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  #1  
Old 01-12-2012, 12:14 AM
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CPMcGraw CPMcGraw is offline
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Question Under Development -- Deep Space Surveyor

Thought I'd share this with you, just keep in mind it's still being fiddled with and is not yet ready for prime time. The engine is 24mm, and I'm trying to keep it to a C11-3. This is an FCOD type of design, with no fins to speak of (if I can manage it, that is...).

The internal core is ST-20. Most of the detail work is just cardstock transitions and matteboard laser-cuts. The large transition is shown at 50% opacity, so you can see the details in 3D.

Needless to say, the static margin is lousy! Above 0.00, but just barely! The one thing I don't want to do is add ballast if I can avoid it. It's heavy enough...

Suggestions and comments welcome!
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  #2  
Old 01-12-2012, 12:02 PM
Les Les is online now
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Is the disc real (is that what you were refering to as the transition with 50% transparency)?
I would think this would act more like a saucer with all that base drag.

Possibly the only issue is how far down the motor projects
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  #3  
Old 01-12-2012, 03:19 PM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by Les
Is the disc real (is that what you were refering to as the transition with 50% transparency)?
I would think this would act more like a saucer with all that base drag.

Possibly the only issue is how far down the motor projects


The "disk", or conical section, is supposed to be a "real" component. It's a cardstock transition; I set the opacity to 50% just so you could see the details hidden within the area - RockSim blanks out those details if I keep it fully solid.

I know that a conical section with enough length and base diameter is "stable" -- the Centuri Point comes to mind -- so my idea was to come up with a design that provides the same general displacement of air around the structure, just with a different shape. Some additional experimentation has shown a little improvement, but not enough to actually justify building this thing...

The engine base is flush with the bottom edge of the "engine bell".
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  #4  
Old 01-13-2012, 12:51 AM
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Exclamation

Here's a revision of the design, trying to work the rear shroud as far as I dare to make it fly straight. I managed to get a 1.09 margin with no ballast using the C11-3.

Length: 19.27"
Diameter 4.54" (Forward transition)
Span: 11.04" (Rear shroud)
Weight 7.52 oz (With C11-3 loaded)

It was critical this time to show the design with an engine loaded. The C11-3 is the only recommended engine, as it takes almost every inch of a 48" rod.


C11-3......223'......Dv 9 FPS......Avg of six sim runs


This is by no means a finished project. I want to tweak it a bit more.
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  #5  
Old 01-14-2012, 03:45 PM
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Exclamation Mk VIII...

A little tweaking has given me a better stability margin, but a need for more power to make it work. The minimum power is now a D12-5, and it fully requires a 48" rod for launch. There is no room to spare, either.

RockSim does not give the true picture of how it should look; the centering ring at the front of the main skirt is rendered as going all the way down to the transition below it, and this is wrong. The ring's ID is only about 1/2" smaller than its OD.

The truss frame was modified with tabs at the forward end to attach into the ring. I need to stiffen the TE of the skirt with a ring, and some truss members to support it. Important, since this is what the model will be hitting when it lands.

One other change: The main skirt is now a gray-tinted "clear" polystyrene instead of cardstock. It's meant to be seen through.

Length: 19.75"
Diameter: 4.54" (Forward transition)
Shroud Span: 11.04"
Weight: 9.18 oz (With a D12-5)
Margin: 1.25......CG: 10.9603"......CP: 13.5119"

Funny alignment: The CP is located directly centered in the "combustion chamber" of the simulated engine.


D12-5......500'......Dv 16 FPS......Avg of 6 runs


More tweaking to come!
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  #6  
Old 01-14-2012, 08:54 PM
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Why did it not work with the larger dish?? Personally I think it looks a lot cooler with the larger (flatter) dish...

Later! OL JR
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  #7  
Old 01-14-2012, 10:10 PM
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Quote:
Originally Posted by luke strawwalker
Why did it not work with the larger dish?? Personally I think it looks a lot cooler with the larger (flatter) dish...

Later! OL JR


FCODs use drag stabilization; where the large disk was positioned must not have been in the right place to be effective. The drag has to be behind the CP, and I think in that version it was either at, or possibly ahead of, the CP.

I'm still new at this FCOD thing. Maybe around the Mk XII version, I'll have it reliably flyable.
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  #8  
Old 01-14-2012, 10:35 PM
Les Les is online now
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Consider Squirrel Works Pizza Pie. A flat plate with the motor tube behind the plate, yet it is stable. I would think if disk was flat enough it would be stable
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  #9  
Old 01-14-2012, 11:02 PM
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Quote:
Originally Posted by Les
Consider Squirrel Works Pizza Pie. A flat plate with the motor tube behind the plate, yet it is stable. I would think if disk was flat enough it would be stable


Interesting... Well, I guess I need to do some study into how these work. I guess they fly like spools, but I'm just not familiar with their dynamics. Always something new to learn!
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  #10  
Old 01-14-2012, 11:47 PM
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Quote:
Originally Posted by CPMcGraw
A little tweaking has given me a better stability margin, but a need for more power to make it work. The minimum power is now a D12-5, and it fully requires a 48" rod for launch. There is no room to spare, either.

RockSim does not give the true picture of how it should look; the centering ring at the front of the main skirt is rendered as going all the way down to the transition below it, and this is wrong. The ring's ID is only about 1/2" smaller than its OD.

The truss frame was modified with tabs at the forward end to attach into the ring. I need to stiffen the TE of the skirt with a ring, and some truss members to support it. Important, since this is what the model will be hitting when it lands.

One other change: The main skirt is now a gray-tinted "clear" polystyrene instead of cardstock. It's meant to be seen through.

Length: 19.75"
Diameter: 4.54" (Forward transition)
Shroud Span: 11.04"
Weight: 9.18 oz (With a D12-5)
Margin: 1.25......CG: 10.9603"......CP: 13.5119"

Funny alignment: The CP is located directly centered in the "combustion chamber" of the simulated engine.


D12-5......500'......Dv 16 FPS......Avg of 6 runs


More tweaking to come!



Where have I seen this before. Oh yeah......
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