Is There Any Logic To Body Tube Designations

bjphoenix

Well-Known Member
TRF Supporter
Joined
May 3, 2011
Messages
1,554
Reaction score
637
They always seemed reasonably logical to me. When I started in rockets around 1964 I remembered BT-10, BT-20, BT-30 and BT-60. I wasn't aware of when BT-50 came out, I thought it was later. I reviewed the 1963 catalog and found that it did contain BT-10, 20, 30, 40, 50 and 60, but it didn't have any kits using BT-40 or BT-50. I wasn't even aware that BT-40 existed, I wonder if it was ever used for anything.
BT-10 was a thin mylar tube, BT-20 was the same as what we have now, BT-30 was a thicker parallel wound tube, so that sequence of numbers made sense. Bt-60 was much larger so it made sense. Then BT-50 and later BT-55 fit in between those. When they came out with the tube about 13mm, it was smaller than BT-10 and BT-20 and became BT-5. If you're going to make 6 products in somewhat increasing size, it's as reasonable as anything to call them 10, 20, 30, 40, 50, 60.
What seems illogical to me are some of the more recent tube sizes that fit in between the classic sizes. I dug through some old nose cones I had looking for some to fit BT-50 and found a few that were just a tiny bit too big for BT-50, I don't have an idea what they are or where I got them.
 

lakeroadster

Improvise, Adapt and Overcome
TRF Supporter
Joined
Mar 3, 2018
Messages
6,414
Reaction score
6,579
Location
Central Colorado
The only sort of logic I recall was that BT-60 was so named because it could fit three BT-20s inside (in a cluster arrangement). That may be apocryphal, but it sounds about right.

As I was drawing up the first stage of my multi stage Saturn V on CAD, using a cluster of (5) D12 motors with BT-50 as the motor tubes, @neil_w 's post once again resonated in my mind.

BT-50: 0.976 O.D. x 3 = 2.928. Guess what the I.D. of a T-300 tube is? 2.930

So the likelihood of tube sizes being based on motor cluster capability seems more than just a coincidence.

Saturn V Dwg Sheet 2 of 3 Rev 00.jpg
 

ghughes1138

Member
Joined
Nov 29, 2022
Messages
7
Reaction score
5
Location
Chelmsford, MA
Oh, logical stuff like 12 mm (really 12.7 so 1/2"), 19 mm (really 19.05 so 1/4"), 25 mm (really 25.4 so 1")...

Sort of Imperial disguised as Metric.

The timber industry is, in reality, about as metric as a pre-war English motorcycle.
The US never adopted the Imperial System. US Weights And Measures Commonly Used is based on the system used by the British in the 1770s. Imperial came along in 1824.

I was living in Australia when we converted to Metric. When I moved to the US I had to learn to convert back to the not-quite-the-same measurements in use here. Mostly similar except for volume measurements. Yet another source of rounding and conversion errors.

Now back to our regular program, already in progress...

Wasn't the BT-30 the tube Estes used to ship engines, before they switched to the diamond packs?
 

jqavins

Слава Україні
TRF Supporter
Joined
Sep 29, 2011
Messages
8,869
Reaction score
5,080
Location
Howard, NY
They always seemed reasonably logical to me. When I started in rockets around 1964 I remembered BT-10, BT-20, BT-30 and BT-60. I wasn't aware of when BT-50 came out, I thought it was later.
I thought that a number of Estes very early designs had BT-50 main body tubes. If it wasn't minimum diameter (BT-20) then it was usually BT-50, I thought.
 
Last edited:

SolarYellow

Well-Known Member
TRF Supporter
Joined
Aug 6, 2022
Messages
653
Reaction score
433
Location
First country to put a man on the moon.
The only sort of logic I recall was that BT-60 was so named because it could fit three BT-20s inside (in a cluster arrangement). That may be apocryphal, but it sounds about right.

I think the thread has rendered that apocryphal, but I hadn't realized the technical aspect of it was true. Just tried it, it does fit really nicely.

As I was drawing up the first stage of my multi stage Saturn V on CAD, using a cluster of (5) D12 motors with BT-50 as the motor tubes, @neil_w 's post once again resonated in my mind.

BT-50: 0.976 O.D. x 3 = 2.928. Guess what the I.D. of a T-300 tube is? 2.930

So the likelihood of tube sizes being based on motor cluster capability seems more than just a coincidence.

My "7x13 cluster in a Baby Bertha" thread came about because I realized "7x24 cluster in a 3-inch tube" would work and be pretty cool.
 

neil_w

OpenRocketeer
TRF Supporter
Joined
Jul 14, 2015
Messages
14,734
Reaction score
8,385
Location
Northern NJ
I think the thread has rendered that apocryphal, but I hadn't realized the technical aspect of it was true. Just tried it, it does fit really nicely.
No, quite the opposite:
Bill Simon: The body tube designations were my fault. I really didn’t know anything about good practice in part numbering, so I just tried to use numbers that would let us add in-between sizes later on. BT-60, of course, accommodated 3 BT-20 tubes inside, and that was the entire basis for the system.
 

