Black powder motors are made under the limit due to the normal variations. I.e. a BP motor typically varies from the rated total impulse by plus or minus 10%, so they shoot for the highest possible power minus 10 percent to assure that all motors (or at least all to two standard deviations) will be under the maximum, which is important for NAR certification (and was more important back then, due to contest certification, which was stricter)

What is so magical about 2.75" length? Standards! In other words, "what Estes sells!" If you sell a 3" motor and all rockets except yours take 2.75" motors, you won't sell many motors.

A perfect case in point: When the current crop of 13mm motors [1] came out in 1971 they were originally introduced by MPC. They had 1/2a through B sizes. They were 2.25" long. Estes almost immediately introduced their Mini-Brute motors, 1/4a through A. But theirs were only 1.75" long.

Besides the fact that MPC was a newcomer and wasn't as familar with the kids buying rockets back then (who were mostly introduced to rockets through mail-order ads), Estes soon dominated that part of the market, and MPC motors wouldn't fit in Estes mini-rockets. MPC soon (for additional reasons) went away.

Centuri then introduced mini-motors that included a B size (off hand I think they are 2.5"--I've got a bag of them in the closet), but they could never get traction, most likely due to Estes market dominance. I think they also had a high failure rate.

Things are different in high power because they started out differently with varied length motors. Expectations were different and standard construction techniques developed differently. In addition, high power flyers aren't as concerned whether a given motor's power rating is at the top of its range.



[1] of course the very first rock-a-chutes from 1954 and the Unijets of 1965 were around 13mm, but they weren't significant in driving the market.

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Roy
nar12605

There is a hobby shop that has some C11-0's left. I don't know how many packs. I think they were running in the $9 range . There are some C11 7's as well. IIRC a whole bunch maybe 8packs. Want me to get them for some one??

Edit: I cant recall the price, but I think that $9 is high.

OK - Looking at the 1973 Estes catalog, these are the engines that were produced then and are not produced now:

13mm
1/4A3-2T, 1/4A3-4T
1/2A3-0T
A3-2T, A3-6T, A3-0T
A10-0T

18mm
1/2A6-4, 1/2A6-0
A8-0
B4-6
B6-0*
B14-5, B14-7, B14-0

From the 1984 catalog, add

C5-3 (I looked at several other years and could not find any other delays for the C5, nor a booster version)

That's 16 motors from Estes. Centuri's 1973 catalog adds:

A5-2

From their 1975 catalog, they added their M motors (equivalent to Estes 13mm T motors)

1/4A4-2M, 1/4A4-4M
1/2A4-3M, 1/2A4-5M
A4-2M, A4-4M, A4-6M

Go to their 1977 catalog, and they Do have:

C5-0

In 1981, they introduced:

B8-3, B8-5, B8-7

12 more motors from Centuri - that makes 28 total to choose from. How do we pare down this list?

Greg

Yeppers. 2.5". Doug

As for me, I would like to see the A10-0 and the C11-0 back again.

On a related subject, I wished we could have your current selection of motors here in Canada.

For example, we can't legally use the E9, because they are not on the approved list here.

In my research, I found that only Centuri did the booster version, C5-0S (S for super, not shortie; their -3 was also super, C5-3S). Since the C5 motor emerged around the time of the merger, my take was that it was a Centuri driven product, and that Estes piggy-backed off it and opted to only market the -3.

As far as other delay options, what I've been told is there was no room for more delay, so only the -3 was made. Given the deep core, that makes sense. The few C5-3's I have are pretty much filled to the top.

Doug



.

Let's take a look at this pragmatically.

First, 13mm:

1/4A3-2T, 1/4A3-4T -- These are pretty small... IMO only good for launching Mosquitos you want to see again.

1/2A3-0T -- Does anyone really want a booster this small?

A3-2T, A3-6T, A3-0T -- Now here are some engines I'd love to see. I'm not sure we need the A3-2T, but if we fly the A3-0T we surely need the A3-6T for the upper stage.

A10-0T -- I don't think there is ANY argument here. Everyone seems to want this engine.

xA4-X -- I'm not sure there is any purpose in having 1/4, 1/2, or full A4 engines given that we have 1/4, 1/2, and/or full A3 engines. I think there is certainly not enough value in them to make pursuing them worthwhile.

Now for the 18mm engines:

1/2A6-0, 1/2A6-4 -- I'd like to see this booster again, and if we have the booster we need the longer-delay upper stage engine.

A8-0 -- YES. We absolutely need this engine.

B4-6 -- I'd sure love to see this engine again.

B6-0 (in three packs) -- YES.

B14-X -- I honestly don't think we'll ever see this engine again. I wouldn't want to be the fellow who drilled the holes in them.

C5-3 -- This would be a nice engine to see again. C5-5 would be nice also.

C5-0 -- If anyone makes a C5-3 again, they'd be fools not to make a booster out of it.

A5-2 -- An 18mm A with a softer thrust curve would be nice, but do we really need it? It surely isn't much softer than a Quest A6-4 (and the delay is freakishly short). Or is this a HIGH thrust A? I haven't looked at the specs...

B8-3, B8-5, B8-7 -- I understand these can be made with a special mold and don't require drilling (does that apply to the C5 also?) so they might be more likely than the B14 engines.

__________________
NAR # 115523
Once upon a better day... SAM #0076
My site: http://rocketry.gonnerman.org

I'll take them.......

__________________
Don
NAR 53455
"Carpe Diem"

Don, I'll get them for you. There is a PM for you.

The B8-x motor used the C5-x core; the Centuri C5 was a relabeled Estes motor, made By Estes for Centuri: remember at this time Estes and Centuri had already merged/ been absorbed/assimilated,whatever.

According to your own exhautive Centuri/Estes motor lineage chart, the Estes made Centuri C5-x came out in 1977; Estes B8-x appeared in 1980; the Estes C5 came out in 1980; the Estes made Centuri B8-x in 1981.

You are 100% corect in that Grant Boyd at Centuri wanted a "distinguishing" product from what Estes was offering at the time. Later Estes marketing decided they also wanted it.


the C5-x used the new "formed" core versus the old B16/B3/B14 that was actually drilled out. This was quite an innovation as now, dangeroud drilling nolonger had to be done; instead MABEL could now create cored motors in one step.

hth

terry dean
nar 16158

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"Old Rocketeer's don't die; they just go OOP".....unless you 3D print them.