ryan1234

This is a rather interesting discussion.. and I'd like to keep it going and perhaps a little deeper...

We should go back to square 1....

Let's do something unorthodox.. throw your lift equation out, here's why:

In order to get more lift, conventional thinking would need:
1. More velocity
2. More wing area
3. More "lift coefficient"
4. Higher air density

*Wing area: This is tricky, it doesn't explain different effects of shape as two equal (area) wings with different aspect ratios will produce different amounts of lift.

*The coefficient of lift is merely a measure of how much the estimated lift the wing will develop vs. the experimentally tested lift as measured. A measure of this doesn't make too much sense when dealing with hard facts, as it is a prediction based on prior performance - dimensionless.

*Angle of attack is not included in this forumla (only figured into CL) but again a bit a circular reasoning.

The velocity and density do have to do with the production of lift. The other figures are almost meaningless. The formula could just as easily be Lift = MC squared as long as the coefficient of lift were to equal 1/C squared x a corrective figure to make the tested performance of the airfoil agree with the formula. Aero Engineering is full of these handy Coefficients.! (Coefficient of drag, etc.)

There are several examples the lift equation fails to provide answers for:


- Also you have to take Bernoulli's principle with a grain of salt because not all fluids act equal under specifc laws:

1) Bernoulli's Principle is not a law for it has never been proven to be so.

2) Fluid Dynamics is the study of directed or conducted fluids; water through pipes, electrical through insulated conduits, air through conducting tubes etc. There are laws that do not act equally on each type of fluid. So it's hard to put a universal label on what will/does work.

3) Considering objects such as airfoils being tested in wind tunnels as the same as testing the airfoils when moving through the undisturbed atmosphere. There is no local force generator in the atmosphere to initiate airflow. There is no airflow; there is no reduction in pressure above or below the airfoil (from airflow) to produce pressure differentials to produce lift. There is no streamline, linear momentum, directed or ordered motion in the undisturbed atmosphere. Since the air molecules are not flowing, there is no velocity to determine so to figure out how much the pressure is lowered due to the velocity of the air.

4) Considering water and air being fluids are both incompressible and inviscid, which is obviously not true! Water is definitely incompressible, while air is almost infinitely compressible at the pressures aeronautics is usually dealing with, and both water and air have viscosity, which increases / decreases with changes in pressures and temperature.


Some physics that don't agree with the conventional approach to how lift is created:

1. It takes the same force to move the air molecules up out of their normal straight line path as it requires to move them back down to their normal straight line path, therefore the motion of the air up and over the upper camber of the airfoil does not produce any lift.

2. In the wind tunnel, when increasing the angle of attack of an airfoil, applying the Bernoulli Principle, we find the greater the angle of attack the higher the pressure developed over the upper surface, and the lower the pressure developed along the lower surface causing negative lift to be produced.






When the airstream and airfoil are considered a venturi, the upper and lower sides both can be considered venturis with the undisturbed air layers above and below the airfoil being the top and bottom of the venturis. As the venturi widens along the top the velocity would lessen and pressure increase: and along the bottom as the venturi constricts, the velocity would increase and the pressure reduce, causing the airplane wing to produce negative lift.


3. Moving the airfoil through undisturbed air, as in flight, is not the same as moving the air past the airfoil in a wind tunnel. Bernoulli stated that an increase in the velocity of a fluid produces a decrease in pressure (as in a venturi). When the airfoil moves through undisturbed, motionless air, there is no increase in the velocity of the airstream. The air molecules are simply moved out of their place and then return after the passing of the airfoil. This up and down movement produces no lift. Our manometer, however, indicates a reduction of pressure as the velocity of the airfoil causes air molecules to move rapidly across the pressure tap.

I know, you're thinking what does this have to do with the price of tea in China? Well we need to get the right lift equation in:

F=(M*A)

shdw

How can it not be included but figure into which implies included in?

