Wing and engine tethers. - RCCanada - Canada Radio Controlled Hobby Forum
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Old 04-10-2004, 06:55 PM   #1
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Wing and engine tethers.

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Getting away from the polotics for a few minutes!

For the last couple of years, I have been using wing and engine tethers in the final setup of my aircraft. These run from the last bolt on the needle valve side of the engine (this is the bolt that attaches the motor to the motor mount), through the firewall, then I wrap a loop of elastic (like you buy at the fabric store) through the wing, around the spar near the center of the wing. Take your tether material that you have now run through the fuselage, coming out of the radio/battery compartment, tie it onto the elastic loop on the wing, then attach the wing in your normal manner.

You will find that in the occurance of a mid-air, if your wing detaches from the plane, you "should" (9 out of ten times) not have the problem of a lawn dart. Your wing will fall off, until the tether holds it, then as the fuselage falls, the still tethered wing will fall behind acting like an air brake giving the fuselage a much softer landing. I also have found that in the case of the motor/mount breaking away from the plane the tether will keep the motor with the plane, so that there is less of a chance of you losing your motor.

Just thought I'd offer some advice. If this a duplication of an earlier thread, my apologies

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Old 04-10-2004, 09:00 PM   #2
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I've read it a few times but I'm not clear on some stuff.

Just some questions, how wide is the elastic? If it's going through the firewall, I would guess it's quite small. How do you attach it to the bolt without it coming off?

Now the elastic goes by the fuel tank, under the battery/receiver, under the servos then loops around the top to tie onto the elastic on the wing spar?

This sounds like a great idea, I just want to make sure it's clear.


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Old 04-10-2004, 11:50 PM   #3
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Actually, reading my earlier post, I'm confused myself

Let me try again

There are two possible choices (at least for the tethers that I make)

1. Braided Kevlar fishing line (30lbs test), 10ft folded back onto itself until you have about 30 inches (should be four doublebacks). Tie off a loop in each end (tie a simple knot to create a loop at the end of the tether). The loop should be 1 1/2 inches to 2 inches at most. Get a 6-32 washer and slip the loop through the hole, then draw the long end of the tether through the loop that is exposed outside of the washer. Pull tight, the tether is now attached to the washer. Prior to mounting engine/installing fuel tank, run the tether through the fuselage, install the tank as normal, before you install the firewall, drill a 1/4" hole in the firewall to allow passsage of the tether, pass the "washer end of the tether through the hole. Mount the firewall. After you have the motor mount installed and are ready to install the engine, the back bolt on the needle valve side(OS 25 FX) is the bolt you want to attach the tether to. This bolt typically goes with the engine when the engine ejects. Pass the mounting bolt throught the washer on top of the motor flange, not under) then tighten the bolt like normal. The elastic is tied around the spar in the wing (I actually use foam core wings with a 1/8" dia fiberglass rod top and bottom for a spar) Just before you attach the wing to the plane, tie the elastic to the tether that should be hanging out of the radio bay.

2. I have also found a 1/16" dia military spec chord that has a 100lb test strength. The steps are the same, except you don't have to make the loop in the end for the washer, just tie on the washer prior to mounting the engine. Make the loop in the elastic end though, to facilitate tying on the wing.

Jay Lawless

Any further questions, feel free to ask.
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Old 04-11-2004, 09:55 AM   #4
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You can also buy 1/8 shock chord at Crappy Tire and that works well for tethers also... and is very hard to break.

Another handy tip used at our club:

If you tie a piece of fishing line to the fuel tubing that runs between the needle valve and the carb on an OS .25, and run that fishing line back along the fuse and attach it to the wing... then when your wing comes off in a midair, it will pull the fuel line to your carb and shut your engine down automatically.
Dave "SideSlip" Plank
MAAC# 64211
Humber Valley RC Flyers
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Old 04-11-2004, 02:43 PM   #5
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I jst use ripstock nylon bolted between the engine and mount, then through the compartment up around the aeleron servo. It has saved a few planes now. I like the fish line around the fuel line idea. I may try that too.
Jason Holdaway

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Old 04-13-2004, 09:26 PM   #6
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headshot, this is a good system you recommend, though i have been using tethers for some time, I have used braided steel cable for the engine tether and the cable somtimes breaks- your system with kevlar cable will probably provide a bit more "give" and be less prone to breakage, excellent system!
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