dpower
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- Jan 18, 2009
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So, I happened to be studying the thrust curves in the Aerotech catalog, and became curious about the different thrust curves of SU vs Hobbyline RMS G motors. I'm sure most of you know this, but it took me a bit of head scratching, until it became clear that this is due to the grain geometries. The SU motors, at least the G77/78/79 would seem to have a circular bore (though AT doesn't specify this anywhere I could find), compared to the C-Slot of the Hobbyline RMS (obvious, since I've assembled those). Then again, the "high-power style" RMS G motors, such as the G77 & G79, must also use a circular bore, though I haven't used those.
Anyone know why they choose to use different geometries? Is one cheaper to produce? Or just to give us choices? Is the regressive curve intentional for certain designs, to get sufficient velocity off the rod? One downside I've had to the C-Slot, some igniters are a very tight fit, and they're a bit more of a pain to assemble, needing to align the grains (for the newer 2 grain 24/40-120 reloads).
Anyhow, I'm just looking for some discussion on this. This is a nice summary for AP rookies like me:
https://en.wikipedia.org/wiki/Solid-fuel_rocket#Grain_geometry
Anyone know why they choose to use different geometries? Is one cheaper to produce? Or just to give us choices? Is the regressive curve intentional for certain designs, to get sufficient velocity off the rod? One downside I've had to the C-Slot, some igniters are a very tight fit, and they're a bit more of a pain to assemble, needing to align the grains (for the newer 2 grain 24/40-120 reloads).
Anyhow, I'm just looking for some discussion on this. This is a nice summary for AP rookies like me:
https://en.wikipedia.org/wiki/Solid-fuel_rocket#Grain_geometry