Hybrid GSE build...

Discussions on hybrid rocketry including rockets, motors and technologies.

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ROCKet STAR
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Re: Hybrid GSE build...

Postby ROCKet STAR » Wed Mar 17, 2010 1:17 pm

PK wrote:
ROCKet STAR wrote:My trouble is I'm a stubborn b*****d and when I get an idea in my head I have to follow it through. My girlfriend hates it :P


I'll leave that one alone.....
:-)


Yeah, I probably could have worded that a bit better. :oops: What I meant to imply is that I get carried away with things and she has to put up with me spending all my time working on them! I shouldn't complain, at least she puts up with it!
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Re: Hybrid GSE build...

Postby Sumo310 » Wed Mar 17, 2010 1:33 pm

hybridhighflyer wrote:As for chosing which system to pick im willing to settle this once and for all. A drag race between a contrail and rattworks of the same size and impulse im certain contrail will be chosen. Simon you up for the challenge?


OK, 5,4,3,2,1.. GO!

Number of RATT motors flown @ QRS, 1
Number of Contrail flown, 0

I win :D
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Re: Hybrid GSE build...

Postby hybridhighflyer » Wed Mar 17, 2010 1:36 pm

See I knew you were chicken simon ;)

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Re: Hybrid GSE build...

Postby Sumo310 » Wed Mar 17, 2010 1:57 pm

HAH! Explain to me how you'd do it. I see issues with needing 2 sets of GSE, 2 different fill times, different ignition types (maybe?), different burn times ;) Its not going to happen. How about an AT J350 vs J333?

I'm not saying the Rattworks motor is the best solution, infact I probably wouldn't buy another one, but at $60US for an H70, up to $100US for an I90, they're pretty good value, and a relatively easy way to get into hybrids.
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Re: Hybrid GSE build...

Postby hybridhighflyer » Wed Mar 17, 2010 2:17 pm

Sorry simon never knew you were so sensitive about the topic..... must have missed it with all the "contrail bashing" that goes on in the forum ;)

More was a I fire off and then you fire off challenge than a drag race. The funnyest thing I see on this forums and at launches is everyone knocks things they know nothing about.

I did hear you and a few boys knocking me at last launch and even laughing at me trying to setup the hybrid. Personally I think behaviour like that does not help promote hybrids positively reguardless of what brand.

The way I see it is i'd love to see the 2 go off close by to help promote hybrids in our club than a competition.

To be honest with contrail it would be like a carola going against a diablo like you said impossible to really compare the 2.

I do agree RATT is a great place for hybrid beginners who are wallet sensitive.

So what you say me and you have a hybrid launch together? for fun than compertition us hybrid boys really need to work together more.... that includes you too PK and even ET star

Thanks
Wayne

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Re: Hybrid GSE build...

Postby PK » Wed Mar 17, 2010 2:41 pm

hybridhighflyer wrote:More was a I fire off and then you fire off challenge than a drag race. The funnyest thing I see on this forums and at launches is everyone knocks things they know nothing about.

There's an ivitation!

I've had a 38mm contrail motor in my hands about two weeks ago. The nozzle arrangement is just too basic. The graphite is right up against the case and will de-temper it over the first few burns. The fact that the casings don't fail there means the tube is too heavy.

If you look at the Rattworks motors, Dave includes a nozzle insulator. He does this because he's been making these things longer than just about anyone and knows that it's necessary.

Dave also uses threaded closures which are easier to prep and don't wear like snap ring grooves.

But the biggest thing wrong with the Contrail motors is the lack of an oring seal between the grain and the nozzle, that's just dumb... Even if you want to stick with the big graphite nozzle hard up against the case, you can still partially imerse it in the grain. Marcus (propulsion polymers) did it that way, it worked well on his small motors..

If you look at the larger contrail motors with the fixed injector heads, they use only three or four bolts to hold the thing together. Again the reason they get away with this poor engineering is because the tube walls are way too thick and hence the motors are concrete donkeys..

As far as U/C valve, commercial hybrid motors go, the Rattworks motors demonstrate decades of experience whilst the contrails are clearly an attempt to get a product to market quickly at the lowest cost and hence the highest margin.

