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  #11  
Old 11-16-2007, 04:41 PM
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Maybe I'm missing some sort of "purest" element here but couldn't you just cut your own basswood fins using the provided balsa ones as a template?
I get the point about the materials should be quality "out-of-the-bag" but they're not; so why not build it to suit you? Personally, I prefer basswood over balsa anyway, especailly when building an "exotic".......but that's just me.
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  #12  
Old 11-16-2007, 04:48 PM
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With Doc's measurements, the closest body tube I've found to match the OD of the Estes tube are the 34" length tube couplers for ST-20 at BMS. Unfortunately, if the numbers are correct, the couplers are even thicker than the Estes heavy body tube. I'm going to take a close look at the tubes that come with the kit and see if I can peel them from the inside to make them lighter. If anybody comes up with a good thin walled 1.99-2.0" OD tube, post up!

As for the braces, I don't see them as being necessary. The glue joint holding the halves together will strengthen the balsa and you can soak the leading and trailing edges with CA to stiffen things even more That will make them more ding resistant as a side benefit. There will be some torque when the pods hit the ground first, but I think a hard impact at an angle would break the 1/8" fin material even with a small strip of bracing. I'm still tempted to go with 3/16" balsa to keep the wings more scale with the original and to make them stronger anyway. I'll have a better idea when I finally get hold of a 1350.

Another option to strengthen the wings while keeping the 1/8" balsa and not using the brace is to use hardwood strips around the perimeter. Trim an 1/8" off the balsa, frame it with 1/8" thick hardwood squares, and glue it all together. You get the added perimeter frame strength plus strength from the glue joints. If you airfoil the wings, use wider strips so that you still have some hardwood after it's sanded. Once it's filled and finished, nobody will ever know.

Barone is using cardstock lamination. Another option would be to use a single layer of 1/16" balsa to laminate keeping the grain at an angle to the original. Once again, the glue will add a ton of strength and the thickness of the wing will be closer to scale with the 1250.

Want to make it super strong for composite motors? Laminate with 1/64" plywood! Almost as strong as regular plywood and less weight than "light ply" (which is pretty weak IMHO).

For now, my mods list will probably include:

**Peeled body tubes
regular BT-50 motor tube
regular homemade centering rings
3/16" balsa fins (or laminated....still haven't decided)
dowel rods for the pitot tubes for the classic look
modified nosecone to fit the peeled tubes

**I doubt I can save much weight by peeling the tube because I'll have to add material to the tube coupler, nose cone shoulder, and afterburner. It might not be worth the effort. However, as heavy as Doc's unpainted prototype is, every tenth of an ounce may be necessary to get safe flights on Estes motors.

I'm about out of ideas to lighten the model without looking at it in person. Some of you present and former NAR competitors need to start sharing your weight loss techniques.
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  #13  
Old 11-16-2007, 04:52 PM
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Quote:
Originally Posted by Sadmug
Maybe I'm missing some sort of "purest" element here but couldn't you just cut your own basswood fins using the provided balsa ones as a template?
I get the point about the materials should be quality "out-of-the-bag" but they're not; so why not build it to suit you? Personally, I prefer basswood over balsa anyway, especailly when building an "exotic".......but that's just me.


I've never thought basswood or light ply gave enough added strength to justify the weight when I was doing R/C stuff (the only time I've fooled with either). Laminated balsa isn't as brittle and might flex enough not to break in some situations where basswood would. However, copied basswood would likely work ok. How much extra weight it would add compared to the strengthened balsa might be a question considering this thing is borderline too heavy for Estes motors already.
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  #14  
Old 11-16-2007, 06:32 PM
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As for the weight......

I've got a total of 11.375 oz for the parts only. Does not include glue, paint or decals. The balsa sheets were weighed as a single piece, that is, I didn't punch out the patterns and weigh them seperately. If you figure the patterns make up about 90% of the weight, then the parts weigh in at 11.127 oz. The plastic centering rings weigh in at .21 oz. They feel pretty light. I tried to fly my Mercury Atlas (weighs 7.77 oz according to the kit specifications) on the recommended D12-3 and it barely cleared the pad, got to about 25' and came down on it's side. I ended up flying it with Aerotech E15s. The maximum recommended liftoff weight for the D12 is about 14oz. The E9 (recommended for the Interceptor) has a lower initial thrust than the D12 and lower average thrust...it just burns longer. Now, the way I see it, if the D12 barely got my Atlas in the air at half the rated max weight, I don't see how I'm going to get any performance from the E9. I wonder if Estes actually flew this or do they expect them to be hangar queens? I'm going to set mine up to fly 24mm Aerotech Es and Fs. By the way...I like the thought of using the 1/64" ply for the laminate.....
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  #15  
Old 11-16-2007, 07:41 PM
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I picked one up today but haven't opened it. I've had it in my mind to use sticker paper on both sides(if they will fit on a standard sheet) and seal edges with CA, rather than cardstock. The braces really don't bug me all that much, but laminating will kill two birds, as Don pointed out. The sticker paper should be plenty strong and weigh a little less than regular cardstock. I'm kind of skeptical, like Fred, about needing the reinforcement at all, but they obviously added them for a reason, and the balsa IS rather thin for this. I doubt an Estes motor has enough thrust to sheer those fins(just guessing here), it's the recovery trials that I worry about.
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  #16  
Old 11-16-2007, 08:18 PM
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From what I understand, the prototypes have been flown many times, and, this is why they added the fin stiffeners.

They came down and sheared off fins.

Here is an idea, if you are looking for a differnt body tube, why not get together, decide upon the size that you want, and place a special order. It would only be worth the while to have a larger order, than the minimum.

You could contqct Euclid about tubes.

Euclid Spiral Paper Tube Corp.
339 Mill St - P.O. Box 458
Apple Creek OH 44606

phone 330-698-4711

Gloria Edmonson - Quotes

gedmonson@euclidspiral.com
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  #17  
Old 11-16-2007, 08:36 PM
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Default Motor Tube

OKay....I'm replacing the kit motor tube with a foil lined BT50 from BMS. Original tube weighed .69 oz...the replacement tube weighs .65 oz. Okay...I'm .04 oz lighter already....
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  #18  
Old 11-16-2007, 09:27 PM
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Default 24mm F motors

Well, since I've decided not to trust the E9 and fly 24mm Fs, I've found they vary in lengths. So, I won't be using the supplied motor block or motor hook and opt for friction fit.

Weight savings is .09 oz. (this may not exist since I now have to account for the masking tape to friction fit)

Total weight savings so far is .13 oz
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  #19  
Old 11-16-2007, 10:18 PM
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Quote:
Originally Posted by barone
Well, since I've decided not to trust the E9 and fly 24mm Fs, I've found they vary in lengths. So, I won't be using the supplied motor block or motor hook and opt for friction fit.

Weight savings is .09 oz. (this may not exist since I now have to account for the masking tape to friction fit)

Total weight savings so far is .13 oz


Attaboy, Don! Keep whittling.
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  #20  
Old 11-16-2007, 10:48 PM
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Default Shock Cord Mounting

Okay guys. I don't know about you but I've got some short, stubby fingers. The nose cone shoulder is a little over 2" long. My finger is barely long enough to mount the shock cord. Something for you guys to think about as you build.....
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