Stall in turn

[motzartmerv]

I had a curely one yesterday while doing forced landings with a student..

 

We were at about 500 feet doing a right turn to line up on his chosen field. We were way to high so i got the student to apply a fair bit of top rudder to slip through the turn to loose the height..we had a bank of about 40 deg and were indicating 68 kts.. As he applied the top rudder (left) the stall warning horn starting squealing.. It wasn't an intermitant squeak like in rough air, it was a full strong continueous squeak. I took over and applied power and pushed the nose over..The aingle of attack wasn't very steep at the time, the nose was below level and the sink was about 850 feet per minute.. The stall warning pikup device is on the left wing so in this case was on the high wing in the wind shadow of the nose no doubt.

 

The student didn't hear the stall warning horn and wondered why i suddenly took over when he had it looking so good..lol..

 

I spoke to the chieff after and he sugested going up to 4000 feet and trying to get it to happen again and let it stall if wants to..

 

As for having a dedicated forum instructor, i can't see many guys wanting to put there hand up..Each aircraft and situation is different, so offering advice on these things in an "instructor role" could have an adverse effect. There's only one place that instruction in these matters should be offered and thats in the aircraft in question and in the air. Every student should be able to discuss these things with thier instructor and practise them in the air if need be. We can all offer an opinion and have it discussed openly but alot of students take what an instructor says as gold and this could have deadly consequences should the wouldbe online instructor get it wrong..And what is right for one aircraft could be deadly wrong in another...

 

my 2 cents

 

 

[Admin]

This reminded me as I have now forgotten but does anyone know what the maximum bank angle an RA-Aus aircraft is allowed to make

 

 

[Guest High Plains Drifter]

And what is right for one aircraft could be deadly wrong in another

Good comment Motza.

 

Methinks if you were doing the manouvers you describe in a mooney for example, you would probably be getting a write up in the crash comics.

 

 

[Barefootpilot]

From memory Ian anything over 60' bank is considered aerobatic (I think its 20' nose up but not sure) I'll chase it up and get back to you.

 

Stall warnings are pretty useless in a slip in saying that its always best to be conservative like you where.

 

If i'm slipping I'll always add minimum 10kts to the approach speed if not alot more. Usually when your slipping you are trying to loose height so if you do this at approach speed - generally pretty close to best glide speed you are actually flying the wing at the most efficiant angle of attack. Therefore the further you get away from the most efficient speed the more effective the slip will be.

 

An example is when I fly the Tiger I always give myself a high approach and end up with a power off - slipped approach at about 20 kts above my approach speed. When I come on slope I raise the nose bleed off speed and then lesson the side slip, flare and hope for the best. 20kts is alot of extra speed but where I fly its not uncommon to get windsheer or 10-15kts on a nice day so 20 is safe for that particular strip.

 

Adam.

 

 

[motzartmerv]

Ian..yes its 60' angle of bank for RAA acft.. 40' would probably be best described as a medium bank turn, i was trying to get the guy to use smaller bank angles earlier rather then large ones later to line up, providing the student keeps a close eye on the IAS and doesn't apply to much back pressure through the turn its ok.

 

 

[motzartmerv]

Mat, no i havn't yet.. I'll take the chieff with me when i do..Im not the most experianced test pilot..

 

cheers

 

 

[Admin]

Thanks merv - I couldn't remember what it was again - just plain lazy to go and look it up but it is good to read these types of things and make the brain think again

 

 

[motzartmerv]

Ian..Np.. When i was doing the instructor rating in the jab we went out of our way to get it as ugly as possible..Stalling at high angles of bank, in climbing turns, descending turns, full power and full flap, and we couldn't get the thing to missbehave.. The stall in the J160 is simply docile. Occasional wing drop but no tendancy to autorotate..What we didn't try was stalling in a slip.. I'd imagine a stall in the slip in a level attitude wouldn't do much (in a J160 that is), but a high alpha stall with lots of power and in a slip would probably get a little exiting..

 

 

[Guest pelorus32]

The aingle of attack wasn't very steep at the time, the nose was below level and the sink was about 850 feet per minute.

So Merv,

 

what is the evidence for your statement that the angle of attack wasn't very "steep" at the time?

 

Regards

 

Mike

 

 

[motzartmerv]

well, what i meant was the nose was low with not much back pressure on the stick..Sorry, bad choice of words..So Mike, what do you reckon??.. i know its hard without being there, but do you think windshadwing of the stall warning intake could have casued a dodgy reading??..The problem is the jab doesn't have any other symptoms of an impending stall, the controls were still quite responsive. He had the nose quite low and as i said he didn't have back pressure on the stick, infact he was poling forward becasue she tends to pitch up abit in a slipping turn..

 

cheers

 

 

[Guest pelorus32]

G'day Merv,

 

can't comment on what might have been going on there but I guess I've got a bit of a thing about Angle of Attack (AOA or alpha), particularly some of the misapprehensions about it.

 

Let's say we have an a/c (normal cruise say 120 knots) in stable flight - level attitude - not climbing or descending flying at 60 knots. Alpha will be modest - not in the 3 degree range but not 16 degrees either. Lets say 7 degrees.

 

Now let's take that aircraft and theoretically set up a/c level, 60 knots but with a ROD of 850fpm. The Alpha has radically increased maybe 10 or 11 degrees maybe more. Now let's put the nose down a little still 60 knots still 850fpm ROD. We decrease the alpha but probably not back to our 7 degrees.