Woah, this is an accepted theory, though not law due to complexities far beyond the scope of what you posted. It is an accurately tested and accepted theory where [Cl = 2 pi AOA]. Even so, the "real Cl" as you put it since this is only the "tested" one, still goes up, even with the newest Cl theories. There has not, to my knowledge, been a theory that proves Cl not going up in ground effect. Though I would be glad to enlightened if there is one.

Airfoil - Wikipedia, the free encyclopedia

Here is an advanced theory for a "more accurate Cl" if you would like to see some advancing theories on this topic:

http://pdf.aiaa.org/jaPreview/JA/1988/PVJAPRE45711.pdf


Otherwise, nice post, the methods aren't unconventional they are just the other factors that cause lift: impact, bernoulli, and deflected air.

ryan1234

The basic lift equation (F=MA) can be re-written a little bit using the Kutta-Zhukovsky theorem,

Lift = airspeed * circulation * density * span

Energy is really the primary component of lift. The ground effect shifts this energy to a smaller alpha value, because of the things explained in the previous thread.

It is really tough to explain circulation dynamics properly in a small amount of time...

Basically any vortex carries momentum. This is what produces lift: the motion of the wing converts some upwashing air into some downwashing air. This results in an increase in the downward momentum of the air, and imparts upward momentum to the airplane. Momentum per unit time is force, and this is the force that supports the weight of the airplane.

The ground effect gives the aircraft less induced drag [and lessening the 'power required' (for the reasons in the previous thread)] this gives more energy at first (which is responsible for the initial increase in CL)... however the energy from the vortex is missing, giving a loss in lift - which contributes to CLmax forming at a lower alpha. The reduction in lift induced drag is what gives the CL shift to the left (per alpha). This doesn't truly increase the total lift.

If you look at the table for alpha/CL values in Aerodynamics for Naval Aviators - you'll see that total lift is never increased (a total shift to the top per alpha with an increase in CLmax), rather net lift is increased at a specific alpha, but total lift remains the same or even less in some cases.

ryan1234

CL = 2*pi*angle

:is for smaller AoAs, thin airfoils, and in a windtunnel. Ref:
Modern Lift Equation

It is fine and we can use it for various things - which I do, but it must be noted that pragmatic values may vary and should be no suprise. Fluid (air) is different in wind tunnels than in the open atmosphere. Net vs. Total can be slightly confusing as well.

I would venture to say that few people (especially student pilots) have an accurate picture of how Bernoulli's principle works and that which doesn't work pertaining to airfoils. This is especially important conducting tests with windtunnels.

An interesting website on the blunders of blindly using Bernoulli's principle to determine lift:

Aeronautics.ws - Aeronautical Engineering Blunder #1

shdw

Would love for you to give me a demonstration on how Kutta?Joukowski theorem - Wikipedia, the free encyclopedia can be used "a little bit" with F=MA.

What the formula shows you is that fluid flow is effected based on AOA. As you tilt back a higher AOA you change the flow pattern around the wing creating a higher pressure above and increasing the Cl. This increase in Cl also occurs due to the changes on airflow around a wing when it is in ground effect, in the case in point it increases.

Stop arguing with obscure terms you likely don't understand, not claiming I do, and read first, then reply. You are going to confuse every single person you have that reads this forum with your garble, some right, some not, and tons of added junk.

PS Further confusing people with discussion on net versus total lift doesn't change the fact that lift, the aerodynamic force perpendicular to path, goes up when Cl goes up. If it didn't, AOA would not make the aircraft gain lift, that you can pretty accurately see is false, AOA does change lift.

ryan1234

We would probably both agree that I wasted money in the Aerospace Engineering program at ERAU. Obscure terms I likely don't understand is a slightly cheap shot though. Perhaps my garble and lack of understanding is evident in a previous conversation about indicated stall speed increasing with altitude. Several people complained that it was too technical - well AE is a technical subject and these subjects are under the technical thread.

Some of these things are hard to dumb down, and often require a proper premise to build upon.

