Lowering the CG of a high-power rocket

[adyabzd]

Hello all,

I am trying to build a rocket that will go up to 2000 feet, but its stability as of now is 2.56, which I think is a bit too much. I was just thinking that I could add some weight above the top centering ring to lower the CG and therefore lower the stability. Does anyone know any other good ways?

 

[watheyak]

Firstly, what makes you think that's too much? That's a pretty typical number.

Just make the fins smaller if you decide you want to make it less stable. Those fins do look very large for the rocket.

But "less stable" isn't something anyone usually tries to do on purpose.

 

[neil_w]

Just make the fins smaller if you decide you want to make it less stable. Those fins do look very large for the rocket.

Yeah, those fins are really oversized IMHO.

 

[thzero]

You can use the optimize feature in OR to help optimize the fin profile (and weight) for different end goals, i.e. calibers, altitude, velocity, etc. Menu->Tools->Optimizations.

Another way is to lengthen the rocket too, as that adjusts the CP upwards, granted it also impacts the CG, so its a trade off.

Or you could add small canards towards the nose cone which will also cause the CP to be adjust upwards.

If you really want to, I guess you can use expanding foam in the fin can and/or epoxy to do the inverse of what people do when they need to add weight to the nose cone.

But unless you are upscaling something or tied to the exact fin design.

 

[Rschub]

Everyone else has good advice, but I'm going to go with Use a bigger motor

 

[Antares JS]

It depends on what you mean by "go up to 2000 feet."

If you are looking to hit exactly 2000 feet and your design currently sims to that goal, leave it as-is. 2.56 is fine.

If you are looking to hit at least 2000 feet, reduce the size of your fins and you'll also get less drag and more altitude out of it.

 

[cerving]

Use a bigger and heavier motor.

Alternatively, it looks like your payload bay has lots of empty space... shorten it.

 

[Neutronium95]

Those fins are a definitely on the very large side. You can reduce their size a bit and be totally fine.

That said, overstability isn't really a problem. An unstable rocket is unsafe to fly in any conditions. A rocket with a high stability margin will be more sensitive to the wind and will have a higher tendency to weathercock. Just be mindful about the windspeed and your rail exit speed.

 

[JoePfeiffer]

Everyone else has good advice, but I'm going to go with Use a bigger motor

There's no such thing as overstable, just underpowered.

 

[cwbullet]

Everyone else has good advice, but I'm going to go with Use a bigger motor

Yup. It will go down when you add a motor. Adding a fatter motor is better than a long thing one.