High speed stall
 

Hi all

Im doing my PPL at the moment (20 hrs) and today we were doing steep angle turns.
We climbed up to 4500ft and began the exercise however when i was doing the steep level turn the stall warner was constantly sounding, it seemed to happen more in the left bank.
My instructor told me that was the high speed stall warner. I was wondering if there is any danger or need for caution when the stall warner sounds during a steep level turn?
The aircraft is a PA38 Thomahawk by the way.
I should really have asked my instructor at the time but did not think to do so.

Thanks in advance

Dave

Hi,

Your stall warner will sound before a full stall develops.(otherwise it would be a stall announcer rather than warner!)

As they would probably have told you you need increased back pressure in the turn to keep the aircraft level, this in turn increases the wing loading and this increases your stall speed.

So basically you will stall at a higher speed when you are in a turn. A good rule of thumb is you need 1 knot more airspeed for every 2 degrees of extra bank.

The Tomahawk may fly very close to the stall in steep turns, too long ago for me to remember but ask your instructor for a thorough de brief on what happened and make sure they brief you thoroughly before you fly so you know exactly what you will be doing and what to expect. You'll learn much more and much quicker!

Enjoy the rest of the PPL.

PS Unless its specific to the Tomahawk it shouldn't make any difference whether you are turning left or right.
:ok:

Thanks for the feedback MVE :ok:

MVE,anymore posts like that and we will have to swaps seats...

Aerofoil, the stall speed of an aircraft will increse by 19% in a 45 degree bank i.e. a stall speed of 50kts would become 60kts (59.5) and the stall warner therefore coming on at 65kts. Check the aircrafts Pilot Operating Handbook for recommended speeds.
On a personal note I would not like to fully stall the aircraft whilst in a 45 degree bank.
Most importantly, sit and discuss it with your instructor....its what you pay him/her for.

I can't believe that any FI actually thinks that there's such a thing as a 'high speed' stall warner....

Were you given a ground brief? That should have covered the reason for the relation between 'g' loading, angle of bank and the relationship between indicated stalling speed and 'g' loading in a steep turn.

Wouldn't worry too much about a stall in a steep turn. One of the more satisfying manoeuvers to practice (in a suitable aeroplane of course) is the "max rate" turn - a steeper "steep turn" where you are in a level turn with full power, turning at a rate where the 'g' loading puts you on the edge of the accelerated stall (i.e. turn any harder and the wing will stall). Get it right and you can feel the pre-stall buffet through the controls the whole way around, followed by a nice bump as you go through your wake. Not easy, and very satisfying when you get it right :ok:

Pulling too hard and stalling is one way to get it wrong (and I guess with crossed controls you could in principle spin out of it?), not much of an issue (like any other stall, release some back pressure to reduce the loading and unstall the wing, wings level, nose to the horizon). More likely is to depart into a spiral dive, again not an issue but max rate turns are not something to try for the first time by yourself...

Evo,
A stall at a high wing loading is very dangerous, and is deffinately something to worry about! OK, so it is huch harder to get the aircraft to that point, and there are more obvious warning signs (like aching arms pulling hard on the controls), but the reaction of the aircraft will be very rapid.

In the fireflies I flew during my PPL training, stalling at a high AoB resulted in an incipient spin - in otherwords a very rapid roll rate. Simple to get out of at that stage - relax backpressure straight away - but would scare the willies out of anyone who hadn't experienced it before and couldn't identify immediately what ws happening. And as I remember it, I didn't cover incipient spins in my PPL...

