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  #41  
Old 11-29-2010, 05:10 PM
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Solomoriah Solomoriah is offline
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I took this as a bit of a challenge; I'm afraid I failed, from some perspectives.

My Mockingbird 1313 (see attached OpenRocket file) is an ST-13 rocket with a 13mm engine mount (hence, 1313). #13 tubing is a lot easier to work with when you are packing a chute, as opposed to #10/BT-50 sized rockets like the Alpha, or even worse, 18mm rockets such as you often see in bulk packs.

According to OpenRocket, it has a DV around 10 ft/s (ascending), with an apogee of 358', on an A10-3T. I used only parts you can get from Semroc, no cutting needed (except for the engine hook slot). The attached file is "quick and dirty" so it's not perfect (for instance, I left out the engine hook) but I think it proves the concept. The fins are from the Semroc Astron.

The failure is this... six of them, purchased as parts from semroc.com, come out to $60.80, or more than $10 apiece. Of that price, the nose cone at $2.90 and the chute pack at $1.60 are the most expensive parts. The fins are next, at $1.65 per set.

Still, I like it.

EDIT: Forgot the attachment.
Attached Files
File Type: ork Mockingbird 1313.ork (49.2 KB, 42 views)
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  #42  
Old 11-29-2010, 07:04 PM
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Quote:
Originally Posted by blackshire
... This could reduce the kit's production cost since more fins could be cut out of the balsa sheets.

just checked the cost of the fins for the Bug Me Not and making them smaller wouldn't have much of a difference unless I went to a placing a sheet in the kit instead of using laser cut parts.

Quote:
Originally Posted by tbzep
...Yes, but kids love chutes. It increases coolness factor ten fold to them....

but the biggest increase in cost. Not only is the sheet more, but you need to add the shroud lines, the time needed to cut them to size, and additional parts.

Quote:
Originally Posted by tbzep
...It makes a huge difference in ease of building. No lines to draw. No need to hold fins while glue is drying. ...

even more of a cost increase. At this point, cheaper to go to a pre-built fin unit.

Quote:
Originally Posted by tbzep
...BTW, I saw the diameter of the kit you linked, but not a total length. About how tall is it?...

you're right. Not on the page. Will update.

Overall length is 11"/28cm.
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  #43  
Old 11-30-2010, 01:38 AM
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Quote:
Originally Posted by Sunward
[Re: parachutes -- Blackshire] but the biggest increase in cost. Not only is the sheet more, but you need to add the shroud lines, the time needed to cut them to size, and additional parts.
For low cost and simplicity of production, how about an "X-type" parachute made from two 12" lengths of plastic streamer material (the 1-1/8" wide plastic flagging tape that Estes and Quest use), crossed and heat-welded together (using a poly bag heat-sealer), with just four shroud lines (actually just two lengths, tied together at their apexes)? This "X-type" 'chute would easily fit inside BT-50 (and even BT-20) size body tubes.
Quote:
Originally Posted by Sunward
just checked the cost of the fins for the Bug Me Not and making them smaller wouldn't have much of a difference unless I went to a placing a sheet in the kit instead of using laser cut parts.
I stand corrected--thank you.
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  #44  
Old 11-30-2010, 07:30 AM
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Quote:
Originally Posted by Solomoriah
The failure is this... six of them, purchased as parts from semroc.com, come out to $60.80, or more than $10 apiece. Of that price, the nose cone at $2.90 and the chute pack at $1.60 are the most expensive parts. The fins are next, at $1.65 per set.



That is the tradeoff with a larger diameter tube - the nose cone is pricier. If the adults are willing to put in some time, a chute pack can be produced very cheaply - trash bag material, a spool of the appropriate heavy thread (I used carpet thread in my youth), and stickers from the office supply section of Wally World.


