What is "lift"?

[photofly]

If you like that, you should also check out Denker's free online book:
https://www.av8n.com/how/

Lots of good stuff on lift, and aerodynamics, there.

[Shinyjetsyndrome]

You are in a 100 KIAS cruise. You alter your situation so as to attain a climb, and maintain 100 KIAS in the climb. Has your angle of attack increased, decreased, or remained the same?

A force produces an acceleration (F = m*a). Once stabilized in a constant speed climb, the airplane’s upward force is equal to that of gravity and you are ascending at a constant vertical speed i.e. No acceleration. So looking at the formula again, if you're climbing at a constant mass with no acceleration, the lift force should remain constant.

Lift is dependant on 3 variables: Dynamic Pressure ((1/2)*P*V^2, or 'Q'), the wing planform area (S), and the lift coefficient (S):

Lift = (1/2)*P*V^2*S*CL = Q*S*CL

We want the lift to remain constant in the climb, so lets look at the three variables and how to change them to keep lift constant:

Dynamic Pressure (Q): This is what the IAS indicator reads. IAS is not a speed, it's a pressure reading. It takes total pressure (dynamic + static) from the pitot tube and subtracts the static pressure from the static port input to give you a reading of dynamic pressure which is converted into a speed reading. The variables of Q are air density - rho (p) and TAS (V). With increasing altitude, the TAS must be increased to maintain the same dynamic pressure (Q = ½ρ V2) as air density decreases with altitude. Essentially you need to go faster for the pitot tube to hit the same amount of air molecules as you did at the lower altitude. You'll need to add power for this. More on this later.

Wing planform area (S): This doesn't change.

Lift Coefficient (CL): This has to remain constant. A coefficient is a dimensionless number expressing degree of magnitude. An aerodynamic force coefficient is a common denominator for all aircraft of whatever weight, size and speed. It is a dimensionless ratio between the average aerodynamic pressure and the airstream dynamic pressure. By this definition, the CL is the ratio between lift divided by the wing planform area and dynamic pressure i.e. CL = L/QS. The CL is influenced only by the shape of the lift surface and angle of attack since these factors determine the pressure distribution of the wing.

We're not modifying the shape of the wing in this scenario so the only thing we can change to alter the CL is the AoA. Since we need CL to remain constant to keep the lift force constant, this implies keeping a constant AoA to maintain a constant IAS climb.

However, as altitude increases, the excess thrust available will gradually decrease and there will be a point where you can no longer increase thrust to maintain the constant IAS. At this point you'll need to reduce the drag to cater for the reduced thrust by decrease the angle of attack.

[AuxBatOn]

You are in a 100 KIAS cruise. You alter your situation so as to attain a climb, and maintain 100 KIAS in the climb. Has your angle of attack increased, decreased, or remained the same?

A force produces an acceleration (F = m*a). Once stabilized in a constant speed climb, the airplane’s upward force is equal to that of gravity and you are ascending at a constant vertical speed i.e. No acceleration. So looking at the formula again, if you're climbing at a constant mass with no acceleration, the lift force should remain constant.

Lift is dependant on 3 variables: Dynamic Pressure ((1/2)*P*V^2, or 'Q'), the wing planform area (S), and the lift coefficient (S):

Lift = (1/2)*P*V^2*S*CL = Q*S*CL

We want the lift to remain constant in the climb, so lets look at the three variables and how to change them to keep lift constant:

Dynamic Pressure (Q): This is what the IAS indicator reads. IAS is not a speed, it's a pressure reading. It takes total pressure (dynamic + static) from the pitot tube and subtracts the static pressure from the static port input to give you a reading of dynamic pressure which is converted into a speed reading. The variables of Q are air density - rho (p) and TAS (V). With increasing altitude, the TAS must be increased to maintain the same dynamic pressure (Q = ½ρ V2) as air density decreases with altitude. Essentially you need to go faster for the pitot tube to hit the same amount of air molecules as you did at the lower altitude. You'll need to add power for this. More on this later.

Wing planform area (S): This doesn't change.

Lift Coefficient (CL): This has to remain constant. A coefficient is a dimensionless number expressing degree of magnitude. An aerodynamic force coefficient is a common denominator for all aircraft of whatever weight, size and speed. It is a dimensionless ratio between the average aerodynamic pressure and the airstream dynamic pressure. By this definition, the CL is the ratio between lift divided by the wing planform area and dynamic pressure i.e. CL = L/QS. The CL is influenced only by the shape of the lift surface and angle of attack since these factors determine the pressure distribution of the wing.

We're not modifying the shape of the wing in this scenario so the only thing we can change to alter the CL is the AoA. Since we need CL to remain constant to keep the lift force constant, this implies keeping a constant AoA to maintain a constant IAS climb.

However, as altitude increases, the excess thrust available will gradually decrease and there will be a point where you can no longer increase thrust to maintain the constant IAS. At this point you'll need to reduce the drag to cater for the reduced thrust by decrease the angle of attack.

No. CL is 0 in the case of a vertical climb. Generally speaking, the CL vs AoA curve is linear until stall (generalization and over simplification I know) therefore AoA will be less in a climb (or descent) than straight and level.

