Simviation Forum - Aerodynamics?

Reply #60 - May 26^th, 2006 at 10:18am

beaky Offline
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I think you're right about the intuitive understanding. I was never convinced that all these scientific explanations are correct.

You have no idea how refreshing it is to hear that from an engineer... Wink

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Reply #61 - May 26^th, 2006 at 12:47pm

C Offline
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Downwind turns? Sounds intriguing... Shocked

Go ahead... Grin

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Reply #62 - May 26^th, 2006 at 11:59pm

beaky Offline
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Downwind turns? Sounds intriguing... Shocked

Go ahead... Grin

Oh no, not me... I just wanted to bring it up and see what happens.
Grin

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Reply #63 - May 27^th, 2006 at 7:30pm

Ashar Ex Member
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Let's take a look at a very detalied diagram to show this effect

Oh that is so detailed...it's about as detailed as Jake's Cessna at his home airport Roll Eyes

&&SS Lazio Website

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Reply #64 - May 30^th, 2006 at 11:24pm

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If you want to know a bit about aerodynamics I suggest "The Illustrated guide to aerodynamics" by H. C. "Skipp" Smith. It has just about everything you need to know about aerodynamics as a pilot.
(IBSN 0-8306-3901-2)

~Drake TigerClaw&&

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Reply #65 - Jun 6^th, 2006 at 12:52pm

Jeph Offline
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im not sure how much this could apply to the discussion, but im surprised no ones mentioned anything about the effect of the wind on your hand when youre driving down the street. its fairly practical, and im sure the wright brothers tried it on their bikes

try a real experiment...hop in a car, and hit the road. at about 30 mph (50km/h), stick your hand into the wind. if you hold your palm (slightly cupped) flat (zero AoA), with thumb touching your index finger, youve created a concave wing, you literally feel the difference in pressure between the two sides. change AoA, and eventually, you feel the "wing" start to stall. then it all turns to drag. flatten your hand, and its more like a conventional wing. youll feel a bit of difference on the top and bottom of the wing.

hope this helps..the concept answered a lot of questions for me when i was learning about it

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Reply #66 - Jun 6^th, 2006 at 3:32pm

Nexus Offline
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Thats an old trick when trying to explain lift, jeph

The problem is...while your hand is getting "lift" from the air being that's being pushed down, the wing of an airliner doesnt get its primary lift component from the air it pushes down, but from the air streaming over the wings.

So it's not really the same, but it works in theory for the common man, but not much more.

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Reply #67 - Jun 10^th, 2006 at 6:15pm

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Yeah, stick your hand out a skyhawk's window, its fun!

Actually your hand does work like an airfoil but flat plate airfoils re not usually good because the airflow is horribly disrupted and it has really bad stall charachteristics.

~Drake TigerClaw&&

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Reply #68 - Jun 10^th, 2006 at 7:27pm

Nexus Offline
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Yeah, stick your hand out a skyhawk's window, its fun!

Actually your hand does work like an airfoil but flat plate airfoils re not usually good because the airflow is horribly disrupted and it has really bad stall charachteristics.

Not to mention it's highly inefficient at creating lift...

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Reply #69 - Jun 16^th, 2006 at 5:30am

Jeph Offline
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ok, ok, valid point, i had a feeling it wasnt quite practical enough for the discussion, but thought it might shed a little light....for someone...

but ill say this. in an emergency*, a C-172 (or similar) cabin door makes a half-decent rudder. ::nods::

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Reply #70 - Jun 17^th, 2006 at 5:15am

C Offline
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but ill say this. in an emergency*, a C-172 (or similar) cabin door makes a half-decent rudder. ::nods::

Or airbrake...

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Reply #71 - Jan 9^th, 2007 at 4:19am

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Here, Ottol.. Read these five pages and if you like.. post it back into active discussion

http://www.simviation.com/cgi-bin/yabb2/YaBB.pl?num=1148281582

I seem to be hearing a lot of noise about "credible sources."

This is from some guys called NASA.....er something. I guess they do some kind of "air" stuff. Huh

Quote:

Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton's Third Law of action and reaction. Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift.

for the whole story (great site): http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

And as far as who's right (Newton or Bernoulli), this answer is.......YES! Cheesy

Both of the following quotes are from this article http://amasci.com/wing/airfoil.html. It's a little long but extremely valuable. I highly recommend printing it and reading it (cuts down on the migraines). My copy is dog-eared (I'm a little slow).

Quote:

....100% of aerodynamic lift can be explained by the Bernoulli principle. And 100% of lift can be explained by Newton's third law. They are two different ways of explaining a single event. However, any appeals to differences in path length are simply wrong.....

This one just for Hagar.....
Quote:

A good low-speed airfoil is much more curved on the top, since lift can be created only if the wing surface carefully deflects air downwards by adhesion. Thus one origin of the misconception involving "more curved upper surface." The surface must be curved to prevent stall, not to create lift.

