Secondary Stalls - What's the dangers?

[HighDreams]

Hey,

I'm currently going through my ppl groundschool and I have a question in regards to secondary stalls. What are the dangers?

Thanks,

JB

[Aviatard]

The danger is that you will stall the aircraft again while trying to recover from the original stall, and at a lower altitude.

[Lurch]

Death

Ask yourself, or instructor where you are most likely to stall and you will have your answer.

I'll give you a hint, it's not at the 3000'agl you practice at.

Lurch

[RVgrin]

Death

Ask yourself, or instructor where you are most likely to stall and you will have your answer.

I'll give you a hint, it's not at the 3000'agl you practice at.

Lurch

So true. This is a sufficiently serious topic that hints and innuendo are perhaps not sufficient.

Every pilot needs to know on every level (intellectual, instinctive, emotional, etc.) that you must always keep the airplane flying, even if (no, make that "especially if") the ground is rushing towards you.

Sometimes that means not pulling the stick back as hard as you can, and sometimes it means pushing it forward. Upper Airwork is designed to teach you this, but instructors sometimes don't realize that students don't completely get that.

Ask yourself this. If a crane lifts a plane to 100 feet and lets go, what happens to the occupants of that non-flying falling metal structure when they strike the ground at 90km/h? Now ask yourself how the survivability goes up by instead flying into the ground at successively shallower angles? Decide which you'd prefer now, because there will not be enough time with the ground (or treetops) rushing towards you.

Only once you are sure that you will choose to fly the plane into the ground (ripping the wings off between the tree trunks, if necessary) instead of stalling over the top and plummeting to a certain death... only then should you be commanding an aircraft.

The plane's wings can't tell the difference between a primary and secondary stall, but the pilot's psychological state is quite different when pulling out of a dive. Think through as many scenarios you can, until you are quite sure you will strive to keep air moving over the wings at a sub-critical angle of attack.

All you seasoned pilots out there. When was the last time you practiced upper airwork in a small plane?

[cgzro]

People tend to panic when faced with the ground rushing up at them and the natural instinct is to pull the stick back into your gut which will naturally have the same effect as the first time you did it.

Kind of like turning into a skid on the side of a cliff .. right thing to do .. but not so easy to tell your brain to do it.

[KAG]

Most stall/spin accidents happen close to the ground on takeoff or landing. There is not usually enough altitude to properly recover. The emphasis is thefore recognition and avoidance as well as proper recovery technique. A secondary is direct result of improper recovery. Each time you enter slow flight and stall you run the risk o a wing drop (spin). You may recover from a stall at low altitude, you will NOT recover from a spin in time. Whats the problem with a secondary stall? It's another chance of entering an unrecoverable spin at low altitude, or in the case of some twin engine aircraft an unrecoverable spin from any altitude.

[lownslow]

I think the question hints at maybe not really knowing what a secondary stall is. JB, I'm sure you already know that a stall is when you exceed the critical angle of attack for your particular airfoil and the smooth flow separates from the upper surface of the wing, drastically reducing lift and increasing drag. In practice (upper air work) this is most commonly achieved by holding altitude and slowing down until the angle of attack required to maintain altitude exceeds the critical angle. Another way to exceed the critical angle is to abruptly pitch up; due to inertia the airplane will initially continue along its original path (more or less) while you've managed to point it in a different direction. This is sometimes referred to as a high speed stall, leading to the notion that stalls are a function of speed. They aren't.

Anyways, the thing about a stall is in normal day to day flying you don't want to do it on purpose. Recovery is an emergency procedure (life and death kind of stuff) so you'll practice it a lot during your training with an emphasis on minimum altitude loss in the recovery. In case it hasn't been covered yet, basic stall recovery consists of lowering the nose (this reduces the angle of attack below the critical angle, at this point you're actually un-stalled), then adding power to minimize altitude loss, then smoothly transitioning to a climb. The thing is, in training you may have an instructor who is yelling "MINIMUM ALTITUDE LOSS!" or in real life you'll have trees rushing up at you which make you want to just yank the controls back to get that climb going after the recovery. This will again cause the wing to exceed its critical angle of attack, the plane will stall again, and you're back at square one still losing precious altitude. Also, you have full power on now so various effects caused by your propellor (torque, p-factor, slipstream, precession) could make the secondary stall nastier than the first one.

So to sum it up: a secondary stall is just another stall caused by poor recovery technique. Two stalls in a row will eat up more altitude than just one. The aim of the exercise is minimum loss of altitude, therefore secondary stalls are bad.

LnS.

[Liquid Charlie]

In my experience the one issue with a secondary stall is that it is usually far more violent than the initial stall and is magnified because of poor or overly aggressive recovery from the initial stall. I'm sure CAT can back me up on this one - I have witnessed guys almost go over on their back in a secondary stall in a DC-3 and the initial stall was very docile.

[Cat Driver]

I'm sure CAT can back me up on this one - I have witnessed guys almost go over on their back in a secondary stall in a DC-3 and the initial stall was very docile.

That is for sure, but even more surprising is the docile old PBY if you let it secondary stall your eyes will be bugging out like a bull dogs nuts before you get it back under control.

[Beefitarian]

Is it easy to cause a secondary stall at altitude for training or is a secondary stall in a C-172 just another mush and not really usefull for demonstration purposes anyways?

The only problem I have had doing stall training, was wanting the thing to actually seem stalled. A fully stalled 172 at a safe altitude doesn't seem stalled, maybe it's the secondary stall that finally seemed like you needed to do something. In the warrior it stalls a bit more like, oops we're falling here.

[trey kule]

Ok, I shall wade into this.

When we talk of initial stalls.

