Serious wing drop at stall [Archive]

Hudson

1st May 2004, 10:36

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

1st May 2004, 11:19

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

1st May 2004, 12:41

"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

1st May 2004, 17:09

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

2nd May 2004, 20:23

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

2nd May 2004, 21:56

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

3rd May 2004, 07:23

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%20Origin%20and%20Performance.htm

thoughts?

fireflybob

4th May 2004, 10:48

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

4th May 2004, 15:50

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

4th May 2004, 18:50

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

4th May 2004, 19:29

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

5th May 2004, 01:50

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

5th May 2004, 06:42

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

5th May 2004, 07:38

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

5th May 2004, 08:24

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

5th May 2004, 08:26

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

5th May 2004, 08:47

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

5th May 2004, 09:30

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

5th May 2004, 10:35

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

5th May 2004, 12:55

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.

gemini76

5th May 2004, 14:17

Thank you....!!!!

regards,

BEagle

5th May 2004, 14:30

I do NOT profess to be an 'expert' and am dubious of those who would consider themselves as such. However, the Standard Stall Recovery I advocate is that which I was required to teach for my CFS A2 QFI test assessed by a CFS Exam Wing examiner, to brief at a FI re-validation seminar asessed by the ex-CAA CFE and to teach to a CAA Staff Examiner on my last FI re-validation flight test.

If it's good enough for them, it should be good enough for others, in my opinion - and it's worked fine for my students for the last 15 years.

I guess we're actually in agreement, it's just the wording that differs.

mad_jock

5th May 2004, 15:08

The 2 methods are being taught on FIC's.

BEagles method was explained to me to be the RAF's method of teaching which is basically unload the plane and the stall shall disappear. Which dates all the way back to the guy that found out that you cure a stall by pushing forward instead of pulling back which was the method before he discovered this fact. I seem to remember he got court martialled for not pulling back,but hey at least he was alive to be court martialled. It works for all types of stall be it low speed, high speed in the turn etc.

The other method of picking the wing up with yaw is also taught along with some more unusual "unusual attitude recovery techniques" which the yanks are all in favour of. I believe it was a factor in the fin coming off the airbus which was caught in wake turb just after sept 11th.

So the method being taught is mainly due to the background of the instructor. If they have any mil training behind them they will unload. US training they will pick the wing up. And home grown will depend on who trained them for there PPL / FIC.

Most staff examiners are ex mil so they will accept both.

Who's right? who cares the full stall is one of the most artifical exercises in the PPL with some examiners making the students hold it in the full stall for 15-20 seconds or until a wing drops and others letting them recover on the buffet.

Until the chief examiner actually expresses an opinion and publishes it. Both methods will be instructed.

Myself personally had to teach the pick the wing up method because thats what the local examiners wanted. So until the examiners get there act together and stick to the party line there is not alot the instructors can do about it.

Its a bit like the instructors who teach point and push instead of power for sink and attitude for speed in light aircraft.

MJ

Raw Data

6th May 2004, 06:28

I would have thought that the "correct" method is specified in some CAP or other - everything else is, it seems. Maybe a JAA publication. That ends the argument immediately.

I have always taught it both ways... "this the warning... recover... this is the buffet... recover... this is abusing the aircraft by holding it in the stall, look how benign it is... recover... this is a wing dropping... recover... oh look, we are in a spin now... recover..."

I once had a Japanese student, inherited from another instructor, who claimed to know spin recovery, but when handed the controls of a spinning Aerobat, didn't recover. I ended up taking the aircraft up to 6000 feet, putting it in a spin, and waiting for him to recover it. After six turns, I gave up and did it myself.

"Do you know a standard spin recovery?"

"Ah, yes"

"Hmmm... describe a standard spin recovery."

Silence.

A cultural problem...

BTW, thank you BEagle for laying out your credentials. I shall henceforth genuflect whenever I see your username... ;)

BEagle

6th May 2004, 07:19

Just throw money :p

Re spin recovery, although it wasn't much use for teaching aeros, the T67a was great for teaching manoeuvre stall recovery, decent stall training and basic spin training.

But I was once doing the 'low steady airspeed, high rate of rotation, high descent rate' patter to a student - only to see him gazing fixedly at the left wingtip! In all the spin training I'd ever done, I'd never come across anyone who didn't look straight ahead in the spin!

