First sorta scratch two-stage. Seeking advice

I'm almost done with this rocket and admittedly I should have done more research.
I did make on OR simulation but the validity of that is questionable at best.
The booster is scratch built from a destroyed older "D" Big Daddy kit with 1/8 birch plywood fins
the second stage is a new Big daddy kit.

Should I be concerned about the size of the booster fins? Are there any major red flags I should address?

What is the OR sim telling you? (And have you entered manual mass/cg overrides?)

heres a screenshot and the file itself, I'm a huge amateur with OR and obviously brand new here
so thanks in advance for everyone's patience

EDIT: I haven't added any overrides. I call it questionable because this is my first time using a sim program.

View attachment aethon.ork

Looks to me as if your margin of stability is not sufficient (0.111 ca).

Just from the eyeball test I'd guess you'll need significantly larger (wider) stage 1 fins.

Tip plates might be a way to do this.

JStarStar said:

Looks to me as if your margin of stability is not sufficient (0.111 ca).

Just from the eyeball test I'd guess you'll need significantly larger (wider) stage 1 fins.

Tip plates might be a way to do this.

Click to expand...

This is a ShortFat rocket it may very well fly on that level of stability. OR and Rocksim neither one sims ShortFats very well because they have increased base drag. Looks like a big daddy with a booster. Make sure to use a longer launch rod, and if flying with a club do it from the HPR pads, this one may fly pretty well. There is a workaround for the shortfats in one of the Apogee news letters.

I plan on using a 4 foot rod. With a D12-0 to E9 or E12 load. Weight is a pretty big concern right now too, I've read the max lift for the d12 is 14oz and this fully loaded weighs 13.6oz

heres the apogee news letter
https://www.apogeerockets.com/education/downloads/Newsletter154.pdf

Whats your off the rod speed, did you set the simulations on the third tab to your local flying conditions. When I set my sims I always use a 15mph wind speed, since that is common in my area.

Speed of the rod is 12.4 m/s. With wind speeds at 15mph which would be normal in MI Its unstable. But if I use apogees weightless cone method it works. Margin jumps up to 0.584

I would recommend launching off a longer rod, preferably one of the mini rails. I like your design shoul be fun to fly.

Neat project. Single stage Big Daddy's can be susceptible to weathercocking and stagers in general can be too so you have double the fun here ! :wink:

That said, I think I wouldn't make the booster fins any bigger. I might be inclined to try D12 to D12 for the first flight; the D12 has a tick less initial kick but weighs less than the E12 and weight is definitely your enemy here.

https://nar.org/SandT/pdf/Estes/D12.pdf https://www.nar.org/SandT/pdf/Estes/E12.pdf

A low wind day and at least a five foot, quarter inch launch rod would be my preferences.

Thanks for the quick response! Will definitely pick up a longer rod.

Amsterdam said:

heres a screenshot and the file itself, I'm a huge amateur with OR and obviously brand new here
so thanks in advance for everyone's patience

EDIT: I haven't added any overrides. I call it questionable because this is my first time using a sim program.

Click to expand...

OR is pretty decent at telling you where the center of pressure is. Mass can be a little trickier -- load all the laundry into the rocket, weight the thing, and enter that as a mass override. Then balance the rocket on a pencil or something to find an accurate (dry) center of mass. That should give a pretty good idea of how you'll fly.

Seconding what others have said about using a longer launch rod or rail if possible.

I’ve scratch- built a whole bunch of “Interesting” two stage rockets; a couple of them have very small fins on the booster and one is pretty short.

Here’s my down and dirty recommendation to insure stability for your rocket.
Weigh the booster including an unburned motor.
Add half that weight to the very tip* of the nosecone and let-er-rip.
Non-hardening modeling clay is good for this.

*I’m assuming that the nosecone is hollow/plastic.

If the cone is balsa you will need to drill/bore a hole as far forward as you feel comfortable.