OverKill.... Do I need to add so much strength n weight..??

Hi Guys...

So, 2m W/S 'Cartoon' Cub.. (It's scale in my mind, but for arguments sake, lets says cartoon scale)

Using 6mm depron, the panels are all flat, no fancy profiling like Glenn does, so no bends, just (weak) square joints...

Thing is, whilst i'm aware that many RTF foamies are JUST foam, maybe with a CF spar, I don't 'feel' the foam is enuf, in sheet form.. ( atleast in the 'square box' form this is in)

To this end, i'm adding a ply 'space-frame' to connect the wings, wheels, and motor... Is this overkill.. ?? Too much weight..?? Clearly I could use depron formers instead, but I want something that'll last....

This is what i'm on about.. A bare side panel..

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And with the ply inner...

Ignore the bolts, they're just holding the two ply sides together. It's 1.5mm ply, so while it's weight is minimal, it's heavy compared to just foam..

There will be front n rear ply formers, and a ply floor panel to join all wing n wheel stress points. Plus an inner motor box. The rear will be 'wood-free'

Similar to my little CH, here

but without the front formers, ( it's a steerable trike, and needed them )

I figure, the stresses on the wing roots, and 'thump' on the gear, will be transfered thru this, instead of the foam, helping with longevity... ?!

The motor, Lipo n Esc weigh in @ 700g by the way...

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Any thoughts, comments, previous experience, idea's, voices in your head, etc....

I just wanna know if i'm OK going this route, or whether I should just stop now and go do the washing up instead..?

Luv

Chrisie.. xx

Edited By Steve Hargreaves - Moderator on 05/07/2012 14:30:49

Hi

I don't build these sort of models myself but a couple of the guys at the club build little else. They always seem to use ply formers in their bigger depron self built models.

JC

Cheers JC.. I'm not on my own then.. Phew..

I should add, what you see, is all the wood.. It's just in the cockpit. not a full skeleton..

Luv

Chrisie.. xx

Looks a sensible measure to me. With a drive train of 700g that's potentailly a lot of momentum in a less than perfect landing. Like you I doubt that Depron alone would happily support that sort of impact many times.

BEB

Well it is rather going to depend on your glazing, how rigid it is and how well it can be fixed to the Depron.

Lets say you had no glazing at all would you feel the resulting Depron 'box' would be strong enough?

I would guess it probably would be but your solution looks eminently sensible.

The final issue is where do you want it to break? A really strong stiff centre might result in more serious damage elsewhere that a weaker but more flexible structure might survive. After all Depron is, within limits, a 'flexible' foam.

Actually designing things to break in a crash is probably a bit 'over the top' but then we don't have crashes, do we!

One point to consider. A flat sheet is weak and floppy. Curve it, or roll it in a tube and it gains a lot of rigidity.

The sides of your cub are flat, so need strengthening. If they had been curved, then they may have needed less.

Think corrugated cardboard!

Plummet

For what it's worth, I would extend the wing root area aft down the top edge of the side some what. You have a very narrow strip of depron above the small curved window, that would love to compress and buckle, (assuming no, or non ridged windows of course)

I don't use depron but looking at what you have done, it looks really sensible. Those narrow areas are also in a highly stressed area and so the ply reinforcement is essential.

I have played with some depron just to see what it is like and there is no real strength in it unless it is in quite laerge sizes or forming a double walled box.

Very neat work too.

Just an observation but the grain of the ply is in its weakest orientation across the high stress areas of the upright pillars. I'm guessing there will be a former at 90 degrees to these jouning the sides so hopefully this will give sufficient strength?

A major part of the "traditional" strength of a Cub's front wing mounting is is the triangular structure through the front screen area as per full size - usually piano wire in models but maybe some CF would be appropriate here?

Edited By Martin Harris on 06/07/2012 09:36:45