DFC

6th May 2004, 20:17

BEagle is correct to say that if a wing drops then moving the stick forward will unstall that wing and prevent any spin.....no stall, no spin.

However, I believe that the emphasis is put on using rudder to stop a wing drop because if the student has a burning desire to use the aileron.

---

-273,

The Vmc speed is based on the lowest speed at which the rudder can prevent the yaw caused by the operating engine(s) with the failed engine feathered.

Thus as the aircraft is about to depart, the rudder is at maximum deflection.........it's all about yaw.

If the aircraft is banked 5deg towards the live engine, then the amount of rudder required is reduced....secondary effect of roll is yaw. Yes there is the adverse yaw factor but most modern aircraft have other measures to reduce adverse yaw.

However, if with full rudder and having used the ailerons to bank the aircraft 5 deg towards the live engine, the speed is allowed to reduce below Vmc then the aircraft will yaw (and roll) away from the live engine unless power is reduced...........the apparent wing drop is not as a result of that wing being stalled it is simply the secondary effect of yaw which is roll....and you won't enter a spin unless the wing does stall which depends on how close the stall speed and Vmc are.

So basically, Vmc has nothing to do with wing drop at the stall.

Regards,

DFC

minus273

6th May 2004, 21:26

Hi DFC

I am trying not to be rude here but can you please at least read my post before you pass a critique on it.

I am well aware of the difference between Vmc and Stall, and if you read the post I think that you will see this.

The comments I made as stated in my post were an addition to the comments on stalls the final comment was an addition on some weird and personally I feel incorrect and dangerous training that I received on converting my FAA and Canadian ATPLs to a JAA ATPL.

Now if I might be so bold as to correct you on your post on Vmc the speed in the US at least is determined from Max power being developed on the operative engine and the inoperative engine unfeathered (windmilling) as VMc is deemed to be in the worst case scenario, the only time that the engine is feathered in a VMc demo is if autofeather is installed on the engine.

Hope that clears that up.

-273

homeguard

7th May 2004, 00:16

I'm glad that at least some people have responded to BEagle's contribution with understanding.

If a wing stalls and drops then the angle of attack of that wing increases further while rolling leading to a wing tip stall. To further increase the angle of attack of the wing tip by using aileron is foolish and simply wrong. The first action must be to pitch forward and unstall the wing whatever the aircraft attitude to the horison. Angle of bank is irrelevent. Rudder is applied only to prevent FURTHER YAW. It does not matter how many engines that you have in this respect, always unstall the wing first. At most, any other actions are simultaneous, are never more important and certainly do not precede any action to reduce the A of A.

It is true that one assesses the INITIAL wing drop during a Cof A flight test to be no more than 20 degrees following the stall and that ailerons should be effective at the critical angle of attack. But, that no way infers that the use of ailerons at the stall is the correct action for recovery. It is an airworthiness control assessment only.

To complain that the wing should drop at all is, with respect, unreasonable. The more stable the aircraft is and therefore resistant to change, perhaps from mishandling, then the more resistant it will be to recovery following mishandling. A double edged sword!

BlueLine

7th May 2004, 06:37

An interesting discussion however, the original thread referred to aircraft maintenance; the line that sparked the debate was:

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

This is taken from CAP 520 Light Aircraft Maintenance. It is written by a test pilot and describes part of the certification test process.

The method described is not, and never has been a recommended method of stall recovery; SSR has been adequately described in this thread and should be used. Before you conduct air tests for aircraft certification you are required to attend a short course with a CAA test pilot who will explain what is required for certification purposes.

Menen

7th May 2004, 13:53

Does anyone know anyone who has written up in the aircraft maintenance document after a flight the fact that the aircraft is not airworthy due to excessive wing drop at point of stall?

And how does the instructor/pilot assess that anyway?

djpil

7th May 2004, 21:10

As Hudson's airplane is in Australia (where the air is different), its relevant to quote from the Civil Aviation Safety Authority Australia's "Flight Instructor's Manual". It is out of print but still referenced by the new, draft Manual of Standards.
"Recovery when the Wing Drops"
Use the standard recovery, ie, simultaneous use of power and forward movement of the control column. In addition rudder must be used to prevent the nose of the aeroplane yawing into the direction of the lowered wing. The ailerons should be held neutral until control is regained, when the wings should be levelled. In aeroplanes where the ailerons remain effective beyond the critical angle, they may be used to regain or maintain lateral level in association with the rudder."