High speed stall= wierd terminology. What you were approaching was more commanly known as the G-stall,
MVE explained it fine.
For a low hr PPl (no insult intended) this is something you should be fully aware of. Tis the cause of many a potential crash. i.e. turning finals a touche late / got too tight / tightening wind that you missed appreciating!!! - So, overbank and pull just a bit harder to prevent flying through the center line, speeds Ok at the usual reading / well above the usual stall speed AND - oops there she goes. You are reasonably likely to get a wing dropping, you are, without training, naturally, horribly likely to try to roll the wings level with stick whilst still pulling to stop the ground getting any bigger = depart spin crash burn die. The stall warner (where fitted) is doing its job just fine - it is warning you that pulling harder / going much slower = you gonna stall.
Just like any departure / stall: unload, full power, counter yaw with rudder, whilst out of buffet (unstalled) roll wings level and climb away to set up for a better circuit next time.
Get an instructer to teach you this, initially it is not a natural recovery procedure and certainly not one you should experience for the first time solo.
:ugh:

this very much depends on the situation, in MOST aircraft, if done at height and planned, it should NOT be a problem, but as said by others, if it is not something you have done before, try it with an instructor first.
And Dusty - you SHOULD have covered incipient spins for the PPL (but fully developed spins are not required).

Incipient spins should be covered, but I wonder how often they are. In my case it was a bit of a joke, 15 minutes of trying to abuse a PA28 into droping a wing - or for that matter doing anything other than mush downwards. We didn't succeed.

Very surprised that no one so far has mentioned the angle of attack.

Whatever aircraft you fly, it will stall at a particular angle of attack. Regardless of what speed you do, the stalling angle of attack remains the same.

The stall warner is a small vane that moves with the aircraft's angle of attack. The angle of attack when the warning sounds will be set below the stalling angle of attack and provides a warning in suficient time so that should you not be expecting it, you can take appropriate action.

In a steep turn the lift vector is tilted to one side and in order to maintain enough lift opposing the weight (vertical), lift must be increased. This is done by inreasing the angle of attack.

Increasing the angle of attack increases the drag. Consequently, unless sometyhing is done, the aircraft will slow, reducing lift and requiring a further increase in angle of attack. During a medium turn, we accept the slight loss of speed.

During a steep turn, the increase in angle of attack required is significant resulting in the angle of attack being closer to the stalling angle of attack and for something to be done to counteract the drag if a constant height and speed is required.

G force is the ratio of lift generated to weight. In theory, with big enough of and engine, it is possible to apply a G force to the aircraft by accelerating the aircraft rapidly to a great speed while maintaining the angle of attack constant........the aircraft would experience a great increase in lift at a constant angle of attack due to the increased speed of the airflow and G would be increased without getting any closer to the stalling angle of attack.

When dealing with the topic of loading, we must always be aware of Va.

Below Va, the aircraft will reach the stalling angle of attack before something breaks. Above Va, it is possible to bend/break the aircraft before reaching the stall!!

Furthermore, when talking about loading, remember that the aircraft is loaded in all directions......think about what a severe Yaw does to the horizontal loading of the fin and rudder!!!. Or think of the F16 in a vertical accelerating climb.....where is the highest loading acting then?

As for stalling in the turn.....one wing will have a higher angle of attack than the other. Consequently, one will stall before the other. We all know what happens when one wing stalls first and nothing is done to stop the wing drop!............although you might have to do nothing for a while in some aircraft while they roll from 60 left to 90 right.......others are a little more inclined to flick but no matter provided it is expected and at a safe height!

Regards,

DFC

PS. Aerofoil, you are now entering the more intersting phase of the training so enjoy expanding your experience of the aircraft envelope!! :D

Neither spins, nor incipient spins were covered in my ppl training.

So one day post ppl, feeling brave, I asked an instructor would he do some with me. He said he wasn't current on spinning, and it wouldn't be safe for him to cover this with me, and that I'd better ask another instructor :sad:

While I very much appreciate his honesty, it did put me off the idea of doing them.....if they frightened him that much....:ugh:

dp

Just because he is an instructor does not mean he has done a lot of spinning, especially with it not being in the syllabus anymore. I would suggest getting hold of an aeros instructor who SHOULD be happy with spinning- also, do it in an aircraft that has a reasonable spin, ie. not a pa28 or Cessna (Pa38 spins well - but don't look back at the tail :ooh: ).

Stall speed = Square root of the `g` applied to the aircraft

Example

60 bank turn with 2 `g` applied to stay level, the stall speed will increase by approx 1.4.

Not massively precise but close enough if you need a rough calculation.

