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Old Dec 31, 2015, 12:06 PM
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Adam RED Weston
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Flying wires or strings for structural support

So, I'm wondering about using strings or wires for structural support like early monoplanes such as the Fokker E.IV

https://upload.wikimedia.org/wikiped....IV_3_vues.jpg

It looks like a mess of strings top and bottom (since you have only tension) but using something like Kevlar thread you could save a bit of weight and a lot of money vs carbon fiber rods.

I did some research on RCGroups here on the f3p Forum and there's only a few posts about them being used on foamie biplanes, but they elude to some other models using the concept, and that it's too much work. Would the idea work better with carbon rods and mylar wing/fuse+tail structures that we use now? Perhaps we're hampered too much by varying environmental conditions and the strings just warp the structure? Perhaps you old timers can set me straight.

RED
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Old Dec 31, 2015, 12:09 PM
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Adam RED Weston
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Some thoughts on techniques...

Consider a post out the top and then support wires running to it... Tension the wires with a knot like this...

http://www.survivalworld.com/knots/t...l#.VoIP-3OIZnE

Or this:
https://s-media-cache-ak0.pinimg.com...1bc7b257ff.jpg

Use a drop of CA once everything is lined up perfect

I was also wondering about miniature turnbuckles done on a 3D printer too... but maybe a lock thingy like this would be easier:

http://cdn2.exped.com/sites/default/...?itok=L9BjaHNa

or this:

http://g03.a.alicdn.com/kf/HTB1.hhlI...r-Activity.jpg

There are about a million different designs for these... maybe machine them on the CNC instead with g-board and a #60 drill bit.

RED
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Old Dec 31, 2015, 12:48 PM
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I don't think Kevlar thread would work because of the problems involved in tying and tensioning. to keep the structure ridgid requires the CF rods. Yes they are expensive but if you make your own they are cheap. I've been making my own for 4 years now. Aprox .020, 025, .030 and .040 thousand rods are easy to make. Once you have the supplies it takes about 1.5 hours to make a dozen rods (prep, start and finish). Just made a dozen .020 this morning because I ran out on my "Guestimate II" build. The other down side of kevlar thread is handeling the airframe when tying the knots. Even with the CF rods all the knot tying is "painful"

A few years back when I began building the CF airframes i refused to do all the tying with kevlar thread. I used a different method that worked quite well but a little heavy. The planes are still flying today.


When I got involved with the DIYS contra boxes I needed a new plane so I began building a suitable plane for the box. I call it the "Guestimate " which was made from pictures of Alexey's Victory. I also decided to do the kevlar thread method ( which I had not done before) thinking it would be lighter and easier. Well, no more tying knots for me ( at least not more than 10 a plane). The knot tying is frustrating to say the least. I revisited my original method from years ago and refined it to be lighter, faster and easier during assembly.

If you are interested in any of this I can elaborate on the rod making and the no knot airframe.

George
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Old Dec 31, 2015, 12:59 PM
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Originally Posted by Ampbomber View Post
If you are interested in any of this I can elaborate on the rod making and the no knot airframe.

George
I'm always interested in new ideas. You never know when a different solution to a problem might be put to good use.
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Old Dec 31, 2015, 01:57 PM
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I'm always interested in new ideas. You never know when a different solution to a problem might be put to good use.
Are you enjoying all the knots on your Victory assembly? It's difficult to tie them and not tear the covering.

I'll have to take a break and put something together on no knot CF airframes and making CF rods.
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Old Dec 31, 2015, 04:53 PM
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The Finish models at the last W/C used strings to brace the wings. A few pictures of them in this thread:
http://www.rcgroups.com/forums/showthread.php?t=2361556

Pretty sure they were only used on the wings. Fuse bracing was normal carbon rod. I also think the idea works better with a carbon structure.
Foam/mylar would not have the required compression strength/stiffness.

At one time Devin used to do a lot of string/line bracing. Look at some of the older images in his gallery:
http://www.rcgroups.com/forums/thumb...u=44222&page=2

Pat MacKenzie
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Old Dec 31, 2015, 05:12 PM
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Originally Posted by 3Dreaming View Post
I'm always interested in new ideas. You never know when a different solution to a problem might be put to good use.
Here is the basics of making CF rods. Keep in mind that I am not out to make the lightest airplane. I just like to keep the cost down where I can. If you need clarification pictures let me know.

Making CF rods.

Supplies needed: epoxy, CF tow of different weights. Tow can be purchased from CST Composites http://www.cstsales.com/ I use 3K and 6K tow either singly or in different bundles for different diameter rods.

A strand of 3K yields a rod of approximately .020 D
A strand of 6K .025 D
A bundle of 9K .030 D
A bundle of 12K .040 D

The tow is tied and CA'd at one end to a reformed paper clip (used as a hanging hook).

The other end gets a bamboo skewer CA'd to it. This is the tensioning and "twister" rod.

Cover your building surface with wax paper. I have been using West System 105 resin and 206 slow hardener. It flows well and wets the CF nicely. The slow gives me plenty of time to wet out about 12 rods and get them hung and twisted.

