Simviation Forum - Aerodynamics?

Reply #90 - Jan 9^th, 2007 at 4:21pm

Brett_Henderson Offline
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Ok..I'll try this angle on how this Newtonian stuff is like trying to push yourself away from a wall that isn't there.. Roll Eyes

Picture a musket barrel with a ball loaded. Now, picture pointing it slightly downward... As the ball is allowed to roll (be redirected) down the barrel; would it create a mathematically defineable recoil, acting on the barrel ?

NO !

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Reply #91 - Jan 9^th, 2007 at 4:28pm

OTTOL Offline
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Sorry....I wasn't mulling that one over.

I just got a call from my 8/9's pregnant wife, who is 8,000miles away and unsympathetic to my cause and important mission here, tonight. Cool

Anyway, between this and her, I just realized that it's 12:30am. Time for bed.....

Try this one on for size http://www.av8n.com/how/htm/airfoils.html#sec-flow-intro

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

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Reply #92 - Jan 9^th, 2007 at 4:46pm

Brett_Henderson Offline
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Tell your wife I'm sorry for distracting you Lips Sealed

And an early congrats.. to you both

I read that link.. What we need are some data/diagrams at a pure zero AoA .. Once you get into the positive AoA (looking at all those pressure patterns), you venture into what I like to call, "balllistic lift" (like the skipping stone).

I understand that there's always going to be some of that going on.. there'll always be some Newtonian stuff too.. because as Rotty pointed out.... just about any winglike surface can be held airborne with enough velocity.

It's all about accepting drag for lift.. and when all the laws are balanced out.. it's pressure differential that makes a wing, a wing.

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Reply #93 - Jan 10^th, 2007 at 2:16am

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Brett_Henderson wrote on Jan 9^th, 2007 at 4:46pm:

Tell your wife I'm sorry for distracting you Lips Sealed

And an early congrats.. to you both

Thank you! This'll be number three. After this one pops out, I'm gettin' my boys tied off!! Undecided

Ouch! My Buddy says that it feels like ya' been kicked in the juevos..... for entire week!

Quote:

...... What we need are some data/diagrams at a pure zero AoA .. Once you get into the positive AoA (looking at all those pressure patterns), you venture into what I like to call, "balllistic lift" (like the skipping stone).

I understand that there's always going to be some of that going on.. there'll always be some Newtonian stuff too.. because as Rotty pointed out.... just about any winglike surface can be held airborne with enough velocity.

Quote:

Cambered wings at high R have a positive effective attack angle even when the geometrical attack angle is zero. This confuses everyone, even the experts.

The statement quoted above was the whole point of my modified version of your first diagram. And Rotty's response was a perfect example of this; he assumed that the second airfoil was different, when in actuality, the camber hadn't changed at all.

Quote:

They see only the zero geometrical angle and believe that the cambered wing is not tilted. They don't realize that the down-tilted trailing edge of a cambered wing has far more effect upon the air flow than the rest of the whole un-tilted wing. In other words, the sloping rear half of an un-tilted cambered wing is strongly interacting with air because of air's inertia. A cambered wing can have a large AOA and a zero AOA, both at the same time.

Quote:

It's all about accepting drag for lift.. and when all the laws are balanced out.. it's pressure differential that makes a wing, a wing.

The problem that I see is that everyone takes the classic airfoil diagram for gospel. That is a two-dimensional, static way of trying to approach a three-dimensional, dynamic scenarion. Quote:

A two-dimensional diagram (also called the 'infinite wing diagram,') is misleading. It only depicts ground-effect flight where altitudes are much less than one wingspan. Any explanation based on this type of diagram does not apply to flight at normal altitudes. These Two-dimensional diagrams are not just simplified, they're genuinely wrong, since typically they neglect to show the floor and ceiling of the wind tunnel which receive the weight of the wing as instantaneous reaction forces. In 2D diagrams the floor and ceiling are an essential part of the system, and their effects do not diminish as they are removed to infinite distance. In other words, Two-dimensional airfoil diagrams depict a type of venturi situation, while genuine aircraft fly far from the ground and have no instantaneous weight applied to the Earth's surface. To explain lift in high-flying aircraft, a 3D diagram with its vortex downwash wake is absolutely required. Real wings are lifted upwards as they fling a mass-bearing vortex-pair downwards. Yet introductory textbooks always use the misleading two-dimensional diagrams which depict only the regime of ground-effect flight.

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

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Reply #94 - Jan 10^th, 2007 at 7:50am

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Maybe I'll just have to go on being wrong (but not alone and in good company) until some expert can convince me that simply redirecting air over the TOP of the wing can not only create a net vector sans outside energy, but that that vector can act ON the wing (ala the musket ball) from above and "pull" it up.. They'll also have to tell me why a vector opposite the lift isn't created when the air is redirected UP as it first passes over the wing.

