- May 15, 2009
- Reaction score
What are you using for a spacer between the rail and the backboard? That will solve a lot of problems. But you are correct, more fins / long fins / tube fins do create issues anytime the rail is attached to a support structure.While I like this design, as it fully utilizes the whole rail length, when I tried this, for 4+-fin rockets, you can get fin interference with a backing board. I had to put the stop near the top of the Jawstand, rather than near the bottom. Nike Smoke fins would hold the rocket up, because the fins would interfere with the Jawstand, unless the rail was moved away from the flat flange of the stand..
This is a non-issue with small rockets. Just watch your fin clearance.
I no longer use that pad (8' rail did not come off and transporting it was a pain), but IIRC the back board was less than 8" wide, or 4" either side of centerline. I used a 1 1/2" spacer behind the 1" rail. Worst case scenario would be a small diameter rocket with the fin root right against the rail (the orange dot in my rough sketch), which is 1/2" from centerline of rail, leaving 3 1/2" to clear the edge of the backboard. A four fin rocket spaced 2 1/2" away from the backboard (with spacer) and fins longer than 3 1/2" long ( = 2.5" / cos 45° ) with the root right against the rail would not clear the backboard. But that would be the exception. Realistically, even a 54mm diameter rocket gives extra room, both because the root is further away laterally from the rail (y axis), and because the body curves away from the rail, giving extra longitudinal room (x axis). The larger the diameter, the more clearance you have from the backboard. Love the Jawstand for ease of setup, but the weight and footprint of these small pads quickly become limiting factors. We use beefier pads for large / heavy rockets, but flew 2.6" to 4" rockets off the Jawstand without ever having a clearance issue. (4 fin max, 2 fin min. YMMV with 5 or more.)