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Old 01-12-2010, 06:43 AM
Slickwilly's Avatar
Slickwilly Slickwilly is offline
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Join Date: Jan 2010
Location: Bourbonnais, IL
Posts: 144
Default X-15 Rocksim 1.6in, 2.2in, 3in & 5.5in

Really enjoyed designing these, it was a real challenge. I could'nt do exact scale because of the stability, so I had to move fins back a ways. I "m still not sure these are still real stable as I've never built one. I was'nt sure if you had any X-15 plans in your past lists.

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File Type: rkt Scratch X-15 1.6in.rkt (37.8 KB, 224 views)
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File Type: rkt Scratch X-15 2.2in.rkt (42.2 KB, 212 views)

Last edited by Slickwilly : 01-12-2010 at 08:18 AM.
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Old 03-06-2010, 10:45 PM
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CPMcGraw CPMcGraw is offline
Join Date: Mar 2005
Location: Mobile, Alabama
Posts: 5,357


Sorry I didn't make a comment earlier about these X-15 models. Thanks for posting them to BARCLONE. I'm starting to get caught up after my long hiatus, and I'm looking them over now.

The only thing I'm seeing about them that needs attention is the low stability margins. This seems to be a consistent issue across the entire family. When you're designing any model, watch out that your margin doesn't drop below the "magic number" of 1.00 when the engine is loaded. You want the model to always stay above this minimum with the engine loaded; if the model has a margin below this, it will fly every which way but straight. Guaranteed.

Models of aircraft are inherently unstable as rockets because of the fin (wing) placement relative to the CG and CP. It makes an airplane design 'negatively stable'. Ever wondered why those Centuri Fighters tended to have their fins and wings shifted toward the rear, instead of more like their real-world prototypes? This is why.

Unfortunately, it holds true for the X-15, too. It's still an airplane, with big wings on the wrong side of the CG/CP zone. Adding more nose weight sounds like a solution, but it's not always the best. More mass means a higher Dv (Deployment Velocity), which means higher stress for the parachute at apogee, which means greater chances of failure.

To keep these designs closer to the prototype, you might try a combination of things, including reducing the size of the engine and adding small amounts of ballast to the nose cone. Pick one engine and use just enough ballast to bring the margin to about 1.10 (a fudge factor of 10%), then stick with that combination. Sacrifice a measure of performance for a better-looking flight that doesn't kill the parachute with an explosive 'pop'.
Craig McGraw

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Old 04-18-2013, 11:22 AM
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Ramjet Ramjet is offline
B.A.R. and RC Geek
Join Date: Jul 2005
Location: New Hampshire
Posts: 68
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Smile Thanks

I appreciate someone going to the trouble for this.
I have the Hangar 11 Kit and they don't seem to have a Rocksim file for it, only the 6" version.

Also I plan on altering it for RC Boost glider flight.
I definitely need a Rocksim file to evaluate my design with.

I will be comparing yours with Hangar 11's and coming up with a 4" in between them.
Then I will modify for RC flight.
I have a novel method of drastically altering CG for converting from Rocket to glider but until I test it I'm gonna keep it under my hat. I will say only that I will not be dropping anything hazardous on anyone or anything.
Yep, Another B.A.R. Gone Hi-Power...

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