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Best place to put rail buttons on the rocket?

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Bat-mite

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There's no one answer. Depends on your attachment method. The one thing to keep in mind is that the rail buttons are there to keep the rocket straight while it is getting up to sufficient velocity for it's shape to stabilize it. So the longer you keep the rocket on the rail, the less likely it will go unstable in the first half-second.

Two ways to achieve this: longer rail, or top rail button farther aft. If you can screw into a CR, great! If you are epoxying to the outside, you have more freedom. Keep them as far aft as possible, but not so close together as to act like a single button.

Let me know if you want clarification. This is the quick and dirty.
 

nickrulercreator

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There's no one answer. Depends on your attachment method. The one thing to keep in mind is that the rail buttons are there to keep the rocket straight while it is getting up to sufficient velocity for it's shape to stabilize it. So the longer you keep the rocket on the rail, the less likely it will go unstable in the first half-second.

Two ways to achieve this: longer rail, or top rail button farther aft. If you can screw into a CR, great! If you are epoxying to the outside, you have more freedom. Keep them as far aft as possible, but not so close together as to act like a single button.

Let me know if you want clarification. This is the quick and dirty.

What if you want to screw them in, but you don't want your CR's to crack or split?
 

AfterBurners

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some use a piece of wood on the inside of the air frame, at least that's one way of doing it? This would have to do with location again
 

Bat-mite

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Most good aircraft ply won't split if the screw is the right diameter in proportion to the thickness of the CR. But of course, drill a pilot hole first.

What material is the airframe?
 

rstaff3

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I like to put one at the back ring. The front often goes on the forward ring and closer to the CP. I've used 2 calibers too. I have always bought into the argument that the upper button should err towards the bottom of the rocket as you lose guidance when the top button leaves the rail. But I have to admit my rail is short. On club rails (6' or so), that often doesn't matter. But then, I'm a heretic who mounts my buttons in the airframe with no backing nut. This has worked on Estes models up to a few J powered ones. I've never lost a button on what you would consider a 'normal' rocket. If I ever did anything more extreme, I would revisit my practices.
 

rharshberger

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Pre-drill the holes for the screws, use a bit the same diameter as the root of the screw that wat the threads bite but the shaft doesn't put as much pressure to split the ring.
Or my favorite method is to glue a hardwood block to the CR for screwing the rail button into and not having to worry about thr ring at all.
 

rstaff3

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What if you want to screw them in, but you don't want your CR's to crack or split?
A minor crack or split won't hurt the ring in one tiny spot. Even if the screw isn't fully in the ring (or is even immediately adjacent), if you put in a blob of epoxy or CA, it will help support the button.
 

smugglervt

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Glue a small block of wood to the CR and screw rail button into that.
 

FlyBoy

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This is why I like fiberglass tubing, just screw them into the body and fly them.
 

qquake2k

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Even with 1/4" centering rings, I still epoxy blocks onto them to screw the rail buttons into. Since I usually build zipperless designs, the rail buttons end up relatively close together.

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manixFan

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Just waiting for Dave Schultz to chime in here...


Tony
 
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Incongruent

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It doesn't matter all that much so long as they are aligned and on the same section of airframe tube.

Ideally, for minimum weathercocking while elaving the pad, the rear should be at CP 90 and the front should be as close to it as possible. For least stress, there are different locations and for ease there are likely others places as well. Just depends on what you want in your rockets.
 

rstaff3

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It doesn't matter all that much so long as they are aligned and on the same section of airframe tube.

Ideally, for minimum weathercocking while elaving the pad, the rear should be at CP 90 and the front should be as close to it as possible. For least stress, there are different locations and for ease there are likely others places as well. Just depends on what you want in your rockets.
Now, this sums up all the rail button threads nicely.
 

Andy Greene

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Why not a tubular blind nut , epoxied in the tube ?
I did that with a small wood standoff with a hole drilled in the center to offset the blind nut sticking out on the outside, then the button on top.
Of course not on HP stuff
 
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