Hybrid Rockets and
I'm interested in hybrid motors for rocketry. Why? I
don't know. But
I'm into the techie side. And I love the loong burns. And the hybrids
are also attractive for the higher power rockets (L2 & L3) as the
reloads are much cheaper - and certified motors readily available -
something difficult to say on both accounts for composites (though
particularly on cost).
My club that flies at Whitakers has HyperTek equipment, though I'm told
that it's essentially not used So HyperTeck is an option. And recently
Doug Pratt donated the adapter set to convert the club's HyperTek
equipment to launch U/C valve hybrids.
The Ratt Works are nice, and have H class motors (perhaps nice for
getting started), and can be fired from HyperTek equipment with an
adapter. Reloads readily available. The disadvantage is the motors are
LONG - essentially due to the 29mm tubes they're based on (one motor,
the I (?) is 36" long (!)) They've now got 38mm tubes. and have also a
64mm K-240 and L/M-900 motor set.
The Propulsion Polymers seem like an improvement on the Ratt Works -
for me mainly due to the 38mm tube yields a shorter motor. Pratt
Hobbies has them, though they don't list the "smaller motors" that span
into the Ratt Works range. RATT now has 38mm motors. They've also added
an L/M combo.
I am also thinking that a Rocket designed for a long 38mm tube could
also take the long Cesaroni & Aerotech motors, which would add a
lot of flexibility in launching.
Hybrids require electronics and there is no motor ejection.
Hybrids also require special builds as the motor tubes are much longer.
This often conflicts with placement of as-designed dual deployment
systems as well as, for custom, shifting the balance point for rocket
design. There's also the issue of lower average impulse so they need
somewhat lighter rockets. The long burns make it all worthwhile though!
I've scratch built my own GSE as I've been frustrated
apparent inability to sync up with the right people with the right
equipment at a particular launch. So for the last 4 launches or so,
I've had my motors, but was unable to launch them for various reasons -
that boiled down to not having my own GSE. This situation will
certainly improve overall - but I
want to fly! The GSE availability at Whitakers is resolved, and the
equipment typically in the trailer.
I've built a master / slave relay control panel along the lines of
the "12 volt relay launcher". I've modified it though to use CAT-5
cable (through DB-9 connectors) and by doing so I get power from the
slave and can also add NOX dump/fill and O2 lines. I won't be using the
GOX, but am adding support for it so that I can launch HyperTek's later
(either mine or others). I will post plans, schematics, and
I've completed my GSE for all extents and purposes. It's complete with
to handling all fill/dump/gox relays and one pad. The launch pad box
installed relays for pads 2, 3, but those aren't wired to the second
or the breakout strip. The LCO box will fully control the launch pad
with respect to pad 1 and the hybrid relays. It does not yet have ANY
for pads 2 and 3 nor does it yet support single box launching (using
the LCO box for a "close, non hybrid pad").
You can look at more details on my Hybrid
I occasionally find myself desiring or needing (sometimes out of field
necessity) to adapt equipment to my own or from my own to others. In
that light I'm starting to work out the Hypertek GSE Pinouts.
Click on that link for what information I've got.
Relief Cuts, and Sheething
On U/C valve type motors it is
important to get the fill tubing to burn through and separate as close
to it's exit point from the injector. The lower the burn through the
lower the average thrust, the higher the O/F ration, the higher
probability of a burn through, esp if the tubing is slightly bent and
pointing even slightly towards a side of a grain. (It's quite common
for the tubing to have a slight bend and very difficult to eliminate
A common technique, that is really the minimun you should do, is to
overwrap the fill tube, for the length of the motor grain and a bit
more, tightly with an overlap to two thicknesses of electrical
tape. Leave just enough of a gap to match the thickness of the
Dave Griffith of Monterey Machine (RATTWorks) now supplies cardboard
tube sheaths for his 29mm motor reloads. These work great
Dave also came up with the idea of using some high temp fiberglass
sheathing for, in particular, his 64mm K-240, Tribrid, and L/M motors.
Here's a picture of a K-240 TriBrid fill tube with fiberglass sheathing
Dave: "For the Ratt K- 240 5/16 dia fill lines use 1/4 i.d. sleeving
(part# 8819k44) mount about 1" below injector and long enough to
reach past nozzle. use black tape to hold in place. On the Ratt TriBrid
and L/M 600-900 motors with 3/8 fill lines use 5/16 i.d. sleeving
(part# 8819k45) mount right at below groove and long enough to go
past nozzle and tape in place. Price is only .31 per foot.
For the larger nylon fill tubings, 5/16" for his K-240 and 3/8" for his
TriBrid and L/M combos, Dave cuts a relief groove in the fill tubing to
further encourage U/C valve separation at the desired opint.
