How Airplanes Fly: A Physical Description of Lift

[W.D. Roland]

Several times in the recent past have mentioned that the Bernoulli principle does not account for all of the lift
a wing produces, especially flapped stunter type wings.
my opinion for several years has been that a part of lift in an airfoil is produced by the Coanda effect and this also accounts for some of the problems with short tail moment airplanes and misunderstandings in what our flaps are actually doing.



http://www.aviation-history.com/theory/lift.htm

[Steve Thomas]

Lift is actually caused by vibration. The air molecules above the wing vibrate more and thus experience lower pressure.

This explains why helicopters fly, why Britten-Norman developed the Trislander from the Islander (50% more lift!), and why the Fox 35 has been such an enduring success.

[Howard Rush]

The Web site you quoted is OK.  One that was recommended to me by another Boeing aerodynamicist (Scott is at Boeing now) is http://www.av8n.com/how/ .

[Clint Ormosen]

I thought it was magic. You guys are ruining it for me.

[wwwarbird]

 If it's got enough power, it will fly.

[Dennis Moritz]

Ether and the music of the spheres.

[W.D. Roland]

Thanks for the link Howard.
Should keep me plenty busy for the rest of the winter.
so far looks like the standard published theories with right and wrong, a good starting place(for those who can later unlearn some things)
John S. Dinker(author of see how it flies) I find little that qualifies him other than he can read write and Pilot.
[[John Denker is certified as a Commercial Pilot, Flight Instructor, and Ground Instructor. He is an FAA Aviation Safety Counselor. He is a past member of the board of trustees of the Monmouth Area Flying Club, and a past member of the National Research Council Committee on Commercial Aviation Security.
He is well known as a prankster and prototypical mad scientist. Some of his exploits were featured in the films “Real Genius” and “The Age Seeking for Genius”, as well as in publications such as “Time” and “IEEE Spectrum”.]]
http://www.av8n.com/how/htm/author.html

How Airplanes Fly: A Physical Description of Lift (from Sport Aviation)
Authors:
David Anderson
Fermi National Accelerator Laboratory
Scott Eberhardt
Dept. of Aeronautics and Astronautics



Will look closer at the under camber section as these can have top and bottom section surface lengths nearly the same and should not produce much if any lift with near equal flow speeds. (Bernoulli or Coanda?)

A little thought on why the poly wog doesn't work well with flaps and why Al Rabes 'Fat trailing edges' work so well with flaps  might give some clues.
Where High velocity(for Coanda) = low pressure(Bernoulli), high velocity(relative) being necessary for both theories.

We already know that If you do the computational fluid dynamics and you run that against the wind tunnel, you end up having to add fudge factors.(wind tunnel data has a flaw built in..my opinion)

One thing I would like to do one day is take manometer readings at numerous stations both top and bottom of section and see for myself if enough force through pressure is available to do what is required.
So how can airspeed at these locations be measured at these same stations at surface and various distance from surface? Real measure and not calculated from pressure?(serious question)

Racing in the rain with ground effect cars gives good visuals on the thrust (upward)behind tunnel exit(diffuser). best seen from behind in person to separate from tire spray and see what you see clearly.
This is best visible in non winged ground effect cars.
Also the rear wing is now used in a different manner. Mounted low enough so that the low pressure created under
the wing helps 'drive' flow from the diffuser to increase tunnel(venturi) velocity.


Another Bug in our world.
Bill Netzeband latest work around 2001( Note: tail moment arm)
http://www.control-line.org/Portals/57ad7180-c5e7-49f5-b282-c6475cdb7ee7/Netzeband_Stunt_Design_Summary.pdf
Some how left out of this list
http://www.iroquois.free-online.co.uk/netze/wildbill.htm
Reminds me of something similar in Established facts .

[Howard Rush]

Will look closer at the under camber section as these can have top and bottom section surface lengths nearly the same and should not produce much if any lift with near equal flow speeds. (Bernoulli or Coanda?)

If you had read either of those Web pages, you wouldn't have written that.

One thing I would like to do one day is take manometer readings at numerous stations both top and bottom of section and see for myself if enough force through pressure is available to do what is required.

Or you could just watch an airplane fly, which proves that there is.

So how can airspeed at these locations be measured at these same stations at surface and various distance from surface? Real measure and not calculated from pressure?(serious question)

This has been done in wind tunnels by making little neutrally buoyant spheres by filling little balls with helium (like microballoons, I guess) and injecting them into the flow in front of an airfoil.  Then they take pictures with a strobe light. (serious answer)  I think the same thing has been done with puffs of smoke.  There is a whole art and science of flow visualization that has a bag of cool tricks to show pressures and velocities.  Don Shultz's buddy, the late Jim Crowder, was the master of this. 

