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...