 

My point really is that nose attitude has nothing to do with alpha, nor does speed.

 

So to your situation: the stall warner might have been spurious, it might not, the fuselage might have been sending an eddy that set it off, it might not.

 

Your CFI had it right. Go up to 4000' and see if you can set it off and if you can induce a stall. Check what stalls first - the tail surfaces can have a tendency to stall in a slip due to being blanketed by the fuselage or canopy or wings or flaps in a slip. That's somewhere you don't want to go as you are likely to get a sudden pitch down.

 

Interesting.

 

Regards

 

Mike

 

 

[motzartmerv]

Thanx Mike. I'll do that.. I smell what your cooking with regards to the AofA.. The fact that we were descending quite fast would have definatly increased it.. I'll have go at altitude and test the scenario again..

 

cheers

 

 

[Guest brentc]

Sounds simple to me. You stalled the aircraft! Take care next time.

 

Stick forward, level with rudder and fly out of the stall.

 

I did a similar thing with about 2 hours under my belt in a Gazelle. Applied too much rudder, there was a bit of a bang as the aircraft basically stalled turning onto final. Others have done this and not walked away.

 

 

[blueline]

Sounds like a scary way to loose altitude!

 

- I hope that every now gets the idea that trying to repeat this technique is not smart.

 

 

[Yenn]

Pelorus. If straight and level at 60kts, why should a rate of descent of 850fpm have a greater angle of attack. I would have expected it to be lesser in a 120kt cruise plane unless you are on the backside of the curve and with a load of power on.

 

 

[motzartmerv]

Fellas..this was a pretty standard slipping turn with a low nose attitude and 25 kts over the stalling speed..there was no back pressure on the stick..Ive been taught this manouvre specific to the jab for loosing height in a turn..The differance was that it was a right turn instead of a left turn..The sink rate didn't increase at all( above the normal sink rate for a slip), and the controls were still responsive.. I seriously doubt it was a stall, perhaps approaching the stall, but im certain (apon much reflection ) that we didn't enter the stall..

 

I went up agian today and did some stalls, i tried to get it into the same attitude and airspeed etc, i couldn't get the thing to do it again.. I am thinking that the momentary squeel of the horn was due to probably 2 things, the shadowing effect of the nose and fuselage and some turbulance producing a change in the AofA aoround the stall warning intake vent..

 

Thanx to all who have contributed...

 

cheers

 

 

[Guest brentc]

Unless I have missed something why has nobody identified that the stall speed has increased because of the angle of bank?

 

Remember back to your BAK the question that says something about the stall speed of an aircraft being 40 knots, what happens at 60 degrees angle of bank?

 

- it increases, and quite dramatically. 50+ knots from memory?

 

I can't remember the figures in the table, however I feel that with the angle of bank, possible high angle of attack as Mike was on about and the rudder applied, you've got yourself very close to the stall. If you did happen to stall you may have found the outside (higher) wing would have dropped and you'd get a heck of a surprise.

 

 

[motzartmerv]

Brent..Ok, the stall speed increases in a turn due to the increased G loading. At 60 ' angle of bank the g loading is 2, so the Vs increases by the sqare root of the g loading...So at 60' and a gloading of 2 the Vs is equell to the old Vsx1.4 (1.4 is the sqaure root of 2).. So at 40' the stalling speed (or rather, the speed at which the stalling angle is reached at max weight) would increase by something like 1.2.

 

And a further thing to consider is that these figures are for a level turn. You can bank the acft right up to 90 deg and not increase the G loading at all.. The Extra G loading comes about by the airfoil needing to produce extra lift to over come the weight (ie remain level)..

 

So we were in a descending turn, therefore the inside or lower wing would have a higher angle of attack and stall before the outside or high wing(not acounting for the slip). This situation is reversed in a climbing turn naturally..

 

 

[Guest pelorus32]

Pelorus. If straight and level at 60kts, why should a rate of descent of 850fpm have a greater angle of attack. I would have expected it to be lesser in a 120kt cruise plane unless you are on the backside of the curve and with a load of power on.

Hi Ian,

 

two scenarios:

 

1. An aircraft flying forwards at 60 knots and in level flight and at a stable altitude. Lets say it has an aoa of 7 degrees;
    
    
   
2. If we change nothing at all about that aircraft except that it is hypothetically descending at 850 fpm then imagine what has happened to the relative airflow over the wing. It is now coming from more below. Angle of attack has increased. You can prove this to yourself with a vector diagram.
    
    
   

 

 

It is an entirely different question how you would get the same aircraft to do those two different things. But if it did then in the second circumstance the alpha would be much higher.

 

Regards

 

Mike

 

 

[facthunter]

AoA?

 

Mike your item 2 is misleading. (very rare for you). Assuming that the dynamic loading remains the same,(g) as the weight is the same, the angle of attack will remain essentially the same until the speed varies (which it will in the situation described). Nev...

 

 

[Derby]

Hi all, a stall can happen at any speed and any aoa

 

 

[facthunter]

Stall?

 

C'mon Derby. Any AoA? Nev..

 

 

[Derby]

Sorry I ment any angle of flight.

 

My mistake.

 

 

[Guest brentc]

Welcome RD !

 

 

[Derby]

how are you going Brent.thanks, long time no see