Now.....if you'll excuse me, I have to go get fitted for a new flame-retardant suit!

.....so I loaded up the plane and moved to Middle-EEEE..........OIL..that is......

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Reply #72 - Jan 9^th, 2007 at 7:57am

Brett_Henderson Offline
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Now.....if you'll excuse me, I have to go get fitted for a new flame-retardant suit!

LOL

no flaming, but I didn't think you'd take me seriously and actually bump this back up Cheesy

This is like a religious debate.

Quote:

However, any appeals to differences in path length are simply wrong.....

That's curious, because in order for the air to be redirected and accelerated, the path HAS to be different AND has to be longer.

The whole idea of "thrust" and Newton's third law explaining a wing's lift is still something like this to me:

It's like trying to push yourself away from a wall that isn't there (and if it worked, sailboats would be able to sail directly into the wind). And.. if you could generate a thrusting force by simply redirecting air; there'd have to be a horizontal component too, as the air is accelerated over the top of the wing, and you'd be getting a magical speed-aiding, forward push.

And what about the action/reaction to the air's initial, upward redirection at the leading edge ? Wouldn't that create an action/reaction component pushing the wing down; counteracting it all.

Achieving lift by Newton's third law can be accomplished (as shown in the lower diagram) and I'm sure it's part of what's happening in flight , but it's Bernoulli's pressure differential that makes a wing, a wing... and gives you the magically efficient, low drag lift, at zero (or near zero) AoA.

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Reply #73 - Jan 9^th, 2007 at 10:27am

OTTOL Offline
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Brett_Henderson wrote on Jan 9^th, 2007 at 7:57am:

.....
That's curious, because in order for the air to be redirected and accelerated, the path HAS to be different AND has to be longer.

I knew it!! I knew those dang so-called-rocket-scientists at NASA were fulla' hot air!! Shocked

Sooo.....I'm guessing that you agree with the idea of "flow turning" but your not buying the whole downplaying the idea of differences in path length and their significance (or lack of).

Did somebody mention boats?

Let's start there. This comment is part of the key to your....IMO...misunderstanding of the whole idea.

Quote:

... if you could generate a thrusting force by simply redirecting air.....

Who said anything about generating thrust? But...you are right "thrusting force" is redirected. Quote:

Forces on sailboat sails are explained using the typical "pathlength/wingshape" explanation ...... But sailboat sails are thin cloth membranes with identical path-lengths on either side. Why should air on either side of a sail have different velocities if the path length is the same?.

Quote:

Achieving lift by Newton's third law can be accomplished (as shown in the lower diagram) and I'm sure it's part of what's happening in flight , but it's Bernoulli's pressure differential that makes a wing, a wing... and gives you the magically efficient, low drag lift, at zero (or near zero) AoA.

I seriously urge you to print and read the above listed article. Here it is again for good measure.. http://amasci.com/wing/airfoil.html

from that article... Quote:

real-world aircraft demonstrate another fallacy. In order to create lift, must a wing have greater path length on the upper surface than on the lower? No. Thin cambered (curved) wings such as those on hang gliders and on rubberband-powered balsa gliders, have equal path length above and below, yet they generate lift. Still the air does flow faster above these wings than below. However, since there is no difference in path length, we cannot refer to path length to explain the difference in air speed above and below the thin wing. The typical "airfoil shape" explanation cannot tell us why a paper airplane can fly, because it does not tell us why the air above the paper wing moves faster.......It is also a fallacy that in order to create lift, a wing *must* be more curved on top. In fact, wings which are designed for high speed and aerobatics are symmetrical streamlined shapes, with equal curvature above and below. Some exotic airfoil shapes are even flat on top and more curved on the bottom! (NASA's "supercritical" wing designs, for example.)

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This is like a religious debate.

Amen Brother!! Trust me, I spent a few years as a CFI and many more as a company I.P., all the while teaching that "pressure differential as result a path-length and that smart guy Bernoulli's theory are the only reason wings work". When I say that my printout of that article has dog-eared pages, I'm not kidding!
I think the problem is that people of all walks, from CFI to Rocket Scientist, like the classic airfoil diagram because........IT'S SIMPLE. That 's the problem though. It's a Band-Aid explanation for something that is a little more complex than just pressure differential. Relative wind IM0 is the key to explaining lift.

.....so I loaded up the plane and moved to Middle-EEEE..........OIL..that is......

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Reply #74 - Jan 9^th, 2007 at 10:52am

OTTOL Offline
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I'm feeling a little malicious tonight, so if you don't mind, I'm gonna get my Crayons out now.....

Okay, I'll admit, I took a little artistic license with the airflow but more importantly notice how easily path length is altered with a small change in relative wind.

.....so I loaded up the plane and moved to Middle-EEEE..........OIL..that is......

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