HyperTek don't like you to hold the button down for too long, 5 seconds
seems to be the maximum recommended by Anthony although that isn't mentioned
in the user guide.
If I knew the rate, I could work out the maximum quantity that might be
The quantity is very low.
Get the smallest O2 tank you can find(the disposable ones dont have enough
pressure) and it will last you several years of flying before refilling.
I would hazard a guess of 100 flights.
Yes ... a small (230l) tank will cost several hundred pounds to buy, and has
to be tested every five years, if you can find someone willing to refill it
- ar about £100 per year to rent, what with fills, delivery, VAT, account
charges and so on (I hear they are cheaper and less hassle to get in the US,
but it's like that here in the UK).
So I was looking at cheaper alternatives. It's probably doable, but I need
to know the flow rate. Anthony has promised to get me figures though.
I was just following up on that talk and doing some research. The presenter
(Scott?) mentioned that hybrid motor average thrust ratings are somewhat
misleadingly low due to their long thrust tails when they switch from using
liquid N2O to gas. So I went to the TMT site to see the curves. I couldn't
find ANY thrust curves there. The few motors with links are broken. What's
up? Where are the thrust curves?
For that matter, most of the motors don't have expiration dates listed, and
of course the last time TMT released any delay accuracy information was when
John Cato was running things.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD"
>>> To reply, remove the TRABoD!
I want that treatment! Then ""my"" motors would never expire and I could
change them anytime I want (like AT, AT by EM, AT by RCS, AT by
"Personally, I wouldn't build anything with Ellis Mountain motors in
mind -- we've seen a VERY high CATO rate at our launches, and I rather
doubt anyone in our club will be buying any more of them."
- Kevin Trojanowski, Tripoli webmaster
there are thrust curves for ProPoly and WCH motors.
SkyRipper have got thrust curves up on their site -
RATTWorks thrust curves can be found at
All of these show the thrust tail-off very well, though the SkyRipper graphs
tend to be distorted by large transients at ignition.
There is also
I don't know how far I trust the data there though - the HyperTek K240 is
listed as ~1450Ns, while all other data I've seen (including the HyperTek
official site) suggests less than 1300Ns fo that motor (regardless of tank,
the TC data is all from the old 81mm tank).
Odd you should mention that. I just noticed it as well.
Rant mode on.
The usefullness of the Tripoli Motor Testing web pages has decreased from its
already abismal level.
There is a note stating that manufacturer certification dates have been removed
because they are "irrelevant to the certified list". I suspect that the real
reason is that too many people were questioning the large number of motors with
dates indicating that they were past due (some way past due) for recertification
testing. Rather than fix the problem (do the required testing and get the data
posted), TMT decided to hide it.
A side effect of this change is that what little testing data was available was
linked off of these dates and is now gone. No thrust curves or performance
figures from the official certification letter anymore.
To make matters worse, the links that did take you to a RASP compatible motor
file all provide "404" file not found errors. Or at least all the ones I tried
before giving up.
So now the TMT certified motor list which was rarely up to date has even less
I just wish that TMT would take a look at the NAR pages. They have many useful
things that TMT does not:
1) Each and every motor has a link to a document with detailed performance
information from the certification test: total impulse, average thrust, measured
delay times, a thrust curve, and RASP data.
2) Perhaps most usefull, an archive of S&T certification announcements.
Certifications, decertifications. What happened and when.
Bob Kaplow wrote:
Got a reply from Anthony, 450 scfh. That's 0.625 cu ft or 17.5 litres if the
oxygen is on for 5 seconds.
The smallest "proper" O2 bottle contains 230 standard litres/8 cu ft, so it
would do about 10 or 11 launches at that rate, allowing a bit for
pressurising the lines, reserve, remainder in the bottle, and so on.
I guess I do not understand.
I said get the smallest O2 tank you can find.
I rent mine from a welding shop.
One time deposit of $50 and $15 to refill. And one fill will last years.
And when you get it 'refilled' they dont actually fill it, they simply give
you another full bottle.
Since this is the smallest tank available I do not understand how you can
make it any 'cheaper'.
The only other tank is the disposable type.
They are $7 each and do not contain enough pressure to work with hybrids.
The only other thing that you might be able to do is take a used tank of
some sort and fill it with pressurized O2 from a larger bottle maybe at a
Since its free it will be much cheaper.
But putting pressurized O2 in just any old tank is asking for an explosion
and should not be done.
I agree with you in sentiment, but I also wonder whose ultimate
responsibility it is. Frankly, the AT site ought be a lot better, too.
For example, I'd like to see tables with links to cert docs, thrust
curves, RASP files and dimensioned motor drawings (24x70 is not enough;
it doesn't include the delay/ejection well (for example)). In fact, I
think every motor vendor should have such tables. Ideally, each table
could be sorted on demand for impulse family, motor diameter, etc.
Having all that combined on one site would be awesome. Thrustcurve.org
was an attempt at that but I think they lost their mojo, and I suspect
that's what happened at TMT.
It's a herculean task. To do it right requires a professional effort.
I've looked at the site several times, and each time I do, it strikes me
as an ovewhelming task to clean it up.
So I wonder whether it's fair to ding TMT with that. It's basically a
motor vendor marketing tool, a central repository of information for
rocketeers. The motor vendors, who are paying for the tests, are the
ones who need to step up and tell TMT to fix it, and then likely put
some money in the kitty to pay for it. At the same time, they all have
legitimate grounds for griping when they've paid for tests and cert's
without getting RASP files, proper entry in the (TMT) web tables,
correct information, etc.
I see undisciplined data gathering and sloppy documentation as the first
things that need fixing. Each test summary should contain the same
info. It's frustrating to see missing and wrong info in the TMT motor
tables because somebody didn't bother to measure and record the motor's
dimensions or propellant weight. That's pretty sloppy test engineering.
Once constistently good motor files are produced, then the web tables
will be much easier to maintain. It's a GIGO thing.
Another thing the motor vendors should ping TMT on is motor
designations. If I develop and test an G47, and I know the average
thrust is indeed within tolerance of 47N, then by dangoes I expect TMT
to list it as a G47 and not a G41 or G56. I'm paying for it, and I have
an investment to protect. People considering buying my motor and taking
the time to research it need to be able to find it without guessing what
it's supposed to be on TMT's site. I know TMT lists both designations,
but they also have incorrectly listed the dimensions and vendors, so
it's real easy to lose confidence in the info.
If the customer doesn't trust the info, he won't buy the motor. The
motor vendors must push TMT to provide quality data. It helps us, and
it helps them.
"Doug Sams" wrote:
At Aerotech they should be able to do it then.
At Tripoli they have professionals "volunteering' to do it, and FAILING
Huh? TMT is the ISSUING AUTHORITY (they BEGGED to have that authority to
Of course they should have EVERY certification ever issued listed as of
the effective date of that certification.
They want it to be vague so the uncertified motors they openly sell can
be flown at TRA launches due to CONFUSION.
Not going to happen with TRA sycophants.
Which is the H motor list from March 2004. I count eight motors that show an
expired manufacturers certification without a burn until date.
Note to Bob Kaplow: You might notice that at least a few of the certification
documents can be found here as well. For example: