Bozarth

My Feedback: (15)

Didn't Major Steve Austin almost die in one of these? I'm so glad he survived!!!

Kurt

rgburrill

Some peopel will do anything for notoriety.

eddieC

My Feedback: (2)

LOL. As if that's all it would take. The same debates go on there.
BTW, many of us are also full-scale pilots.

Like revive an old thread?

BMatthews

You can doubt all you want but that is exactly what happens. It manages this due to the speed it flies at.

Sure, they work the same as a regular wing. They just don't get as much turbulent boundary layer so they generate less drag to make the same amount of lift.

It manages the same way that they would, or should, have taught you in flight school related to how your private plane flies at the same speed with one pilot or a pilot and three passengers along with baggage. The pilot trims for a higher angle of attack to generate more lift at the same airspeed. You sure you didn't sleep through that part?

I'll make you a deal. I'll look at the direction the air moves if you go and look at the pressure measurements taken around the airfoil at the same time and in the same place.

Way back in papers written by NACA in the 30's and 40's they measured and determined that the pressure changes around a wing did indeed fully support the idea of the pressure values holding up the airplane. I'm not making that up. I've seen these write ups in the books many years ago.

Than some years later along came someone with a new method that was able to examine and measure the downwash velocity and air mass off the trailing edge and shows that this too was able to support the weight of the plane.

So we have TWO sources of lift? Obviously that can't be. But is ONE right more than the other? Clearly that can't be right either. But if you consider that both are valid and both are happening at the same time it supports the idea that it's one method of lift which can be shown to have two different aspects to the phenomenon. And if you really have to attach early discoverer's names to the effect then it suggests that BOTH Bernoulli and Newton are right and that BOTH are working together at the same time Take away either and the other is left unable to do the work and we get NO lift. It's not an either/or situation. It's a "both together" situation.

Clearly you are in the "Newtonian" school of lift theory that says it's the air being pushed down off the trailing edge that generates the lift. And you obviously think I'm purely in the Bernoulli school that says it's all about the pressure. But in reality one creates the other and the other generates the first. The airflow sets up both together at the same time. Do something to mess one up and the other suffers equally.

If you subscribe to the Newtonian thrust idea at least get it right as to where the acceleration occurs. The acceleration of the air that results in the downwash doesn't happen at the trailing edge. It starts up where the air is stopped from being pushed up by the leading edge and is pulled back down by the suction created by the air initially being pushed up (and yes I know that it doesn't suck the air down. But in this case it's easier to say that than describe the surrounding air pushing the upward moving air back into the low pressure zone).

So we have the air moving up and away from the airfoil which creates a low pressure area that then pulls back down a mass of air hard enough to lift the airplane. And oddly enough the pressure changes needed to accelerate that much air is also the same amount needed to make the lift to hold up the airplane. Again we see two faces of the same effect. It's conservation of forces. The energy needed to pull that air back down comes from the same mass of air pulling away and creating that low pressure area that then works to pull the air back down.

Finally, what connects the air to the wing's surface? Moving air isn't like a rock or even like pebbles. It's a gas. And as a gas the only way it can affect an object is by the local pressure on the surface of the object. Wind moving past an object piles up and creates a zone of higher pressure on the windward side. Meanwhile the rolling turbulence on the leeward side produces a reduction in pressure. If the gain in pressure on the windward side added to the drop in pressure on the leeward side is big enough then the object slides or tips over.

Similarly the wing on our plane does not have a mechanical connection to the air. So the mass of air being accelerated by the wing isn't actually connected to the wing. Instead the connection is through the low and high pressure pockets above and below the wing that is created by the nature of how the air flows around the airfoil and by the acceleration of the air by the wing. If the skin of the wing could not "feel" the airflow by way of the pressure effects at the skin then how would the air actually connect with the skin of the wing to hold it up?

Your posts on this have only proven what other pilots have mentioned over the years. Namely that the theory of lift given to pilots is an abbreviated course aimed at giving them enough understanding to develop a feel for why planes do some things during flight. If I really wanted to learn the WHOLE truth about lift I'd go to university.

ltdive

That is not how a jet engine works sorry look it up

ltdive

Originally Posted by ltdive
explain a laminar flow wing
"Have you ever seen a laminar flow wing . both the upper and lower surface of the wing is exactly the same ie same pressure on upper and lower side when at zero angle of attack and even at a nominal angle the pressure is the same

I will agree that back in the 30's and 40's air pressure was the best explanation but since it had only been some 10years since they discovered how a monoplane could work and the fact that they had no real way of getting real time accurate air pressure results over the entire wing other than theory's and looking at small fabric tabs to look at the airflow over the wing or smoke trails to see boundary separation today's scientists are much better equipped to work out exactly how a wing works
i'll come back to the jet engine, if low pressure was an equal partner in generating lift then how does an axial flow jet work as it relies on highly compressed air to function if low pressure was there it wouldn't work in today's highly efficient engines

ltdive

.HUH???? so wings don't work when a plane is vertical??

Lone Star Charles

Sounds like you are finally catching on! In vertical flight, the wings have zero contribution to lift, it's all engine.

