motor retention idea, think it will work?

Hello...I have a couple of kits that are in need of motor retention (Loc Onyx & Estes Oracle using 24mm RMS). I wanted something simple and light
weight. My idea is to screw a couple of small screw eyes into the rear centering ring on either side of the engine (in the oracle, it would be into the plastic at the rockets rear with the screw on part removed). I would then stretch a piece of Kevlar between the screw eyes (affixed with snap swivels at each end) with a the Kevlar forming a loop around the base of the nozzle. The engine itself would be installed using normal friction fitting and the Kevlar harness would be serving as a safety belt in case the friction fit wasn't tight enough. Anybody see any problems with this technique...in my mind's eye it looks like it should work. It's not as strong as a clip, but given that it is just acting as a back up to friction fitting it seems like it should work okay. Craig
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The heat from the motor exhaust would degrade the Kevlar. You could replace the Kevlar with steel safety wire. Just wrap it around the screw eyes a few times.
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I considered some fine copper wire (have that on hand), but the wire (or the kevlar) would be out of the way of the exhaust stream, so I would think that the heat shouldn't be a factor. The wire (or string) would be up near the base of the engine and wrap around the nozzle there. I might go with the wire anyway though and just skip the swivels....might be easier to make to snug. Craig
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snipped-for-privacy@netzero.net wrote:

If the screw eyes are strong enough to hold themselves in, why not just replace the screw eyes with some screws, and let the heads overlap the rear of the motor. If they aren't big enough or close enough to the motor, use washers.
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Have a look at www.rowesretainers.co.uk I do 24mm retainers with a flat base or a cone retainer. Email me if you have ant questions. Colin

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I've used that technique, with wire instead of Kevlar. I used it because I installed t-nuts in a rocket for Kaplow-style clips, but couldn't find a washer or any brackets that fit right. Instead of waiting until I could fashion some brackets, I just inserted screws into the nuts and twisted wire between them. It worked fine.
-- Roger
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I use screws and conduit holders. Never had a failure.
Mark Simpson
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Craig wrote:

An idea shown to me worked very very well in my last launch.. a simple hose clamp around the motor mount tube and tightened, compresses the motor so that it isn't going anywhere.. and since you're using a small diamater motor to begin with, that shouldn't be a problem as long as you've got a 1/4" to 1/2" length of motor mount tubing coming out of the bottom of your rocket.. if it's flush against the bottom, it obviously wont work..
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A simpler solution. Use L shaped bolts instead of screw eyes and hook them over the back end of the engine. I've used it for years and never lost an engine.
Dave
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I've used bothe the automotive hose clamp method (you want the worm gear style) and scew eyes with steel safety wire; both work fine. I prefer the hoseclamp due to it's ease of use.
I'd use wire rather than Kevlar, it will degrade quickly from the heat.
Dave

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First, many thanks to all who responded to this thread. Due to time constraints, I didn't have time to order any commercial retention methods (and some, like the Oracle can not be readily retrofitted with one anyway). Over the weekend I flew my Oracle and am pleased with the results. Here's what I did. I purchased some tiny screw eyes and using my dremel drilled small holes that were about the same diameter as the screw eyes. I then glued them in place using gorilla glue. (When doing this on the Oracle, make sure that you position them such that it does not interfere with the Estes retention ring).
First flight of the Oracle...Estes D12-5. Nothing special, as it flew "stock".
Next flight was with an Aerotech D21-4T and an 18mm to 24mm adapter. I secured this engine using wire wrapped around the engine nozzle and the screw eyes. Flight performed fine and and engine was retained. (Except the ejection charge from the D21 blew the body tubes apart where they are glued to a plastic coupler...nothing that a little epoxy wasn't able to fix. Luckily the ejection came way late (more like a 7 second delay) and the tube sections landed close to each other.)
Third flight came with my 24mm RMS loaded with an E18-7W. Engine retained with wire, but instead of looping it around the nozzle I just stretched along side the nozzle and through the hook "slots?" on the aft closure. Rocket flew fine and engine was easily retained. In all flights the wire used was very fine (around 30 gauge) copper wire that I had laying about. HOWEVER, it was a real pain threading the wire and wrapping around the screw eyes. Took some time to prep this way (at least for this old man with weak eyes and thumbs for fingers). Next time I might solder some snap swivels to the wire and try that. But, overall, the method works and is cheap and simple to retrofit just about any rocket. Next will be my Blue Ninja.... :-) Craig
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Craig,
Bob Fortune turned us onto this...
Go get some of the metal strips that come in windshield wiper blades. They're 18" to 24" long, of decent properties, and can be bended into as long as a spring clip as you need. Wrapping with wire will work but you want to fly, not endlessly prep. The only other better metal I can think of is the stuff Aerotech uses.
Build another, go get the metal strips and try it...
Regards, Andy
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