Wing drop during stall

[BEagle]

Oh well I will tell all 3 examiners that they are wrong!

Good! Please do.

Firstly how much is some? and how much reduction in AOA

There is NO mandated maximum acceptable height loss. As regards quantifying the specific reduction in AoA, that is something I told them had been omitted from their procedure. Current teaching for light aircraft stall recovery pitch attitude states (or should state) 'contol column centrally forward until the warning/ident ceases, then maintain that attitude'. That would seem equally applicable to large aircraft stalls - it's what I used to use when taking the VC10K to the stall warning during full flight tests. If applied promptly and correctly, the attitude change can be very small indeed and the loss of height will also be very slight.

It's important also to note that you could be very close to the stall when the stick shaker operates (assuming the aircraft is so fitted) if the wing has collected leading edge icing - which might not be obvious at night or in cloud. Which is why the recommendation is to recover using the same technique whether you receive a stall warning or a stall ident.

[Pace]

BEagle

As far as I can make out these are discussion documents for interested parties including the FAA.
in the documents it acknowledges the differences of effect on AOA between adding thrust on jet aircraft with engines above and below the wing.
Adding full thrust with engines high above the wing causes a reduction in AOA.
The Citation is such an aircraft as are many heavier jets.

Mad Jock implies that stalls do not occur in stabilised approaches I presume from that he considers them to only be in the areas of takeoff and cruise??

I can assure you that a postive push forward as may be used in a light piston aircraft would result in a large loss of height in the Citation.
a steady reduction will result in minimal height loss with full application of thrust.

How you can be so demeaning of examiners who have spent all their lives in the industry just because they happen to be FAA Looses me! One spent 10 years with the FAA accident investigation.

Would I make a positive push down in a low level stall in the Citation??? Hmmm I will take some convincing!

Different horses for different courses springs to mind as does different techniques for different aircraft.

Pace

[mad_jock]

The reduction in AoA can be less than 1 deg its just enough to unstall.

And you are right an inadvertent stall is multiple cockups. Which is why I tend to bang on about attitudes and knowing what's going to get you into trouble. You should be able to see that your approaching the stall by looking out the window and the control feel without any reference to instruments.

Windsheer is a special case as we all know.

My types procedure is to purposely pitch to just before the stall, full power you play with the pitch to just keep the stick shaker occasionally going off and leave everything as it is. Which is significantly different to the stall recovery which calls you getting rid of any drag falp and gear ASAP. This for us would entail a pitch up of about 8 degrees from the approach attitude.

And the other stall which we are worrying about when the freezing level is low is the tail stall and the recovery for that is pull back and deselect what ever you have just selected. But to be able to spot you have a tail stall instead of a wing stall you have to know that your wing isn't stalled.

Pace I don't see any problems at all with the procedure you have been given. The nose on the horizon will mean there is a reduction in AoA but its just a limited max pitch down which is no bad thing. The amount of wellie is neither here nor there and is type dependent. What might be a ball hair on your type might be a fist full on others.

And your statement that this procedure is only for the older models leads me to suspect that the boffins at cessna have redesigned the wing to get rid of this feature of ball hair or huge other issues.

There has been quite large differences in certain procedures across the atlantic for quite a few years, the tail falling the airbus just after 9/11 started the process for the flight upset recovery but it still not there. There are still some FAA pilots that hold that you use boots full of rudder to lift the wing. Again in stalling we are taught as has been discussed but the FAA have taught to power out with less than 100ft.

With my Engineers hat on the FAA power out is crazy it relys on the fact that the pilot can't but help reduce AoA because of the forces involved and the aircraft wanting to unstall itself despite what the pilot does.

I can sort of see the point of minimal height lose when your landing configured from a fully developed, which to me gets into windshear training. But clean 200-300 ft is fine.

[mad_jock]

And you meantion stalling on departure how on earth are you going to power out of that.

You are already at max power your wings are over AoA you haven't got anything else to play with apart from reduce the pitch.

[BEagle]

How you can be so demeaning of examiners who have spent all their lives in the industry just because they happen to be FAA Looses me! One spent 10 years with the FAA accident investigation.

It wasn't me - it was the Boeing chap who told the meeting that the problem had arisen due to FAA examiners mis-applying the 'minimum loss of height' requirement as 'no loss of height' - hence the potentially dangerous 'TOGA and don't descend' nonsense which has spread across the industry. I also suspect that 'windshear go-around' techniques have been confused with stall recovery techniques by some.

