Monday, November 2, 2009

More information on AT 24mm Gs

On this thread on TRF, Gary Rosenfield has released some more information about the possibility of 24mm Gs.

He confirms they'd be for 24/120 hardware, which would presumably be a 2-grain configuration. According to the 24/60 assembly drawing helpfully located in the 'resources' section on the Aerotech website, the fuel grains in the 24/60 case are 2.85" long, hence the 24/120 case would be 7.2 (=2.85+4.35) inches long, including the forward closure but not the aft closure.

He also confirms that they're working on other loads for the 24/60, including Redlines. This makes the EGE very very happy. The fact that he says loads, plural, prolly indicates a Black Jack and/or Blue Thunder load in the works.

He says that the single G load currently in the works will be a core-burner, because a C-slot grain would require either a thicker paper liner or phenolic liner, which would be more expensive. Also, for multi-grain motors, aligning the slots requires taping the grain together - an extra step that if forgotten would likely prevent proper ignition of the motor, certainly result in a strange thrust pattern with a much higher initial spike, and possibly cause a CATO.

He also mentions that because it would be a core burner, it would prolly be over 80N average thrust, making it a High Power motor instead of a Model Rocket motor, which may or may not be allowed at the Salem field I usually launch at.


KenKzak said...

Yes, aligning multiple C-slots [or moons] is a PITA.
Since the new grains will be coreburn instead of C-slot, all bets are off on final case length. Moreso, since the longer the core, the larger the core diameter needs to be, which means more length, which, which.... And yes, the average thrust goes up yet again.
This may keep me awake tonight!!!

The EGE said...

I just figured it'd be a set 2-grain size, similar to all their 29-98mm hardware (except the few weird ones like the 29/100), and I figured they'd just use the 24/60 grain size.

What shape are moonburner cores?

KenKzak said...

I understand your initial assumption.
But since the new grains will be coreburn and not C-slot, there is no commonality constraint, therefore other considerations can drive the design.
Allowing for 62.5g of propellant with the denser formulas and/or with the largest core diameters [lowest propellant volume per x length] would be good starting points.

Given that Gary is calling it a 24/120, some lower ISP formulas may still fall in the F category, while only high ISP formulas are G's. OTOH; Maybe full capacity G's, and spacered F's like the 29/120 case.
It's all suppositions for now.
Make'em long Gary, make'em hot.

A moonburner has a core or shallow slot at one side of the grain, against the case wall. In endview, as they burn, the remaining propellant resembles the waning crescent moon. A handy way to double the burntime, but the burntime and pressure graphs are sometimes a bit strange, labor is higher, and they're more difficult for rocketeers to use.

Aerotech used to make them in all sizes in SU, now just in 54mm and above. I think the J90W is still the current smallest.

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