blackshire
01-19-2009, 02:39 AM
Hello All,
It is both interesting and instructive to observe how growing experience and improving technologies foster changes in the production techniques and building methods of model rocket kits. Looking through the Ninfinger Productions web site and Jim Zalewski's web site, I have been able to track both the development of the Centuri Micron kit (Catalog Number KA-5) and the rocket kit construction methods that changed as the manufacturers gained more experience. In the case of the Micron, the changing construction methods also resulted in a change in the model's body tube length.
When Centuri first released the Micron kit in 1963 (see: http://www.dars.org/jimz/ka-5.htm to view a scan of the original kit instructions), the instructions called for the rear end of the rocket motor to be flush (even with) the rear end of the body tube. Since this made removal of the spent motor case the way we do it today (by grasping its protruding rear end and pulling it out) impossible, this earliest version of the kit came with a dowel so that the spent motor case could be pushed backwards out of the rocket.
The instructions in the original kit show how the manufacturers were still in the process of developing their building methods in these early years of the hobby. To give a humorous example, the original kit instructions said to position the "engine bulkhead" (thrust ring) inside the rear end of the body tube using the motor spacer tube. After removing the motor spacer tube, the builder was was then told to drip several drops of glue into the top end of the body tube, aiming at the joint between the bulkhead and the body tube!
Today it seems obvious to FIRST apply a ring of glue the proper distance inside the tube (using a cotton swab or a "Q-Tip" having the proper distance marked on it) and THEN to push the thrust ring into position using the motor spacer tube (with a dowel "handle" glued into the motor spacer tube for flush-mounted motors). As is the case in many areas of human endeavor, however, this seemingly obvious solution wasn't obvious in the beginning.
This initial version of the Micron used the 1.875" long (2.5" long including the shoulder) balsa BC-72 nose cone (Semroc number BC-719 today) and the ST-76 body tube (a 6" length of 0.759" Outside Diameter #7 tubing, see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen30.html ). The kit came with a 1.125" wide, 36" long crepe paper streamer. The shock cord was a 16" length of 1/8" wide rubber, and it was attached to the rocket's body tube using the original "slit-and-glue" method. The fins had to be cut out using a printed fin pattern. Although the kit came with a large checkerboard decal that wrapped around the body tube, no "official" decor scheme was given in the instructions. They merely suggested that paint colors such as white, yellow, orange, red, silver or black would aid tracking.
By 1965, Centuri had changed the Micron's decor scheme to include a black roll pattern decal on the front end of the body tube and a narrow band decal just ahead of the fins (see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen6.html ). This is the decor scheme it would have for the rest of its time in production. For a brief period in the 1960s, the Micron was even offered as part of a starter set (see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen12.html ).
Beginning in 1969, the Micron's ST-76 tubing was changed from 6" in length to 6.5" in length (see: http://www.ninfinger.org/rockets/nostalgia/69cenp54.html ). This must have been the time when the construction method was changed so that 1/4" of the motor would now be left protruding from the rear end of the rocket's body tube. This facilitated easy removal of the spent motor case, and it also eliminated the need to include the "pusher" dowel in the kit. Since this change moved the rocket's Center of Gravity (CG) rearward, the body tube was lengthened by 0.5" to compensate for it by moving the CG further forward.
That year's Micron catalog listing did not mention a plastic nose cone or printed balsa fins. It did, however, say "Now With New Streamer Recovery" (see: http://www.ninfinger.org/rockets/nostalgia/69cenp24.html ), which suggests that the streamer material was changed from crepe paper to fluorescent orange plastic flagging tape at this time.
In 1971, the Centuri catalog touted the Micron's new printed balsa fins and plastic nose cone (the 2.3" long PNC-73, see: http://www.ninfinger.org/rockets/catalogs/centuri71d/71dcen20.html ). This nose cone is reproduced today in balsa by Semroc (Semroc Part Number BC-723P) and in polyurethane resin by Sirius Rocketry.
In 1975 yet another innovation, die-cut fins, was incorporated into the Micron kit (see: http://www.ninfinger.org/rockets/catalogs/centuri75/75cen10.html ). Oddly though, during its last two years in production (1980 and 1981), the Micron's catalog listing again described it as having printed balsa fins (see: http://www.ninfinger.org/rockets/nostalgia/80cen010.html and http://www.ninfinger.org/rockets/catalogs/centuri81/81cen10.html ). By this time, Centuri was winding down. Perhaps their cutting die for the Micron fins wore out before they had gone through all of the remaining Micron kit parts and, not wanting to pay for a new die, they went back to printed balsa fins to finish out the production?
In 2003, Semroc brought the Micron back after 22 years of oblivion for model rocketeers both young and old to enjoy, either again or for the first time. Their version depicts the "intermediate" 1969-1970 era Micron with its longer (6.5") body tube and balsa nose cone. They have brought this venerable old design up to date, incorporating laser-cut fins, a combination Kevlar/elastic shock cord, and the durable "to-the-thrust-ring" shock cord mounting method.
