What is "lift"?

[Schooner69A]

The level/climb/AOA question was thought up to generate some discussion a provide for some thinking on the subject. It worked.

While it may be too 'esoteric' for under-training students, it's a worthwhile talking point for those with PPLs to ATPLs.

Another thought problem:

Everybody knows that in spin recovery, you use neutral aileron: out-of-spin aileron is BAD. Right?

However, what would be the effect of pro-spin aileron?


Throw that out at the next kaffee klatch at your flying club and sit back and listen.

[porcsord]

What is lift?
Oh baby, don't stall me
Don't stall me
No more

Oh baby, don't stall me, don't stall me
No more

What is lift?
Yeah
No, I don't know why you're not in the flair
I give you my lift, but you don't care
So what is up and what is down?
Gimme a sign
What is lift?

Oh baby, don't stall me
Don't stall me
No more

What is lift?
Oh baby, don't stall me
Don't stall me
No more

[photofly]

However, what would be the effect of pro-spin aileron?

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

[Big Pistons Forever]

However, what would be the effect of pro-spin aileron?

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

Nobody should be spinning an aircraft without understanding the effect of pro and and anti spin aileron on the spin, yet sadly that lack of understanding of the effect of flight control placement on spin dynamics seems to be pretty common in flight instructing. This is why I strongly believe no flight instructor that is not trained in the execution of basic aerobatic maneuvers, which will always include spins, should ever let a spin develop beyond 1/2 turn

That being said the state of the art in very high performance aerobatic airplanes can really bend the rules. For example they be recovered from a spin with full antispin aileron which should instead inhibit or even prevent recovery. The ailerons are so powerful the aircraft basically rolls out of the spin despite being stalled.

[photofly]

In which corpus of aerobatic airplanes is this training in basic aerobatic manoeuvres to take place?

And where is to be found the cadre of aerobatics instructors to provide this training?

Or is it about time that the requirement for spins in the PPL and CPL syllabi was removed?

Is there data to suggest the current situation is to be improved? What are the stall/spin accident rates in training, and in ga flying, in Canada, recently, anyway? What problem are we trying to solve?

[2R]

What is lift?
Oh baby, don't stall me
Don't stall me
No more

Oh baby, don't stall me, don't stall me
No more

What is lift?
Yeah
No, I don't know why you're not in the flair
I give you my lift, but you don't care
So what is up and what is down?
Gimme a sign
What is lift?

Oh baby, don't stall me
Don't stall me
No more

What is lift?
Oh baby, don't stall me
Don't stall me
No more

If there was a prize for winning the internet , you got gold !!!

[Heliian]

Here are the FAA basics of airplane aerodynamics.

Pages 23 and 24 explain this hot topic.

It's actually a pretty good read.

Cheers.

https://www.faa.gov/regulations_policie ... ak_ch5.pdf

[RedAndWhiteBaron]

Here are the FAA basics of airplane aerodynamics.

Pages 23 and 24 explain this hot topic.

It's actually a pretty good read.

Cheers.

https://www.faa.gov/regulations_policie ... ak_ch5.pdf

This is a far better explanation than Transport provides in the Flight Training Manual IMHO. I'd have to look it up, but I think it's better than how FTGU explains it, too.

However, what would be the effect of pro-spin aileron?

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

I would actually like to hear the aerodynamic explanation of this. To increase drag on the outside wing and therefore reduce the rate of spin, perhaps? It goes against all spin training I've ever been taught. Actually, "difficult" spin recovery would be good to practice, but you'd need an aerobatics instructor for that, and even then, I don't know if it would be allowable or even worth risking. You might need a test pilot.

As may have been made obvious, I don't like keeping it simple. Sure, in flight, I keep it simple - reduce RPM for descent here, pitch down for descent at this airspeed. Don't think about the spin, just recognize which way you're spinning, and put the rudder to the floor the other way. Don't think about the aerodynamics of slow flight, just learn this recipe for achieving it. It's worked so far, at least for training. But for scholarly studies, it helps to delve more deeply to me. I mean seriously, when was the last time you drew a 10 degree drift line? If there's value in teaching that, if there's value in teaching precautionary soft-field landings that haven't been done since the 60's, I fail to see the value in exploring aerodynamic theory more deeply.

