Interesting reading about foam core panels.

[linuxmanxxx]

I'm not either so we must be low low low on the totem pole lol.....

[KCStudly]

Sharon helped me with this recently.

Remove the "_page" from your image url when you paste it between the img bars, so that the middle part there reads "...image.php?..." without the "_page" part.

I, too, was not authorized, and when I tried to post your image for you with the technique noted above it did not work for me. Maybe it will for you.

[GPW]

Yes, 1/4” ply on each side adds up pretty quick .. Heavy!!! I know they manufacture Thin plywood ... I measured the roof ply on my Jayco @ 3/32” .. That’s real Thin , but they have a sandwich of that with 2” beadboard in between which “they” think is strong enough for a roof ... and it is light ... maybe too light for a roof ? gallery/image_page.php?album_id=1860&image_id=67505

[linuxmanxxx]

Here and here is what I have been using and it is actually the thinnest you can get and less than a 1/4" sometimes sized in mm and gives plenty of strength and actually is the cheapest priced product at both lowes and home depot unless you want to just use some of the cheaper panelling which is right around the same price on the inside.

[GPW]

If you wanted to get some high grade thin ply ,there’s the Aircraft grade stuff... really Nice , but somewhat Pricy ... I’ve seen and used a 3 ply as thin as 1/64” ... for what you ask .... to cover Foam wings ... cool stuff , cuts with scissors ... Strong despite being very thin , and it’s very flexible too .. http://www.aircraftspruce.com/menus/wp/plywood.html

[loaderman]

Looked at the aircraft plywood, man it is nice, to bad the price isn't

Is plywood heavier than fibreglass?
What about canvass?

[GPW]

Loaderman , I guess we need to make some kind of chart listing comparative weights of materials ... I’d think fiberglass would be heavy because of the resin/epoxy which stays the same weight instead of a lot of it evaporating ... but then, plywood has to be finished , canvas has to be glued and painted ... would be interesting to see what each weighed (finished) Vs. the strength added by each method..

[loaderman]

Yep have to look at a 'finished system'

Fiberglass and epoxy and filler and paint
Plywood, adhesive, paint
Canvass, tb2 and paint

I am thinking there may not be a lot of difference in the end

[pete42]

Back when I was helping cover airplanes with fabric what started out light soon turned into a heavy airplane.
dope was used on the fabric about 5 to 6 gallons for a piper cub about the same for a taylorcraft.
then it was painted couple coats of paint again with lots of paint.
the planes were designed to fly with the weight but like trailers each pound saved while building means
more beer can be carried when finished........ or like your trailer either beverage is your choice to make........

Pete

[Treeview]

There's about 1,200# of paint on a 747

Ask google if you'd like...

[loaderman]

Ok I am Gullible is that true?1200#?

[pmowers]

Ok I am Gullible is that true?1200#?

I seem to remember that when Lockheed quit painting the main tank on the space shuttle, they saved at least 600 pounds, so 1200 for a 747 seems reasonable. Remember, besides the outside,that there is all of the interior spaces and structure which needs to be painted or coated to prevent any corrosion.

[wagondude]

I can't remember how much fuel FedEx claimed to save by repainting the planes so that only the tail was purple. The story was that the origional top half purple paint job was so heavy because of the lead in the paint (purple is one of the highest lead content colors).

[GPW]

Paint is HEAVY .... On my small Foamie planes , I avoid a thick coat of paint , adds weight that affects performance... on a trailer I doubt it would add that much weight , none that would affect anything ...

I still believe the canvas/T2 /paint to be the Lightest of all ...
Since plywood and canvas are essentially made of “plant fibers “ (Cellulose) I’d expect their density would reflect on the weight.. It was stated (somewhere? ) that plywood weighs 57 lb/ cu. ft. , The large pile of canvas I used to cover my Foamie trailer didn’t weigh anywhere near that ... likely < 20 lb.
Water based T2 and Latex paint has the advantage of the solvent evaporating away , leaving the pigment , which is Most of the weight ... I’m sure other oil based paints do this too, but resins do Not , so the weight of the can is what goes on the trailer ...

[angib]

Light thin skins are perfectly possible - we used to build racing boats with some bits having skins less than 1mm (just over 1/32") thick. But then you run into durability problems - sure the structure is strong enough overall, so the weight of the roof won't collapse the walls or the roof won't distort under wind pressure when towing. But the thin skins can be easily punctured by small sharp objects like stones. The structure will still be OK, but there will be a small hole in one skin!

A former boss had something he called the ball-pein rating - the skin thickness of the outer skin was determined by how hard you wanted to be able to hit it with a ball-pein hammer before the skin broke. So there was 'gentle knock' thickness, 'light tap' thickness, 'heavy tap' thickness and 'good wallop' thickness, which was about four times as thick as 'gentle knock' thickness. 1/16" ply either side of 1" foam is plenty strong enough overall, but you will be able to poke your car keys through it, if you try.

Once you make the outer skin thickness enough that it has the local strength you want, that may be enough for the whole structure, if you just add some light framing to stop overall bending. That's the reason the latest design I did, the Wanderer, has a single 1/4" skin with a little 1x2 framing - really simple to build. Some foam can be added between frames for insulation (and a purely cosmetic upholstery fabric glued/tacked over it for appearance), but a sandwich structure isn't needed for overall strength.