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CTI 75mm reloads
- Thread starter Ccolvin968
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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
This chart shows which AT 75mm motors that can be used in 75 mm CTI hardware:
I should have clarified, I should have said this is my preference because I choose not to buy a 3g case and I have plenty of snap ring cases. I'd just soon as jump to the 4g, very cheap price for an M motor in CTI and AT reloads, as far as availibility, the AT M1297 4g and M1315 5g are bargains in my book. On Wildman's site, most 4 and 5g 75mm CTI reloads are not available, AT ones are.
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.
Thrust is in Newtons, which is simply abbreviated as N. Impulse is Newton seconds or Ns. The s does not mean plural, but "seconds".
So, just look at the cases available from a manufacturer and see what the difference is between sizes. That's probably the difference in impulse for a single Bates grain.
Case size has nothing to do with average thrust.
Edited to correct my mistake and misinformation about 2560 case, thanks to AdAstraPerAspera for the needed correction.
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Ccolvin968
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Got it.
Thanks for the clarification!
Thanks for the clarification!
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........ Customers who currently have 75mm reloads that use a Medusa nozzle will require a new single-throat Medusa nozzle in order to use them with CTI hardware. Customers can purchase a single-throat Medusa nozzle drilled to the specifications of their motor on the RCS Store at www.rocketmotorparts.com. 75mm Crossloads that use the Medusa nozzle will now come with a single-throat Medusa nozzle and will have an “AT Crossload Compatible” label on the packaging for easy identification. Instructions will be available online as both a PDF file and as an instructional video on .......
Tony
You're welcome. I'm sorry if I beat that horse too long.
Ccolvin968
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Not at all Steve. It's good info and I appreciate you helping me out!
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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.
Ahh, thanks! I wondered why when I divided 2560 by 5 I ended up with a larger than average grain mass.
I'll go back and edit my earlier post to avoid spreading bad information.
Steve Shannon
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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...
I've been flying them since 2000, but I never caught on to the missing 5 grain case.
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
Interesting.
watermelonman
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There are few holdouts such as the M685 and the super thunder motors.
watermelonman
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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
Cesaroni 75mm are nothing like 54mm, more like Aerotech. You have to build them grain by grain. After one or two, though, you will feel like an expert.
So do you see any Cesaroni 75mm motors available anywhere? I have not, for some time now.
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