Long burn M's - Northern Colorado Rocketry

This topic has 32 replies, 6 voices, and was last updated 18 years ago by Anonymous.

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June 29, 2007 at 11:03 pm #39895
Chris LaPanse
Aerotech just released 2 new motors – the 75/6400 M650W (9.13 seconds) and the 98/10240 M750W (12.65 seconds)

I can’t wait to see these – they’re debuting at LDRS 8)

(Altitude junkies rejoice)
June 30, 2007 at 2:05 am #44836
Anonymous
Aerotech just released 2 new motors – the 75/6400 M650W (9.13 seconds) and the 98/10240 M750W (12.65 seconds)

I can’t wait to see these – they’re debuting at LDRS 8)

(Altitude junkies rejoice)

This is good news. I have a 4″ project that I’ll fly later this year (at Oktoberfest if we have a window) that is designed for the M1939, which is the 10,240NS casing. Perhaps I’ll slip an M750 in there instead?

FWIW, the CTI M795 is a 98% M with a 12.76 second burn. The new AeroTech M is a 91% M. I’d still take the extra newtons of the CTI load in a heartbeat.

I might still fly the M1939, just because I’m not sure surface mounted fins will survive that much heat for that long of a burn. It will be interesting to compare the 3″ x 6000NS “M” with the 4″ x 10,000NS “M”.

I sure hope we get the 30K window….

J
June 30, 2007 at 2:09 am #44837
Chris LaPanse
The M750 isn’t quite as big as the M795 (it’s 9,325Ns), but it comes as several grains that are glued together with epoxy in assembly. Result: none of the shipping problems or DOT issues that you have with the big CTI moonburners 😀

Also, I’d bet that your fins would survive – with tip to tip and decent epoxy (something with a TG of 200+, like Aeropoxy or Pro-set), it should be fine. It’s hard to say though, as I don’t know the details of your rocket (or how it would perform with that motor).

I’d love to see it with an M750, that’s for sure 🙂
June 30, 2007 at 2:15 am #44838
Anonymous
The M750 isn’t quite as big as the M795 (it’s 9,325Ns), but it comes as several grains that are glued together with epoxy in assembly. Result: none of the shipping problems or DOT issues that you have with the big CTI moonburners 😀

Also, I’d bet that your fins would survive – with tip to tip and decent epoxy (something with a TG of 200+, like Aeropoxy or Pro-set), it should be fine. It’s hard to say though, as I don’t know the details of your rocket (or how it would perform with that motor).

I’d love to see it with an M750, that’s for sure 🙂

I did use AeroPoxy for the fillets, and will do likewise with the tip-2-tip. Odd as it sounds, the M1939 sims to very nearly the same as the M795. There is only about 800′ difference.

If anyone sees a sim file for these new loads, gimme a heads up?

JW

PS Don’t miss Oktoberfest 😉
June 30, 2007 at 2:24 am #44839
Chris LaPanse
I’ll definitely try to post it here if I see a sim file 🙂

I’d love to see one too 🙂
June 30, 2007 at 2:26 am #44840
Chris LaPanse
It isn’t a rocksim, but I found the thrust curve…

Here are the instructions for the M750

One thing to note that I forgot about before is that the M750 needs a new, larger aft closure (it uses a medusa style nozzle that won’t fit through the standard one).
June 30, 2007 at 4:44 am #44841
Anonymous
I really dislike medusa nozzles. I have had many flights that corkscrewed with medusa nozzles, but I knew the fins were on absolutely straight because the same rocket flew fine with a traditional nozzle.

The medusa sits below a core that is either slotted or off to one side, like these moonburners. There is an area of void below the bottom grain, and the thrust is supposed to be equalized and distributed evenly through the medusa.

I flew Joyride on a J135 (medusa nozzle) and it corkscrewed badly. I then put a K550 in it, and it was bullet straight. Same thing happened with beLLwether (L330, medusa nozzle, squirelly – regular load, just fine).

I’d hate to pay what an M750 will cost and then have it loop-d-loo….
June 30, 2007 at 6:37 am #44842
Chris LaPanse
The J135 has a medusa?

I thought that the long burn 54’s only had the central throat open, essentially making them single throats…
June 30, 2007 at 6:48 am #44843
Anonymous
J135s and K185s both have medusa nozzles. IIRC, the J90 is in the same boat. Ditto for the Ellis L330 and the AT K250 single use motors.

I’ve had erratic flights with all the above, except the J90 which I have never flown, and the K185 which I have flown only once.

My latest experience with this was the L330 at BALLS last year. The same rocket, same motor flew bullet straight at the north site. So they don’t always do it….

There was a lengthy discussion on this on the old ROL forums. I’ve seen enough of it firsthand to really avoid medusas if possible.
June 30, 2007 at 7:22 am #44844
Chris LaPanse
I know the J90 has a medusa with only the central throat open, essentially making it a single throat. I thought the other 54 long burns were the same. I’ll have to look at that and see – now I’m curious.
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