This is another design that is not what I actually intended. Its rather a happy accident. I played around with the motor choice and have achieved an Deployment velocity of 1.10 with the Quest C6-5 and the Estes was a Dv of 5.23. Kind of interesting.

Thanks and Enjoy, JP

James Pierson
NAR #77907

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Thunder Strike.rkt (67.5 KB, 99 views)

There is a difference in the power and formulation of those motors. They're not the same, just in the same range. Notice the big difference in the Estes B6-4 and the Quest B6-4 in your other runs? The Estes had a 30 FPS Dv, while the Quest only has an 18 FPS Dv. I haven't taken the time to study the differences in the RocSim motor files, but it's clear there is a difference in the power numbers.

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Craig McGraw

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SAM 0044
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James noticed an interesting way to work with inside tubes with his Thunder Strike design, and it may be better than the cut-and-paste method for simulating tubes that are partially hidden and partially exposed.

I had to try his method out, and here's what I came up with.

Another "Schoolyard Sounder"...

Length: 18.3"
Diameter: 0.759" (ST-7)
Fin Span: 4"
Weight: 0.6 oz

1/2A3-4T.....235'.....19 FPS
A3-4T........565'.....20 FPS

Although the Dv is high for both motors, they're within limits. Just reef the chute and you should be safe.

As with some previous designs, the fin shape makes a big difference in the stability numbers. Adding that step in the leading edge can raise the margin while reducing the fin area as a bonus. Also, pulling the fin tip back at an angle is having a positive effect on the margin, while also reducing the total fin area.

Enjoy!

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Scrappy.rkt (56.0 KB, 116 views)

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Craig McGraw

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Reminds me of a certain Prometheus...........
(Sorry if I butchered that spelling. I'm too lazy to go back and check.)

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Bill Eichelberger
NAR 79563

http://wallyum.blogspot.com/

I miss being SAM 0058

Build floor: Centuri Mini Dactyl Estes - Low Boom SST Semroc - Marauder, Shrike, SST Shuttle

In paint: Canaroc Starfighter Scorpion Estes F-22 Air Superiority Fighter, Multi-Roc, Solar Sailer II, Xarconian Cruiser Semroc Cyber III

Ready to fly: Estes - Solar Sailer II Semroc - Earmark, Groonie Der V 1/2

But skinnier in the middle. Kind of like the seemingly anorexic teen models we're seeing these days. (Now, I *didn't* say "teen *model rockets!* )

--Seriously, guys, wouldn't having a tiny body tube like that BT-3 (with 6 of its 8" length exposed) contribute to a serious case of the "bends?" (Nothing personal, Craig, but as a klutz, I seem to instinctively understand the laws of physics, and at this particular scale -- especially given Estes' currently "Thermonuclear" ejection charges -- I'm just a little concerned for this design. ) Of course, you *could* do an SLS ~2.5OX upscale with Semroc's thick-walled "LT" tubes (LT-085, -125), but then you'd probably have to cluster it for the additional weight. Hmmm...


And now, for those of you who may have missed the Prometheus:

http://forums.rocketshoppe.com/show...60&postcount=48
http://forums.rocketshoppe.com/show...71&postcount=12

But yeah, Bill, you got the spelling write... er, "right." (You should *see* some of the news copy that comes over the TelePrompter. The folks who get Closed Captioning complain every once in a while. )


Cheers,

--Jay

For the record, I *do* think that fin shape is pretty cool!


Cheers,

--Jay

The thought did manage to inch its way across my brain as I worked up the design. If this were being done for 18mm A-C motors, I'd agree completely. The smallest tube I would have used in that configuration would have been an ST-5 or BT-5. But since this design uses the 13mm motors instead, I felt it should be safe, even with those T-Nuke deployment charges.

In reality, though, I think the model will suffer less from actual flying and more from "hangar rash"...

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Craig McGraw

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I'll probably be using some variation of the shape in future projects. I'm still curious as to why the shape has so much of an effect, as opposed to an increase of fin area. It's like that issue we beat to death about the Hi Flyer fins: A smaller fin with this step in the LE greatly improved that model's margin.

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Craig McGraw

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Having that step in the leading edge moves the center of area, and therefore the center of pressure, for the fins further back than it would be with fins having a plain triangular shape. That moves the CP for the rocket further back.

I'll see if I can figure out where the CP for the two styles of fins are, and I may follow this up with an edit or another post if I do.

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John Thro, NAR #84553 SR
I was too old when I started! Now I'll *never* become a BAR!

Thanks, JRT. That makes sense, it's just the degree of change that caught my attention. You wouldn't happen to know of a text on the subject that we could pull up and read, would you?

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Craig McGraw

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