There is no controversy among aerodynamicists about how wings work.  It is difficult to explain, though.  This is made worse by people who do not understand it writing magazine articles and books that are read by pilots and model airplane fliers, who, never having the occasion to do any calculation using the bogus explanations, accept them.  This is OK, I guess.  As long as they fly by the book and by experience, pilots can survive to old age.  Successful model fliers generally disregard theory (real or bogus) and do what experience tells them works.   

[Igor Burger]

yes yes ... upper surface must be longer than lower ... that airfoil on pic must work well ... perhaps some nano labyrint paint will work even better, air particles must be very very quick until they find proper way   


... I think that is why sponge skin of dolphins works so well ... high speed = low pressure = low friction 

[Tania Uzunova]

"It is simple. Ask yourself this. Is there lift on the moon? Answer no there is no air. OK add some air and ask again. Is there lift now? Answer is still no because there is no gravity or very little



ARE YOU SERIOZ ?! 

[Igor Burger]

Righ ... the gravity is the reason ... my arfoil is so ugly that also gravity will repel it (especially on pretty moon) ... so it will fly also there and also without air  

[Tania Uzunova]

Simply the rule of  Bernoulli and the question why does it fly!

[Joseph Patterson]

  I'm too "etherial ", David, like some of the rest of these guys except Howard. Some good websites, but most is "over my head"- no pun intended.

[W.D. Roland]

Whoops! Al you blew it with your real world testing! Musta been influenced by the engines cooling fan.

There is no controversy among All  Flat Earthers in history and currently Global warming fanatics(we told you what to Know, no thinking required).

[[It is difficult to explain, though.  This is made worse by people who do not understand it writing magazine articles and books that are read by pilots and model airplane fliers, who,....
You mean like  this writer working for AT&T, right Howard? http://www.av8n.com/how/

[[[If you had read either of those Web pages, .......]]]
Thats what I said I thought?:
>>>>Will look closer at the under camber section as these <<<
Yes I am still reading these as well as other publications and flow visualizations as I have off and on for over 40years.


[[[[This has been done in wind tunnels by making little neutrally buoyant spheres by filling little balls with helium (like microballoons, I guess) and injecting them into the flow in front of an airfoil.  Then they take pictures with a strobe light. (serious answer)]]]
Cool, sounds out of my budget! Do these micro/helium balloons have same, more or less mass/kinetic energy at same displacement of air?
 [[I think the same thing has been done with puffs of smoke. ]] This is what Anderson and Eberhardt show and then managed to leave out the word 'puffs' or pulsed from the text.

I wouldn't think  physicist Carl David Anderson would need Math for his work either

Professor Scott Eberhardt with his Ph.D at Stanford University in Aeronautics probably can't even add.
I would guess that was the main reason for His working as a research scientist for the NASA Ames Research Center,
and why he has been funded by the Office of Naval Research, the National Science Foundation, Northrup, Rockwell International, Boeing and Cray Research.

Anderson and Eberhardt;
[[[The authors wish to point out that this may appear to contradict an accepted
application of Bernoulli. But, what is suggested is that Bernoulli is not
applicable unless the wing is 100% efficient. That is, there is no energy loss in
producing the lift. In classical presentations of lift on a two-dimensional
airfoil, the wing is 100% efficient, and so Bernoulli can apply. That is because
an infinite amount of air is accelerated at almost zero velocity. It is only when
considering a true, three-dimensional wing, which cannot be 100% efficient,
does Bernoulli become inapplicable. In this case a great deal of energy is
given to the air so either energy has to be added (with an engine) or there can
http://home.comcast.net/~clipper-108/AppBernoulli.pdf

With some math:
http://www.aviation-history.com/theory/lift.htm


For now can we at least decide if were going to continue to use meaningless measure of tail moments or the
correct Physical  and aerodynamic location of tail moment?

This all reminds me of Co increase caused GW taught in schools across out nation ignores the fact that the Co rise comes after temperature rise...?
be no lift.]]]]

[W.D. Roland]

 That's the point Joseph. keeping it over our heads even if level flight laps may be below tall peoples heads.

Damned Ty! you wont let me the fly pattern up wind and now wont let me argue?
Translation: Thanks for your help in Arkansas!

