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Old May 09, 2004, 09:24 PM
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silicon valley CA
Joined Mar 2004
436 Posts
hollow mold vs. foam core on scale plane

So I won an auction on a sailplane fusalage. It comes with plans for balsa wings, but, with how I fly, balsa wont last long, not on the slope. So im thinking, since i want to try hallow mold or foam core, covered in balsa/obeechi sheets and then fiberglassing and vac bagging, this would be a good project to try it on.

I think, I'd like to try the foam core version, why? Should be strong, weight is not an issue, and its simpler to do. I dont really know how to do either, so thats a whole nother part, but, several people around here do foam and vac bagging, so, thats a little helpful.

Also, on these big gliders (mine i guess is small, considering its "big" 136" wing), they seem to be designed to have a little flex in them, for strength and smooth flight.

I'll ask more on how to do either one later (probably wont start for a while yet anyways, as im working on project #1), but, do you think foam core like I described would be best for starting? and do you think its strong enough for lazy rolls and lazy big loops? I guess i could also just build it from balsa, then sheet the entire wing with balsa and add thick fiberglass to it...

Thoughts?
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Old May 10, 2004, 05:13 AM
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Punta Gorda, FL
Joined Apr 2002
4,952 Posts
Vacuum bagging composite skins over foam cores is the way to go. It can be light enough and it can be strong enough. Much depends on using the right kind of foam, the right type and weight of skin fabric and the right stressed skin reinforcements.

You can cut your own cores if you or a friend have the core cutting equipment. If not, you can buy custom cut cores. See:
http://www.compufoamcore.com/
You can find out just about all there is to know about vacuum bagging wings from the two DVD tutorial that Phil Barnes did. One of your vacuum bagging friends may have it. If not, you can buy it from:

Mr. William Haymaker
107 Schofield Drive
East Berlin, PA 17316

$61 for the two DVD set of Vacuum Bagging Made Easy, including shipping and handling.

This may seem like a lot of money but it will be the best $61 you ever spend because the knowledge in it will last you a lifetime. Planes break and get lost but knowledge and skills last.
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Old May 10, 2004, 05:24 AM
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silicon valley CA
Joined Mar 2004
436 Posts
Thanks Ollie...

I thought it would be the way to go as well, $61 is a lot of pocket change, but, it gets you very far, lets say you only build 6 wings, thats still makes it only 10 bux extra per wing, not too bad .

I need to talk to a local that I know, he has a hotwire cutter, thats kind of a cross between a regular hot wire cutter and a cnc cutter, you make stencils of the airfoil i guess, and then use a special jig (i think) to pull the wire through the stencil evenly. Something along those lines. I havent talked to him about it yet but another local that has talked to him about it.

He also already has all the equipment so im hoping if i ask nicely he'll help me out a little, with setting things up and hopefully getting equipment for me as well.

I figured "Vacuum bagging composite skins over foam cores" as you put it, would definately be the way to go (would sheeting it be a plus? or just a waste if you use heavier FG and kevlar or CF?). I have heard that these large scale planes like extra weight, and to be quite honest, im really not too worried about weight, atleast not yet.
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Old May 10, 2004, 02:20 PM
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davidfee's Avatar
San Diego, CA, USA
Joined Mar 2001
3,068 Posts
You won't need the balsa sheeting if you use adequate composite skins. For the bending loads on that long-ish wing you'll probably want to incorporate some sort of spar system. I'm sure Ollie could help you with that... my experience is more with small (~1m) pylon racer wings.

Sounds like a fun project. I have a 3.5m Ornith sailplane glass fuse in the garage... kit has balsa wings but I have always thought bagged wings would be nicer on it. I'll be watching this thread.

-David
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Old May 10, 2004, 06:44 PM
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silicon valley CA
Joined Mar 2004
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I was thinking of using some ei-70 stiff golf shafts, if there is room, for spars, as they are fairly strong and dont flex much, but, should flex enough. But im sure there is a better way of doing spars on these giants.

