What's my strategy?

OK, suppose I can control the high point of my CL Stunt wing airfoils, and can have a different airfoil at the Root and Tip of the wing panel.

Do I want the Root airfoil to have its high point further aft (say 30% of its chord length) and the Tip airfoil have its high point further foreward (say 22% of its chord length)? Or vice versa?

Or do I want both Root and Tip airfoils to have their high points at the same % of chord points?

Why or why not?

Same question for % thickness at Root and Tip?

Thanks kindly in advance for discussions.

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I went into this bar and sat down next to a pretty girl. She looked at me and said, "Hey, you have two different colored socks on." I said, "Yeah, I know, but to me they're the same because I go by thickness." -Steven Wright

>OK, suppose I can control the high point of my CL Stunt wing
>airfoils, and can have a different airfoil at the Root and
>Tip of the wing panel.
>
>Do I want the Root airfoil to have its high point further
>aft (say 30% of its chord length) and the Tip airfoil have
>its high point further foreward (say 22% of its chord
>length)? Or vice versa?
>
>Or do I want both Root and Tip airfoils to have their high
>points at the same % of chord points?
>
>Why or why not?
>
>Same question for % thickness at Root and Tip?
>

I was always taught that you wanted a slightly thicker airfoil at the tip. That way if it stalls, it will stall at the root first. (Well, it works on big airplanes with ailerons. Don't see why it wouldn't help on ours.) I don't know why you would want to change the airfoil, however.

do neither. Get copies of Igor Burger's flapped airfoils. Use those. Or copy Al Rabe's airfoils. Al came up with the idea first, and Igor refined it with computers. Fortunately model planes aren't too fussy about airfoils, so you won't go far wrong using something similar to what has gone before.

LAST EDITED ON Feb-10-04 AT 10:31 PM (CDT)
 
>OK, suppose I can control the high point of my CL Stunt wing
>airfoils, and can have a different airfoil at the Root and
>Tip of the wing panel.
>
>Do I want the Root airfoil to have its high point further
>aft (say 30% of its chord length) and the Tip airfoil have
>its high point further foreward (say 22% of its chord
>length)? Or vice versa?

Well, it depends on the root-tip chord relation and if you want the "hight point" line to be swept back or what.

>Or do I want both Root and Tip airfoils to have their high
>points at the same % of chord points?

If tou want the so mentioned "high point" to run paralel to the LE, i figure t you do.

>Why or why not?

darn.... now ya got me

>Same question for % thickness at Root and Tip?
>
I think I read about this, but I can't remember. If you can get together a list of these numbers on some well know ships I wouldbe interesting.

Ion

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Larry,
Allen Brickhaus taught me to have the tip rib thicker by 2-5 % and the the high point forward by 5% too as compared to the root rib. I think it keeps the tips flying while the rest stalls. Of course we never stall our planes doing our tricks! I have to admit, I've followed his advice and have some very good flying airplanes. Looking at the Impact and T. P. plans it looks like the HP are the same %. I haven't measured the tip thickness to tell if they are thicker too. For what it's worth....

Larry,

And what about an elliptically curving high point that follows the LE in some sort of relationship on an elliptical wing? Hmm....

You're MEAN, Randy!

Previously, StuntRib interpolated between Root and Tip along lines which are the same percentage of chord of each. It made sense, particularly when the Root and Tip airfoils had their high point at the same % of chord (e.g. NACA00XX at 30% of chord). However, now that I can move the high points of each independently, I wondered if this would still hold up.

An alternate scheme would interpolate along equal percentages of the fore and aft portions of the airfoil (fore and aft of the high points).

I'm going to have to draw up some extreme cases to see which might be better, but I suspect I'll stick to the % of chord lines.. My mind can visual possible unexpected distortions with the latter.

I went along with the "stall tips last" idea which would suggest a thicker % on the tip and/or moving the high point a little forward. But I wanted to hear it from others.

I had the {subjective) viewpoints of more than one person that the ships with thicker tip airfoils flew a little better.

Randy, the old StuntRib currently supports both linear and elliptical interpolations of airfoil heights. But I'm pretty sure the % of chord lines of an elliptical planform will yield a high point line that is elliptical, just like the LE of the wing.

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"Before you criticize someone, walk a mile in his shoes. That way, if he gets angry, he'll be a mile away - and barefoot." -Jack Handey

LAST EDITED ON Feb-11-04 AT 10:06 PM (CDT)
 
Larry,

An alternate scheme would interpolate along equal percentages of the fore and aft portions of the airfoil (fore and aft of the high points).

What about a system that takes into account a decreasing percentage high point measured from the leading edge? Hmm, not sure how to describe that more clearly. Sort of a curved line that starts at the root high point and curves elliptically, following the leading edge but with a decreasing curve that move closer to the LE at the tip. Ah, still not really describing it, but you get the idea.

Randy, the old StuntRib currently supports both linear and elliptical interpolations of airfoil heights. But I'm pretty sure the % of chord lines of an elliptical planform will yield a high point line that is elliptical, just like the LE of the wing.

So, it will likely happen anyway...COOL!

Larry...

Good to see you thinking wierd stuff again!

You may recall my ATAVISTS? #1 had far less taper than #2, and was otherwise as near identical as any models I've ever built. Both even weighed 49 oz, tho one was built-up wing and the other foam. The foamie had an OS 40 FSR-S and the other a big-case Fox 40BB...

The higher tapered one was loose in roll in level flight in choppy air. The airfoil was NACA-equation-developed 4 digit at the same % root to tip... Since, I've had better results with the tip airfoil developed to the percentage that yields half the thickness-difference that the same percentage would give. Saay, whuh?

If a 12" root chord @ 20% were 2.4" thick, an 8" tip chord would be 1.6".
Difference between the two thicknesses is 0.8". Change the tip airfoil so that the max tip rib depth is 2.0" (1.6" + half of 0.8").

I "ruled" the airfoil surface, using the same high point %location.

Does anyone really believe they can detect, much less evaluate, the effects of exotic high-point lines? There may be more gained from enlarging LE radius toward the tip, than by playing with thickness percentage, anyway...
All good fun, and all the best to you, sir!

Hi Lou,

Actually, Randy's questions have made me realize that I'll have to come up with a little more sophisticated system for interpolating rib contours for the elliptical planforms..

Good memories stirred about the Atavist - I remember looking it up to see what it meant! Hahaha. I also remember destroying 2 or 3 of your hand-whittled props trying to launch for you at Tucson - sheesh, I'm still sorry about that..

I'm guessing you're still as onery as ever? Maybe worse?

Take care, Lou!

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"I'd rather regret the things I have done than the things that I haven't." -Lucille Ball