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Old 01-11-2009, 07:59 PM
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CPMcGraw CPMcGraw is offline
Join Date: Mar 2005
Location: Mobile, Alabama
Posts: 5,357

Originally Posted by rkt2k1
Here is my first Rocksim v9 design. All but a couple of design components in design are from the Semroc part sets we've been collectively working on.

Optimal engine for this design seems to be the C6-5.

I used Jay's "screw-eye" trick to add some nose weight and extra stability to the design.

I think it could use a good set of military type decals. Hope you like it!

... Bill

Design Name: Predator Advanced BGM-18M

Length: 22.1"
Diameter: 1.64" (ST-16)
Fin Span: 4.498"
Weight: 2.841 oz

Engine Size: 18mm
Launch Guide Length: 36" x 1/8"

Motor......Max Altitude......Dep. Velocity

A8-3...........71.76 ft.........37.39 ft/s
B4-4..........223.26 ft.........24.10 ft/s
B6-4..........233.09 ft.........24.55 ft/s
C6-5..........668.50 ft..........2.55 ft/s

I agree, that C6-5 is the optimum motor in your list, and I would not recommend using any of the others. They are either at the edge of, or deep into, chute-shred territory. Getting about 670' on a C6-5 is good, though.

One thing I have to caution you on is the guide length. You call out a 36" x 1/8" rod, which is standard. However, you need to look at the flight summary. Double-click the line on the simulations screen where you flew the C6-5, and start reading through. You'll get to an area where it says "Launch Guide Data". RockSim says this design doesn't reach safe flight V until it's 38" up the rod. You're 2" short. This rocket needs a 48" x 3/16" rod using that motor, so that you get a full 38" of guide length. The extra won't hurt it.

Try simulating instead with the D13W-7. This is a composite D13 White Lightning. It jumps to velocity in only 20", reaches 1581', and has a Dv of just 5 FPS. Here is your optimum motor! Of course, it also has a Max V of 435 FPS, and an acceleration of 614 FPS/S. Really quick, but I think the TTW construction will hold up.

Good work for a RS9 first!
Craig McGraw

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