Why? It'll work just fine. Or are you trying to suggest that, if the CG of a heavy rocket is in the same place as the CG of a lighter rocket with the same external dimensions, that the heavy rocket will not be exactly as stable as the light one? If so, I call BS.
- Rick "Who's Ray Bolger, and what's he got to do with it?" Dickinson
My experience has been that a C6 engine puts the Fat Boy at the edge of stability, into the neutral zone until it gets some speed. They usually get to 25-40' and then take off straight in whatever direction they happen to be pointed. These are built stock, with yellow glue, so I don't think it is overbuilt in rear end. Does anyone else have similar experience?
Curtis Reynolds
Thanks, Bob, but I'm just a little concerned about the apparent over stability of a stock FB based upon several online flight logs.. I'll check the margin on a stock setup and see wnat it is.
If not one caliber, what would you consider to be "safe" for a stubby?
I decided on an alternating 18/24mm ring cluster in the BT-80 so I can start with 3x18 and work up to a 3x24 + 3x18. I'll hack off the bottom of the NC and epoxy a removable eye bolt forward in the NC so I can change nose weight (washers) based on motors. I can tweak the stabilty margin to whatever is necessary. Just looking for a reasonable, safe starting point.
Seems like good advice for kit bashing to me.
What is your concern with the method?
Given the erratic flight I had with mine the first time I tried a D13 reload (and then added nose weight) I'd agree. Another solution for C6 flights is a much longer launch rod.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
I think they should change their name from Fat Boy to Arch Rockets. Launching one is like target shooting with a bent rifle barrel.
Randy
THat's not how "The Master" did things
OIC. Well, thanks for that technical critique.
Gotta go, have to break out the slide rule and do some more flight sims.
Just think, if you did an article about THAT these days you would seem like a GOD. Technology indistinguishable from magic to the computer game fixated generation.
The batteries cannot die, the HD cannot crash and it works in bright sunlight. Better!
Jerry
I wonder what it says about me that, although I write computer software for a living, and carry a Treo 600 PalmOS-based phone with me at pretty much all times, I also keep a Pickett slide rule in my backpack and prefer to write with fountain pens?
To prevent cheating (by storing text in a programmable calculator), my Economics teacher last semester had a policy that any calculators used during his tests had to have less than thirty buttons. He got a funny look on his face when I pulled out a slipstick for the first test....
- Rick "It qualified" Dickinson
I'd call that a slapstick slickstick
You are a quality individual?
It qualifies!
Jerry "old technology is good technology" Irvine
Vacuum tube based amplifiers. Black Powder Free over the air TV etc
So YOU invented zero tolerance!!!
I think that's EXACTLY how the master did things...
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
Hmmm, my PDA has 6 buttons, including the POWER switch...
Even cell phones have calculators that can store text.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
How do you think he BECAME a rocket god?
Phones and PDAs were also specifically prohibited during exams. As mine is a Treo 600, it got hit by all three prohibitions. The slide rule just seemed to be the solution that made the most sense, to me. After all, I already had it and knew how to use it, and it *did* have fewer than 30 buttons....
- Rick "Actually, just as fast in most cases" Dickinson
Finally attended a non-school launch today, first time since last August.
Fast Boy (nicknamed Stumpy by my sister) was ready to fly (without finish) after a furious late night build session. Fast Boy is a 6 motor (3x24
The inner layer of BT-80 tube paper delaminated up forward where I had soaked it with thin CA and it seemed scorched and brittle. Haven't seen this before and it looks like a heat effect from 3 ejection charges. The tube without CA on it did fine. The nosecone could not be replaced on field because of the delamination, so the
3xE9 flight will have to wait till next time. Looking forward to a full-on 6 motor launch.In other news, the Lake got two of my favorite rockets today. Reverse Causality caught another thermal on an E9-6 flight and this time never came back. PL-1 went horizontal off the rod on two D-11's and a C-11 core motor. Did a pretty impressive cruise missle demo and ejected at high warp velocity. Chute shredded and the tethered payload-rocket flat spun into the lake. A fisherman pulled it out, but too late; the body tubes delaminated and the swelling engine cases split the outboard mount tubes. Sigh. I could not have aimed the thing more directly at the water. Ironically, one design goal of this rocket was a predictable flight path to keep it OUT of the lake. Ten months is too long between flights. It didn't dawn on me till I was on the way home that PL-1 NEEDS payload weight with motors in the outboards.
COOL flight with 'Stumpy' Fast Boy! :-)
It's interesting to here about the delaminating BT. Always thought I was doing good by coating the ends with woodglue or epoxy? Maybe woodglue wouldn't go brittle?
Ejection must be a real BLAST (Pun intended) :-)
Dang it!!! Them Rocket Gods are everywhere. And here I am thinking they were just picking on me...... :-)
Cheers, Clint
It was pretty neat. Thanks for the inspiration.
This was a difficult, but interesting build. These short, fat rockets mess with my paradigm of stability and I learned a lot by doing it.
For those who read this thread and want to stick more or bigger motors in a kit; you cannot just put more motors in a kit and fly it. You MUST consider stability and weight issues. Changing ANY parameter of a commercial kit that is outside the manufacturer's recommendations may result in a potentially unstable and dangerous rocket. If you are not comfortable with checking and ensuring the stability of a rocket, do not modify a kit. Buy a kit which is made for the motors you want to fly.
If you are interested in learning about kit bashing, read up on rocket stability. Apogee Rockets has a LOT of info on stability and they offer a free, demo version of Rocksim. Ask questions here on r.m.r. Don't be afraid to get into rocket design, its one aspect of rocketry which keeps it fun and exciting. Just take your time and never launch a modified rocket unless you KNOW its Center of Gravity, Center of Pressure, and stability margin and how those three parameters affect the flight of a rocket. If you fly at a club launch, tell the RSO it is a modified kit. He/she will give it a closer look and ask you some questions that you should be able to answer before flying a modified, or scratch, rocket.
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