In which corpus of aerobatic airplanes is this training in basic aerobatic manoeuvres to take place?

And where is to be found the cadre of aerobatics instructors to provide this training?

Shameless plug - my soaring club (York Soaring), offers aerobatic instruction in gliders. Not currently, due to this damned virus, but they have the instructors and the aircraft to offer it.

And for the record, I still disagree with the commonly accepted definition of lift. All parts of the airplane can generate lift - including the propeller (and, for that matter, the horizontal stabilizer, which in stable flight generates negative lift). But I do recognize that I am arguing over a definition, which is of limited value.

[photofly]

It goes against all spin training I've ever been taught.

The only spin recovery you should have been taught is to follow the procedure listed in the Approved Flight Manual for the aircraft you’re flying at the time.

If the flight manual says to use into-spin aileron, then that’s what you should do.

[RedAndWhiteBaron]

Very true. But muscle memory lasts forever. I haven't practiced the piano in fifteen years, but I can still play the Moonlight Sonata's first movement.

[RedAndWhiteBaron]

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

I would actually like to hear the aerodynamic explanation of this. To increase drag on the outside wing and therefore reduce the rate of spin, perhaps? It goes against all spin training I've ever been taught.

I must be fair to my instructor - he taught differently. He taught spin recovery by the PoH. It goes against all my training previous to the aircraft I am training in now, but this is not contrary to what my current instructor is teaching me.

[Bede]

However, what would be the effect of pro-spin aileron?

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

Interesting. I have never heard of that before. What type is that?

[AuxBatOn]

Bede: any fighter aircraft (large fuselage mass vs wing mass).

[digits_]

I fly a plane where the approved spin recovery procedure includes pro-spin aileron, to recover from “difficult” spins.

I would actually like to hear the aerodynamic explanation of this. To increase drag on the outside wing and therefore reduce the rate of spin, perhaps? It goes against all spin training I've ever been taught.

The following explanation is based on a Pitts, but I'm sure there are other aircraft with similar characteristics, and probably a few with different ones.
Let's say you enter a vanilla spin. Once you are established in that spin, usually after one rotation, you can do 2 things with your ailerons: turn them into the direction you are spinning, or turn them to the opposite direction.
If you turn them opposite, you'll flatten out the spin. A bit like the flat spin in Top Gun that killed *spoiler alert* Goose.
If you turn them into the spin, you'll start to turn faster and lose more altitude. I have the impression the nose is a bit lower in this scenario.

If you are turning in a flat spin, there is a lot of sideways force on the rudder, not much forward force. Like a car out of control on the highway. This makes the rudder les effective. The rudder could be, sort of, stalled.

If you turn into the spin with the lower nose and more altitude loss, there is a bit more airflow over the tail, reducing the angle of attack on the rudder. I assume this makes the rudder more effective.

Generally, if you are trying to recover from a flat spin, you want to turn it into a "normal" spin first.

Note that there is a big difference between the POH spin recovery, and what aerobatic airplanes do. The POH spin recovery is designed to demonstrate certification requirement compliance. -now I'm on pilotDAR territory so I'll proceed with caution-
It's unlikely a plane would get certified if the spin recovery depended on wether you are in a flat spin or a normal spin. The manufacturer will decide what the most bullet proof way is to recover from any spin, in particular a spin you didn't plan to enter.

You don't necessarily need power idle to recover from a spin, you don't necessarily need full rudder, you don't always need ailerons neutral. But if you find yourself spinning out of control outside of your control, the POH spin recovery procedure is the most likely to get you out of it.

And for the record, I still disagree with the commonly accepted definition of lift. All parts of the airplane can generate lift - including the propeller (and, for that matter, the horizontal stabilizer, which in stable flight generates negative lift). But I do recognize that I am arguing over a definition, which is of limited value.

