Engine experts riddle me this

NAR S&T makes exceptions to the rules for Estes.

Poor Jerry.

Randy,

This came up in the "Nozzle Question" thread back on Jan 27. Dale Greene posted then that "They streamlined production to reduce costs, I don't know all specifics but the larger nozzle is part of it."

Today, the B4 and A8 share the same nozzle, so perhaps that's when that commonality was established.

FWIW, I gave an A8-0 to Buzz McDermott today, and he flew it in his Centuri Blask Widow clone. Buzz determined the orange (1/2A3) plug was the best fit for the 1973 vintage A8-0.

As for the need for Estes and NAR to have recertified it after this nozzle change, it becomes a discussion of how much tweaking is allowed before that's required. In my business (computer chips) we provide process change notifications (PCNs) to our customers to advise them of changes in our parts but we don't issue them for just any tiny, minor change. And sometimes we internally get into arguments over whether a given change requires a PCN. In hindsight, we occasionally decide we shoulda done something different. The point is that honest, well-intentioned people don't always make the right call.

I'm not saying that anyone did anything wrong in this case, just that it's not always so cut and dried what needs to be done.

Doug

Thanks, Randy

I would assume that as long as performance parameters were within tolerance, production methods and outward appearance would not necessarily require a recert. IIRC, motors used to be tested triennially, and spot checks were done if there was a significant change in performance. Third parties could also get motors retested. Don't know if this is still the process.

The biggest changes with Estes motors occured around 1968 when they went not only to the metric system, but also changed nozzle shapes from curved to linear and the inside diameters of the A,B, and C motors increased to 1/2 inch. (the 1/2a stayed at the smaller diameter for a few years). Does anybody (Chas??) know if Estes and Centuri had everything retested or if S&T just let it slide until the next regular testing?

When did Estes switch to Metric motor designations? There were several ".8" average thrust motors when Imperial measurements were used, .8 pounds being about 3 Newtons. I'm sure it was before 1974, it just came to mind is all.

Mike D.

I think it was between 1967 and 1968 - the '67 Estes catalog (the first one I had) showed the ".8 pound thrust" motors (and the "Series 2" B3 cored motors, which became the B14); the '68 catalog showed the new type numbers with thrust rated in newtons.

(This was when they had the inch-shorter "-S" motors in the 1/4A and 1/2A sizes, but this was a few years before the "mini" and the "D" sizes showed up.)

-dave w

Thanks Dave.

I have a few tubes of those -S motors in my collection. The casings are so thick and heavy I wonder if the 1/4A's can lift their own weight off the rod. Maybe I'll fly one at LDRS this year just to scare everyone. Have to build a Streak for it I guess.

I wonder how many rockets were built out of those blue engine tubes over the years?

Mike D.

I dunno... on the small and windy fields of my youth, a 1/4A or 1/2A seemed like plenty of oomph for a basic BT-20 rocket with something like a 9 inch tube, and the shorter "S" casing left a useful amount of extra room for the recovery system and wadding in that size rocket.

-dave w

That's NOT what either the NAR rules or the NFPA code says.

Sorry.

I am guessing about 1966-67.

They were good motors. They were just fine for minimal diameter rockets. I flew alot of them. The mini-motor was a HUGE technological improvement for 1/4A, 1/2A, A and B (remember Centuri, MPC, AVI mini-B's?)

Mass matters with low power rockets.

But they more than got out of their own way.

Many, but I used them as motor conversion mounts too.

Can you fly uncertified motors at LDRS?

I think I only built one. My little brother built several.

That doesn't count the one we put on a kite string and used to launch rockets up the string. Think of it as the worlds longest launch rod!

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

Rules? No.

Practice? Yes. Shhhh.

TRA = Calvinball rules

Yes - EX motors.

No - Poor Jerry's decertified motors.

"Alas, the problem isn't posts FROM Jerry. It's endless posts ABOUT Jerry. They come from Phil, Fred, Dave, Ray, and even occasionally from me!"

- Bob Kaplow

Cry baby...(:-)

I see them flown at NAR launches too.