So to aviod further strife I will give websites that explain the content which I am trying to convey. In this instance, we all know now that the ground effect has a relation to Vortices (or the lack thereof) - here is a website to explain them:

Vortices: Momentum and Energy Near a Wing


Now back to an obscure term I likely don't understand:

Kutta-Joukowski
Kutta-Joukowski Lift Theorem

basically lift is produced by creating downward momentum of the air flowing over the wing in any case

F=MA has everything to do with lift being created.... as a matter of fact all of Newtons laws are evident here.

shdw

Maybe this was a bit of my own miscommunication here, by understand I meant apply. Take the formula, combine it with F=MA like you say, and use it to prove to us that Cl does not increase with AOA. Then use it to show us how in ground effect Cl doesn't actually go up.

If you do understand (application/correlation level of understanding) them, kudos to you, but you are doing a horrid job trying to get your point across. Cl does go up with AOA by every accepted academic book in production because accepted theorem proves it.


I agreed with you there, not because your a great guy, but because it was right. Your ideas were clear, you accurately assessed what was happening, you didn't confuse basic terms, and you explained it sufficiently. I added my own explanation for variation but agreed with you.

I disagree with you here, not because everything you are saying is wrong. It might be the revolutionary way, but for now the generally accepted is what a pilot and even an engineer needs. In the process of digging into these unconfirmed theories you demonstrate many misconceptions with various basic aerodynamic principles.

Because you are the "guy with the degree" doesn't mean you cannot be wrong. You have yet to admit any of these wrongs which even further confuses the general reader. Instead you take each one and cover it up with more theory, more advanced aerodynamics, and more things that only few will comprehend to hide your fallacies. As a leader on the forum, that is a poor, closed minded approach, to reading and replying to a forum post.



Again, I am not trying to say your wrong with everything your saying. But sir, you have a lot of misconstrued information scattered throughout your posts. Your aim should be to discover, accept, and learn to absolve these scattered miscommunications.

shdw

This is exactly what I mean by covering up your fallacies with new arguments that were not presented prior to your own introduction.

Here is where you agreed that Cl does go up by acknowledging that a higher lift will be encountered for each given AOA, this is because Cl went up.

Nobody ever argued that Bernoulli was the only form of lift, in fact, here:

We were already in agreement, this was just a waste of time to divert attention. Fact, Cl goes up for any given angle of attack when an aircraft is introduced into ground effect. Fact, that increase in Cl has an effect on the aircrafts lift (increasing it slightly). Common sense, when entering ground effect we lower AOA because AOA directly effects Cl (Cl up = lift up | Cl down = lift down) again and we just had Cl go up, wouldn't it make sense to lower it?



Finally, students stop here, Ryan, while various other forms of lift have an effect on lift, some may act down some up, it doesn't change the fact that Cl goes up and increases upward lift. No matter how you cut and slice it, you cannot link together formulas and ideas (impact lift and downwash lift) that do not pertain to the Cl formula and pawn them off as effecting Cl, they do not.

What they do is apply their own forces and by product forces which may act upward, downward, or any other variance of degrees. This application of force will have a vector component up or down in relation to the aircrafts path of flight and thus effect the net lifting force. Again, that does not mean Cl did not go up, just other forces, computed using other formulas, may have applied a downward force exactly equal to the increased Cl, but Cl still went up.

ryan1234

I have to ask... where did I say that CL didn't relate to AoA?

In a previous post I mentioned that the basic CL formula didn't account (properly) for AoA - and the NASA website gave the conditions for the CL formula: Lower AoA values, thin airfoils, and windtunnel.

A coefficient of lift is just that, a coefficient. This is different than total lift (obviously if the coefficient is part of the lift equation conventionally speaking)

Trust me - I'll be the first to admit I've been wrong on this forum - dead wrong.

Miscommunications - sorry about that, you're probably right though - it's pretty late.

Everything that Cubdriver said previously I agree with, not because he has an AE degree, but because I've seen it before - sorry for the miscommunications.

Cheers - I'm going to bed!

ryan1234

............