This revised technique has now, I understand, been issued as a B737 requirement and also on Airbus aircraft. Certainly ba now use it on their B737 fleet.

[Pace]

Mad jock

I really think we are talking the same language. There are two ways! You are either going for the quickest way at all costs to break a stall or your going for minimal height loss to achieve that!
There is a subtle difference.
If you are at max N1 in the climb and stall you have to go for AOA reduction to get the wing flying as well as pitching for speed tapping into potential energy as you have no other option.
But isn't that what it's about? Different horses for different courses and being able to think out of the box!
Pitching strongly maybe fine at altitude where it doesn't matter whether you loose 100 feet or several hundred feet.
That may not be the case if terrain is a few hundred feet below.
We also have to consider that different aircraft have different behavior patterns so it partially about being familiar with your craft.
How many pilots do you know who are not speed aware, who stick flaps down above speed limitations etc ?
How many do you know who's strengths are not spatial awareness or being able to feel and sense what there craft is doing ?

Pace nb written on I phone

[mad_jock]

At no point has anyone here said pitch strongly just "enough"

And you don't have to tap into potential energy you just need to reduce your AofA which will reduce your rate of climb but it won't be required to decend. In fact recently this exercise was added into the UK syllabus as one of the set exercises.

As for not speed aware yes when they come online they are a bit ****e but we soon sort that out and usually its more wanting to shoot the approach at Vref + 30 or some such. As I said the only real time they can get anywhere near stalling is forgetting to power up on level off after decent. Aka the Dash crash in Colgan US. This crash is one of the reasons why the FAA is revisiting the FAA training on stalling. In the same way that the tail coming off the airbus has changed there views on controlling a flight upset. But the change is struggling to come through because there are so many folk out there keep going for this minimal height lose stuff and its very hard to teach old dogs tricks especially when they actaully believe that the new way is bollocks when it isn't.

As for the feel thing, as you well know there are pilots out there that have been flying for 40 years who appear to have relatively little feel for the aircraft what it is doing and little or no 5th sense about what the aircraft needs to sort itself out. Which is why I quite like your limit of nose to the horizon because its gives them something set to go for.

[Pace]

And you don't have to tap into potential energy you just need to reduce your AofA which will reduce your rate of climb but it won't be required to decend. In fact recently this exercise was added into the UK syllabus as one of the set exercises.

No you dont HAVE to tap into potential energy but effectively consider this?
Forget jets you are flying a small aerobatic machine you have full power but your climb is so steep that your speed falls off sharply.
Now the speed had dropped way below stall the nose falls! where are you getting energy from to get enough air moving over the wings? Just the engine?

I always think of an aircraft having two power sources and two throttles. One the conventional throttle the other the elevator which allows you to tap into the potential energy in the airframe.
How does a glider in still air with no lift and no engine break a stall?

Pace

[mad_jock]

We were taking about stalling on departure not an extra mid airshow. And it could very well be that the hot ship which has an airspeed of 0 isn't actually stalled, even though she is hanging in the air.

In fact instead of buggering about with FAA examinors why don't you just contact Cessna Citation support and get them to clarify what they mean in the manual. And to be honest if things have changed and it hasn't filtered down yet to the troops.

[Pace]

We were taking about stalling on departure not an extra mid airshow. And it could very well be that the hot ship which has an airspeed of 0 isn't actually stalled, even though she is hanging in the air.

Mad Jock

I know what you mean but this is a private pilots forum and as such with low time pilots we should discuss in full.

We talk about Jets as if they are somehow different to other aircraft.
The Airliner which ran out of fuel, all engines stopped glided onto a disused airfield the same with the 777 at Heathrow.

Something produced enough airflow for them to fly?

Had the Airline Gliding to the disused airfield decided to try and fly level it would have eventually stalled.
Would AOA on its own make it fly again where would it have got airflow enough to make the wing fly from?

This is getting silly and point scoring.

I am sure at my next renewal which will probably be in a sim feb next year I will be brought up to date.

Pace

[mad_jock]

I am not disputing the use of potential energy to aid in a stall recovery if so required. Just on the example you used you don't have to decend because you already have enough energy getting pumped in by the donks.

An aerofoil doesn't have a clue whats giving it energy, all that effects it, is the angle of attack it is to the airflow. How much air it requires over it to produce enough lift to support 1t or 5t or for that matter 300tons is a function of the design.

