Monday, July 06, 2015


Over the last two weeks John and I have built and failed 10 or so short tank samples.
We have a tank solution... fully allocated with fittings and end caps we have a MR of about
15 at 795 PSI burst. (16 at 500 psi)

Now we have to put together the tooling to make flight length tanks , ie longer than the samples.

I did a 3d printed regen motor design and sent off to have a SLS nylon version printed to evaluate.
That should be here today.

Not sure if I want to put gimbal at the nozzle (as test print) or up at the top of the motor...
Been busy....


Bob Steinke said...

Pretty neat! Is the mass ratio with peroxide or with both propellants at the intended mixture ratio?

Paul Breed said...

Both at the intended ratio... full.... so doing blow down achieved number will be 1/2

Paul Breed said...

Got my nylon model, the cooling passages are all blocked....
Grumble Grumble....

Alexander said...

Was nylon model the same size?

Is it possible to design the chamber so channels could be (better) cleaned after manufacturing? That will de-optimize chamber, but still - manufacturability?..

Paul Breed said...

Yes I'm redoing it so the coolign channels are cleanable.
This probably means leaving the bottom part of the open and then welding a ring in place to close it after makig sure its clear... hope to finishe that design and send it off tonight.

Anonymous said...

Why don't you take what you've learned with the 4" tube and scale it up to 8" or so? That way you'd get the square cube law working for you rather than working against you--especially when you lose the weight of all the extra fittings and plumbing lines.

For the size rockets you're considering, it seems to me the Otrag approach doesn't help because Otrag was comparing a simple tube vs. the complex tanks of much larger rockets--tanks which had many feet of welds, complex internal bracing, and so on. In your case, a 6 or 8" (or even 10 or 12") tube is no more complex than a 4" one, nor is it that much more costly--almost anyone who can wind you a 4" tube can probably wind you a 12" one for about the 4" price plus the cost of the additional materials. Certainly a 12" tube won't cost 12 times what a 4" tube would cost, which is what the ratio would have to be to make the Otrag approach viable (using your 1-6-12 rocket as a basis for comparison). So you're losing on mass and you're not gaining anything on cost--in fact, I'm pretty sure the clustered approach will end up costing *more*.

When you factor in the additional complexity of the Otrag approach (have you figured out how to reliably air-start 6 motors simultaneously?) I think a single tank/single motor (per stage) is going to start looking very, very appealing. My own feeling is that you have to solve enough problems getting to orbit (like spinning up the third stage while aiming it where you want it and doing so within a very tight mass budget) that you don't need to encumber yourself with the non-essential complexity, mass, (and probably cost) of clustering.

I might also point out that when you double the length of your tank to allow for pressurizing it, you're effectively cutting the density of your propellant by half (same mass, twice the volume)--thereby making it comparable to or slightly less than the density of nitrous. Not sure that's a win, either--may as well just use nitrous and omit the extra complexity of a separate pressurization scheme.

All that aside, I'm not saying you can't make a clustered approach work; I'm sure given enough man hours, persistence, and dollars you can in fact do it. It's just that I don't see the point when a simpler, lighter, and cheaper solution exists.

Sorry about the cold water.

Paul Breed said...

Air start is easy with a cat pack, just turn it on it runs.
Yes the task would get easier in larger scale.... it would also get more expensive...

Trying to do this for minimum cost once... may go to 6" tanks if cant make weight at 4". The other problem is that the 6" vacuum motor would not 3d print, it gets too big....

So trying the thread the needle here...

Lars said...

Looks very cool paul.

What CAD did you use to model the regent engine, and do you have some more images of the cooling channels? Are they equally space radially around the chamber?

Paul Breed said...

I did the motor in Rhino,
I've been evaluating CAD systems and I'm on the verge of buying solidworks as much as that is distasteful.

Yes equal radial passages, so speeds up in the throat and exit cone slows down around the chamber...

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