Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Airfoils

Reply

Old 12-02-2001, 07:47 PM
  #1  
mvigod
Thread Starter
 
mvigod's Avatar
 
Join Date: Nov 2001
Posts: 14,189
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

I start things off here with a basic airfoil question I was always curious about. With an airfoil lift is created because of the different speed at which the air flows over the wing and thus creates lift. Correct me if this is wrong.

Question is with a fully symmetric airfoil wouldn't the air flow over the wing top and bottom exactly the same and thus cause the same forces above and below it? If this was the case how would upward lift be created with a fully symmetrical airfoil?
mvigod is offline  
Reply With Quote
Old 12-02-2001, 10:40 PM
  #2  
Hossfly
 
Hossfly's Avatar
 
Join Date: Dec 2001
Location: New Caney, TX
Posts: 6,130
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Re: Airfoils

Originally posted by RCadmin
. With an airfoil lift is created because of the different speed at which the air flows over the wing and thus creates lift. Correct me if this is wrong.

Question is with a fully symmetric airfoil wouldn't the air flow over the wing top and bottom exactly the same and thus cause the same forces above and below it? If this was the case how would upward lift be created with a fully symmetrical airfoil?
<<<<<<<<

The Lift formula is L = CsubL x 1/2 (Vsq. x air mass density x area).
CsubL is Coefficient of Lift or basically Angle-of Attack (AOA).

While lift increases by 50% of the square of the airspeed, it also requires some positive AOA. In any case there must be some outside force to hold a wing in that positive AOA. In conventional aircraft within subsonic convergent airflow that is normally the function of the horizontal stabilizer. Some near imperceptible "up" is applied providing a negative lift of that airfoil (the stab) which then forces the wing into some near imperceptible or more AOA.
AOA is measured between the oncoming airflow versus the wing chord line. Important to notice that a Clark Y (flat bottom airfoil) can produce lift in what appears to be negative AOA -- referencing the bottom of the wing -- as the chordline is actually NOT the bottom but up in the curve of the Leading Edge.

A pilot cannot well control airmass density, other than altitude as Nature determines that. Other than with flaps, etc., a pilot cannot control area as that is a given with his craft. A pilot CAN control AOA of the various lifting surfaces and he can control velocity, the airspeed.
If RCers could actually understand these functions, I predict that 70% of the crashes would not happen.
1. Each surface is an airfoil, and moving/changing that airfoil changes the lift/force arrangements around it. "Lift" is not just a product of only a wing.
2. A certain amount of velocity is required to maintain smooth airflow to produce some desired result. Keep the airspeed up.
3. AOA can be increase to a point that produces turbulent air wherein all force vectors (lift) may well disappear. This point is not a factor of velocity. Yes, you can high speed stall a wing. Done it many times in the 1:1 scale as well as RC.
4. Drag uses the same formula. More speed = more drag and more AOA = more drag. Learn to use the power to maintain glidepaths.
5. Lift is NOT a function of Bank Angle, as the most popular myth in aviation so promotes. Bank angle is a vector function of lift.
If you wish the wing lift function to keep you away from the solid earth, then place the wing to a position to best use the perpendicular function of the lift vector. You may not then need to increase AOA up to the point where it removes itself from the equation. "Stall, Snap, Spin, unintentionally.

Enjoy
Hossfly is offline  
Reply With Quote
Old 12-02-2001, 11:44 PM
  #3  
Walt-RCU
Junior Member
 
Join Date: Dec 2001
Location: Coolidge, AZ
Posts: 16
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

A good column by Art Hood "Large Model Basics"
in the January 2002 issue covers this subject
very well.
Walt
Walt-RCU is offline  
Reply With Quote
Old 12-05-2001, 01:31 AM
  #4  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Put your hand out the car window...That should explain things...
Brian-RCU is offline  
Reply With Quote
Old 12-05-2001, 04:42 PM
  #5  
maverick
Senior Member
My Feedback: (12)
 
Join Date: Nov 2001
Location: Alameda, CA
Posts: 1,575
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

I asked this exact same question on RCO quite a while back and the general consensus was the list was generated by the angle of attack.
maverick is offline  
Reply With Quote
Old 12-05-2001, 04:56 PM
  #6  
greg-RCU
Senior Member
 
Join Date: Dec 2001
Location: Gibsons, B.C.
Posts: 123
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Lift...

