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  #1  
Old 09-23-2012, 05:10 PM
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CPMcGraw CPMcGraw is offline
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Exclamation New Design -- Rangesetter

Just some doodles on a Sunday afternoon...

Length: 31.20"
Diameter: 1.04" (ST-10, ST-8, ST-2)
Fin Span: 3.91"
Weight: 2.00 oz


B4-4......328'......Dv 13 FPS
B6-4......336'......Dv 9 FPS
C6-5......785'......Dv 7 FPS


All engines reach flight V on a standard 36" x 1/8" rod. The A8-3 is not recommended.

Enjoy!
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  #2  
Old 09-23-2012, 08:41 PM
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I was hoping to see a new design of yours here again (for a change), and here we are.
You definitely have a different eye than I do for design details. But I like!

A question from looking at the RS schematic: When building a rocket in that prog (or even ORK), does it behoove the designer to think about things they will encounter when trying to build one of their designs?

For example, generally-speaking I've only seen 18" total tube lengths for sale and I wonder if I wouldn't want to keep that in mind in the design phase and actually edit a tube's total length to that 18" and then add a tube coupler & more tube length to get what would be in the real world... I suspect the addition of a coupler in RS or ORK would bring you closer to what you'd really get during a flight sim... True? Unimportant consideration?
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  #3  
Old 09-24-2012, 10:44 AM
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Quote:
Originally Posted by Brain
I was hoping to see a new design of yours here again (for a change), and here we are.
You definitely have a different eye than I do for design details. But I like!


I've been in a dry spell for nearly two years. The itch to do something is really just getting started again.

What I've been trying to do with my more recent stuff is to design for low-Dv. Simply put, to achieve a low velocity at the apogee so that the parachute(s) don't open "explosively". I've got a few like that where you think the chute is going to rip itself off; the sound of the chute opening (even 300-400 feet up!) is as loud as a gunshot. If I design to avoid such, then the end result is usually a better-flying rocket overall, even if I have to sacrifice some top-end performance to get it.

Quote:
A question from looking at the RS schematic: When building a rocket in that prog (or even ORK), does it behoove the designer to think about things they will encounter when trying to build one of their designs?


If you do enough of it over time, it starts to become "second-nature"; you don't think of it so much, it's just the way you work. You can get longer tubes; the 18" lengths are easier for the model companies to bag up. Longer tubes have a greater chance of getting folded. I think "TotallyTubular" and maybe BMS sells up to 36" lengths, but when you place an order for those, you need to order enough to fill a decent-sized shipping box so that they tend to protect each other.

OTOH, there are times when you have to think about the assembly sequence, like if you have a long BT-20/ST-7 tube that is also the engine tube. It helps to break that tube into two smaller lengths, like placing a 2.75" or 3" length at the rear with the coupler acting as both a coupler and an engine block. Double-duty. Or, as you've seen, you separate what actually remains a single tube into smaller sections for working within the program (like hidden lengths inside a transition, for example). Such tricks become part of your kit-bag after awhile.

Quote:
For example, generally-speaking I've only seen 18" total tube lengths for sale and I wonder if I wouldn't want to keep that in mind in the design phase and actually edit a tube's total length to that 18" and then add a tube coupler & more tube length to get what would be in the real world... I suspect the addition of a coupler in RS or ORK would bring you closer to what you'd really get during a flight sim... True? Unimportant consideration?


I've used random-length tubes in some designs, placing a coupler at known tube lengths to keep the mass correct, but not breaking the long tube down otherwise. From the POV of the program, it doesn't care. It calculates aerodynamics on the total exposed length(s), not the individual lengths that may be internal. It calculates the mass on the total of all the parts based on their area totals and the mass values per unit in the database; not on any specific part. We've run into issues with the database on this already; some component materials have bogus entries, or values that are at best whacked. It catches us occasionally...
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  #4  
Old 09-24-2012, 01:54 PM
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Quote:
Originally Posted by CPMcGraw
What I've been trying to do with my more recent stuff is to design for low-Dv. Simply put, to achieve a low velocity at the apogee so that the parachute(s) don't open "explosively". I've got a few like that where you think the chute is going to rip itself off; the sound of the chute opening (even 300-400 feet up!) is as loud as a gunshot. If I design to avoid such, then the end result is usually a better-flying rocket overall, even if I have to sacrifice some top-end performance to get it.


Has anyone done any testing to determine how accurate the deployment velocity predictions are? With things like the Altimeter Two available, it should not be a difficult research project.



Quote:
Originally Posted by CPMcGraw
I've used random-length tubes in some designs, placing a coupler at known tube lengths to keep the mass correct, but not breaking the long tube down otherwise. From the POV of the program, it doesn't care. It calculates aerodynamics on the total exposed length(s), not the individual lengths that may be internal. It calculates the mass on the total of all the parts based on their area totals and the mass values per unit in the database; not on any specific part. We've run into issues with the database on this already; some component materials have bogus entries, or values that are at best whacked. It catches us occasionally...


Do not be surprised if smaller kit manufacturers who cut their own own tubes use seemingly random lengths of tubes in their designs. For example, 17", 11.3", 8.5" and 6.8" are 34" tube stock divided into two, three, four and five even pieces.


Bill
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Old 09-24-2012, 02:04 PM
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Bill,

As far as actual testing of any design, I'm relying here on the RS prediction results. Some designs produce very low Dv numbers, but the actual results will depend on the final construction of any given model. Some builders (like me) are a bit heavy-handed with finishing, so YMMV with every model...

When I say "random-length tubes", I mean I have used a single tube in the design phase that is the full length of what I need, rather than piecing the tube together from smaller lengths. I added the couplers later for mass balance. Most designs use standard tube lengths from the start. It works either way.

For me, I usually build with SEMROC stock lengths for convienience...
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  #6  
Old 09-24-2012, 04:01 PM
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Hmmm... still, does not the addition of items (that you may well use in the real build) in RS make for a better sim, what with the weight issue added by an item such as a tube coupler? I know it's not much weight, but the way most BARS 'round here go on about weight I gotta wonder that such a thing might be fairly important (if not just a good idea)...
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Old 09-24-2012, 04:13 PM
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Quote:
Originally Posted by Brain
Hmmm... still, does not the addition of items (that you may well use in the real build) in RS make for a better sim, what with the weight issue added by an item such as a tube coupler? I know it's not much weight, but the way most BARS 'round here go on about weight I gotta wonder that such a thing might be fairly important (if not just a good idea)...


Yes, and I wasn't implying that I didn't add those components. I do add them, it was just the use of a "single tube of needed length" that I was talking about as opposed to using each piece from the database. The net result is the same.

It reduces the confusion about it if I just use each piece, according to the [SEMROC] catalog page. Six-of-one, half-a-dozen of another, and neither look nearly as good as Seven-of-Nine...
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  #8  
Old 09-24-2012, 07:44 PM
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Quote:
Originally Posted by CPMcGraw
Yes, and I wasn't implying that I didn't add those components. I do add them, it was just the use of a "single tube of needed length" that I was talking about as opposed to using each piece from the database. The net result is the same.

It reduces the confusion about it if I just use each piece, according to the [SEMROC] catalog page. Six-of-one, half-a-dozen of another, and neither look nearly as good as Seven-of-Nine...

Ooooooh...Seven-of-Nine!
Uh, what were we talking about?
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