Ye Olde Rocket Forum

Ye Olde Rocket Forum (http://www.oldrocketforum.com/index.php)
-   SVDT - Semroc Virtual Design Team (http://www.oldrocketforum.com/forumdisplay.php?f=20)
-   -   Bt-30 (http://www.oldrocketforum.com/showthread.php?t=2549)

Mark II 12-09-2007 11:31 PM

Quote:
Originally Posted by kurtschachner
Ya, I am assuming it is spiral wound BT-40. IIRC Estes never made parallel-wound BT-40, it was only the leftover MMI stock, right?

No, when I mentioned the part about them only having a spiral-wound version, I was referring to Semroc's BT-30.

I started ordering from Estes in 1967, but I don't recall ever seeing the engine mailing tubes (aka BT-40) during that time. My orders used to come in a long box - almost exactly like my orders from Semroc do! ;) - and the engines would come lined up end to end and rolled up in some newspaper, and then packaged in their own little parcel post box, as I recall.

I'm not 100% sure about this, though; it was a long time ago, I only had about 3 or 4 orders with them altogether (didn't have much money then) before taking a 30+ year hiatus from the hobby, and nothing that I had from that era has survived (my folks threw away all of my rocket stuff - including live engines! :eek: - when I went off to college). :(

Mark K.

Ltvscout 12-10-2007 08:04 AM

Quote:
Originally Posted by Mark II
No, when I mentioned the part about them only having a spiral-wound version, I was referring to Semroc's BT-30.

I started ordering from Estes in 1967, but I don't recall ever seeing the engine mailing tubes (aka BT-40) during that time. My orders used to come in a long box - almost exactly like my orders from Semroc do! ;) - and the engines would come lined up end to end and rolled up in some newspaper, and then packaged in their own little parcel post box, as I recall.

I'm not 100% sure about this, though; it was a long time ago, I only had about 3 or 4 orders with them altogether (didn't have much money then) before taking a 30+ year hiatus from the hobby, and nothing that I had from that era has survived (my folks threw away all of my rocket stuff - including live engines! :eek: - when I went off to college). :(

Mark K.

Mark,

The engine mailing tubes and the BT-40 were two different animals. The BT-40 was from what I recall leftover stock from MMI. I have some scratch-built rockets here that I bought off of eBay six or seven years ago that have BT-40 tubes and those old, rubber nose cones. This tube had an inside diameter of .765". They had a balsa cone, a plastic skyrocket cone (fit over the outside of the tube) and two rubber cones available for this tube. The BT-40 size derived from the skyrocket size tube if I'm not mistaken.

The engine mailing tubes were much larger in diameter and much thicker-walled. Estes only offered one cone for the engine mailing tubes. That was the BNC-MTD. This tube had an inside diameter of .937".

kurtschachner 12-10-2007 08:12 AM

Quote:
Originally Posted by Ltvscout
Mark,

The engine mailing tubes and the BT-40 were two different animals. The BT-40 was from what I recall leftover stock from MMI. I have some scratch-built rockets here that I bought off of eBay six or seven years ago that have BT-40 tubes and those old, rubber nose cones. This tube had an inside diameter of .765". They had a balsa cone, a plastic skyrocket cone (fit over the outside of the tube) and two rubber cones available for this tube. The BT-40 size derived from the skyrocket size tube if I'm not mistaken.

The engine mailing tubes were much larger in diameter and much thicker-walled. Estes only offered one cone for the engine mailing tubes. That was the BNC-MTD. This tube had an inside diameter of .937".


Yes, this is correct. BT-40 is pretty similar to BT-30, much smaller than the mailing tubes.

Carl@Semroc 12-10-2007 08:21 AM

Quote:
Originally Posted by Ltvscout
The engine mailing tubes were much larger in diameter and much thicker-walled. Estes only offered one cone for the engine mailing tubes. That was the BNC-MTD. This tube had an inside diameter of .937".
As Scott said, the ID was .937". The OD was 1.002" which meant most of the balsa nose cones for it had a flat spot since the balsa was 1" x 1". One of the biggest problems with convolute (parallel) wound tubes is their "roundness" which is not as good as spiral wound tubes and the fact that they are different thicknesses around the inside of the tube.

I had always wondered why there was a seam on the inside of a convolute tube and the outside had very little seam. I thought the paper was tapered on the outside edge, but someone recently told me that the final tube was sanded smooth on the outside.

Mark II 12-10-2007 09:02 AM

Quote:
Originally Posted by Ltvscout
Mark,

The engine mailing tubes and the BT-40 were two different animals. The BT-40 was from what I recall leftover stock from MMI. I have some scratch-built rockets here that I bought off of eBay six or seven years ago that have BT-40 tubes and those old, rubber nose cones. This tube had an inside diameter of .765". They had a balsa cone, a plastic skyrocket cone (fit over the outside of the tube) and two rubber cones available for this tube. The BT-40 size derived from the skyrocket size tube if I'm not mistaken.

The engine mailing tubes were much larger in diameter and much thicker-walled. Estes only offered one cone for the engine mailing tubes. That was the BNC-MTD. This tube had an inside diameter of .937".

A-ha! My knowldege of early model rocket history is even sketchier than I thought! I had read about the old mailing tubes, and had also read about BT-40, and had assumed that they were the same thing. I stand corrected. In any event, back in the day I never saw either one.

BTW, when I went to build my Li'l Augie (EIRP-10) this summer, the plans called for cutting the augmenter tube out some mailing tube, by which I assumed they meant the engine mailing tube. I thought that I would need BT-40 for that, but it turned out to be the wrong diameter and I ended up using ST-10, which worked fine. Now you have cleared up that mystery for me. Thanks!

Mark K.

Doug Sams 12-10-2007 12:40 PM

Re: Li'l Augie
 
Quote:
Originally Posted by Mark II
BTW, when I went to build my Li'l Augie (EIRP-10) this summer, the plans called for cutting the augmenter tube out some mailing tube, by which I assumed they meant the engine mailing tube. I thought that I would need BT-40 for that, but it turned out to be the wrong diameter and I ended up using ST-10, which worked fine. Now you have cleared up that mystery for me. Thanks!.
I used BT-50 for mine. I think anything in the 1" vicinity will work well. FWIW, I epoxied a tin foil liner to the augmenter tube. It has held up well so far although I don't fly it often.

With the extra motor in it, space for the recovery system is quite limited. I end up stuffing the shock cord into the hollow plastic nosecone.

Doug

Bob H 12-10-2007 09:34 PM

Quote:
Originally Posted by Mark II
- and the engines would come lined up end to end and rolled up in some newspaper, and then packaged in their own little parcel post box, as I recall.

The little boxes would hold 9 tubes of engines and that's the way I always got them. Supposedly, that was the maximum number of engines that could be mailed in one box.

They never came rolled in newspaper. They were always in the mailing tubes. You could buy single motors so maybe if you were only ording 1 or 2 of a specific type they would wrap them in paper. I always ordered them in quantities of 3 because they were cheaper if you bought 3.

Whenever I ordered motors, I would order enough to fill one of the boxes. I still have one of those boxes and the postage sticker is from September, 1969 and it cost $.85 to ship.

Mark II 12-10-2007 10:12 PM

Quote:
Originally Posted by Bob H
They never came rolled in newspaper. They were always in the mailing tubes. You could buy single motors so maybe if you were only ording 1 or 2 of a specific type they would wrap them in paper. I always ordered them in quantities of 3 because they were cheaper if you bought 3.

You're right. I think that the most engines that I ever included in an order was 6 - 2 each of three different kinds. Even with the quantity discount, my budget was too meager to allow me to order any one kind of engine in quantities of three. Back then, ordering 27 engines at once would have just boggled my mind. These days, of course, I have a slightly different perspective, and regard a quantity order like that as being merely astonishing. :eek:

Mark K.

Bob H 12-11-2007 06:44 AM

Quote:
Originally Posted by Mark II
You're right. I think that the most engines that I ever included in an order was 6 - 2 each of three different kinds. Even with the quantity discount, my budget was too meager to allow me to order any one kind of engine in quantities of three. Back then, ordering 27 engines at once would have just boggled my mind. These days, of course, I have a slightly different perspective, and regard a quantity order like that as being merely astonishing. :eek:

Mark K.
I was a little older when I discovered model rocketry so I had a part time job at the local ice cream shop. I was probably pulling in $20 a week and I mowed lawns in the summer also. So by the time I used up my last order of engines, I had saved up enough to buy another box.

By 1969 (the box that I still have), I was out of High School and had a full time job and still living at home so rocketry money wasn't a problem. Heck, I bought a brand new Z28 Camaro in 1969 and the car payments were only $55 a month.

Ltvscout 12-11-2007 08:05 AM

Quote:
Originally Posted by Bob H
Heck, I bought a brand new Z28 Camaro in 1969 and the car payments were only $55 a month.

Cool! Did it have the high output 327 small block in it?

My dad was new car manager of a large Chevy dealer here back then. He had a '69 Z28 as a demo that was all tricked out and custom painted. I still remember cruising around in that thing. He'd let me shift it from the right seat. I was all of seven years old. :D


All times are GMT -5. The time now is 04:04 PM.

Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.