jqavins

Слава Україні
TRF Supporter
Joined
Sep 29, 2011
Messages
8,869
Reaction score
5,080
Location
Howard, NY
I've understood, second hand, that "clicks" for kilometers is because map grid lines are at 1 km intervals, so one goes "click, click, click..." through grid squares. If so, then the usual spelling with a 'c' would be at least as appropriate as spelling it with a 'k' (at the beginning).
 

cwbullet

Obsessed with Rocketry
Staff member
Administrator
TRF Supporter
Global Mod
Joined
Jan 24, 2009
Messages
31,693
Reaction score
9,063
Location
Glennville, GA

jqavins

Слава Україні
TRF Supporter
Joined
Sep 29, 2011
Messages
8,869
Reaction score
5,080
Location
Howard, NY

bjphoenix

Well-Known Member
TRF Supporter
Joined
May 3, 2011
Messages
1,554
Reaction score
637
I thought that a number of Estes very early designs had BT-50 main body tubes. If it wasn't minimum diameter (BT-20) then it was usually BT-50, I thought.
If you're talking about kits- there weren't any BT-50 kits in the 1963 catalog, well there weren't very many kits of any size in that catalog. It appears that the only BT-50 kit in the 1964 catalog was the Farside. (I don't believe I've ever seen a Farside actually.) The next catalog I have is 1966 and it has a lot of kits including a lot of BT-50 kits.
 

augendoc

Well-Known Member
TRF Supporter
Joined
Jun 8, 2017
Messages
63
Reaction score
42
I dug through some old nose cones I had looking for some to fit BT-50 and found a few that were just a tiny bit too big for BT-50
If you’re talking about BT-55 nosecones, Estes once had a package of blow-molded blunt tip long ogive cones that fit a BT-56 and were just a hair too big for the BT55. But of course they don’t sell a BT-56 tube. I believe theses are holdovers from the old Centuri days. I have an old Estes Maniac that uses these tubes, nosecones and a molded fin can (great flier on a D engine, BTW). And Istill have a handful of those cones that I got in a 5/6-pack from Estes. If you think this may be what you have, search for “BT-56“ in the forums. eRockets still sells a Semroc ST-13 body tube, which is the same size as the mythical BT-56.
 

bjphoenix

Well-Known Member
TRF Supporter
Joined
May 3, 2011
Messages
1,554
Reaction score
637
If you’re talking about BT-55 nosecones, Estes once had a package of blow-molded blunt tip long ogive cones that fit a BT-56 and were just a hair too big for the BT55. But of course they don’t sell a BT-56 tube. I believe theses are holdovers from the old Centuri days. I have an old Estes Maniac that uses these tubes, nosecones and a molded fin can (great flier on a D engine, BTW). And Istill have a handful of those cones that I got in a 5/6-pack from Estes. If you think this may be what you have, search for “BT-56“ in the forums. eRockets still sells a Semroc ST-13 body tube, which is the same size as the mythical BT-56.
That is probably what I have.
 

SolarYellow

Well-Known Member
TRF Supporter
Joined
Aug 6, 2022
Messages
653
Reaction score
433
Location
First country to put a man on the moon.
If you’re talking about BT-55 nosecones, Estes once had a package of blow-molded blunt tip long ogive cones that fit a BT-56 and were just a hair too big for the BT55. But of course they don’t sell a BT-56 tube. I believe theses are holdovers from the old Centuri days. I have an old Estes Maniac that uses these tubes, nosecones and a molded fin can (great flier on a D engine, BTW). And Istill have a handful of those cones that I got in a 5/6-pack from Estes. If you think this may be what you have, search for “BT-56“ in the forums. eRockets still sells a Semroc ST-13 body tube, which is the same size as the mythical BT-56.

Still on the Estes site, and listed by several retailers: https://estesrockets.com/product/003164-nc-56-nose-cone-4-pk/

There are also a couple of couplers for it included in the "large tube coupler pack."

There's a whole thread on it here: https://www.rocketryforum.com/threads/info-on-the-estes-pnc-56-nosecone.137939/

BT-56 is really ST-13. There are only a few scraps of it left for sale new that I can find anywhere in the world:

@JackHydrazine has modeled the fin can. https://www.thingiverse.com/thing:3641770

I asked him about making the PNC-56A for BT-55, and he said he'll add it to his list to eventually get to.
 

beeblebrox

8 C6-0, 12 D11-9, 20 D20-0, 20 E5-0, 3 Cinerocs
Joined
Mar 19, 2016
Messages
955
Reaction score
614
Location
West Chester, PA
The US never adopted the Imperial System. US Weights And Measures Commonly Used is based on the system used by the British in the 1770s. Imperial came along in 1824.

I was living in Australia when we converted to Metric. When I moved to the US I had to learn to convert back to the not-quite-the-same measurements in use here. Mostly similar except for volume measurements. Yet another source of rounding and conversion errors.

Now back to our regular program, already in progress...

Wasn't the BT-30 the tube Estes used to ship engines, before they switched to the diamond packs?
BT-30 was slightly bigger than the BT-20 but was parallel wound not spiral and was thicker walled...

Here is a screenshot of the 1964 catalog page with tubes...

1670867496597.png
 
Top