In response to post 13426 by Dave Schultz on DARS-General, I thought I’d see if moving the rail buttons as he suggested would have any affect on how smoothly a rocket might move on a rail. I devised a simple experiment that anyone should be able to try on their own. I’m sure someone can compute the math, but I’m more of an empirical kind of guy.

I made a simple rocket using a 4 foot long PVC pipe and attached rail buttons as usual and added a 340 gram weight (a c-clamp that was handy) to the aft end. I  slid the rocket on a rail held horizontally with the buttons at a 90 degree angle to the ground to side load the buttons as in a cross wind. I tilted the rail towards vertical and measured the angle at which the rocket started to slide freely down the rail. On average, it would start sliding at 35 degrees from vertical. I repeated this experiment about 10 times and got consistent results. (I used a new rail free from exhaust residue.)

I then did the same experiment with the rail buttons in the location Dave Schultz suggested in the post referenced above. I had to tilt the rod much higher – to only 20 degrees from vertical before the rocket started to slide freely. I also repeated this experiment about 10 times.

To me this shows that the new button arrangement is more likely to bind as the rocket moves along the rail. Without compelling evidence that moving the buttons mitigates some other safety concern, it seems like a better idea to leave the buttons in their typical locations.