Nearing completion of my Mega Bertha. Now what?

[Senior Space Cadet]

The last three days I've been working on a rocket one might consider a Big Bertha on steroids.
It uses the Big Bertha nose cone, is 40 inches long, has elliptical fins and takes 24mm motors.
I ordered some D motors for it, but it's just screaming for an E.
I have 29mm, BT-55, and BT-60 tubes and corresponding nose cones. I think I'll do a 29mm with 24mm motor mount next.
Attached is an image of the Mega Bertha and another rocket I would consider building if I could figure out how.

 

[jrap330]

You have to start testing your rockets by launching them . You built what 5 rockets , now do a field test and launch. Again you getting ahead of yourself. Launching is your next logical step.

 

[jrap330]

Not sure why I am not seeing you answer to my post above. What I meant you are stuck in a design loop and are NOW getting highs (w/o drugs) by all the unique designs you created in Open Rocket. The "balls one will be hard to built and fly? So get off this high and launch them...with a motor that you think will work and recover your rockets.

 

[neil_w]

Two quick comments on the first rocket:
1) Do you have a more complete OR model than that one? I would expect to see all the innards there, and motor configurations, etc., so you'd have reasonable CG and stability estimates.
2) If it ain't got the fins it ain't a Bertha. It seems like a perfectly fine rocket though.

 

[Senior Space Cadet]

Not sure why I am not seeing you answer to my post above. What I meant you are stuck in a design loop and are NOW getting highs (w/o drugs) by all the unique designs you created in Open Rocket. The "balls one will be hard to built and fly? So get off this high and launch them...with a motor that you think will work and recover your rockets.

I thought I did reply, not sure what happened.
I did launch one of my rockets and it flew fine.
I'm not sure what you mean by getting ahead of myself. I can't test launch a rocket without building it first, so that's what I'm doing.
I've watched dozens of videos on construction, I've read numerous articles, I've asked you guys all kinds of stupid questions. I've spent many hours playing with Open Rocket. I'm pretty sure I can build and launch a decent rocket.
With this big rocket, my concern isn't that there is anything wrong with my design or construction, it's that the launch rod is short and it won't be going fast enough by the time it reaches the end of the rod. Unfortunately, this means the first launch will be with a fairly large motor, if I can't find a longer rod. Not an E, but certainly a D.

 

[Funkworks]

Actually, I'd say one can do pretty much everything worthwhile on OpenRocket (or RockSim), including launches and getting all the numbers. I consider all that outdoor hassle to be optional. It's a crazy world out there.

 

[Senior Space Cadet]

Two quick comments on the first rocket:
1) Do you have a more complete OR model than that one? I would expect to see all the innards there, and motor configurations, etc., so you'd have reasonable CG and stability estimates.
2) If it ain't got the fins it ain't a Bertha. It seems like a perfectly fin I think what I did is calculate where the CP was and marked that on the body, then I put an engine in it and checke

Two quick comments on the first rocket:
1) Do you have a more complete OR model than that one? I would expect to see all the innards there, and motor configurations, etc., so you'd have reasonable CG and stability estimates.
2) If it ain't got the fins it ain't a Bertha. It seems like a perfectly fine rocket though.

I used OR to find the CP, then made an engine mount and just shoved it in the back with a motor to make sure the balance point was ahead of CP.
I now have it all painted and ready to go. To be sure, I can run the OR program again, and see where the CP is, since I've forgotten (or use the image above, since the CP should be accurate, just not the CG), put the recovery gear and motor in it and make sure it still balances at least a caliber ahead of CP, but I'm pretty sure it's over stable if anything. If not, I can always add weight to the nose cone.
I know those aren't Big Bertha fins, but with the longer body, I thought new fins that mirrored the nose cone shape might be appropriate.

 

[Senior Space Cadet]

OK, I just did a quick stability check. With a motor, but no parachute or shock chord, the CG is about 170mm in front of CP, with a body diameter of 66mm.
This isn't exact, but close enough. So, it should be pretty stable. I could actually shorten it a bit.

 

[Senior Space Cadet]

Oh, yeah, the paint. I won't win any awards for my paint job, but the nose cone and fins are black and the body is red. Looks pretty good, but that long body needs something to break it up. Graphics or a stripe or something.

 

[Funkworks]

If I was primarily a scratch builder, I'd consider getting a vinyl cutter like a "Cri-cuit", or some top notch color printer, and do my own decals. The rocket's name is a common theme.

 

[neil_w]

OK, I just did a quick stability check. With a motor, but no parachute or shock chord, the CG is about 170mm in front of CP, with a body diameter of 66mm.
This isn't exact, but close enough. So, it should be pretty stable. I could actually shorten it a bit.

Good practice at this point would be to override the mass and CG of the whole rocket without motor, and then sim the whole thing to test different motors. That's a pretty big rocket for 24mm (bigger than an Executioner), worth double-checking it flies OK on a D. What's the final mass?

 

[tsmith1315]

Actually, I'd say one can do pretty much everything worthwhile on OpenRocket (or RockSim)

Except experience the 3 S's - the Sound, the Smell, and the Suspense!

 

[Senior Space Cadet]

Good practice at this point would be to override the mass and CG of the whole rocket without motor, and then sim the whole thing to test different motors. That's a pretty big rocket for 24mm (bigger than an Executioner), worth double-checking it flies OK on a D. What's the final mass?

Yeah, I'm not expecting much altitude from the D.
My original thinking was that it would be hard to see the rockets, since my eyesight is bad, but I went to a launch last weekend and had no problem. It was a really clear day, not a cloud in the sky. On a hazy, overcast day, I might be glad I built such a big rocket.

 

[Senior Space Cadet]

If I was primarily a scratch builder, I'd consider getting a vinyl cutter like a "Cri-cuit", or some top notch color printer, and do my own decals. The rocket's name is a common theme.

If I were more artistic, I'd get an airbrush. Can you imagine the rockets a real artist with an airbrush could do?

 

[Senior Space Cadet]

I made some progress on the next build. I did go with the 29mm body with a 24mm motor. Kind of making up for the oversize body on this build.
I've got the motor mount made and the baffle.
What I need to do today, before going any further, is weigh all the components, so I get a really accurate CG. I actually think I did that with the Bertha build. Somewhere, on my computer, is the file. I should see if I can find it so I'll know where to look for this rocket.