What do the BT numbers mean?

[TheSamurai]

Thank you all for the info. I'm definitely interested in learning how to make my own as well. Eventually want to get into scratch building but for now I am much more comfortable with the kits and maybe making modifications to those.

 

[luke strawwalker]

Here ya go...

View attachment SemrocTTTubesizechart[1].txt

I wrote this up a couple years or so back... It's posted on here somewhere, but never hurts to toss it out again in a new post from time to time...

Basically the tubes are listed from smallest to largest. This is essentially all LPR/MPR tubes. Some new ones have probably come out (say for the big new Estes kits) but I haven't bought any of them and haven't added them to the list. It's a good start anyway if someone wants to add to it, have at it...

I didn't put "Estes" as a mfg. on the list-- basically anything with a "BT-" designator is an Estes tube... (not that they offer all of them for sale, hence the Semroc and Totally Tubular references). Quest uses metric-sized tubes where the tube number is the outer diameter in millimeters IIRC.

As for the naming conventions, it's a long story, but basically they started with the BT-20 size tube (which an 18 mm motor fits nicely into) and then as they added new sizes, they assigned an arbitrary number from there, like old code jumping in tens to leave room between the numbers in case they came out with a size "in between" two already available sizes later on... For instance, when they came out with a tube between the size of BT-50 and BT-60, they called it a BT-55. Centuri used a tube a hair bigger than BT-55, and when Estes bought Centuri they ended up with them, and ultimately used that tube size on some of their rockets (like the Astrocam 110) and thus called it a BT-56. There's more to it than that and someone could really explain the history of it if they wanted to...

Later and good luck! OL JR

 

[luke strawwalker]

So there isn't a coupler I can buy that will work for the Ventris?

You can make your own if you have the tubing... just cut a piece you want the length of the coupler you want, and cut a slit down one side, roll it slightly tighter and slide it into the tube, mark the overlap, remove it and cut the strip off the edge so the edges of the cut now butt together... glue the small strip you cut off to the inside of the butt joint, overlapping each half of the joint for a strengthener... instant tube coupler...

I do this all the time with various size tubes if I don't have a coupler handy... and if you use "found" tubes (Christmas wrapping tubes, etc) this is your only choice to make couplers... Heck I've even "rolled my own" motor mount tubes this way using toilet paper rolls...

Later and good luck! OL JR

 

[luke strawwalker]

Umm.... 2.5" - 2.42" leaves .080" new math?

I mean if you are going down to a thousandth of an inch, you shouldn't round numbers..... just saying.....


Jerome :wink:

Yeah, 0.040 for the tube wall on ONE SIDE, and 0.040 for the tube wall on the OTHER SIDE...

He was right...

Later! OL JR

 

[fyrwrxz]

I always wondered why my rockets built on BT-101 tubes always crashed, sometimes before I even launched them, yet I was always coming home with more parts than I put into the rocket.

LMAO! At Last! A perfect description of a mystery eluding me for years. For you history buffs-Eastman came out with a glue called EA934. This was the commercial grade 'superglue' everybody uses now and it was hella expensive back in the day. I just had to try some out on a rocket and mind you, this was 'before' superglue was commercial, so the workings were pretty much a mystery. Whatever it was , a scratch built bird with BT-101 was involved and was doomed before it flew. I glued that sucker to every body part and other useless things on my bench before I figured it out. Shoulda known-BT-101+EA934=Rocket 1035. Static display...until I chipped it off my desk....more parts than I started with.....

 

[hcmbanjo]

Here ya go...
View attachment 132285
I wrote this up a couple years or so back... It's posted on here somewhere, but never hurts to toss it out again in a new post from time to time...

OL JR

Thanks OL JR,
That tube list is handy to have for quick reference.

Here's another tube "fit" I found a while back -
The Quest 40mm tube is a slip fit inside the Estes BT-60.

 

[JeromeK99]

Thanks OL JR,
That tube list is handy to have for quick reference.

Here's another tube "fit" I found a while back -
The Quest 40mm tube is a slip fit inside the Estes BT-60.

Very cool. Good to know! I'll have to remember to order a couple of tubes next time.

See, you learn something everyday!

Thanks Chris!


Jerome

 

[boomtube]

I always wondered why my rockets built on BT-101 tubes always crashed, sometimes before I even launched them, yet I was always coming home with more parts than I put into the rocket.

It is for that very reason that Estes never brought to market their “Mega-Scale” rocket kits based on the BT-200 tube.

Not only did the rockets based on the BT-200 tube crash and burn they inevitably took the rockets on either side with them. And this was assuming these “Mega-Scale” rockets actually managed to make it too the launch site. Estes’ employees were loath being the designated driver; just how do you explain to the insurance company that "all four of your wheels falling off simultaneously" was the result of you transporting a BT-200 based rocket kit?

I could go on about the tragedies incurred in hobby shops throughout the United States as a result of the attempts to stock these kits, but that’s a story for another day.

 

[TheSamurai]

Here ya go...

View attachment 132285

I wrote this up a couple years or so back... It's posted on here somewhere, but never hurts to toss it out again in a new post from time to time...

Basically the tubes are listed from smallest to largest. This is essentially all LPR/MPR tubes. Some new ones have probably come out (say for the big new Estes kits) but I haven't bought any of them and haven't added them to the list. It's a good start anyway if someone wants to add to it, have at it...

I didn't put "Estes" as a mfg. on the list-- basically anything with a "BT-" designator is an Estes tube... (not that they offer all of them for sale, hence the Semroc and Totally Tubular references). Quest uses metric-sized tubes where the tube number is the outer diameter in millimeters IIRC.

As for the naming conventions, it's a long story, but basically they started with the BT-20 size tube (which an 18 mm motor fits nicely into) and then as they added new sizes, they assigned an arbitrary number from there, like old code jumping in tens to leave room between the numbers in case they came out with a size "in between" two already available sizes later on... For instance, when they came out with a tube between the size of BT-50 and BT-60, they called it a BT-55. Centuri used a tube a hair bigger than BT-55, and when Estes bought Centuri they ended up with them, and ultimately used that tube size on some of their rockets (like the Astrocam 110) and thus called it a BT-56. There's more to it than that and someone could really explain the history of it if they wanted to...

Later and good luck! OL JR

Excellent info. Thanks for sharing!!!

 

[luke strawwalker]

Excellent info. Thanks for sharing!!!

You're welcome...

Enjoy!

Later! OL JR

 

[sed6]

Here's my theory...

 

[asm109]

Holy thread revival Batman!!

 

[Rschub]

So that's why all those Saturn 5 models crash. Huh, I never made the connection.

 

[MALBAR 70]