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solrules

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Originally posted by Joe Burger
It is called the J825 and is on engineering hold. This motor has big bugs to work out.
Heh. I bet!

Without divulging company secrets, can you tell me if I'm on the right track:

Erosive burning. This is a huge one. The motor is very long, so the gasses are moving pretty quick at the nozzle end, shearing off propellant from the aft few grains. To combat this, you could either put a "slow redline" propellant in the load, as you do "slow WL" with the J570 (possibly needing another TMT testing becasue of a different formula!). Another way to combat erosive burning would be to make the aft 2-3 grains have a larger core, letting the gasses expand, thus slow down at the aft end, reducing erosive burning. There could be problems with the larger cores, however. If the cores were not exaimened, the directions read improperly, or people simply did not realize that the 2 or 3 grains with the larger cores need to be at the bottom, KABOOM! There would be no way to prove they installed the propellant improperly, so you would have to reimburse them.....

Also, with the longer motor length, the aft grains get a considerable compression force acting on them. This could lead to the grains cracking, increasing surface area and, again, KABOOM! This is espically important for AP based propellants, as they are "spongey" (a la Spongebob propellant by Ellis Mountain), and have less of a compressive loading ability before they crack as opposed to brittle propellants (candy).

Plus the fact that redline is a fast propellant by nature, so there would be a greater buildup of pressure in the case, and you may not be able to make the nozzle throat wide enough to make up for the insane pressure. If you were able to make the throat wide enough (which I imaine you could), you would have a less than ideal expansion ratio, limited by the 38mm OD of the nozzle, making the propellant inefficient. A way to lower the pressure would be to decrease the Kn of the motor. This would entail longer grains, and I assume all AT 38mm grains are the same length, so a different machine may be needed if you were to make the grains longer. This would also lead to a progressive burn, a thing not all too common in AT motors.

That's just my brainstorming, though......
 

Donaldsrockets

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I'd like to see a Redline and Blue Thunder reload for the 38/120, I might be getting one of those casings now that I have something other than my Small Endeavour to put it in.:D

I bet there are serious issues with the J825, sounds like a very, very, very nasty motor.
 

Oliver

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Originally posted by andysrockets
It is good to hear that the ball is rolling on both sides of the pond. When I met Gary Rosenfield recently, things certainly seemed to look positive, but as with anything related to Governments (especially EU burocracy), these things take time and money
Andy, as far as I understand, specially the money plays a large part. To receive a CE mark, a company needs to invest a large amount of it to test and certify a product line. Possible more than they are able to sell here in Europe for a couple of years.

Greets,

Oliver
 

Stymye

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Oliver is correct,It's not an easy task to become CE compliant.
 

rstaff3

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I can attest to the costliness in the computer/electronics area. There you can in general use US labs. Some areas, such as medical electonics IIRC, requires a certified/competent body in the EU to do the work. More costly and more difficult to coordinate. The cost for testing isn't the big item for someone who will sell a million computers, but it was for <10 custom items. There was also a lot of cost to make mods after the tests failed :(

The terms may be off since its been a while since I looked into CE and was never that much of an expert. Plus things have changed in the last 5 years. You can probably find a US company to use as a consultant to find out exactly what's needed. I worked with one who had a contractual relationship with a EU entity, which made my life far easier.
 
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