Model Rocketry (larger scale) (models, buy, cheap, legal)
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Hi All,
Am looking for some resources/clubs that are into high-powered rocketry…. Doesn’t really matter where they are. Currently I am designing (after a long hiatus from the hobby), a rocket for high altitudes. The basis is similar to the configuration of a Delta…. I can do all the electronics myself. The main tube will have one of the small gas turbines that should have a burn time of several minutes, and then at a determined altitude (haven’t calculated that yet), solid boosters will kick in, as the turbine becomes really inefficient at high altitudes. A simple RF system will give me all the info I need on the ground, and of course a recovery system is critical. (Not going to lose a $5K turbine). I need some guidance, as this is my first attempt at a main-stage liquid-fueled propulsion system. Also need some guidance about FAA rules.
Back when I was a kid, a reverse charge for the chute was simple. This will have to be quite a bit more complex than that. A GPS chip/transponder will make be able to locate it, as I imagine it may drift quite a ways coming down… Not sure how to deal with the CG shift as it blows through the kerosene….
Any suggestions?
I wrote you a detailed response, but your numbers don't add up. There is no way you can launch a "model" rocket with SECO more than 10-20 seconds after liftoff, air-start SRM's, and a staged-combustion sustainer engine from anything but a missile range.
Why are you saying your "gas turbine" (do you mean gas generator?) sustainer becomes less efficient at altitude? Do you mean from nozzle under-expansion? Is this rocket really so big you need to worry about that? What are you doing with this thing?
My advice would be to scale down your ambitions, and explain a bit more about with how much payload, how far, how high, and why you are launching this rocket.
I wrote you a detailed response, but your numbers don't add up. There is no way you can launch a "model" rocket with SECO more than 10-20 seconds after liftoff, air-start SRM's, and a staged-combustion sustainer engine from anything but a missile range.
Why are you saying your "gas turbine" (do you mean gas generator?) sustainer becomes less efficient at altitude? Do you mean from nozzle under-expansion? Is this rocket really so big you need to worry about that? What are you doing with this thing?
My advice would be to scale down your ambitions, and explain a bit more about with how much payload, how far, how high, and why you are launching this rocket.
We can go into more detail in a DM...
When I stated 'gas turbine', it is something like a US Simjet LLC, or any of another dozen machine shops where the larger ones (though tiny in size), can generate up to 100 lbs of thrust. When I say 'gas turbine', it is exactly that... compressor vanes, combustion chamber, exhaust temperature sensor.... this stuff has become relatively common over the last decade, and they are really small for models (something like 6 lbs for the turbine, but the fuel weight is dominant). Fortunately, one of my friends works for the FAA, and he can get the rules. No payload.
It is clear I have too much time on my hands, but the whole goal is the intellectual challenge.
Ok, you threw me off when you said it's configured like a Delta. So you've actually got an airbreathing turbojet sustainer which you want to take you up to altitude, then you want to light off solids to go even higher. Got it. You should include a good altimeter/range system because you're not going to see much of this jet/rocket, just the telemetry data.
Launch stability is going to be tricky because you've got such a low T/W ratio at launch. Most model rockets kick off the pad with their maximum thrust to get them up to a speed sufficient for them to achieve stability by keeping the CP behind the CG after they clear the launch rail. Full-scale launch vehicles use active systems like engine gimballing, verniers, and gyros/ballast to keep them stable and pointed in the right direction. You can't afford that (in terms of money, space, or weight) so I don't know how to solve your problem. I guess you could do something really innovative like putting your thrust vector above your CG; tractor style ala Goddard.
I would stage the turbojet, dumping it at altitude when you light your solids. No reason to tow all that dead weight once it's done. But I predict serious issues with reliably air-starting your SRMs. Also, again, you are going to run into problems with the legality of a high altitude launch. But there might be areas near you where you could buy some range time for cheap maybe.
Ok, you threw me off when you said it's configured like a Delta. So you've actually got an airbreathing turbojet sustainer which you want to take you up to altitude, then you want to light off solids to go even higher. Got it. You should include a good altimeter/range system because you're not going to see much of this jet/rocket, just the telemetry data.
