Margin of 4

[gary7]

I have a Loc IV and want to extend the length with a payload bay of about 11 inches which is a stock item from "Melissa". That increased my margin to just over 4 which is of course overstable where as the stock Loc IV has a margin of about 2.63. These numbers come from Rocksim. My question: how large can the value for the margin be and the rocket still be considered stable enough to fly? In other words, can the margin be too great or can a rocket be too overstable?

 

[TheAviator]

I've had SuperRoc models with margins of something like 11 or 12, so my sincerest guess would be no.

 

[Pat_B]

Run your sims with the 'overstable' rocket and keep increasing the wind speed. See what wind speed eventually noses it into the ground. That'll give you the tolerance that your rocket can take.

 

[Pantherjon]

What Pat said..But to elaborate a little. The more over stable the rocket is the more prong it is to turn into any wind. With stability margins as high as 11 or 12 I wouldn't be surprised if a gust of 5mph wind would be enough to get it into a more or less horizontal flight path..The size of the fin span also plays a role in this as well..That is why most long skinny rockets that have huge margin numbers have fairly small fins.

 

[Rocketjunkie]

What Pat said..But to elaborate a little. The more over stable the rocket is the more prong it is to turn into any wind. With stability margins as high as 11 or 12 I wouldn't be surprised if a gust of 5mph wind would be enough to get it into a more or less horizontal flight path..The size of the fin span also plays a role in this as well..That is why most long skinny rockets that have huge margin numbers have fairly small fins.

It also depends on how fast the rocket leaves the launcher. Use high thrust motors and longer rails/rods on windy days.

 

[hardinlw]

This is not intuitively obvious, but with a strong tendency to weathercock (turn into the wind) it is advantageous to angle the launch rod slightly downwind so that the rocket is weathercocking back to vertical or slightly upwind rather than going almost horizontal upwind. For max altitude, you want an angle that causes the rocket to end up going vertical. For minimum walk to recover, you want it to end up angled somewhat into the wind. The ability of Rocksim to accurately predict this behavior is dependent on how well you model the mass distribution. Some people just put in a point mass that makes the simulation have the correct total mass and the correct CG, but you really need to have the mass correctly distributed because that determines the moment of intertia which in turn determines the rate at which the rocket will yaw into the wind.