I have rejected airplanes off a production line for unacceptable stall behaviour - back to change the rigging. I've flown in-service airplanes where pilots have complained about their handling and given my opinion that they were acceptable. I've flown in-service aeroplanes where I've wondered how it was certified with a wing-drop like that - it wasn't just one example of the type.
Hudson presumably knows how a typical Cessna behaves, has he sought advice from other pilots who have flown it?

In considering the regulatory requirement you must start with the Type Certificate Data Sheet for that particular aeroplane and go to the original certification standard. Look at the configurations required to be tested. The 15 deg limit on roll doesn not apply to all situations - some simply require that "it shall be possible to recover" - quoting from the old Civil Air Regulations Part 3 here.

mad_jock

8th May 2004, 00:09

And how does the instructor/pilot assess that anyway?

They can't. Its completly outside there training .

if they can't control it they moan about it. But moan is as much as they can do with out getting sacked.

The joys of being a FI!!!!!!!!!!!!

MJ

Hudson

8th May 2004, 11:59

Djpic.
You say "has he sought advice from other pilots that have flown it".

My initial post was based on C150 aircraft stalling characteristics in general, although I have flown this type and noted a significant wing drop tendency in some. In fact a CAA inspector advised that a 500 ft height loss is normal in a C150 during a full flap power on stall entry and recovery. I would be thoroughly alarmed if this observation was true.

Seeking advice from other pilots who have flown a C150 on what they think, will elicit a wide range of opinions - which is why new instructors in particular, who may have hardly 250 hours in their log books, need reasoned guidance on what constitutes an unacceptable wing drop characteristic.

Regretfully there is no shortage of clapped out Cessna 150's that would never pass a searching no-nonsense airworthiness check by a diligent inspector. Never happens of course. Yet instructors and their students accept these aircraft as the norm, and because that is all they have ever known, happily accept these aircraft if the hiring price is right and the hours are logged.

Unexpected wing drop at point of stall can usually be traced to mis-rigging. This costs time and money to rectify especially if the pilot has the temerity to log the defect officially. As Mad_jock alluded earlier, now we are talking job security!

Perhaps the acid test of such aircraft is would you be perfectly happy to send a student on their first solo, knowing the aircraft possessed a savage wing drop at the stall? A courageous decision Prime Minister...

homeguard

8th May 2004, 14:58

Hudson

I don't really understand the reason for not refering to maintenance if the aircraft is not correct rigged. A quite simple adjustment to do. More likely, if your description is so correct, it is to do with a twistered fuselarge which will not be practical to fix, almost impossible in reality.

Experiment with a clean stall, power at idle. Does it drop a wing while in balance. Then with max flap again at idle. It is possible to do a small adjustment to the wing incidence. Flaps may also be adjusted independently. Eigther could be the problem or a mixture of both. If the fuselarge is twisted nothing will resolve the fault other than a rebuild and loads of dosh - a write off!

A factor of most high wing types like the Cessna is that the flap when lowered lowers into the propellor wash ( which is predominately portside) deflecting this turbilent air outwards causing an early wing tip stall and making the port alieron stall without it reaching it's critical angle. Any addition of aileron will in this condition agravate causing a rapid increase in yaw followed by a rapid increase in the angle of bank beyond the flight test initial 20 degrees.

However if the large wing drop is only present with say a typical approach RPM of 1700 then what I have described is the case. A pitch forward will unstall the wing very quickly and you will not experience the same phenomena. Rudder only sufficient to prevent further yaw, ailerons only when the wing is unstalled.

DFC

8th May 2004, 20:41

The amount of wind drop at the stall can depend on how prompt the stall recovery is........a very prompt recovery could result in only 20deg of wing drop with no effort being made to stop the wing drop while holding the aircraft in the stall for even a slightly longer period could produce a significantly larger wing drop.

What is important is that when the controls are applied correctly, the yaw can be stopped.

