Cl(VII)
Chris Bender
I flew my first V-2 when I was 10 years old. I started back in the Hobby in '99 at 40 years old. Between my brother and I we have flown nearly every size V-2 from 3" to 7.5". Von Braun made an effective weapon. It had advanced motor and guidance technology, was short and fat so mobile launchers could take it it most anywhere to avoid the bombers.
Key words: It's short, fat and unstable compared to my 13' long IRIS.
I looked at the M-650 thrust curve and yes that 1250 newtons is there but only for a brief period. Regardless what the sims may show it will start to layover and look like it's headed to London. That kind of flight profile may have a higher velocity at apogee which you may not want.
I fly V-2s with somewhat flat thrust curves at about 7: 1 wt/avg thrust ratios. You get a nice leap off the pad and after burnout you get a nice , loud whistle near apogee, during that long coasting phase, that will impress the crowd.
If you want to do a test flight in the same case (assuming 6400n) fly it with an L-1170, then do your L3 with an M-1297 (with 1 AT spacer) or go for it with the M-1315.
Great looking build and finish, nice work!
I see your point, and no doubt there will be more weather cocking with the M650 than the M1315. To save anyone interested the trouble I have pasted a pic below with the worse case (35 lb pad weight, probably be closer to 32 in reality) thrust to weight ratios marked. The M1315 does give it a harder kick off the pad, and keeps it about 7:1 thrust:weight for much longer (3.9 s versus 0.9 s), but the time above 5:1 thrust:weight is almost the same at (4.4 s versus 4.1 sec). I don't think I will be far off the flat 7:1 thrust curve you have gotten good performance at. Given your experience how much trouble do you think I'd be in during that first 4 sec? As the motor tails off I'm sure I'll see some degree of arching. Preventing damage from an off vertical flight/deployment is one of the reasons the fin can blows first and not the nose...should decrease the chance of zipper as everything will likely stay in line.
I'm not fundamentally averse to changing to the M1315, and holding the M650 back for next year's big project (75mm MD CF altitude seeker). The point of the M650 was for the long burn white fire/noise/smoke trail awesomeness. The M1315 will be way up there till it burns out at 5.5 sec though.
In the end I will work some of this out by discussion with my L3CC. Dave could safely fly a Borg Cube, and possibly put it into an RC controlled glide as well for that matter. If he isn't comfortable with the motor choice I will definitely wave off.
Thanks for the well informed advice. I do value such advice, even if I ultimately ignore it.
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