Howard
Digging for knowledge here. Wana Help?
Taking what the 'experts ' TELL us and think about what is correct and what is not for our use.
Describe what you think make Al Rabes airfoil sections work so well.

Hell, No flying and very little building for the next year for me, Gota do something or go stir crazy.


Igor
Hope you didn't read that OMNI article(1980s?) where friction and resulting static gravity repels aircraft away from Earth....or some such way out there malarkey.

[W.D. Roland]

Igor
Textured surface has less drag then polished on displacement hulls.
Planing hulls are best polished.
Sail boat racers will polish and then scuff with steel wool or 600grit....thats how the 2 racers I knew did it.

[W.D. Roland]

Will see how this crude drawing post after silly program shrunk and no telling what else to it.

Station '0' is not at L.E.(made less work for now)
Hinge line all 3 is Station 10.5
Flap deflection is 35deg+/-
#1-Quiky drawn Polliwog or Re-flexed. With out flaps this is the type airfoil used on Rileys original Mag plans Quicker
and on Hi Johnson's Stuka design.  
#2-Sig Super Chipmunk
#3-Rabe type. Tip for FW190A with aft curvature flattened for looks.
   Root has more aft-section curvature.(and matches Rabe Sea Fury)

Why?
#1 reported not very good with flaps
#2 works well with flaps
#3 apparently works best with flaps( Al claimed as much as 50% more lift than conventional)

Out of juice for today.

Click to enlarge.

[W.D. Roland]

Darkened the lines in above airfoil drawing to be easier to see.

consider:
What is this in following drawing.

[Igor Burger]

That my example was ment to show that the surface longer or shorter or whatever is not the key for making (or understanding) lift, you can have lift also from flat plate. And surprisingly - does not matter if it is flat, or undercambered, or symetric, you have always in its best part of lift curve dradient cl=0.1 per 1 deg AoA ... I thing it clearly shows that it does not come from shape itself.

good shape of the airfoil only allows higher angle of attack (allows air to stick attached at high AoA) and thus making of more lift. The key for understanding creation of lift is understanding of acceleration / decceleration of air mass ... exactly like it does Benoulli equation, what is only application of that acceleration and decceleration encapsulated to math equatin ... that equation does not "explain" something, it simply evaluate it if you already understand it and if you can properly apply it ... the good example is that flap

if you want compare good and bad airfoil, you must understand much much more than only making of lift, you must understand boundary layer, its stability, separtion (gives that maximum lift) and drag (gives gliding ability)

[john e. holliday]

With enough power, anything will fly some distance.

[Don Curry AMA 267060]

I was told that helicopters fly only because they make so much noise that the earth rejects them.

[Jim Thomerson]

Frank Zaic had an explanation something like this (too lazy to look it up), Bernoulli moves the air out of the way on top of the wing and Newton punishes it up from the bottom. I've been flying a Guillows #2 trainer with an old McCoy 19 fourstroking.  I am amazed that that little wing, at that speed, generates enough lift to fly that much repaired and heavy airplane.  If you calculate air pressure as @15psi x wing area, you find it takes a tiny percentage difference between pressures above and below to fly your airplane.   

[W.D. Roland]

That my example was ment to show that the surface longer or shorter or whatever is not the key for making (or understanding) lift, you can have lift also from flat plate. And surprisingly - does not matter if it is flat, or undercambered, or symetric, you have always in its best part of lift curve dradient cl=0.1 per 1 deg AoA ... I thing it clearly shows that it does not come from shape itself.

good shape of the airfoil only allows higher angle of attack (allows air to stick attached at high AoA) and thus making of more lift. The key for understanding creation of lift is understanding of acceleration / decceleration of air mass ... exactly like it does Benoulli equation, what is only application of that acceleration and decceleration encapsulated to math equatin ... that equation does not "explain" something, it simply evaluate it if you already understand it and if you can properly apply it ... the good example is that flap

if you want compare good and bad airfoil, you must understand much much more than only making of lift, you must understand boundary layer, its stability, separtion (gives that maximum lift) and drag (gives gliding ability)

---------------------------------------------------------------------------------------------------------------
{if you want compare good and bad airfoil, you must understand much much more than only making of lift, you must understand boundary layer, its stability, separtion (gives that maximum lift) and drag (gives gliding ability)}

Hey Igor
Boundary layer separation is one of the things going through ol noggin at the moment and taking a look at the
Reversion end of it and how is it different in free(airfoil) vs contained(venture/pipe)
First have to find out where the heck my CFD stuff is at and one text with a lot of tunnel smoke work.
Hope they are in the shop or at Dads house.