As for downwash.. Hagar posted some interesting pictures/links on page 3 of this thread....

Months ago, when this thread was first active; I did some research that rattled my faith in Bernoulli, but it really didn't surprise me that pressure differential alone could not produce enough lift to hold a plane aloft... And along that line of thought, neither could the lifting force created by redirecting air, if conservation of energy means anything.

For now, I'll let all the complex, aerodynamic goings-on be a black box and go on believing Bernoulli makes the end product, lift... because I just took a shower.. and we all know what the shower curtain did

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Reply #95 - Jan 10^th, 2007 at 2:05pm

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Pretty soon you won't even need to read poor Mr. Beaty's article....I'll have cut-n-paste'd the entire thing on this thread!!!.... Cheesy

Quote:

The presence of multiple possible explanations can trigger religious wars, "Swiftian Battles" between adherents to one side and the other, and sometimes one side wins, stomping out the other explanation... even though both explanations are valid, and even though both explanations are essential. , We cannot really understand wings unless we know several different ways to explain them. A toolkit needs hammers AND screwdrivers... and anyone who searches for a "One True Tool," while emptying the rest of their mental toolbox, is going to severly limit their own expertise.

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

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Reply #96 - Jan 10^th, 2007 at 3:33pm

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I love the Internet!! I think it has actually surpassed sliced bread!

I was searching for some info on the Coanda Effect and found this very intertaining article by Jef Raskin (that name might sound familiar to you Mac guys).

Since nobody seems to think that NASA is that bright, maybe the guy that got Mac's up and running will sway you.

Seriously, it's fairly brief and this guy has an excellent sense of humor (which makes reading this kind of stuff much less tedious).

http://jef.raskincenter.org/main/published/coanda_effect.html

Three items that really made me chuckle: the UnderCambered Wing, The Lumpy Wing and the fact that even Einstein got it wrong and eventually "came around".

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

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Reply #97 - Jan 10^th, 2007 at 10:03pm

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Read that essay.. still no answer to my question (s)..

I spent some time at the club today.. we're getting ready for a four-booth dispaly at the convention center next month (if any of you are near Columbus, come see me .. I'll be the goof standing by the Liberty XL2 acting like I know something about airplanes.. lol )..

Anyway, as the three of us; our AP guy, the club president (nearly 25,000 hours logged and a degree in aeronautics), and myself were rigging the trailer that will transport the Liberty to the show, I got brave and brought this debate up... The AP guy would remind you of the mechanic on the sitcom, Wings, so he was mostly just nodding and agreeing with both of us. Richard (It still gets filtered to "thingy" when I type the name he goes by) (the pres) didn't want much to do with the debate, but I was relentless..

Turns out, he did a thesis on this stuff many moons ago (he's well over 60) and admitted that he's still a pressure differential guy, but HAD to write that paper from the Newton camp. All that really resulted from our discussion was that he knows pressure differential alone cannot do the job, and that he had never heard or pondered my dilema (if there's lift as the air goes down the airfiol, there's anti-lift as it's going up).. and he was REALLY puzzled when I posed the musket ball scenario (because the re-directed air is indeed directed by the wing, but NOT FROM the wing ... and indeed would create action/reaction (as any revectored mass will), but should be as likely to ifluence the wing about as much as the rolling ball would the barrel (in it, even touching it, but by know means "linked" to it)).

Then we got to sketching as he intended to show me how you could get the air to go down without it having to go up first (or at least down more than up)... BUT.. sans exagerated, positive AoA (enough to clearly show "ballistic", flap-type (skipping stone) lift, it can't happen.

I still(and now Dick <<see !) can't resolve that there can be a net, downward redirection of air without significant AoA.. and even then, there's more air being re-directed from UNDER the wing ( a force that can clearly act on the wing, flap-like )...

I'm still standing with Bernoulli's stuff as what makes the difference (acknowledging that there's more to it)...

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Reply #98 - Jan 10^th, 2007 at 10:09pm

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Footnote:

"Thingy" ( delta india charlie kilo) finally said, "you wanna know what makes an airplane fly ?" as he took a bill out of his wallet.. shaped it roughly into an airfoil, blew over it and made it lift (I was about to say, "aha.. you're a convert")... "MONEY"..

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Reply #99 - Jan 11^th, 2007 at 2:44am

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Brett_Henderson wrote on Jan 10^th, 2007 at 10:09pm:

Footnote:

"Thingy" (delta india charlie kilo) finally said, "you wanna know what makes an airplane fly ?" as he took a bill out of his wallet.. shaped it roughly into an airfoil, blew over it and made it lift (I was about to say, "aha.. you're a convert")... "MONEY"..

From the Young Ones... Quote:

...his name is Rick....spelled with a silent "P"....