When making C of A test flights, as well as checking that the figures are correct, a check is made that the aircraft is typical of type and if it is typical to have a wing drop when stalling with significant power and full flap as it is in the C150 then provided that it is easily contained, there is no serious problem with the aircraft. Reporting the direction and magnitude may give the engineers a reason to check the rigging but then again it may not.

Instructors teach stalling and spin awareness so that the unintentional stall can be avoided not so that people can becaome good at stalling the aircraft. Having a nice wind drop could reinforce the teaching that stalls are something to be avoided.

---

Mad Jock,

I believe that instructors are perfectly capable of reporting what they believe to be excessive wing drop. They seem well capable of reporting rough running engines despite not being given any specific training in how smooth the engine should run. ;)

---

-273,

So over here we use ailerons to roll the aircraft and you say that is unsafe. What safe method to US and Canadian ATPLs use to roll the aircraft 5 degrees towards the operating engine?

Still think that this has nothing to do with the wing drop described.

Regards,

DFC

minus273

8th May 2004, 22:04

Hi DFC

I guess I will bite to your post although I was going to stop as it was off topic to the the rest of it.

In the US and Canada we also roll into the good engine a maximum of 5deg and that initial roll whilst flying fast enough not to worry about VMc will be accomplished using aieleron and contolled rudder. The ball will be half out of the track as they like to say.

If however you so happen to be flying slow for whatever reason and try to control the the increased roll rate whilst approaching VMc with aieleron you will only make the matter worse.

It will eventually lead to an aggressive roll toward the inoperative engine, at which point or sensibly before hand: reduce power to idle, pitch for blue line, return aircraft to correct flight attitude and then smooth addition of power should be carried out.

You also seem to be confused about engine out ops and VMc, control of the aircraft whilst opertaing with an engine out is for all intents and purposes the same as with all of them working. VMc on the other hand occurs after the aircraft has been treated incorrectly either from pilot error or from other factors beyond his control whilst the aircraft is operating with engine(s) out.

The ground school teacher I had during my conversion and whilst sitting in his principals of flight class, was trying to convince me that it was fine to use aeileron during VMc, to which I said politely that that was not correct.

If you so wish to use your aielrons during VMc, please advise me of where and when you fly and I will oblige by not being anywhere near by, as the VMc accident pictures I have seen are not very pretty.

I really do not want to carry on the conversation on VMc as it is detracting from what the topic is about on the thread. So if you want to carry it on I can start a new thread and you can expalin all about your feathered engine VMc demos.

I am also not sure how many times I can say it I was never equating stalls to VMc. I also do not think in the post were I wrote about Vmc anything like that was written, I could be wrong but the way I read my post that was not how it sounded.

-273

Hudson

9th May 2004, 04:45

Normally if a pilot experiences a severe wing drop at point of stall in an aircraft such as the Cessna 150, which is designed so that severe wing drops are not supposed to occur at that point

- deep breath here, as he continues to the next sentence -

The pilot should report the problem in the approved maintenance document and an engineer does what he is paid to do - that is rectify the defect.

For some reason in Australia, GA pilots who do the correct - and legal -thing, are often rapped over the knuckles by their operator, and in some cases, sacked, for recording the defect(s). Its called "making waves". Every GA pilot knows of the perils. It is a culture which even the CAA have not been able to eradicate. It often starts from the attitude to defect reporting instilled in flying schools instructors and is self perpetuating.

That is why such defects as a mis-rigged aircraft can continue for years as the defect is not picked up during routine maintenance.
Hence the original post.

How bad must a wing drop be before the pilot can safely report it? Do the original certification flight test requirements have current validity in the flying training business? And what are the certification requirements, anyway?

whatunion

14th May 2004, 20:42

I love all this, this is better than a night down at the pub!

the original question was how bad should a wing drop be before a pilot reports it. how about show me 10 pilots and i will show you 10 different interpretations of how bad the wing drop was.

there is quite a lot of duff info on these posts

the thread seems to have gone onto recovery action. so here is a question for all of you to think about. is an a/c in a spin stalled? if you belive it is stalled how many of you would like to change your statement of, stall recovery always starts with FULL POWER.
Can i suggest those of you that believe that the first thing you do is select full power never accidentally stall at low level with a low nose attitude

when discussing stall recovery the mistake that most instructors and all students make is the failure to mention C of G. Not one post here mentions C of G yet it is the one factor that can turn a docile a/c into a lethal macine from which you could be in a position from which you could never recover from a stall or spin.

