Lite Ply or Birch?

[Flyer]

Just pondering the design of the AC130. At approx 1.9m in length, am I best using normal 4mm birch ply as the central crutch? I will be using lightening holes. I have also considered the apporach of a vertcial central crutch , along with a horizontal one (i.e crucifix style) along with supporting fuselage 'ribs' of depron . Am I over engineering this? I just think that a suitable crucifix central crutch could be both light and rigid. I am concious of the weight towards the tail, but if I use lite ply, I think it will give good rigidity along with relative light weight.

Or am I desiging a brick ?

And as I am using 'ye olde skool' version of pen and paper I'm afraid I cant put fancy cad drawing up.

Advice welcome

cheers

Ade

[Dave Hopkin]

I would have thought that a central box or better still a double box of 6mm Depron with shaping formers round it then skinned in 3mm would have given ample strength aft of the wings

[kevin b]

Hi Flyer.

Lite ply is not a reference to its weight, but its construction. Generally there is no difference in weight with birch ply. I wouldn't have thought it necessary to use ply for the full length. You could always laminate some balsa "ply" for the tail if you're worried about torsional stiffness.

Kevinb

[Flyer]

Thanks both for the input. I must confess that I find lite ply definitely lighter than birch though. I'm just a little concerned about the rigidity of the tail given that it is going to be quite large. I will reduce the ply to the rear, and will try to make sure the tail is supported well by using balsa/depron . If it end's up a brick, I will have to make the second one lighter.....

cheers

Ade

[Denis Watkins]

It is always worthwhile revisiting new materials and retrying construction techniques with a view to innovation and maybe find overlooked ways and building techniques, with a view to saving on time and cost, but unlike Depron, balsa is not brittle, and exhibits a strength along the grain that outstrips most lightweight materials in existence, and even gives expensive carbon fibre a run for its money, due to adverse costs and handling of said the said fibre. If aeroplane construction could be completed in a jigsaw interlocking manner, without the aid of glue, I believe that Depron would win hands down on time and cost. But again, with the addition of glue and emulsion paint, the established balsa material, due to its strength to weight ratio far out strips Depron in longevity and the usual mishaps colliding with Earth.

Depron does win in the 50 gram – 100 gram indoor flying league, as the flat plate wing is efficient in such aircraft, flown in a still air atmosphere, but once we retreat into the wild blue, something of greater strength and substance is needed to hold all manner of surfaces squarely and stiffly aligned with the fluid we call air.

This is just my opinion.

[Dylan Reynolds LaserCraft Services]

Reduce the O/A weight immediately by 25%, use 3mm ply not 4mm, plenty of strength if using birch. Liteply is flexible and not very crush resistant, poplar ply is stronger than light ply, but not as strong as birch, but is lighter than birch.

Strength can be built in where it is needed, as can lightness, if you use a vertical crutch with formers and stringers, skin with 2 or 2.4mm and glass cloth, this will build in strength but is lighter than wood itself. So much so, that usually the inner structure almost becomes redundant

[Dave Hopkin]

Posted by Denis Watkins on 19/01/2016 17:04:50:

It is always worthwhile revisiting new materials and retrying construction techniques with a view to innovation and maybe find overlooked ways and building techniques, with a view to saving on time and cost, but unlike Depron, balsa is not brittle, and exhibits a strength along the grain that outstrips most lightweight materials in existence, and even gives expensive carbon fibre a run for its money, due to adverse costs and handling of said the said fibre. If aeroplane construction could be completed in a jigsaw interlocking manner, without the aid of glue, I believe that Depron would win hands down on time and cost. But again, with the addition of glue and emulsion paint, the established balsa material, due to its strength to weight ratio far out strips Depron in longevity and the usual mishaps colliding with Earth.

Depron does win in the 50 gram – 100 gram indoor flying league, as the flat plate wing is efficient in such aircraft, flown in a still air atmosphere, but once we retreat into the wild blue, something of greater strength and substance is needed to hold all manner of surfaces squarely and stiffly aligned with the fluid we call air.

This is just my opinion.

Yep Depron is only fit for indoor flying..... just as this video goes to show..........

**LINK**