When building the D-tubes for my Mitchell Wing I found that 1.0 mm Finnish Birch aircraft grade plywood was excellent for the inboard section of the leading edge. It was stiff enough to make for a not so flexy skin (oil-canning) and still wrapped around the foam nose ribs without too much trouble by wetting the outside of the plywood when the bending radius got tighter toward the wing tip.

The out board leading edge, especially at the tip, was so difficult to wrap, even with wetting the outside of the plywood that I switched to 0.8 mm plywood which made all the difference in the world while still leaving a very stiff non-flexy D-tube. The leading edge of the elevons were almost impossible to wrap with 0.8 mm even with using lots of water and gradual pre-bending of the plywood over time before gluing.

The tighter radius needs less thickness to make for a stiff surface. This makes sense if you think about it or if you do what I did and play around with different thickness plywood and different bending radii.

For the nose ribs I used denser foam, sliced the ribs thinner and spaced them closer together for less flexing between nose ribs. I calculated that it cost me 1.5 lbs extra weight for the denser foam while the thinner ribs spaced closer together was a draw. I just can not remember if that was 1.5 lbs for the whole wing or 1.5 lbs per side. | I would bet that I have the the stiffest D-tube skin of any Mitchell wing out there.

Billj3cub


On 7/29/2011 4:30 AM, Philip Lardner wrote:


Does anyone have a schedule for laying up the main spars using carbon rods for the spar caps and carbon cloth for the shear webs? How many rods (round or rectangular) - and their lengths per spar cap? Jim Marske describes the various calculations in his 'Composite Design Manual' but I'm not entirely comfortable with my knowledge of the subject. Kenny?

Does anyone have the details of Steve Arndt's Magic Dragon wing spars?

Phil.

PS - my newly converted 29' long workshop is now re-roofed, re-floored, painted, insulated, electrified, lit, secured and ready for action! Tools are arriving from various corners of the earth... progress is imminent!

PPS - I located a number of suppliers of 0.8mm plywood in the UK - all charging around £50/sheet of 4' x 4'. Expensive stuff! A little more research turned up a wood veneer supplier in Dublin (practically on my door step) who is offering 0.5mm veneers from €1.50 - €5/m-sq! ...and it comes in 4' x 8' sheets With sufficient support along the long dimension, between the external rib forms, this stuff should be perfectly suitable for use as a female mold for the leading edges. At that price I could even use two layers to beef up the mold skin and still not break the bank!