I've been reading and puzzling away, trying to figure out how we "inherited" 13/18/24/29 ; is it as simple as an approximation of either OD or ID of some standard pipe diameter? One motor manufacturer picked 'em, and everybody followed on? Other?

How 18x70mm became the standard model rocket motor size is described by G. Harry Stine himself starting at the bottom of of page number 7 (eighth actual page of the .pdf) here: http://www.questaerospace.com/image...tine_Memoir.pdf

I'll leave it to others to explain the other sizes.

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Bernard Cawley
NAR 89040 L1 - Life Member
SAM 0061
AMA 42160
KG7AIE

I believe it was Irv Wait that selected 29mm 1.125" based on available fibreglass tubes of the time. I developed 1.5" 38mm and 2.125" 54mm and 2.5" 66mm. Unclear on who first did 75mm 2.98". I did 3.5" 95mm to fit a TC-39 and allow hotter moon burners, and Gary Rosenfield did 98mm 3.875" to fit in a Estes BT-101/Ace BT-39. The first HPR motor flown at LDRS was a 38mm motor I flew. 2.125" fits in a BT-70/BT-22. 38mm fits in a BT-60/BT-15.

Estes developed 13mm 0.49". Quest did micromax. AVI had a bunch of oddball diameter motors because they used common fireworks tubing. FSI had 1.04" for that reason as well. Virtually all the convolute wound virgin craft motor casings were made by Ball Paper. To this day when I have a can of MGD I see Ball printed on the can.

Jerry

HPR 76mm became popular in the EX world long before AT and others started releasing commercial motors in that diameter. It was used because it was available and practical, which is most likely why a lot of other diameters of motors, both paper, phenolic, and aluminum, have been used, including our 18mm motors that began with the common fireworks lifting charge casing as brought up by BEC and told by GHS.

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I love sanding.

75mm was in use before Tripoli started in CA at our launches. It might be IBCo that started it.

Thanks for that piece of history!

Estes had BT-5 body tubes well before the 13mm motors. My guess is that the motor diameter was chosen to fit this already available small diameter "motor tube".

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Lee Reep
NAR 55948

Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor
In the Paint Shop: Nothing! Too cold!
Launch-Ready: Farside-X, Maxi Honest John, Super Scamp

I was under the impression that Centuri drove the development of the 13mm motors, and that Estes was following suit. Granted, Centuri also had tubes of the same dimensions.

Doug

.

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YORF member #11

Wasn't AVI the first out with 13mm motors?

I understand that MPC came out with the 13mm Minijets first.
Then Estes, then Centuri.
AVI was MRI first (Myke Bergenski). Myke joined MPC and came out with the 13mm engines.
After MPC (under General Mills) got out of the rocket business, he started AVI (Aerospace Vehicles Inc.) selling the original MPC kits and supplies.

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Hans "Chris" Michielssen
Old/New NAR # 19086 SR

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