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Building Tips and technical articles. => Building techniques => Topic started by: Dennis Saydak on August 31, 2016, 12:32:45 PM
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When is it appropriate/necessary to upgrade from 3/32" wire to 1/8" wire control horns? Does the model weight play a role here?
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When you need it (isn't that helpful). Yes, model weight matters.
Folks seem to think 3/32" is OK for a 500 square-inch model; I would only use 1/8" on a 600 squares or bigger model. People concerned about making things rigid will make the change to a bigger wire sooner; people who want to tweak flaps by bending the wire may hold off, or may use something other than music wire.
Sorry for not giving you definitive answers -- you'll find that there's a lot of personal preference involved.
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The length of the arms has a influance too . Though epoxied in they shouldnt twist . Torsion - if its twice as long its twice the spongyness .
Like Soft Flaps . VD~
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The length of the arms has a influance too . Though epoxied in they shouldnt twist . Torsion - if its twice as long its twice the spongyness .
Like Soft Flaps . VD~
This point concerns me as well ......... example - Berserker flap horn where the upright is offset significantly to one side, which may cause a spongy opposite side flap if 3/32" wire is used. Perhaps in reality there is nothing to be concerned over but I'll opt for 1/8" wire to be sure.
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I use 1/8" for most everything. A 'springy' horn can ruin an otherwise good airplane. To save some weight I thought I could get away with 3/32" wire (Sig flap horns) on just the elevators of two planes I built last winter. They were so spongy in the air they were almost not flyable. I had to dig into them and change the horns-major PITA- but the ships fly fine now in that respect. I'm going to put 1/8" in even my .35 classics going forward.
Dave
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I used the wire pushrod from the kit of my Flite Streak. Put a "L" piece as a guide in the center.
All my other built models have CF pushrods from Tom Morris.
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I used the wire pushrod from the kit of my Flite Streak. Put a "L" piece as a guide in the center.
All my other built models have CF pushrods from Tom Morris.
The subject is control horns, not push rods. R e a d t h e s u b j e c t l i n e ! !
Type at you later,
Dan McEntee
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The subject is control horns, not push rods. R e a d t h e s u b j e c t l i n e ! !
Type at you later,
Dan McEntee
Thanks Dan.
Probably my meds. n~
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I use 1/8" for most everything. A 'springy' horn can ruin an otherwise good airplane. To save some weight I thought I could get away with 3/32" wire (Sig flap horns) on just the elevators of two planes I built last winter. They were so spongy in the air they were almost not flyable. I had to dig into them and change the horns-major PITA- but the ships fly fine now in that respect. I'm going to put 1/8" in even my .35 classics going forward.
Dave
Do you mean those SIG horns that are wire with a nylon lever? I tested one to destruction, and it took a lot of abuse, but they just aren't rigid enough to suit me. They're scary; I wouldn't use them. D>K Steve
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You can feel the torsional deflection of 2 inches of 3/32"-diameter rod through 70 feet of .018" cable blowing in the wind? I doubt it, but the relative springiness of the lines and torque rod should be readily cypherable. Show me.
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These particular horns seem pretty soft. I think the 'give' is an accumulation from the three bends embedded in the nylon center, and the 90 degree bends on out. Not sure about the temper of the wire itself either but if you would twist the elevators in opposite directions they would go quite far before you felt much resistance- maybe 3/8". It didn't take much on a large elevator with the .76 up front to change the flap to elevator ratio in a hard turn or even to get the airplane to track with any reliability. I could likely make more rigid 3/32" horns but 1/8" just solves the problem so I'm off on other things.
Dave
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You can feel the torsional deflection of 2 inches of 3/32"-diameter rod through 70 feet of .018" cable blowing in the wind? I doubt it, but the relative springiness of the lines and torque rod should be readily cypherable. Show me.
Like Dave says -- I think it has more to do with a change in flap:elevator ratio with speed than with the absolute amount of spring from surface to handle.
Should be readily cipherable....
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Like Dave says -- I think it has more to do with a change in flap:elevator ratio with speed than with the absolute amount of spring from surface to handle.
Should be readily cipherable....
Assuming you want constant flap:elevator ratio, then the ratio of elevator control horn springiness to flap control horn springiness is the ratio of flap hinge moment to elevator hinge moment. Control horn springiness is proportional to distance from the solder joint to the arm * the wire diameter^2, right? So maybe you want to make the same-diameter elevator control horn a foot long.
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Assuming you want constant flap:elevator ratio, then the ratio of elevator control horn springiness to flap control horn springiness is the ratio of flap hinge moment to elevator hinge moment. Control horn springiness is proportional to distance from the solder joint to the arm * the wire diameter^2, right? So maybe you want to make the same-diameter elevator control horn a foot long.
Boy, ask a sensible question and Howard comes out of the woodwork n1 n1 y1 y1
TSK, TSK, Howard
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I think it was a sensible question, but I don't think you were getting sensible answers. I don't know the answer. I suspect that having the control surfaces stay put when they get bumped on the ground may be what's sizing the rods, rather than air loads. I get away with 1/8" flap rod and 3/32" elevator rod on my 70-oz. Impact. I just copied Paul Walker's control horn sizes.
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I doubt the wire itself can twist under these loads in this short a span. But each time a bend is made the wire is weakened substantially at the bend. In the case of the Sig horns in particular there are multiple bends involved creating a potential flex point at each. Chain those together and you can get a pretty good deflection without actually twisting the straight portions. A straight- through braised wire horn would be very much stronger. If you hold the Sig horns up to the light you can see the zig zag bends embedded in the nylon molding. That's where the problem begins. If you bend a piece of wire a few times back and forth it gets very easy to bend- until it just snaps off at the bend.
Dave
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The SIG horn that I torqued to destruction just had opposing flats smashed into the wire and the nylon horn molded around that. At least, that's what mine had. But maybe they changed 'em. H^^ Steve
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If the control horn wire is flexing why wouldn't it flex the same on both sides?
MM
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If the control horn wire is flexing why wouldn't it flex the same on both sides?
MM
Pushrod offset on typical profiles usually makes one side longer than the other. They could be made equal length, but many folks don't bother. We should be all about optimal. Here's the cyphers, etc. That's why these forums and PAMPA exist, IMO. To understand all the many various problems and help us improve all stunt things. D>K Steve