Statistically, when is a stall more likely to happen?

[ben87r]

Full and free.

 

It's the thing that I forget off the checklist the most!! But, that's what the checklist if for. I normally end up doing it just as I line up.

 

It is dumbfounding the amount of stupid things that I've NEARLY done before departing because of late pax, late aircraft, late notice charters OR getting on in the day.

 

Pitot covers on, control lock in, baggage door open, chocks, fuel caps, pump static lines, you get the picture I think! A walk around and an unrushed time in the AC after engine start (remembering that once the engine is running people feel like they are on the way so you can take enough time to get settled ;) is what has picked up on these.

 

The worst one being pax window on a check flight and rolled!! Stupid nervs

 

 

[ben87r]

And there is an old wives tale about the C210 baggage door in flight closing procedure that I might be able to vouge for ;)

 

 

[poteroo]

I think there's a reg that says you HAvE to check the controls for free correct movement immediatly before flight.

Yes, non compliance with that particular Reg might have been the one that sealed their fate, but, consider what transpired before this. Aircraft signed off 'unsafe' control locks, time & duty hours waaaay over by 10pm, unlit country strip, passengers who'd been at the pub for some time, pilot probably didn't have dinner, and probably more. Charter flying can be a pressure operation - but when things turn to......!

 

 

[facthunter]

It's confession time is it chaps and chicks? Controls free and full travel usually gives someones leg or foot a shove. There are a couple of times when any restriction should have been noticed in the normal process. Correct sense I try to do before I get in the aircraft, but you can't do the rudder in some types. Don't be rushed folks . Think aeroplane. Live longer. Nev

 

 

[DWF]

SAFETY PRECAUTIONS BEFORE TAKE-OFF (CAR 244)

 

"Immediately before taking-off on any flight, the pilot in command of an aircraft shall:

 

• test the flight controls on the ground to the full limit of their travel and make such other tests as are necessary to ensure that those controls are functioning correctly;

 

• ensure that locking and safety devices are removed and that hatches, doors and tank caps are secured; and

 

• ensure that all external surfaces of the aircraft are completely free from frost and ice."

 

 

 

Controls - Full, Free and Correct Movement. Is the last item on my checklist - for all the aircraft I fly.

 

 

 

The pilots First Commandment:

 

"Maintain thy airspeed lest the earth arise and smite thee."

 

 

 

The ONLY reason a wing stalls is because the angle of attack has exceeded the critical angle.

 

 

 

In (almost) all cases the angle of attack correlates very closely with the stick (control column, etc) position - even with a fully flying tailplane.

 

 

 

I think the base/final turn is probably the most likely inadvertant stall situation:

 

- Reduced airspeed - increased AoA required to maintain Lift (approx)= Weight

 

- Reduced airspeed - causes yaw to the right in most aircraft if not corrected by appropriate rudder application to maintain Balance

 

- Glide or Reduced power - requires lower nose attitude in a turn to maintain airspeed

 

- Turning - requires increased AoA to provide turning force

 

- Flap Down - masks "apparent attitude" change due to AoA increase

 

Add to these Distractions and close ground proximity and things can go wrong very quickly.

 

 

 

DWF

 

 

[WayneL]

I vaguely remember a Aviation Digest story on base to final stalls, it had a very good diagram of a Cessna in a descending left turn with flaps down and wing tip "track lines" overlaid and AOA notes for the port and starboard wing.

 

The article makes the point that skidding in the final turn is a major factor in bringing on a sudden stall and wing drop to the lower inside wing which is usually fatal at this low altitude.

 

A pilot with a tailwind on base may realize too late that his final turn will overshoot runway center line.......so he banks a little bit more.......still overshooting center line so he pull in some more elevator to tighten the turn..........still doesn't look good for making the center line............he does not want to bank any steeper so almost subconsciously he kicks in more left rudder to 'push' the nose towards the center line.........the bank starts to increase so he now adds opposite aileron (right in this case)! He now has a situation where the AOA on the port wing is greater than the starboard wing (traveled path of inside wing is shorter and therefore at a greater AOA & with port wing aileron down, the mean chord line of the port wing is at a greater AOA than the starboard wing.

