No problem, Laura. Reach me directly at jmarino1 (at) sbcglobal
Contrail looks like it has some pretty good numbers for it's motors.
But... Are they CSFM certified for use in Kalifornia? I don't know... But
I'll see what I can find out.
I took a look at Sky Ripper Motors, but it's still not clear to me how
the grains work. Do you have to weigh the N2O to change the impulse?
One of the things that attracted me to Contrails is that I could see
all the impulse possibilities with a set of hardware.
I want to give Sky Rippers a chance so can you tell me a little about
how the various impulse configurations work (or a link) or maybe why
Mark A Palmer wrote:
Despite recommending the Contrail motors, I think *very* highly of the
Skyripper motors as well. Although they offer fewer grain / injector /
nozzle combinations, they are strong performers, very reliable, and easy to
fly. I find they are also easier to clean than the Contrail motors,
generally showing far less blow-by. The quality of machining and finish is
Skyripper motors currently hold the hybrid H & I TRA altitude records. They
are well worth a look. I certified L1 on the 38mm H155, and between the 29mm
& 38mm motor sets I fly just as many SR motors as Contrail.
FWIW, the 29mm Skyrippers are probably my favorite hybrid motors. They are
serious performers, and very economical to fly. I recently lost one, and
bought two to replace it, if that tells you anything.
The 38mm SR motors have 2 certified motors per case size. You select the
impulse by choosing the reload type: PVC is good, polypropolene (PP) is
slightly better. The four SR 38mm cases give you eight motor combos, full G
thru baby J.
As far as weighing N2O - historically Aerotech hybrid motors required you to
weigh and pre-load the N2O, but all of the current crop of monotube motors
require you to fill the N2O flight tank from a distance of no less than 100
feet, just before launch. At a nominal operating pressure of 750psi, there
is only something like a 2:1 safety margin on the flight tank.... not
something you want to stand close to.
I didn't get the impression that anyone was putting Sky Rippers down.
I have read a lot of good things about them. Thank you for helping
clarify some confusion about the grains. Am I wrong or do the contrail
motors seem to have greater lift. My rockets are a little heavy.
My L1 rocket weighed in at 5.5 pounds with glass and all. When I
start to add electronics, I can see the weight going up even more. I
will try to keep the weight down, but so far it's not my forte.
Anyway, I guess I'm saying that I like the thrust that seems to be
greater with the I impulse Contrails motors. From what I could find
out about the Contrails motors and I could be wrong, it seems that the
hybrid average thrust approaches the AP of the same class. I thought I
saw that Sky Rippers, like the Contrails motors have a set of hardware
that will work for both L1 and L2 flights.
Let me know your thoughts..
I will be looking for some 29mm motors and I will certainly take your
advice regarding the 29mm Sky Rippers. I like to fly some smaller
rockets with my relatives in Illinois and the 29mm motors are just the
ticket. As an aside, the fact that I go to Illinois to fly is another
reason the hybrids look attractive since I can freely move them around
without the cumbersome permits.
Kevin OClassen wrote:
Thrust numbers of hybrid rockets are hard to compare to that of APCP motors,
for a couple of reasons. Take a look at
http://www.skyrippersystems.com/documents/FAQ.htm About halfway down the
page there is an outstanding explanation of how the operation of hybrids
affects the certified thrust.
Add to that monotube hybrids have a highly regressive thrust curve, and the
initial thrust is much higher than the average thrust. I frequently launch a
6+ pound (dry weight) rocket on the SR H155, and it flies beautifully. The
rocket, all up on the pad with nitrous loaded is a bit over 7 lbs.
The Contrail motors do have good average thrust, but it comes at a price. A
given amount of nitrous plus a given amount of fuel, burned at the same
rate, yields a certain total impulse, no matter the manufacturer. The rub is
in how fast it is burned. If you look at the impulse ratings for the "slow"
Contrail motors you'll find they match the SR average and total impulse
ratings pretty closely. What Contrail has done is to add different size
nozzles and injectors, causing the engines to burn the same amount of
oxidizer/fuel in a shorter time, giving higher AVERAGE thrust. However, as
the motor speed goes up it appears that the efficency of the motor goes
down, so that the faster motors have higher average impulse but lower TOTAL
impulse. Not a huge amount, but enough to be noticeable.
Also, the conditions under which the motors are rated/certified makes a
difference. The most important factor is temperature of the N2O. If I
understood correctly, SR bases its' ratings on an ambient temp of 70F
(~750psi), Contrail on 85F (~875 psi). This difference will affect the
published performance of the motor. As the temp of N2O rises it becomes less
dense, thus offering less O2 for total thrust, though it pushes the average
thrust up a bit. Personally, I like to use pressures of 650-700 psi, since
it gives killer performance and creates much less strain on the hardware.
