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COVINA, California USA — Liquid-fueled rocket motors appear to be the next generation of hybrid motor technology, at least if left to Dave Griffith of RATTWorks.  Griffith successfully flew an M850 "tri-brid" motor at this past weekend's LDRS during the experimental launch event, and is ready to raise the bar.

The "tri-brid" motor basically introduces a liquid fuel component to the traditional hybrid's nitrous oxide and expendable plastic fuel grain, creating a motor configuration that burns in hybrid mode initially before releasing the liquid fuel when entering "tri-brid" mode.  The liquid fuel in this case is an alcohol.

According to Griffith, "I've been working on this design for more than 10 years and it's pretty much perfected these days.  I've had 40 consecutive flawless motor firings."  Griffith's next step appears to be TMT certification to allow the "tri-brid" to be used at sanctioned Tripoli launches. "Right now it's approved by the NFPA 1125 which allows liquid fuels with hybrids so long as they're ethyl-alcohol or methyl-alcohol," Griffith stated, adding, "I talked to Paul Holmes and plan to certify the motors this October." 

Dave Griffith's M850 "tri-brid" flew at LDRS using alcohol and nitrous oxide.

The "tri-brid" uses traditional mono-tube hybrid design with the addition of a central liquid fuel tank connected to a specially ported injector to route both the nitrous and the alcohol into the combustion chamber.  The fueling of the alcohol is done during assembly of the motor, with the nitrous being loaded remotely once the rocket is on the launch rail, as is done with traditional mono-tube hybrids.

At ignition, the igniter lights the preheater grain, which in turn burns through the nitrous fill line.  Nitrous oxide enters into the combustion chamber and, combining with the burning preheater grain, begins the consumption of the plastic fuel grain.  At this point, the motor is operating as any traditional nitrous oxide hybrid.

By this point, a plug retaining the alcohol in its chamber burns through, releasing the alcohol into the combustion chamber, causing the motor to enter "tri-brid" mode.  Roughly 2 seconds into this stage, the remainder of the hybrid fuel grain is consumed and the motor transitions into liquid-only bi-propellant mode, burning the balance of the alcohol and nitrous oxide.

This type of burn sequence for nitrous oxide liquid-fueled motors will most likely become an advantageous way to go, according the Griffith's RATTWorks web site, as the motor runs extremely smooth and should not be subject to "hard starts." The site heralds the "tri-brid" concept, saying "a problem-free high power rocketry liquid motor appears to be in the works."

Griffith's M850 reached an altitude of 14,790 feet with a maximum velocity of 1,306 feet/second, a burn time of 4.5 seconds, maximum thrust of 650 pounds and an approximate average thrust of about 350 pounds.

Website: http://www.rattworks.net/

Reader comments:

#1 Tribrid technology

This looks really interesting. The Tribrid rocket motor tutorial walks you through the theory of operation step by step.

k3td on 07-18-2007 10:21 PM

#2

Wow I love this idea! I am by no means even a regular hybrid user, but I love the idea of bi-liquids if they can be about as easy and safe as a hybrid. I know there were a few DIY bipropellant kits out there from time to time, never knew anyone who made one however.

Will the ATF let us use IRFNA?

New Ocean on 07-19-2007 12:42 PM

#3 Tri-brid

I was at LDRS and got to see this rocket fly. The thing that got me was the scream of the motor.

mikewhorley on 07-20-2007 09:45 PM

#4

Quote:

I was at LDRS and got to see this rocket fly. The thing that got me was the scream of the motor.

I have seen them since day one. I admit to being spoiled.

The "scream" has improved to the point where dogs suffer, children whine, and adults "need".

RATT indeed.

Just Jerry

Just Jerry on 07-21-2007 12:08 AM

#5

Looks like an interesting setup... I wonder if it'll come in 75mm...?

Len_Lekx on 07-21-2007 03:21 PM

#6

Quote:

Looks like an interesting setup... I wonder if it'll come in 75mm...?

The concept is certainly scalable, so no reason it couldn't done in a 75mm!

ddmobley on 07-21-2007 04:23 PM

#7

I also got to wondering about using fuels instead of denatured alcohol.

What kind of performance-boost would result in replacing it with R/C "Glow-Fuel", which is a combination of Methanol and Nitromethane. GUIPEP gives it a fairly impressive Isp, but would the combustion result in an overpressure failure?

I might get one, just to do some static tests...

Len_Lekx on 07-22-2007 11:23 PM

#8

Just realize that if you take a motor that is certified (which the RATT tribrid would be in October after going through TMT testing) and then change the fuel from what it was certified with (ethyl/methyl alcohol), it is no longer certified and would not be able to be flown at any certified launch. So you would be limited to just static testing, unless flown alone.

ddmobley on 07-23-2007 02:03 PM

#9

Quote:

Just realize that if you take a motor that is certified (which the RATT tribrid would be in October after going through TMT testing) and then change the fuel from what it was certified with (ethyl/methyl alcohol), it is no longer certified and would not be able to be flown at any certified launch. So you would be limited to just static testing, unless flown alone.

Would it qualify for a TRA EX launch? I know you can't put certified propellant into another case or configuration and call it EX but as you're changing out the propellant (well, one of them) I think it'd qualify. I'm curious about switching to something like kerosene or even liquid methane.

-Aaron

heada on 07-23-2007 02:07 PM

#10

Quote:

Would it qualify for a TRA EX launch? I know you can't put certified propellant into another case or configuration and call it EX but as you're changing out the propellant (well, one of them) I think it'd qualify. I'm curious about switching to something like kerosene or even liquid methane.

-Aaron

It looks like you might be able to as long as you previously obtained TRA BOD approval. At least that is my interpretation of the following TRA Research Safety Code sections:
3.2.4 Rocket Motor. As used in this code, Rocket Motor shall refer only to Composite Propellant, Sugar Propellant, and Hybrid Rocket Motor.
3.2.10 Hybrid Rocket Motor. A rocket motor in which the fuel exists in a different physical state (solid or gaseous) than the oxidizer and that derives its force or thrust from the combination thereof.
5.2 (Exclusions) Liquid Rocket Motors
5.2.1 With the exception of nitrous-oxide hybrid rocket motors, liquid rocket motors are prohibited at Tripoli Research Launches. BOD approval may be given for very well documented liquid motor projects.

Your best bet would probably be to contact the manufacturer and ask their advice. In time the manufacturer might use Section 6 of the Research Safety Code to get its motors included.

Steve_Shannon on 07-23-2007 02:59 PM

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