Serious wing drop at stall

[Hudson]

It is generally well known that some Cessna 150/152 aircraft exhibit a marked wing drop at point of stall with full flap down and a trickle of power. This assumes a balanced flight entry. In fact mis-rigging can also cause a savage wing drop even with idle power and flaps up.

Some say that this is a good thing, because it teaches wing drop recovery technique. This disregards the fact that modern trainers are not supposed to drop wings at point of stall.

It is my understanding that at certification for these and similar types, the maximum wing drop at the stall should be no more than 15 degrees whether a clean or dirty stall configuration.

So, if the stall entry is accurately flown (no skid and wings level), and yet the wing drops suddenly without prior warning beyond (say) 20 degrees, should the maintenance log be endorsed that the aircraft is un-airworthy?

Obviously there is a safety issue here. When students are authorised for solo stall recovery practice, or even first solo circuits, is it too much to expect that the aircraft should exhibit safe stalling characteristics commensurate with that expected during type certifcation tests?

While to an experienced pilot, a sudden unexpected savage wing drop at point of stall might be good fun in the hack-flick-zoom department, it can be thoroughly frightening for a student pilot who might just happen to hold off high during landing.

The discussion is about sudden and unexpected wing drop at the instant of stall. Of course all bets are off if the pilot deliberately holds back stick after the aircraft has stalled, where a wing drop may well occur.

Is it agreed that instructors who teach stall recoveries have a duty of care responsibility to write up an inappropriate wing drop, and to ensure the aircraft is not flown again until a rigging check is carried out and the aircraft further test flown before students are permitted to fly it.

The question is therefore, what would you define as an inappropriate wing drop?

[IRRenewal]

After writing the response below I noticed you are in Australia. The answer is based on UK requirements and CAP520 is a UK publication.

For the purpose of air tests (3 yearly CofA renewal), the book (CAP520) says:

Power off
Balanced entry
Decelerate at 1 Kts/sec (accept height loss)

Then:

'Any tendency for a wing to drop at the stall should be containable primarily with aileron assisted by rudder to within 20 degrees bank'

Note the recovery technique, aileron assisted by rudder.

It only says that in this particular set of conditions the wing drop should be containable to 20 degrees. When no action is taken the wing could drop more and that would be acceptable

If these conditions are not met (power on, quicker deceleration) it is quite well possible (and not unacceptable) for the aircraft to drop a wing more than 20 degrees if immediate (and correct) recovery action is not taken. Most student would fall in that category. The correct recovery method in most A/C requires the use of rudder. The fact that CAP520 calls for aileron builds in an additional safety factor if the student in his panic applies the wrong controls.

So, if you are worried about the handling of the A/C try some stalls exactly as described above. Only if you cannot limit the bank angle to 20 degrees in those circumstances should you put an entry in the tech log.

Regards

Gerard

[BEagle]

"The correct recovery method in most A/C requires the use of rudder."

It most certainly does NOT! That old nonsense of 'picking up a wing with rudder' or 'stopping wing drop with rudder' positively invites student over control and an incipient spin. The only use of the rudder is to keep the ball correctly centred!

STANDARD stall recovery is:

FULL POWER and Control Column centrally forward until the stall identification has ceased, maintain that pitch attitude, then and only then level the wings and recover from any descent. Throughout the entry and recovery, use only sufficient rudder to keep the a/c in balance.

[IRRenewal]

FULL POWER and Control Column centrally forward

In that order? Sounds like a spin waiting to happen to me.

BTW, I never used expressions like 'picking up the wing with rudder'. I merely pointed out that for a CofA air tests any wing drop should be contained to within 20 degrees using the ailerons as the primary (and possibly the only) control, whereas in a training situation you'd use rudder a bit earlier on in the recovery.

[MEI]

Errr, full power??

Hmm, always taught to get the nose down to get her flying again, then again that was FAA what do I know??

[Tinstaafl]

Don't quite agree with 'keep the balance ball in the middle', although it's close to my thoughts. I prefer 'prevent yaw with rudder' (aka 'stop the nose moving sideways').

If that's not achievable then an incipient spin technique is on the cards.

[ovum]

http://www.gliding.co.nz/Operations/Instruct/p1.pdf

or

Rudder in the stall
A spin can be prevented even when aggravated by the ailerons if the pilot maintains directional control through use of the rudder. A spin can only occur with the addition of yaw in the stall. The rudder can and should be used to prevent any yaw in the stall and the recovery procedure. The correct use of rudder in stalls is essential. The rudder controls the yaw which means it can keep the speed of each wing the same or cause one to be ahead (faster) than the other. The slower wing will stall first and drop. Any effort to raise the wing with aileron will add drag and deepen the wing's stall.

The rudder is the last control to lose effectiveness. Even in the stall if there is some forward momentum there is some degree of effectiveness. In a stall entry you first lose aileron control, then elevator and lastly rudder. On recovery, you gain rudder control first then elevator and lastly aileron. As the most effective control during slow speed maneuvers rudder, correctly applied, can compensate for the lost effectiveness of the ailerons. The rudder can be used to keep the wings level to the relative wind. Such level wings causes the stall break to be without a wing dropping. Keeping the ball of the inclinometer in the center gives assurance that the tail is following the nose. This is coordinated flight. If the heading indicator is held steady with a very gradual application of right rudder, little or no aileron movement will be required to keep wings level.

