new design SPRINT PARK FLYER

[andrew scott]

SPRINT PARK FLYER

This design is for small parks

Length: 547.15 mm, Diameter: 24.79 mm, Span diameter: 224.85 mm

Mass: 87.085 g, Selected stage mass 87.085 g

CG: 383.73 mm, CP: 445.98 mm, Margin 2.51 (no motor)

Engines -- A8-3, B4-2, B6-4, C6-5

[CPMcGraw]

Andrew,

I like the appearance of the Park Flyer. It's a challenge and a half.

One thing I need to bring to your attention, which you might not be aware of, is the very high Dv numbers this model is showing in the simulation runs. Most of the numbers you've rung up are in the 30s, and up to 40, feet per second at the moment of parachute deployment. This is instant death territory. The standard Estes / Quest / SEMROC 12" parachute will immediately be ripped off the shrouds at these velocities.

Your motor selections have good acceleration, with all of them reaching flight V in less than the length of a standard 36" x 1/8" rod. This model is a ringtail, and ringtails are notoriously draggy. It also doesn't help that RockSim does not calculate ringtails correctly. You really have to work the power and delay times carefully when you tackle these models.

Read THIS MESSAGE (http://forums.rocketshoppe.com/showpost.php?p=59063&postcount=70) for a better idea of where the Dv numbers need to fall to be considered "safe".

Right now, Andrew, Park Flyer needs some adjustment before I can post it to the Master List. I'm thinking you'll need to boost the power to "D" level, and make some length adjustments to keep the stability margin in check, before this bird can take flight. Or, to keep it in a small-field range, try adjusting the length of those rings, even moving them back a little. Make small adjustments and watch the DV and launch guide length values before trying something else.

I know you'll get the hang of RS9 before too long. Just be mindful of those numbers. They're telling you something about the flight envelope of your model. It's a continuous revision and test procedure on some designs to get them right. Always be aware, some designs just never get it right, no matter how much you tinker with them. I've got dozens in my files that will never work for the same reasons that are messing with this one.

[andrew scott]

there the mod file

[CPMcGraw]

Much nicer Dv numbers, Andrew. I don't understand what the formula is for working up a ringtail, I just know RockSim treats it far differently than it does a simple "inside tube" that's on the outside...

I'll get this version posted on the Master List. Thanks for the re-work.