rickster75
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What is a "Grain"? When looking to purchase engines, it refers to them in quints of "Grains".
This is a guess, open to correction.Anyone know why they are called "grains"? Why not just call them slugs or segments?
you cannot have a motor with less than one grain
I have no idea, but the term has been used by the pros for nearly 70 years.Anyone know why they are called "grains"? Why not just call them slugs or segments?
Anyone know why they are called "grains"? Why not just call them slugs or segments?
They are called grains because before they invented APCP they used to make rocket motors out of oats and quinoa.
What is a "Grain"? When looking to purchase engines, it refers to them in quints of "Grains".
One of the difficult things for people new to the hobby to figure out is the relationship between vendor hardware and reloads and the terms we use. For example, a person may say they used a 3-grain 38 mm Aerotech motor. However, Aerotech designates the cases by impulse as 38-240, 360, 480, etc.
Similarly, the reloads area not intuitively matched to cases. For example, J275W, J90W, J460T reloads all fit the 54-852 case. Without experience, or a secret decoder ring, it can be difficult to figure out. The Aerotech price list (or the old RouseTech matrix) can be used to match reloads to cases, but none of them say how many ‘grains’ are in a particular reload.
Makes sense to me. Didn't CTI have the advantage of looking at how several other vendors, including AT, had already done it?Exactly. Then, Aerotech introduced "grain" spacers to fit in "impulse" cases with little to no explanation of how this works. Horrible nomenclature and documentation by Aerotech. Cesaroni is far better in this regard.
Makes sense to me. Didn't CTI have the advantage of looking at how several other vendors, including AT, had already done it?
I was speaking of course to CTIs update to the multi-vendor "customary" OD-Ns nomenclature, not your bug report on AT 54mm spacer documentation ( which I believe they've already amended and published ).I believe CTI came out with the spacers first.
Quick quiz for you: Will a J401FJ reload fit into a 54/2560 case, and if so, how many spacers, and of what length, are required?
5...4...3...2...1...time's up.
Hint: I already bitched about this in the Propulsion forum.
I was speaking of course to CTIs update to the multi-vendor "customary" OD-Ns nomenclature, not your bug report on AT 54mm spacer documentation ( which I believe they've already amended and published ).
Yes x-grains can be more intuitive especially in a spacer context -- still doesn't tell us what the OAL of that case is and thus whether it will fit in our MMT. Further since the length of "grains" varies by load, it's worse in other contexts.
And if we're to be making propulsion selections in five seconds or less, I'm not sure any amount of simplification will help us.
AFAIK the only error on that table is that for the 54/2800 case you need the short spacer and two regular spacers to use a 54/1706 reload, and for the 54/2800->54/2560 you need only the short spacer.However, this table is incorrect in some instances
It would be a lot cheaper than AP!How did that work out as rocket fuel?
Maybe we should bring it back?
rofl!
AFAIK the only error on that table is that for the 54/2800 case you need the short spacer and two regular spacers to use a 54/1706 reload, and for the 54/2800->54/2560 you need only the short spacer.
Oops, OK, you're right. The 54/2560 line should say that with 2 regular spacers you can use 54/1706 and there are no options for 1 spacer. I tried to explain the situation in your thread but I guess I didn't do a good enough job. To compute the number of grains in an AT 54mm case, divide by 426. So 54/426 is 1G, 54/852 is 2G, 54/1280 is 3G, 54/1706 is 4G, 54/2560 is 6G, and 54/2880 is a weird special case, it uses 6 grains that are longer than the standard grain length, hence the need for the short spacer. (Of course, not all AT reloads even have multiple grains -- the long-burns are single monolithic grains, for example.)The J401FJ fits the 54/1280 case. Per the table, it should fit a 54/2560 case with two spacers.
Nope, AT amended somebody else's bug report, not mine. Answer to the quiz: No, that load will not fit in that case, even with all possible spacers. I didn't figure that out until I purchased the load, tore it open, and tried to assemble it.
A simple table, like this, would provide a 5 second answer. However, this table is incorrect in some instances and led me astray on the J401 purchase:
I believe CTI came out with the spacers first.
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