Here's a close-up of that same fill tube illustrating the relief
This tubing is high pressure 3/8" nylon tubing. The ID is 0.25"
providing a measured wall thickness of 0.065". The OD of the relief
groove is 0.325" so 0.050" has been removed. providing a
new calculated wall thickness of 0.065 - (1/2)(0.050) or 0.040" so
we've removed about 1/3rd of the wall thickness.
Pyro-Free GSE (ignition)
The HyperTek system seemed cumbersome requiring all the
GSE. Now that I'm building out my own GSE, adding O2 seems only
more of a slight additional expense.
Basically it's a flare fitting T. The leg would carry the
"ignition gas" to the outer sleeve. One end of the T would have a
compression with the larger ignition gas tubing; the other end of the T
would have the N2O tubing running through it. The specific orientation
is only to allow the N2O
tubing, which goes through the fitting, to go straight through. The
ignition gas tubes terminate at the fitting so can be on the leg and
end of the fitting.
West Coast and
Polymers have been up to this. Here's the West Coast Hybrids instruction document and
they're Pyro-Free GSE plans; and the
Polymer's instructions (well, one variant anyway) has pyro free info.
Here's a NOW Hybrids page on Pyro Free for RATTWorks
Hybrid Rocket Motors.
I've purchased a Propulsion Polymers I160
from Pratt Hobbies. I've
since purchased the other tubes and floating injector in the set. I
hoped to then use the larger J140 tube to attain my TRA L2
certification. But for various reasons that didn't pan out and I got my
L2 cert on a solid. I bashed
Pride, my PML Black Brant VB, and re-christened her "Periwinkle's Pride
Gets N2Oxious". The J-140 motor took up most of this
body tube I doubled it's length adding a recovery module
main chute bay.
I've flown Periwinkle half dozen times or so on the I-160 and J-140
tubes. both are sweet rides. Nice kick off the pad and nice long burns.
They don't have the raspy "farty" note of the RATT Works motors, so
some folks don't recognize it for a hybrid flight.
Propulsion Polymers now has a nice 54mm "Penta Max" motor with two
tubes and configurable injectors.
Do see Designing Rockets for
down below and, in particular, my efforts at bashing
I'm interested in one of Rene Caldera's
Micro Hybrid. It offers something unique but also inexpensive
flights as well. Plus fancy hardware for my tool fetish page. Roy Trzeciak-Hicks and Caveman Rocketry are
producing finished motors. Since I don't have a lathe to finish a kit,
I bought an assembled motor from Caveman Rocketry on a Rocketry Online
I've received this motor and plan on building a rocket
for it. Since the motor has no recovery provisions I'm planning on
using a Magnetic Apogee Detector to fire the main chute. These are
inexpensive (~$30) and quite compact. I've got a "Kinda Jayhawkish" LOC
kit for it.
Update: I've picked up some N2O micro-cylinders from
(cheap!), but haven't done anything with it yet. I think I'll try it
in a Art Applewhite UFO so I can test it in a rocket not requiring
(I haven't anything small that has electronic recovery - though I DO
have a MAD detector on my bench). And the LOC kit on the bench too.
This page discusses rocket recovery electronics. The
is on altimeters, timers, tracking transmitters, beepers, etc. Look
elsewhere on this index page for other electronics.
Designing a rocket for Hybrids is a little more
challenging. Partly due to the longer motor tubes (very long in the
RATT, particularly the M-900!) Also the need for electronic deployment.
And, if one wants dual
deployment, the weight of those components is shifted farther forward.
For such a more neutral balance (vs short motors in the ends),
either a longer rocket is required
OR smaller fins. This to keep the rocket "stable" but not over stable.
Small fins requires a longer launch rod/rail depending on the initial
motor thrust. The other issue is the relatively low average impulse of
hybrids. Long motor burns, yes, but lower average impulse. Fortunately,
most thrust curves are regressive providing a nice kick off the pad.
Note that Apogee Rocketry's Hybrid
Motors In RockSim page they erroneously state that the worst case
scenario is when the motor is empty. This is not correct. The worst
case scenario is when the nitrous level matches the CP in the rocket.
It is at this point that the nitrous is "doing it's worst" making the
CG/CP relationship unstable as it's at this point that the nitrous
weight is pulling the CG back the most. The situation actually improves
again as the nitrous is consumed.
So CG/CP is at it's best when motor
is at it's worst when nitrous matches CP
is, well, somewhere inbetween when nitrous consumed.
Here's a specific link to a cool rocket. It's built for the HyperTek,
but the ideas apply. This link is from Star Rocketry. They also have
some good build info.
Scratch Built Purple Reign
There doesn't otherwise seem to be much info, concentrated at least,
for designing for hybrids.
I've been bashing
Periwinkle and have her ready to go. I plan on launching her at
August Whitakers. I've had her ready for a while but this time I'll
have my own GSE so that I'm self-sufficient and can launch no matter
who attends otherwise.
I missed August Whitakers, and misplaced my large floating injector for
Whitakers, so am not targeting October Whitakers, with a bashed
with my new GSE.