Dont know about the knot per 2 degrees of bank but this works on more high performance aircraft that pull `g` to turn.

The stall speed varies as a function of the load factor and not angle of bank. The stall speeds quoted in the POH are all based on 1g, and in testing, great pains are taken to ensure that the load is 1 g by reducing speed at 1 knt per second.

Any more or less than 1g, the stall speed will differ. Quite simply, it is the square root of the load factor. So if your clean stall speed is 50 knots, at 2g it will be 70.7 knots (1.41 x 50), at 3g it will be 86.6 knots (1.73 x 50), at 4g it will be 100 knots (2 x 50), at 9g - the wings would have come off! But if they hadn't it would be 150 knots. And at less than 1g, you can see speeds on the ASI at less than basic stall speeds. At a 0g bunt, you can't stall the aircraft as there is no load on the wings.

When I teach stalling, I demo this to the student. I get him to tell me at what speed we have seen the aircraft stall. I then tell him it's possible to fly the aircraft at a speed lower than that and demo it with a gentle wingover and about 1/2 a g getting the ASI to read less than the noticed speed. The key to this part of the exercise is to point out that there is no buffet and therefore the wing is not stalled. I then fly the aircraft in a level 60 degree angle of bank turn which should be at 2g and pull back to the light buffet noticing the speed. Another point to this exercise is to demo that the aircraft can be stalled or still flying in attitiudes other than the one we have become accustomed to.

Buffet is the only true indication that the wing is stalling - this is the key to the whole exercise. It's not the stall warner - that's only there for certification reasons and it may be unserviceable or not be installed in the first place. I know of no GA aircraft that have such poor stall characteristics that they do not give adequate aerodynamic warning.

A lot of this should have been covered by briefing if not in the air.

Hey, controversy fans, whaddya think?

Proposition 1: Any instructor who is not proficient and confident in spin recovery should not be allowed to fly as P1 with (a) any pre-licence student or (b) any student at all.

Discuss.

Proposition 2: Any instructor who does not brief their PPL student in advance about what happens during steep turns, about the dangers/needs for caution incidental to steep turning, and about why this is significant to everyday flying, should, at the least, be taken behind the hangar by the CFI and given a polite, friendly, caring, sharing, mentoring, right good kicking.

Discuss.

PS: Aerofoil: whether or not you presently have any interest in aerobatics, if you get the chance, pre or post PPL, to have a trip with a spinning/aeros instructor, you could perhaps explore further pulling to the buffet, in the manner mentioned by Mr Winterland, and feeling the effects of the g. If you find that informative, you might then ask the instructor to show you a spin and recovery, and maybe let you try one or two yourself.

PPS: I agree with everything said by Flyin Dutch in the posting below.

Agreed

Obviously we have to be careful to judge an instructor's performance based on just this posting but if your pupil writes:There is something fundamentally wrong with either the basic knowledge of the subject or the ability to transfer sound knowledge.

FD

DFC, I recon no one mentioned AoA cos they didn't think it practically relevent in a GA puddle-jumper when replying to a new PPl.
AoA guage not fitted in any I regularly get to play with!
Shame really cos AoA IS the never failing winner in the race to never depart.

Edit addition: FNG agreed with all propositions + sack the oxygen stealing waste of space

I shall have anuvver glass of red and wait.:cool:

Dan - wash your mouth out! Don't forget that, in a level turn, N (which is L/W) = Sec (theta), where theta is the angle of bank! And, as the indicated stalling speed varies with the square root of N, stall speed is indeed dependant upon AoB in a level steep turn!

stillin 1, it is true that our rubbishy elastic powered amateur death machines don't have alpha-ometers or whatever they are properly called, but surely it's still relevant for instructors to tell PPL studes about AofA. I recall that my instructors went on about AofA a great deal and told me not to get fixated with the idea that the aircraft will always stall at speed x or sometimes at speed y, or only when going slowly, or only when the nose is pointing up. I read "Stick and Rudder" and "See How it Flies" at the time, which further shoved the "angle of attack is, er, quite important, really" point home.

