Corkscrew Rocket - Wobbly Will or Sky Scribbler

[mbeels]

My son saw the corkscrew rockets as described in a recent Sport Rocketry magazine and thought that would be a fun rocket to build. He drew some initial concept art...



And then some more formal engineering plans:



At which point I was consulted to help generate a simulation file. After some back and forth (you know how consultants are) I convinced him to increase the size of the rear fins, decrease the size of the front fins, and we still ended up with a bit of nose weight. Compromises all around.

 

[mbeels]

While he sanded fins, I cut out "off-centering" rings. And starting to look a bit wobbly. Following the article, one fin has a small angle to give it some spin. I put a thin tube through the centering rings to make a replaceable shock cord.

 

[mbeels]

Spray paint time...

 

[BABAR]

I have lots of experience with corkscrew rockets, although mine have always been due to asymmetric fin placement rather than off axis motor. Suggestion now that you have already painted it, maybe some small paper spin tabs to get this rotating as it leaves the rod. So this should be self correcting..

That said, probably overkill, I think you should be good to go.

Many think of rockets that corkscrew as "flawed." I always prefer to think of them as "cool". Unless you are a speed or altitude junkie or carrying a camera, I think corkscrew flights are more fun (at least after your 10th 3FNC straight run of the mill flight) than classic flights. They are definitely attention getters at well attended launches!

MAJOR KUDOS for working with your son on this project. Always fun to see.

 

[mbeels]

Suggestion now that you have already painted it, maybe some small paper spin tabs to get this rotating as it leaves the rod. So this should be self correcting..

I think we'll probably do that.

Even though we started with a simulation, after finishing the build, I went back and added more nose weight plus lengthened the fins to get more stability. We flew it today and the corkscrew was pretty subtle, although noticeable in the smoke trail. We'll put a bit more tilt in one of the fins to try and crank up the corkscrew a bit more.

Many think of rockets that corkscrew as "flawed." I always prefer to think of them as "cool". Unless you are a speed or altitude junkie or carrying a camera, I think corkscrew flights are more fun (at least after your 10th 3FNC straight run of the mill flight) than classic flights. They are definitely attention getters at well attended launches!

I agree! It's fun to see something different.

MAJOR KUDOS for working with your son on this project. Always fun to see.

Thanks! Yeah, we had a good time. He started with the idea, so I wanted to be an enabler.

 

[mbeels]

Flight today was a partial success, we got a bit of corkscrew, but it drag separated right at motor burnout resulting in a pretty bad zipper. We'll rebuild it and try again.

 

[BABAR]

Flight today was a partial success, we got a bit of corkscrew, but it drag separated right at motor burnout resulting in a pretty bad zipper. We'll rebuild it and try again.

View attachment 571999

I understand drag separation in terms of electronic staging.

Please educate me on what drag separation means in a single stage rocket?

Edit

never mind, I did what I should have done first and bothered to do a google search, which led me right back to the forum. Have to say I have never experienced this, seems unusual for low power rockets.

https://www.rocketryforum.com/threa...drag separation force, if - then there isn't.


Also, is your instability similar to dynamic gas stabilization failure, where once thrust stops, stability goes to pot? (so goes unstable prior to coast phase?) If so, I don't understand why this rocket would to this, I would expect it to be MORE stable once the eccentric thrust ceases, rather than the opposite.

 

[mbeels]

never mind, I did what I should have done first and bothered to do a google search, which led me right back to the forum. Have to say I have never experienced this, seems unusual for low power rockets.

I ended up adding a fair bit of nose weight to get to a caliber of stability, and the nose cone did not have a lot of friction. If we end up in the same boat after the rebuild, I'll probably add shear pins. And yeah, I don't think I've ever seen in low power rockets.

Also, is your instability similar to dynamic gas stabilization failure, where once thrust stops, stability goes to pot? (so goes unstable prior to coast phase?) If so, I don't understand why this rocket would to this, I would expect it to be MORE stable once the eccentric thrust ceases, rather than the opposite.

I followed the general guide lines in a Sport Rocketry magazine, I didn't think that the offset motor caused any major changes to the stability (either more or less), it just helps with corkscrew effect (in combination with a tilted fin). So I don't think that our stability changed when the motor burned out, just that the nose cone wanted to keep going a lot faster than the rest of the rocket. Had the nose cone stayed on, I think it would have continued in a stable coast.

We're still figuring it out, and so far he's still motivated to try again, so I'll take that.