The way I see it is i'd love to see the 2 go off close by to help promote hybrids in our club than a competition.

That's hardly a definitive test.
It all comes down to what you think "better" means. In a club environment I'd argue that "Number of sucessful launches vs attempts" is a good metric.
You could argue performance, easily settled with a load cell and two motors. I reckon density ISP is a pretty good measure of a hybrids performance. Maybe total cost of ownership over 20 actual launches, include things like GSE, relaod cost, actual NOX used (including misfires)..

If you take any of those metrics other than density ISP, then the old Aerotech hybrids win hands down, about $20 of GSE, almost 100% sucess rates (pyrovalves are very reliable), and MUCH cheaper to run because you're not venting NOX when you fill...
PK

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Re: Hybrid GSE build...

Postby hybridhighflyer » Wed Mar 17, 2010 3:11 pm

When I get home PK ill show you the "thing" that seperates the grain from the nossle. its quite a nice washer some people dont use it and that might be their issue.

It does exsist however some people dont use it.

I have had 14 test burns using 1 nossle and the nossle after a small wash looks good as new. I have tested a "large range" of contrail motor sizes too.

Sometimes simple things work best. Contrail should always launch first time every time my luck on public launches with a new gas bottle is a exception.

Like I said PK im more than happy to do a "lab test" with you guys and remember what one person wants from a rocket is different than others. I am thinking of going your way for a launch to check it out over there.

I do have a interesting question for you though PK ... I have seen one of your "creations" and how it works however have you fired a contrail? I have fired almost every type of hybrid on the market.

Not discounting your opinion on this but I live on the theory dont knock it till you try it. Again each person wants something else out of rocketry.

Thanks
Wayne

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Re: Hybrid GSE build...

Postby PK » Wed Mar 17, 2010 4:41 pm

hybridhighflyer wrote:When I get home PK ill show you the "thing" that seperates the grain from the nossle. its quite a nice washer some people dont use it and that might be their issue.
Umm you mean that stainless steel washer? Hate to be the one to have to tell you, but that goes between the nozzle and the snap ring. If you've put it between the nozzle and the fuel grain then you have assembled the motor incorrectly. (See step 13 on page 8 of the instructions)

I have had 14 test burns using 1 nossle and the nossle after a small wash looks good as new. I have tested a "large range" of contrail motor sizes too.


The nozzle will hold up fine, It's the case that takes a beating, the contrail cases only hold up because they are made from a much heavier aluminium tube than you need to make them from. This isn't necessarily a bad thing from a reliability point of view, but that doesn't make it a good piece of engineering.

Sometimes simple things work best. Contrail should always launch first time every time my luck on public launches with a new gas bottle is a exception.
Like I said, number of successful flights from number of actual attempts means a lot more than just saying "My hybrid is better than your hybrid"

Like I said PK im more than happy to do a "lab test" with you guys and remember what one person wants from a rocket is different than others. I am thinking of going your way for a launch to check it out over there.

I agree, I don't think ISP or total impulse is actually a relevant measure of a hobby rocket propulsion systems goodness.

I do have a interesting question for you though PK ... I have seen one of your "creations" and how it works however have you fired a contrail?

Nup, I've never owned a commercial hybrid, I think I once owned a 29mm Aerotech 120 case. Probably the most money I've ever spent on a commercial motor.

I was the LCO for about 5 years and I've launched just about everything though, we've had PP/Rattworks/West Coast Hybrids/Hypertek/Aerotech/Even Rene's Microhybrids.
The contrail stuff is very new.

There's nothing about the contrail motor that makes it any more or less reliable to start than any other U/C valve motor. What makes these things reliable is the rate the preheater dumps heat into the combustion chamber and the way you protect the bit of the fill line you don't want to rupture from that heat. Other than that they're all identical from an ignition reliability perspective.
If you want ignition reliability from a commercial hybrid then you need to look at a pyrovalve or Hypertek system. Having said that, once you know what you're doing, U/C valve motors can be very reliable. Troy probably has the most experience with big ones and he seems to get close to 100% these days...
PK

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Re: Hybrid GSE build...