for anybody who is not convinced can i suggest you stall and spin a cherokee with a front seat passenger and then try it with 4 heavy male passengers on board (but dont do it until i give you the recovery technique in my next post)

no one has mentioned degree of stall, how for instance would you explain control surafce stall(no one has mentioned wing wash out either)

there are some crackers here

Unexpected wing drop at point of stall can usually be traced to mis-rigging.THIS IS A DANGEROUS STATEMENT how on earth did you come up with that?

wing drop at the stall is caused by one wing TIP stalling before the other and can be caused by a variety of reasons how about a big dose of hangar rash on the outboard leading edge of one wing for just one instance

several respondents mention using aileron at the stall. FAA certification requires wing drop in certain configurations to be shown to be capable of being picked up with AILERON. i wonder if some of you have actuall fully stalled a modern a/c. birch and bramson by the way was written for tiger moth pilots,

THIS IS MY FAVOURITE
A factor of most high wing types like the Cessna is that the flap when lowered lowers into the propellor wash ( which is predominately portside) deflecting this turbilent air outwards causing an early wing tip stall and making the port alieron stall without it reaching it's critical angle. Any addition of aileron will in this condition agravate causing a rapid increase in yaw followed by a rapid increase in the angle of bank beyond the flight test initial 20 degrees.
COMPLETEY WRONG esp making the port aileron stall without it reaching its critical angle thats if you undrstand what that means

PICKING UP A WING

the hallmark of someone who knows very little about practical stall recovery. Why do you need to pick the wing up, yes it can be done but why would you want to cause adverse aileron drag and aileron drag at or around the point of stall, why would you want to use the rudder which produces yaw at or around the point of stall. again why does everyone feel you have to return the a/c to straight and level after a stall, the object is actualy to regain control with the minimum height loss(something else mentioned by no one)

the inspector who said to expect to loose 500 ft in a c150 recovery must have been in the pub beforehand!

HERES ANOTHER
Perhaps the acid test of such aircraft is would you be perfectly happy to send a student on their first solo, knowing the aircraft possessed a savage wing drop at the stall?

the phantom had such a violent wing drop at the stall which you wouldnt belive so much so that all students were told never to make any rearward pressure after going over the threshold merely to let it hit the deck with power on.

by the way the bigest danger to students from stalling in c150/52s is the go around with full flap not the landing!

HERES ANOTHER

and you won't enter a spin unless the wing does stall which depends on how close the stall speed and Vmc are.

WRONG that should read" unless the wing TIP on one wing stalls before the other."

HOMEGUARD
But, that no way infers that the use of ailerons at the stall is the correct action for recovery. It is an airworthiness control assessment only.
WRONG some manufaucturers advise the use of aileron at the stall(check out some handbooks) who knows more about the a/c you or the manufacturer. when you get to court you will find the prosecution barrister will be quoting from the pilots notes not your opinion!

just to conclude you need to determine if you are teaching stall recovery on type or for all a/c there is a difference esp on spinning. thats why a lot of peole spun in on chipmunks and travellers who had been taught spin recovery on c150s.

mad_jock

14th May 2004, 21:12

DFC

You are getting confused between an educated thats wrong and **** off I am not flying in that heap of ****e. :=

Very short learning curve on that one. And the descion is completly variable on the level of hassel and chance of not getting to the pub. ;)

MJ

whatunion

15th May 2004, 08:04

who decides what the standard stall recovery is. it seems to me that a lot of you are talking about your own experiences or how you were taught. do you take that as gospel. it seems quite a lot of you should review how you teach stalling and how you explain it.

lets take birch and bransons book for instance, this was written by wartime pilots for british a/c , good in its
day training has moved on considerably. i banned this book from my school 25 years ago because it was not upto date so i am suprised to see somone quoting it now.(quite embarrasing i might add because neville birch was a member)

there are several missing pieces to all of your explanations and quite a lot of knowledge gaps.

no one for instance mentioned c of g or weight. no one mentioned degree of stall, in fact no one tried to even define a stall. you all blindly assume that every stall is the same. its not so.

