minimum button gap

1.0 cal is an easy and fast enough rule for static stability. Anyone have one for a minimum gap between rail buttons? I would guess between 3 and 4 cal but that is only a guess. I am building an oddly separating Leviathan and could benefit from a fairly small gap here.

You could put them pretty close to each other. It's really about holding the rocket in place while on the rail, so a longer heavier rocket would need more space between them for security, but with a Leviathon there's not all that much torque. As long as the rocket's weight can't twist one of the buttons out, you're actually better off having them closer together.

Think of it this way - once the uppermost button passes the top of the rail, there's nothing really keeping the rocket vertical any more. So in this sense, if you had the upper one very far up the rocket, you have effectively shortened the rail length and you might find that your rocket is not up to speed and stable yet. Better to err on the side of "too close together" as opposed to "not far enough apart". Of course, just right is better.

s6

Agree with stealth6. It's really about keeping the rocket straight up and down until it has sufficient velocity for the corrective moment to fly straight. I think the location of the buttons is more important. Farther down the rocket means longer effective launch rod/rail.

How does six inches sound on a Leviathan? I agree with the concepts though I am a little concerned this is too short a distance when the instructions want a foot for the stock lugs. I am using the coupler for separation, though, so the forward button has to be a little lower or a lot higher than I would normally want.

My rule of thumb, one at the rear centering ring, one at the CG.

One other thing I would think might be a factor here is the lever created by putting both buttons too close to the bottom end of a rocket. The upper button presumably has more force applied to it the farther down it is, I would think mostly gravity pulling the rocket away from the rail (pushing the lower button inwards but pulling the upper button away from the tube), and this probably gets worse if you angle the rail as there could be sideways forces as well. This would probably only be a concern for a heavier rocket, but positioning the buttons closer probably makes it more important to ensure the buttons are well-attached and can take the stress without bending, stripping, etc.

Get your own rail, use three buttons, two close together near the bottom, and one further up the airframe.

It gives the rocket max support as it gets moving. It give max guidance when it is moving the slowest, and it maintains control until it is nearly off of the rail.

Some will argue that it is hard to line up three buttons- to them I say hogwash.

markkoelsch said:

Get your own rail, use three buttons, two close together near the bottom, and one further up the airframe.

It gives the rocket max support as it gets moving. It give max guidance when it is moving the slowest, and it maintains control until it is nearly off of the rail.

Some will argue that it is hard to line up three buttons- to them I say hogwash.

Click to expand...

Agreed. If you plan on tilting the launch rail, then 3 buttons is a solid approach (3rd one in the av-bay coupler works for me.)