My latest oddroc

[teepot]

It's 60" long, weighs 54 ounces and is 3" in diameter. I used 6" styrofoam balls for the nose cone and in place of regular fins. It has a 38mm x 15" motor mount.

 

[kuririn]

Wow, this rocket has some balls!
(Just a statement of fact).

 

[kuririn]

PS How can this possibly be stable?

 

[neil_w]

PS How can this possibly be stable?

I was wondering that too.

 

[mbeels]

Fun design!

PS How can this possibly be stable?

I bet drag stability does the trick.

 

[teepot]

The CG is well in front of the CP. Also drag stability. I've flown some other high drag rockets. Both of the attached have flown.

 

[Sooner Boomer]

PS How can this possibly be stable?

CG/CP in proper relationship, plus base drag. It's a lot like a badly deformed spool.

 

[Cape Byron]

CG/CP in proper relationship, plus base drag. It's a lot like a badly deformed spool.

In a good way.

 

[Nytrunner]

But unlike a spool, it has curved surfaces that reduce the drag effect.

How did you determine a center of pressure?

 

[teepot]

I make an educated guess as to the CP position. So far of the 83 scratch builds I've only has one that was unstable. I've been lucky.

 

[Daddyisabar]

I make an educated guess as to the CP position. So far of the 83 scratch builds I've only has one that was unstable. I've been lucky.

Base drag is one of the few friends an oddrocketeer can always count on! Mindsim: a terrible thing to waste!

 

[Jeff Lassahn]

The center of pressure of a sphere is at the geometric center of the sphere.
The aerodynamic force on a sphere is pure drag, no lift, and proportional to the area of the sphere.

If the five spheres are the same size, and you ignore body and interaction effects, that means the CP would be 4/5 of the way between the center of the nose sphere and the centers of the fin spheres.

Given that there is a body tube and interactions, that might be a bit optimistic -- I'd probably design for a CP like 3/4 of the way back.

Which kinda looks like what you did.

 

[teepot]

The rocket is 60 inches long and I put the center of pressure 14 inches from the leading edge of the fins. CG is 18 inches from the leading edge of the fins. That's almost to the center of the rocket. If the first flight is unstable I'll add some nose weight.

 

[Rktman]

It's 60" long, weighs 54 ounces and is 3" in diameter. I used 6" styrofoam balls for the nose cone and in place of regular fins. It has a 38mm x 15" motor mount.

VERY cool design! Can't wait to see how this turns. Hoping for a video of its first flight, it should be spectacular no matter what happens.

 

[Aeronerd]

It's 60" long, weighs 54 ounces and is 3" in diameter. I used 6" styrofoam balls for the nose cone and in place of regular fins. It has a 38mm x 15" motor mount.

Wow awesome oddroc. Ingenius concept.

 

[GlenP]

You could reduce the base drag of the spheres a little if you add some surface features on the windward side, kind of like the dimples on a golf ball, you know? Or equally proportional height discs in a circle around the front facing perimeter just ahead of the max diameter sides of the spheres.

 

[modeltrains]

Oddrocs - now there's some real 'rocket science'!

 

[BABAR]

Why do I expect the first crew members to be
Mel Brooks, Bill Pullman, John Candy and Rick Moranis?

 

[dhbarr]

Lonestar's Raspberry Jammer

 

[burkefj]

I believe this rocket was part of Operation Vacu-Suck