before you can talk about recovery you need to know something about how you got there and the handling characteristics of THE PARTICULAR a/c you are flying.

the first consideration when flying any aircraft is to read the flying manual or approved document. any a/c that has a c of a in this country has a CAA approved manual/ document. this is the first place to find out about the stall spin characteristics of the a/c. i mean why kill yourself in the a/c trying to find out about all this when the manufacturers test pilot has very kindly been there and got the tee shirt. you will also find the manufacturers test pilot has much more experience than you have. the other reason for going here first if you are a proffesional is when you have seriously injured your student in a stall related accident you had better hope than your stall recovery tecnique matches the one the prosecution barrister has in the handling notes!

there are so many holes in all of the above threads i hardly know where to start!

standard recovery FULL POWER; really. if you fell out of the bottom of a loop at 200 feet you would really recover with full power. i would have a re-think there. an a/c in a spin is in a stalled state so again you would recover with full power first,would you, i dont think so.

before you start talking about blindly appying full power as standard recovery ask yourself what you are trying to achieve by recovering from the stall(again not mentioned) how many real stalls are a result of poorly executed aerobatics or configuration or attitude changes at low level. NOTE low level. reducing HEIGHT LOSS must be a major consideration.

not mentioned at all is the degree of stall. is the wing fully stalled along its length or is it partially stalled. or the difference between being in a stall 1 degree above critical incidence and 10 degrees above critical incidence can change the stalling characteristics markedly. years ago many instructors used to say certain a/c didnt actuall stall they just wallowed,rally commander, cherokee for instance. what they actuall meant was at the c of g that
they stalled them at, at the weight they stalled them at, and at the slow change of incidence they brought them into the stall the a/c demonstrated the abillity to still have contol function with full up elevator without the nose pitching excessively down and staying down

amyone who has done a walk round on a high winged cessna surely must have noticed the washout towards the wing tips which INCLUDES THE AILERON. this is why correct aileron control will still be available at certain stall entries in certain configurations. (this a/c
is atually certified to have aileron respose at the power off stall).

the chap that gave the explanation about why the wing drops at the stall using propwash over the flaps needs to do some serious revision on elementary aerodynamics.

when you put flap down you are changing Cl over that part of the wing the flaps affect. you have in fact two different wings on the a/c.an inboard high lift section and an otboard standard section. on a cessna you have two other high lift considerations the slots above the flaps nd the sheer size of the flap in relation to wing area. what this results in is an inboard wing section that will remain unstalled with a normal approach into the stall. there will be a wing drop because the tip must stall first,whichever one goes first goes first. the large wing drop is due to the very large change in Cl across the breadth of the wing coupled to the unstalling of opposite tip.

i could go on and on but my wife dosnt like me being on here!

homeguard

16th May 2004, 15:02

what union, what are you saying?

'when you put flap down you are changing Cl over that part of the wing the flaps affect. you have in fact two different wings on the a/c.an inboard high lift section and an otboard standard section. on a cessna you have two other high lift considerations the slots above the flaps nd the sheer size of the flap in relation to wing area. what this results in is an inboard wing section that will remain unstalled with a normal approach into the stall. there will be a wing drop because the tip must stall first,whichever one goes first goes first. the large wing drop is due to the very large change in Cl across the breadth of the wing coupled to the unstalling of opposite tip.'

When lowering flap you increase the Aof A of that section of the wing. The wing tip is unchanged by this action. The wing root will, therefore, stall at an earlier stage when the a/c pitch is increased further and even sooner than the wing tip in this condition than when the wing is clean. The a/c is of cause less laterally stable with flap lowered. There is no vortice control to the edges of flap unlike a wing tip. The outflow will become turbulent. On lowering aileron you must also increase the angle of attack of the wing tip. The combination of lowering aileron together with turbulent airflow must cause a likelyhood of an unwanted wing tip stall.

