What is "lift"?

[jakeandelwood]

Lift is the opposition to gravity and thrust is the opposition to drag.

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.

AOA is lower in a climb as a component of power is countering gravity. Your load factor will also be lower. The extreme would be a 90 deg climb angle where the load factor would be 0g thus the wing generating no lift but the engine(s) acting solely against gravity.

It makes a lot of sense when thought about like that. I remember when I was a kid flying RC planes some of the models guys would have could fly straight up they were so overpowered, they could make them nearly hang in the air off the prop, the prop wash providing the only airflow over the control surfaces

[digits_]

Now on the other hand, my thinking here is rather two-dimensional. Lift can also produce a sideways force, and then what would we call that?

I think you are referring to yaw?
The P-factor which you might have or will encounter would be an example of that force.

[DirtyDashDriver]

Lift can also produce a sideways force, and then what would we call that?

The horizontal component of lift. That way it keeps it nice and simple. You're either talking about induced drag during climbs and descents, yaw (as digits_ pointed out, and why I came back to add this), or both.

I'm going to suggest that you read Flight Without Formulae or Mechanics of Flight, both by A.C. Kermode or Aerodynamics for Naval Aviators by the U.S. Navy. You can find both Kermode books on Amazon for about $30 for the first and $70 for the second while the Navy book runs $20 or so, also on Amazon.

You can also find Mechanics of Flight in PDF from some universities as "the Kermodes" are relatively hard to come by. Just Google the name(s).

If you do pick up the books, read them at least three times each. The first time just to get a feel for the material, the second time to start learning, and the third to start understanding the material.

I'm not trying to be obtuse and not add to the conversation, but the depth of answer you are looking for is already answered in those books.

[photofly]

Aerodynamics for Naval Aviators is available for free download as a pdf; it's US Government copyright, and they make it available to the public for free.

https://www.faa.gov/regulations_policie ... 80T-80.pdf

[RedAndWhiteBaron]

Aerodynamics for Naval Aviators is available for free download as a pdf; it's US Government copyright, and they make it available to the public for free.

https://www.faa.gov/regulations_policie ... 80T-80.pdf

Where has this book been all my life?

[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