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is the chassis made by plywood or just body?

Chassis is plywood, with an expanded cardboard layer sandwiched into the floor panels.
Chassis is a series of boxes, sills are triangulated with a divider down their length.
The engine compartment uses a steel space-frame as the sub-frame.
The fiberglass body closes the top of the wood box structure.
There are chassis pics at the link a couple of post back.

Further notes, the wood chassis must not be completely sealed as the wood has to "Breath".
Think of wood as the Neanderthal version of modern composites.
Frank Costin did the Marcos chassis after successfully designing plywood BOMBERS!

Modern composite can blow away wood for ultimate performance, but this a "Locost" forum.
Since CF is still* so silly expensive I will use wood and 'Glass for my build.

*"Carbon Fiber (CF) cost will be falling by orders of magnitude very soon now".
Been hearing that for decades!

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Better than a crap designed steel frame or not, I can't say that this exactly instills me with great confidence in the plywood chassis either.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

how about basalt fiber?

I've never worked with Basalt but seem to recall it as being heavy?
Long ago I found a chart comparing weight/strength/cost of several materials.
Wood was fairly impressive.
To get back to the original question, I would use foam only as a filler between layers of plywood.

Good reminder about the Marcos Tyres, but should not be an issue if size is part of the original design parameters.

Here's a simple experiment.
Single ply of thin plywood, clamp one end and bend to failure.
Two plies of thin plywood, clamp one end and bend to failure.
Two plies of thin plywood, bonded to a layer of foam, clamp one end and bend to failure.
Two plies of thin plywood, bonded to a layer of foam, wood bonded to the edges of the foam and plywood. Then clamp one end and bend to failure, if you can.
Add a wood diagonal brace and I doubt anyone can break it without mechanical help.
Of course the larger the span the thicker/more reinforced it needs to be.
Adding curves can be a PITA, but can be done and is stronger.
Marcos had (/) sills as torsion beams, [/] should be nearly as good.
This discussion is pushing me to do more on the Tatum, I did recently buy an engine for it.
Have to complete some simpler projects first.

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heavyer than CF but still very light

Frank Costin worked for DeHavilland (who had produced the Mosquito plywood bomber during WWII), but he certainly didn't design it. The Mosquito was well before his time and his role for DH was as an aerodynamicist. By the time he was with them, they were producing aircraft like the Sea Vixen and Comet (the first jet airliner), which were conventional stressed metal construction. The last aircraft they did using plywood construction were the Vampire and Venom fighters, which again were before Costin's time.

He did design his own glider out of plywood, though.

In terms of the original question, foam core is actually rather heavy, as is wet lay-up fibreglass, but it can certainly be made to do the job.

This is rather more effective, though:




...which was designed by ex-Lotus F1 Chief Designer Martin Ogilvie and fabricated from pre-manufactured flat panels of honeycomb core skinned with glassfibre in epoxy.

Monocoques in general, and sandwich panel construction in particular was discussed at length on THIS THREAD.

I am fortunate to have never been bitten by the private aircraft bug.
Flying at ground level is expensive enough!

Visited a small UK aircraft museum, I think it was in Coventry?
Two pieces really stood out, the Vulcan Bomber of which I got to sit in the pilots seat, and the Vampires.
If I had the time/wasted funds to build it I would like a Vampire, even just as yard art.

OK, so Frank did not design the plywood planes, but having worked there must certainly have had some impact on his automotive work.

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is that a huge matter what the core made by apart from weight?

Apart from weight, no - but of course stiffness: weight ratio is probably the main reason you'd want to do a composite monocoque in the first place, so weight will be a big deal to most people.

Wet lay-up with foam core is also a lot more work, so why else would you bother?

I think that the the best core should be strong in both compression and tension. Cohesion and Adhesion to the outer skins I think would be other important considerations. A lot would depend on the expected forces seen in both normal and abnormal operating conditions. IAMAE (I am not an engineer)

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

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For myself I want to avoid wet lay-up as much as possible.
So pre-cut panels of wood or glass panels bonded at the edges and to the foam core.
Hoping to get into a hobby store soon and make a quick scale Balsa model.
With a central tunnel (Box) and two outer tunnels/boxes plus F&R bulkheads/boxes all capped with the hand-laid 'Glass upper body I am confident it will be plenty strong.
The tricky part becomes attaching front and rear suspension.

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If I must be a one-man PC free zone, so be it!

because I have no tools & skill to bend pre cut panel, I can only make 90 degree joint with pre cut panel

If you design the structure right, you can make it pretty much self-jigging at whatever bend angles you want. The angle depends on the width of the 'slot' you rout in the inner face of the panel - which can be calculated quite easily - and you can then fold the panel around profiled bulkheads. You can even do smooth curves by routing a series of parallel slots.

You need little more than a router and a jigsaw as the basic tools, and you're going to need those (plus a hot wire cutter) for foam core work in any case.

In terms of core strength, remember that it's only there to stabilise the outer skins. Certainly you don't want it to delaminate from those skins, but apart from that the main consideration is shear strength, 'cos you're trying to stop the skins moving relative to each other in torsion.