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  #45  
Old 11-30-2010, 07:35 AM
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Quote:
Originally Posted by blackshire
For low cost and simplicity of production, how about an "X-type" parachute made from two 12" lengths of plastic streamer material (the 1-1/8" wide plastic flagging tape that Estes and Quest use), crossed and heat-welded together (using a poly bag heat-sealer), with just four shroud lines (actually just two lengths, tied together at their apexes)? This "X-type" 'chute would easily fit inside BT-50 (and even BT-20) size body tubes.



When I was a kid, auto drag racing was a very popular sport. A chute like that would have been very well received then.

Yellow "caution" tape would yield a somewhat larger and draggier chute in addition to being interesting to the kids.


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  #46  
Old 11-30-2010, 08:02 AM
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X chutes are finicky enough about opening when they are made from nylon. I don't know how successful a plastic X chute would be.
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  #47  
Old 11-30-2010, 02:37 PM
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For these kind of educational kits, square chutes, with a shroud line at each corner work just fine. Square chutes are what the original Model Missiles kits shipped with. Square chutes are simple to cut and dirt cheap. You don't even need tape dots, the shroud lines can simply be tied to each corner of the plastic square.

Shroud lines can be made from any lightweight string. I routinely cut large numbers of shroud lines for competition parachutes. You can cut a huge number of shroud lines very quickly using a simple technique. Get two small blocks of wood and hammer a nail with a flat head on it into each of the blocks. Place the blocks on a flat surface (floor or table) the distance apart you want the shroud lines to be. Tape the blocks to the flat surface. Tie one end of your shroud line material to one of the nails and then wrap the line back and forth around the nails however many times you need to to make the number of shroud lines you want. When you're ready, just grab all the strings together and cut the lines at each end near the nail.
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  #48  
Old 11-30-2010, 03:46 PM
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Quote:
Originally Posted by blackshire
.... simplicity of production, how about an "X-type" parachute made from two 12" lengths of plastic streamer material (the 1-1/8" wide plastic flagging tape that Estes and Quest use), crossed and heat-welded together (using a poly bag heat-sealer), with just four shroud lines (actually just two lengths, tied together at their apexes)? .....

that is simple?

anything that needs to be done manually is expensive. Everyone likes to say it only take a minute, until you do it.
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  #49  
Old 11-30-2010, 03:55 PM
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I offered him a turn-key solution in email that near as I can tell meets ALL of his requirements, save for some price mod for the features he insisted on.

Quote:
Originally Posted by Sunward
that is simple?

anything that needs to be done manually is expensive. Everyone likes to say it only take a minute, until you do it.


You should let him do manual tasks for you for about 2 weeks and then see what he says.

I suggest offering him minimum wage to start to "help save cost".

Attached is a serious attempt at a school home run kit.

Jerry
Attached Files
File Type: pdf Omega 13 (lubbo).pdf (2.7 KB, 61 views)

Last edited by Jerry Irvine : 11-30-2010 at 05:00 PM.
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  #50  
Old 11-30-2010, 07:31 PM
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Quote:
Originally Posted by Jerry Irvine
I offered him a turn-key solution in email that near as I can tell meets ALL of his requirements, save for some price mod for the features he insisted on.


I'm not sure who the "him" is that you are referring to, but I'm the original poster and I've not received any email from anyone on this forum.

This thread was started over two years ago by me. I've since discovered that nobody can come anywhere close to Bill's (BMS) $5.25 bulk price for a BT-50 sized school rocket with features for very easy assembly and damage prevention.

The whole point of the thread was to try to give the kids the most rocket for the least price. Our system is full of students who are poverty stricken. There are constant fundraisers for all kinds of stuff and we just can't ask for more money. We've been scraping by with small grants and some of our own money the last several years.

I discussed all this with our teachers and others locally not long after I posted the thread. We decided to stay with the Estes Generic E2X and A8-5 three packs, and have done so the last two years. If I go to a more traditional rocket, I will just go with Bill's School Rocket and fly it with stock streamer and most likely with A8-5's.

I considered this thread dead two years ago. I think it's time to let it go, once again.
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