Currently I agree on the length, at least in a venture.(where they are the same)

Another thought, if pressure is recovered or mostly so how this fits in with down wash.
I remember some smoke work in missing book, on a flapped wing very much like what we use in PA
( think the other has some similar in CFD)

Before anything else will have to let the worst of this round of poison pass...worst one yet.

Don
Have you ever tried to fly a helicopter? I think they are so damned stupid they ignore gravity.
Collective collects stupid apparently .

[dale gleason]

Fourth grader's thoughts- The wind blows on the bottom surface of a kite, and since the string keeps the kite from blowing away, it goes up. Same as water skiing, the ski mashes water down to hold the skier up, or the water pushes the ski up.  When airplanes fly, the motor and propeller are the string, but you can't see it. The wing mashes air down, so the plane stays up. Wings don't suck, they blow....down.  Sometimes up can be down, though.

dg

[Tania Uzunova]

hm ok... what now ?

I have a look to that website which you post http://www.av8n.com/how/....it's just gives my mind back to many questions which i want to know also before. You can not stopped and concentrate only just in one dott (point of view) and ask why is happening like that and why not. It's little bit, hm actually definatly more complicated than you think. Mostly because you had not only to accept but also to understand some rules how they works? It's just more than 30 years airplanes have to  increasingly obtain their power from  JET rather than internal-combustion engines. why i am saying that, because simple - must be faster, speed because of  the indeed type of it and role in air at all, right? But the principle that gave them flight, and the principle that kept them aloft once they were airborne, reflected back to Bernoulli's drawings (rules)  of more than 100 years before their time, forsure! And simply  this is the CONCEPT OF AIRFOIL - at all!
And exactly of creating that airfoil you must mind that it must had a clear (pure) design. I suppose you already read about it's shape - an elongated, asymmetrical teardrop lying on its side, with the large end toward the direction of airflol,.after that to mind also that must be a narrow tip pointing toward to the "back". In grafic that means the more larger is curves of its upper surface in comparison to the lower side is referred to as the airplane's camber. And do not put dott here, because also the front end of the airfoil is also CURVED, and the chord line is an imaginary straight line connecting the spot where the air hits the front!!If my mind do not lies me it's called Stagnation point, or opposite Point of Stagnation which reflect directly to the rear, or trailing edge, of the wing...and that what Igor says about " does not matter if it is flat, or undercambered, or symetric, you have always in its best part of lift .." it's just simple become from the shape of model at all and whole construction in wings, flaps, tail and etc. Those parts of model actually are the main reason that flies to happend - even build them in incorrect way you will again reach the point of lift soon or later : ) it's just about to understand what you reading how to put in practice and how to use it...
ps..please let me be excuse if  my engilsh is not on level : )

[W.D. Roland]

Tania
[You can not stopped and concentrate only just in one dott (point of view) and ask why is happening like that and why not.]
Exactly
First sentence in thread:
[Several times in the recent past have mentioned that the Bernoulli principle does not account for all of the lift]
Although 5 years ago I 'believed' 100% Bernoulli principle did.

While laying there being miserable and distracting my self from that with thought....

Anyone aware of any work done on the temperature drop of the venture and/or same on airfoil?
How is the interface between surface and medium effected.....and so on

I have seen real world evidence on venture in use that would indicate that even at fairly low flow rates may be well
over 100deg F drop.

What is this doing to the density and viscosity of the near surface flow?

At a guess the largest temperature drop is near the 25-35% separation.

This is separate from temperature absorption from things such as fuel evaporation but includes humidity.

[Howard Rush]

Also during flight, virtually all wings are at a slight positive angle of attack, thus the air under them is being compressed, the air above is moving faster with lower pressure, just like the kite in Dales example..  The two airfoils facing each other were discovered to have a low pressure point where they are the closest, thus sayeth Giovanni Venturi. No joke his actual name thus the name for that devise we use on our IC engines.

The laws of physics are immutable. Ain't a lawyer alive can change them, nor any aeronatical engineer.

Go to our drawings of the three airfoils. Draw a line from the LE to the TE of the flap, on the boottom of the airfoil. See the induced undercamber. Thus the airfoil is no longer symetrical.

Ty, I don't think you can even spell aeronautical engineer.  No, for subsonic flow, the air under the wing is not compressed. 

[W.D. Roland]

Ty, I don't think you can even spell aeronautical engineer.  No, for subsonic flow, the air under the wing is not compressed.  

