hi may i ask is there a diff between lift and coefficient of lift?. I do understand that lift will increase as velocity increase but why?

and wat is maent by the ellipse, plate, cylinder and ball of the same area as your airfoil?...and by the way how do i know which is the leading and trailing edge of a graph (velocity VS lift ) thanks...i am very confused!!!!

Lift is total lift in pounds or other units. That occurs at a set speed with so much wing area. For level flight if obviously matches the weight of the model.

Lift coefficient is more a ratio and to tell the truth now that you ask I don't really have a bullet proof explanation. So I'm going to wait for Ben or John or one of the other guys that spent more time in the engineering end of things to come out and play...

The ellipse, plate and ball stuff relates to "test" panels of these shapes and down their drag relates to a given airfoil. It's for comparison purposes. For example you can then say that a B2 or Ford Excursion or your latest model has the same drag as a flat plate that is "so" square.

The may be a little confused about the graphs. Leading and trailing edges would indicate a pressure or local airflow velocity distribution. In that case I believe it's leading edge to the left and trailing to the right. Southpaws need to adjust... I'm not sure if a velocity vs lift chart has any significance since you can change that with a simple angle of attack.

The lift coefficient is a dimensionless force coefficient. It lets you figure out the lift on a wing for a variety of external conditions.

For a given angle of attack up to stall, there is a definite value for the lift coefficient (assuming you measured or calculated it). Knowing the value of the lift coeffiecient, the value of the dynamic pressure, and the area of the wing, you can calculate the total lift.

The dynamic pressure is related to how fast the aircraft is travelling... faster aircraft, higher dynamic pressure... more lift. This is why the wings on jets tend to be small in comparison to prop-planes (that is a very simplistic comparison though!).

thankS!....but i am still confused with my leading and trailing edge for my Surface VS velocity graph now!!...is the leading edge the one when chord% is equal to zero???...and also when a plane is takin off, issit true to say tt the thrust has to be more than the weight but less than the lift and more than the drag?

"leading edge the one when chord% is equal to zero???..."

That's right.

"thrust has to be more than the weight but less than the lift and more than the drag"

Nope, in any steady speed flight condition the thrust matches the total drag and the lift matches the weight. This not only applies to level flight but also to a steady climbing flight. But in the case of the climbing flight power has been added and that power went into creating enough extra lift that the plane is climbing and possibly going slightly faster.

The only time the forces are out of balance is when the plane is accelerating in some direction. This can be speeding up, slowing down, or transitioning from one climb rate to another. Level flight is 0 climb rate, + is accelerating upwards or pitching into a climb and - is accelerating downward or pitching over into a dive.

hi...thanks!!...u guys been great help but i am still learning how to read those graph...the graph looKS SOMETHINg like this shape...thus can anyone tell me which is the trailing edge and which is the leading edge..!!.. ..thanks!!..how abt he max velocity and min velocity??...very very confused!!!
and also if the spin is zero, radius is 0.3048 and span is 16.9 for a graph of the cylinder, why izzit that the lift will be zero and the lift of ball is also zero but the lift for plate has something??/...
sorry hope these are not dumb questions

I have a dumb question too :-) What are the axes on the graph? Doesn't the program you are using indicate that?

The cylinder and ball don't have an angle of attack unless they are moving vertically or in the case of the ball, moving laterally. Otherwise as in a wind tunnel it just doesn't matter. A flat plat that is aligned with any angle other than 0 or 90 degrees respect to the air flow will have lift.

hi the graph is juz an example for the shape of the graph but the axis should be surface VS velocity...
thanks...=)

why izzit that the lift for the ellipse will be more den the plate...how do u actually calculate the lift for these ???

stoned-X,

Are you using a software package to calculate lift for airfoils, or looking up airfoil data, or something else? If you are using software, which package are you using? What is you goal, designing a plane, boning up on aerodynamics, or something else. I think you might get more helpful answers if you give a little more background information.

banktoturn

hi thanks i am using nasa airfoil and my primary aim is to calculate my thrust, learn the graph and hmm i have some last question
1)does the pressure at the leading edge has a higher or a lower one than the pressure at the trailing edge?
2) Why izzit that the Lift generated by ellipse is more than the lift generated by the plate?
thanks!

stoned-X,

The pressure at the leading edge will be higher. I suspect an ellipse will have a higher lift coefficient than a flat plate because the curvature of the leading edge and top surface of the ellipse will allow the ellipse to stall at a higher angle of attack than a flat plate. If the ellipse is very fat though, it will have a lower lift coefficient than a flat plate.

banktoturn

however both the angle of attack is the same for the ellipse and the plate??..so how can u explain that..??..Hmmm..thanks alot !!!

Stoned-X,

Are you talking about an elliptical wing planform? OR are you talking about an elliptical wing section?

I think we are all still struggling to understand exactly what you are asking.

stoned-X,

An airfoil generates lift by producing lower pressure on the top surface than on the bottom surface. Every airfoil shape produces a different pressure distribution, and some are 'better' than others. If that weren't true, then airplane wings would be flat plates. What you are observing is that an ellipse produces a bigger pressure difference between its upper and lower surfaces than a flat plate does, even at the same angle of attack. Is there a reason that you find this surprising?

banktoturn

so what u are trying to say is that the result behind why the ellipse has a higher lift is because Every airfoil shape produces a different pressure distribution?..
from my results, my ellipse has a thicker chord than the plate..so can i say the reason between this lift diff is due to the thickness of the chord?
but how do i explain it?
sigh i am getting really ocnfused..guess i need to read up more

stoned-X,

Are you reading the responses people are posting for you? You seem to respond rather selectively. As has been mentioned several times, a bit more background would be helpful.

banktoturn

hi kemlito i am talking abt the section..=)