Lift is the sum of all those little forces. To make it easy to visualize, people draw the lift vector on the wings in drawings and schematics. But what you are really interested in, is the center of lift for lift, and the center of gravity for gravity.


If you want to annoy your instructor a bit more, ask him if the tail on a plane generate an upwards or downwards force

[photofly]

... for that matter, the horizontal stabilizer, which in stable flight generates negative lift

If you want to annoy your instructor a bit more, ask him if the tail on a plane generate an upwards or downwards force

It's been a few years since we last kicked that one around the patch.

[RedAndWhiteBaron]

If you turn them opposite, you'll flatten out the spin. A bit like the flat spin in Top Gun that killed *spoiler alert* Goose.

The spin didn't kill him. An ejection malfunction did.

As for the tail, I sure hope that if the centre of gravity is foreward of the centre of lift that the tail generates a downwards force to counter that turning moment, but I don't know if the CoG can ever be aft of the CoL.

If you want to annoy your instructor a bit more, ask him if the tail on a plane generate an upwards or downwards force

I don't need to. I flew my first solo yesterday, so I know everything now.

[digits_]

If you turn them opposite, you'll flatten out the spin. A bit like the flat spin in Top Gun that killed *spoiler alert* Goose.

The spin didn't kill him. An ejection malfunction did.

As for the tail, I sure hope that if the centre of gravity is foreward of the centre of lift that the tail generates a downwards force to counter that turning moment, but I don't know if the CoG can ever be aft of the CoL.

If you want to annoy your instructor a bit more, ask him if the tail on a plane generate an upwards or downwards force

I don't need to. I flew my first solo yesterday, so I know everything now.

Start a new topic about that question and we'll have some fun.


Oh, and congrats!

[tbayav8er]

Sorry, I didn't read every reply here, so my apologies if this has already been mentioned. It also depends on aircraft type. A multi engine propeller aircraft definitely has a lower angle of attack with climb power while maintaining the same airspeed as was maintained while level before starting the climb. For example a Q400 has about a 13' propeller diameter, and the prop hub is pretty well in line with the leading edge of the wing. So there's 26' of accelerated airflow going over the wings in the prop wash. If you go from 40% torque in level flight at 200 kts to 90% torque in a 200 kt climb, there's a massive increase in lift just from the increase in airflow over the wings from the props. I know you're not flying a large turboprop yet, but you will some day, and it's some theory worth taking into consideration.

[RedAndWhiteBaron]

If you turn them opposite, you'll flatten out the spin. A bit like the flat spin in Top Gun that killed *spoiler alert* Goose.

The spin didn't kill him. An ejection malfunction did.

As for the tail, I sure hope that if the centre of gravity is foreward of the centre of lift that the tail generates a downwards force to counter that turning moment, but I don't know if the CoG can ever be aft of the CoL.

If you want to annoy your instructor a bit more, ask him if the tail on a plane generate an upwards or downwards force

I don't need to. I flew my first solo yesterday, so I know everything now.

Start a new topic about that question and we'll have some fun.


Oh, and congrats!

There is no point in debating. Goose died because Ice pointed his jetwash at him. It was Ice's fault.

I'd love to have the tail lift argument (I really do love a good argument), but I'll have to take a raincheck. I'm off on a family camping trip for a few days, then back for a few days, and then off to Armstrong and Wabakimi for a wilderness expedition. You can expect my argument around the middle of August, if I don't drown in a rapid.

Another topic I'd actually like to ask the hive mind - if all else fails, in a piston single, would full power produce additional empennage authority in a flat spin?

I know you're not flying a large turboprop yet, but you will some day

I like the cut of your jib, sir.

[Zaibatsu]

Most lift discussions are academic. There’s absolutely no way to tell through empirical data what it’s actually doing, and for the most part it’s a complete waste for piloting an airplane.

I could teach lift completely wrong and it would have no net effect on the safety of a pilot provided these points are made:

Maintain your airspeed, coordinate your aircraft or cross-control in a safe manner (top rudder, raise dead engine), and respect stall warnings.