Rail Buttons and Tube Fins

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accooper

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I am in the process of starting to build my Level 2 rocket. It will have eight(8) tubes around a four inch body tube. How and where should I put the rail buttons since there in not enough room between the tubes and one button will have to be inside one of the tubes.

Andrew
 
try using rail button standoffs and then have the rail go through one of the tube fins.
 
Thanks. I guess it would only need a small stand off. Just the thickness of the tube fin itself?

Andrew
 
I would put a button immediately after the end of the tube fin and then one higher up or if the tube fins are not directly mounted on the back of the body tube ut one before. im guessing the back of the tube fins are lined up with the end of the body tube so just put the first button at the end of the tube fin and one higher up and you should be good.
 
I used some "doughnut holes" left over from cutting some centering rings. These are 5mm ply, and just give more bite surface for the threads of the button screw to hold onto.

From a build thread, https://indianarocketry.fr.yuku.com/topic/551/Not-a-Build-Thread-Exactly?page=2#.Uyob_c5p9fc

:flyingpig:

That is one cool lookin' tube fin rocket. I love 'em. Mine will be 4 inches in diameter 48 inches long, 8 tube fines, 38mm motor mount. Powered by a DMS J270W-14A with the delay tuned to 8 seconds.

Andrew
 
Thanks. I guess it would only need a small stand off. Just the thickness of the tube fin itself?

Andrew

I did my L2 with a 4 inch tube fin rocket. You may not be thinking this all the way through...

You will need at about a 1/4" separation between the airframe and the button. The rail rides "inside the curve" of the tube-fin, and you need to make sure to have clearance between the rail (corners of the rail actually) and the inside of the tube-fin.

Sorry - I don't have a picture handy at the moment - I think an Illustration might help you visualize it better. With 8 tube fins... you must be using less than 4 inch diameter tube-fins >>>> which means a tighter curve, and more stand-off is needed.
 
Check with Bill at Doghouse Rocketry. He sells rail buttons and standoffs.

The standoffs will allow you run the launch rail through one of the tubes without rubbing...assuming your tubes are large enough.

In my case, a 1010 rail fits neatly inside a 3" diameter tube fin. A 4" tube fin should pose no problems at all.

BTW, Bill also sells wellnuts which will make installation a bit easier. Just drill a hole in the body tube, stick the wellnut in and it will swell up when you drive the screw home. Easy peasy.

If you forget to leave a bit of body tube extending past the tube fincan like I once did, you can drill a hole through the outside of the tube fin and then into the body tube, a wellnut, a standoff, a rail button, and Bob's yer uncle. You can fill in the hole in the tube fin if you like.

Note to self: Tube fin rockets don't like Mach.
 
OK, just got an idea. How about faucet washers as stand offs? They are about 3/16 inch thick and 17/32 inch wide. I got a package at Lowes for 98 cents. After playing with them they seem to work.

Andrew
 
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