The advice comes to mind, "engage brain before opening mouth"

fireflybob

16th May 2004, 19:05

whatunion

>if you fell out of the bottom of a loop at 200 feet you would really recover with full power.<

Not quite sure what you mean by this - could you please clarify?

whatunion

18th May 2004, 11:33

Homeguard i have to say if you are an instructor you should keep that theory very much to yourself.

you obviously do not understand the relationship between a of a and Cl, in fact you do not seem to understand basic aerodynamics.

i would love to know where you got that from.

perhaps you could also explain why you can buy leading edge spoilers to minimise wing drop on cessnas, using your theory.

to firefly bob

when you have a very low nose attitude the selection of full power increses height loss. not to be advised if you fall out of the bottom of a loop when close to the ground.

beware of "book" instructors who have only ever taught stall recovery!

BEagle

19th May 2004, 06:25

Please explain the previously unheard of phenomenon 'falling out of the bottom of a loop'? Is it another of those fabled manouevres known only to aviation fiction writers, ranking alongside the 'tailspin' and the 'power dive'?

Too many words have fallen out of bottoms various on this thread. There is a fundamental misunderstanding by some of the difference between Cl/alpha curves with and without flap, the reasons for tip stall, the difference between design requirements for stalling behaviour and the standard stall recovery techniques for a stall with wing drop....

The reasons why power assists recovery in vertical manouvres are:

From low speed the a/c will accelerate to a safe manoeuvring speed with less height loss.

When being pitched firmly to recover, energy loss will be less if thrust is opposing drag.

Tinstaafl

19th May 2004, 14:03

The way I taught it was:

1. Pitch to fix the stall problem. Will work with or without power although significant height loss without power.

2. Rudder applied as necessary to prevent yaw.

3. Power application to reduce height loss. If the recovery results in a significant nose low attitude eg after a spin or whatever, delay power application until at least in a S&L attitude or nose is above the horizon.

whatunion

22nd May 2004, 12:07

ah Tinstaafl at last someone who actually understands stall recovery.
your instructor was probably experienced in aerobatics and would have also known what falling out of the bottom of a loop meant too!

i learnt both of these lessons under the watcful eye of barry tempest, an ex member of the british aerobatic team and panel examiner

however pitch to fix is not really the way a proffesional instructor would explain the recovery, its too vague
but this is a cracker, even better
imagine trying to teach the local milkman to fly using this explanation.

the reasons for tip stall, the difference between design requirements for stalling behaviour and the standard stall recovery techniques for a stall with wing drop....

what a load of twaddle and thats even if you can understand it and i cant even after 35 yeras of profesional flying!

BEagle

22nd May 2004, 13:18

whatunion, do you find English difficult....

1. The reasons for tip stall:

Cl v AoA curve and actual AoA at each part of the wing. Exacerbated by poor rigging, power effects and flap angle (eta tab)

2. The difference between design requirements for stalling behaviour and the standard stall recovery techniques for a stall with wing drop....

One is an airframe design requirement, the other is a technique.

Given your "35 yeras of profesional flying" (sic), please explain what on earth 'falling out of the bottom of a loop' means? In 35 years of professional flying I have never come across this phenomenon before. Others have also asked you to expound on this, but all we've heard so far is a deafening silence.

Earlier you stated:

".....for anybody who is not convinced can i suggest you stall and spin a cherokee with a front seat passenger and then try it with 4 heavy male passengers on board (but dont do it until i give you the recovery technique in my next post)"

You do know what the spinning limits on the PA28 are, I suppose?

Tinstaafl

23rd May 2004, 02:41

erm, minor point but...

...that *is* how a professional would explain it to the local milkman, the local car mechanic, truck drivers, farmers, labourers, chinese & vietnamese cadets with minimal english language skills, doctors, lawyers etc. Namely me! :p I spent 10 years instructing at all levels from aeroclub to airline cadets. I also used to teach basic aerobatics & do licence tests.

My students didn't get to a stalling lesson without comprehending that exceeding the Crit AoA is the primary problem. Ergo, pitch to correct the problem. One goal (as an instructor) is to minimise the verbiage the poor bloody student has to attend while at, near or over their capacity. Hence 'Pitch to fix' as a short-hand (er...-speak).

cheers
T.

whatunion

23rd May 2004, 10:07

dropping out of the bottom of a loop, isnt that self explanatory!