It comes down to definitions. People tend to mix up aerodynamic forces and lift...

[Gino Under]

An excellent instructional video courtesy of Oxford Flight Training
https://youtu.be/xISONIwGc7k

You’ll find lots of instructional stuff from Oxford as you progress through your training.
Best of luck.

Gino

[Big Pistons Forever]

YOU GUYS ARE ALL WRONG !!!!

Here is the TRUE story


http://messybeast.com/dragonqueen/liftdemon.htm

[fur1ough]

[Heliian]

To climb, more lift needs to be created to overcome gravity. The lift is created by increasing AOA and then more thrust is added to overcome drag to maintain airspeed.

Ughh. Shudder.

AuxBatOn is correct, but I believe he flies something with huge thrust to weight. For most GA airplanes, AOA reduction in a climb is negligible but it certainly doesn't increase (except when pulling G).

A change in state would come with a change of AOA. This is a dumb fucking question that is worded poorly.

[RedAndWhiteBaron]

This is a dumb fucking question that is worded poorly.

And that, sir, is your opinion. Given your insulting use of vulgar language, it is equally arguable that yours is a dumb fucking post that was worded poorly. But that is just my opinion.

[Heliian]

This is a dumb fucking question that is worded poorly.

And that, sir, is your opinion. Given your insulting use of vulgar language, it is equally arguable that yours is a dumb fucking post that was worded poorly. But that is just my opinion.

Sorry, how about "what is the difference in AOA between 100kts level and 100kts climb". Just take out the whole transition from cruise to climb.

It's a pointless theoretical discussion that doesn't give enough specifics for an actual answer and is solely meant to confuse the subject. Hence a dumb fing question.

[digits_]

What other specifics do you need?

[Gannet167]

A change in state would come with a change of AOA.

You can hold AoA constant and change state with power alone.

Attitude + Power = Performance. The old adage could also be stated: "AoA + Power". Keep variable 1 constant and change variable 2. The resultant will change.

[2R]

The engine converts money into lift and pixie dust .The pixie dust attracts the pixie fairies

With a zero angle of attack can you really achieve true ballistic flight path ? Asking for a friend ,as I am stuck in the bunker

The useless complexity introduced by some instructors and students is nothing new . Mushasi described that behaviour and confusion being taught at the two hands school of swords in the 17th century . Mushasi advised the fastest sword is the least complex . A wing cuts the air like a sword . Practice this and you will become enlightened as to the Way of the Sword and the Wing .

The Kiss method is best , Keep It Simple Stupid

[Gannet167]

Good on the OP for asking questions and not accepting things just because the instructor said so. He/she may or may not just be parroting what they were told in overly simplistic explanations and may or may not be correct. Thoughtful questions that show a logical and reasoned approach to comprehending the concepts are excellent. They show genuine interest and thought - and reveal the students understanding/misunderstanding of concepts which will facilitate a good instructor's ability to enrich not just knowledge but also understanding and the ability to apply knowledge practically (which is quite different and important.) If and instructor can't answer thoughtful questions then they should be able to go find out and then give you the answer.

Some of these things do not make sense at face value. I too struggled with some of these concepts as they were presented and misrepresented in flight school. I focused on memorizing the dogma and regurgitating it for the exam. I did well. I did not understand conceptually what was going on however. The over simplification makes it easy to present fairly complex concepts and teach them quickly at an absolute minimum level to facilitate getting new students able to fly. Some students will get confused with more thorough explanations and they need it simplified. Many instructors and professional pilots lean on these overly simplistic explanations and take them as gospel. Asking or engaging in a thoughtful conversation can devolve into an argument from authority or argument from popularity.

I used to fly with a test pilot who was incredibly smart. I loved flying with him because for hours in cruise I'd ask and get very good explanations that really furthered my knowledge and conceptual understanding. Some things all of a sudden made sense and I was able to apply that knowledge at the controls better because I understood why, whereas previously I was conflicted between knowing what was supposed to be done and what I believed actually worked. I firmly believe I was a better instructor in my next job because I knew how to explain things better. Things that students were able to answer correctly on an exam but didn't understand or believe in.

Keep it simple principle is great for children or for quickly building a conceptual understanding. But when a student is interested and able to ask and learn, they should never be discouraged or dictated dogmatic answers. If we stayed with KISS principle, we'd still be flying Wright Fliers and our understanding of meteorology would rely on how many statues we built to the gods.

[DadoBlade]

What is aerodynamic lift? A vertical suction caused by an area of low pressure created on the top of the wing at certain airspeeds. Signed: Ace McCool, Capt., D.E.I. Ret.

[2R]

“There are some ideas that are so wrong only A very intelligent person could believe them “ George Orwell

The Advantage of keeping it simple prevents the simple mistakes that very intelligent people make that kill them. How many accident reports have you read where a simple error caused misery ? Not enough fuel ? Too much weight ? Zigged when they should have Zagged ? Did not check Weather ?

Einstein simplified his theory of relativity so even a non-scientist could understand his conceptual theories .

Simple works

[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.