Re: Prototype 'M' motor test flight entirely successful

4.00" OD IS a standard "industrial size for tubes". 98mm (3.875") [fits in BT-39 coupler] is a non-standard size hence Composite Distribution used 95mm for expendables.

The only problem with a 100mm hybrid is the total lack of rockets. All will have to be custom built.

Jerry

I heard a tail some time ago that it 98mm was used cause someone got a good deal on a bunch of AL tubing, whether this is true or not is beyond me ?

JD

Outstanding! Congratulations, Marcus.

Nope. It was a diameter that fit in BT-39 (ACE BT-39 to be exact). It had three incarnations initially: 95mm, 98mm, 100mm. That's 3.75,

3.875, 4.00 for you unwashed masses :)

Now fiberglass tubes for SU were available in any of these (talking mid/late-70's now)

Metallis was still discouraged even by the CA amateurs as a precursos to HPR forming. Metalic rockets required terst ranges for shrapnel mitigation, and non-metallics merely required a field big enoulgh to launch at.

This is why you do not see reloadables 10 years earlier from Irvine or Composite Distribution or Internal ballistics or some such.

It worked. Well before 1984-6 when TRA and NAR "became HPR" HPR was known as MRT (model rocket technology, only bigger). So once again non-metallics was the mantra.

The "best deal" on fiberglass tubing was the 95mm 3.75" OD which at the time was used for government military program and the local fiberglass distributor had it in inventory at all times. So it originally was 95mm.

Then some of the guys wanted to get "a bit more power in a small space" thinking like rocket scientists not engineers of course, and commissioned SU motors that fit with less space in an ACE BT-9 with its coupler in place. Coupler was thermal barrier and main tube was the mounting point for airframe parts.

These SU's were moonburners and got hot. L, M, N and this was before 78 mind you.

So much, much later in January 1990 USR released reloadables to "advanced consumers" and AT followed with RMS in April 90 and he released his to the general consumer before they w ere either classified, certified or even had any legal basis in law. That was a major rub for folks like Vern and harry I assure you.

That thread of the story has a long sad end with authorities retailiating against HPR for AeroTech's misdeeds.

But back to 98mm.

So when reloadables were released the standard sizes had already become:

13mm, 18mm, 24mm, 29mm, 38mm, 54mm, 66mm, 75mm, 98mm, 152mm.

So what we had was a bunch of rockets with 4" OD motor mounts designed to accept 98mm motors (and can be sleeved down to 95mm). Then the reloadable manufacturers had no choice to "sell into the existing market" and bite the bullet on making custom machinings of 98mm motor cases, charge what you must for them and live with it. Hence AT/K/AMW (K and AMW are actually converted Jerry Irvine reloadables from Powertech) excruciatingly expensive hardware.

So return of the master. The originator. The pioneer. 98mm hardware:

So as you wonder why 98mm tubing is not $ a foot remember, it is not a standard size: 4" OD.

Jerry

98mm is *not* a standard tubing size.

My understanding of the history of 98mm is that it was based on the BT-101 that was used on the Estes Saturn V model. BT-101 had in ID of about 3.9", and that seemed like a good size for a honking big HPR motor.

So you either get a custom mill run done (2000lbs minimum order), or you start with 4" x 0.188" wall tubing, and turn down the OD. Aerotech/Dr Rocket to this day chose the "turn down standard tubing" approach. OD turning operations are expensive.

Getting 4" ID motor mount tubing made is very cheap, and I can't for the life of me understand why that route wasn't chosen, all those years ago.

I'm nitpicking here, but 4.00" = 101.6mm

Thanks for the info regarding motor sizes. Very enlightening!

No. The coupler for BT-39 or BT-3.90

Which means a 98mm M will fit in a Centuri Saturn V just fine :)

But you get consistent OD at least and a nice surface finish. Mind you, I'd much rather have the ID on the money.. as one of the nagging issues in motor mfg.

You had to fly that motor when I wasn't there didn't you? ;-)

Mike D.

This was yet another personal attack by BB.

This should be in the FAQ

I can't either, Marcus... Silly, Silly, Silly.

I would like to do a real 2" motor line. A MMT adapter for a 2" motor in a 54mm MMT is an easy thing - just a piece of 54mm coupler tube. I say the hybrid MFG. guys get together on this, and buck the system by making 2", and other 'standard' size motors, along with tubing options for them.

Dave has gone standard by going with a non standard rocket motor size of 2.5" (64mm). IMO, A great thing! The beautiful K240 is cheaper to the end user becasue of his standard tube choice, I'm sure.

I think Scott from West Coast is thinking about a standard 3" (not

75mm) tube for his new very nice L motor...

Is it time for a new standard?

What say you?

Todd Moore Sky Ripper Systems.

Which is why the East Coast guys have taken to 115mm motors, with a 4" ID. I just use 4" body tubes and couplers as the liners and casting tubes.

It's also the same reason 2.5" is wonderful...

-Darren

For EX purposes 2.5 (our 66mm) and 115mm (no equivelent here) that is great where each part is a one off. But when you get into manufacturing you have to sell into an installed base. I installled the first installed base BTW.

The installed base has 24mm, 29mm, 38mm, 54mm, 66mm, 75mm, 98mm, 152mm.

Period.

115mm is in a sense the most INCOMPATIBLE size possible. To me that makes it yet more perfect for EX. No confusion.

Jerry

ROTFLMAO!

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

But a damn funny one!

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

The only reason I brought it up is because I own a 102mm (4") refractor telescope. It is Japanese made, and they make the clear aperture 102mm so it is a true 4" in English units. It used to be that 100mm scopes were advertised as 4", when in fact they are 3.93". It might seem insignificant, but it does make a difference in the actual limiting magnitude.

Actually, Todd, 54mm *is* a standard tubing size. 2.125" cold-drawn (ASTM B210) tubing is available--0.065" wall is reasonably easy to find, while 0.095" is somewhat harder (ok, more than "somewhat", but less than "impossible").

I was going to do a 2" line a while ago, but chose to make a "real" 54mm instead. Slightly better mass fraction, since my 2" motors used 2" x 0.125" wall tubing. I have a very happy friend out west (Dave Johnston) who flys the 2" K all the time. Dave recently bought up nearly all of my remaining stock of paper liner tubes for that motor, since I have no further use for them.

LOC 2.6" BT works just great as a motor mount for his motors. My friend Bill Wagstaff has a 2.5" N2O/HTPB motor that he flys at BALLS.

I thought that AT/AMW/CTI 75mm motor tube *was* 3" tube. Am I confused?

Ohh. As a guy who works in the metalworking field, I've never seen

2.125" tube. Been looking for a while, too ;) Would you care to throw a buddy a bone here, and cite a source or two? I have seen 2" and 2.25", but 2.125" is not something I have seen.

I have a source for 2"x.083" wall tube. Not too bad.

As far as I know, all 75mm tubes are smaller OD than 3" - 75mm is

2.95" 3" is 76mm. To fit in a 75mm MMT, 3" OD tube must be turned down some.

Todd