OffroadBEAR

My Feedback: (2)

Dick, a piece of string is 5 meters long.

The point I was getting at is that a dragster traveling forward deploys its chute to generate drag in order to slow the car down more quickly. The point was that the force generated by the parachute on the car is in the same direction as the air flow (if looking at the car). These parachutes are designed to prevent flow from spilling out the sides so the parachute will not generate side forces or lift destabilizing the car and maximizing efficiency of the chute. They are designed to generate force in one direction, the opposite direction of car travel, which is the physical definition of drag.

However, I now realize that this in an oversimplification of the parachute situation since parachutes do not travel directly downward in real life.

Top_Gunn

My Feedback: (6)

No, it's not one or the other. They are the same thing, looked at in different ways. The only reason a vacuum would "hold something up" is that the pressure beneath the object under the vacuum is greater than the pressure on top. Consider thermals, which are sometimes described as "warmer air rising," but which can just as accurately be said to consist of cooler air falling and pushing the warmer air upward.

Thich is not to say that lift and drag are the same thing; they aren't, for the reasons several people have explained. It's true that you can't get lift without drag, but you can certainly get drag without lift. If they were the same thing, you couldn't.

rmh

Steady there
if you can measure drag it is obviously doing something
If I stick a little panel out the side of a fuselage -like a "turn signal on an old VW what does it do?
it adds drag -which does what ?
it creates one half of the condition to create an unbalance of pressure on the fuselage sides
so the craft turns .
If I ad a drag/drogue at the tail -it lessens pressure there which allows pressure up front and on the sides to help slow the craft .
lift and drag are all part of the the same thing.
unbalanced pressure.

da Rock

Actually, even when the chute is traveling straight down, the air beneath it and the air above have motion that is not straight up. And any air that follows the outside of the chute moves sideways for some of the journey.

The air that goes up the side of the chute is no different than air that goes up a sailplane's wing's LE top to the highest point. So what's the difference between a chute and a glider's wing? As far as the air that sees the top of the chute or wing, nothing. OK, the speed of the airfoil, is different. One sees zero or slight airspeed from the object and the other sees more airspeed. A chute is basically the front half of a cambered airfoil that goes around it's entire circumference, all to meet at the top. And the air that follows that domed arifoil has a horizontal motion as well as a vertical, whether the chute is moving sideways or straight down. Both motions are relative to the chute primarily, just as the air's motion is around a wing. The air is displaced. The only real motion is displacement. But there is both vertical and horizontal displacement resulting from a wing passing just as from a parachute passing. And the displacement produces the result.

Call the result what you will, but it's only the aeronautic industry that describes the result in two ways. The air doesn't call what it does to a chute or a wing by any name. But the way it acts is the same with a chute or a wing. It is forced to follow the surface. And creates a force that acts on the surface. It's the convention of a few humans that choose to try and describe what the force does the way they do.

Top_Gunn

My Feedback: (6)

I have no problem with that. But if lift and drag "are" the same thing, you could say "lift and lift are all part of the same thing," which would not convey useful information. The fact that two things (i.e. two kinds of effect on the airplane) are manifestations of the same thing does not make the two terms interchangeable.

There was a thread here a while back on whether a slowly spinning prop creates more drag than a prop that's not turning. That's a coherent question (whatever the answer). It's also reasonable to attribute thrust to the "lift" of a spinning prop, if it's understood that the direction of this lift is (mostly) forward. But it would just be confusing to ask whether a prop turning at 10,000 RPM creates more "drag" than a fixed prop.

Do you really think anyone's understanding would be advanced if we just stopped talking about lift and used the term "drag" in its place? They are different in the sense of their effect on the airplane. Would communication be enhanced if people said that speed brakes slow a plane down by creating lift? That a Clark-Y airfoil has more drag than a flat wing, so a plane with the Clark-Y will climb faster, other things equal? What we're talking about here isn't aerodynamics, it's communication. As an earlier commenter pointed out, adopting your terminology would not help anyone understand what's happening. Are you really trying to help people understand the issues here?

rmh

Yes (your deliberately absurd interpretations aside) If they get one point - the idea that lift produces/includes/is part of drag/ can be part of drag . At least they may look at a situation with a different view-instead of just parroting old terms.
Also if more of the old "aerodynamic experts" spent some time actually building and flying unconventional super light or super slow or super aerobatic models - they may broaden their tunnel vision.
And actually have fun doing it.
What positive assistance comes from reading
"flat plates only produce lift at a positive angle of attack
however
cambered airfoils produce lift at zero angle of attack.
splain that.- It is totally misleading.
The "effective angle of attack" on a curved shape has been ignored.
Zero effective angle of attack =zero lift.

Mike SVOR

My Feedback: (1)

Lift and drag are not the same thing. Drag is a by-product of anything in this world if you care to phrase it that way. Nothing is 100% efficient, there-for drag exists. If there was a 100% efficient wing, there would be no drag.

Everything about the top of a wing is designed to reduce drag. If designers didn't care about stalling out at low speed, then all wings would be as flat as a razor blade.

The curved top surface is all about redirecting air around a curved leading edge. (angles of attack, efficient air speed, and stalled out top wing air flow.)

Mike SVOR

My Feedback: (1)

The top of a wing redirects air flow to a downward sloping direction

and actually, that's a loaded question.

What you might consider 'zero angle of attack' is probably not the same on a curved top airfoil.

Take a wing with a curved top wing and the bottom of the wing is flat.
Now draw a line from the center of the trailing edge to the CENTER of the leading edge so that there is equal surface on both top and bottom.
You'll find that the bottom now slopes up and the top slightly slopes down (equal amounts). Similar to a symetrical airfoil.

