Detailed Wing Structure

I'm working on the detailed wing structural model, starting with the front D-Section.
Ribs - 20 mm extruded polystyrene 28 kg/m3
Spar is 100 x 10 x 3000 mm dimension
Spar Caps - unidirectional carbon
Spar Web - Vertical Grain Light Balsa, 120 kg/m3
Spar Faces - 45 deg. fiberglass 0.2-0.5 mm thick to be determined
D-Section shell: 0.8 mm aicraft plywood
Strut attachment is not yet in place in these pictures (it will be at 50% span)

Wing Analysis

Here is the negative 3G case. The struts do not take any load. The required spar cap sections in unidirectional carbon fiber are:
Red - 60 mm2
Orange - 40mm2
Green - 30mm2
Light Blue - 15mm2
Dark Blue - 6mm2

We need to use for each spar cap, the larger of the two sections for the 6G positive or 3G negative case. This means, basically, tapering from 60mm2 at the wing root (required for the 3G neg case), down to about 35 mm2 at the strut attachments (required for the 6G pos case), and then tapering down to zero at the wingtip.

Analysis of the wing in 6G positive loading.
Principal flight loads are handled by unidirectional carbon fiber in the spar caps.
The color corresponds to the mm2 of unidirectional carbon that will be necessary (spar cap section):
Red - 40 mm2
Orange - 30 mm2
Yellow - 25 mm2
Green - 15 mm2
Light Blue - 10 mm2
Dark Blue - less than 5 mm2

The behaviour in negative G will be different because the struts do not have any compression capacity. Negative G is handled by the wing root and it will increase the forces in the center section between the struts.

Definitive Design Choice

Jean-Pierre showed the previous iterations to a group of pilot friends and they felt that the prop rotating around the boom was a good idea and that we should go back to it. So our latest design combines the high wing with the boom going through the prop hub. Spec is still 31 kilos dry.

Another version. The fairing construction is not fully decided. The wheel is a standard 305-mm bicycle rim with 375 mm outer diameter. It's very sturdy and if it breaks you can rebuild it with more spokes or thicker spokes. Conventional controls with a side mounted stick (on right hand) and rudder pedals. The transparent color is fabric, 57 g/m2 (1.7 oz per sq yd). The opaque color is 0.8 mm plywood. 

The previous version had a connection from the feet up to the motor, for this version we chose to remove it because the largest magnitude forces involved are transmitted by the two struts from the pilot's CG up to the wing; there is not really much added value to the super-rigid loop or triangle type arrangement.  

triangular frame

Jean-Pierre suggested that the front bar go down directly between the pilot's legs since the fairing will be rigid enough to support the pilot's feet with the rudder pedals. That way the frame is a triangle. I don't always use the computer; here I just drew it up in pencil. The structural members are boxes made of thin spruce (10x10 mm) with some carbon fiber reinforcement and internal foam stiffeners. The weight of the bare triangle, not counting all the attachments - engine mount, wheel mount, fairing mounts, wing mounts etc - should be 2.7 kilos;

New Design

For this version the weight is still 31 kilos, and the engine is the same 14hp. Cruise speed higher, about 125 km/h. Faired pilot makes radical improvement to efficiency. The skin is 0.8 mm plywood (wing) and 0.4 mm plywood (rear of fuselage, tail, and pilot fairing).  Plywood is glued to foam cores and local carbon reinforcement.