Source: http://whitts.alioth.net/Pagea8Stall...erformance.htm

thoughts?

[fireflybob]

Beagle's explanation of the "Standard Stall Recovery" is absolutely correct. The selection of full power will minimise height loss which may well be critical in the event of a stall at relatively low level.

The only word I would add is "simultaneously" to select full power and move the control column centrally forward etc.

[minus273]

Hey all

I am just wondering if part of the difference in techniques here is that different countries expect different things in the stall.

By that I mean that in the US and Canada where I flew during training you were expected to go to a full stall until it broke i.e full stall. From when I did my JAA training you went to the initial stall indication i.e recognition, buffet etc.

From my limited understanding of the matter using the aielerons to recover at the buffet is not as much of a problem as using them when the aircraft has fully stalled.

I also think that the different stages of the stall have to be used when you are talking about them i.e. entry, recognition, full stall, recovery. As talking about what you are doing without each section being explained can be misleading.

I have seen my students attempt to use aieleron instead of rudder when we are fully stalled and we seem to go upside down and start a helical pattern toward the ground just above stall speed. That requires use of rudders to stop it as well as in some aircraft a puch forward on the column to break the stall.

One of the teaching methods that we used if the student was not using rudder was to get them to sit on their hands and the instructor would then move the column and they would have to use their feet to control the aircraft through the full stall process.

I also think that some of the problem, and I am not having a JAA versus the rest of the world thing here, is that some of the JAA courses teach the students to fly a little trainer aircraft like a big jet and the two of them are completely different.

Aside from stalls I have seen some weird teachings on other items as well:

An example of this is when I was sitting in ground school in the UK and the instructor was trying to tell me that it was OK to use aieleron to recover from VMc. That may be fine in a big plane but in a small one that is going to make for a bad day.

So I may be wrong and I usually am but thought that this may explain some of the differences.

-273

[DFC]

Those who advocate the application of full power before moving the control column forward should remember the secondary effects of increasing power - pitch and yaw. Most trainers will pitch up and yaw to the left when increasing power. If you are using the elevators to reduce the angle of attack (recover from the stall) the last thing you need is to have to work against a pitching moment caused by a sudden increase in power.

As instructors we frequently have to remind both students and PPLs to apply rudder when increasing power to enter a climb........if they can't keep the aircraft balanced there does anyone think that they will be able to apply full power while stalled and remember to prevent the resultant yaw.

When stalling with flaps, lateral stability is reduced.

With power applied, we can prevent any yaw with the rudder but as speed reduces, the torque from the engine can cause a rolling force which needs to be counteracted with aileron...thus putting one aileron down, thus increasing the angle of attack on the outer part of a wing that aleady has reduced lateral stability with flap extended.

The result is that one is more likely to get a wing drop when stalling with power and/or flap.

SSR is stick forward, full power establish the aircraft in a climb.

The stall recovery comes from reducing the angle of attack - moving the stick. Minimising the height loss comes from the use of power.

Note - if the nose drops significantly during the stall and recovery, adding power may simply accelerate the aircraft towards the ground. In such a case, it may be more prudent to delay application of full power.

-273,

You mention recovery from Vmc.....are you not mixing up Vmc and the stall........they are two totally different things. If the aircraft is departing from controlled flight below Vmc then it must be a multi and the only recovery option is to reduce the power on the operating engine......that is why it is called Vmc

Regards,

DFC

[minus273]

Hey there.

Nope not mixing VMc and Stalls up I have a lot of experience in teaching both, the comment I made was more to do with people being taught to fly small planes like big planes and that during a ground school class in the UK to convert my licenses the GS instructor decided to teach the class that it was ok to use aileron to control the movement of the aircraft during VMc.

I told him he was wrong, politely of course and the rest of the class thought I was mad. I did explain to them that they would have a lovely view of the world below them if they decided to use this method but hey I was only an FAA ATPL and Instructor so what did I know.

Anyways sorry if my first post made it sound if I was equating VMc and stalls.

-273

[Raw Data]

I think BEagle is thinking of a stall recovery in a transport-category jet, in which case he is essentially correct.

In a light aircraft, you have other considerations (propwash, secondary effects of adding power etc), and not adding rudder will simply allow the wing-drop to develop into an incipient spin. You don't use the rudder to "pick the wing up" (unless you are showing off!), you are simply limiting yaw, and the secondary effect thereof.

It wasn't so long ago that "rudder only" was taught in the recovery technique, and using ailerons was a complete no-no at the stall.

Anyway, if the CAA says "do it this way", you have little choice in the matter when renewing your licence...

[BEagle]

No I wasn't. I was referring to STANDARD STALL RECOVERY:

FULL POWER and, at the same time, Control Column Centrally Forward until a pitch attitude is reached at which the stall identification/sign/symptom (call it what you will) ceases. Maintain that pitch attitude

Then - and only then - level wings and recover from the descent.

