Horten Xc - The ultimate hang glider-part 2 - Page 2 - RC Groups
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Jan 17, 2012, 09:45 AM
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Stuart A's Avatar
Any progress?Thanks for posting the drawings btw
Stuart
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Jan 17, 2012, 10:14 AM
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Knoll53's Avatar

Elevon linkage and hinge


Sure Stuart, I've been fiddling around with hardware needed for the pull/pull system. One thing that was immediately clear is that the drive and driven wheels for the cord must be concentric with the hinge line. At the elevon the hinge must have no slop in order to assure that the cord stay properly tensioned through out it's travel.

To accomplish this, an axle is used in the Robart pin hinges. This axle lays in a center point notch in the driven wheel thus providing simple alignment.

Also, the tip skins were applied with contact cement.

Kent
Jan 17, 2012, 12:11 PM
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nmasters's Avatar
Quote:
Originally Posted by Knoll53
At the elevon the hinge must have no slop in order to assure that the cord stay properly tensioned through out it's travel.
A spring loaded idler pulley can take up some slop. In full size pull-pull systems they're used to adjust to thermal contraction at altitude.

--Norm
Jan 17, 2012, 12:45 PM
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Stuart A's Avatar
Quote:
Originally Posted by nmasters
A spring loaded idler pulley can take up some slop. In full size pull-pull systems they're used to adjust to thermal contraction at altitude.

--Norm
Do you have any diagrams?Used to use a similar system to tension rope drives on textile machinery;a fixed idler in conjuction withe a tensioned one,the drive arranged in a"S" around the two
Jan 17, 2012, 12:49 PM
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Knoll53's Avatar
Really

Thanks for your comment Norm, but I would never do that. Intentionally putting springyness into the linkage would lead to elevon flutter. I plan on terminal speed dives on occasion so this system will be fully tested in flight. I have used the stiffest materials I can find in this linkage. Specifically Kevlar cord, pin hinges and a stiff framework. Also there is an adjustable slide mount at the servo in order to tighten the system. I plan on running it tight in order to absorb as much initial springyness as possible.

I intend to do a wiggle test at the end of the elevon when done to compare to the conventional inner elevon.

Kent
Jan 17, 2012, 07:29 PM
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nmasters's Avatar
Quote:
Originally Posted by Stuart annat
Do you have any diagrams?Used to use a similar system to tension rope drives on textile machinery;a fixed idler in conjuction withe a tensioned one,the drive arranged in a"S" around the two
No, I don't have a drawing but the rope drives you have seen are basically the same thing. Just find a long unsupported run with good structure near the middle to support the tension pulley. You need a strong structure to mount it on because it requires a strong spring to keep the resonance frequency above the aileron flutter speed. Remember stiffer structures vibrate faster. Actually if the control surfaces are properly mass balanced stiffness in the control circuit is not so critical. There's also a way to run the cables that adds some self damping into the system but I don't remember which wire goes where right now. I seem to remember that Irv Culver wrote an article about it.
Anyway, if you over tighten the wires, wing flexing during flight can cause structural failures if the wires don't stretch.

--Norm
Jan 17, 2012, 08:35 PM
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nmasters's Avatar

Flutter and control circuit diagrams


Those letters from Irv Culver are in two issues of the TWITT newsletter. The copy rights are basically "give credit where credit is due". I think I've satisfied that by stating who wrote and published them. The links are on this page. If he's not hosting them anymore send me an e-mail and I'll e-mail them back. There are also some patent drawings on the TWITT site. Several of them are pull-pull systems. They're just the drawings with numbered callouts if you want the text for the callouts you you can get the full patents from the USPTO

--Norm
Jan 18, 2012, 03:52 AM
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Stuart A's Avatar
Thanks for the links.Who needs Wiki,we've got Norm!
Jan 18, 2012, 11:11 AM
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Knoll53's Avatar
Quote:
Originally Posted by nmasters
Anyway, if you over tighten the wires, wing flexing during flight can cause structural failures if the wires don't stretch.
--Norm
Not sure what you mean by structural failures. I can't imagine any main spar failing because the aileron linkage was too tight. Maybe a weak alum. bracket. Can you cite any examples?

Kent
Jan 18, 2012, 11:41 AM
Just call me crash for short
Quick61's Avatar
Looks like your coming right along with the build. Nice setup on the pull/pull system. It's giving me new ideas.

Just a stab in the dark here, but to my mind I think Norm might be referring to such tings as hinges, turnstiles, hing facings, servo mounting plates and the like. I'm sure he will clarify in his next post. He's like that you know.

Mark
Jan 18, 2012, 12:57 PM
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nmasters's Avatar
Yeah, what Mark said.
Small structural items in the control circuit. If all pivot points are mounted in double shear it's a lot less likely but, if the wire doesn't have enough elasticity to keep up with the elongation of whichever spar cap it's closest to, something will have to give either the wire itself or structure. That's where an idler comes in, it makes the wire look more elastic than it really is. Other methods are to put all the wires on the neutral axis of the structure so that there's no elongation with bending or the method described by Irv Culver in those newsletters: run the wires close to opposite skins so that when the spar bends on wire will tighten and the opposing wire will relax. Of course this last one causes a surface to move when the spar flexes but if you follow Irv's instructions that actually causes the elevons to fight body freedom flutter (the mode that makes 'wings explode not just shed elevons)

--Norm
Jan 18, 2012, 01:49 PM
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Knoll53's Avatar
Quote:
Originally Posted by nmasters
the method described by Irv Culver in those newsletters: run the wires close to opposite skins so that when the spar bends one wire will tighten and the opposing wire will relax. Of course this last one causes a surface to move when the spar flexes but if you follow Irv's instructions that actually causes the elevons to fight body freedom flutter (the mode that makes 'wings explode not just shed elevons)

--Norm
That Irv was a clever guy. Good article. Neat trick. My control cables will be at the neutral axis and tight.

Kent
Jan 18, 2012, 09:04 PM
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nmasters's Avatar
Quote:
Originally Posted by Knoll53
That Irv was a clever guy.
That's probably what the pentagon guy thought when Irv answered his boss's phone "Skunk works, inside man Culver speaking"
Jan 23, 2012, 01:23 PM
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Knoll53's Avatar
The wings are not joined yet but it's time for a little patio flying.

Kent
Jan 23, 2012, 02:06 PM
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Vernon Hunt's Avatar
Kent,

Oh, that wing is looking good. Whats the wingspan? Very nice.

Vern


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