Balsa - Depron Equivalent for wing ribs

[Martyn K]

Thanks all.. Getting some really useful information and that is appreciated.

What size Depron is used for sheeting? I would have thought it would be 3mm but if 6mm is used to replace 1/16 balsa ribs then I am not too sure .

As I am going to transfer the wing section to CAD - to produce paper templates as suggested by Tony then I will need to allow for this.

How does Depron compare with balsa in the handling department?. How torsionally stiff is it? Remember this is an 5kg aerobat which takes multi G loading..

At best, I am a clumsy bugger person at worst a very clumsy person.. And the last thing I want is a wing folding in mid air. Reassure me please

[Colin Leighfield]

Hi Martyn. There are much smarter blokes than me on Depron within the Forum, but this is my take on it so far:- the need is to make sure that the aerodynamic load is spread as evenly as possible over the wing area, because if properly distributed it's quite low. The key to that is getting the connections right and avoid excess bending load concentration points, e.g. at the wing roots. The bending loads generally translate into compressive and tension in the upper and bottom surfaces respectively, the reverse when upside down! There are some twisting loads as well. With a fully sheeted wing you can transfer this into the skins via the connections with the spars and ribs, so the glue connections need to be good. If the wing is covered with film or fabric, you need to concentrate on the framework strength more, the covering will handle the tension loads but not the compressive loads. The spar needs to be full depth and Simon Chaddock's technique, which I use, is to make the booms out of balsa and the webs from Depron. If you are worried about maximising strength you can obviously use balsa if you wish, but I've not seen any problems so far. However, my biggest Depron composite wing to date is the current 58" Super Marauder and you are going a sight bigger! I favour using balsa for the leading and trailing edges, so the composite approach finishes up as Depron top and bottom skins, ribs and webs, balsa spar booms, or at least boom caps, leading and trailing edges. Localised load points like undercarriages need some wood reinforcement. I use 6mm grey Depron for the ribs and would have though that even for your project that would be ok? 3mm Aero quality Depron for skins and webs. It has been pointed out that although more nicely finished and easy to work with, the Aero quality is more flexible than the standard weight. However I still prefer to use it and because I am covering with Ezekote and light glass-cloth, finished stiffness and toughness is as good as you could wish for. That's where I am on this subject right now, let's hear what the other guys think. I fancy doing a bigger Depron composite build, your Mama Mia looks like a great choice and a simple shape as well. Can't see you going wrong with it.

[Martyn K]

Thanks Colin

Thinking of the wing roots it may be worthwhile doing a Depron over a partial balsa skin. It will toughen up the handling area as well

I note that you are planning to use glass cloth and Eze Kote. Does that combination add a lot of toughness? I am trying to avoid paint if possible as I have had too many bad experience with crazy paving and paint simply going sticky with the Nitro that I need to use.

Maybe getting ahead of myself at the moment but just trying to think this through

Martyn

[kc]

Has anyone here actually used thin card for wing covering? An article in RCME years ago ( by a Mr Newberry? ) gave the exact type of material - white & glossy one side, rougher the reverse - and several kits like Regal Eagle used card too.

[Colin Leighfield]

I haven't KC, although it's certainly been done successfully before.

Martyn, I've found that simply adding the lightest glass cloth, in my case seventeen gramme per square metre with Ezekote, transforms the surface and to me gives a result equal in toughness to balsa. It makes it much stiffer and resistant to "ding" type damage, as well as giving a much better surface for subsequent finishing than raw Depron does.I will be painting mine though, purely for the sake of appearance.