Back in 1964, Estes released the B3 motor, which under the English unit nomenclature of the time meant that the motor had an average thrust of a whopping 3 pounds (13.3 newtons). The B3 was a Series II motor, which meant that a) it had high thrust and b) the manufacture required an additional step - drilling a deeper nozzle into the black powder propellant. The result was a motor with a short duration (~0.3 seconds), spike-like thrust curve with a peak thrust around 7 pounds (31 newtons) - the Estes catalog described the thrust as "like a sledge hammer blow." And it was true - the B3 could move single stage rockets so fast that poorly attached fins would rip right off, and easily had the power to loft heavy 3 stage payload carriers like the Farside-X. When I first started rocketry in '68, the motor classification system had just gone metric, so the B3 became the B14. Same characteristics, different label.
|Comparison of B6 and B14 thrust curves in the 1968 Estes catalog (Click to enlarge).|
So why this foray into rocket motor history? It's because I have recently acquired some old Centuri B14 and Estes B8 motors, and I tested a couple of them - along with a current B6 - on my motor test stand last Saturday. I measured the thrust on the 50 newton maximum scale at 50 samples per second; the resulting curves are shown below. Note that the blue B14 curve is very similar to that shown in the catalog image above - a sharp spike up to 21 newtons, followed by an impulsive event at the end of the thrust (this was a booster motor, so no delay). However, there is a bit of a puzzle, as the peak thrust should have been over 30 newtons, whereas this Centuri motor produced only two-thirds that amount. I'm at a loss to explain this, except maybe to invoke motor deterioration over the 44 years since this motor was made. The red Estes B8 (manufactured in 1980) curve shows a similar sharp rise to 23 newtons peak, and then drops down to a thrust of just over 4 newtons, similar to that of the modern B6-4 (black curve). It is spent after 0.5 seconds, with the ejection charge occurring about 5.9 seconds after burnout.
|Saturday's thrust measurements (Click to enlarge).|
2018 is gonna be a fun year!