Sorry to butt in chaps, I'm only a PPL but..

I learned to fly on gliders, and one of my instructors once said the wing will always stall when the stick is at the same place - this is something that has always stuck with me.
If you are flying slowly at 1G this position will give you 'the' stall speed. If however, you are pulling hard in a tight turn the wing will also stall when the stick is at that point.

I have to say, the same instructor never explained how on a k7, we could go up the wire with the stick on the back stop without stalling though!

Forget about the ASI - it's the biggest lier in the cockpit and the information it does give is always out of date.

Kingy

DFC, it never fails to amaze me that angle of attack appears to be so little understood in light aviation. Flying is all about agle of attack, and Kingy has got it right when he says that broadly a wing will stall when the stick is in a certain position, and when the chips are down and you are screwing around low level in bad weather it is much easier to recognise that the stick is getting close to this critical position than to monitor speed. The stick is your angle of attack indicator! Read this again and go and fly it!

Just to stick my oar in.

Broadly true, when doing 1G as Dan has already explained. I haven't done aeros for a while, but I clearly remember that in doing a loop, during the slow speed inverted (nearly zero g) section of a loop it goes so mushy that you pull to the stops without stalling. On the other hand, at the base of the loop when pulling, say 4G, you can only pull the stick back a little way before the buffet.

Seriously, I don't concentrate on the stick position when thinking about stalling, and in a spam can sensing a relative position of the yoke seems very difficult. Its much better to feel what’s happening.

I have to agree with those that say the best thing to do is to go up with an aeros instructor to learn to nibble the buffet round a max rate turn and (if you want) pull a bit beyond to an incipient spin. Once you've done it you'll realise its
a - not difficult to get the hang of
b- not scary, but in fact, fun and rewarding!

Then you can go onto full spins and aeros and have lots of fun.;)

quote:
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Kingy has got it right when he says that broadly a wing will stall when the stick is in a certain position,
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There are a few if and buts associated with that statement - one is "for the same cg position"

Yes indeed BEagle, and I remember that diagram well from the CFS bumper book of being an instructor. I am quite happy to accept that the stalling speed varies with the square root of N. The L component is increased to provide the turning force and maintain the aircraft in level flight. However, to acheive the extra L, the angle of attack has to be increased thus increasing the load factor.

It's just easier to explain to a student that the load factor increases with manouevre, or g, and that the stalling speed increases as well. Draw that diagram on the board and you will lose him very rapidly.

But the point of the exercise I mentioned is to show that a stall can occur at a speed and or attitude other than the one the student has been used to from the precceding practice. It was part of the CFS syllabus in 1993 when I went through.

And I can't agree that angle of attack is always dependant on stick position. It's a clue, but there are lenty of circumstances when this won't be true.

Dan

I'd be intrigued to hear how much aerodynamic warning you find on a late model PA28 and how you define that.

They always seem to stall without buffet s&l (althought the subsequent mush down is a non event), unlike the PA32, where the buffet shook the fillings out of one's teeth about 4-5 kts before the breaK.

Would be genuinely interested in your 'pilots notes' for my continuing education - maybe I am missing the symptoms.

FNG

Any instructor who is not proficient and confident in spin recovery should not be allowed to fly as P1 with (a) any pre-licence student or (b) any student at all.

You may be right, I don't know. The counter argument is that the only time a GA non-aerobatic pilot is going to get near to stall/spin is when turning base-final and overcooking it, and then he may well be too low to recover from a spin. Therefore, spending time to teach IAS maintenance/control as an essential safety procedure may be more important overall. Let's face it, the time is limited. Very few people do it in 45hrs (those that do usually got very lucky with the weather) and most people that do a PPL don't really want to spend any more money than they see as necessary...

djpil, you're right - the cg makes the biggest difference to stick posn at the stall, but for most side by side two seat

light singles, the c of g does not vary that much day to day.

Also if you have any significant "back elevator" at the top of a loop, you are flying an egg shaped figure. You will stall the wing at the top if you pull back to the "stall" position, and on the way down, if you pull to the same posn the wing will also stall, assuming you stay within the design envelope. One other point, the stall warner is not a speed dependant device, it is an angle of attack indicator.

