- This topic has 30 replies, 7 voices, and was last updated 18 years, 3 months ago by
Conway Stevens.
Conway Stevens.-
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Anonymous
OK, Geeks – I’ll toss this one out to the collective knowing someone has a brilliant solution (I hope).
I’m building a 98mm, minimum diameter project. There is enough glass going tip to tip on the fins of this bird that the diameter on the aft end of the airframe is going to be substantially greater than up top. Too much slop for a tower, I’m afraid. I’m not interested in a sabot or a collar up top to offset the differential.
So… we look to buttons. While I know they will cost me perhaps 500-700′, I’m guessing the rattling in the tower may do that, too. Mounting the upper button is a piece ‘o cake. The lower button, however… has me a bit stumped. I have an idea, but I’d like to hear what y’all come up with.
I’m just not comfy drilling and tapping into the convolute wound glass. Not enough “bite”. If that button comes off as an N motor comes up to pressure, very bad things will happen. I’d rather avoid 3 buttons, but have not ruled that out.
As the motor is greater than half the length of the rocket, I cannot just toss buttons up high.
Thoughts?
Ed Dawson
HMMM… sounds interesting.
Do you have any space aft of the fins? What if you had a band clamp (similar to a hose clamp but without the big screw fitting) holding a thin threaded plate for the rail button? Then you could cover with glass as part of the tip to tip and then feather it in.
The plate would give the threads some bite, and the stresses would be passed around the base of the BT. If you don’t have any space aft of the fins than you could put the band and plate in place before the fins are attached.
It’s kind of like glassing in an Acme rail guide with a band clamp.
Ken Plattner
Rather than puting the screw in from the outside, how ’bout puting the screw in from the inside and have the nut on the outside. Maybe a stove bolt or machine screw thats counter sunk into the tube just enough so the motor case doesn’t touch it. I assume you are using the large buttons, so something like a 1/4 x 24 should do it and provide enough strength to hold the button firm. I have a tool that’s used to create the tapers for stove bolts and other screws that have the tapered heads. With a 98mm tube there should be plenty of room to work.
Ken.
Ed Dawson
Oh, and I’m not sure if I’m insulted or complimented by the GEEK comment.
Warren B. Musselman
I was going to say that after all the tip to tip is done, drill it for a pem-nut, install the Pem nut with a bit of epoxy. Install the button and screw, then grind off the bit projecting through the inside of the airframe. With the right Pem Nut and enough epoxy I bet it’ll be fine. How heavy will the bird be?
Warren
Anonymous
Oh, and I’m not sure if I’m insulted or complimented by the GEEK comment.
Ha! that is a compliment. The UprOar was flown by the “League of Extraordinary Geeks”. Trust me, Ed– you’d know it if I insulted you 🙂
Anonymous
I was going to say that after all the tip to tip is done, drill it for a pem-nut, install the Pem nut with a bit of epoxy. Install the button and screw, then grind off the bit projecting through the inside of the airframe. With the right Pem Nut and enough epoxy I bet it’ll be fine. How heavy will the bird be?
Warren
Warren, that was actually one of my thoughts — grinding down a PEM. The rocket will weigh perhaps 12# dry, twice that loaded.
Ken, your comment above is intriguing… so is the hose clamp. I could even wrap the motor with a piece of tape, and put the hose clamp on there, so the majority of the drag woudl be below the airframe, though that would dirty up the aft end of the rocket.
I’ve also thought about buying another aft ring and drilling and tapping a hole into the aft closure itself, though that would be “modified”.
Keep the great ideas coming! I’ll share my initial idea in a day or two… I’m curious if anyone else comes up with a similar idea? THANKS EVERYONE! This is helpful…
Bruce R. Schaefer
Depending on how you’re retaining your motor casing… you could make a plate (with a hole in the center to allow the nozzle through but small enough to retain the motor) and weld either a 1/4×20 nut or bolt to it to screw down the button. Just use 4-6 screws to bolt the plate to the aft; this would take care of the rail button and motor retention. But the bolts to hold the plate would have to be bonded to the outside of the airframe. More drag, even with cool-looking covers. Of course, that’s going to put that button awfully low, the one above will have to be relatively close to it. I’ve never seen a bird turn on the last button left in the rail… but I heard it can happen. Though you should be quite stable by the time that last button is riding up the rail alone. 😉
Ken Plattner
This is an enigma. Without really knowing the design, how the motor is retained, where the fins are positioned relative to the airframe, etc., it’s an interesting challenge. But then, I guess that was the purpose of posing the question in the first place. Upon reading the initial question, I assumed the problem was only how to attach the button to the airframe securely, but I think there is more to it. How do you attach the button or something similar to the airframe while keeping the drag and turbulance induced by the button to a minimum.
John, can we have more specifics about the rear end of the rocket?
Ken Plattner
Here’s another thought. Position the end of the motor about 1/2″ into the tube – or – at least leave enough airframe exposed for a screw. Add the rail button to the bottom of the tube aft of the end of the motor as you normally would with a screw and a nut, but only after the motor is loaded and retained.
Anonymous
Ed Dawson
Ken Plattner
Warren B. Musselman
Bruce R. Schaefer
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