Lift is NOT created by a difference of airspeed over the top vs bottom of a wing. Common misconception. Definitly that would create lift (or at least a preasure difference). For airplanes that's not what does create lift.
As Brian points out so adequately, your hand, or even a flat plate will fly. Try handling a sheet of plywood in a good wind. What creates the lift is the angle of the wind hitting the flat part of your hand, or that plywood, so that it is 'blown' back and up.
The back part is called Drag, the up part is Lift and the angle is called Angle of Attack.
Airfoils are designed to ballance (not always maximize) the Lift and Drag at certain Angles of Attack. As Hossfly explained, non symmetrical airfoils create lift at zero or even small negative angles because the angle is measured from a line between the leading edge and the trailing edge not the aerodynamic center line.
greg-RCU is offline  
Reply With Quote
Old 12-05-2001, 04:59 PM
  #7  
greg-RCU
Senior Member
 
Join Date: Dec 2001
Location: Gibsons, B.C.
Posts: 123
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Nice pic Maverick
greg-RCU is offline  
Reply With Quote
Old 12-05-2001, 07:54 PM
  #8  
maverick
Senior Member
My Feedback: (12)
 
Join Date: Nov 2001
Location: Alameda, CA
Posts: 1,575
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

That is Maverick flying off into the sunset in his F-14 Tomcat!
maverick is offline  
Reply With Quote
Old 12-06-2001, 08:44 PM
  #9  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Marc, considering you fly Heli's (like you said on RCW) how could you not know this?

I am starting to wonder...
Brian-RCU is offline  
Reply With Quote
Old 12-06-2001, 09:09 PM
  #10  
mvigod
Thread Starter
 
mvigod's Avatar
 
Join Date: Nov 2001
Posts: 14,189
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Brian,

I'll admit I am far from being an RC expert. More than half the people in this hobby and probably more know alot more than me. I do however know how to fly planes rather well and heli's not quite as good yet I don't know all the dynamics that go into why they do what they do. I do some some of it but I won't claim to know it all.

Seems like your real cautious about me for some reason. It appears like your looking to find some reason why this site isn't good or going to continue to be good. No one, including me, is going to force you to visit here. I will only make sure this site is as good as it can be and if you decide to frequent it that's great. If not, then there is nothing I can do about it.

I have no affiliation to any other sites. I don't come from another site. Don't know anyone at the other sites. I do know I wanted to buy a couple planes this year and it was the most frustrating experience I ever had so I made RCUniverse. Trust me, if your looking for something bad or a hidden agenda I guarantee you will not find one and I don't care how hard you look. Do you yourself own a site and are threatened by this one somehow? I can't figure out why you care so much.

So please stop second guessing me, my motives and such and just enjoy the site. If you don't want to moderate let me know and I can remove that. If you want to stay on board that is fine with me but understand this is a site for RC users, nothing more, nothing less. Use it, enjoy it and have fun for god sake.

Marc
RCadmin
mvigod is offline  
Reply With Quote
Old 12-07-2001, 12:19 AM
  #11  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

I am not trying to find some reason why this site isn't good or isn't going to be...I love this place! Makes me feel better about being on dial-up...

I just questioned what you said because it seems a little hard to fly heli's and and not know how a fully symmetrical airfoil creates lift...What kind of Heli do you have?

You said you were thinking of buying a few planes, what were you considering?
Brian-RCU is offline  
Reply With Quote
Old 12-07-2001, 12:33 AM
  #12  
greg-RCU
Senior Member
 
Join Date: Dec 2001
Location: Gibsons, B.C.
Posts: 123
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default questions!

Heck Brian, I figured he asked just to get some responce happening and the board posts up. Only reason I added to your responce.