"dishing out of a roll",

sorry when i did aerobatics all this was common language. also seems common sense

mind u these days it seems everyone is frightened to even spin a/c!

i have just taken this off my previous post

"when you have a very low nose attitude the selection of full power increses height loss. not to be advised if you fall out of the bottom of a loop when close to the ground."

perhaps instead of trying to make snide remarks (another hallmark of a poor instructor)you should just read the posts

"pitch to fix" explanation to chinese and vietenese
no sorry i would prefer my explanation. "move the cc forward until flying control is fully regained" (that works for stalling or spinning)

heres another cracker for an explanation for wing tip stall

Cl v AoA curve and actual AoA at each part of the wing. Exacerbated by poor rigging, power effects and flap angle (eta tab)

what is the arrival time for the tab and if it be real where do it come from and where do it go!

"a of a curve" thats a new one. that was called camber when i was an instructor. again the local milkman will know camber but, a of a curve, i dont think so!!!!! perhaps i just taught more local milkmen!

oh yes good try but you missed out another major consideration wing area
try defing Cl - 1/2r - V2 - S that may help u understand what you are trying to say (s = area)

you only gave 3 reasons for wing drop , again, wrong.

others you can add are surface irregularities on leading edge or upper surface, yaw, wing area inc due to flap selection (with flaps that increase wing area.) mis handling of ailerons
spanwise movement of centre of pressure etc

wing tip stalling isnt rocket science instead of trying to impress with complication try impressing with simplicity.

tips stall before roots because of a difference in lift between tip and root, end of story

if you can get the root to stall before the tip you can greatly minimise wing drop at the stall, putting flap down does the OPPOSITE, thats why tip stalling can be more pronounced with flaps down on certain a/c.

also said was
".....for anybody who is not convinced can i suggest you stall and spin a cherokee with a front seat passenger and then try it with 4 heavy male passengers on board (but dont do it until i give you the recovery technique in my next post)"

You do know what the spinning limits on the PA28 are, I suppose?

yes i do know and so does the caa who prosecuted the handling pilot at the local magistrates courts after both wings had to be replaced on G-AWXS due to the excessive G on recovery.

my point which you failed to replicate is that c of g is the most important factor on handling characteristics on stall/spin recovery as this pilot found out ( he is currently a captain with a major airline, Hi Nick!)

as a matter of interest they only recovered within feet of the ground because the instructor in the rear(hi graham!) leant forward to try and jockey the throttle backward and forward. the shift in c of g allowed the handling pilot to recover.

its events like this that teach us all more than is written in any book.

remeber mike lythgo, selecting full thrust for stall recovery didnt help him, in fact it just made it worse, so much for STANDARD RECOVERY.

now u have been in flying 35 years tell me who he was and how selecting full thrust didnt help him in one the steepest learning curves of stall recovery of all time.

BEagle

23rd May 2004, 14:42

Mike Lithgow was a famous test pilot.

If you don't know the difference between camber and the lift curve slope (that's the Cl vs AoA curve with Cl on the y-axis and AoA on the x-axis), don't bother to comment further.

I certainly agree that CG position has an effect on stalling behaviour - the T67A demonstrates that very well.

But what in earth is 'falling out of the bottom of a loop'?

eta tab is the deflexion angle of a control surface - sorry, no Greek on this PC!

paulo

23rd May 2004, 15:26

whatunion - There's no need to try and wind people up. If you mean stalling at the bottom of the loop, just say it.

BEagle

23rd May 2004, 17:41

If he really means an accelerated stall at the bottom of a loop, then not using full power in the recovery will certainly make things worse.

Full power on the buffet nibble will always maximise performance.

'...the phantom had such a violent wing drop at the stall which you wouldnt belive so much so that all students were told never to make any rearward pressure after going over the threshold merely to let it hit the deck with power on'. Well, that's not the way I was taught to fly the F4. It was flown at constant AoA on the approach at the correct datum speed; it wasn't 'merely allowed to hit the deck', the descent rate was very easily reduced immediately prior to touchdown - although throttling back excessively in 12th stage air would certainly cause a high RoD to develop as the flap blow reduced. The a/c certainly had some vices at high AoA; roll reversal being one and wing rock another. However, unloading for control was quite straightforward.

whatunion, your rudeness and level of knowledge are all too obvious for all to read. I don't think that I've ever come across such postings as yours on PPRuNe before.

(Edited because I was rather harsh yesterday!)