 

He is also slow with a higher than normal bank angle with an increase in G force due to pulling in more elevator, meaning the stall speed has increased and his margin of airspeed above the stall has decreased.

 

A stall in a slipping turn, it seems, is less alarming to a pilot than an inside wing drop and also less likely to happen.

 

Off topic but in line with the above posts about instructors methods. Read in an american Flying magazine column about the instructor that used to throw his joystick out the door of the J3 Cub when he thought his pre solo student was good enough to land without his assistance. Word got around the students so on student decided to play a trick on him.....he hide a spare joystick in the cockpit and when the time came and the instructor threw his stick out the door......the student held his stick up and then threw it out too! Instructor never did that again!

 

 

[SDQDI]

Off topic but in line with the above posts about instructors methods. Read in an american Flying magazine column about the instructor that used to throw his joystick out the door of the J3 Cub when he thought his pre solo student was good enough to land without his assistance. Word got around the students so on student decided to play a trick on him.....he hide a spare joystick in the cockpit and when the time came and the instructor threw his stick out the door......the student held his stick up and then threw it out too! Instructor never did that again!

 

Oh for some go pro footage of his face:roflmao:

 

Having said that, there isn't much room in a j3 to hide a joystick.

 

Also in regards to the stall/spin in a skidding turn I'm not totally convinced that it is because the inside wing is going slower. The way that I understand it the difference in speed from left to right wing would be very minor compared to the effect of the aileron, for example in a left turn onto final using too much left rudder he would be compensating with right aileron which would straight away increase the angle of attack on the left wing which would cause the stall. Just ask yourself what happens if you try to recover from an incipient spin using aileron????????

 

The whole wing speed difference thing IMHO confuses a pilot to what is really causing the wing to stop flying.

 

Please if I'm wrong don't shout me down:blush:

 

 

[WayneL]

No there is no much difference between wing tip airspeeds in the turn but AoA to the relative airflow is higher for the inside wing which travels less distance than the outside wing for a given altitude loss.

 

off topic again..

 

My cousin trained on winjeels and Maccihi's

 

and while in a briefing on stall turns ( don't remember which aircraft) the instructor asked why the stall was indicated higher by a few knots in one direction! The answer was that the pitot tube was out on one wing.

 

 

[Jabiru7252]

I would have thought the dial would be 'cramped' down around the stall speed (like most light aircraft I have flown) and a few knots would not be apparent.

 

 

[facthunter]

The speed difference wouldn't be much ..Better to be balanced (No skid or slip). If you get slow the stick will be well back and you are set up to stall. The inevitable result of that will be the nose will drop, and many instinctively pull the stick further back, making things worse. As stated in a previous post, you need more lift in a banked turn. so the AoA is getting closer to the "NEW" stall speed as you have pulled the stick back some. and that controls your AoA.. Nev

 

 

[SDQDI]

The speed difference wouldn't be much ..Better to be balanced (No skid or slip). If you get slow the stick will be well back and you are set up to stall. The inevitable result of that will be the nose will drop, and many instinctively pull the stick further back, making things worse. As stated in a previous post, you need more lift in a banked turn. so the AoA is getting closer to the "NEW" stall speed as you have pulled the stick back some. and that controls your AoA.. Nev

But if you are skidding at the time (turning base or final) that aileron input will exacerbate the stall so your lower wing drops and you will find yourself upside down low enough to touch the ground if you extend your arms...... Not a nice picture.

Wayne bear with me, I still don't see how there would be a higher AOA for the Lower wing. The speed difference worked out on a 10 metre wing with a 1 Km diameter for a flat skid turn (I have never tried to do a skid turn for a full circle to work out the actual diameter) is approximately 1% from my rough maths which isn't much. But (well for the hornet at least) even a little aileron input would be enough to change the AOA for that part of the wing. I think the balance part is extremely important (unless deliberately side slipping) and to be flying out of balance is flirting with danger.