To wet the rods, pull together all of the single CF rods (one paper clip and one bamboo skewer) at both ends and pour a bead of epoxy from end to end of the bundle and use a sponge to dab the epoxy into the bundles. I find it best to dab instead of sliding the sponge from end to end so as not to tear any of the fine filaments of CF from the bundle. After wetting the tow, they are hung from the ceiling by the paper clip (be sure to bend the clip tightly around the hanger). After hanging the rods wipe each between a thumb and forefinger from top to bottom. The bamboo rod is then twisted between each thumb and forefinger for 25 turns and stapled to the work bench with a 3/8 staple. After the rods are twisted, tensioned and stapled it is necessary to wipe the excess epoxy from each with swatch of paper towel (wipe from top to bottom). You will be surprised how much squeezes out! At this point I wait about an hour for the epoxy to begin curing and then I roll each rod from top to bottom between the palms of my hands. This helps even out the rod and roll up any stray filaments of CF.

After all of the rods are hung I go back and tension all of them one by one by tightening the staple with a tack hammer.

It sounds complicated but only takes about 90 minutes to do 12 rods from setup to finish. The more tow in the rod bundle the longer it takes to make each rod. If you do 9 or 12 K bundles it is probably best to do only 6 rods the first time (wetting a larger bundle takes longer-donít want the mix to cure). Care has to be used in CA'ing the CF bundle to the bamboo skewers and paper clip. Tie a knot at the paper clip before applying thin CA so they don't pull off during the twisting. Let them hang for 12 hours. Before removing them from the hangers itís best to wipe each rod with 320 grit sandpaper several times to remove a little epoxy and smooth the rod. After cutting the rods down lay them flat and straight for a couple of days to complete the cure of the epoxy.

I'll work on a writeup on how to get away from tying all those knots.
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Old Dec 31, 2015, 08:33 PM
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Lots of good info above, but I know some top level pilots have been experimenting with/using string to brace at least their wings.
I am interested to see more experiments done with this.

Free
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Old Dec 31, 2015, 09:04 PM
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Adam RED Weston
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Yes, thanks for the immediate feedback, but I guess I'm less concerned about cost and more concerned about finding the best techniquefor building one of these.

My experience with rod tension and compression members is they need to be perfect in length to work well... Now tying knots may be even harder to do, that's the kind of info I'm after. As far as knot tying goes, I've found the tiniest drop of CA fixes any knot in place.

Also there are some neat tensioner concepts too... Tie it close and fine tune it...
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Old Jan 01, 2016, 06:54 AM
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Tension

Michael Feuilly's Tension, circa 2006:

http://www.rcgroups.com/forums/showt...hlight=Tension
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Old Jan 01, 2016, 07:28 AM
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Quote:
Originally Posted by pmackenzie View Post
The Finish models at the last W/C used strings to brace the wings. A few pictures of them in this thread:
http://www.rcgroups.com/forums/showthread.php?t=2361556

Pretty sure they were only used on the wings. Fuse bracing was normal carbon rod. I also think the idea works better with a carbon structure.
Foam/mylar would not have the required compression strength/stiffness.

At one time Devin used to do a lot of string/line bracing. Look at some of the older images in his gallery:
http://www.rcgroups.com/forums/thumb...u=44222&page=2

Pat MacKenzie
Even Lantsov braced the wings with strings in one of the earlier iterations of his plane. In this case, the string bracing had the added benefit of making the wings removable.
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Old Jan 01, 2016, 08:42 AM
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Even Lantsov braced the wings with strings in one of the earlier iterations of his plane. In this case, the string bracing had the added benefit of making the wings removable.
I don't beleive it was an added benifit but more of a draw back. He used the string because the wing was removable. He hasen't used string since then.
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Old Jan 01, 2016, 08:49 AM
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I don't beleive it was an added benifit but more of a draw back. He used the string because the wing was removable. He hasen't used string since then.
I wasn't suggesting it as a benefit necessarily. Just a valid alternative. We don't all have the time to roll our own CF rods.
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Old Jan 01, 2016, 01:48 PM
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Originally Posted by Ampbomber View Post
Are you enjoying all the knots on your Victory assembly? It's difficult to tie them and not tear the covering.

I'll have to take a break and put something together on no knot CF airframes and making CF rods.
So far most of the tying has been fairly easy, but there have been a few spots where I have torn the covering. Those spots can be easily patched after the fact on the side of the covering without the paint.

Also you need to be really careful where that thin CA goes to. I have a couple hinges that I am going to redo because of that.
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Old Jan 03, 2016, 07:54 AM
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[Also you need to be really careful where that thin CA goes to. I have a couple hinges that I am going to redo because of that.[/QUOTE]

In regards to the figure 8 hinges, After doing the hinge take a sliver of wax and lay it on the hinge and melt it with a TF trim iron. Also, try fixing the hinge that got a little CA on it by putting a drop of acetone on the hinge and working the hinge ( do it several times).
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Last edited by Ampbomber; Jan 03, 2016 at 08:00 AM. Reason: more info
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