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Old Apr 27, 2015, 04:08 PM
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OK, if there is dihedral, then this is possible.
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Old Apr 28, 2015, 01:39 PM
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Can we assume that you want to use a gull like dihedral to add to the "organic" look? If so then keep in mind that gull dihedral puts the most angle in the wrong place to provide roll from the rudder induced yaw.

Also 3 degrees of straight dihedral is going to result in a very low yaw to roll rate. It'll roll, but not as fast as we're typically used to getting.

If you go with the gull dihedral then it's back to the tip mounted elevons for you. But they don't need to be anything like as large as you showed in the previous post with the red elevons unless you're after a model that will duck and loop like a whirling dervish.

The narrow tips will certainly cause problems for tip stalling. But if you extend the elevons out as shown previously to incorporate the tips and then use them to provide the reflex of the outer and rearward portion of the wing as needed on this design then the tips from the hinge line out will be at a few degrees more negative an angle than the rest of the wing. So that should aid on avoiding tip stalling.

You've likely also found that the amount of elevator throw needed on a plank is minimal compared to the aileron throw angles. So I would not worry too much about any drag from pitch control inputs. Instead more of the possible drag issues will come from larger amounts of roll control.
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Old Apr 28, 2015, 02:01 PM
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Thanks Bruce.

There is no gull wing dihedral for me............I am just not that dedicated. So I'm looking at straight dihedral. I believe that I have about 3 degrees on my Slice-n-Dice Plank......I'll have to check. I'm happy with the roll response of that plank. This project is a thermal ship so I'll just be floating around in mostly calm air. Too much dihedral can cause handling problems in gusty air.

I get how outboard elevons add washout when you need it, so without them, I thought that I would add a lot of twist to the outer panel, kinda Horten style. Again it is a thermal floater so drag should be less important at those slow speeds.

Yes, organic, inspired by nature......all of that. It is novelty project. If it has a limited flight envelope, that's OK, just as long as there are no bad habits, so the tip stall is my biggest worry. Worst case scenario, I cut elevons in after flight testing.

If I put a V tail on it, I could have a clean wing.
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Old Apr 28, 2015, 08:46 PM
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All your videos seem to be at the slope off that beach. So I just assumed. And we know what THAT produces right?

For a lazy flying thermal model I'd still want more like 5 degrees myself. But if you're happy with your other design copying it will certainly provide similar response.

Quote:
If I put a V tail on it, I could have a clean wing.
And then we'd have to kick you out of the Nurflugel forum for this thread....

Quote:
Worst case scenario, I cut elevons in after flight testing.
Hedge your bets by building in the hinge line "spar" and the doubled rib at the inboard end which can be cut down the center of the strip to cut away the surface. Or make the trailing edge wide enough that you can safely cut away the elevons from that material at the later time if needed.
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Old Apr 29, 2015, 10:17 AM
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I test at the beach and FLY in the mountains, which is thermal or some times slermal. I've been unable to get up the mountain this year so all recent videos are at the beach.

I like every thing about 5+ degrees of dihedral, except what happens when there is an unexpected gust of air from the side. It induces an unwanted roll, which the big rudder stabilizes............not really a problem for lazy floating around. I'll bet that the Turkey Vultures have about 5 degrees of dihedral, plus upward swept primary feathers. This glider would certainly look better with 5+ degrees of dihedral.

WHEN I build this one, there will be no hedging of bets, although I recognize the comment as good advice. This one will be a dedicated effort at a "look". I'm eager to see the blurry glow of the buried spar through the Koverall and the thread like TE. No exposed linkage and no visible servos......just like a bird. The drawings posted so far are more than concept sketches, they are working drawings. Construction will be with 1/8" diameter fiberglass LE, built up carbon fiber TE. Both just strong enough to withstand Koverall shrinkage. All wing torsional strength comes from the big box spar.

Still looking for a good construction method for the TE.
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Old Apr 29, 2015, 03:03 PM
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Hmmmm.... in that case what about splaying the ribs out in a semblance of the finger bones found in the Pterodactyl's wing? I'm not suggesting you use only 5 ribs. But some artistic license especially at the tips could do a lot to achieving the organic look you're after.

If you go that route you could steal the trick used by the current FAI free flight models that use a flat rectangular strip of carbon fiber as the trailing edge. Or to get the shape use very small CF strips standing vertical and laminate a few around a form to create a roughly 1/16 deep x 1/8 wide trailing edge. Something like this would prove to be both tough and rigid.

If you find that you're getting a lot of side gusts from 5° straight dihedral models you clearly didn't fly much with the polyhedral gliders. Getting bumped around with sudden side gusts is just a fact of life for RES sailplane fliers. I sort of welcome these since when they happen at altitude it's often due to a nearby thermal. But if the ground you fly at is lumpy, like on a mountain, it can certainly make for anxious times fighting down through the ground turbulence and gusts.
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Old Apr 29, 2015, 04:30 PM
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Organic meets Engineer

Quote:
Originally Posted by BMatthews View Post
Getting bumped around with sudden side gusts is just a fact of life for RES sailplane fliers.
I get that. It IS one of the charms about flying polyhedral wings. The Turkey Vultures get thrown around even in light lift.......it's part of the fun. I've got a couple of tricks up my sleeve for landing so there is no real compelling reason to shy away from dihedral.

I should consider spoilers directly over the spar at the root to aid in landing ..........shouldn't hurt the "glow" too much. Disturbed air over the rudder doesn't scare me (yet).

I have tons of 50K carbon tow, so I'd like to find a way to make a sharp TE, that matches the airfoil and curves to match the planform. Haven't quite got that one worked out yet.

Cool idea but splaying ribs is probably too complex for me. I do better with simple projects. Also the airfoil would not be parallel to the direction of flight. Not really my comfort zone. Who knows, it could provide some much needed turbulation at tips.
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Old Apr 29, 2015, 04:37 PM
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We fly lots of polyhedral at our slope........it's pretty tame.

Day Hiker catch (0 min 34 sec)
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Old Apr 29, 2015, 04:53 PM
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This plane is getting heavy.
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