RATT Works and HyperTek were the
early certified sport hybrid rocket motor vendors. To many, the RATT
K-240 is the quintessential hybrid rocket motor.
As of this writing they have 29mm ,38mm, and 64mm motors. That they
didn't have 38mm motors was one reason I bought my Propulsion Polymers
set though I must say I'm very happy with that set. The 64mm motors,
now spanning a K-240, through K-350, through an L/M-900 combo, are an
odd size, but fortunately PML 2.5" BT is a perfect MMT and CRs are
available so there isn't any real reason, from a build perspective to
not consider these motors.
I have the H-70. It's a nice easy flyer. 29mm and 18" long. I bought it
to fit my PML BullPuppy 2.1 after a slow Kosdon G-40 skywriting session
shortened the rocket so it wouldn't balance for my favorite Kosdon
29-150 loads. It was long enough for this motor to use the rocket as a
booster section and I built a payload bay with dual deploy and have
been getting nice 1,000 foot flights off her.
K-240 / K-350
To many this is the quintessential hybrid rocket motor. A nice, loud,
farty resonance, 8 second burn, it is recognized by many. As folks say
"A serious ride for a 10lb rocket." Now available is an (uncertified at
this writing) new injector that ups the impulse and ISP and provides a
full K flight and higher average impulse as K-350.
I have one from a ROL Auction (motor and 4 reloads for $230). I am
looking to build a new booster section for "Ignorant Of My
Destiny" to fly this motor. I am working with Dr Zox on a "ratfink" fin theme
just for fun. I will
probably call it Ratfink too. Right now, this is looking to be a 14lb
rocket. I need to do the sims to see if it needs to be flown on the
K-350 injector or whether the K-240 stock motor will be safe on
Recently introduced is this L/M motor combo. 900 Ns average thrust with
a nice pad peak on a regressive thrust curve. It's still 64mm and this
the M variant is long - about 78" whereas the smallest M HyperTek is
about 40" it comes as a 42" long L-900 along with an extension tube
that makes it an M-900. Aside from it's length it looks like a sweet
I'm considering using one for my L3
. It's flexible and nicely priced at $375 for
the L/M combo and reloads are about $80 for the L and $95 for the M vs
$125-$150 for the HyperTek M reloads..
One minor advantage, perhaps, is I maybe be able to use it for larger
EX flights, moreso at least than if I bought a HyperTek. and in the
larger sizes, I'm not sure if there is an easy L/M HyperTek combo.
Now hybrids has a RATT
resource page with McMaster part numbers. It's here
Aerocon / Bill Colburn
Bill Colburn produced some 38mm H/I
hybrid rocket motors with the intention of certifying them. They were
never certified, but I managed to pick one up on a ROL Auction. Since
it's now an EX motor at this point, I'm documenting it and my
activities on my Experimental
Hybrid Rocket Motor Page
/ West Coast Hybrids / HyperTek
I mean no disrespect glomming these
vendors together. It's mostly that I have less to say about motors that
I don't own. ... which is no longer true about HyperTEK ,...
Aside from RATT Works, HyperTek is the quintessential sport hybrid
rocket motor. They're available for 54mm J motors through farily large
98mm M motors. They require more complex GSE (get your club to buy it;
Whitakers has it) but motor prep is much easier than for a U/C valve
motor. Overall, it's your preference, but you'll find a wider selection
of motors in the larger sizes (J and up) with HyperTek. Many of their
motors are configurable using different injector combinations for
different flight characteristics and one of the J loads can be flown
The only reason I don't have one (at this time of writing) is that now
having my own U/C GSE I can fly anywhere ther's a rail. Whitakers is my
main flying home now, and they've got a HyperTek GSE, so there's less
reason for me to not consider one.
Well, I've got a HyperTEK Hammerhead J now and will be flying it sport
Here's the HyperTEK Manual
Here's the current HyperTEK
Here's a favored way of preparing the hv speaker wire. Well, several.
The "split" and also the "Breathe Right Strip" Technique:
West Coast Hybrids
WCH has a nice 38mm motor and I think is working on others. It seems to
be popular on the Western US. I believe they're working on a 54mm motor.
Sky Rippers is a newer entry in the market. They have a nice 38mm tube
set and are gaining in popularity. One nice feature is they use snap
ring cases (made by Woody at http://www.ProXHardware.com) so fit
standard retainers. I've also considered one as a candidate for EX
Hybrids as I may need to do nothing more than slip in a Loki 38mm
o-ring'd nozzle and fly some pipe. I believe they're working on a 54mm
Hybrid Rocket Motors
General / links
Bill Shamblin - Bill was an early hybrid flyer at
Whitakers and has an experiment hybrid rocket motor page.
Robert Gaejis (sp) - the inventor of the MAD Apogee sensor has been
flying experimental hybrid rocket motors.
Cold Fusion N2O systems http://www.coldfusionN2O.com
- ask for Mike and for the eBay pricing; should be lots off their list.