that with a Stabilator, a tailplane stall wouldn't even occur.

Why couldn't a stabilator stall?

 

[Stewartb]

...and if tail ice is a problem on those airplanes, you’ve got bigger problems to worry about.

I don't think so. Apples and oranges. As I understand it Caravan tails lift. My plane's tails provide down force. Again, with a down force tail, what would happen if it iced?

 

[MauleSkinner]

I don't think so. Apples and oranges. As I understand it Caravan tails lift. My plane's tails provide down force. Again, with a down force tail, what would happen if it iced?

Same thing that would happen to the rest of the airplane with ice in it.

On the other hand, if the tail stalled because of that ice and your flap configuration, you’d lose the downward force and your airplane would pitch down quite abruptly.

But as I said, if you’ve got ice on the tail of your airplane, you’ve also got it on many other parts, so tail stall is the least of your problems.

 

[RudyP]

Tail stalls are pretty rare for most airframes. That video that got a lot of attention around the time of the Colgan crash in upstate New York hyped them up a bit too much IMO.

That said, if you suspect tail icing the right answer is to increase speed and minimize flap use on approach in the first place. You shouldn't be retracting flaps because you should not have full flaps in the first place. I have FIKI IPS including all three tail surfaces but the POH states that flaps should be kept to 50% or less on approach if one is using the IPS on the approach.

 

[nauga]

If you've got the altitude, raising the flaps and lowering the nose (forward stick/yoke) will both reduce tail AOA.

EDIT: Just dawned on me that with a Stabilator, a tailplane stall wouldn't even occur.

There are slots on Cessna Cardinal stabilators to treat a stabilator stall issue. F-4's had them too. T-45 just got honkin' big strakes (called "SMURFs" for a while)...all to deal with tailplane stall.

Nauga,
and the 'phantom dive'

 

[Grum.Man]

If you've got the altitude, raising the flaps and lowering the nose (forward stick/yoke) will both reduce tail AOA.

There are slots on Cessna Cardinal stabilators to treat a stabilator stall issue. F-4's had them too. T-45 just got honkin' big strakes (called "SMURFs" for a while)...all to deal with tailplane stall.

Nauga,
and the 'phantom dive'

Incorrect, pulling back on the yoke will decrease tail plane angle of attack. The answer on the CSEL test is to reduce flaps, and apply more back pressure on the yoke.

 

[nauga]

Incorrect, pulling back on the yoke will decrease tail plane angle of attack. The answer on the CSEL test is to reduce flaps, and apply more back pressure on the yoke.

If the tail has a downforce, pulling back will put it closer to or deeper into the stall. Reducing flaps will decrease downwash on the tail, reducing the AOA and giving you more stall margin so that you can pull back (increasing AOA) on the recovery. Pulling back without reducing flaps will only make things worse.

My "reducing" and "increasing" may be confusing - I'm thinking of a tail with a downforce, "lifting down", so up elevator (or stabilator) increases stab lift "down" by increasing AOA. It just happens to be inverted as compared to the wing.

Nauga,
tucked and rolling

 

[dtuuri]

If the tail has a downforce, pulling back will put it closer to or deeper into the stall. Reducing flaps will decrease downwash on the tail, reducing the AOA and giving you more stall margin so that you can pull back (increasing AOA) on the recovery. Pulling back without reducing flaps will only make things worse.

My "reducing" and "increasing" may be confusing - I'm thinking of a tail with a downforce, "lifting down", so up elevator (or stabilator) increases stab lift "down" by increasing AOA. It just happens to be inverted as compared to the wing.

Nauga,
tucked and rolling

FWIW, I agree with you. However take a look at the slide @ 17:00 to 17:30 in this video making the rounds back before the Colgan crash:

I'm pretty sure that crew thought they had tail ice and fought the stick pusher all the way to the ground. Not convinced it's even worth worrying about, myself.

 

[MauleSkinner]

Incorrect, pulling back on the yoke will decrease tail plane angle of attack. The answer on the CSEL test is to reduce flaps, and apply more back pressure on the yoke.