Had a real pointless but fun thread going on that other place some months back about flight dynamics in a null or microgravity situation. - does a plane trimed to fly level in gravity accelerate up indefinitly if you remove the gravity? I ended up getting a couple guys in the vanpool BSin on the topic. The women in the vehicle had the usual conniptions when they actualy get forced to listen to a guy conversation. - Your wife ever ask you why you don't talk anymore?
greg-RCU is offline  
Reply With Quote
Old 12-07-2001, 12:43 AM
  #13  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

"does a plane trimed to fly level in gravity accelerate up indefinitly if you remove the gravity?"

I think the airplane will NOT accelerate up...Gravity is one of the 4 forces you have to have for something to fly...If you take one away, well...No flight. When theres no Gravity, what is considered "up"?
Brian-RCU is offline  
Reply With Quote
Old 12-07-2001, 01:09 AM
  #14  
mvigod
Thread Starter
 
mvigod's Avatar
 
Join Date: Nov 2001
Posts: 14,189
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Originally posted by Brian
I am not trying to find some reason why this site isn't good or isn't going to be...I love this place! Makes me feel better about being on dial-up...

I just questioned what you said because it seems a little hard to fly heli's and and not know how a fully symmetrical airfoil creates lift...What kind of Heli do you have?

You said you were thinking of buying a few planes, what were you considering?
Brian,

In that case I apologize for jumping all over you. With some of the posts you made recently I was wondering what your state of mind was. Glad to have you on board.

I sold my Excel 60 awhile ago as it scared the heck out of me after a year of flying that and picked up a Kyosho ep to toy with in the backyard for now. I knew that airfoils created lift but the visualization on the symmetrical thing made me wonder. The poster above made it nice and clear how this all works (thanks).

Well, I was buying planes over the summer and ended up with my Extra 300 and Cap 232. Love them both. Now I'm looking at an Ultimate Biplane (Dave Patrick maybe) and a fun fly model. I fly some of the ff's on RealFlight G2 and they seem like they would be lots of fun and I've never had one. Also a Stearman is an interesting one too. I want to get a bigger bipe. I had an old Ace All Star Bipe (.15 Magnum in it) but it was too small and squirelly.
mvigod is offline  
Reply With Quote
Old 12-07-2001, 01:14 AM
  #15  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Most of the people that have known me for a while know how much I like Somethin' Extras. If you are looking for a great sport airplane that will do insane aerobatics and even 3D manuevers, get one! The kit is the best you will ever see too...I have had two of them, BTW.

The Dazzler is another one I would recommend, just as good as the SE, but it is lighter so it has much better vertical performance. It doesn't look as good as the SE though...

I am building a Tower Hobbies Extra Special, which I hope I can recommend in a few weeks...
Brian-RCU is offline  
Reply With Quote
Old 12-07-2001, 01:25 AM
  #16  
mvigod
Thread Starter
 
mvigod's Avatar
 
Join Date: Nov 2001
Posts: 14,189
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Originally posted by Brian

I am building a Tower Hobbies Extra Special, which I hope I can recommend in a few weeks...
The Somethin' Extra I have also heard great things about. The Dazzler is on the G2 simulator and the reason I started to look at ff's.

Keep us posted on that Extra Special. Since you have had them all you can make a good recommendation although any of the 3 I have the feeling are seriously FUN!

Marc
RCadmin
mvigod is offline  
Reply With Quote
Old 12-07-2001, 04:11 AM
  #17  
maverick
Senior Member
My Feedback: (12)
 
Join Date: Nov 2001
Location: Alameda, CA
Posts: 1,575
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Somethin' Extra!

I am building a Somethin' Extra right now. It is my first kit and I am enjoying every minute of it.

If it flys half as well as it builds it will be a winner.

I can't wait!
maverick is offline  
Reply With Quote
Old 12-07-2001, 04:14 AM
  #18  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

It will fly 2 times better then how it goes together..

What engine do you plan on using?

