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Old 11-25-2006, 09:05 AM
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snaquin snaquin is offline
Join Date: Jun 2005
Location: Louisiana
Posts: 1,933

Originally Posted by CPMcGraw
I spotted the nose cone and body tube on the SEMROC website, and thought I'd toss an old favorite together to see what could be done. Mercy!

This is a 1.885X upscale of the long-body Cherokee-D, using Carl's BTH-70 tubes and his BNC-70HAC nose cone. The fins are TTW . I used the LT-150 tube for the motor tube.

Length: 43.16"
Diameter: 2.497"
Fin Span: 11.377"
Weight: 28.70 oz

H123W-10......3033'......Dv 19 FPS......36" x 1/4" launch rod
H153-13.......3775'......Dv 25 FPS......36" x 1/4" launch rod
H45W-10.......4898'......Dv 17 FPS......60" x 1/4" launch rod
I125R-14......5514'......Dv 14 FPS......36" x 1/4" launch rod
I211W-14......5902'......Dv 8 FPS.......36" x 1/4" launch rod
I195J-14......6015'......Dv 11 FPS......36" x 1/4" launch rod
I240-15.......6616'......Dv 10 FPS......36" x 1/4" launch rod

The last motor in the list -- the I240-15 -- pushes the model to 1167 FPS, which is greater than Mach 1 at 70 degrees F. Now, only an experienced HPR builder can tell if this design would even hold up to that stress if built lightly, the way RockSim would expect it to be. I make no predictions beyond what the simulator suggests it could do. This is a genuine "what if", and I only offer it as a possibility.


Nice upscale of the Cherokee-D Craig. I think a Cherokee-D upscale in that size would be just right and given the new BNC-70HAC Secant Ogive you wouldn't need to have a custom nose cone turned.

At first glance your design seemed a bit heavy at almost 29 ounces dry weight for a rocket that size. A 46" long Public Missiles Callisto with G-10 .063 thick fins and heavy phenolic tubing with a 38mm MMT and piston ejection weighs in at just under 25 ounces dry in the design file and that includes a 6 ounce mass object for epoxy/paint and tweaking.

Semroc has the BTH-70 tubes listed as 2.175" ID x 2.247" OD with a .036" wall thickness. Your OD for the tubing is set at the same OD as the BNC-70HAC nose cone, 2.497" OD. I'm not sure if those Semroc dimensions are correct but by sizing the tubing to the same OD as the nose cone accounts for an extra almost 9 ounces of added weight.

Since the Semroc BTH-70 wall thickness would be correct at .036" given the stated tubing dimensions, should the BNC-70HAC nose cone really be 2.497" OD or I wonder if that is a typo? I would think it should be 2.247" as well?

Steve Naquin
TRA# 677 L2
NAR# 85518 L2
SAM# 0052

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