AT ALL TIMES during Standard Stall Recovery, Rudder is only used to maintain balanced flight .


All the BS about 'torque effects', 'secondary effect of power inviting an incipient spin' on this thread should be ignored. If a wing drops at the stall, do not attempt to control it with aileron, rudder or anything else - just let it drop. Then follow Standard Stall Recovery and use aileron to roll the wings level, rudder only as required to maintain balanced flight WHEN THE STALL HAS CEASED!!

[gemini76]

BEagle

N H Birch and A E Bramson - FLIGHT BRIEFING FOR PILOTS 1

" THE FULLY DEVELOPED STALL

Due to manufacturing inaccuracies and particularly on aeroplanes with highly tapered wings it is usual for one wing to stall slightly before the other. The early stalling wing will drop first causing the relative airflow to approach from below, thus still further increasing its angle of attack and stalling that wing even more. Concurrent with these developments the up-going wing partially unstalls because its relative airflow comes from above. If allowed to develop the nose will swing towards the lower wing because of increased drag on the fully stalled wing and weathercock action. All the conditiond for a SPIN would then apply. An attempt to raise the wing with aileron would merely aggravate the situation since in the case illustrated the left aileron would be depressed. Such action would in effect still further increase the angle of attack. Likewise the up-going aileron on the raised wing would,in effect,reduce its angle of attack, aggravating the roll/yaw situation already mentioned. When a wing drops during a stall, yaw must be prevented by application of opposite rudder (in this case RIGHT), when the wings may be levelled after flying speed has been regained. The full recovery procedure is outlined under Flight Practice.

Flight Practice

The Standard Recovery
( Stall and Recovery with Power)

a) Proceed into the stall as before, noting height shortly before the stall.
b) As soon as the nose commences to drop, open the throttle fully and gently ease the stick forward. It should not be necessary for the nose to go far below the horizon. Note that very little height is lost.

Recovery when a Wing Drops.

If a wing should drop. opposite rudder must be used to prevent a yaw developing. Level the wings after flying speed has been regained "

Always found Birch & Bramson literature to be easy reading, and after all I think its the wording that matters here.

In my early PPL training my instructor, whose words I often recall even after 25 years, were

" PREVENT FURTHER YAW WITH OPPOSITE RUDDER "

regards,

[fireflybob]

gemini76, much as I respect Birch and Bramson things have moved on since those days and the STANDARD STALL RECOVERY which Beagle has enumerated is absolutely correct and is what, I believe, is now taught by the RAF CFS - a respected body which has extensive experience in the teaching of basic flying.

[BEagle]

Rudder is only used to maintain balanced flight. That doesn't mean using more rudder than, as gemini76's instructor told him, is required to prevent yaw.

Just keep the ac in balance, that's all. "When a wing drops during a stall, yaw must be prevented by application of opposite rudder" means the same thing, in my opinion, whereas an overenthusiastic hoof full of top rudder may well cause an incipient spin in an unexpected direction! But use of aileron in the stall is fundamentally incorrect and, in some SEP Class aeroplanes, will certainly cause significant undemanded roll rates - the classic hallmark of an incipient spin.

[Raw Data]

BEagle

The recovery you gave is for recovery from the first indication of a stall (ie a stall warning horn or buffet). In fact, the aircraft is likely not fully stalled at all; but it will if you persist. If you look at the top of the thread, it is about recovery with a wing drop , which is different; the aircraft has fully stalled, and is departing.

Of course, you might be right and the CAA, and other experts as quoted here, might be wrong.

or, more likely, not...

[BEagle]

Nope, I am indeed talking about a fully developed stall with a wing drop.

If it drops, let it - don't try to pick it up or prevent it dropping further, carry out STD STALL RECOVERY promptly. Significant departure will only develop if the recovery is mishandled, usually by incorrect use of aileron or rudder. Recover from the stall using STD STALL RECOVERY, keeping the ac in balance with rudder throughout.

To which 'Experts' do you refer?

[NinjaBill]

In the half dozen or so aircraft types I have flown, the standard stall recovery described by BEagle works perfectly on every single one.

The only time i have come accross a diferent recovery was when flying gliders, where the recovery was the same, but without the application of power (for obvious reasons)

Why anyone would seek to make this any more complicated than necessary, is beyond me.

NB

PS I dont know what the criteria for defining expert are, but judgeing by the past posts made by BEagle, he meets all of the critera i can think of to be judged as one.

[Raw Data]

Hmmm, let's see:

I said

You don't use the rudder to "pick the wing up" (unless you are showing off!), you are simply limiting yaw, and the secondary effect thereof.

You said

Recover from the stall using STD STALL RECOVERY, keeping the ac in balance with rudder throughout.

We are talking about the same thing - keeping the ball in the middle - limiting yaw (to keep the ball in the middle). I am not suggesting for a minute trying to oppose the direction that the aircraft is turning should a wing drop, or use a bootful of rudder - and I don't think anybody else is either.

Experts - N H Birch and A E Bramson - FLIGHT BRIEFING FOR PILOTS 1

...and contrary to what fireflybob said, I don't think much has moved on "since those days", as most trainers in use today were either around, or being designed, then.