Re: Prototype 'M' motor test flight entirely successful

Hey, we'll be flying Marcus' waycool Pentamax K350 at Culpeper on November 1 or 2, depending on the weather. And Marcus will be there. Y'all come down and watch!

Doug Pratt

Close but 3" is actually 76.2mm 8o) I talked to Ken of AMW in the past and they have tubing run at 2.950 or 74.93mm. At Roc Lake we learned just how close MMT are to 3", but we did have to build a make-shift hone and bore out a MMT ( not fun ) I have been bashing this question around for some time! The 76.2mm or true

3" K-M system would definitely have to have a rocket custom build around the motor due to length of the M case.

So, is the rocket community ready for another "non standard" but "standard" type motor? 8o) West Coast's true 3" I'm planning on supplying a MMT with the motor. What the general senses???

Scott ...

3" motor mount tubes are 3.00 ID 3" motor casings are ground to 3.97" to slide fit properly

The only sizes that do not have to have a 2nd operation grind are

29mm 1.125 38mm 1.500 64mm 2.500 152mm 6.000 24mm 0.935 typically has to be ground from 1.00 54mm 2.125 typically has to be ground from 2.250 75mm 2.970 typicaly has to be ground from 3.000 98mm 3.875 typically has to be ground from 4.000

It is less work to grind a single reuseable casing that someone is paying the big bucks for in the first place than grinding thousands of installed base paper rockets :)

Jerry

Standards. They matter. Set a good one that has legs.

Didn't know you missed it too, well that's different then.. Similar situation to ROC Lake, which is the first time I actually got to see a Pro54 fly.

From the sounds of what's planned for ROC Lake next year, it will be a banner event, Canadian scale or otherwise. A plethora (my monthly chance to use that word) of high altitude flights are in the works in various camps.

With luck even more of our buddies from the South will make the trip. Adds a lot to the event. They always leave talking funny too.

Mike D.

Yarde Metals stocks the 0.065" wall, and they list 0.095" wall. Tube Service also apparently carries 2.125". Both CTI and Dr Rocket get the stuff somewhere as well.

I know they had to lightly "hone" Andrew Mcmillens BSD THOR a tad to get the West Coast prototype 'L' motor into his 75mm motor mount, but no way did they have to take 0.050" off of it!

Jerry:

I do standards in my other life. Heck, I spent several years as a senior management type in an important internet standards organization.

The notion of "standing on the shoulders of giants" is an important currency in standards.

The fact that you have to take standard, OTS, metal tubing, and muck with it to fit some ill-conceived other standards is just wrong. It's the state of the world, but it's *wrong*.

Take 75mm, for example. There's simply *no* reason that 75mm motor mount tubing couldn't have been made as 3.015" ID, allowing OTS 75mm aluminum tubing to be used for corresponding motors. But no, some weeny probably thought that if the motors were 3.00" OD, then the corresponding MMT should be exactly 3.00" ID. Bing! Or it may have been that they went to the paper tube maker, asked for 3.015", and the lame-ass folks said "we don't have a mandrel for 3.015, but we can make 3.000". Pick a different paper tube manufacturer, one that uses more modern equipment with extreme flexibility in ID and OD. In bulk, tubes up to about 4.5" ID x 34" long can be made for about $1.50 each. Contrast that to a turning operation on aluminum tubes.

So how about we set ONE new standard right here and now.

3.00" tubing shall now be 3.02" actual. The blow molded cones will need tape and the rings will have to be resized and the motors will fit right.

Or grind the tube OD at the same time you cosmetically prep it for anodizing and save all the 5 company kit retooling cost. In some cases it is simple economics.

But if you pick one I say pick 3".

Jerry

But every time a new size is created, there isn't an installed base.

Until the CTI O5100, there was no installed based of 152mm rockets out there of any significance. The attitude of "let's take an existing airframe size, and make motors that fit it" leads to the unpleasantness I've described. Having custom paper tubes and corresponding centering rings made up is quite cheap. For a $200.00 investment, I can get 75-150 custom paper MMTs made up, depending on size. For the same $200.00 investment, I can get about 5-6 motors turned-down to fit existing airframe sizes. Which makes more economic sense?

More or less. I was going to make up a shorter motor tube for your rocket of only 42", whereas this motor was 54".

The loaded motor weight in the shorter configuration would be about 8kg.

Putting rockets on a diet is always a Good Thing(tm), if you ask me :-)

Dave Ross is a craftsman of some considerable skill. He can make schemes like that work, and make it seem easy, cheap, fast, and straightforward.

To be fair, he did luck-in to a source of fairly thick LE phenolic sheet for next-to-nothing. Cutting rings for this motor from this material was fairly straightforward, and structurally sound.

Sweet.

If you think that "PentaMax" is cool, the 100mm motors will debut with a 17 injector cluster. I can't think of a pithy marketting name like "PentaMax" for a 17 injector cluster. "SeptDecaMax" just doesn't cut it :-)

The version that Dave Ross flew of the 100mm used 9 3/16" injectors. I guess that would make it a "NonaMax".

So do you need someone to simply supply you with 98mm OD tubing?

No Mike, that's "always leave talking funny, eh?".

I should, I guess, have said "no installed base of any significance in the HPR market". Granted, there were some EX 152mm motors around, and as you point out, some/many military motors at this size range. That doesn't count when you're looking at the HPR market.

The way I look at it is this. CTI introduced a 152mm 'O' motor into the high-end HPR market. How many people were/are screwed by the fact that it's a new size. How many people just said "it's the only O motor currently available in the HPR market, and I'll just build my rocket accordingly, rather than whine about it not being 98mm, 75mm, 54mm, 38mm, 29mm or 24mm?"

If you're building rockets at the 98mm size range, and you are utterly stopped by the fact that new motors in this range are actually 100mm, then I'm kinda scared about the degree of competence in the hobby...

How about this. When I do bring my 100mm hybrids into production, the first 50 customers get a complementary set consisting of an MMT, and centering rings to match either 5.5" or 7.5" "standard" airframe tubing? I'm willing to bet that grumbling would stop pretty quickly, and the PMLs and LOCs and BSDs and...of the world will start carrying the appropriate parts.

Why do you need a cardboard tube to put a structurally superior aluminum tube into? Why not just build centering rings/thrust rings to fit the motor? I'm planning to do just that for a 54mm mount.

Layne Rossi CAR S767

All of them because of the strange coupler technology making install a brute. It's not like it's JUST an oddball size like your cool hybrid. Maybe the solution is for you to commission some kits from LOC tailored to your kits and both you and he sell the kits as needed.

The utterly stopped language is not right. I simply pointed out 90% of the installed base or more have standard sizes.

There will always be a small minority of people willling to make purpose built rockets.

Or do as I do. Put fins on the case and be done with it.

Point.

Jerry

The O5100 is *not* 152 mm (6"). It's more like 160 mm. I have a rocket with

6" mount that I built in 1995 and the O5100 *will not* fit. CTI is very misleading calling it 152 mm.

Tom

Well, I can get whatever I want, as long as I buy a boat-load of it ;) Thanks for the source on the .065" wall, Marcus. Hey, Jerry; I guess you CAN find 54mm tube, right off the shelf.

Woody told me before how much had to come off his 3" EX motors to make them 75mm compatible and IIRC, it wasn't all that much, so you are right. BUT, each one still has to be turned down. Doesn't really matter at that point if it's .005" a side, or .025".. It still has to be done.

Todd