Full fuse mold

[shoe]

I'm in the process of designing a fuselage for an open class thermal glider and I'd like to build a mold for it. My question is how in the world do they build them with the rudder live-hinged, with wipers all in the mold a la the NYX?

a couple of pictures
http://rc-sailplane.com/nyx/nyx_tail1.jpg
http://rc-sailplane.com/nyx/nyx_miya_c-tail.jpg

[davidfee]

The live hinge part is easy. You lay in a strip of peel ply (as your hinge material) right in the surface layup. When you demold the part, you scribe through the outer glass and break the hingeline free. You need to also relieve any core material you may have behind the hinge (like on a wing or stab).

I may be wrong, but I believe the wipers are molded seperately and bonded in after the rudder is cut free on the one side. I have seen molded-in wipers, but those molds were complicated and the control surface was deflected so the exposed surface included the wiper. Make sense?

Anyway, I wouldn't bother. I'd just do the tape wipers, with a tape-thickness recess to allow the tape to be flush with the surface.

[shoe]

The live hinge part is easy. You lay in a strip of peel ply (as your hinge material) right in the surface layup. When you demold the part, you scribe through the outer glass and break the hingeline free. You need to also relieve any core material you may have behind the hinge (like on a wing or stab).

Yeah actually I've done many live hinges with kevlar on bagged wings. I guess it would be very similar.


I may be wrong, but I believe the wipers are molded seperately and bonded in after the rudder is cut free on the one side. I have seen molded-in wipers, but those molds were complicated and the control surface was deflected so the exposed surface included the wiper. Make sense?

Anyway, I wouldn't bother. I'd just do the tape wipers, with a tape-thickness recess to allow the tape to be flush with the surface.

Now that is interesting. So they just have a "wiper mold" and make them separately? What about the neat little bit of fuse below the rudder, how does one close that out? Can you get a seam roller back that far? AFAIR the nyx fuse only has one opening, the main hatch up front. How in the world do they roll those seams back there?

*in awe of some mad molding skillz*

[davidfee]

Yup, they would have a separate mold for the wipers. It can be quite simple, actually.

I haven't looked at my friend's NYX in over a year so I dunno for sure. They may use the "bonding ledge" technique where the two halves are vacuum bagged separately with the overlap flaps molded with special removable mold sections. Or maybe they just have a long rod/roller to press it down. Sometimes places like that just get a butt-joint, since an overlap is too difficult. I'd really have to look at it to tell.

-David

[shoe]

Yup, they would have a separate mold for the wipers. It can be quite simple, actually.

mmmm tell me more ;)


I haven't looked at my friend's NYX in over a year so I dunno for sure. They may use the "bonding ledge" technique where the two halves are vacuum bagged separately with the overlap flaps molded with special removable mold sections. Or maybe they just have a long rod/roller to press it down. Sometimes places like that just get a butt-joint, since an overlap is too difficult. I'd really have to look at it to tell.
-David

Is this what is sometimes known as a "joggle gasket"? The butt joint area might me the LE and TE of the fin and rudder? I assume that would be joined just like a molded wing correct? Thanks for your info.

[davidfee]

All you need to mold a wiper is a channel with the correct radius. You may find something on the shelf, or you could use an appropriately-sized ball-end mill and cut the mold... or you could carve a wiper mockup "plug" and pull a mold. Many ways to skin a cat. You could even use a dowel with plastic tape around it as a male mold... but then you wouldn't get the nice finished surface on the outside.

Yes, "joggle gasket" is a term used for the extra mold parts used in the "bonding ledge" process. The fin perimeter will definitely be a butt-join (just like a wing), but the little piece of fuse under the rudder may be also. Hard to tell without poking your head inside there. ;)

[DLD]

Something that works well to make the indentation for the wiper is to CA a strip of mylar into the mold. It makes a ledge for the wiper to be glued to, and also makes it easier to cut out the part, since threre is an edge to follow.
Kevlar layed into the outer skin always works well for live hinges, just make sure you don't use anything that wil cut through it when you scribe through the outer layer of glass.

Good Luck,

David Layne

[davidfee]

Pinstriping tape works well for making this ledge too, if your wiper will be tape. Or if you use the same tape you'll make the wipers from, then the tape on the outside of the finished part will be completely flush with the outer surface.

:)

-David

[shoe]

Thanks for the comments guys. I decided to just go the easy route for my first large fuse mold and do a separate rudder...I know, I know..cop out. I could always mod the plug later to include the rudder and do a new mold though.

The plug is under construction right now. I've carving it out of white pine and it has been quite a challenge. I'm learning more than I ever wanted to know about wood carving techniques. :)

[Phat2Wheel]

This is not my idea. I saw this concept Integral hinge somewhere before and sketched from memory. The rudder, or flap, or aileron can be build with wiper integral with the mold using the concept in the picture below. The moving surface is force to be deflected in the mold. After everything is cured, the wiper is cut from the mold and the hinge line is scored. The extra material on the wiper side is removed to permit free movement. I never want to try this since it's really complicated.

So here is the sketch:

[erikdahlchriste]

Hi,

Somebody may make the wipers with a sepperate mold.

I go in between the tape and the molded wiper:
First I make a tape Wiper - it takes 5 minutes for a whole wing.
Then I add epoxy/micro ballons/color to the glue side of the tape and make sure some of it gets un the inside of the wing as well.
When it is cures I remouve the tape and presto - molded wipers

cheers

Erik Dahl Christensen
Denmark
www.gliders.dk

[chris higdon]

This may be a silly question but I am constructing a spitfire out of fg and these wipers seem like a tidy way to do the hinges.

My question is could you please post a sketch of roughly how the wipers work as I am thinking of it I cant see how the tape would work.

Also if i were to do the integral moulded wiper how could i do it with a surface that has material on both ends,? <like the rudder in the original post> wouldn't it give release <from the mould> problems if the surface were deflected like that?

[ruud zandvliet]

Hi guys,

An nice building thread at www.composite-models.nl

the best, ruud