It is both interesting and instructive to observe how growing experience and improving technologies foster changes in the production techniques and building methods of model rocket kits. Looking through the Ninfinger Productions web site and Jim Zalewski's web site, I have been able to track both the development of the Centuri Micron kit (Catalog Number KA-5) and the rocket kit construction methods that changed as the manufacturers gained more experience. In the case of the Micron, the changing construction methods also resulted in a change in the model's body tube length.
When Centuri first released the Micron kit in 1963 (see: http://www.dars.org/jimz/ka-5.htm to view a scan of the original kit instructions), the instructions called for the rear end of the rocket motor to be flush (even with) the rear end of the body tube. Since this made removal of the spent motor case the way we do it today (by grasping its protruding rear end and pulling it out) impossible, this earliest version of the kit came with a dowel so that the spent motor case could be pushed backwards out of the rocket.
The instructions in the original kit show how the manufacturers were still in the process of developing their building methods in these early years of the hobby. To give a humorous example, the original kit instructions said to position the "engine bulkhead" (thrust ring) inside the rear end of the body tube using the motor spacer tube. After removing the motor spacer tube, the builder was was then told to drip several drops of glue into the top end of the body tube, aiming at the joint between the bulkhead and the body tube!
Today it seems obvious to FIRST apply a ring of glue the proper distance inside the tube (using a cotton swab or a "Q-Tip" having the proper distance marked on it) and THEN to push the thrust ring into position using the motor spacer tube (with a dowel "handle" glued into the motor spacer tube for flush-mounted motors). As is the case in many areas of human endeavor, however, this seemingly obvious solution wasn't obvious in the beginning.
This initial version of the Micron used the 1.875" long (2.5" long including the shoulder) balsa BC-72 nose cone (Semroc number BC-719 today) and the ST-76 body tube (a 6" length of 0.759" Outside Diameter #7 tubing, see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen30.html ). The kit came with a 1.125" wide, 36" long crepe paper streamer. The shock cord was a 16" length of 1/8" wide rubber, and it was attached to the rocket's body tube using the original "slit-and-glue" method. The fins had to be cut out using a printed fin pattern. Although the kit came with a large checkerboard decal that wrapped around the body tube, no "official" decor scheme was given in the instructions. They merely suggested that paint colors such as white, yellow, orange, red, silver or black would aid tracking.
By 1965, Centuri had changed the Micron's decor scheme to include a black roll pattern decal on the front end of the body tube and a narrow band decal just ahead of the fins (see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen6.html ). This is the decor scheme it would have for the rest of its time in production. For a brief period in the 1960s, the Micron was even offered as part of a starter set (see: http://www.ninfinger.org/rockets/catalogs/centuri65/65cen12.html ).
Beginning in 1969, the Micron's ST-76 tubing was changed from 6" in length to 6.5" in length (see: http://www.ninfinger.org/rockets/nostalgia/69cenp54.html ). This must have been the time when the construction method was changed so that 1/4" of the motor would now be left protruding from the rear end of the rocket's body tube. This facilitated easy removal of the spent motor case, and it also eliminated the need to include the "pusher" dowel in the kit. Since this change moved the rocket's Center of Gravity (CG) rearward, the body tube was lengthened by 0.5" to compensate for it by moving the CG further forward.
That year's Micron catalog listing did not mention a plastic nose cone or printed balsa fins. It did, however, say "Now With New Streamer Recovery" (see: http://www.ninfinger.org/rockets/nostalgia/69cenp24.html ), which suggests that the streamer material was changed from crepe paper to fluorescent orange plastic flagging tape at this time.
In 1971, the Centuri catalog touted the Micron's new printed balsa fins and plastic nose cone (the 2.3" long PNC-73, see: http://www.ninfinger.org/rockets/catalogs/centuri71d/71dcen20.html ). This nose cone is reproduced today in balsa by Semroc (Semroc Part Number BC-723P) and in polyurethane resin by Sirius Rocketry.
In 1975 yet another innovation, die-cut fins, was incorporated into the Micron kit (see: http://www.ninfinger.org/rockets/catalogs/centuri75/75cen10.html ). Oddly though, during its last two years in production (1980 and 1981), the Micron's catalog listing again described it as having printed balsa fins (see: http://www.ninfinger.org/rockets/nostalgia/80cen010.html and http://www.ninfinger.org/rockets/catalogs/centuri81/81cen10.html ). By this time, Centuri was winding down. Perhaps their cutting die for the Micron fins wore out before they had gone through all of the remaining Micron kit parts and, not wanting to pay for a new die, they went back to printed balsa fins to finish out the production?
In 2003, Semroc brought the Micron back after 22 years of oblivion for model rocketeers both young and old to enjoy, either again or for the first time. Their version depicts the "intermediate" 1969-1970 era Micron with its longer (6.5") body tube and balsa nose cone. They have brought this venerable old design up to date, incorporating laser-cut fins, a combination Kevlar/elastic shock cord, and the durable "to-the-thrust-ring" shock cord mounting method.