Lets talk a bit about wing design. With designs like washouts, cuffs, twists etc, it might be, as in the 172s for example (pay attention beefie) that only the inboard portion is reaching the critical angle and the c of p is still forward over the outboard portion. What you really have is a partial stall. Whch is why you will see power being applied to a 172 to increase rudder and elevaor effectiveness and bring the ourboard portions of the wing through the critical angle, when you are trying to spin it.

Now the secondary stall, sometimes manages to accomplish the same thing, that is more of the wing is stalled ( so to speak) , and thus the stall is more violent and sometimes unpredicatable.

One of the first things to do in a stall is to neutralize the ailerons. Without getting into a bunch of technical mumbo jumbo, it is simply because their effect can be exactly opposite to what it normally does.. Designers realizing this many many years ago, went out of their way to try and keep the aileron section of the wing below the critical angle, so that, in effect the alerons could help in the first part of the stall recovery..that is they would be "flying" first.

In the secondary stall, with more of the wing stalled and with such things as limited rudder and elevator travel, the result can be dramatic, and recovery much more interesting.
Anyone who feels a secondary stall is just a number two , has never really experieced them in a plane that was not designed to be flown by the lowest common denominater.

I am always amazed that the people, right up to the CFI's who teach these things really dont understand them at all. I have heard new CPLs (ex instructors) tell me that if everything goes to hellin a handbasket just let go of all the controls and the plane will recover.....and they believe that.

[Beefitarian]

Excellent, the "We're all passengers now." method of recovery works great in a 172.

Lets talk a bit about wing design. With designs like washouts, cuffs, twists etc, it might be, as in the 172s for example (pay attention beefie) that only the inboard portion is reaching the critical angle and the c of p is still forward over the ourboards. What you really have is a partial stall. Whch is why you will see pwer being applied to a 172 to increase rudder and elevaor effectiveness and bring the ourboard portions of the wing through the critical angle.

See, I kind of figured something like this without actually connecting the dots. Thank you sir.

Meanwhile the passingers I were paying to ride around at the time and tell me I'm not good enough to take a CPL ride yet were hoping I'd recover just because the stall horn started singing, I would sometimes just to show them the exercise the way they wanted to see it. Usually I'd make sure I was stalled just for my own benefit. I'm bothering to do this I might as well practice recovering from an actual stall.

[trey kule]

I have never heard that expression before but it sends chills down my spine.

Take a minute and think about it. When you are training The aircraft is thousands of feet in the air. It is at or below the weight limit ( yes.. I think the 172, or some of them have a lower weight limit for spins..less than McTOW). The trim is neutral or very close to it. The c of g is well forward.. That is not the situation you are training for.

Bring the weight up to max allowable. Put a couple of people in the back seat to bring the cofg back to near the rear limit. Put down 10 deg of flaps and try a maximum power climbing stall..You may find that old 172 when it stalls does not recover all that well . Stalls that occur on climb out, happen because when the trees are coming at you the tendency is to pull back and once you ae below Vx pulling back is going to do you no good and take you to an unpleasant(er) solution. (
And , for the most part, the majority of planes you fly in your career wont typically be as benign. There should never be a "we are all pax" solution in your mind. It is why one of the FTM procedures is to positively and briskly move the control column forward..There is a reason for that being there. Positively and briskly...

I have not spun an airplane in years, but I did spend years teaching spins. I never, not once , met a pilot who could not , without hesitation go through the spin recovery technique listed in the FTM, and who could do a proper recovery. You need that implanted in your subconscious
Take some time. Memorize those items. Then sit on a chair (cheap simulator), and go through the motions...throttle to idle...neutralize the ailerons...been 20 years for me and I can still recite it pretty close I think. Practice it until you dont have to think..Word perfect Visualize what the plane is doing.
Allah willing no one will ever get into an unplanned stall, but if should happen you dont want some little portion of your subconscious telling you just to let go and all will be well...Maybe it will, but keep in mind there was no promise those 72 virgins would be female..Fear really changes reactions

I wish I could walk around with a bat and swat any instructor who even mentions this technique on the back of the head.

[Beefitarian]

I've had a few decent instructors but way more lame ones that must have been better than me because they had something on their licenses proving they were instructors. :eyerollguy

I allways figured the point of the exercises are to help you learn to recognise what part of slow flight you were in and how to recognise what the plane does just prior to stalling to help you avoid getting that close unless you want to intentionally stall. Maybe the americans are right and there's no value in spin training because too many instructors don't understand it.

I want a refund for most of the spin/stall training I paid for now.

[Beefitarian]

The "We're all pax now." was a running joke of mine about people that don't do anything when they're supposed to be piloting the plane. Once in a while I'd use it when an instructor either didn't think I was acting quickly enough or told me a story of someone freezing up that kind of thing.

For example we were doing a forced aproach and I'd changed fields as a better one showed up. The passanger I hired that day lectured me on going to the first field I picked. I told him there's no way I'd use that field now that we could tell what was in it. I understand the concept that you should try to use the first field you pick to keep things simple during an emergancy. I also think that even though I'm in a glider now, I'm going to land in the nicest spot available and I'm not done flying until the plane is stopped there. I'm not changing unless the new field is an easy switch and quite a bit better. I have enough problems with the reduced climb rate due to no engine I'm not landing in field that looked ok until I got closer and noticed a way better one that's not all rutted, sloped, full of cows, has a dry creek in the tall grass or whatever.

Just because I don't lost engine power is no excuse to stop thinking and flying the plane, "Oh no, we're all passengers now."

[iflyforpie]

I know that for spin recovery in the Citabria (two turns fully developed) that the standard method, centralizing controls, and letting go each affect recovery within seconds of each other...