Hey to all you composite masters. I have a question about the layup for my next moulded Scorcher 2M. Its a ds plane so weight is not an issue and I mostly use glass instead of carbon. My first one was, from the outside in, 2oz/ 6oz/ 1.5mm balsa/ 6oz (all glass) with a healthy over lap in the centre on the wing. This gave me a nice strong layup and the weight could go up more with no issues. I think this is a balanced layup, but I have heard lately about putting the two layers of 6oz cloth outside the balsa and just capping the inside with 2oz to hold it all together. I can imagine this would give me a tougher skin but will I be losing some of the stiffness out of the sandwich because its no longer balanced? I can always use 6oz cloth on the inside of the balsa if I need to but just wanted an opinion on it.
Thanks, Josh

If weight is no problem, why don't you put 2 6oz outside and 1 6oz inside to get a stiffer skin?

Thats what I was thinking too and will probably do that. I just wondered if any one had tried both and knew the difference.

I'm not sure what your airframe is but if your using 2x6 oz, balsa is not needed.

The wing shown is 1 6oz and 1 4oz. It does "oilcan" if pinched but will not, and has not failed in flight. Free atmosphere lay up, no vac bags.

This configuration does not dent like balsa skin in glass. Even when dropped.

Nitro .OS 46VF 2 stroke engine powered. Lots of vibration, is still flying after around 5years. Not much wear.

steve

Josh is building a DS glider with a very thin airfoil (8%) that is capable of going 300 mph. Telemetry has measured 90 g's in these things. I think that the sandwich construction on the wing is mandatory unless there are many weblets to keep everything in the right shape.

Josh, I'd recommend laying up some samples with varying layups so you can feel for yourself the difference.

Josh,

I'm going to agree with Adam, you must test. I know on my DLG wings I use the reasonably lightest glass on the inside of the rohacell but this is to reduce weight as much as reasonably possible. I will say the layup is fairly balanced with 0.73oz glass on the inside and outside skins.

Perhaps more glass on the outside will be better, as you gain a bit more strength from laminates on the outside of the wing, but the thickness of your balsa shear web has a large say in the matter. If this is relatively thin, say 2-3mm, putting glass on the outside or inside is reasonably similar in overall structural performance. One factor that should be considered is warping, by running a highly unbalanced layup on the inside and outside of the skin, are you going to induce a twist into the wing? I don't have a good answer to that question other than I do my best to match up the glass on the inside and outside of the rohacell so I am at ease on this issue.

-Sam

Thanks guys, I'll have to do some testing. I dissected my poor broken D60 wing the other day and found the layup to be (roughly) 2oz glass/ 6oz carbon/ 1.5mm balsa/ 2oz glass. These skins are very stiff but are unballanced.
I'll have to work out what weight I want my next wing to come out at and build the weight into the layup. I reckon I can afford to put at least another kilo into the airframe without spoiling the flight (may need more than ten knots to fly now though!) so I have plenty of room to move with layups.
Cheers, Josh

I don't see any problem having unbalanced Layuos, since they're balanced when you take in count the other wing skin.
The important thing about balance, is that the fabrics have balanced thread count. If they do, then everything will be fine. If you put the heavier fabrics on the outside of the wingskins you have more distance between the top and bottom skins, this means stiffer structure. That's why everybody puts the carbon outside when doing single carbon wingskins, and not on the inner side of the sandwich.

Thanks Chet, that makes perfect sense.

As a data point, I use 1.4 glass/3.16 glass/2.5mm 51IGF Rohacell/2.3 glass. Center 5.7 glass doubler between the layers. My wings see 25+G and up to 230mph.

Thanks Craig. I didnt realize people were using such thick cores, no wonder its so stiff! Do you taper the edges of your rohacell?

I do, at the leading edge and tips to help it conform, and at the trailing edge for clearance. The center 5.7 doubler is just to help with landing gear loads, it tapers to the fuselage width at the trailing edge.

Thanks mate

Josh,

Have you watched the "Raketenwurm" thread? It doesn't answer your question about the layup, but it does appear to put to rest the question regarding the "balanced" layup myth. I, like you, was concerned to have it ballance on my first moulded wing job. Many examples, like the one above, use all structural layer outside the core and a veil layer only on the inside. Like Chetomachine and others have said above.

I'm about to make a choice for a light layup to build set of wings (and fuse) for a light version of my plank. Somewhat opposite set of consideration to yours though.

Jim.

Hey Jim, I made a light version of my 60" moulded wing with 2oz glass/ 1.5mm balsa/ 2oz glass. It was nice and light and stiff for the weight. Only problem was that it dinted very easily, mostly because the balsa was pretty soft and crap quality. I reckon 4oz glass on the outside would have helped me along with some better balsa or maybe vaneer.
Good luck with it.