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Old Jul 30, 2010, 04:10 PM
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MentalDekay's Avatar
erie pa/grand rapids mi
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Tip Dihedral

Looking at the attached file...

If everything else is the same (airfoil, span, chord, etc), what is the difference in terms of lift, drag, efficiency, stability between the wing on the top and the wing on the bottom??

I've made a Piper Cub from Comet's plans. They (generally) have the modeller construct wings to look like the bottom example even when at full scale the wing is more like the top example. Their Monocoupe designs do this too, whereas Sig's Monocoupe doesn't (the real Monocoupes and Sig's both using the top wing shape).

From a construction point of view, Comet's wingtips are probably a little easier to build. But if it only takes 10 minutes to do it IAW the full size wing, and there are definite performance benefits to its shape, then I'd gladly spend that 10 minutes.

Anyone?

-des
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Old Jul 30, 2010, 04:19 PM
one flew
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erie pa/grand rapids mi
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...if I wasn't so lazy/cheap I'd get this SAE paper (looks to hit the topic right on the nail)

Influence of Wing-tip Dihedral and Planform on Induced Drag

-des
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Old Jul 30, 2010, 11:09 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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Well anything that angles the tip up like the upper example is going to aid the dihedral issue. Is it enough to make a difference? I'd have to say yes. But it would be a small difference.

Years ago a buddy built an early electric racer/sport model with a low aspect ratio wing and the tips were as per your upper diagram. No other dihedral other than the rather large tips angled up the the flat upper surface just as you show. Yet it was a rudder and elevator controlled model with no ailerons. It was also a fairly small section fuselage with the wing shoulder mounted.

He was pretty new to flying at the time and didn't trust himself with it so flying duties fell to me. It flew OK if not spectacularly. The rudder roll response was fairly weak but positive nonetheless. But as you would expect with those tips acting the way they did there was a positive rolling action to yaw only when the wing was lifting in a positive way. If I went to a long pushover sort of like a low to zero G arc then applied rudder it would yaw only with no roll at all. Same with inverted flying. No rolling action at all. Just yaw.

YET.... if I fly a model with regular dihedral it will respond to rudder induced yaw just as though it has ailerons. I can fly a rudder elevator model with regular dihedral at zero and negative G and in all cases the dihedral and rudder combo acts just like ailerons.

So yeah, the angled tips do give some positive dihedral LIKE effect but not like proper dihedral.
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Old Jul 31, 2010, 01:08 PM
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Neenah, WI
Joined May 2006
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My 2 cents: Does your Cub have ailerons?
If "no": use top version with up-sloped tips; increases effectiveness of rudder to induce roll/turn.
If "yes": use bottom version with down-sloped tips; reduces the effects of "adverse yaw" when aileron is applied; improves "roll" effectiveness of the ailerons for top-wing aircraft.
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Old Jul 31, 2010, 02:29 PM
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My 2 cents: Technically, the top picture will give a little bit of dihedral effect. Practically, though, I don't think you'll be able to tell any difference, except maybe a tiny bit if you're building a R/E plane. But in that case you'll want to build the whole wing with dihedral anyway.
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Old Jul 31, 2010, 02:45 PM
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Carlsbad, Ca
Joined Mar 2007
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Since we are talking wingtip only,

...the difference in performance is probably negligible.

If we were talking outer wing panel on a 3M thermal glider, Tiphedral would be significant.

I'd suggest you build it how you like
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Old Aug 02, 2010, 09:39 AM
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MentalDekay's Avatar
erie pa/grand rapids mi
Joined Jan 2010
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wellll...

So the answer is. Yes, maybe, but not a lot, though probably worth it since I haven't figured out how to control airelons in a rubber free flight plane ....yet....

I do think I'll lean towards the top tip for most rubber FF models.

And since my Cub is already built, I'll let it continue having its "adverse yaw" suppression system ..despite it's lack of airelons...


...one more question...
...Does anything about any of your thoughts change when it's a low-wing or mid-wing plane (being that the plane's stability properties probably change a little when the CoL is at or below the CoG...)?


-des
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Old Aug 02, 2010, 12:49 PM
B for Bruce
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Nope, anything that the tips give will be there the same amount regardless of low, mid or high wing.

Mind you on a low wing scale model I would use the angled up tips even if the effect were minimal just so I could reduce the dihedral required by even two degrees and to aid in achieving a more scale like appearance.
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Old Aug 03, 2010, 02:30 PM
one flew
MentalDekay's Avatar
erie pa/grand rapids mi
Joined Jan 2010
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Quote:
Originally Posted by BMatthews View Post
...
Mind you on a low wing scale model I would use the angled up tips even if the effect were minimal just so I could reduce the dihedral required by even two degrees and to aid in achieving a more scale like appearance.
I'm down with that...who wants their P-51 or Senior Dart to look like an uppercase "V" from the front?

-des
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