13mm B Motor History
 

Over on the "other" forum Alan15578 and I were discussing the 13MM B motors: the MPC/AVI Mini-Jet B3M, and the Centuri B4M.

https://www.rocketryforum.com/threa...50/post-2119066

If anybody has any history they would like to share, pics,engine flyers,etc please do.

Some additional info I was able to dredge up was that the paper casings were spiral-wound paper tubes like body tubes, not the traditional convolute/parallel wound body tubes.
Centuri discontinued them based on a "hi-performance paper shortage" and manufacturing problems by summer 74.


IF anybody has an original copy of the 1973 Estes Model Rocktery catalog and would scan page D frm the front.....TIA

I have multiples of MPC and Centuri mini-B, but none are in spiral wound tubes. Maybe Myke did them at avi but no avi motor I’ve seen were spiral.

On the other hand, Estes definitely experimented with spiral tubes for mini-motors and they some how got out because I have a couple of examples. Photos are up here in some thread. I asked Ed Brown and he said those should never have gotten out in a retail package. I’m pretty sure I bought these in 72 or 73 at a small hobby/toy shop in Athens, GA.

Roy.Thanks. that reference to spiral-wound Centuri was made in a Model Rockeeteer. So you got some A or B Estes spiral-wound?

David Stribling over in the Centuri Model Rockets facebook group shows some pics of both and the graphite infused clay nozzle is verified but they are parallel wound too.

I have a number of packs of the Centuri Mini-Bs and they are not spiral wound. I have not seen any spiral wound tubes in any of my Centuri-made mini motors (i.e., the longer mini motors before they were shortened, at which time they were made by Estes and the Centuri motor making facility was closed).

Earl

The ones I have are 1/2a boosters. Yes, those existed too!

It is entirely possible that Centuri, when they had their own machines, also experimented with spiral tubes, but just as with Estes, I doubt they were intentionally released.

Here are those pics...

so here's the message in a thread of a little over three years ago. The motors were A, not half A, and in the intervening years I remembered buying them at a little hobby shop that spun off from the news/tobacco stand we usually got our hobby stuff from. The "71" in the markings us why I thought they might be from NARAM 13, but it is also possible that whatever anomaly (probably someone found a box and said, "hey these look perfectly good, let's sell them") let them out put them into some retail packs .

https://oldrocketforum.com/showpost...310&postcount=9

some interesting comments and pictures in that old post. SO now we know that Estes as Early as 1971 experimented with spiral-wound motor casings.

https://oldrocketforum.com/showthre...23&page=1&pp=10

Gus shows pics of the original 2.5" Centuri along side a later 1.75" Centuri (Estes made)

And look at the size of those nozzle cores ! looks like a smaller version of the B4 throat

Jeff Flygare authored an article about ( I believe Flygare either worked at Centuri or Estes at one time later) 8th Annual Pittsburgh Spring Convention on March 16-18,1973.


"Randy Gilbert was there for Centuri and Enerjet, and both of the product lines were very popular. .......The Centuri mini-motors will be 1/4"(.250)in longer than the AVI Minijets, and the same diameter as both the Minijet and the Estes minibrute. Centuri plans to produce both a 1/4A engine and a full-range B in their small casings, which are spiral-wound to reduce weight."

Estes spiral-wound in 1971....now Centuri spiral-wound in March 1973



Wasn't BOTH Estes and Centuri owned by Damon Corp. during this time frame?

Flygare would work for Centuri in the latter 70s; starting about 77 or 78. I think he was there for about three years maybe.

I have some (pretty sure) March 1973 Centuri mini's and they are not spiral wound. Maybe they thought they would use spiral wound casings at one point but eventually something fell through with that. Or, maybe they actually did, but turned out to be very limited production before going by to parallel would casings.

Earl

Couple of date adjustments: all from Lee Piester's mouth...

Damon approached Centuri in 1970, didn't close the deal until 1971.

Centuri built their own machines in 1969, requiring a large investment. Therefore, one of the reasons (along with move into retail) to make the deal.

And the deal was structured similarly to the Estes deal (Purchase with employment contracts). Lee left the company in 1974.