airfoils again

Is the flap a part of the airfoil? If I use a NASA 63 section as suggested in th previous thread on a wing with a 12" overall root chord with 2" flaps, do I base the section on the 10" of the wing without the flaps, or the 12" with flaps included. If I move the hight point to 28% is this of 10" or 12".
I used Berringer's section on my last plane and the flaps blended into the curve aft of the HP, the LE of the flap was almost 3/4 " thick, while mostothers form a reflex curve, and the flaps are much thinner??? Which way should I go?

> Is the flap a part
>of the airfoil?

Yes.

It's literally doing some of the "heavy lifting" at zero degrees deflection. Earning its pay.

And don't forget that a Reynolds Number calculation starts with a chord length value. And please don't mention to the flap that it's not a part of the chord. It would be very angry. Might separate from the elevator pushrod in protest. But enough already...

This question is a classic CL FAQ.

Flaps: the Rodney Dangerfield of model aerodynamics. They just don't get no...

> Is the flap a part
>of the airfoil?

Currel has it right, the flap is considered as part of the total chord legnth.

>If I use a NASA 63
>section as suggested in th
>previous thread on a wing
>with a 12" overall root
>chord with 2" flaps,
>do I base the section
>on the 10" of the
>wing without the flaps, or
>the 12" with flaps included.
> If I move the
>hight point to 28% is
>this of 10" or 12".

I use a section long enough to give me the right legnth including thickness at the flap hinge line. I realize this makes the actual thickness somewhat less than the percentage of the airfoil, but it seems to work fine for me.

> I used Berringer's section
>on my last plane and
>the flaps blended into the
>curve aft of the HP,
>the LE of the flap
>was almost 3/4 " thick,
>while mostothers form a reflex
>curve, and the flaps are
>much thinner??? Which way
>should I go?

For a true airfoil section, Berringer's doing it right, but, it's been my experience that the normal practise, which gives a reflex section, works for most of us, and is easier and often lighter to build. I don't believe there's a huge amount of degradation happening by going that way.

There's also this to consider.

At least one writer, I wish I could remember who, has written that the standard method of attaching the chord extensions on a non-flapped ship, resulting in a reflexed section, act, for a brief moment, like deflected flaps usually at ~15 degrees when the plane is manuevered. If this is true, then for a very brief moment, as your plane pitches, it will have ~ 15 degrees more flap than it actualy has, right at the moment of pitching, where it might be most needed. After that brief moment, the percieved deflection will settle in to ~ the amount the the flaps are actually deployed.

You might want to consider your needs and skill level in making the choice between flap styles. I believe it would be interesting to build identical ships each incorporating one of these considerstions for comparison. The trouble is that in the real world, few of us have the time and rescources to make this type of comparisons.

I just read my previous posted reply, and realized that I made an error. The writer I reffered to estimated the "percieved flap throw achieved was ~ 7 degrees, not 15.

John,
I don't have your e-mail of physical address, so I sent it to the only John Miller in the PAMPA Guide at Magna UT
Al

Thanks Al, That will get to me fine. I'm looking forward to studying your work.

Al Rabe did some experimentinng on this subject a number of years ago so we don't need to reinvent the wheel. The flat flaps work better when deflected! If you build the wing with the flaps as part of the airfoil, you will lose lift with deflected flaps. Al scrapped a plane he was building after doing the experiments. The flat flaps are not only easier, they are the way to go. (Check his "Go For Broke" article on the Sea Fury.)

Leonard Neumann

Thanks for the reninder about Al's work. I've never had the chance to read any of his work so wasn't aware of his findings.

His findings about the difference between flat flaps and the continuation of the airfoil shape, kind of supports the idea that a reflexed foil shape has the advantages suggested by that other author whos name I can't remember.

In any case I prefer them because they are much simpler to build and use.

Jim and John
Quite the contrary. I do not believe that reflexed airfoils are optimal for stunt. As a Result of my airfoil tests I believe that the best airfoil for stunt has a significant curvature aft of the spar to continue the curvature of the wing into the deflected flap. I called this a "profliled" airfoil. I published airfoil data in the Go for Broke article based upon running tests at our reynolds numbers by running a 10" airfoils plus 2" flaps at 20-60 MPH. If you are interested in the information I can send a Xerox copy of the article. I think optimum results will be had with 22-25% profiled airfoils with moderate leading edge radius (fairly sharp 7/8" radius). I use flaps which are about 1/3 the width of the chord (about 3" at the root and 2" at the tip). It is not necessary to go to these extrems as most builders use a large excess of wing area and lightly deflected inefficient flaps. Any flap or no flap at all work just fine when the wing isn't loaded. The profiled airfoil is intended to work its best when the wing is loaded and the flap deflected. I try not to disrupt the airflow over a loaded flap by having a discontinuity at the flap hinge line. A reflexed airfoil magnifies thes discontinuity.
Al

Al, Thanks for jumping in here with your comments and clarification. First let me tell you that I am pleased to meet you and admire what I have heard of your work with our models.

What I am refering to as reflexed is, if what I understand is correct, very similar to what you have described. The NA63a modified airfoil is very similar to what you are describing. It has a smaller radiused entry. The modification involves moving the high point forward to ~ 26-28%. The curvature continues behind the high point to the flap attachment point. The flaps are tapered, 3/8" at the hingeline, tapered to 1/8" at the trailing edge. So, the reflexig I refered to only occurs in the flap area, vis, the flap does not continue the shape of the airfoil.

This isn't a true reflexed section as I understand it, rather a point, at the hinge line where there is a departure from the airfoils shape.

Is this in line with your findings?

I agree with you re. lightly loaded wings and flaps, and am one of those who never had the need to gain optimum efficiancy from a smaller wing as you have with your outstanding designs, so I am in new, to me, territory.

Lastly, I would welcome a copy of your article. I've been told that there is a wealth of information there, and like most of us, I feel I could benifit from studying your work.

John
the whole idea of using a "profiled" airfoil is to avoid a departure from the airfoil's shape at the hinge line when the flaps are deflected (working).
Al

Al --

Wow! Would really send the article? My fax is 540.289.7010. Or snail mail to:

Larry Fulwider
1180 Jacob Burner Dr.
McGaheysville, VA 22840

Or attach to an e-mail to [email protected].

Thanks!

I notice an online copy of another Rabe article

http://www.iroquois.free-online.co.uk/rabe.htm

on the evolution of his Mustang stunter.

Igor Burger's website presents Igor's "ultimate" PA airfoil and some data that others may find interesting. What got me was that Igor's new ultimate airfoil is VERY much like Al Rabe's. Both types of flaps are shown and discussed, also. And you can buy foam wings & stab/elevators with various airfoils, as well as other objects d'Stunt. http://www.netax.sk/hexoft/stunt/notes.htm is the URL for the airfoil data page, but check the home/main page for the index and check it thoroughly. Good website! I recall seeing Mr. Rabe flying his first Bearcat (I think) at the Sandpoint NAS Regional Contest in May, late '60s or so. It was blowing a gale, and the Bearcat looked good in the wind. I believe Al placed 1st. Steve

Same article printed in Flying models in 1978 and reprinted in Stunt News last year
Al