Depron or Foam Board as Balsa replacement

[Robin Mosedale 1]

I'm about to start my next project, probably a Vickers FB5 Gunbus, about 36" wingspan. Electric

Thinking of the materials, carbon fiber rods come to mind for much of the birdcage, and probably wing leading edges, and wing rib lateral box spars.

 

However, interest has been piqued  bu some modellers venturing into to using alternative materials to balsa.

 

I would probably CAD/CNC (that's not laser) most of the repetitive wing ribs and was wondering if I should stick with tradition balsa ribs.

 

2 or 3mm Foam board or depron?

Anybody successfully milled these?

 

But the concern is covering. As the preferred method of covering would have been natural solartex, which seems to have disappeared, it looks as though I'd have to resurrect unused skills in tissue/silk with dope.

 

Would depron or foam board withstand the cellulose thinners, or would they disolve.

 

What think?

Traditional balsa or something new?

 

I'd be most grateful for any experience and advice.

 

Robin

 

[leccyflyer]

Depron and foamboard would both dissolve with cellulose thinners. Have a look at Deluxe Materials Eze-Dope as an alternative.

[Robin Mosedale 1]

Thank you Leccy. That opens up a whole new avenue

Splendid

[Dad_flyer]

My experience is with foamboard for speed of building, particularly wings. For covering I have used just paint (brushed or rattle can) or covered with iron on film or laminating film. It can take moderate heat, but not solvents. Cutting foamboard blunts a knife very quickly, it might also be hard on a milling cutter.

 

It is really good for thick-ish wings. No need for ribs, just folding over a spar. Also really good for boxy fuselages. So perfect for a Stick, a 3D / Funfly, or Telemaster-type. Ok for cartoon scale warbird.

 

I don't think that it would be very helpful for an FB5. The wing section is quite thin and there is not much of a fuselage. All probably much easier in balsa, especially if you have a CNC. Balsa is in many ways nicer to work with, and also nicer to repair.

[Robin Mosedale 1]

Thank you Dad-flyer.

As you say, it's not a solid skinned wing but open structure. 

So it looks as though traditional balsa then

Thank you 

 

[Robin Colbourne]

Most First World War wing ribs consisted of top and bottom capstrips separated by spacer blocks, and the spars passing through the ribs.
Have you considered making a wide built up rib, then running this through a bandsaw to create the individual ribs?  Clearly with the number of ribs required for a Gunbus, you will need to make several of the wide ones to slice up. 
The spacer blocks could be balsa or depron, and by having balsa top and bottom cap strips, you may be able to get away with using ordinary dope.
The cutaway below shows how solid ribs were alternated with lightened ribs.

[perttime]

An open structure might be a good candidate for tissue over mylar or thin doculam.

[Robin Mosedale 1]

7 hours ago, perttime said:

An open structure might be a good candidate for tissue over mylar or thin doculam.

Thank you Pert, the doculam is a good tip if I can find some very thin.

[Robin Mosedale 1]

11 hours ago, Robin Colbourne said:

Most First World War wing ribs consisted of top and bottom capstrips separated by spacer blocks, and the spars passing through the ribs.
Have you considered making a wide built up rib, then running this through a bandsaw to create the individual ribs?  Clearly with the number of ribs required for a Gunbus, you will need to make several of the wide ones to slice up. 
The spacer blocks could be balsa or depron, and by having balsa top and bottom cap strips, you may be able to get away with using ordinary dope.
The cutaway below shows how solid ribs were alternated with lightened ribs.

Thank you very much Robin.

I have a cnc mill which I use for live steam model engineering, together with sketchucam which includes aerofoil sections, so rib manufacture isn't an issue.

I'd already reconciled myself to traditional built up spar and caps, hopefully with CAD interlocking.

However, research to date hadn't thrown up this sectional drawing which is tremendous.

So very many thanks for taking the trouble to post this

Robin

[John T]

3 hours ago, Robin Mosedale 1 said:

Thank you Pert, the doculam is a good tip if I can find some very thin.

I've used 38 micron laminating film on all but the very lightest structures, and is readily available. This 36" span model has tissue over 38 micron Doculam applied with Wilco satin varnish, which should avoid any concerns about thinners attacking foam.

 

[Robin Mosedale 1]

Excellent, John, and a lovely clean simple evocation of a pusher too.

Is that own design?

Robin

[John T]

Yes, it's an own design. I blame the first lock down for it!

I tried to combine features from some of the early pushers into something that would cope with the typical weather we get.

[Robin Mosedale 1]

Well, that's an excellent evocation. What motor/esc battery did you settle on?

[John T]

Thanks Robin. I've used an Airtek 3536 1100Kv motor with a 40A ESC. The battery is a 2200mAh 3s and with a 9 x 6 prop it draws about 25A at full throttle.

I wasn't sure how much drag I would get from all the struts and rigging, but to be honest it's overpowered with this combination. If the mood takes me it's capable of some very surprising and inappropriate aerobatics.

[Robin Mosedale 1]

Perfect. That's what I was planning around identical motor/esc and battery