 

Doing a balanced stall on a base or final turn would be deadly enough without adding a spin to the mix.

 

 

[Jabiru7252]

Just some rough (back of the envelope) maths. A turn of 360° in 60 secs at a radius of 600 meters puts your speed at about 122.2kts. An object on you OUTER wingtip 2 metres away is doing 122.6kts. An object on your INNER wingtip 2 metres away is doing 121.8kts. A difference of 0.8kts. Correct me if I'm wrong. No angle of bank factored into this scientific revelation.

 

 

[motzartmerv]

The lower wing in a turn has a higher angle of attack. Add to that the aileron increasing the angle of attack at the TIP of the wing as you deflect it DOWNWARDS to pick up the wing. Forget about turn radius etc.

 

1. In a level turn, lift MUSt be increased to remain level.

 

2. In a descending turn, lift MUSt be increased to keep descent rate constant

 

3. Lift is increased by increasing angle of attack in both 1 and 2.

 

4. Angle of attack is increased by increasing back pressure

 

5. A wing with dihedral will have a higher angle of attack on the DOWN GOING or inside wing. Thats how it works. Thats why theres a tendency for the aeroplane to right itself. Its a basic principle of stability.

 

 

[SDQDI]

Thanks Merv that makes sense, up to then I couldn't really picture why lower wing would be different but that has helped. I mean I understood the bad effect of the aileron in said situation but understanding the difference in AOA for wings in a turn was eluding me.

 

 

[motzartmerv]

 

Crood picture I just made for you. But you can try and imagine the relative airflow in a descending turn. In this instance coming from below and left in a left turn. The right wing shows clearly, a lower angle of attack.

 

Sorry its a dodgy pic, but hopefully it makes sense.

 

 

[SDQDI]

Dazza has 2 accounts?? Lol just kidding.

 

Yes that's all good Merv as soon as you said dihedral it made sense.

 

 

[WayneL]

Wayne bear with me, I still don't see how there would be a higher AOA for the Lower wing

This is the way I see it, I hope it helps. I have drawn a diagram, the traveled distance are only examples not actual worked out figures. Also, I have drawn the wing (chord) parallel (in relation to a horizon) but the of course a descending aircraft wing would be lower on the leading edge, this does not change the anything with regard to the AoA differences though.

Another way to visualize it is to think of a spiral stair case. Let's put a nail in the same place on each end the steps ( dead centre say) then run a string from nail to nail on the inside of the spiral steps and on the outside. Look at the angle between the step and the string line, comparing the outside angle with the inside angle......it's not hard to picture the difference.

 

Now... the AoA difference may be very small for the aircraft in that descending turn but even one half of one degree is going to make a difference.....and that's with neutral ailerons.

 

 

 

[Ada Elle]

I wondered if anyone had actually thought of what part of a flight was an airplane more at risk of stalling. I think the riskiest time is climb-out from the runway.

At 3000' AGL, during a BFR. Seems to happen there every time.

 

 

[facthunter]

I would suggest turn back or turn onto final is the most likely time to stall. If flying unbalanced (ball off centre) one wing will stall before the other. Exaggerated...... that is how you do a flick roll.. Altitude should have little effect if you use indicated airspeed as your reference and there's usually not much else to go on.. If you are at your absolute ceiling height you will be right on stall speed.

 

Instructors used to teach and emphasise the holding Off or On of the ailerons in a climbing or descending turn. It's there but often not very marked and any out of balance would be more likely to degrade climb performance or range if gliding. If you are doing a steep turn the difference in distance of the wing tips travel is less marked. If you are close to stall speed aileron use can be a bit critical in some aircraft. If the plane is misrigged it will tend to stall one wing first (or if any damage to the wing as in post bird strike, spoiler float etc). Nev

 

 

[Ignition]

Statistically the number one scenario of an unintentional stall is below circuit height in the circuit, turning base-final, followed closely by initial climb out. There are numerous studies that the FAA in particular have done specifically on that which are relevant anywhere in the world, so I won't beat that old drum that was already smashed out in this thread a year ago.

