With no wind, the stability reversal occurs as the vertical velocity
crosses 0 and it shows apogee about 0.25 sec later.� If I run it with
the default 4.5 mph of wind, the stability goes negative at about 40
ft/sec of vertical velocity.� Moving the fins forward to get 2 calibers
of stability doesn't have an appreciable effect on the behavior at apogee.
-Bob
On 12/30/18 12:58 PM, rebel without a job wrote:
> OpenRocket shows Mach 0.75 for the 10 second burn and 0.92 for the 15 second burn.
Go for the 10s then. No reason to deal with transonic stresses, plus the lighter load means a little faster off the rail. With 60ft this might not be an issue at all. At that length you have a different worry in wind: the faster you go the more force the fins generate, and those forces are reacted against your launch lugs.
> I wish it was easier in these sim programs to create motor files for liquids. Ideally you would specify some tank parameters and depletion rates instead of having to make a fake motor mount in the middle of the rocket to place the "motor".
Agreed. Hybrids have the same problem.
> OpenRocket 15.03 does plot both CG and Cp though and it shows a 3.0 of stability margin at at start and 3.5 at burnout. At apogee it drops rapidly to -.75 so I'm not sure what to make about that.
Might be a bit too stable, and you will weathercock and chase the wind a bit. OR usually shows loss of stability at apogee but it�s worth looking at the plot to determine the direction of causality: are you losing stability due to apogee or hitting apogee due to stability loss?