I am instructor following the JAR/AOPA syllabus.

Point 1: Exercise 10 is slow flight and stalling, and 11 is incipient spins and a demonstartion of spinning (if the aircraft is cleared for it). The actual GFT only contains one stall (power off, clean...in a straight line) and two incipient stalls in base and fnal configuration. However to complete a PPL the student needs to have done 2 hours of stall and spin awareness training (usually signed off in training record). So all new students over last 4 years should have done a reasonable amount of stalling and slow flight

Point2: All intructors have to do spinning as part of their FI training and they are tested on it in their initial Instructors Test. If the aircraft airworthiness permits, I demonstrate it to all students...to discourage them from mishandling the controls at low airspeed.

Point3: A steep turn to the left in most current training aircraft, when taken to the stall will result in 'departure' (i.e. roll) to the right. This can often be quite slow and only requires the angle of attack to be reduced by moving the stick forward a little . If done to the right the a/c may roll inverted into an incipient spin... sometimes. Taking the power off and releasing the back pressure should get things back to normal fairly quickly before a true spin develops in a C152 or C172. The spin recovery for your aircarft will be detailed in the POH. How many pilots actually have read their POH?

Well, all the ones who were properly taught, plus a few others who realised later how important it was to use the operating documentation.

G

As part of the instructor test a prospective FI has to demonstarte competancy in spin recovery, so at least at the beginning of their career they should have no problems with spinning.

Since the the requirement to teach fully developed spins was taken out of the syllabus, apart from teaching the incipient spin, not many FI's or students feel willing to go into it fully.

The reason that it was taken out was that far more people were being killed in spin training than in stall/spin accidents. The fact remains that with the vast majority of GA types you have to be either unlucky or incredibly ham fisted to end up spinning inadvertantly unless you are doing aeros.

How many accidents have been attributed to spinning in recent years? I cant think of any, but I certainly can remember of couple of horrible accidents due to spin training.

Any FI should of course be proficient in stall and spin avoidance, since that is what we want students and PPL do. If you teach someone to recognise the symptoms of a stall etc, then hopefully they'll never need the ability to recover from a 'real' event.
Another way of looking at is if someone is daft enough to to get into a spin turning onto final, then what is the likelyhood of them having the skill to recover sucessfully?

IO540, that may true enough, in relation to the students, and I didn't mean to re-open here the perennial debate as to how much, if any, spin recovery should be demonstrated or taught to student pilots. I was addressing the skills-set which the instructor should possess. I know of course that instructors do spinning during their FI training, but was struck by the reference above to an instructor who felt uncomfortable about demonstrating spins to a student.

During any flying training, the student may put the aircraft into a situation of potential danger. Indeed, doing so may be part of the learning proceess. One of the difficult judgments for an instructor must be when to let things carry on going wrong in order to demonstrate a point, and when to intervene*. Suppose the student really stuffs it up before the instructor has a chance to take over? For example, during the steep turning exercise, the student pulls like mad, and the aircraft spins out of the turn. This could happen with a very new student, or maybe with an advanced student in whose abilities the instructor has some confidence, doing some pre-test revision. In that situation, if the instructor himself has hardly ever spun since hois course, and isn't confident in his spin recovery skills, a bad situation could get much worse.

*I was recently speaking to a friend who instructs at CFS about this, and he told me that the flying he is now doing ranks as amongst the most dangerous flying he's ever done because he is teaching other highly skilled instructors how to deal with dangerous mistakes made by advanced students, and this involves deliberately putting the aircraft in big trouble (and this is a guy who has flown in some very hairy, sandy places and been very severely shot at).

Genghis the Engineer

I don't think reading the POH is very common among PPL students. It was never even mentioned to me, nor to anyone else I know.

I have a few pilots names on my plane; I photocopied the POH and ensured all of them bought a copy. But I know this is pretty rare.

Possibly a factor in why the POH is not often referenced is that it tends to be very generic and bear little relation to what is actually fitted to the aircraft.

Finals 3 greens.

I teach on both slab wing PA28s and the newer wing design and I find the aerodynamic warning on a new wing PA28 quite adequate. In fact, it displays all the classic characteristics of a stall, is quite well behaved and is very docile. I recently renewed my instructor rating on a PA28-161 - the exercise I demonstrated for the test was stalling.

You may be confused about the origins of the buffet and where to notice them. You mention the PA38 which I remeber does shake at the stall. But it was designed as a trainer and this may be a deliberate design feature. The PA28 was designed as a tourer with comfort in mind. However, the buffet is there and like a lot of low wing aircraft it is first noticed through the control column as the turbulent airflow breaks off the wing and is felt through the stabilator.

When you train someone, you are not just training him/her for that one type. They will go and fly something different at some stage and need a thorough grounding in all the aspects of an exercise. It the emphasis on buffet recognition in the stalling exercise is not made because the buffet is so obvious, there is a danger it may be missed when that student flys another aircraft.

Croqueteer,

If you are at the top of an inside loop, you are inverted.

Take the position described where you are holding the stick back against or close to the rear stop. Now keeping the aircraft still, extend the stick through the floor and imagine yourself sitting on top of the inverted aircraft. You will se that from this perspective, the stick is at or close to the imaginary forward stop......i.e. similar to being upright and pushing over the top.

True, there is no angle of attack indicator in many light aircraft. However, teaching that the stall always ocurs at the same angle of attack is true and also is easy to relate to the required movement of the stick to prevent or recover from the stall. It is also easy to relate to the fact that as angle of attack is increased, drag is increased which explains the closing in of the margins in a high G situation and also for budding aero's pilots, explains one useful way of recucing the acceleration when pointing towards the ground.....pull to the bufett (G limits permitting).

G loading at a particular speed is a function of angle of attack.

It is possible to complete a 60deg bank turn at 1.01 G.......it will have a very big radius though. :D

IMHO, to put into a student's mind that proximity to the stall is in some way related to G loading could lead them think that they have a margin above the stall....when they don't simply because they are about to stall at 1G.

Try an outside 60deg turn....and stall it by PUSHING too hard......much easier to explain using angle of attack!!!

At the end of the day, for most students, the high speed stall is of theoretical value only because in many aircraft that they fly, something will break before they stall at anything above Va........which is why I relate the G loading to steep turns and other cases of loading both positive and negative.

Regards,

DFC

DFC, I don't what being inverted has to do with it - if you pull too hard at the wrong speed YOU WILL STILL STALL and it will still be a POSITIVE stall.
I also do not see how you are going to do a 60degree bank turn at 1.01g, certainly not if it is level and in balance, and I believe this is what is being refered to here.

Quite right! It wouldn't be a level, balanced 60 deg AoB turn at 1.01G!

The "It'll stall at any speed" demo (as Dan says) which we used to do on the Bulldog was very useful in pointing out that AoA, not speed, causes the stall. Dive to about 110 KIAS, pull up on the pre-stall buffet to about 60 deg nose up, then push over the top at zero G and the IAS off the bottom of the ASI, show that it was still flying unstalled. But it could be a bit of a honk-making demo!

It is easy when flying into an unfamiliar strip with a tailwind on base leg to fly through the centre line and if all your attention is outside, you can still feel if the stick or column is a bit far back and warning bells will ring if you've thought about what I've said. DFC, I don't know what you're blethering about, unless you're thinking of Neil William's Stampe pictures!

DFC, not quite sure what you mean by being inverted at the top of a loop. You are upside down, but if the manoeuvre is done correctly then you are still at positive 'g' and the a/c thinks it is still the right way up. It has no idea where it is in relation to the ground unlike the pilot, who's senses tell them all sorts of nonsense.

I have had the pleasure of being stalled at a relatively high speeds and not had anything fall off the machine. Ahh, I love teaching aero's.....:yuk: I'm never quesy no matter how bad I stuff up, but with a ham phisted student.........

Can't see how a 1.01g turn at 60 deg AoB would be level? Am I missing something?