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Yup, that's what I use, but you could also reasonably use an inert-gas gauge.

I've been down this road. The problem with using casings intended for solids is that they aren't really long enough to make a "serious" hybrid motor. Not enough volume for N2O, once you make your fuel grain long enough to provide an adequate O/F ratio for the proposed thrust level. Robert Galejs has been down this road recently, you should get some of his thoughts.
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snipped-for-privacy@propulsionpolymers.com (Marcus Leech) wrote:

Couldn't you make a device to use the reloadable case as the fuel grain and nozzle retainer and in stead of a bulkhead closure, screw a huge N2O tank on top?
Jerry
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Jerry Irvine wrote:

That sounds a lot like the original Aerotech hybrid... (Actually, there's a piece that screws into the front of the casing in place of the solid motor's closure, and a fitting on the tank screws into that...)
-dave w
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Ya, I know.
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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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My upgrade would to install a long motor case diameter tank that is considerably lighter than a conventional tank. Heck use a different regulation system so it can be "pad loaded" like AeroTech (by Kline).
Jerry
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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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On 10 Oct 2003 08:08:39 -0700, snipped-for-privacy@propulsionpolymers.com (Marcus Leech) is alleged to have written:

That is a potential problem. Hybrids do, in general, suffer from lower thrust than solid motors of the same overall size, since the oxidizer is stored in a seperate compartment from the fuel, so your "combustion chamber" volume is necessarily reduced in volume if you keep the overall motor size the same. However, two things are working in my favor, here:
1) I don't necessarily care to get the highest possible thrust from the motors. Rather, I'm looking at this as an inexpensive way to reuse existing casings to allow people to fly a variety of hybrids without a huge investment in new hardware. Any time there's a new motor design, people resist trying it because they have sunk costs in their existing hardware. It makes sense to me that giving people a way to apply that same investment to a new motor line would be welcomed.
2) Instantaneous thrust is dependent on burning surface area, not volume of the combustion chamber. If people are willing to pay a little more per flight for higher thrust, there's no reason that the fuel grain geometry couldn't be tweaked to increase the burning surface area. Professional hybrid motors use multiple cores to acheive greatly increased surface area in the same volume -- as an example, think of a grain with 7 cores arranged like the holes in a "medusa" nozzle....
I'll definitely look Robert up, and see what he has to say. If nothing else, this has given me something to experiment with in my CFT.
- Rick "Gas passer" Dickinson
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Rick, your work sounds fantastic! I hope you're documenting it. If you have pictures and information, I could create an "experimental" section on flyhybrids.org for it.
Gary Rosenfield once showed me a prototype AT G hybrid. I had a very hard time handing it back to him!
Doug Pratt www.pratthobbies.com www.flyhybrids.org
(Marcus

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#3
I will keep that in mind. Thanks.

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It's probably better to invest in proper solenoid drivers, irrespective of the "heavy dutishness" of the solenoids.
There's a huge difference between "pull in" and "hold" currents. No sense driving _any_ solenoid at "pull in" currents for more than you have to. Especially if you're worried about battery life.
They do this (mechanically) in car starters.
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There are high pressure solenoid valves available with 12 volt continuous duty coils. Parker skinner make nice valves Why use cycle duty coils for a continuous duty application. The coils usually draw 20-26 watts. NOS valves are not designed for continuous duty. You most likely will not find high pressure 12 volt continuous duty valves on the shelf but, they can easily be special ordered. Be careful when ordering. there are dozens of options for valves. Working pressure, bust pressure, CV, body material, plunger material, seal material, seat material, ect. Make sure you check ever option for the valve. Gary Deaver

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HEY! I resemble that remark. i'm in the same boat....hybrids just seems way to complex and fail way too often to be any fun.
-Darren
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That's funny, I was thinking the same thing as I watched a L3 cert attempt with AP (1/6 scale V2 from SkunkWorks). I have a clear video of the rocket lifting off to about 30' and the flight of the motor out the nose, impacting 20' from where we were standing. It proceeded to burn out both ends, leaving the casing oval and threads smooth.
That was a lot of Fun at 4x the cost of Hypertek launch.
Joel. phx

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A defective motor should be replaced.

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rocket
impacting
It may have landed 20 feet from you; JD and I were a lot closer. One nice thing about a hybrid motor is that when one comes apart, the fire goes out. I'd much rather face a failed hybrid spraying nitrous than a failed AP motor spraying flame and burning chunks.
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says...

Bzzzt. I saw a L hybrid fail by spitting the end closure and nozzle. The motor went through the rocket and then continued on a parabolic arc, burning for a LONG time. Burned until it was out of sight a long way downrange (and off the field).
Therefore hybrids are not only a pain in the rear, they are downright dangerous and should be heavily regulated.
(or you hybrid guys could lighten up a bit ;-)
--
Kurt Kesler

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BOY,... I get a dig in at Jerry (solids bigot), and THIS is the thanks I get?!
:)
Joel. phx

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snipped-for-privacy@thegroup.thanks says...

Hey, this IS RMR, you know.
;-)
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I'm bad at distances. I don't think it went up 30' either. We can watch the video this weekend, I'll have to do some editing.
If you recall the shortened Tomahawk that went all the way up to the top of the rail under nitrous pressure managed to keep burning after setting down next to the pad (now I WISH I had that one on video).
Joel. phx

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One of the nice things about hybrids, is that it's almost impossible to overpressure one. Blow the ends off (defective closures) certainly, outright burst? Extremely rarely.
If the chamber overpressures, it simply stops the nitrous flow. This is part of the reason why some howl on boost - boost oscilation...

Not too long ago, as LCO, I watched someone's carbon fiber rocket on a solid J chuff - sort of. It threw the thing up about 100 feet. Started to arc over (at this point I was yelling heads-up over the PA system because it was still emitting smoke & flame), and it finally "caught" just as it was going below horizontal...
Skipped across the field under full thrust leaving burning bits in its wake...
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snipped-for-privacy@dca.net says...

Now you've gone and stepped in it...
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