This is the issue of teaching "stall speeds" if everyone was just taught AoA from the start and for that matter flew on AoA for approches we could cut the amount of mis conceptions out there by 90%. We could also get rid of rafts of performance manual charts pissing about with different weights.

Please contact cessna and see what they say.

[PA31flyer]

The stall upon departure can be corrected either by 'tapping into potential energy ' or simply a reduction in AoA. Depends on the stall being due to a lack of airspeed or the aircraft exceeding the critical angle of angle and it still has airspeed.

[Lemain]

What is the reason that there is a possiblity of a wing drop during a stall?

I can only think of 1 reason:
Left & right wings are not 100% same (though in theory they are supposed to be designed that way, but nothing is perfect), and also the airflow at left & right wing might not be the same due to sideslip or wind or some other force of nature, therefore the wings might stall at slightly different time.

Do I score at least 90%?

I assume you are talking about a single-engine propellor monoplane? Only one reply has mentioned prop torque. But it isn't just the torque (or should one really say 'couple') that is the issue. The most asymmetric thing that you'll find on the aircraft is the prop -- and that varies according to whether the prop is stalled, stopped, providing power, retarding airflow.... Without doubt, the largest single factor that affects which wing drops first is the prop; but it isn't simply a matter of 'torque'.

On recovery, torque comes into play (and the gyro effect) as any taildragger pilot knows only too well.

[mad_jock]

There is only ONE thing which makes an aircraft stall and thats exceeding the critical angle of attack.

The only requirement for tapping into potential energy is if there isn't enough power to over come the drag just prior to exceeding the angle of attack. Then you have to find energy to get the aircraft through that high drag part of the curve until the engine can produce more power than the aircraft produces with drag.

[BEagle]

Depends on the stall being due to a lack of airspeed or the aircraft exceeding the critical angle of angle and it still has airspeed.

I've heard everything now......

[Crash one]

Depends on the stall being due to a lack of airspeed or the aircraft exceeding the critical angle of angle and it still has airspeed.

The ASI reads through a line roughly parallel to the angle of incidence so if it still has airspeed in that direction it isn't stalled. If the AOA is exceeded the airspeed has bugger all to do with it. I think!
Jock will now kick my arse no doubt.

[Lemain]

There is only ONE thing which makes an aircraft stall and thats exceeding the critical angle of attack.

I don't suppose anyone is going to take great issue with that....but it wasn't the question the OP asked.

[Lemain]

The ASI reads through a line roughly parallel to the angle of incidence so if it still has airspeed in that direction it isn't stalled. If the AOA is exceeded the airspeed has bugger all to do with it. I think!
Jock will now kick my arse no doubt.

Yikes! It's a wee bit more complex than that particularly when you get to the edges of normal operational conditions (which a stall or spin is, of course). To keep the airframe 'flying' you need essentially non-turbulent airflow over the aerofoil surfaces. Wings, fuselage and tailplane/elevator. At a certain angle of attack (let's call it zero) the lift from the aerofoil surfaces equals the downward gravity force of the aircraft and load. As the aircraft gets heavier (more pax, fuel, baggage) the AOA needs to increase to match the downforce. That's fine all the while the airflow over the surfaces is essentially laminar. At some stage -- maybe low speed, an attempt to climb without power, engine output reduction (carb icing?) the airflow might become turbulent and the airframe approach a stall -- the pre-stall buffet due to non-laminar airflow. At this stage, in principle, the pilot can either push the stick forward to reduce the AOA, and increase airspeed or he can apply more power -- though the latter is dodgy if he is very close to a stall as he could end up in a power stall or power spin. It seldom happens presumably because it takes a bit of a clot to get into that position and clots don't often get licences? Darwinian principles tend to reduce the number of clotted pilots.

[Pilot DAR]

Hmmm, some not so accurate information is emerging....

Letting alone any discussion of jets,

in a C172 the right wing is actually at a slightly higher AoA than the left due to the fuel return, the fuel return on goes to the right

Not really. Both wings of a 172, like most trut braced Cessnas, can be indepedantly adjusted with cams, so as to change the angle of incidence. 172's (at least carburetted ones) do not have fuel returns. The 172S might, I'll have to enquire. A fuel return would not affect stalling characteristics. You will find that only the most precisely manufactured metal plane has both wings the same. Those minor variances will create wing drop in a stall. In small amounts, it is a non event. I have test flown aircraft where it was certainly unacceptably high though.