You will see that the wing was at positive angle of attack to get lift.

rmh

If there is any lift produced an effective AOA exists.
Redirected air?
the attached air will only follow (stick to) till the edge. after that- it simply tries to equalize.
measuring the downward flow of air from the TE as a method of determining lift is a bit dicey.

Mike SVOR

My Feedback: (1)

Take a triangle. (wing) face one point away (trailing edge). Now round the leading edge's points.

What do you think creates zero lift? The underside being horizontally level, or the underside's angle matching the top sides angle?


edited to correct the quotes..............

rmh

100% efficient wing?
A wing operating in a total vacuum?
(sorry about that gag)
You are describing efficiency- and that is extremely important but no matter how well you do it - no drag will only occur when there is no lift.
You know what I mean.

rmh

Trick question
The answer is that when the flow from front to rear is equal (over and under)- there is no lift.
If one assumes the bottom of a Clark Y airfoil is the ZERO line - then the true Zero line is ignored.



.......... edited to correct the quotes .............

Mike SVOR

My Feedback: (1)

dH, I think you're using the term 'drag' too loosely.

There can not be lift until a downward redirection of air is obtained. To counteract gravity.

rmh

No problem with that and no downward flow is produced unless lift (and drag ) are at play
That is from whence the downward flow originates.
Downward flow is simply low pressure which has not recombined with high pressure- reverting to equal pressure..
Mother Nature is a bit slow at times.
She is old but damned determined.

Mike SVOR

My Feedback: (1)

This is where you are losing me.

How on earth can you have a flow or thrust made of vacuum???

Ambient air is neutral pressure, air under wing being forced down is high pressure, air above wing is lower than ambient pressure (upon + angle of attack).
Any downward thrust/flow would be from high pressure.

Ever fly your plane very low? So low that the grass gets blown down when you pass over it?

That tells me that there is MORE downward pressure/flow/thrust than vacuum sucking it up.

airraptor

My Feedback: (66)

If you put a prop on and engine backwards does it still make thrust?

da Rock

Yes

And the lift generated along the top of a cambered wing from the LE to the point of maximum camber generates drag toward the front of the wing. And a force pulling forward would be called thrust, right......

Sometimes, semantics wars can be fun.

Top_Gunn

My Feedback: (6)

If I understand Mr. Hanson, he has made three claims. First, that it's not possible to generate lift without also generating drag. I doubt that anyone disagrees with that. Second, that the shape of an airfoil means nothing. I don't know anyone else who believes that. Third, that because you can't have lift without drag, lift and drag are "the same thing." This is not a claim about aerodynamics, it's a claim about language. And it's wildly exaggerated. It's like saying that "suction" and "air pressure" are the same, because the reason the milkshake rises in the straw is that it's being pushed up by air pressure. This is indeed why the milkshake rises, so in that context suction and air pressure are the same in the sense that you need to discuss air pressure to explain suction; the thing we call "suction" exists because of air pressure. But it doesn't follow that your shop vac will clean your shop if you run it backwards.

I suspect that, for some people, these forums are more a vehicle for showing off than a way of exchanging information and ideas. I'm outta here.

rmh

Ah
we are looking at FLOW-
The flow is from the higher pressure recombining with the low pressure ( from top side of the wing)- This is of no use for lift - it is just a result.
look at the disturbed air (low pressure air) produced by a 757.) The recombing with the high pressure makes a horizontal tornado- which sinks slowly as it dissipates.
The compressed air in ground effect is not the same thing.
Grab a sheet of 4x8 plywood and stand it up in a dusty room - let it fall- you get to see all the forces involved in lift displayed for your viewing enjoyment.

rmh

You completely mis understood me -
I never intimated that the shape of the airfoil means nothing
where did I say that?

Steve Steinbring

MORE POPCORN PLEASE

Please don't stop now!

This is discussion/debate is getting more interesting by the post. Dick Hanson has got you thinking and exploring what you've learned instead of accepting everything at face value and often parroting it back from rope memory.

You should ask Dick about some of his other principles they too provoke some thought.

propbuster

My Feedback: (1)

Regarding the original question; We had a similar discussion in ground school when I was in my primary flight training. In the end, it was realized that a barn door will fly with the correct AOA and enough thrust. So I would say that while a wing will FLY (not generate lift) without the top, having the top there certainly makes it fly better!![sm=wink_smile.gif]

Top_Gunn

My Feedback: (6)

Two quotes from Dick Hanson. But perhaps, in a world in which "drag" means "lift," "NADA" means "important."

Rocketmagnet

As someone who's got almost no experience with wings at all, I'm probably sticking my neck out here. But I'd like to say that I think it's terribly misleading to say that lift and drag are the same thing. If they were the same thing, you literally wouldn't need two different words. However, you do have two words, and furthermore, one of these things is considered 'good' in an airplane, and the other is considered 'bad'.

As an analogy, consider matter and energy. Now they literally *are* the same thing. E=mc^2 basically means E=m. In fact, when you hear particle physicists talking about the mass of particles, thay always state the mass in eV (electron volts, a measure of energy). Because mass and energy are the same thing, physicists have done away with one of the words because it's redundant.

However, imagine trying to have a discussion about flight using only one word "drift" as someone suggested. Someone might say "How can I design a wing to reduce the drift as much as possible?" and you might reply "Why? Do you want it to fall out of the sky? If you want to reduce the drift, just don't put any wings on at all!" This obviously leads to absurdity, and is no help at all.

Hugo

da Rock

But to suggest that they actually are inseparably tied, and suggest that there really is just one force, isn't bad at all. If you're trying to get people to loosen their tie and unbutton their collar and think a little less technical, it makes perfect sense.

And nobody has yet tried to convince the masses to quit using descriptive terms when talking about the details they were created to describe.

whatever.........