90 Second Vehicle.
John Carmack was really kind and sent me some peroxide catalyst material Armadillo was no longer using. I’m going to rebuild the present motor with these cataylsts. I’ll try to provide some pictures. I’ve ordered some stainless parts and some sintered stainless screen to spread the peroxide out. I figure about 4 days of work and this will be ready.
Things to fabricate /do:
- Fabricate New Motor upper section.
- Revise my safety plan with no liquid catalyst and get the waiver extended/approved for this configuration.
180 Second Vehicle. #1
We have a pressure fed 180 second airframe 95% fabricated. It will be a Peroxide RP1 biprop. To finish this vehicle we need to design a chamber and switch to thrust vector controls. If we get the same percentage of theroretical perfomance as we got with our monoprop vehicle this will hover for about 195 secondds in blow down mode. If we put active presurization on the vehicle it will hover for 240 seconds. My friend Steve Harrington of Flometrics is dying to try out a liquid nitrogen presurization system modeled after the liquid helium system on the origional apollo lunar lander system. So if we don’t quite get there from a performance stand point with blow down we will add this Ln2 system.
Things to acquire fabricate/do for this vehicle:
- Fabricate a regen chamber. Currecnlty working on an aluminum design, have stainless and nickel designs sketched out, but will try aluminum first.
- Fabricate TVC controls, both Masten and Armadillo are using Bug actuators, a bit pricey, but I’ll probably go that way.
- Fabricate valves usign the existing valve design(s) we have.
- Start the paperwork process so we can do tethered flights in Jan/Feb time frame.
180/300 Second vehicle concept development work:
I’ve done a lot more modeling of a 4 engine electrically pumped vehicle. I really like the results I’m seeing. Even more I like the fact that the propulsion is almost 100% decoupled from the tank design.We are going to go ahead and purchase one set of parts to build 1/4 of the propulsion system. I’ve found a vendor for a positive displacment peroxide compatible pump that is the right size for a 4 engine pumped vehicle.I’ve alos found a vendor for the the motor and speed control of the approriate size. If this works the parts could be easily transfered from a hovering LLC vehicle to a 100Km+ capable reusable suborbital sounding rocket. If the all the LLC $$ had been won this would be my primary project. If this sounds interesting to anyone my priorities can be altered with the proper application of funds ;-)
Things to change in the flight test program:
The Rough terain forklift worked really well so it is going to return for an encore performance. Since construction is slow in california the rental prices have really fallen. One problem with the testing I did for the 90 second vehicle was the cost of each full fuel test. I’m going to modify the vehicle(s) to carry lead bricks to simulate a full fuel load. This way I can verify I have the necessary propulsicve performance without burning up 2K of peroxide for each test. I can put in a single Jug of peroxide and time the hover with the weight and know if I have the proper performance.
13 comments:
Wow. It's exciting to hear that you're going strong. Did you think you'd be at this now into your third year?
If I understand correctly, the 90-second vehicle is intended to be a continuation of your current vehicle but with solid catalyst packs. But I'm not sure of the 180-second vehicle. Is it too going to require a catalyst? Or will the heat of burning the fuel cause decomposition without a catalyst?
We are currently looking at using a catalyst in all three configurations. There is a possibility to revert to liquid catalysts in all three cases, the base line is solid catpack.
I agree with time. Very exciting - glad to see you looking beyond the competition and building a larger platform. Keep up the good work.
Good to see you back at it, Paul! Lots of cool ideas for future development...
Are you at all concerned with the past problems AA had with its various solid pack configurations? Seems like they never settled down on a particular solid-catalyst solution...
>Are you at all concerned with the
>past problems AA had with its
>various solid pack configurations?
Yes ;-)
Aluminium probably works OK provided you don't go to too high chamber pressure, maybe 10 bar (150 psi) is about the max, but higher is possible if you're careful with cooling.
The problem with aluminium is the low melting point. The other problem is that AFAICT most of the likely alloys you would use are marginal on their lifespan at the likely temperatures. As in, you run it and it works fine, but you put the chamber on the shelf for a few weeks or months and then when you return to it, the chamber has age-annealed itself and distorted due to internal stresses, and it may no longer seal properly or something.
You'd have to get the best data you can find on the particular material you want to use, but IRC the maximum working temp on aluminium ~6063 is about 200-250C...ish for a few minutes. You might be able to go a bit higher, but the temper will be gone by maybe 400C. The thing on your side is that there's a useful temperature gradient across the chamber wall, so the stronger metal supports the weakened annealed metal, but you would need to have a fairly good idea of the temps at different points in the metal of the chamber to avoid overcooking it.
Lifetime for a chamber at these sorts of temps would probably be measured in minutes, perhaps 10-20 minutes or something and then you might have to retemper it.
It's all rather complicated and fiddly.
I think the safer engineering route is to use a higher temp material unless you know *exactly* what you're doing.
lead bricks ? Yes, but you will have a constant weight. While testing why not go to water wheigt with an hose?
Aluminum has been used for regen chambers.
Copper has been used for Regen chambers
Steel has been used for Regen chambers
Copper/Nickel has been used for regen chambers
Stainless Steel has been used for regen chambers.
For peroxide you either have serious dangerous material incompatibility problems or you are limited to Aluminum and Stainless.
Stainless does not conduct heat well and is an SOB to fabricate.
So the first attempt will be with aluminum.
Why not water? Because Bricks - with very few exceptions - don't tend to slosh. They also don't freeze and expand, or boil (easily), or leak all over sensitive electronics. Finally, you can strap a brick onto a vehicle with just a couple of straps or some safety-wire - try that with an amorphous blob of water! Even with a bladder or containment vessel its usually more complicated, and then you have the weight and complexity of the containment device.
K.I.S.S.
Paul,
When using the corrugated catalyst from AA, you should spray the peroxide into the catalyst so that the drop sizes are smaller than the catalyst passages so that it won't spit out unreacted droplets.
I would be hesitant to pursue schemes that allow you to think that you can get by with less actual flight time. As already mentioned in a comment, bricks don't slosh, which is an argument against using them. There are others.
If you want to have a chance of performing on demand at the challenge, you should be plan on conducting at least ten full load flights before hand. Be prepared to do several times that number.
Test like you fly, as much as possible.
John Carmack
OK, first of all:
John Carmack = NG-LLC Winner
Me = Estes Model Launcher
But... while I understand all of John's points, I thought the idea for using bricks and a light propellant load was just for checking out the new engine scheme? Can't that at least be useful for gauging basic engine performance and catalyst performance? I seem to recall AA performing a lot of tests "back in the day" with engines and vehicles that weren't capable of going suborbital... ;-)
--Noel
(retreating to his humble world of airplanes and IT)
I would agree with John that to do real tests and as many as you can afford to do. Having said that preliminary tests for basic ISP and estimated engine performance is understandable while in early development and tuning. His comment also backs up your choice not to do the hail mary flight. I do look forward to some long flights in the early new year - one per-month leading up to the comp later in the year (assuming they retain the current format).
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