Re: Propellant Breakthroughs?

Hmmm.... as far as "minimum GSE" goes, do you really need all those solenoids and stuff for a Rattworks or similar "UC valve" hybrid (where the nylon hose is melted by an igniter grain to release the nitrous into the chamber)?

It would seem that all you would need is the nitrous tank itself, and a bit of copper line with an adapter union at the rocket end to connect to the nylon tubing, and the correct fitting for the tank valve CGA thread at the other: open the tank until the motor's vent spits liquid, then valve off the tank and fire. (There would be some loss of nitrous since the contents of the length of line between the tank valve and the rocket would just vent out after launch, and if you really wanted to be able to abort the flight and disable the motor (without just letting the nitrous evaporate via the vent), you would need something like a small hand-operated valve connected to a T-fitting near the supply tank end of the line, but it seems like it should basically work... am I missing anything critical?

-dave w

Like standing next to a pressure vessel which has been pressure and temperature cycled and possibly bounced a bit, but not hydro tested?

Joel. phx

David W. Schultz

That's what the length of copper line is for - so the tank isn't in close to the motor during the fill, but can be located remotely (near the launch controller, for instance).

-dave w

And 100' of copper line is cheaper than a solenoid?

Joel. phx

Hmmm.... last time I bought a roll of 1/4" copper tubing it was $9.54 for a 50 foot roll, at my friendly neighborhood refrigeration parts distributor. (I just dug out the receipt and checked.)

Where y'all gettin' an oxidizer-capable solenoid valve, with the right pressure rating for nitrous, for $19? (The "hot rod" ones aren't _that_ inexpensive, are they?)

-dave w

Also it is a VENTED tank and the fill line itself could have a reasonably low burst pressure.

Nobody can fix the TRA safety code.

That's sort of strange come to think of it - the Aerotech system uses a sealed tank which is designed to be filled manually (by weight) via a short adapter hose, and then screwed into the motor assembly, and the whole thing is then installed like a solid motor. Do the vented-tank "UC valve" motors use a construction that is so much less robust that the fill operation is considered by the safety code to bear the same degree of "close-in hazard" as the actual firing?

-dave w

The only difference is the AT system used a DOT certified tank (paintball) and the monotube tanks are "uncertified", but they are vented and also pad filled.

Jerry

So how do the actual mechanical mechanical safety factors compare between a typical "vented monotube" and a DOT-rated "paintball" style? (And does a flight tank, even if it's being filled manually at close range, need the same safety factors as a tank intended to be used as a container for common-carrier product shipments?)

-dave w

This is yet another example of transferring (improperly) DOT standards for shipments (subject to high impact accidents) and a pad loaded rocket by a consumer.

If the real issue is pressure safety, why NOT add a hydro-test to at least the motor cert protocol?

This is irrational laziness by TRA and probably another example of "prophylactic overcompliance" just like asking for ATF permits for obviously exemt goods.

No wonder both ATF and DOT are confused over us. Tripoli confused them.

Jerry

NFPA1127 requires that hybrid tankage be proof tested to 2000PSI, which is nearly 3 times the MEOP of these systems. Contrast that to requirement for solids that the casings merely be "sensibly engineered" (not the exact words, but that's the gist).

For CAR testing, at least, monotube hybrids must be hydro-tested to 2000PSI. Propulsion Polymers tests to 2250PSI.

The requirement for testing to 2000PSI for hybrid casings, but no such test for solids in NFPA1127 constitutes an unreasonable unlevel playing field. While I certainly would *insist* on proof testing for hybrid tankage that was filled "up close and personal", the requirement makes no sense for remote-filled tankage. I ended up re-designing the PentaMax 54mm series from a nicely-flightweight 0.065" tubing to a somewhat-heavier wall tubing, not because of any *real* safety issues, but because the margins for NFPA1127 compliance weren't as high as I would have liked.

In any real scenarios the nylon fill tubing will rupture during a fill long before the tankage lets go, so why make the tankage heavier than it really needs to be?

$50. How many times will that $10 copper un-roll and re-roll? Not mention the joy you'll add to setup and tear down. At 200' I'm already considering the additional expense of wireless. If you want to go the disposable route, Homedepo sells O2 in tiny bottles for $10. If you had an adapter made, you could just buy those instead of the $60 tank. Of course refills of the $60 tank are less than one HD bottle.

Joel. phx

Yes, and one after each flight in case it came down rather hard. Oh and in order to fly you have to first show the RSO your motor AND the recert card so they know you had it tested. Oh, and since you just flew it you better have another tank.

Joel. phx

Ranting doesn't (and won't) make people listen to you.

Guys, please spare a little thought for safety here. I'm not trying to push everyone to buy my GSE, but if I could make it cost less, I would. I'm already hearing horror stories about someone filling a floating injector hybrid by opening the tank valve, then running up to the pad after launch to close the valve. We don't need a new chapter of "stupid rocket tricks" just as people are starting to take hybrids seriously.

Doug Pratt

You are being intentionally extreme. A hydrotest uses a $200 tool that can be universally used with all manufacturer's systems.

If the motor test firm is so concerned about tank pressure, test it. Or just eliminate the stupid rule.

There are so many stupid rules.

Has anyone ever seen a tank overpressure in the entire time hybrids have been used?

Jerry

As I said in the prior post, too many rules!

I agree. So either:

1. Eliminate the remote rule (preferred to allow low cost fill methods) or
2. Eliminate the fixed pressure standard. or
3. Both.

Point.

Jerry

Certainly - that's why I'm basically asking what can be safely done... assuming a safe fill distance equal to recommended safe launch distance for floating injector "monotube" hybrids, that's still something like 30 feet for an F motor IIRC. If I run a line from a tank at the launch control point out to the pad, and control the fill from the tank valve, does this introduce a hazard not present in filling via a solenoid valve from a tank out at the pad?

Clearly, the "direct line" method is more oriented toward the "micro hybrid" end of the spectrum... for a larger bird, solenoids would make sense, but at 20 cents a foot, 30 feet of copper tubing can almost be considered an expendable item.

-dave w

Oh, small hybrids. Ok how about this. Ball valves at the tank with levers. Pull the line, it pulls the lever, and stretches a spring to close the valve when you let go. Second set for dump. Easier to wind up than tubing.

Joel. phx