Launch stability is going to be tricky because you've got such a low T/W ratio at launch. Most model rockets kick off the pad with their maximum thrust to get them up to a speed sufficient for them to achieve stability by keeping the CP behind the CG after they clear the launch rail. Full-scale launch vehicles use active systems like engine gimballing, verniers, and gyros/ballast to keep them stable and pointed in the right direction. You can't afford that (in terms of money, space, or weight) so I don't know how to solve your problem. I guess you could do something really innovative like putting your thrust vector above your CG; tractor style ala Goddard.
I would stage the turbojet, dumping it at altitude when you light your solids. No reason to tow all that dead weight once it's done. But I predict serious issues with reliably air-starting your SRMs. Also, again, you are going to run into problems with the legality of a high altitude launch. But there might be areas near you where you could buy some range time for cheap maybe.
Sorry I wasn't more descriptive of the design... there are nuggets of knowledge on CD (though rare, and take that as a compliment). As so you stated, my biggest concern is the first several hundred feet, as stability is an issue. I have seen tiny military-surplus gyro's for sale, cheap, but it is starting to enter the realm where I am not well versed, though I have time (and researching efforts) on my hands.
I understand your point about achieving sufficient speed quickly.... my one concern is setting off the solid boosters from the ground (two solids and the turbine, once up to speed, all at once)... there is no 'off' switch on the solids. Have seen more than one rocket either blow up on the rail, or go up about 200 feet and nose-dive. I like the idea of dumping the turbine, with empty fuel tank (with 'chute, of course), for weight reasons, once it is exhausted. I will research the Goddard-style (they wanted me to come and work at WPI, his alma-mater, but that is for another thread). Not sure about the reliability of starting the solids at altitude... though if one fails to ignite, oops....
Pitch, yaw and roll and location are somewhat easy to measure, and one of my former embedded-design engineers is figuring out a circuit board design. I gave away all my UV etching equipment to do it myself.The telemetry is fairly straightforward, though the total power consumption for everything is not that small, as the update rate needs to be fast... but it only has to work from the time off the ground until it lands (hopefully close to me and the launch site).
I really want to get further into this discussion, but the size and scale of your rocket makes me keep thinking "what if this guy is in Palestine?" because you're really building a cruise missile (backwards) when you talk about such long burn times (minutes). Check with your FAA friend first before you start designing for 20kft apogee and 50nmi of range.
I really want to get further into this discussion, but the size and scale of your rocket makes me keep thinking "what if this guy is in Palestine?" because you're really building a cruise missile (backwards) when you talk about such long burn times (minutes). Check with your FAA friend first before you start designing for 20kft apogee and 50nmi of range.
Naw.... ever see the show on TV where they launch a porta-potty? This is purely a hobby. Just like past and present hobbies; 1200HP street rod, ice boat, tons of audio equipment (took a U-Haul to get it to my place in college), computer algorithms, making a 'big ear' out of a retired 10' satellite dish, grinding a telescope mirror for a Newtonian, way too many digital circuits... etc, etc.... The intellectual challenge is the fun (and only) part. Once done with the project(s), will test them, and then move on to the next. It keeps the mind active, when you attempt things that initially you are not sure you can do.
I'm very active with the National Association of Rocketry and also Level 2 certified. You run into problems as soon as your rocket has active guidance and a propulsion system that falls outside of using solid propellant materials.
The FAA has definitions for model rocketry and high powered rocketry. I'd suggest that you review those definitions to see what they allow.
What you see on TV is nothing more than reloadable motors that are already approved by the various governing bodies, ie- NAR, CPSC, DOT, BATFE, and NFPA. When doing HP activites you need to be certified by either NAR or Tripoli.
There is amateur rocketry where the rules are looser and those guys handle their own insurance. I'd suggest that you hook up with an amateur rocketry club. Most of those are located in the southwest part of the country and those clubs will handle the appropriate waivers that are needed for such rockets.
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