So a legitimate response in discussion might include 'the slower moving thus relative higher pressure......'  ??

Search engines are funky...found the following while looking for info on Temperature......

From NASA
[Such airfoils do produce a lot of lift and flow turning, but it is the turning that's important, not the distance.]
>(Great shades of Mr. Coanda! or sumpthin like that.)<

[Before considering what is wrong with this theory>(Bernoulli's equation)<, let's investigate the actual flow around an airfoil by doing a couple of experiments using a Java]

My Java is acting up so have not been able to watch video--yet. This will put me behind.
Think I know who the problem is...gota root em out.again.

http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html

Dale, this is put across at grade/high school level so I hope that helps! David

[Howard Rush]

W. D., I can't make out what your point is.  It sounds like you are trying to set us straight on how wings work, but your invoking the names of Bernoulli and Coanda suggests that you have some of the misconceptions that are rife in popular airplane culture.  Those two Web pages attempt to show how wings work without using math.  This is hard to do, because it seems that most people initially learned it wrong, so legitimate authors have to include in their explanation--which is hard enough anyway--a refutation of the balderdash.  One problem an author has in refuting the balderdash is to try to guess which incorrect explanation the reader has heard so the author can correct it.  It looks like you skimmed Scott's article looking for ammo to support your intuition and received balderdash, and thought you found it.  Had Scott anticipated your Coanda fixation as well as the more common equal-transit-time misconception, he might have picked a different way to introduce viscosity.   A second problem that authors who try to correct these misconceptions without math have is that they can't show how they know what they know.  Therefore, it's one guy's word vs. another's.  If you want to see proof, alas, it takes some math.  The way to tell whether your hypothesis about how wings work is correct is to see if you can use it to calculate anything.  If it can't predict quantitatively what wings actually do, it is at least useless, if not bogus.  

There's nothing elitist about this aero stuff.  I can't explain the Navier Stokes equations, but I can point you in the right direction.  You can get most everything online for free.  If you want it condensed into a book, I've posted some recommendations previously. XFoil or Javafoil will do airfoil calculations for you free.  As the designer of the current European and World F2B champion airplanes can tell you, this stuff is of use in designing a stunt plane.

To get a less abridged explanation of how wings work, Google Reflections of a Paleoaerodynamicist and take the fourth item that comes up. The title will be "Conceptual Design and Configuring Airplanes".  If the title goes on to say, "Thoughts on the design process and innovation", you've got the wrong article.  This is a little convoluted, but the URL I get is possibly Firefox-unique, and the author reused the title (and many of the pages) for various presentations.  The first 35 pages are pertinent.  After that, he goes on to other things.  The author is the late John McMasters, who was one of my teachers in school when he was a grad student.  I'm not sure if he thought I was a complete idiot, but I know he considered me to be on a lower plane of cognition somewhere.  John later came to Boeing, where he ultimately worked full time on engineering education issues.  I think Scott Eberhardt may have taken over that role at Boeing.

A good explanation at a fourth-grade level, as Dale says, is that the wing mashes the air down.  This is what Scott said in the Web page cited in the first post above. I sent that page (or an earlier version) to Alice Cotton-Royer for her elementary-school students, and I sent Scott's book, http://www.amazon.com/Understanding-Flight-Second-David-Anderson/dp/0071626964/ref=sr_1_1?ie=UTF8&qid=1330127907&sr=8-1 , to a sixth-grade nephew who asked how wings work.   Scott is a former chairman of the Pacific Northwest Section of the AIAA, so you know that he really knows his stuff.  

[W.D. Roland]

LOL Howard!
No, Im trying to get straight on the subject myself!
First post.[Several times in the recent past have mentioned that the Bernoulli principle
does not account for all of the lifta wing produces, especially flapped stunter type wings.]
Coanda is what I was trying to find a place for in our airplanes: Flaps.
Mostly rounding up all info I can, and attempting to understand it all at a higher level
than current.The more I have right and wrong the better.


