- This topic has 79 replies, 13 voices, and was last updated 14 years, 8 months ago by
John A. Wilke.
John A. Wilke.-
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John A. Wilke
I flew a minimum diameter, 98mm rocket (“Higher Calling”) on an M1939 a few years ago… it was not optimized for altitude. I’ve learned so much since then. I did recover cleanly, and it was a cool boost.
Warren, I think you’d go far higher with a 75mm rocket on a big M – even if it wasn’t a full M – than what you’d go on any 98mm rocket… even if it was an N.
There is clearly a point of diminishing returns, and I think it is going from 75mm to 98mm. Until there is a very full, long-burn N, I think a 75mm rocket is the way to go.
Regarding KISS vs. complex – Both are valid pathways. That said, I once saw a Bobby Kennedy quote on the side of an L3 project – “Only those who dare to fail greatly can ever achieve greatly”. That always stuck with me.
Bruce R. Schaefer
Well-said, all. I went far more complex, ironically, on my L3 than I would do, and do-do (pun intended) now, but that was the learning aspect of it. Six switches initially, as opposed to two, and now I understand the looks of those who saw the six switches. (And they didn’t humiliate me then, we after all are friends, and they didn’t have to cert me, but now I understand their smiles.) What is this guy thinking? Yeah, he’ll hit L3. I just picked a rocket, modified it, and the design that I wanted to build and fly, so be it. It “be’d” well. A very good day, one that I will remember all my life and beyond that. Done deal. So, I, too, did NOT keep it simple. What was I thinking?
Chris LaPanse
I flew a minimum diameter, 98mm rocket (“Higher Calling”) on an M1939 a few years ago… it was not optimized for altitude. I’ve learned so much since then. I did recover cleanly, and it was a cool boost.
Warren, I think you’d go far higher with a 75mm rocket on a big M – even if it wasn’t a full M – than what you’d go on any 98mm rocket… even if it was an N.
There is clearly a point of diminishing returns, and I think it is going from 75mm to 98mm. Until there is a very full, long-burn N, I think a 75mm rocket is the way to go.
Regarding KISS vs. complex – Both are valid pathways. That said, I once saw a Bobby Kennedy quote on the side of an L3 project – “Only those who dare to fail greatly can ever achieve greatly”. That always stuck with me.
I have to say, I think a well-optimized, carefully made rocket on an N5800 C-star could go higher than any 75mm rocket on any current commercial 75mm load. You certainly do sacrifice a lot in the drag department when going from 3 inch to 4 inch though.
John A. Wilke
I have to say, I think a well-optimized, carefully made rocket on an N5800 C-star could go higher than any 75mm rocket on any current commercial 75mm load. You certainly do sacrifice a lot in the drag department when going from 3 inch to 4 inch though.
It would be an interesting duel 😀 There are 75mm motors that approach 8500NS, and the N5800 is a tick over 20KNS. That 98mm vs. 75mm hole you must punch is pretty daunting, though.
What we really need is a 54mm “M” motor….
Bret Packard
I find it interesting to read about what different people think is or is not a KISS design. For me, the way most of us overbuild, I think structural failure is really pretty rare . Most of the failures I’ve seen are attributed to things like forgetting to arm the altimeters, forgetting to attach the chute, improper building of the motor, too small of an ejection charge etc. and other similar stuff. I’m just not sure if that type of failure has anything to do with how “difficult” a particular design is.
Warren B. Musselman
Most rockets aren’t complicated at all. People leave tons of space in their designs to fit things like shock cords and chutes and electronics. Where things start getting interesting is trying to fit everything into as small a space as possible (read shorter rocket) and getting everything to work properly. Serious altitude birds try to pack everything into as short a bird as possible. That’s a far larger challenge than just a reliable rocket. Also, you’re quite correct, most of us substantially overbuild. I know I do – mainly because I want to build rockets that last for a bunch of flights.
Bruce R. Schaefer
For me, the way most of us overbuild, I think structural failure is really pretty rare .
Now this thread is getting good! Question is, as Warren and Bret said for durability, we do over build. But do any of us want to have a 40-365 pound rocket coming in without chute? We have no control over them once that candle is lit. The higher you go, the safer you must be. Altitude flights are the cream of the crop. Drag is the enemy. The wider the rocket is, the more drag; the longer it is, the more drag; the longer the fin span, the more drag. Those nasty high drag rail butons, and anything sticking out from the airframe, switches? Nose cone shape versus speed is another key, but how long will a rocket be at an optimum speed for your particular nose cone? Cones are always best, IMHO and testing and literature, for Mach+, but how long will your rocket fly over Mach? Most of the time, also considering coast time–when the velocity drops pretty quickly, and how long will you coast? There are so many variables. And, yes, this has everythihng to do with L3 and above.
Chris LaPanse
Cones are always best, IMHO and testing and literature, for Mach+, but how long will your rocket fly over Mach?
Not really…
Von Karman is quite a bit better.
Bruce R. Schaefer
Chris, you are right on. A fellow German, from my German side, who bridged that gap, and, I believe, one of Warren’s favorite nose cones, and rightfully so. Chris, this is at a new level. Carry on, young man…
Warren B. Musselman
Ah Bruce – you should place credit where credit is due. The altitude king of NCR is John Wilke and I have borrowed more ideas from him than I could list. Of course I’ve liberally borrowed wherever I found good ideas, but John has by far been the pack leader in this area. He may not own so much as a screwdriver, but the man has a serious track record for extreme altitude shots and he has been more than generous in mentoring others in the art. I’ve certainly learned a thing or two along the way.
I also don’t want to leave out Adrian and Sean who are also chasing altitude records. While I’ve never seen anything they’ve built fly, they’ve been refining some of the same obvious ideas – shorter birds, smaller fins, optimized weights, etc.
I’m one of those guys that builds projects and waits for optimal conditions to fly them – unfortunately along the way someone else builds something that is a bit more optimized and I back off and rebuild my projects to include the new ideas I found. I have a bird that I built 4 years ago to take the TRA L altitude record on an Ellis L330 SU motor. At this point it has been rebuilt 4 times and still hasn’t flown – first to shorten the airframe by using the motor as coupler, second to accommodate a shorter e-bay, third to go from a conical nose to a Von Karman, and now most recently to use a nosecone-deployed main chute. I might even rebuild it yet another time to convert it from dual deploy to apogee deploy if I can figure out where to put a GPS tracker. At this point it is roughly 18″ shorter than when I built initial design and it still hasn’t flown. Of course, that has much to do with the fact that this may well be the very last Ellis L330 left in Colorado – I don’t want to waste it on anything less than optimal conditions and a fully optimized bird.
My 4″ MD project has been in process now for 4+ years and has gone through a similar evolution of thought, although I have yet to lay-up a single piece of carbon or glass. I’ve been acquiring components and refining the design for years now and am right now on the edge of beginning construction. While JW swears that I should go 75mm, I don’t think anything in that diameter comes close to what a full 98mm 6 extended grain case can deliver in terms of total impulse. My one remaining problem is that I still don’t have a motor or a motor builder to provide one yet.
Like my L3 project, I’m in no rush – I’d rather be relatively confident in success and patient about getting there than waste hundreds or thousands of dollars on failed attempts and expensive motors. I’ll get there when I get there and along the way try to build the most optimized bird I’m capable of. The joy is in the journey, not the final few seconds of glory – that’s just the proof that the journey was well-taken.
John A. Wilke
Bruce R. Schaefer
Chris LaPanse
Bret Packard
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