Binder Design Excel Plus 54 Motor Limits?


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Jan 18, 2016
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St. Louis, MO
I'm planning out motors for a launch at MWP in Nov. I'm thinking about a 6-grain longburn. Has anyone ever flown this on a CTI K260-CL? Seems like it shouldn't tax the airframe too much.

Flight calculations:
Motor: CTI 54mm 6-grain K260 CL
Stability calibers: 1.39
Thrust-to-weight: 260 N / 4.17 kg = 6.4:1
Velocity off rail (6’): 17.2 m/s (38.5 mph)
Velocity off rail (8’): 20.5 m/s (45.9 mph)
Max acceleration: 81.6 m/s2
Max velocity: 263 m/s (588 mph = mach 0.78)
Apogee: 2,648 m (8,687 ft)

Has anyone pushed this airframe past mach? I'm a bit nervous about having it sit in the transonic region, so I'm staying under mach 0.8.


Well-Known Member
Oct 15, 2011
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I've flown a stock 4" Binder design kit (2014 NXRS Research Test Vehicle) on an AT K375 to about Mach 1.3. It held up well, but had a slight kink in the body tube just above the fin can, probably from the trans-sonic transition. Video from the flight is here. I reinforced the region with a spare coupler afterwards and have had no further issues.

I've also seen the kit you mention fly on K1100's without issue.

Point being, the Binder Design kits are stout, despite being cardboard. I would be comfortable flying the motor you suggest. If built reasonably well, they can handle high thrust and they'll hold up to trans-sonic flight, but I would recommend inspecting the rocket post any such flights... though really you should do that on any rocket.