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Q: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) ( Answered ,   11 Comments )
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 Subject: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) Category: Miscellaneous Asked by: bummer-ga List Price: \$50.00 Posted: 10 Dec 2002 19:57 PST Expires: 09 Jan 2003 19:57 PST Question ID: 122809
 I know how to figure the lift of a Cessna wing, 1/2 rho V squared and all that. How would I figure the lift on a large cambered wing with approximately 200 knots over the top and zero airspeed (ambient, 14.7 psi) underneath? I know it sounds goofy but humor me, I've got a plan. I expect this will require more exlpanation....
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) Answered By: krobert-ga on 21 Dec 2002 11:35 PST Rated:
 bummer-ga rated this answer: My question was not answered, but the discussion surrounding it was well worth the price.

 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: dansanswers-ga on 11 Dec 2002 02:38 PST
 I'm not exactly sure how this whole process works (i.e. - Google questions/answers), but just for your info, the lifting force on a wing is 2/3 suction (from the top) and 1/3 "pushing" (from the bottom). Therefore, it's my belief that if any part of your equation has a zero in it, there won't be much lift. One way of imagining it is to look at the top of modern cars or a race car. The roof is cambered to improve aerodynamics, but there is no lift (as far as I can forsee) from the roof. But then, what do I know... Dan Dalton, A.E.
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: bummer-ga on 11 Dec 2002 09:24 PST
 Dan, I'd like to know your source for the "2/3 suction, 1/3 push" formula. The conventional lift formula applies the coefficient of lift to the dynamic pressure (q) and multiplies that times the sq. ft. in the wing. I can do that. What I can't do is figure the coefficient of lift when I've got lots of air passing over the top of a (nearly) conventional wing, and zero airspeed underneath. Like..... blowing over the top of a sheet of paper... There's got to be a way. Kent
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: flajason-ga on 11 Dec 2002 10:20 PST
 There's a neat applet called FoilSim on Nasa's website that can be used to calculate lift on a number of different objects, speeds, cambers, etc. http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html I doubt it would be of much help to your current question as airspeed beneath the wing would be the same. Still you might find it useful for other applications. Just out of curiousity, are you planning on rotating a wing over a fixed surface? I can't comprehend how to get 200 knots over the top and 0 underneath?
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: bummer-ga on 11 Dec 2002 11:11 PST
 Visualize a flattenned bell shape with the "skirt" forming a large cambered, (Infinite Aspect Ratio) wing. Now picture a counterrotating (to zero out the torque) ducted fan mounted over it; the first stage brings air straight down, the second, counterrotating stage reaccelerates and redirects the air (approx 60 degrees)parallel to the lifting surface. Compare all that turbulant, high speed, low pressure air on top to the zero airspeed, stable, high pressure ambient air underneath. That has to produce massive amounts of lift, right? I've been working on this thing for a few years now. Have reached the point where I need a Devel's Advocate to explain what a really stupid idea it is, before I invest even more time and money in a project destined to fail. Then I can move on to the next dumb project. Thank you for your time Kent Vandervelde
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: flajason-ga on 11 Dec 2002 12:42 PST
 Pardon my ASCII art, but something like this? |////////| (Ducted Fan) | || | |\\\\\\\\| /----------------------\ /-----------------------------------\ (Airfoil)
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: bummer-ga on 11 Dec 2002 13:23 PST
 That's it, the "shell" has an aerodynamic shape. I bench checked it with a leaf blower and lifted it off the floor. Airspeed was 20 kts coming out of the nozzle and 15 off the bottom of the the skirt. Understanding that lift varies with the square of the airspeed, 200 kts should generate a lot of lift. I've missed something I'm sure, but damned if I can figure out what. Kent
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: jickster-ga on 11 Dec 2002 18:00 PST
 Do you have any drawing/photo/mockup of the device in question? I ask because I'm at the cusp of understanding what you're talking about, but I'm still slightly behind the point of comprehension. Post links if you do... this question intrigues me. Jickster-ga
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: bummer-ga on 12 Dec 2002 20:06 PST
 Yes I have drawings/pictures/mockups. Don't understand "post links if you do." I scanned a couple drawings onto a floppy, would like to email them to you but am not sure how... will see if "post links" helps. Let's not let this question "time out." I badly need some definitive answers.
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: jickster-ga on 13 Dec 2002 17:50 PST
 My apologies for being obtuse... I was hoping that you might have had the photos available on a website, or could make them available and list an web address for where they could be seen. Unfortunately, if I remember correctly, the rules that govern Google Answers researchers prohibit us from providing direct contact info for ourselves. If you can make your pictures or drawings available on a website, please place a comment or clarification with their address. If not, I'll just have to squint at that ASCII art a bit harder :) jickster
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: charles75-ga on 16 Dec 2002 00:30 PST
 This discussion is as old as aerodynamics itself, What about a wing that is equally curved top and bottom like a fighter plane and a stunt plane. It has always been an argument between Newton principal and Barnulies principals. Newton says for every action there is an opposite reaction. Lets look at an aircraft on a takeoff roll with cemmetrical wings, and zero wind conditions. As the speed increases the air moving over the top and the bottom of the wing is traveling the same speed. When the pilot raises the nose of the aircraft it increases the angle of attack, and the air on the bottom of the wing has more pressure than the top of the wing, due to the relative wind, thereby lowering the pressure on the top of the wing. The air on top of the wing is being diverted due to the increased angle of attack and has to travel further and faster to met the air on the bottom of the wing. This is where Barnulies principal comes to play. I don't think I spelled his name right, but I think you know who I am talking about.
 Subject: Re: Incompressible Aerodynamics (I need a professional aerodynamicist for this one) From: bummer-ga on 16 Dec 2002 18:27 PST
 I do indeed know what you're talking about. Still I believe raising a sheet of paper by blowing over it successfully marries Newton and Bernoulli (sp?). All of which begs the question - how can I predict the lift of a wing that has lots of air over the top and zero airspeed underneath? I'm coming to the realization that nobody can - so - I've been talking to the "Kirston Wind Tunnel" people at the U. of WA. Am going to take a couple of my airfoils in to see if they can jury rig the airflow over (parallel to) the lifting surface on my 360 degree circular wing. It'll cost \$500 to "rent" their small, slow wind tunnel equipment for a day. Hopefully that will prove or disprove the viability of the idea. It will be worth \$500 to get this monkey off my back. Am anxious to either fly this unmanned lifing platform or trash it and get on with the next dumb project. Please weigh in if you comments, criticism (constructive or otherwise) questions, better ideas or whatever. I love Google a lot but this may not be the best venue for this discussion. Thank you for your time