If you ever have any questions about it, let me know. I have had more experience with them then I would like to admit...
Brian-RCU is offline  
Reply With Quote
Old 12-07-2001, 04:51 AM
  #19  
maverick
Senior Member
My Feedback: (12)
 
Join Date: Nov 2001
Location: Alameda, CA
Posts: 1,575
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

I'll be using an OS .46FX with hopefully an APC 12.25 x 3.75 if I can find one anywhere!

Is the landing gear going to be long enough to give clearance for this prop?
maverick is offline  
Reply With Quote
Old 12-07-2001, 12:44 PM
  #20  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Get some 3 inch wheels and you should be fine...

A lot of people have been getting that TNT landing gear for them, but I never did. I flew off grass and used one for almost every flight. You don't have an option when it comes to 3 pointers though...You could always use a 12x4 if you have to...
Brian-RCU is offline  
Reply With Quote
Old 12-07-2001, 04:13 PM
  #21  
maverick
Senior Member
My Feedback: (12)
 
Join Date: Nov 2001
Location: Alameda, CA
Posts: 1,575
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

Would a 12 x 4 be good for hovering?
maverick is offline  
Reply With Quote
Old 12-08-2001, 04:42 AM
  #22  
Brian-RCU
Banned
 
Join Date: Dec 2001
Location: Kansas City Missouri
Posts: 21
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

The next best thing after a 12.25x3.75!
Brian-RCU is offline  
Reply With Quote
Old 12-08-2001, 03:41 PM
  #23  
Ollie
Senior Member
 
Join Date: Dec 2001
Location: Punta Gorda, FL
Posts: 958
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Lift

A wing passing through air produces lift by deflecting air in the opposite direction from the direction of lift. The component of the down wash behind the wing that is in the opposite direction from the lift is the velocity of the air that has been accelerated from rest, before the wing passed. The lift force is the mass of the air deflected times the acceleration produced by the passing of the wing.

The flow of the air around the airfoil the mechanism which produces the acceleration opposite to lift. Bernouli’s principal is part of the explanation for the behavior of the flow around the airfoil.

In the case of a symmetrical airfoil operating at a positive angle of attack, the stagnation point, where the flow seperates to go over and under the airfoil, is below the nose of the airfoil. As a result the flow over the top goes back and around the nose of the airfoil before proceeding over the top surface. In the case of a flat plate, at an angle of attack, the stagnation point is somewhat aft of the leading edge.
Ollie is offline  
Reply With Quote
Old 12-08-2001, 04:53 PM
  #24  
kriegsmacht
Senior Member
My Feedback: (12)
 
kriegsmacht's Avatar
 
Join Date: Dec 2001
Location: Castle, OK
Posts: 171
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Zero G plane

I say the plane in zero gravity would climb continuously. Imagine the plane was flying over land at an altitude of 1000 feet. Suddenly it flew over a barrier and gravity was 1.5x normal. In order to hold the 1000 feet altitude, the pilot would have to nose up slightly and trim for a new angle of attack, and apply more power to counteract the extra drag.

Then the plane passed over a barrier that caused it to experience .5 normal gravity. The plane would zoom up suddenly and to hold the 1000' altitude the pilot would push the nose down, and reduce power.

Now finally it flew into a zone where there was zero gravity. The plane would once again climb, unless the pilot pushed the nose down more into a zero-angle of attack. You would only need minimal engine power to keep the plane moving. But at the original normal-gravity power and main wing AOA settings you could imagine the plane would be climbing at a steady rate.

Of course if it were zero gravity, eventually the atmosphere would dissapate into space anyway, so...
kriegsmacht is offline  
Reply With Quote
Old 12-14-2001, 04:13 AM
  #25  
ftomteen4cat
Member
 
Join Date: Dec 2001
Location: Chicago, Illinois
Posts: 91
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Airfoils

"does a plane trimed to fly level in gravity accelerate up indefinitly if you remove the gravity?"

greg - interesting question. i'd say no. there is a drag component to every axis of motion. eventually the lift force and drag force would stabilize, just as a bubble released underwater reaches a terminal velocity, or an object falling from the sky.
ftomteen4cat is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service