At some stage -- maybe low speed, an attempt to climb without power, engine output reduction (carb icing?) the airflow might become turbulent and the airframe approach a stall -- the pre-stall buffet due to non-laminar airflow. At this stage, in principle, the pilot can either push the stick forward to reduce the AOA, and increase airspeed or he can apply more power -- though the latter is dodgy if he is very close to a stall as he could end up in a power stall or power spin. It seldom happens presumably because it takes a bit of a clot to get into that position and clots don't often get licences?

I'm not in agreement with this either.

A quick list of factors which affect the stall "speed":

AoA (flap position can affect), weight of the aircraft, C of G position, G loading (angle of bank), and aerodynamic "cleanliness" of the wing.

Power affect where you are going while the stall is happening (up or down).

Speed, in conjunction with power will affect your AoA. Drag affects speed.

Aircraft (other than momentarily, on inertia) do not climb without power. Laminar vs turbulent airflowcan be an element of a stall, but turbulent airflow over much of the wing can still sustain lift enough to prevent a stall in some aircraft types (and most GA types).

Yes, pushing the stick forward reduces the AoA, and this important for preventing/recovering a stall, but the reduction of G loading is another important element. Other than speeds presented relative to angle of bank, stall speeds are presented in one G flight. It is possible to fly at less than one G for brief periods, and this could be an aspect of stall prevention/recovery. An aircraft flown at a half a G is still fairly controllable, and has a much lower stall speed. Obviously, you can't do this for long, but sometime, just long enough to get yourself out of trouble. This is a coupled effect with AoA reduction.

Applying more power changes your direction of flight (let's presume from a little downward to a little upward for ease of understanding). If nothing else changes (attitude relative to earth), the AoA has been reduced by doing this, and the speed will increase. Both of these will create an increased margin from the stall.

A wing will stall when its critical angle of attack is exceeded for the G loading. Though speed plays a role in this, if the G is not one, the speed may not have the direct relationship to the stall that a pilot expects.

"power stall" and "power spin"... Well... with the exception of control limited aircraft, any aircraft can be stalled and spun at any power setting. Power will affect this, and torque can certainly effect handling entering and recovering. Pilots are wise to seek out good training for this type of flying, and when competent, practice regularly.

Stall spin accidents are a result of the pilot failing to maintain flying speed for the conditions, but are not isolated to new or careless pilots. Unforseen conditions can lure a pilot in. The only way is for that pilot to use remarkable wisdom, and experience to avoid the condition - 'cause once you're there, it is what it is. Stall spin is too common, I have cleaned up some wrecks. The most common example of this is a floatplane departure from a lake, where once crossing shore in the climb, unfavourable wind, or downward moving air prevents a climb over the obsticle, and the pilot pulls back more in an effort to clear. This can become very bad fast, and only careful departure path planning is going to prevent it.

The circuit at a well used airport is a naturally safe place to fly close to the ground, as there are few surprises. Start flying planes close to the ground, away from airports, and the risks increase quickly. Stall spin is probably close only to CFIT as the greatest risk.

Do not assume that because you are a "good pilot" you cannot find yourself approaching an unexpected stall (which puts you at risk of a spin). All planes will warn you in feel (some earlier than others). only lots of practice will teach you to feel the plane's approach to a stall.

"Good" (non Darwinnian) pilots have learned (so far, anyway) to anticipate those conditions, leave themselves an out, and are current with the handling of aircraft they are flying, in that regime.

[mad_jock]

Well in my opnion the reason why wings drop has got nothing to do with the most of the discussion its pure and simple pilot error. Most pilots have to go and annoy the poor aircraft and upset it.

When I first started instructing in tommys I had a wing drop every time. A year and a bit later and 900 hours they didn't drop a wing. Same airframes. So I can only conclude it was me being cack handed or cack footed. Give it to the students and it used to drop a wing again (much to thier disgust).

And yes crash one a kick up the arse is required. Its all to do with flow over the aerofoil and when the boundary layer becomes unstuck. Although I would slightly disagree with the turbulence comments because sometimes the engineers induce it with vortex generators because it delays the boundary layer becoming unstuck.

The best way to have a play with this is take a piece of card and get some one to drive down the road and have a feel of the forces required to hold it at various angles to the airflow sticking it out the window. If you can get hold of an aerofoil profile even better. As you go from flat lifting the front edge and droppping the rear you will feel an upwards force and a small rearward and when you go too far it will disappear and be replaced by a relatively large force in the opersite direction to the direction of travel. Once you lower the front again it will go back to an up force with a bit of rearward force.

Go have a play with it, its much more intuative if you can see and feel whats going on.