The IFH says to apply “appropriate” back pressure...basically, whatever the change required for the flap reduction. Up elevator increases tail AOA, but the flap retraction decreases it much more.

 

[Stewartb]

What is the typical small airplane reaction to a tail stall?

 

[Tantalum]

^instant death

 

[Stewartb]

Just say you don't know. Maybe somebody else does.

 

[dtuuri]

Maybe somebody else does.

The one instance I recall in these parts was a Cessna Skymaster, back when they were a new design, crashing into a house on final approach to Lost Nation Airport not far from where I live/d. It wedged between two walls in the kitchen and set the house on fire. A nine year old boy died in the house, but the pilot and passengers somehow escaped with their lives. I was attending ground school sessions with my dad who was learning to fly (I was still in high school) and one of the other pilots was a fireman who was at the scene. Later in life, as a corporate pilot, I had a phone conversation with an aeronautical engineer who was researching tailplane icing incidents. He was looking for suspicious crashes on final. In the conversation, I mentioned this accident and he was familiar with the crash, since it involved icing conditions and flap extension. Apparently, Cessna limited the flap range after the crash to prevent a sudden pitch down attitude and loss of control upon flap extension.

 

[Stewartb]

I’ll be more specific. If my C-180 had a tail stall in flight how would the airplane react? Would the nose go up or down?

 

[MauleSkinner]

I’ll be more specific. If my C-180 had a tail stall in flight how would the airplane react? Would the nose go up or down?

if the tail stalled because of that ice and your flap configuration, you’d lose the downward force and your airplane would pitch down quite abruptly.

 

[Stewartb]

So the theory is that the horizontal is a lift producing airfoil? Change the airplane to a Cub. Same result? Both have trimming horizontals. Interesting brain exercise, but I doubt my planes fit the model addressed by the FAA.

 

[MauleSkinner]

So the theory is that the horizontal is a lift producing airfoil?

what else would you consider it?

Change the airplane to a Cub. Same result? Both have trimming horizontals.

what kind of flaps do you have on the Cub?

Interesting brain exercise, but I doubt my planes fit the model addressed by the FAA.

If you fly in significant icing with the 180, I’d be careful extending flaps, but otherwise, no.

 

[nauga]

So the theory is that the horizontal is a lift producing airfoil? Change the airplane to a Cub. Same result? Both have trimming horizontals. Interesting brain exercise, but I doubt my planes fit the model addressed by the FAA.

Lift, either up or down, produced by the horizontal stab is what trims an airplane. If the horizontal is producing lift downwards and the tail stalls the nose will pitch down. If producing lift upwards, nose will pitch up on tail stall.

Nauga,
summing his moments

 

[MauleSkinner]

Lift produced by the horizontal stab, either up or down, is what trims an airplane. If the horizontal is producing lift downwards and the tail stalls the nose will pitch down. If producing lift upwards, nose will pitch up on tail stall.

Nauga,
summing his moments

So...stupid question...are there type examples of tail stall when the tail is lifting up?

 

[nauga]

So...stupid question...are there type examples of tail stall when the tail is lifting up?

The only cases I can think of off the top of my head are at very high angle of attack and not GA.

Nauga,
not flying so much as plummeting

 

[Stewartb]

There is no airfoil in a Cub tail and very little if any with a Skywagon tail. With the Cub it relies on deflection. I presume the 180 is similar. I’ve flown with residual hard ice on the tails of both with no problems. I’ve never given tail stalls much thought.

My Cub has 9’4” split flaps that deploy to 70*, but 50-55* appears to be the more practical limit.

 

[nauga]

There is no airfoil in a Cub tail and very little if any with a Skywagon tail. With the Cub it relies on deflection. I presume the 180 is similar.

Even a flat plate produces lift with angle of attack, positive or negative. If a stab didn't produce lift it would just be excess weight and drag hanging off the back end, that's how it stabilizes and controls.

Nauga,
because it's there

 

[Stewartb]

An aerodynamic stall caused by ice is harder to explain in the absence of a lift-producing airfoil.At least to my feeble brain.