Hybrid beginner questions and some answers

I received an email recently from a modeler who is considering hybrids.
It occurred to me that his questions are probably pretty common, so I
asked him if I could post them on some newsgroups, and he kindly
consented. Herewith our conversation. I hope people will find it
On Wed Jan 19 19:39 , Ed sent:
dear Doug:
>Wow way cool product, the econo tanker. Sounds like the ideal
>hardware for me. My situation: certified level one in 2003, '04 was
>consumed in a new job and moving, looking at the landscape now, with
>the BATF, LEUP (which I'd have a hard time getting), etc, Hybrids seem
>the way to go. I hope you have a few moments to answer some
Thanks a lot, Ed! Hybrids have a lot to offer...of course, there are a
lot of excellent conventional solid motors you can fly with your Level
1 and no LEUP. I try to design systems that will give you the best
value. One problem with hybrids is that they require special ground
support equipment. My RTLS Modular system
addresses this; the Module 1 Baseblock can be used to fire conventional
motors, in fact it's really a Surefire with extra plugs and relays. Add
the Module 2 and a tank, and you're filling and firing
floating-injector hybrids. Module 3 gives you K-
M motor capability, and Module 4 gets you into GOX-based ignition for
HyperTEK...and all four modules cost about the same as the HyperTEK
ground support system, which only fires HyperTEK motors. The RTLS has
been well received, and I'm proud of it.
The Minitanker was inspired by a couple of things. First of all, the
RATT Works H70 is the most popular hybrid I've sold. It's 29mm, has
enough oomph to fly a lot of common LOC and PML kits, and doesn't cost
much. Then Sky Ripper announced their 29mm G and H motors, and I could
see that there is strong demand for motors in this size range. All
these motors are easily handled by my RTLS-M1 and M2, of course, but I
wanted to try to come up with a lower priced way for people to get
involved with the smaller motors. The RTLS-M1 and M2 together cost
$310....of course, that gets you a relay launcher with built-in battery
that will fire clusters, so it remains a good value. But you have to
get a tank as well, and it's kind of tough to look at $500 in ground
support equipment to fire a motor that costs $80. So I started thinking
about alternatives.
Most clubs have a launch system that supplies 12 volts to a number of
pads. If that's already there, let's use it. By connecting the
Minitanker valve to one set of pad clips and the motor igniter to
another set, you can use one channel to fill the motor and another to
fire it. The Minitanker doesn't have a dump valve, so if
the motor misfires you will have to wait for the N2O to vent, but on G
and H motors this should take no more than a couple of minutes. By
going to a 5 pound tank, which costs me $40 less than a 10 pounder, I
can lower the price some more, and 5 pounds should be good for six or
eight fills depending on conditions...not a bad
day's flying. So instead of $500 in ground support equipment you're
looking at $200 and the use of the club's launch system.
The only thing I'm not happy about is the lack of a dump valve. Adding
the dump valve and associated hardware would kick the price up a lot
since it would be identical to the RTLS-M2 Valve Manifold, which costs
$200 and doesn't include a tank. With the G and H hybrids this isn't a
problem because they have less than 1/2
pound of N2O onboard fully loaded, and that won't take long to vent in
a worst-case scenario. But I'm concerned that people might try to use
the Minitanker on bigger motors. It isn't enough of a concern to keep
me from introducing the Minitanker, because I think there's a need for
it. I'm trying to address the issue by offering to take the Minitanker
valve and hardware in trade to reduce the cost of an RTLS-M2. I can
reuse the components, and I hope the trade-in makes the point that
people really need to upgrade the system for anything bigger than an H
I hope this helps. Specific answers to your other questions are below.
Doug Pratt
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>- The Econo tanker will fill, is there a dump feature in case
>of misfire?
Nope--see above.
- I assume typical pre heater grains are APCP, do they pose a problem
>with 62.5 g and regulation? Especially the Shyripper 29 and 38 mm
>systems, which look very nice (That and propulsion Polymers)
No problem. Sky Ripper preheaters are less than 1/2 ounce. Even the big
RATT Works
K, L and M motors have preheater grains that are under the 62.5g limit.
- Shyripper: I assume the 29mm system will be in the H-I range, any
>prospect of TRA/NAR cert?
Absolutely. Todd Moore, who created the Sky Rippers, won't sell them
until they are Tripoli certified. The 39mm motors have been certified
for a year, and the 29ss are being tested this month.
- I'd be looking at Prodex canisters for recovery deployment, any
>feedback on reliability
We did some tests a year ago and found out that Pyrodex works great in
our Ejection Canisters as long as you wrap the canister with a layer of
stretchy PVC electrical tape. That provides the containment that the
Pyrodex needs to burn completely. We've used Pyrodex instead of BP in
most of our hybrid flights over the last year.
- Last, but not least, recovery has to be electronic. I have very
>little experience there, any advise.
There are some very good products available for this. Personally, I
like the G-Wiz accelerometer, the cheapest one. It fires at apogee
only, but with G and H motors that's all you need, and accelerometers
are very good at telling the difference
between up and down. We like to use the G-Wiz and an Ejection Canister
filled with Pyrodex and taped. A single 9v battery powers the whole
business, and the G-Wiz does not need to be in a vented payload
compartment since it doesn't measure air pressure. In my faithful old
PML Black Brant that I fly with RATT H70s, I wrap the
G-Wiz in bubble wrap and tape and stuff it in the nose cone. Works like
a champ.
We are working on an altimeter, and also on a very simple (and
hopefully cheap) timer. Don't know when they'll be available, but we
have made some test flights.
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Doug Your getting very close to a "Beginners How to do it" Book!
Let's see , A small H70 or H124 , Mini Tanker setup and some recovery cheap and easy to use. This G-Wiz acelerometer is available where?? Ken
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Kenneth Jarosch
I highly recommend Aerocon as a source for the G-Wiz products. He has a nice special going on his website right now.
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Funny you should mention the book. I hope to have a book ready for publication by summer. The working title is "Hybrid Rocket Motor User's Guide." I'm setting up a little publishing company called Robin Hill Press to put out this and a revised edition of "Basics of Model Rocketry."
Doug Pratt dad-at-pratthobbies-dot-com
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