Model Rocketry and Spacemodeling?
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Estes Body Tubes: The Early Years
There's Fact and Fiction Floating Around Out There!
First...What Got Me Thinking About Early Estes Body Tubes
I was corresponding with a fellow modeler about scale modeling recently and he told me that the original Estes Saturn IB was 1/72 scale because it used BT-50 body tubes for the first stage tank cluster. Well, I know for a fact that the first Estes "Uprated Saturn I" (as it was officially named by NASA when Estes first introduced the kit...but by 1969 NASA and Estes were calling it the Saturn IB) used unique BT-51 body tubes for the tank cluster. As I compose this article I have pulled out a set of old Estes Saturn IB tubes and measured them...the BT-51 tubes are exactly 1" in diameter. Mike Dorffler who began work at Estes in 1969, also told me in early 2000 that the Saturn IB used BT-50 tubes and wouldn't budge until I showed him my scans of the original Estes Uprated Saturn I instructions clearly showing the BT-51s for the tanks. Oh, there was also a single BT-50 in the kit which was used as the "stuffer" tube (to route ejection charge from motors to the parachute compartment). I also sent him photos of an Alpha, which used the BT-50, sliding INSIDE one of the BT-51 tubes from the Saturn kit. It was during a visit several years later that he acknowledged the use of BT-51 tubes...and the Saturn IB was 1/70 Scale...not 1/72 as some would have you believe to this very day. Even employees can "misremember" facts and details from many years past.
Trivia: Estes was actually developing a Saturn I Block II model which most likely used a BT-50 tube for the first stage tank cluster during development. That model quickly morphed into the "sexier" Uprated Saturn I which was released in the 1967 catalog and actually used the true scale 1" diameter BT-51 tubes.
The "BT" for Estes body tubes is pretty obvious. It stands for "BODY TUBE." The designation was created by Vern Estes. The first record that I can find for Estes body tubes carrying the BT designation was in the 1961 Estes catalog showing a parts list for the Astron Scout and listing the Body tube as a BT-3A. The catalog also listed a BT-1. The particular number designations didn't last long. A couple of years after the 1961 catalog the BT-3 became the BT-30 and the BT-1 became the BT-40. Both were parallel wound cream colored paper that Gleda Estes hand-rolled. The BT-30 was used in both the Astron Scout, the Astron Mark and the Astron Space Plane that year (1961). The BT-1 was intended to be used with some fin units (from fireworks and carried in the Estes catalog) and plastic nosecones listed in the catalog at that time. Estes never produced a kit that used the BT-1 though a couple of years later (as the BT-40) is was used with some Estes Free Plans. The change from BT-1 and BT-3 to BT-40 and BT-30 can be credited to Bill Simon who came to Estes in 1962. He envisioned many more body tube sizes and "expanded" the numbering system with fairly large jumps in numbering so that any "in between" body tube sizes of the future could get its own round number.
By 1963 several new body tubes had appeared. The BT-10 was a spiral wound, almost clear, mylar plastic that was the smallest diameter tube available that would fit the Estes model rocket engines and it was feather light. It had a wall thickness of only .005"! The only model that Estes marketed that used the BT-10 was the Astron Streak (also in the '63 catalog). It could only withstand the heat of the ejection charge if the engine were ejected...which is precisely what happened with the Streak. The BT-20 was the first paper spiral wound tube from Estes. It was used in the original Astron Apogee 2-stage model. By now, the BT-3 was called the BT-30 and the BT-1 was called the BT-40 (but still not used in a kit). The BT-50 also appeared at this time (and it was yet to be used in a kit) as did the BT-60. The BT-60 was created for the new Astron Ranger which used a cluster of 3 engines mounted in BT-20 tubes...a "triad" of BT-20s just slid into a BT-60.
The first kit to use the BT-50 was the Astron Cobra as its forward payload section...a new 3-engine cluster rocket introduced in the 1964 catalog.
Trivia: Many people think the "Big Bertha" was the first to use the BT-60 and that the Astron Ranger was a "modified" Big Bertha. Nope...the Astron Ranger came first. The original Big Bertha was also just a plan offered by Estes about 3 years before it appeared as a kit in an Estes catalog. It appeared as a kit in the 1966 Estes catalog.
The BT-5, BT-55 and the BT-70 appeared in 1965 in the 1966 catalog (there was no 1965 catalog). The BT-5 was first used in the forward "payload" section of the Scale Aerobee 300 and the fin "pods" of the Mars Snooper. The BT-55 made its debut with the V-2, and the BT-70 first appeared simultaneously as the tail ring on the Astron Sprite and the main body of the Gemini Titan.
Estes had also introduced clear plastic tubes to be used as see-thru payload sections. These largely mirrored the sizes of the BT-20, BT-40, BT-50, and BT-60 tubes but the PST-65 tube, just slightly larger than a BT-60 (or the PST-60) made its first appearance in the 1966 catalog but no model as yet used it. However, it WAS in the '66 catalog as the tube for the PS-50E and PS-60C payload sections. Modelers quickly discovered that a Grade A Hen's egg would fit the tube and it was a "natural" for the newly "hatched" NAR Egg Lofting event. Three years later it finally found its way into a kit in the Astron Scrambler specifically designed for Egg Lofting.
As to the BT-70...It is said that it was designed for the Saturn I Block II prototype...which later became the Uprated Saturn 1 released two years later after the first appearance of the BT-70. I would personally call this speculation as if it were designed for the (presumably) 1/70 scale Saturn, it would have had a diameter of exactly 2.2 inches and the Gemini Titan and the Sprite would have had body tubes/tail rings of that diameter...but the BT 70 was actually larger. I suspect the the association of the BT-70 as being developed for the Saturn has to do the "70" in the tube's designation and the "70" as the scale factor of the Saturn. The Saturn was actually designed with 1" tank cluster tubes in mind. The BT-70 just happened to be "close" for the Service Module tube (but a bit oversized) to 1/70 scale and was therefore used in the Saturn kit as "close enough."
Until 1967, any body tube that was part of a kit was available in the current catalog. This trend was broken by the new Uprated Saturn 1. The Uprated Saturn 1 was, contrary to some sources, really a 1/70 scale model designed around 1" diameter BT-51 tubes (never to appear in a catalog). Further, it utilized a BT-100 tube (never to appear in a catalog) for the second stage and a BT-101 for the tail compartment which was scaled specifically for the 1/70 Saturn. NONE of these tubes appeared in the 1967 catalog. The Mars Lander was the only other model to use use the BT-100 two years later in 1969. The BT-101 made its first appearance in a catalog in 1971.
The Saturn V used the "close enough" BT-101 from the Uprated Saturn I as its main body tube. The BT-101 was 3.93" in diameter which was just .03" shy of being the exact 1/100 scale of 3.96 needed for the Saturn. It was, however, close enough not to warrant a special, almost microscopically larger tube just for the Saturn V.
The Saturn V in 1969 debuted the next body tube in the BT-80 which was used for the third stage body tube. There was also the BT-58 for the Service Module and the BT-63 tube for the engine mount introduced in the kit, neither of which made it into a catalog. The BT-80 eventually made it into the 1984 catalog 15 years later (!) though it was used both for the Maxi Brute Honest John and the Maxi Alpha in the mid-70s.
There have been many other "special" body tube sizes used only in kits over the years but this covers all the tubes available in the Estes Catalogs to date that had their origins in the 1960s.