Glass Rotors?

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Bob Kelly

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I believe its regular Polyester reson...
a cozy uses the blue foam in it right ?
so what reson or stuff do you use ?

I hurd that Epoxie Reson is the way to go now days as its supposed to be alot better in many ways... however i have yet to see any in the stores I have shopped in in the last year .... I live in the back of beyond anyway so thats not too suppriseing !
thanks Dust !
every little bit helps !

Bob.....
 

wsimpso1

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Polystyrene foam is soluable in polyester resin and thus they can not go together.

Epoxy is standard stuff in airplanes for several reasons:
Styrene foam can be hot wired for accurate airfoil shapes;
 

wsimpso1

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Contiuing where I had left off:

Epoxy is used for several reasons:
Styrene foam is able to be hotwired for accurate aero shapes;
Styrene foam is the only safe foam for hotwiring;
Styrene foam will dissolve in polyester;
Epoxy makes a better composite than polyester (Glass/Epoxy is two to three times as strong as Glass/PolyesterPolyester);
Polyester won't bond to some other fibers at all;
Polyester has the nasty habit of continuing to change forever. Its molecular weight keeps going up, its toughness keeps going down, its crack sensitivity keeps increasing, and it keeps shrinking, which allows the weave of the cloth to "print through" over time;
Epoxy is about as close to perfect as an adhesive for wood as mankind knows of, so we have automatic compatibility between wooden reinforcements and the rest of the composites

So, epoxy does work with styrene foam, epoxy makes fine composites that last, so we use epoxy. Vinylester resins are useful in composites, but then you have to bond with it too, and it has a short shelf life, plus other issues.

Bob Kelly, I agree that the rotors (and other structures) only have to be "strong enough", but how does one know that they are beyond that boundary? The consequences of falling short are severe, so how do we make sure, except by doing some engineering?

Twist is a tough one... All structures have stiffness, that is a deflection versus load relationship. Nothing just does not move. Twist under torque can not be eliminated, just reduced. And torsion stiffness on a long slender structure requires some planning to do it without excess weight. So the issues become "How stiff in torsion does it need to be?" and "How do we build it to be atleast that stiff". And that IS engineering.

Even if the engineering is simply duplicating the wooden part's axial strength and torsional stiffness in fiberglass, that is engineering the rotor too.

I will give you that the existing wooden designs are probably adequate, and that good scarf joints are fine, and that the layer of glass on the outside is mostly to seal it, so it will be fine when glassed. That does appear to be the object for our determined do-it-yourselfer.

SonnyJ seemed interested in how to do a composite set of rotors, and that requires more than just a little design knowledge. Even reverse engineering from the wooden one requires some education on composites. Catastrophic rotor failure can easily kill the pilot or someone on the ground. No matter the path taken, it does have to be done correctly.

Billski
 

Dust

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Originally posted by wsimpso1
Contiuing where I had left off:
Epoxy is about as close to perfect as an adhesive for wood as mankind knows of,
Billski
Thats what i thought. My other hobby is making furniture. Since epoxy is so water resistant, i used the west system to make a bunch of cutting boards for christmas gifts.

Long grain to long grain - great gluing surfaces - NOT with epoxy, the joints failed.

FAILED

i called gougen bros tech support. the problem - i had not sanded the maple, the miniscule jointer marks had stopped the epoxy from penetrating.

never had that happen with yellow glue.

I now rarely use epoxy for wood and when i do i take extreme precautions, sand all surfaces, apply the epoxy twice with 5 minutes between applications, often add just a little flox (cotton micro fibers) since the new procedures - no failures.
 

wsimpso1

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Dust,

I have never had any problem with epoxy joints on wood, and I have made plenty of them. Somewhere my training must have been pretty good though, (my father? West's boat building and repair books?) because I have always sanded the faying surfaces to make sure that the wood was open and then saturated both surfaces with thickened epoxy. Without even knowing that I was doing it, I had already been taking your precautions...

This piece of news is kind of scary, because not everyone has had the knowledge base and training that we have, and a bunch of boats, airplanes, and other man rated stuff has been built with wood and epoxy...

Billski
 

Dust

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Well, when you run hard maple over a jointer and through a thickness planer you can see little cupped ridges

The fibers are cut and compressed in the machining operation.