I'm gonna go get some popcorn now!

BMatthews

First off laminar airfoils come in various shapes. Look at the airfoils used on modern sailplanes. They are anything BUT symmetrical. And even in the case of your symmetrical laminar flow airfoil example the upper and lower pressure distributions are only identical when it's at zero degrees angle of attack. As soon as you alter it to have a positive or negative angle the stagnation point moves and the pressure distribution changes and you have a lower pressure on one side and a higher pressure on the other. This is how any symmetrical airfoil, laminar or otherwise, generates lift. And a good thing too for your case with your aerobatic plane.

Well, they do. But when the plane is vertical in a climb or dive the pilot is holding the wing at the zero lift angle with the elevators. If they weren't then the plane would be generating some lift and it would be pitching away from the vertical line. The point being that when the plane is holding a truly vertical line the wing isn't generating any lift because it's being held at the zero lift angle of attack. On something like a Cessna 150 that is strongly pitch stable the pilot would need to hold a noticeable amount of forward stick to hold a vertical dive. You in your aerobatic plane with a greatly relaxed amount of pitch stability might find that it takes only a hair of forward pressure or maybe none at all depending on how close to neutrally pitch stable the plane's balance is set.

All through this you seem to think that I'm saying "Bernoulli" even though I've never mentioned that word... I fully appreciate that it's not a Bernoulli situation. But the point I'm trying to make is that there's more to it than just "Newton" turning the air and throwing it down. Yes the air is being pushed down. But as I noted earlier this also produces a pressure distribution around the wing. The two things work together and are related.

It's like a suspension bridge such as the Golden Gate. If the road way is the wing the hanging catenary cable group is the air being accelerated down and the ladder cables connecting the main cable to the roadway is the pressure effect. It's just in this case there isn't a second cable and rods pushing up from below. But it serves as an example of how the air being turned down and the pressure work together. Take away the main catenary cable and it all falls into the bay. Take away the ladder cable connectors and the road falls into the bay. But the two together holds up the roadway and all those commuters. The air flowing around the airfoil and the pressure changes it generates when the flow is deflected and accelerated works together in the same way. Or is it the speed and pressure change as it speeds up over the upper surface that pulls the air down?

That's the thing. It's not all one or all the other. There's no doubt that the air speeds up as it passes over the upper side of any airfoil, symmetrical or cambered, that is operating at some angle that produces lift. That's been shown and can be seen on any number of actual You Tube videos. It's this change in speed and pressure in association with the camber and angle of attack that produces a downward acceleration.

The trouble is that in the end and as I said above is that we can correctly measure the lift amount in two ways.

If you set up the wing with a big grid of pressure sensors on both sides and fly along and use a computer to figure out how all those pressure readings add up it'll equal the amount of lift. NACA did stuff like this and wrote it up back in the 30's and on.

But it's also possible to look at the mass, velocity and direction of the air coming off the trailing edge and measure the energy as being the same as the lift being generated.

But we can't have TWO values of lift. So what's going on? What we're seeing when we run these methods of measurement is simply two ways of measuring the same thing.

It comes down to the same question as our suspension bridge. What's holding up the roadway? Is it the main catenary cable or the cable ladder connectors?

In the end it's sad that it's turned into a popularity contest. We've got a "Bernoulli" camp and a "Newton" camp for the most part. But in actual fact it's a little of both working hand in hand. If it were possible to remove one in isolation the whole "bridge" would collapse. It's simply unfortunate that so many authors seem to want to say it's all black or all white and then spread the word when it's far more a case of complex and interlocked grey.

Lone Star Charles

I have absolutely seen a laminar flow wing. Have you? Perhaps you could tell us how the determination of laminar vs. turbulent flow is made? I am sure it would enlighten us all.

I'll go get more popcorn now.

ltdive

The wings still produce lift because they are still moving through the air. better put down that popcorn and think some more

da Rock

Actually, wings produce lift whenever they're at any other angle of attack other than their zero lift AOA. A wing moving through the air often produces no lift. Examples?

The jet fighter doing an impression of a rocket will do it's best rocket like climb trimmed for the least drag. That'd be somewhere around trim that moves the wing at it's zero lift AOA. and...

Aerobatic flights that change the pitch direction and carry the movement through.

Just a couple.

Now let's settle down and go eat our popcorn in another room for awhile.

ltdive

so you agree with me great

ltdive

is a stall maneuver

BMatthews

You seem to have a rather myopic view of the whole issue.

da Rock

Not always. The change from upright level to inverted level doesn't come close to a stall, yet obviously passes through the zero lift AOA. An axial roll in level flight, while holding constant altitude must pass through that zero lift again and again, with no stalls at all. Stalls are the result of too much AOA, not no AOA.

ARUP

This thread is sooooo ridiculous! EVERYBODY knows that voodoo magic holds airplanes up in the sky! Gooooooood grief!!!!!!!!!!!!

bjr_93tz

Thank heavens the vertical thing out the back is called a fin and not a wing otherwise it would be producing lift too