Most of the rest may be irrelevant to anything or anyone, Burnt to a crisp and ready
for a nap.Rambling. May have to heavy edit in the AM

I More or less took your post as dismissing what I had posted.
Reminded me of the Tail moment arm(aero)thing...And I still say the method of hing line
to hing line is invalid  for comparison and design.
Doesn't help much with when some want to call the "Barbell' effect either.(Polar moments
inertia)

A side trip back in time.
The fact of the matter is that not many on this planet have much to say that is
meaning full.
What you say and think, to my mind is and has been important since about 1973?.
Original Reason( more since):
I had designed a combat plane with long tail moment around 1969/70(14years old)
Base on ideas I pick up from my Dad.
Man was it a hoot! the older combat guys convinced me it was to radical/hot/ jumpy/
what ever to fly in a match. My flying buddy, Tommy ( flew Sneeker/Fox)did have trouble
with doing less that 3 loops when attempting one. I thought is was just right myself.
Well base on local expert opinion off came the S.T. and on the top shelf the airplane went.

One Day Tommy comes a running with magazine(MAN?) in hand hollering " David, someone
stole your airplane!"
Sure enough there was my (yours)airplane on the cover!
Closer inspection revealed I used 1inch longer tail moment( from high point)
and a one inch shorter (from high point L.E.)with smaller elevator.
You we instantly my hero and the airplane came off the top shelf.
From that day on the little Kid in me says Howard rulez!

So now that I have been back to C/L long enough to figure out how to trim a PA(barely)
airplane its time to learn more aero stuff.
And like what I learn young from airplane was a tremendous help racing and experimenting
with Formula cars for 25 years(and didn't poke anyone's eyes out!) I find what I bring back
 from that a big help in my newest sport, C/L PA although with lots of gaps to fill in.


Like I posted earlier, I will go back and read the link you posted as well as finish and
reread other info, Internet, hard copy and anything else I can get my hands on that is
relevant to PA design.
If you would or could PM me or post any links you consider worth someones time
that would be fantastic.

My main interest currently is what is going on with flow and lift and drag
(cd?-worm hole in brain) at the Re range that we operate in and what changes are going on
 with our high lift sections before, during and after flap deflection. changes in pitching
would be use full as well.
So far I do not find much real work on our machines that fits so have been rounding up
ideas and opinions from various places. In other words so far the hard way has been the
only way.

I did find the tunnel smoke work on section with flaps very similar to our PAs...
Something is wrong with the work or it indicates magic may be involved.LOL!
The paper is on Trapped vortex flow and is by J.J. Cornish, Chief Engineer Loughead 1968(?).
Old and yellowed. will try to clean it up and post.

Please please, even if you don't like someone, if you take time to type a response why not
give some info with it! I always need practice at this as well.

My interest and always my time is dictated in living mad dashes between 48weekchemo rounds
Please excuse my 'attitude' that has developed. I do look forward to the new experimental drugs,
(its all experimental. LOL!) that gets added in a month and last till mostly dead and then finish
the 48. increases my chances of winning to a whopping 38%
And make a living at same time.

Believe me, all links from you get book marked.

David.

[W.D. Roland]

Howard
Comments from you on post #17 and the airfoils posted with flaps at 35deg would be appreciated.
Why #1 does not like flaps and why #3 is better than #2 in its use with flaps.

#3 is what repeatedly makes me want to go back to Coanda.
Thanks
David

[Tim Wescott]

Ha!  You guys are so naive.  Airplanes fly by magic -- that's why they're so much fun.

[Brett Buck]

Howard - I finally learned my lesson on Nov 16, 2003, at 05:30 AM. Different topic, same sort of problem. It's also why my "design" column went over like a lead balloon.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=74867&mesg_id=74867&listing_type=search#74932

   Brett

[Howard Rush]

OK, I looked up the references.  http://www.amazon.com/Fundamentals-Aerodynamics-Aeronautical-Aerospace-Engineering/dp/0073398101/ref=pd_rhf_se_shvl1 , although it costs an arm and a leg, is possibly the most readable aerodynamics textbook, but any aero textbook should have the nitty gritty.  A cheaper one is http://www.amazon.com/Theory-Wing-Sections-Aeronautical-Engineering/dp/0486605868/ref=pd_rhf_se_shvl1 , one of whose authors is George Aldrich's cousin.  You can compare your three airfoils free with Javafoil, http://www.mh-aerotools.de/airfoils/javafoil.htm , or cheap with Profili, http://www.profili2.com/ .  Profili contains XFoil and has a bunch of other stuff pertinent to modelers .  If you look for stuff on the Web or in airplane magazines, you'll get a lot of crap.  Remember the calculation test.

Comments from you on post #17 and the airfoils posted with flaps at 35deg would be appreciated.
Why #1 does not like flaps and why #3 is better than #2 in its use with flaps.

Try them with Javafoil.  Igor gives you a head start: http://clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=133808#133821 .

