98mm N5800 MD rocket for BALLS

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Doug Gerrard mentioned at one MHM or O'Fest that he might bring an optical tracker to the next event. He was looking for fast, high altitude rockets and was putting the tracker on the hill.

Actually my tracking cameras are limited to pretty much the take off. John Hornkol has been working on a tracking system with an extremely long range lens camera specifically for flights like this and he attends BALLS every year. But as far as I know he has not successfully used it on a flight yet.

Doug
 
A few years ago I saw an optical system in use at a CNES HPR launch in France. The army (DGA) brought their optical tracker. Pretty cool. It froze the rocket on the screen and it only got smaller. I tried searching for some more info, but can not find it. I did find some other CNES videos that you may like Doug. See here: https://www.dailymotion.com/D-V-P#video=xtkkhe. All Pro54 and Pro75 Classic.

Jeroen
 
Nope - there was a gap of around 1/2" to 1" between the end of the case and the start of the nosecone shoulder, and at the moment, all evidence points to that 1" of unreinforced fiberglass tube as the point of failure. This motor is extremely unforgiving of even small weak points on a rocket.

When I was designing my 3" rocket I was struggling with what kind of forces to design for, and then realized that I would be covered as long as the composite tube was as strong in bending as the motor case. It doesn't actually take all that much more uni carbon to do that. The radio-transparent section is more difficult to make that strong, but you can do it with extra interior thickness.
 
I would be very interested both in seeing it and in seeing the methodology behind it (what assumptions and equations are used, mostly - flow through a hole can be a non-trivial calculation)

Yes, it is a non-trivial calculation. That is why he did it recursively. Remember, he’s only a sophomore in high school. He hasn’t yet had calculus, much less differential equations. But, the spreadsheet gives a good idea of how much force builds up with different vent hole sizes. He used an analogy to an RC filter. It wasn't his original idea (he cites the work he used), but the RC filter made sense to him because he is a ham and understands electronics.

We posted it here:
https://www.rocketryforum.com/showt...ze-Calculator-Spreadsheet&p=406284#post406284
 
Chris,

If you decide to rebuild I'd be happy to offer machining services and provide you with another 60" toroidal parachute.

Edward
 
Thick - I don't know an exact value, sorry. I don't know the exact construction technique, but I believe it was constructed from a two-part mold, yes. It survived a shred at mach 3 and a bounce from a mile up with only a chip in the shoulder, so it's definitely a sturdy piece. If it's at all helpful, it weighed around a pound and a half...
The nosecone was fabricated in a two-part mold and is double-thick compared to stock layup, with 4 layers at the interior/exterior shoulder junction. Each layer is 18 oz., so the main body of the cone is 36 oz, the junction is 72 oz. All of the resin used, including the surface, was 500 degree Cotronics. The Cotronics has a very interesting property... when finish sanded with fine wet sandpaper, the aluminum content in the resin results in a very shiny metallic finish. Unsanded, it's a dull gray and you would never know it has any metallic content.
 
...the aluminum content in the resin...

Does the aluminum content effect GPS reception and APRS transmission range? That was the second-biggest reason we chose to avoid cotronics in our build (the other being the raw tensile strength difference, 9500psi vs 37,100psi).
 
Never tested RF transparency, but Chris was able to use the nc as-is. Would be nice to quantify.
 
CCotner said:
Does the aluminum content effect GPS reception and APRS transmission range? That was the second-biggest reason we chose to avoid cotronics in our build (the other being the raw tensile strength difference, 9500psi vs 37,100psi).

You have to be a little careful when comparing specified strength values for epoxy - just from looking at the values you've quoted, I can almost guarantee that they were taken in different ways. Some companies specify properties for the neat resin, with nothing else added (which is usually in the 6000 to 12000 psi range for a good laminating resin. Some specify the strength with fillers though, which can boost the strength substantially, and some even specify strength of a reference layup with fiberglass, which will be much, much higher than the strength of the epoxy alone.

As for the effect on transmission? The bulk epoxy, despite the aluminum content, is a pretty good insulator, so I didn't notice any significant effect. I was also not too concerned, since after deployment (if it had worked), the antennas would not have been inside the nosecone anyways.
 
Yeah, I've run into different manufacturers' using different testing schemes. PTM&W documentation is excellent; cotronics documentation (w/ respect to mechanical properties) is not. It just didn't seem like a structural/tooling product to me.

Actually, I forgot the real reason we went with PTM&W...imagine explaining the cotronics MSDS to a lawyer who has sign off to protect the school from lawsuit on everything you do... :(

The lack of RF problem, however, is intriguing. I'd like to try to use it to make better ablatives for the next time we try to launch, if I can convince the school safety people to allow it.
 
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Chris you never took any pictures, and you said to bug you to do that, so I'm doing it publicly :D
 
As for the effect on transmission? The bulk epoxy, despite the aluminum content, is a pretty good insulator, so I didn't notice any significant effect. I was also not too concerned, since after deployment (if it had worked), the antennas would not have been inside the nosecone anyways.

The main reason I would be concerned about RF transparency in a design like this is to enable GPS reception before apogee.
 
Adrian, would it usually be good enough to just get acceleration data during the motor burn and perhaps a few seconds of coasting? Presuming high altitude data is not useable that is... I would expect that would be enough to test out simulations and give a solid ballpark apogee. Not for recovery obviously, but for altitude info.
 
That's actually one of my more...um...ambitious? Yeah we'll go with ambitious here. That's one of my more ambitious ideas for a future project. Make the entire rocket one solid, glued-together piece, with no seams at all, and then eject the entire motor casing out the back for recovery. It has substantial structural and aerodynamic benefits, since there's no external seams at all, and the nose cannot possibly wobble, but there's the difficulty of kicking 4 feet and 10 pounds or so of motor case out the back reliably, with as minimal of a chance of binding as possible. I think it would be doable though. It also introduces some unique headaches with the electronics design, but at least at the moment, it's my leading contender for my next design when I get around to rebuilding. I'll need to figure out a full recovery schematic, but I'm cautiously optimistic about the possibilities here.



Now I feel really bad about how long it took me to get around to posting a flight report :blush:

3D printing that should work right?
 
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