question about stabilizing

[gerbs4me]

ok guys, I'm to the point where I need to stabilize the PVC rocket. I'm gonna assume the I212 weighs 410g. Ok my question is, once I stabilize it with a 410g motor in it, what if I wanna throw in something bigger like a J, will it still be stable? plez explain this HPR flyers.

 

[shrox]

Nose weight excises a host of stablity demons...have you run it thru RockSim?

shrox

 

[gerbs4me]

yes
I only have the demo version, but it doesn't come out right. So if nose weight can host problems, how else could I stabilize it?

 

[Missileman]

Typically a rocket that is stabilised for X size motor will not neccesarily be stable for a larger motor.
Basic principal is that a rocket must have the center of gravity (balance point) forward of the center of pressure (this is where the forces exerted by air passing by are centered)
lets say your rocket is balanced 1 body diameter ahead of your CP with the smaller motor. Put a string at the balance point. Now put the bigger heavier motor in. You will find that the center of gravity has moved back closer to the aft end. Since the CP does not change you are no longer balanced 1 body diameter ahead of your CP. Nose weight is now needed.
Some people keep extra nosecones balanced for specific motors.
Myself I usually balance my rockets to the weight of the largest motor I anticipate ever using in it.
I am kicking around an idea for some of my larger cluster rockets (where engine weight can differ quite a bit) where I would have a threaded rod in the nose where I can put removable weights.
Hope this helps

 

[wwattles]

I've posted this elsewhere, but I'll mention it again. You can put removeable noseweight in the nose with self-adhesive velcro strips and pinewood derby weight strips.

Noseweight tends to make a rocket more stable. Overstability does become a problem eventually, but usually we don't go THAT far in how much we modify our rockets.

WW

 

[gerbs4me]

thanks guys for the help
I like the idea with the rod and weight, but the NC i'm using is styrofoam. Depending on how much weight I need, if I don't need to much I use the velcro method.

 

[shrox]

No no no, I said "Nose weight excises a host of stablity demons..." excise as in remove, like demons running out of a pea-soup spitting; head rotating child.

Add nose weight.

shrox

 

[cls]

definitely add nose weight ... and make them a little bigger ... and move your fins back ... and do a swing test (might be difficult with a big heavy rocket LOL)

 

[gerbs4me]

Thanx guys for the help

 

[bobkrech]

gerbs4me

Why don't you try canting the fins 2 degrees or so and spin- stabilize the rocket. It's pretty effective at increasing the stability margins and doesn't add any weight to the rocket.

You can get the FinSim program from AeroRocket if you want to precisely calculate the angle.

Bob Krech