[fred krueger]

In his 2nd posting, Mr. Roland mentioned the work "How Airplanes Fly: A Physical Description of Lift".  A few years ago the Fermilab Barnstormers had David Anderson (one of the authors) as a guest speaker at one of our monthly monthly meetings.  Summarizing Mr. Anderson's comments in 3 words......."angle of attack"

Fred

[Tim Wescott]

Any time you travel through still air, it gets pushed aside and is in fact compressed.

Ahh, Ty.  How ironic that you recently posted a note to people to remember that when they come from mutually foreign lands, they should remember that words mean different things.

Yes, any time you change the pressure of a gas it's volume changes.

But in aerodynamics-land the word "compressed" and more importantly "compressibility" means something different.  Like many engineering disciplines, there's a distinction between situations where you can do the mathematical analysis using linear differential equations and situations where the equations become nonlinear.  In no situation that I know of is the use of linear differential equations actually completely 100% valid -- but in many, many situations (like subsonic aerodynamics) the errors introduced by assuming that the equations are linear are small enough to justify the assumption.

And, of course, Howard is speaking from aerodynamics-land.

What Howard meant when he said that the flow is "not compressed" was that "the speeds are slow enough that I can put on rose-colored glasses, solve some vastly simplified equations, and still get answers that mean something".  So when you're flying at 50 miles/hour, the dynamic pressure is about 360 pascals and the air pressure is about 100kPa -- so the dynamic pressure is about 0.4% of the air pressure, which means that the air compresses not much at all.  Howard, who is a trained engineer and therefore (probably) tends to have a blind spot about just how universally invalid the linearity assumption is, says the flow is "not compressed" when a stickler might say the flow is "so lightly compressed that I'm going to ignore it in order to preserve my sanity and get answers before I die of old age".

[Howard Rush]

Ha!  While I typed the following, Tim posted the item above:

 You may be using your own definition of compressed. The standard definition is to take a given volume of air and cram it into a smaller volume, such as an air compressor does.  It means that density changes, not necessarily pressure.  That sounds peculiar.  You'd think "compressed" would apply to pressure.  In subsonic, "incompressible" flow, density stays the same while pressure varies a bunch.  

[Tim Wescott]

In subsonic, "incompressible" flow, density stays the same while pressure varies a bunch.  

But (I would contend, having to contend with similar approximations in analog circuit design), that truly incompressible flow only exists on paper: in real life the air must compress at least somewhat, because that's what gas does when the pressure goes up.

I just checked: A 747-300 has a wing area of 5500 square feet, and a takeoff weight of 833,000 pounds.  That works out to about 1PSI average on the wings to keep the aircraft in flight.  So you're talking about absolute pressure differentials from sea level of over 10% in spots.  I'm not saying that this means you can't use the incompressible approximation quite effectively and profitably, just that it is, indeed, an approximation and not real, physical, truth.

It probably also explains why guys who do aerodynamics ends up using wind-tunnel data so often, even at "slow" speeds like 200mph.

[Igor Burger]

just small note ... lift (and also pressure) appears also in incompressible liquids    

[Igor Burger]

Tim, any real compression of fluid in which the airfoil makes the lift, will only limit its creation, if you carefully read where the lift comes from, then you will see that its compression will only damage all mechanics leading to lift  

however it is true that the air on the high pressure side of airfoil is little bit compressed, but the effect which Ty described is not hiting of "compressed air wall" it is simply dynamic pressure, so the same effect causing lift, but it has nothing with real compression in meaning higher density or harder stuff or something like that

[W.D. Roland]

Thanks Howard!

Just glancing at Igor and serge comments in other thread I assume there is a way to add flaps(at fixed deflection?) into the program X-FOIL? same for Javafoil?

I did get the Java for the NASA link up and running..Has my old Dell on the verge of mental breakdown.
It seems to run fine once its all up and running and finishes locking up the machine.

The NASA simulation was very helpful and understandably cleared up my misunderstand of the text with out the simulation.
I like the PSI and MPH readouts so that inches of fluid or FPS needs no conversion to what my simple mind relates to.
The pressure and velocity changes are well outside of anything I previously would have believed.
Would have thought pressure differences would be higher and velocity changes less.

Will try to swing acquiring both books you recommended.

Bad day today, back to bed.

Dale, Luke..Daughter called couple hours ago. Took Dad  to emergency room trouble breathing.
Latest report Blood/Oxy 82% pneumonia or congestive heart fail....testing.

Howard and others willing to 'argue' with until I see the light might be,
A tremendous Thank you!  
Never know what you don't know until you know it!

