This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From Jeff Vincent, Chas Russell & Brett Buck:
(Note - This one belongs with the Gliders, is not a FAQ, but sorta interesting)
> >>What ever became of the practice of epoxying a
> >>mini-motor (13mm) into the top of a standard size (18mm)
> >>booster motor to kick it into the next impulse range?
> >>Example - C6-0 with an A3-4T sustainer.
Verboten within a year or so of its origin (late '70s). Thus the "do
not permanently attach anything to a casing" rule in the Pink Book.
"Tandems" got their start in California, as far as I know, in the '
'70,s. A couple of guys in the Bay area were flying the Estes
Skyraider on a D12-0/D12-7 epoxied together in a BT-50. Really were
neat. Static testing showed that some performance increase was
obtained from all of the extra mass eroded from the booster
motor. However, the fine people in Penrose (fine compared to the
current crew) decided that tandems did not meet the test of using the
product "as intended". Read liability issues. The NAR concurred and
the tandems had a short lived history. The later availability of
composites made the point essentially moot. I had flown a few prior to
the boom being lowered..
... my cohorts and I were flying tandems in 73-74 time frame in
central Kentucky ( about when Centuri Mini-Engines first came out
). Never heard of mixed tandems, though, like a C6-0/A3-4T. I always
figured that using the wrong sized nozzle for the upper engine - a C6
nozzle is much bigger than an A3 - wuoldn't work. . Plenty of people
had the idea of weakly gluing them together for conventional staging,
since they telescope so nicely. I assume that one failure to separate
would plant the idea.
I guess now that we can glue stuff to motor casings again, tandems are