5 July 2019
I am basing this idea on Walt Mooney's peanut scale model plans, printed enlarged to A3 paper is 133% and that makes it about 17.29" wingspan. It ought to be good for WLToys' receiver servos board and give slow flights.
There is many aspects to like for this DH-6 configuration, but balancing it correctly might not be easy. The stabilizer looks huge but is relatively small when it is compared to the area of the combined wings. The area of the stabilizer is ok since it would be providing me with downward force to get the wings at a bigger angle of attack for higher lift and slower flights.
Doing this obviously meant that the as noted by the famous Walt Mooney the centre of gravity is going to be very forward and since the nose moment is short, static balancing would not be easy without nose-weight. The first consideration is to minimize the nose-weight and the first step is to bring the equipment as far forward to the nose as possible.
I like the idea of an integral motor and receiver and this can be done by gluing them to a piece of a horizontal keel/former. The space at the nose section is very limited and it seems the most obvious place is along the top of the fuselage with the gearbox and receiver on the underside of the horizontal keel. This means that the 2 servo horns will only be accessible from the bottom of the fuselage. It is not an ideal solution because the bottom is left opened. Any cover hatch is only just that and does not add structural strength.
If there is sufficient depth in the fuselage after the pushrods are installed, perhaps the bottom can be covered with a hatch and a little paper pocket glued to it for the lipo. If not, then a deviation from scale is required, perhaps making a bigger engine cowling to conceal the lipo placed on top of the horizontal keel.
The next consideration is the landing gear and I noticed former 2 is in-lined with the front landing gear and we have an instant solution. A wire bent will be tied and glued to former 2. A pair of V-struts cut from thin plastic can be glued to the wire. If I am not painting the V-struts, then I will glue the V-struts to the wire with coloured tissue.
The fuselage could be made from 2mm foam sheets, covered with tissue. Or, 1/32" balsa sheet. Seems to much work to make longerons etc.
The wings could be a simple curled sheets of foam or balsa. It seems a natural to do a tissue covered wing though and I am tempted to do a single tissue surfaced wing but with a few different ideas.
For the ribs, I do not like to cut out many identical ribs. I could shape a sheet of 1/8" balsa sheet to an airfoil shape, with the wood grain running chordwise. Then this shaped sheet can be sliced to the required thicknesses. Instead of angling ribs for dihedral, I can sand the end first to the required slant and then slice off from the shaped sheet. Wider ribs can be sliced for the strut points. This extra width allows drilling for strut points and rigging points.
To simplify the structure, maybe a single leading edge would be good enough, say a hard 1/8" balsa, 1/2" wide. The sliced ribs are glued butted against it. There will be no wood at the trailing edges, just the covering tissue folded against itself. Ribs at the root and the wing tips will require diagonal bracings if they are sliced thin. If they are thicker, then 1/16" gussets can be used instead.
For the tissue covering, draw and paint in all the rib lines, aileron lines, roundels etc on the coloured tissue. One straight edge is folded sharp and glued together. Then this folded edge is glued to the unsupported tail ends of the sliced ribs. The other long edge of the tissue then goes round the leading edge and is glued to the bottom of the leading edge and then trimmed. The covered wing is drilled through for the struts and riggings. Only the top wings might need some touching up after the rigging are in placed, e.g. by using patches of coloured tissue and touching up with paint.
I am making the struts and riggings functional and I am relying on them, meaning they are required for rigidity of the biplanes. I can only think of small diameter carbon fibre rods for struts. The lengths of the interplane struts are identical and so it should be quite easy to snip them to their lengths. I suppose coloured paper can be used to simulate the width of the struts.
Now if I were to cover the wing both sides then I might approach it differently. First, 1/16" balsa leading and trailing edges are pinned to the wing's shape. Then the tip and root is added. I think 1/2" wide for the leading edge, and 1/4" for the trailing edge and ends are enough. 1/8" wide rib bottoms are glued to the leading and trailing edges. Since the intermediate and end pieces are of the same length, they can all be sliced off from a sheet of 1/16" that was first cut to length. If diagonal bracing is needed, then these have to be cut to length and their edges trimmed exactly against the completed wing lattice. Instead of cutting many identical ribs to glue onto these lattices, I think I can just replace them with 1/16" spars of differing heights. This gives it strength but if covered thus, I don't like the many lines since this does not coincide with the wings of biplane. I might have accepted it if I was modelling skinned wing, e.g. P-51 etc. I could also do a shaped balsa sheet as earlier mentioned and slice ribs off of it. The shaped balsa will have slots sawed into it to receive the spars. It would be difficult to cut across the grain with a NT cutter.
Slicing off might sound simple, but it is not easy to get identical widths and perpendicularity. It gets more difficult with harder and thicker balsa.
