I need help. Somewhere along the line I started to think we were taught a load of rubbish on how a wing flys.

I supposed it started when still a student and we turned our little plane upside down. Hey, it flew. So what about that story about the upper surface of the wing creating lift because of the shape?

The books also showed laminar flow wings that looked totaly tear-drop shape and they flew too.

Then they mentioned down-wash off the wings being felt from about the wingspans height over the runway. They reckoned it would help you float way down the runway if you were a bit fast.

Soon after I read of some aerobatic pilots with wings curved same top and bottom so as to get the same performance any way up they happened to be.

Just a minute I thought, they'd fly down as much as up, according to the basic theory.

Soon I saw a movie of the astronauts trying out a wingless craft getting towed down the runway.
The damn thing was shapped like an upside down VW beetle. The opposite to what one would expect.

Well I got to thinking someone was putting one over on us. So what's the answer?
The first example to "prove" it was the shape of the top of the wing causing lift was to put a spoon under a running tap, and watch it move into the water stream.

Sure, but I also noticed the water being deflected back off the end of the spoon.
Here we go, I reckoned, downwash off the rear of the wing, aided by the shape of the wing and the angle of attack. Equal and opposite reaction. Problem solved.

So where did I go wrong?

Are you familiar with the term "angle of attack"?

If not, you might spend a bit of time reading up on it, it sounds like that might answer your question.

Captain Dave, You should be more observant, like all good pilots. Read the last few lines of my post.
Then imagine a wing of exact same shape (curved) top and bottom. Now does this wing fly because of the low pressure on the top of the wing? Would one expect the few degrees angle of attack to exempt the speeding up of the air under the wing (again curved), or does maybe the angle of attack create downwash for an equal and opposite force?

Come on people give me something other than old wifes tales.

Like I said before, go back and review your basic aerodynamics. The angle of incidence is the angle between the wings cord line and the airframes longitudinal axis. Even airplanes like the Extra 300 or Pitts Special have a slight angle of incidence for upright cruise flight. When your upside down, you have to have a slightly higher nose angle than when your right side up to maintain altitude at the same airspeed.

To sum it up, yes, the angle of attack has a lot to do with lift production. The spoon example has more to do with gravity and water than lift production, but it is an excellent example of down wash. The other phenomena your described is ground effect and it has more to do with the compression of the air between the ground and lower surface of the wing than downwash.

A better lift example would be to blow over a piece of paper shaped like an flat bottomed airfoil and then do the same thing with one shaped symmetrically. You still get some lift out of the symmetrical shape.

I have spent my share of time upside down, having flown the Extra 200/300 series a bit, owned a Pitts S2a and Stearman among other aerobatic planes.

I think it is called the surfing effect

Jal,

Good question! My redneck .02 cents worth is that the more one takes advantages of Bernoulli's Principle in airfoil design the more efficient the performance. For example, if one wants an aircraft that will handle heavy loads at slow speeds a wing with lots of area (aspect ratio) and the classic airfoil design of flat bottom, curved top would be ideal. If one wants to compete with Kirby Chamblis a symmetrical airfoil would be more desireable with a buttload of horsepower (Good power to weight ratio). Buttloads of horsepower is good no matter what one is doing!! Someone please correct me if this makes no sense! I am by no means an aerospace engineer and it has been years sense I actually studied this material.

Dang I thought I had posted this yesterday, musta hit the wrong key as I was being called to dinner-

Tear off a strip of paper , hold it right below your lower lip and blow over it, the paper moves up.

Put the strip on your upper lip and blow, the strip will also move up.

The first example is Bernoulli-induced lift, the second example is Newtonian reaction lift.

There are a few exceptions I am sure, but all wings use both these principles, it is just the ratio that changes. And that ratio most likely changes from one instant to another while the wing is moving.

And I agree with Mississippian that induced lift is more efficient so it uses less horsepower, everything considered.

Well we're starting to get somewhere.
But model and paper don't do much for me. I once made a simple balsa glider with an unshaped chord area, ie completely flat top and bottom. Jeese it flew well. Obviously shape wasn't doing it.

F224, You keep getting off track. What's the use of me going back to basics when that is what I'm disputing. Not that speeding up the airflow doesn't work, but flight theory to Commercial standard pilots license seems a bit one sided to me.

And of course angle of incidence has absolutely nothing to do with it. Maybe not always angle of attack either. EG. I have been told that the turbine powered Thrush,Airtractors etc. are flying so fast in ground effect that they are actually at negitive AOA. They still have downwash into the crop though.

And I don't think its just compression of air under the wing re landing, definatly pressure from downwash. This downwash is usually never mentioned in flight theory in my experence.

