Lesson in Stability #1

Name: Rock-010

Built By: Tim Scott

Status: Retired


Type: Scratchbuilt

Component/Kit Mfr.: Estes Industries


Files: Rock-010

rock010.rkt

Simulation File

(73.69kb) RKT File


Design: Rock-010

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I don't adhere to liking the 'run of the mill' rockets. I like things to be just a little bit off-the-wall, or somehow different. I have never owned a Wizard, Yankee, Sizzler, etc, because I think that 3FNC rockets are fairly boring unless there is a GIANT motor in them, and they go really really high or really really fast. Prior to my exploration of G. Harry Stein's 'Handbook of Model Rocketry', I obtained RockSim from Apogee. It really is a fantastic program, and an invaluable tool for taking a good guess (if you do things right, you can almost get altitudes, acceleration and sub-sonic top-speeds spot-on) at how a rocket will perform. But then you have to factor in the 'real world' to that equasion, and that's where things went wrong.

I have since read in G. Harry Stein's book that he has staged Estes motors from as far away as 12", but I question the reliability of this, especially since I have failed to ignite a C from a D12-0 booster when they are butted up against one another. Perhaps Stein's theory is correct that the pressure from the charge dismisses the booster, allowing all of the flammables to escape before igniting the next stage, but it has happened to me at least once that I can recall. Therefore, in wanting to get some altitude out of this one, I figured I needed a booster at least. I made the booster short, and light-weight, as it only has to support a motor through it's short burn, and not through coasting. The fins on the sustainer are no larger than they need to be (without adding nose-weight) to keep it stable, so the added aft weight of a motor, and the booster's body tube, etc. needed extra fins. Quite significant ones, actually. It probably helps that there are 5 fins, which helps keep the size down, but I still think that they are pretty big for the size of the rocket. I also thought it would be somewhat cool if this rocket were able to 'stand' on it's own, so I swept the fins enough to allow for that.

Little did I know, my design decisions would lead to the end of this rocket. I didn't know about TTW fin mounting at this point, so the best I could come up with was a strong glue joint on the body tube, and a decent fillet. I had been doing this for years without problems, but this is probably the largest rocket I had made up to this point, with the possible exception of my Helio Copter, but that always came down with a parachute. I figured 'tumble recovery' was good enough for the booster for this rocket, seeing that it really didn't have much weight to it, and was going to be ejected really soon after liftoff. I just didn't think or test it through, I guess.

Fast forward to it's first flight. Loaded up with a D12-0 and an E9-8, it was all ready to go. There was a bit of wind, so it was aimed accordingly. The countdown came and went, and the igniter got the booster going. It lifted off cleanly, and cocked into the wind just a little. It had plenty of speed, and it quickly staged. The booster was shed instantly to it's own path, and apogee. It didn't spin, or roll, or loop, it just had a nice ballistic arch, and then headed straight down toward the ground. The sustainer took off like a bat out of hell once the E9 got some pressure behind it, and was out of sight very quickly. The booster came plowing in at terminal velocity, the only thing slowing it down was it's blunt forward end, and *foomp* into the ground it went. Now, mind you, this is only 1.6" in diameter, so it is really small, but it got some momentum going on the way down, and it hit the ground as square as it could, and on impact, all but one of the fins literally just popped off. While everyone else was keeping on eye on where the sustainer went, I was able to see this, and I couldn't believe it. I think I was the only one that did see it, and I can still replay it in my mind, it was one of the funniest things I had seen a rocket do this far, except for maybe the flight of Rock014.

Split between thrilled at my highest flight yet, and disappointed that this design flaw would prevent me from simply re-building the booster, it required a complete re-design, I decided to scrap the rocket (it flew a couple more times that day though) all together, and build a re-designed version, hopefully with some sort of recovery for the booster. This design became 'Match This' once it got painted.


Videos: Rock-010

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el-mirage_03_02.00.avi

A lesson in independent booster stability. The booster was stable on it's own, and came in ballistic, popping all five fins off. - (0:16) - Video Courtesy of Brian Scott

(2.7Mb) Video Clip

--RD

 

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