 

If you are close to stall speed

What is this 'Stall Speed' business Nev? Angle of Attack...

 

 

[facthunter]

Being a little pedantic aren't we?. When I commented on indicated speed being the only reference, for most of us and that indicated speed is useful is it changes responding to the same air density as lift does. Absolute ceiling is the max alt that level flight can be maintained. Ie No dynamic loading. When you get there, IF you increase your speed (indicated) , you descend , reduce it and you descend as well.

 

If we all had an AoA indicator you would observe it by that method, but we don't. You have to allow me to present in a way I see as appropriate, which you are perfectly within your rights to criticise. but I have explained why I chose to make the case the way I have, because that is the way it will present in the actual situation .

 

You won't get a more ardent presenter of stall AoA and stall stick position than me on this forum. If you go back through my posts. I try to de mystify low speed flight, but still respect it...Nev

 

 

[Ada Elle]

You won't get a more ardent presenter of stall AoA and stall stick position than me on this forum. If you go back through my posts. I try to de mystify low speed flight, but still respect it...Nev

I have a stupid question about stall stick position and AoA - I tried an aircraft that would mush if you tried to enter the stall from straight and level, but if you brought the nose up with power, then held it there with the power off, it would do a proper aerodynamic stall. I'm guessing this has to do with the fuselage shadowing the elevators in certain pitch attitudes leading to less effective elevator not letting you stall, but I've never seen this described before (pitch dependent stall).

 

Anyhow, I was just snarking that I do a fair number of intentional stalls, and have never had an unintentional one, so for me the most likely place to stall is at a good height.

 

 

[Head in the clouds]

I have a stupid question about stall stick position and AoA - I tried an aircraft that would mush if you tried to enter the stall from straight and level, but if you brought the nose up with power, then held it there with the power off, it would do a proper aerodynamic stall. I'm guessing this has to do with the fuselage shadowing the elevators in certain pitch attitudes leading to less effective elevator not letting you stall, but I've never seen this described before (pitch dependent stall).Anyhow, I was just snarking that I do a fair number of intentional stalls, and have never had an unintentional one, so for me the most likely place to stall is at a good height.

I rather doubt that you truly wish to have your question considered as 'stupid'. It might seem less so if you mentioned the aircraft type ... of course if you get the nose high by whatever means and then un-power it, it will stall. Isn't that obvious?

 

And after three or so years of flying and thinking about it in your detailed manner, are you still not aware of the differences between progressive, power on, and accelerated stalls?

 

Fuselage shadowing the elevator? How would this occur? There's no such thing as a "pitch dependent stall" stalls are solely dependent on the angle of attack.

 

 

[Ada Elle]

I rather doubt that you truly wish to have your question considered as 'stupid'. It might seem less so if you mentioned the aircraft type ... of course if you get the nose high by whatever means and then un-power it, it will stall. Isn't that obvious?

It was a FlySynthesis Texan.

 

Why do you think that a power-on or accelerated stall was at all involved?

 

Both times I attempted to stall the plane without power. In one situation I started with the nose level, and attempted to keep it there while the power was cut. It did not stall aerodynamically (nose drop). In the other situation, I started with the nose about 10 degrees high, and attempted to keep it there while the power was cut. It did drop the nose. In both situations the stick was back into my guts.

 

Stick position roughly corresponds to AoA, given CoG/flaps/etc. So why did it still in one scenario and not in the other? The only thing I can think of is that the elevator is not as effective in one situation, and can't get the plane into a stalling AoA.

 

 

[Happyflyer]

If you bring the nose up with power, the airflow from the engine over the elevator will make the elevator effective and get the nose up higher. If you then take that power off the nose will drop every time. This does not mean you have necessarily stalled. It just means the airflow over the elevator can't hold the nose up any more.

 

Just as a nose drop doesn't necessarily mean a stall, if you don't get the nose drop it doesn't necessarily mean you haven't stalled. You could be mushing down fully stalled but the design of the aircraft is such that the centre of pressure hasn't moved back far enough to over power the elevator and cause a nose drop. In the end, if you don't get the stick back too far you won't stall.