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I personally do not want to fly 75mm 1, 2 or 3 grain reloads due to cost. That's where I use my larger 54mm reloads, the AMW L-1276 has a total impulse of over 2700n.
This I don't understand. Look at the Wildman website:CTI 54mm 6gr reloads : https://www.wildmanrocketry.com/ShowProducts.aspx?Class=754&Sub=763&Sub1=768
Then look at these: CTI 2 grain 75mm reloads: https://www.wildmanrocketry.com/ShowProducts.aspx?Class=754&Sub=776&Sub1=777
$120.00 for all the 2 gr 75's except the L585. And $135.00 to 142.00 for all the 6 gr 54's. All comparable "k" loads AND a L910 for only $120.00....
Yes the 75mm three grain are more expensive than the 54mm 6XL, but not by much.
Adrian
No, when used to describe a case the second number is not the average thrust. It's the impulse, which is the product of the average thrust and the burn time. I explained using 38 mm cases because I was lazy and didn't want to look it up and because the difference is easy to remember. For 38 mm each grain adds roughly 120 Ns more impulse. For Aerotech 54 cases each grain adds roughly another 420-430 Ns, so the cases are 426, 852, 1280, 1706, and 2560, but a 2560 case is six grains, assuming typical commercial Bates grains. For some reason, AT doesn't have a five grain case.(snip)
That brings me back to my other question though.
How do I know the size of a casing in grains given a designation or whatever it's called such as 54/2550.
I know the 54 is the motor size, and the 2550 is the average amount of thrust in Ns expected to be produced by said reload in said casing.
It was explained earlier that in 38mm it's easy to convert to grains. because it's roughly 120 Ns per grain.
Is there an easier way to convert or is there a chart for larger and smaller motors?
Thanks!
This chart shows which AT 75mm motors that can be used in 75 mm CTI hardware:
View attachment 307982
Got it.
Thanks for the clarification!
The 2560 is actually a 6 grain case. There is no 5 grain Aerotech case for 54mm. The 2800 is equivalent to a 6XL case.For Aerotech 54 cases each grain adds roughly another 420-430 Ns, so the cases are 426, 852, 1280, 1706, and 2560, so a 2560 case is five grains, assuming typical commercial Bates grains.
The 2560 is actually a 6 grain case. There is no 5 grain Aerotech case for 54mm. The 2800 is equivalent to a 6XL case.
No problem. I've been flying Aerotech a long time, and exclusively until very recently. I'd still love to know how the nominal size numbers for the 54mm were picked...
The nominal size numbers are goofy. That's why I initially used the 38 mm sizes. They're very convenient to remember. All the other sizes seem easy too, but 426, 852... Such precise integers with no obvious (at least to me) reason.
426.66Ns = 1/3 full J.
853.33Ns = 2/3 full J.
The 3G and 6G casings appear intentionally matched to the boundaries of the impulse classes, as are the 75mm and 98mm casings. Not sure why the 54/426, 54/852 and 54/1706 designation contain those rounding errors - maybe they thought odd numbers would appear ... odd?
Reinhard
All 75 and 98 motors are cross certified.
So I recently purchased a kit that flies on 75mm motors...
It will be my L2 rocket, and I'm starting to wish I would have checked the cost of the reloads before buying.
Do the 75mm reload the same as every other CTI motor size? (No individual grains and the sort.)
Does CTI do the certification special on 75mm reloads?
If not, I already have plans to fly it on 54mm motors with an adapter and rarely fly it on 75mm.
I would eventually save up and drop the money on it for a "once in a while" flight.
As you can imagine, I was kind of surprised to see that a 5g casing was $380.
Plus $27 per spacer. Then $44 for the wrench. Then $187-$330 per flight after that.
I know it's nobody's fault but mine.
I'm just exploring some of my options.
So... I guess what I'm getting at is this:
Should I suck it up and drop the cash now and fly it as it was built with 75mm hardware?
OR... should I fly it on 54mm (already had the adapter to flip flop if I wanted) for a while until I can afford the bigger hardware and motor casing? I definitely flubbed this up a bit.
Try to reserve judgement.
Thanks for any guidance/constructive harassment. ;-)
-C
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