Once I watched an old Snow spraying head on.
The markers were whinging he was miles too high. (about 20feet up?). Well he had a cross-wind of about 12 knots. The spray could be seen hitting the crop before the centre of the ac.
About 2 swaths (44 yards) downwind I wasn't getting droplets on me as they were pushed into the crop.
So, all this air being pushed down off the wing.
Are you all still going to tell me it has little or no effect on the wing?
As in standing in a little dingy and jumping ashore, you may not make it.

And it's been along time since I've seen a flat underside to a wing. The Wright Flyer wasn't it.

Also how about all this lowpressure area on the wing, you give it up aileron (disturb the downwash) and wow. down goes the wing in a hurry. All that dang lift just disapeared.

So as you can see I'm pretty far gone.
I probably will take a fair bit of straightening out. Don't you all fail me now.

JAL,

Here is one problem with air- you can't see it! Oh sure sometimes you can, but actually you're seeing stuff suspended in the air.

If air was visible believe me we'd know a LOT more about it, and probably have some fundamental changes in aircraft design that we as yet are still blissfully unaware of.

Another problem with air is that it is not a solid, and not a liquid, and even between those 2 parameters it can change quite a bit. So when we look at techincalities as absolutes, it might be at that moment but then evolves into something else.

Your mentioning crop spraying where you can see visible effects, but you also aren't noticing the tip vortices, which are the spiral tornado like things that trail off the wing tips, they are caused by the difference of the high pressure developed below the wing and the low pressure developed above the wing. They also change with the variables.

Hopefully Missippian can chime in more about spraying.

Maybe it would help if I made a very, very crude statement- Induced lift from the top of the wing works more efficiently but requires increased velocity. Reactive/newtonian or whatever you wanna call it lift occurs from the bottom of the wing, works at much lower airspeed, but costs more energy to create. Life is usually a compromise between the two, making the best of whatever situation you are in at the time.

Yeah, know about the wing vortices, they go down while they're going around.
I mentioned spraying mainly because it's the only real time that down-wash is mentioned.

It is very real and very strong. By memory, it has been measured about 500 feet down from airliners taking off.

To reinterate my point. The wing seperates the airflow. It's stated the airflow over the top of the wing speeds up due to the "curve".
And yet vertually all wings are also curved under as well. So by that, they must tend to also create low pressure to some extent.
Angle of attack would not negate a lot of airflow going under the wing.

Now the fact is, regardless of speed or AOAttack, downwash is created. A law states this MUST create upward forces on the wing.
WHY is this not given any credence.
WHY did the wingless test a/c, shaped like an upside VW beetle fly at all, and at a low enough air speed to be towed by a vehicle. ?

PS for what it's worth, I've been spraying for 30 years, I'm just wondering what was keeping me up.

JAL, I understand the question. I've wondered about it myself. I think the Angle of Attack is probably close to the answer.
Could it be FM?
By the way, Piper Cubs have a flat surface on the bottom of the wing. They are actually slightly curved upward.

quote:

PS for what it's worth, I've been spraying for 30 years, I'm just wondering what was keeping me up.

Jal, What kind of aircraft and crops are you flying down under?

quote:

Originally posted by TJ:

Could it be FM?
By the way, Piper Cubs have a flat surface on the bottom of the wing. They are actually slightly curved upward.

Yep prob. FM. I'll bite, what's FM?
And yep all the better to get that down-wash going.

quote:

Originally posted by Mississippian:

Jal, What kind of aircraft and crops are you flying down under?

"Was" flying mate. I'm burnt out. Quit at about 55. Ag.trained in a 180, started in Ag-cats, then Ag-wagons/Ag-truks, Pawnee, Snows, Air-tractors, Thrush, Fletchers, Just missed out on the turbine fashion.

Started on top-dressing (superphospate on pasture), then 20 years on hill-side bananas,&
bugs and weeds in grain crops, then cotton.

Turbines and cotton are the money makers these days. Lotta rice done in places.
Wot you upto? And what keeps you up?

And that Palmer fella, I've always thought he looked like he was standing in front of an Ag-plane yellow something. If that's him in the photo.

JAL,
Thats me in the photo but I am not even close to you Ag fliers and bush pilots in ability - I'm only a recreational flier.

By the way the plane in the avitar is my Citabria. It is the first photo in the thread "Your favorite rides" on this forum.

regards -

quote:

Thats me in the photo but I am not even close to you Ag fliers and bush pilots in ability - I'm only a recreational flier.

Palmer, After hearing the story of your inverted approach to your airport I will have to argue this statement! It was nice meeting you at Dallas and hope to see you at a future DRSS meeting.

Airplanes and Helicopters fly because of one thing and one thing only, Money. That is the real Theory of Flight, how much do you think the DOC's are going to be, have seen some real typwriter theory in that regard.

I agree with George on the "money angle" but would add that it is is a known fact that helicopters fly by "beating the air into submission" Mags