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Old Dec 06, 2012, 06:29 PM
dougmontgomery is offline
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Mold riser insert


so here is the process-

Made a fiberglass part of the riser.

Sanded it to be flat on the bottom to mount to a piece of glass.

Poured urethane rubber over it to make a mold

Then used the negative to pour my liquid polyester foam into it.

Mixed up 2 grams of polyester foam

used 1 gram to pour into part.

cut off extra once cured

weighed,

right where i want to be, .5 grams, now I will remove the foam where the hardpoints will go.

This gives me room for fabric around the riser, some splooge for the hardpoint and insert the foam.

continue with lay up

doug
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Old Dec 07, 2012, 12:25 AM
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Doug-
If you post the total reinforcement weight and FAW(fiber area weight-gr/m^e
I may be able to give you a theoretical CPT(cured ply thickness)

This would tell you if a perfect part has much excess resin.

Scott
Old Dec 07, 2012, 07:00 AM
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I been p[laying around with S glass the last few days My nose layup was 1 layer 3/4 E-glass 1 layer 0/90 3 oz crowfoot http://www.aircraftspruce.ca/catalog/cmpages/120.php and a final layer of the S glass on a bias http://www.aircraftspruce.ca/catalog/cmpages/4533.php. Killer strong . The way the nose should be

Im really liking the S glass. I think its equally as good as the 5 oz kevlar in fact , I think it takes a impact better. Its half the price and doesnt drink resin like the kevlar
Old Dec 07, 2012, 07:53 PM
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S-2 glass is a very good product. Only downside is the limited selection at low area weights.

I have been pestering my supplier for some 4180, he got me some 4 oz. a while back.
Old Dec 07, 2012, 08:11 PM
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I will do a lay up in the morning with the new HM uni. I have everything ready tonight but have a friend coming over in the morning to watch.

If i cannot make weights I am considering a change to the bottom of the fuse.

Doug
Old Dec 08, 2012, 11:21 PM
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Doug,

What Tom said is probably very important about the cg of the finished fuse. In addition to tracking the weight , I'd also suggest tracking where the fuse balances. Ideally, what you probably want is the lightest fuse for the strength, with the most forward cg.

While a larger cross section will use more fabric and epoxy, it may well be stiffer and stronger than a smaller cross section.

When you get close to your target weight, put tail feathers and gear in it and see where the cg is. But the weight of the tails is important as well, as it is going to influence whether the nose is going to need weight or not.

Opinions may vary.

Gary
Old Dec 09, 2012, 07:48 AM
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I did a fuse as a test this past summer that's considerably bigger than my normal. I was able to make parts in it that were only 3-5g heavier than my smaller fuse but were very strong because of the shape and profile. I couldn't build them with the same layups, I had to use less fabric and strategically place layers, but I was able to do it. Larger size doesn't mean heavier... just means you have to use different layups.

For example: bigger booms can be made with lighter uni and lighter bias wraps. I was shocked how stiff this was with minimalistic cloth. In the fuse area, I had to go with fewer layers and add a servo tray but it still came out very stiff and roomy...

Stay with it and please PM me if I can help. I have made alot of different stuff over the past couple of years.
Old Dec 09, 2012, 10:51 PM
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Strength increases with the square of the area, but material mass increases because the surface area increases as well. A small increase in diameter is a large increase in strength. What Tom said...

Sean
Old Dec 10, 2012, 12:28 PM
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On the flip side, getting a bigger fuselage to be light means a thinner wall, and therefore lower crush resistance. Plus more drag.

Too bad there isn't a hollow carbon fabric or a hollow Kevlar fabric, like there is for glass.

Gerald
Old Dec 10, 2012, 02:28 PM
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In the late 80`s I was involved with several hydroplane builds. You know , boats that do 120 mph on water. We couldnt mess with the underside surface much because it created drag but to gain strength to the boat we made a lot of curves on the top structure. Kind of sucks but the more we try to stream line or fuses for DLGs the less chance we get to utilize other means of gaining strength without adding more material .Pylons for mounting the wing is one way but I dont know many others.
Old Dec 10, 2012, 03:43 PM
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Doug,

S glass contains copper and thus blocks RF signals. I agree its a nice material but I would stick with Kevlar for that reason. You can go down to a 1.7oz kevlar in the nose. Using 1oz kevlar in the tailboom really helps with impact resistance.

-Sam
Old Dec 10, 2012, 04:15 PM
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http://www.asminternational.org/cont...81G_p27-34.pdf - I do not see copper in the list of contents for S-glass.

It is not that glass contains a metal or metals, or not, but whether the glass is conductive. Silicon for instance can conduct, but SiO2 tends not to, and is the main constituent of glass.

Are you sure you are not thinking of some of the specialized building materials for making tempest rooms?

Gerald
Old Dec 10, 2012, 06:47 PM
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How about quartz cloth.LOL. in 1971 it was going for $64 a yard. And the main idea was that radio wave's could go right through it. And it had to be strong because it was used on the nose of an F-14 Tomcat.
Old Dec 10, 2012, 08:06 PM
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Gerald, it's always been my understanding that s glass is simply stronger e-glass, until I was told otherwise by a source I trust. Looking at your rather definitive document, my statement may have been inaccurate but the crux of the matter may not. According to the ASTM standards, s glass contains twice as much aluminum oxide as e-glass. That would be a concern from an rf standpoint for sure, I use aluminum enclosures to block rf.

To close the matter, Doug do you mind range testing with your s glass fuselage vs. a Kevlar fuselage vs. bare receiver? I realize that might be tough given winter is upon us.
Old Dec 10, 2012, 08:07 PM
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Quote:
Originally Posted by prodjx View Post
How about quartz cloth.LOL. in 1971 it was going for $64 a yard. And the main idea was that radio wave's could go right through it. And it had to be strong because it was used on the nose of an F-14 Tomcat.
Special fabrics are still used today in rf applications.


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