Building a 4.1x EAC Viper (link in sig). Using Wildman tubes and 1/8" G10 for fins. In trying to do a bit of flutter analysis to see what happens with a K motor. The closest fin pattern that I can find is the Wildman Cherokee 98 (WM Cherokee Link). LE, TE and tip cord are all swept (TE and tip inward), see diagrams. WM fin is longer and a smaller aspect ratio (AR). First review (by @Ken McC) on the Wildman site for the Cherokee 98 says, "It has been up to 10,794 feet and achieved Mach 1.29 on an CTI L935" When I run flutter analysis, Cherokee 98 Vf comes out to about 596 and 477mph with 80% margin. Viper Vf comes out to about 490 and 392mph with 80% margin. Makes sense given the AR. I'm using a thrust plate, so I'm less concerned about the fin can and more concerned with Flutter. (Fin area is not going to match between planform and flutter calc because of the sweeps. The relative difference is reasonable for the accuracy here)
- What do you make of running 1/8" G10 at speeds above these Vf? (i.e. how does M1.29 NOT flutter?)
- There are 5 J motors that exceed 390mph. The lowest K runs 469. If I want to run these higher speeds, do I need to go to 3/16" G10? If I change to 3/16", Max Safe Speed goes to 720mph!!!
- The viper fins are dumbo ear fins relative to all the other 4" kits, and the viper is on the small end for OAL at 55", so I'm less drag, less mass, larger AR, and faster speeds with a K. Do I punt running on Ks and let this be an I/J rocket and build something bigger/heaver with more appropriate fins to run K motors?
- Any other thoughts to consider?
Last edited: