Modern version of TPG - Or the search for "Black Wood"

Any example of an aircraft with fiberglass layup of same thickness?

 

I can’t verify the “same thickness” criteria, but Myron Jenkins, after building a champion Glasair III, built a GlaStar wing of glass. See https://glasairtraining.com/wp-content/uploads/2016/05/Article-12134.pdf


BJC

 

That's a nice looking plane, thanks for the link. His wings came out lighter than the factory aluminum ones, it would be interesting to know how thick he made the skins.
The wing skins (carbon fiber) were attached to fiberglass ribs. Apparently the nose skins were made in female molds and the skins for the rest of the wing were laid up flat and then bonded to the ribs, held down by clamps and weights. In the photos, the skins show slight ripples coincident with the ribs. I wonder if Glasairs (factory made with composite skins) also have these slight ripples.

 

I’ve seen Glasair wings at +6g with no visible ripples. Unlike Myron’s skin’s, Glasair skins have a 1/2 “ core.


BJC

 

Thanks. That core would make a big difference.

 

That's about the only one. I don't see widespread "black aluminum" in EA-B kitplanes.

 

When he was building, I asked Myron, “Why?”. His reply was that a Glass Star should be made of glass. I got the impression that he just wanted to do something different.


BJC

 

Guilty. You've been very patient about this, and I've seen it come up a lot.
I'm not proud of it, but I'll admit I haven't thrown in the towel on the idea of "synthetic ply."

 

https://www.google.com/amp/s/travelforaircraft.wordpress.com/2018/04/11/spit-mk-ix-at-boca/amp/
This full size Spit copy is made of a sort of synthetic ply. It’s all made from a sandwich of some harder than balsa wood core with Fiberglass on one side and carbon on the other. 1/4”-3/8” total thickness. Don’t know why. I did talk to the owner/ builder and see a ground run back in March.

 

If you come up with a composite replacement for 1mm to 2mm thick ply:
Same density or lower
Same cost per surface area... or even slightly higher
Same strength or higher
In other words "Black Wood" that could directly replace thin ply.

You will have a pretty good material.
Raw composites materials are cheaper to ship, even including the Hazmat fee.
Composites don't change with humidity, or rot.

 

What good is that dual but disparate laminate structure if the joining substrate is weaker than both?

 

I don't know if it's relevant here (and I know that billski explained very well why wood core is not a good idea), but in the very interesting horten microlight blog, they use it in a critical part because of "wrinkling" : https://hortenmicrolight.wordpress.com/2018/07/27/pretty-avant-garde/#more-4951

 

Yep. CF/epoxy can beat 1mm plywood in tensile strength and compressive strength per unit mass, but the lower density of plywood gives thin ply the edge in stiffness compared to CF/epoxy of the same weight. Yes, add some thin core material and a skin on the back and we can match plywood stiffness, but not weight (or cost). Ply has moisture/stability issues, but even that comes with a plus side (being able to steam and wrap it around a LE, etc).
I haven't given up hope, but I'm pretty sure we'll have to accept some limitations on local compressive strength and hangar rash resistance, just as we do with fabric covered airplanes. We don't walk on their wings, use them as writing surfaces, etc.
It is often necessary to make compromises to achieve weight goals (there--I tied this discussion back to Raptor.)

 

Unless I misunderstood you, many composites structures are made like that, eg; have a core of balsa, foam etc. that is far weaker than the surface layers.

Cost mostly, but I came within a whisker of doing it this time. Aluminium still wins out at about half the material cost, but CF is gradually coming down, 10 fold reduction over the last 10 years, so maybe next time.

Then again, what sort of idiot would want an easier to build, lighter, stronger, smoother, faster, more economical plane?

But it's Black Aluminium!!!

 

If smooth carbon sheet was available in thin sheets and stronger, stiffer and lighter than .016" aluminum as promised for the last 40 years, then I would consider it. But I am not seeing it.
And here we have the 1000 pound overweight carbon Raptor instead?

 

I understand sandwich composites, but I was picturing a FLAT sheet with different composite layers with different properties on each side of the soft core. I wasn’t sure how the two separate properties were supposed to complement each other when the joining substrate was not strong enough to transfer loads. On a flat surface, how does the core add anything compared to just a two-ply laminate made of CF and GF without a core between them.

 

For these fairly moderate (per sq in) loadings, the core is strong enough to transfer shear loads between the two skin layers, so one is in compression while the other is in tension. This way, the two plies are much more stiff than if they were just bonded together with no core..

 

Think I may start a new thread later today for this subject.

Edit: Thread started. Modern TPG