I'm still working on a diagram to explain the imparted forces (in your Musket example) for my own entertainment but your example really doesn't apply to an airfoil....

Quote:

When two solid objects interact in a mechanical process, forces are transmitted, or applied, at the point of contact. But when a solid object interacts with a fluid, things are more difficult to describe because the fluid can change its shape. For a solid body immersed in a fluid, the "point of contact" is every point on the surface of the body. The fluid can flow around the body and maintain physical contact at all points. The transmission, or application, of mechanical forces between a solid body and a fluid occurs at every point on the surface of the body. And the transmission occurs through the fluid pressure.

and...I think the answer to your biggest question is probably another question....

Quote:

the wing has also spent some of its energy, necessarily, in moving the air forward. ………That's a way to think about the drag that is caused by the lift the wing generates. Lift cannot be had without drag. The acceleration of the air around the sharper curvature near the front of the top of the wing also imparts a downward and forward component to the motion of the molecules of air (actually a slowing of their upward and backward motion, which is equivalent) and thus contributes to lift.

What "induces"....induced drag? Shocked

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

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Reply #100 - Jan 11^th, 2007 at 8:02am

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I'm going to type the full name of the guy who hosted American Bandstand, and until recently, the big New Years Eve celebration in NYC. You'll see what comes through:

Dick clark

Ok...
Quote:

I'm still working on a diagram to explain the imparted forces (in your Musket example) for my own entertainment but your example really doesn't apply to an airfoil....

Sure it does. It shows how the barrel can be the directing device of an accelerating object without being acted upon by that acceleration. However I do see a flaw there, in that there is a force action/reaction between the barrel and ball relaltive to gravity; much like the car door that holds you in the car as you go around a corner. And it does ignore the Coanda Effect that would explain how the redirected air could "pull" the wing up... So I withdraw and replace it with ball and barrels that address the multiple redirection: (I hesitate to post another jpg.. we might be nearing the thread's limit, but this is only 10kb)

The pistols are isolated from the secondary, bent barrels (tubes) so their initail recoil is no factor. The upper drawing shows a tube that would indeed have a net displacement (up). The lower drawing shows a tube that would oscillate, but (accounting for drag and lost ball velocity) have no net displacement.

One represents an AoA lift (which I acknowledge HAS to be there, supplementing pressure differential); the other shows how redirecting something up first, then down can't yield a net force in any one direction.

You can get a net lift (traded for drag) from Bernoulli with zero AoA. You cannot get a net lift by redirecting air WITHOUT an AoA sacrificing that lift too, to the drag gods.

AoA lift is barn-door lift. Bernoulli's lift is wing lift..

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Reply #101 - Jan 11^th, 2007 at 3:06pm

OTTOL Offline
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Brett_Henderson wrote on Jan 11^th, 2007 at 8:02am:

Sure it does. It shows how the barrel can be the directing device of an accelerating object without being acted upon by that acceleration.

Aaaannnddd.....right back to my previous post. Air isn't an object, it's a fluid.

Apples and Oranges buddy.

...ever been thwacked by an out of control garden hose? I guarantee you that the bends in the hose didn't neutralize the imparted forces!!

Oh........and uh.......that's you in the picture.......not me....... Tongue

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

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Reply #102 - Jan 11^th, 2007 at 3:49pm

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LOL.. well.. it aint me.. but it's a pretty.. umm .. oh nevermind.. Cheesy

The whacking garden hose is the gun without the isolated barrel.. and the water would be like an independent thrusting source (like an engine on the wing) (not the passive stuff that air is, as a wing passes through it) (that's why I detached them)).. A single balll can represent fluid in this argument.

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Reply #103 - Jan 11^th, 2007 at 4:11pm

Brett_Henderson Offline
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I could have said, "Picture the ball being tossed up.. and just as it peaked (ala a tennis serve) the bent tube came rushing along and with perfect timing, met the ball at its peak".. Roll Eyes

The tube would first move down and then up, as the ball was redirected through its length...

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Reply #104 - Jan 12^th, 2007 at 4:09am

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Brett_Henderson wrote on Jan 11^th, 2007 at 4:11pm:

I could have said, "Picture the ball being tossed up.. and just as it peaked (ala a tennis serve) the bent tube came rushing along and with perfect timing, met the ball at its peak".. Roll Eyes

The tube would first move down and then up, as the ball was redirected through its length...

You can manipulate your balls in any way you like (mild pun intended)......

But a solid and solid will not behave in the same manner that a solid and a fluid will. You are trying to isolate Newton in a corner. It's been stated many times already. It is essential that you include Coanda, Bernoulli and Newton in a complete and accurate discussion of wing fluid dynamics.

The Grapeshot can only apply force to a single point in a single direction, the fluid tries to move in all directions at the same time.......HUGE DIFFERENCE.

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

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