For yellow glue this is a perfect mating surface and i would never sand the surfaces because the sanding could and would deform the mating surfaces. for epoxy pre joining i use 120 grit glued onto a FLAT wood sanding block to stop this from occurring.

i do not think softer woods or joints that are cut with a table or band saw would have this problem, as no compression of the fibers would happen during the machining process.

but i only use epoxy for large glue ups - like a chair with many pieces going together at once requiring a long working life or a very complex cabinet
 

Bob Kelly

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Wsimpso1 :
( or something like dat ! )
Thanks for the Info ! definately tought me something ! I'll see if I can find some epoxie at the hardware store ... or perhaps auto supply place ! ...
I know the boat supply place would have it but their expensive arround here and a pain to get to to boot ! <grin>

Again ! thank you .... and thank you for takeing my coments the right way ... even if it came out sounding kind'a bad !
suttlity is not one of my strong points <GRIN>

C ya !
Bob....
 

Dust

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i would not use the hardware stuff - sets too fast and is probably too thick for good wet layup.

the west system is available at the boat stores and they have auto ratio pumps available - very handy. Also get the Sloooooow hardener. the slower the set the stronger the epoxy and make sure each batch is throughly mixed, we mix each batch at least 1 minute and ours is stored in a hot box at 95 degrees - makes it more fluid, easier to mix and wet out. do not over wet the glass - weakens it and you will need micro baloons - to make thick micro to fill blems and thin micro to fill the pores.
 

Dust

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Bob - i am building 2 cozy mark 4's and have laid up about 600 yards of fiberglass so far - am very familiar with the procedures.

if you or anyone wants a more detailed explanation, i'll just type and type away.
 

Bob Kelly

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Dust thats the plane I would build if I had the bucks and inclination !
its a realy nice cannard ! pure speed !
for minimal fuel ...the only way to go !
...
thanks for the offer on the info!
I am no stranger to fiberglass by any means but I've never touched the epoxie stuff ...hopefully that will change soon ! hehehehe
take care !
Bob......
 

Dust

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Originally posted by Bob Kelly
Dust thats the plane I would build if I had the bucks and inclination !
its a realy nice cannard ! pure speed !
for minimal fuel ...the only way to go !

Bob......
thanks for the support of my decision

on another note, in epoxy/glass layups we use micro balloons extensively. a runny mixture to fill foam pores and a very thick mixture to fill blems and radius inside corners.

what do you do with polyester resins?
 

Bob Kelly

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Micro balloons !
(or saw dust ! hehehehehe)
....from all intents and purposes the epoxie resons and polyester resons are used with the same methods I believe
the fiberglass cloth is used as the striength of the layup and the reson used to hold it there
... its truely amazing what you can do with fiberglass , regardless of the reson's used ... just ware long sleves when handleing it or be real carefull not to get the cloth on ya !
.... I've had big red welts on my arms ONCE .... from fiberglass sense then I am carefull what the stuff touches ! its down right mean ! worce than a catcus ! hehehe ...
c ya !
Bob.....
 

Dust

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Originally posted by Bob Kelly
Micro balloons !
(or saw dust ! hehehehehe)
... just ware long sleves when handleing it or be real carefull not to get the cloth on ya !
.... I've had big red welts on my arms ONCE .... from fiberglass sense then I am carefull what the stuff touches ! its down right mean ! worce than a catcus ! hehehe ...
c ya !
Bob.....

yeah - i use saw dust when filling blems in wooden furniture - great stuffff - on the glass and arms, the glass we use on the cozy is not that way at all, wear short sleeves and never had a problem, must be the weave and fiber combination you been using.
 

Bob Kelly

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So ya got any Pic's you can show us of your cozy so far ? love to see it ...
and the hot wire foam cutter if ya still got it laying arround .... I've alwayse wondered how ya regulate the wire to get red hot and not too hot ... must have a reostat er something ? and a real good 12 volt battery ????

never made a hot wire knife before ...lay it on us Dust !!!!!

Thanks !
Bob.....
 

Dust

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no current pics laying round but i just posted these of the wing jigs i made a few years ago

http://canardaviationforum.dmt.net/showthread.php?p=19749#post19749

on the hot wire the wire is not red hot, well it was when my partner plugged it into the table power instead of the rheostat, heh heh heh

when you start working with the foam blocks you have to make many straight cuts that will not be harmed by wire lag.

As you do these cuts you are really practicing for the money cuts on the templets where too hot will cut/melt the foam too much and too cold will cause wire lag and bad shapes.

As it turns out - cutting the wings,(the only wire cutting job) is quick and simple - we cut all of the cores for two planes in 1 day - shockingly easy
 
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