David, i just checked out your website and it was very insiteful. I doubt I will actually be doing any building till atleast the end of the month, just because im still working on building up my spirit. The fuse is supposed to get here tomorrow, so, i'll try to take some pictures so you can check it out.

I dont think it has any coating on it, im thinking about gelcoating (but its supposed to take ages to cure) or automotive spray paint, not sure yet, any insites on that either? I may just keep it "naked," it looks like it was painted, but, maybe just not with something smooth.
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Old May 10, 2004, 09:53 PM
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Punta Gorda, FL
Joined Apr 2002
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For an efficient design of a structure like a wing every part of the wing has a purpose and that purpose should be fulfilled with no more nor no less than the correct amount and type of material that is necessary. To design a structure you must quantify the loads it will carry and the stiffness it must have throughout its shape. Without that, there is no rational design process. There is an interplay between the shape that will produce the forces and at the same time limit the size of the structure. At the same time, the strength, stiffness and weight of the structure will limit what can be acomplished aerodynamically. All this begins with a clear concept of what the aircraft is to do and assigning numbers to the forces and moments to fulfill the aircraft's intended function. These forces and moments may be calculated by considering the most severe conditions that the aircraft is intended to survive. Where there are uncertanties, safety factors may be needed and the bigger the uncertainty the bigger the safety factor.

When the wing is pulling its maximum high G maneuver, what forces does it produce? What are the values of those forces along the wing span? What kind of load and what size load do the upper and lower wing skins carry? What type and value of load does the wing core carry? What type and size of materials are capable of carrying these extreme loads? Are there external conditions, not in control of the pilot, that can increase the intended loads and by how much? Do we want the plane to be able to survive these unintended loads?

To begin to answer these questions we have to start somewhere and that somewhere is a quantitative statement of the mission of the aircraft. How big? How heavy? How fast? How maneuverable? What duration? What rate of climb? What stall speed? What pay load? etc.
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Last edited by Ollie; May 11, 2004 at 11:38 AM.
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Old May 11, 2004, 12:30 AM
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silicon valley CA
Joined Mar 2004
436 Posts
wow, can we have that in english, lol.

I do understand for the most part what you mean, and for now, I cant answer any of your questions, partly because i dont have the fusalage, partly because I dont know if i want to thermal it, slope it, put a motor on it, etc etc etc.

All in good time .
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Old May 11, 2004, 11:17 AM
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Pa
Joined Jan 2003
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Quote:
Originally Posted by Ollie
you can buy it from:

Mr. William Haymaker
107 Schofield Drive
East Berlin, PA 17316

$61 for the two DVD set of Vacuum Bagging Made Easy, including shipping and handling.

This may seem like a lot of money but it will be the best $61 you ever spend because the knowledge in it will last you a lifetime. Planes break and get lost but knowledge and skills last.
Hi Guys,

The address that Ollie provided has changed, thanks Ollie. Please send me an e-mail at hayman@paonline.com or go to http://www.paonline.com/hayman/video.htm if you would like more info on the Vacuum Bagging or the Composite Molding Made Easy DVD's.

By the way, the cost of the Vacuum Bagging Made Easy DVD is now $59 and is 4 1/2 hours of information on two DVD's.

Bill
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Old May 11, 2004, 11:23 AM
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La Mesa, CA, US
Joined Jan 2001
419 Posts
Quote:
Originally Posted by hayman

.....By the way, the cost of the Vacuum Bagging Made Easy DVD is now $59 and is 4 1/2 hours of information on two DVD's.

Bill

And well worth it!

Brad
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Old May 11, 2004, 12:11 PM
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North Hills
Joined Nov 1999
6,073 Posts
Thanks for the updated links Bill. I just purchased Composite Molding Made Easy.

Regards, Pete
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Old May 11, 2004, 03:42 PM
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silicon valley CA
Joined Mar 2004
436 Posts
thanks for the update, before hand I need to order something thats about $30-40 and im on a serious budget this month, so I probably wont be sending any money this month , though its really to early to tell yet. Hopefully you will get an email from me soon however .
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