Postby RobAust » Wed Mar 17, 2010 6:22 pm

Thanks guys for your quick response.

As soon as you mentioned liquid N20 I got it.

The websites are great and will provide plenty of reading material, I can then ask "more better" questions....

Regards,

RobW
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Re: Hybrid GSE build...

Postby hybridhighflyer » Wed Mar 17, 2010 8:31 pm

Hey PK they come with 2 washers one either side is what I do. Even spoken to Tom about this and he said he did the same.

Ok so we are clear you have never flown one ... i do suggest it.

As you said PK actions speak louder than words so with that note ill gladly send you a motor kit and a reload to try.

We can argue engineering all day however from a rocketeers point of view contrail have given me the best results.

If there is a better design let the aussie rocketry community come together and make one ;) Ill gladly make it

Anyhow back to topic hope we helped rob.

Thanks
Wayne

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Re: Hybrid GSE build...

Postby OverTheTop » Thu Mar 18, 2010 8:05 pm

I'm no expert on rocketry, but we use stainless steel in our scientific instruments when we need a "thermal insulator" (relative terminology, of course!).

While it is not like a vacuum flask as far as heat transfer, it's thermal conductivity is around 1/12 that of aluminium. Depending on thermal masses and burn times, it may be sufficient insulation.

Just an interesting fact. That's why stainless steel cutlery works well.
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Re: Hybrid GSE build...

Postby ROCKet STAR » Wed Nov 03, 2010 8:13 am

Time flys when you are having fun, and I have just realised how long it has been since I posted an update on how this is going. I am the first to admit I have been rather slack here and should have had this finished months ago, but one thing after another has slowed me down somewhat (excuses escuses).

I have made some further progress, but I have changed the design somewhat. I was finding the backlash between the gears was less than desirable, maybe I am overcomplicating things by reversing the motor to close the valve. Anyway I have ditched the gears in favour of coupling the motor and valve directly and I'm using a cam (very simmilar to Craigs design) to indicate the position of the valve.

The other thing I'm introducing to the mix is a vent sensor. At a recent launch we were struggling to see any sign of a vent due to the very low humidity at the time, so I figure a vent sensor will make things a great deal easier. The challenge there is going to be determining what kind of temperature drop I am going to see when the motor is venting liquid as apposed to just cold gas.

What would be very cool would be to have a microcontroller close the fill valve when venting is detected... But I should probably just get the bloody thing finished!

I'll post some more photos soon.
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Re: Hybrid GSE build...

Postby Andrew Burns » Thu Nov 04, 2010 5:16 am

I'd avoid having an automatic feedback system control any of the GSE events if only because I could see it being a huge pain if it goes wrong (imagine being stuck in a field with the GSE automatically closing the fill valve 3 seconds after you start because of a false reading etc). What would be cool is a wireless system to display tank pressure and vent temperature during filling.

We had the 'no visible vent' problem at a recent launch of a larger hybrid, luckily there was a load cell under the rocket on the pad measuring its weight so we knew exactly how much nitrous was in the tank and when that number stopped going up we fired. We think the lack of vent in that case was because it was very hot and the nitrous in the tank was very low density near-gas rubbish.

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Re: Hybrid GSE build...

Postby ROCKet STAR » Thu Nov 04, 2010 10:16 pm

Andrew Burns wrote:I'd avoid having an automatic feedback system control any of the GSE events if only because I could see it being a huge pain if it goes wrong (imagine being stuck in a field with the GSE automatically closing the fill valve 3 seconds after you start because of a false reading etc).


Yeah, I think you are right.


What would be cool is a wireless system to display tank pressure and vent temperature during filling.


The wireless thing is something I have seriously been thinking about... when you compare the cost of a couple of hundred feet of cable, with the cost of wireless transceivers (something like this http://www.littlebirdelectronics.com/pr ... r-x-2.html) It seems the logical thing to do... not to mention the fact you don't have to roll it all out, roll it back up again and lug it about!
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Re: Hybrid GSE build...

Postby hybridhighflyer » Mon Nov 08, 2010 7:57 am

HA!


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