Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Phil » Tue, 10 Aug 1999 04:00:00



I figured out that the "BT" in the description stands for Body Tubes - what
I'm wondering is the number afterward.  It is some sort of measurement, but
of what?  Is it the diameter of the body tube?

Thanks,

Phil
www.felixculpa.com/phil

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Ann Mcka » Tue, 10 Aug 1999 04:00:00


Could it be millimeters ?

                    Bryon...


Quote:
> I figured out that the "BT" in the description stands for Body Tubes -
what
> I'm wondering is the number afterward.  It is some sort of measurement,
but
> of what?  Is it the diameter of the body tube?

> Thanks,

> Phil
> www.felixculpa.com/phil


 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Gene Costanz » Tue, 10 Aug 1999 04:00:00


As I understand it, they were randomly chosen but they are progressively
larger.

BT-5 is .5", BT-20 is .736", BT-50 is .976" (?), BT-55 is 1.325" and
BT-60 is 1.63" .

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Brett Buc » Tue, 10 Aug 1999 04:00:00


Quote:

> >I figured out that the "BT" in the description stands for Body Tubes - what
> >I'm wondering is the number afterward.  It is some sort of measurement, but
> >of what?

> It's not a measurement.  Once upon a time there was only one tube, a
> parallel-wound 3/4" id tube.  Estes called it "BT-40" which seemed a nice
> middle number with room for bigger and smaller numbers.  When the diameter of
> the engine was reduced to .7 and a spiral tube was added, that was called
> "BT-20", and when a slightly larger tube was introduced it was called "BT-50."
> It just grew from there.

   The old Centuri system was somewhat superior. ST-13 was a spiral
wound tube wound on a 1.3" mandrell, et cetera.

   Brett

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Peter Cl » Wed, 11 Aug 1999 04:00:00


Quote:
>I figured out that the "BT" in the description stands for Body Tubes - what
>I'm wondering is the number afterward.  It is some sort of measurement, but
>of what?

It's not a measurement.  Once upon a time there was only one tube, a
parallel-wound 3/4" id tube.  Estes called it "BT-40" which seemed a nice
middle number with room for bigger and smaller numbers.  When the diameter of
the engine was reduced to .7 and a spiral tube was added, that was called
"BT-20", and when a slightly larger tube was introduced it was called "BT-50."
It just grew from there.

Peter W. Clay NAR 18619 SR L1
"Experience is a good teacher, but her fees are high."

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Stefan Jone » Wed, 11 Aug 1999 04:00:00


Quote:

> It's not a measurement.  Once upon a time there was only one tube, a
> parallel-wound 3/4" id tube.  Estes called it "BT-40" which seemed a nice
> middle number with room for bigger and smaller numbers.  When the diameter of
> the engine was reduced to .7 and a spiral tube was added, that was called
> "BT-20", and when a slightly larger tube was introduced it was called "BT-50."
> It just grew from there.

How's this for confusing: The ORIGINAL original tube was the "BT-1".
Later they added the skinnier "BT-3". Eventually these became the BT-40
and BT-30. The latter was around until the early 70s.

--
Stefan Jones, Certification, Interactive Television Division
650-506-1032

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Peter Cl » Thu, 12 Aug 1999 04:00:00


Quote:
>How's this for confusing: The ORIGINAL original tube was the "BT-1".
>Later they added the skinnier "BT-3". Eventually these became the BT-40
>and BT-30. The latter was around until the early 70s.

Thanks! I knew that BT-40 was labeled BT-1 in MMI Rock-A-Chute kits and in the
Aerobee-Hi plans I used in '72.  I'm not sure when the BT-3/BT-30 arrived, but
probably was introduced with the 18mm casing about 1960. The Brown/MMI motors I
had wouldn't fit in BT-30.  BT-20 would have been added when the technology
became cost-effective -- or more to the point, when sales justified tooling a
spiral tube.

My Brown/MMI motors were .75" x 2.25". Do you know anything about an earlier
motor that was more like .5" x 2.25"? About the size of Centuri and MPC
mini-motors?

Just curious.

Peter W. Clay NAR 18619 SR L1
"Experience is a good teacher, but her fees are high."

 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Roy Gre » Thu, 12 Aug 1999 04:00:00


Quote:

>>How's this for confusing: The ORIGINAL original tube was the "BT-1".
>>Later they added the skinnier "BT-3". Eventually these became the BT-40
>>and BT-30. The latter was around until the early 70s.

>Thanks! I knew that BT-40 was labeled BT-1 in MMI Rock-A-Chute kits and in the
>Aerobee-Hi plans I used in '72.  I'm not sure when the BT-3/BT-30 arrived, but
>probably was introduced with the 18mm casing about 1960. The Brown/MMI motors I
>had wouldn't fit in BT-30.  BT-20 would have been added when the technology
>became cost-effective -- or more to the point, when sales justified tooling a
>spiral tube.

>My Brown/MMI motors were .75" x 2.25". Do you know anything about an earlier
>motor that was more like .5" x 2.25"? About the size of Centuri and MPC
>mini-motors?

>Just curious.

Carlilse's original motors were .5" x 2.25", but I don't think they
were mass produced, at least for MMI.  G.Harry's story goes that they
were shopping around for some fireworks manufacturers to build their
motors with Carlilse's form-factor, but that the eventual manufacturer
(Brown, I guess) wanted to use his own tubes, because his machinery
was already set up for it.
--------
Roy Green, Atlanta
NAR #12605   SoAR #007  (SoAR Web at www.soar571.com)
http://roygreen.home.mindspring.com/
to reply by E-mail, remove the 'xxx' from the address given
 
 
 

Newbie Question...Body Tubes - BT-5, BT-20, Bt-50, BT-55 and BT-60

Post by Bob Kapl » Mon, 16 Aug 1999 04:00:00



Quote:
> As I understand it, they were randomly chosen but they are progressively
> larger.

> BT-5 is .5", BT-20 is .736", BT-50 is .976" (?), BT-55 is 1.325" and
> BT-60 is 1.63" .

Not quite. In about 1963 the tubes were numbered in size order BT-10, BT-20,
BT-30, BT-40, BT-50, BT-60. As tubes were later added, they were inserted by
size. BT-10, -30, and -40 are gone, but were very close to BT-20.

So there is no direct relation between diameter and number, other that
larger diameters have larger numbers.

Other companies have used either inch or metric designations for their
tubes.

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://members.aol.com/myhprcato/KaplowKlips.html
NIRA:           http://www.nira.chicago.il.us  NAR:    http://www.nar.org