I've seen folks tank and launch at 900psi, but I'll pass at that pressure...
The Skyripper 38mm motor set does indeed span the range of motors from G to
baby J, so is great for L1 & L2. Todd also has a series of 54mm motors in
process for certification. One thing I noticed on the SR website is a larger
nozzle/injector set for the 38mm motors, which will increase the average
thrust of the motors to ~250NS on PP fuel. I'm looking into that for
Also, RockSim or SpaceCad are your friend :) When in doubt, sim it out....
Thanks for replying Kevin. I could not have said it better myself. I
recently flew the 29mm H at XPRS in my daughters Snitch. Easy set up easy
clean up! In fact I found it mucheasier to build and clean then AT RMS. They
are extremely reliable, simple and easy to use (1 set of internal
components...Noxxle, Injector, bulk head etc). Nothing to mix up. I have
seen a whole bunch of these motors fly..they sound, look and perform great!
"Kevin OClassen" < firstname.lastname@example.org> wrote in message
It's still back under construction, but their links work to the
different motors and pricing if you click on "Products" at the top..
Their domain expired earlier this year and someone snatched the name
out from under them before they could renew so they lost their primary
website.. The above site is what they're working on to rebuild it..
They're not going anywhere.. I just picked up the H70/I80 casings as
well as the L600/M900 set and they've still got reloads for all of
them.. Dave is a good guy, but this is not their primary business..
They're a very old machine shop (Monterey Machine Products) doing
aerospace parts since the 50's so don't expect them to be picking up
and going anywhere anytime soon..
Skyripper, Ratt, or Contrail. These will all fly from Doug's ULS system +
RTLS2 without any additional ground support, except various sized fittings.
I personally like the Skyripper motors for reliability and Contrail for the
large number of certified combinations.
The monotube motors I fly use four different sizes of fill line, so I made a
series of quick-connect hoses with the correct fitting on each end. That way
swapping out the fitting is a matter of a few seconds and requires no tools.
To give you even more food for thought, check out the yahoo group
A lot of those folks are doing stuff that is way over my head, but they are
wellspring of advice and encouragement, and the archives are invaluable.
PS> If I were in your position (already L1), knowing what I know now, I'd
probably start with the Contrail 38mm motor set. Motors from G100 to a 45%
J800, reasonable hardware and reload cost, good performance. I used the
38mm set to certify L2.
I found a PDF document with an article you wrote about hybrids. Do you
have any ideas on which system is best to start with? I am mostly
concerned with cost and versatility over the Classes H through K. I
also need to know how to modify my rocket to accommodate the motors. I
am currently am building a 3 inch rocket that would be nice to put the
necessary motor mount into. I also have a 54mm, 4 inch rocket, but the
motor tube is only about 16 inches long. I don't care so much about
the sound or smoke, or even complexity. I look forward to a challenge.
Alex Mericas wrote:
I have a 3" rocket with a 54mm mount that flies very nicely on a
Hypertek 54mm 440cc or 835cc motors. With these two tanks I can put
together 11 different motors ranging from an I260 to a K240, but mainly
in the J range. With the smaller 300cc tank I can fly 6 different I
combinations. I really like the Hypertek system and it was what I used
to get into Hybrids. I've also flown RATTworks 29mm and 76mm motors. I
personally don't like the 29mm RATTworks but love the 76mm K240. I have
a WestCoast Hybrids I110 which I love, nice sound and smoke.
The HT system uses non-pyro ignition which requires an O2 tank. Most of
the mono-tube hybrids use a sliver of APCP (under 62.5g) to heat the
motor and burn through the fill stem. If you like that concept and you
want to fly L1 motors you should look at Skyripper or West Coast hybrids
as good starter motors. If there are gas passers nearby, find out what
As far as how to modify a rocket for hybrids, it's pretty simple. The
rocket has to be long enough for the motor. You don't have to fully
support the top part of the motor but you can't have the motor sticking
out the top! Watch your stability to make sure you don't run into
problems with extra weight at the back of the motor (sim it fully loaded
with N2O). Make sure you have a way to vent the motor externally, which
will vary depending on your motor.
I appreciate all the information on the Hypertek motors. I didn't
realize there were that many possible variations with the two tanks.
Is it possible to ignite the Hypertek using pyrogen and do all the high
voltage ignitors need O2?
Alex Mericas wrote:
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