David

[Howard Rush]

Just glancing at Igor and serge comments in other thread I assume there is a way to add flaps(at fixed deflection?) into the program X-FOIL? same for Javafoil?

As I recall, both Javafoil and the Profili interface to XFoil include a flap function.  They bend the last however many percent of the airfoil you specifiy down by the amount you specify.  This doesn't tend to look like stunt flaps.  I wrote my own program to include the actual flap and hinge shapes we use.  Profili (or XFoil) barfed at those shapes.  I guess it abhorred the dents at the hinge line.  I then had it fair in the hinge line.  That worked.   

[Tim Wescott]

just small note ... lift (and also pressure) appears also in incompressible liquids     

True (and I won't even argue that water, hydraulic fluids & such will compress if you squeeze them hard enough).

Tim, any real compression of fluid in which the airfoil makes the lift, will only limit its creation, if you carefully read where the lift comes from, then you will see that its compression will only damage all mechanics leading to lift  

I wasn't arguing that, nor was I even arguing that one shouldn't assume incompressible flow when doing one's calculations, if that made sense.  I was just pointing out that "incompressible" flow is an approximation.  A darn good one at 50mph, perhaps, but an approximation none the less.

however it is true that the air on the high pressure side of airfoil is little bit compressed, but the effect which Ty described is not hiting of "compressed air wall" it is simply dynamic pressure, so the same effect causing lift, but it has nothing with real compression in meaning higher density or harder stuff or something like that

I think Ty is misunderstanding the actual pressure distributions at work, and he's obviously discounting the action of rarefied air behind things.  It'd be interesting to see a wind-tunnel picture of a car drafting behind a truck -- it might make things clear.

[Tim Wescott]

Just glancing at Igor and serge comments in other thread I assume there is a way to add flaps(at fixed deflection?) into the program X-FOIL? same for Javafoil?

You can use the "flap" function like Howard said, or you can just make an airfoil in the shape of your wing with the flaps bent (which is really what a wing with sealed flaps is, discounting the interruption of flow over the hinge line, and any mechanical compliance in the flap allowing the air to push the flap flat).

Javafoil will also simulate multi-element airfoils, so you can do biplane wings and slotted flaps and such weirdness.  I don't know if X-Foil will or not -- it's been a long, long time since I've messed with it, and it didn't when I was messing with it.

I've always gotten the feeling that simulating airfoils isn't something that you can do accurately as a dabbler: it's got to be worse than simulating analog circuits as far as the ease of getting convincing yet nonsensical results from the simulator, and I'm not enough of an aerodynamics engineer to know sense from nonsense.

[Howard Rush]

I've always gotten the feeling that simulating airfoils isn't something that you can do accurately as a dabbler: it's got to be worse than simulating analog circuits as far as the ease of getting convincing yet nonsensical results from the simulator...

Amen. 

I've always gotten the feeling that simulating airfoils isn't something that you can do accurately as a dabbler: it's got to be worse than simulating analog circuits as far as the ease of getting convincing yet nonsensical results from the simulator, and I'm not enough of an aerodynamics engineer to know sense from nonsense.

Neither am I.

[wwwarbird]

 Holy crap, we've got a novel upstairs. Like I said earlier, if it's got enough power it will fly. The wing is only a secondary consideration.   

[jim ivey]

I thought that also, till Imounted an OK 60 on a red brick. It just went round and round on the asphalt like a teather car. If I could have gotten it to fly, I was going to enter it in a novelty event.  jim

[wwwarbird]

I thought that also, till Imounted an OK 60 on a red brick. It just went round and round on the asphalt like a teather car. If I could have gotten it to fly, I was going to enter it in a novelty event.  jim

 That only proves the theory Jim, the OK 60 wasn't enough power for the intended application.

[Howard Rush]

Try it again with the long axis of the brick spanwise.  That maximizes the aspect ratio. 

[W.D. Roland]

To continue with Howards idea of flying a brick it might also be worth:
1-hand selecting the lightest brick on the pallet. there are some incredibly light weight fire brick as used in Kilns.
2-Dremel tool or mill/ drill lightening holes, radius edges fore and aft then cover with monokote.
3- Tip plates to help reduce span wise flow and reduce tip vortex drag. Plates, being round can be used for the wheels,
 weight and drag reduction. The lady of the house will not be happy even when she sees how good your results are.
offering to wash the dishes may or may not extend life.
4-K&B 6.5 Rat engine or similar. gobs of power for the size and weight.