Thats odd, both the J90 and J135 I flew had only the center hole open. All of the others were closed. Interesting. I was told that only the center hole should be open. John, could it be that the nozzles you had were flawed? Or, the ones I had were flawed in the sense that more of the holes should have been open?

Looking at the drawings on the Aerotech site, the J90 should only have the center hole open, the J135 should have the center and 2 side ones (if you oriented this carefully, you could get perfectly even flow), and the K185 should have the center and 3 side ones.

Hmm - looking some more at the drawings, it appears that the M750 only has the central nozzle of the 98mm medusa open - I wonder why it has the medusa then...

8)I traded E-mails with Mike D at Cessaroni last week. He was doing the last test on the M795. Then on to recert...The M520 is next and the N1100 after that. All should be ready to go soon. They will ship 1.4c and be 'glue your own'. The 54's the nerxt up to bat. Should be a interesting summer. 8)

Or, the ones I had were flawed in the sense that more of the holes should have been open?

Ken, a closure would have blown on your casing if it was flawed in this way.

I don't know about that...

The 54mm casings can take a LOT more pressure than they normally run at - failure should be around 1600psi from what I've heard, while they normally run at 700-900. So, it could easily have had the central nozzle only and still only run maybe 1300psi or so...

I wouldn't want to do it intentionally or often, but it would probably survive once.

Thats odd, both the J90 and J135 I flew had only the center hole open. All of the others were closed. Interesting. I was told that only the center hole should be open. John, could it be that the nozzles you had were flawed? Or, the ones I had were flawed in the sense that more of the holes should have been open?

Interesting question... I distinctly remeber the J135 had multiple orifices because I had a bit of a tough time getting an igniter in there, and I thought about running the igniter through an orifice that lined up better. I decided against this, but sure thought about it for a while.

I'm not going to LDRS. Would someone take a look at these and verify if they have multiple open orifices or not? many thanks!

JW

If you go to http://www.aerotech-rocketry.com/ and click on "resource library" and then go to "RMS motor assembly drawings" and if you start pounding around there, you will find all the drawings for the various reloads, nozzles, etc.

At any rate, the drawings for the J135 say there should be one hole that is .228" and two holes that should be 0.161". The J90 drawing shows a single orifice of 0.266.

As noted, I've never flown a J90, but I've flown several J135s. I set, and later re-set the J records with J135s a long time ago, before I got the nerve to do a J570 in a 38mm rocket. It burned a L-O-N-G time, but it did not go straight. Not at all....

I'll definitely be looking out for it at LDRS - I'm quite interested in it. If you look at the drawings though, it certainly implies that only the central hole should be open.

It states in the drawing that the nozzle should be a "NOZZLE (98MM MEDUSA) 4M DRILLED .256"
No other holes are described.

Is it just me, or is that a heck of a tiny nozzle for an M, even a long burn?

I'll definitely be looking out for it at LDRS - I'm quite interested in it. If you look at the drawings though, it certainly implies that only the central hole should be open.

It states in the drawing that the nozzle should be a "NOZZLE (98MM MEDUSA) 4M DRILLED .256"
No other holes are described.

Is it just me, or is that a heck of a tiny nozzle for an M, even a long burn?

0.256" x 1 does NOT seem doable for an M. No way, no how...

0.256" x 1 does NOT seem doable for an M. No way, no how...

Maybe it's using old jetex fuel. 🙂 A nozzle throat 6 1000ths over a quarter inch for an M, even if it has many openings? 1500' isn't far enough from that puppy!

I'm thinking it means 4of them at .256" 4M = 4 Medusa??? That would seem more likely. Though not a whole lot of area.

Edward

To throw more confusion into the long burns. I helped Gary and Karl take the 75mm long burn apart and I can remember Karl holding up the nozzle to show Gary how much it eroded. And as I recall it was a normal single throat nozzle not a Medusa. I know I'm getting old but I was helping, put it together and take it apart to appease the EX'er in me. I was surprised to see in the instructions and in the RMS assembly drawings that it was a Medusa nozzle. This was the 75mm long burn, I also saw them fly the 98mm motor at another launch. It was in a 8 or 10" V2. The booster was never found so, other then saying it was a cool long burn not much to report there. One other thing, if you plan on flying one of these make sure you make arrangements to have or get one of the new aluminum forwars seal disks that they use.
Tony

I was able to fly one of the AT M650 motors at XPRS. I got 35,250 on the ARTS2.

Tony

Tony, I'm looking forward to catching up w/ you at BALLS and hearing about your 35K blast on the M650. That is incredible! I always thought the TRA "M" record had been somehow miscalculated. You were right on the doorstep with that boost -- with a pretty small M. Yowza!

I'm flying my M shot (which will not go over 27K but I'm always about 1.5 to 2.0 miles behind you) on Friday. I'd like to catch up w/ you before I light it. Will be there Friday AM early, arriving very late on Thursday---

JW