R. SOMMER monoplane (fully covered version)

23 May 2016

I did these over the long weekend:

I made my mount by first marking out the angled slot for the motor and the openings for the servo motors mount on a scrap piece of 2mm basswood. Right thrust slot was off set to the left so that the propeller will be centred.

I soldered additional battery connector to the WLToys receiver board. This way I can use both types of battery connectors.

The board was cut out with a pair of scissors/shear snip.

The openings were first drilled and then enlarged.

I made the Gnome Omega 7 rotary crankcase by first making my former. I had no suitable sized former so I took the smaller diameter piece and wrapped card around it to make a larger diameter former. Two rings of card formed the sides of the crankcase. The front of the crankcase was glued onto the ring and trimmed. The backing in the crankcase was a piece of 2mm flexible foam.

I used the 'Dremel' type mandrel to screw in a piece of flexible foam and cut a ring by spinning the mandrel in a portable electric drill against a sharp cutter.








My idea then was to have the Gnome rotary spinning with the propeller. I push fitted the crankcase to the propeller and cut the bendy part of the drinking straws and hot-glued them to the crankcase.

The large paper clip was hotglued to the motor to provide visual reference to the height and longitudinal position of each cylinder.

I drew a circle around a plastic cap and drew 16 radiating lines.

PVC plastic cover sheet was placed over the drawn diagram and the spoke lines were first scored with the cutter and then with a pen.

The plastic discs was cut and glued to form cones.



A bushing was glued to the bottom cone and the top cone glued with a this was the result. What it needed was a slit silicone tubing and that would be a wheel.

However I noticed the spokes were mis-matched. I was puzzled for a while until I realised that the mistake lies in drawing the finished spoke lines when I should have allowed for the lapping.

I will do the spoked wheels again. Here's the result of a day's adventure.
The motor and receiver board is hotglued to the mount.
The motor was held at a slight down thrust angle, so I get both down thrust and right thrust.
Crankrods are from soldering lead and hotglued to the cylinders and crankcase.

I could do the main landing gear in thin wire but I wanted to make it out of the 2mm dowel rods from Daiso. The wood was very flexible and soft, it was not as springy as bamboo. I would prefer bamboo but it was light and is 2mm diameter so I wanted to try using that. I think I want the completed landing gear to be inserted in silicone tubing (which I have misplaced) glued to a fire wall which in turn will be glued securely to the mount.

I taped two lengths of the dowel and marked the location of the bends. Both front and rear legs were left extra long for trimming later. The bending portions were wetted. I used my old 30W soldering iron and held the pair of dowels flat on a flat surface and lifted the other end free off the surface to form the bend. I added water constantly with a cotton bud to the bending length but the wood was still charred. The photo is of the bended dowel. I had to taped the dowel again later to form the slight bend at the firewall.

I used the same technicque for the tail skid. It splintered slightly.
It might not have splintered if I had soaked the dowel longer or make the bend slower.

Here the tail skid was cut to length. I don't want to make the 4 tail struts out of the same dowel, I think that would be too thick and I don't want to spend time splitting and sanding the dowel. I used the same PVC cover sheet and cut a length of perhaps 2mm strip. The length of the strip was cut in half and glued to form a cross. The four ends were bent and the tail skid glued.
So the tail struts will be very flexible but since it is so small and light, it might be ok.

1. I will also buy some 3mm silicone tubing (2mm inner diameter) from Banggood since I misplaced mine.
2. I will do the spoked wheels again because I think it is quite attractive and simple.
3. The rotary engine was a bit heavy because of the card and hotglue used but that is ok since the nose moment is so short. However it is not a good idea to have the rotary engine spinning with the propeller because it is unbalanced, I will open up the crankcase so the propeller spins clearly and the crankcase can be glued to the firewall/cowling.

Ideas on making my fake spoked wheels:
My pair of wheels shall be 1.5 inches, i.e. 38mm diameter, the wall thickness of my silicon tubing will be 0.5mm. There will be a difference between flat radius and cone radius but since the desired height of the cone is so short (I am thinking 3-4mm thereabout), the difference is so small that it makes no sense to replicate the exactness since I can't do it so accurately to a fraction of a mm anyway. With this idea, I ignore the thickness of the silicone tubing. I have to decide on something before progressing, so I decided 16 spokes each cone, 22 degrees in each segment and 8 degrees of overlap (all these from googling "cone height construction").

The first step is to draw construction pattern. I have a protractor but I don't have a compass:

1. Draw a single line on a sheet of paper, the back of the plan will do.
2. Mark a point in the middle of this line and this will be the centre of circles.
3. Place the protractor over this line and centre point. Draw around the circumference of the protractor, repeat for the other 180 degrees for a complete circle.
4. Mark a segment of 8 degrees, divide the remaining 352 degrees of circumference into 16 equal portions at 22 degrees each segment.
5. Connect these points to the centre with lines, mark out the lines where it will be 19mm from the centre.

The second step is to scribe and draw out the spoke lines on the pvc sheet by first taping it to the pattern to secure.

The third step is to cut the disc to the correct diameter. There are 4 cones to construct so accuracy is important for aesthetic purpose.

1. Punch a pin hole to each scribed blank, slightly oversized.
2. Apply small patches of double-sided tape and assemble all 4 scribed blanks to the cutting disc mandrel. I didn't try this yet, maybe the blanks will be too thick for the tightening screw.
3. Attach the mandrel to a drill or dremel and cut out the blanks with a heated cutter. I think heating the cutter will be necessary because unlike the it will be quite difficult to cut the pvc sheet, possibly one at a time.

The fourth step is to assemble the cones.

1. Cut at the 5 degrees line (one cut per disc, do not cut out the 5 degrees segment).
2. Coil into cone shape so that the 5 degrees lines overlaps each other and glue.
3. Drill out the cone to the diameter of the bushing, in my case, 2mm diameter.
4. Place the bushing in the perpendicular block, insert a cone to the bushing and glue.
5. Remove the bushing and cone, it looks like an umbrella. Insert another cone from the other end of the bushing. Glue the edges of the cones together. Also glue the bushing to the new cone.
6. Cut the excess length of bushing and we have a spoked wheel rim.

The fifth and last step to make the basic spoked wheels is to add the tyres:

1. Colour the silicone tubing.
2. Slit the tubing, apply glue along the rim and insert rim into the slitted tubing, rolling the rim at the same time until the tubing overlaps.
3. The excess tubing is trimmed away with sharp razor blade and the ends glued.

19 May 2016

I am going on leave tomorrow, I may do a simple R. Sommer's monoplane.

The shape is based on a peanut scale plan by Jan-Francis FRUGOLI downloaded from www.outerzone.com.

 

 

 

 

 

 

 

 

 

 

Wing

• Cut the right and left wing panels without the cutout.
•  Press the trailing edges of the wing panels.
• Join the wing panels to form a pair of wings.
• Cut a piece of carbon fibre rod to the combined length of the leading edges, press down with a hot soldering iron at the middle and lift up one end to form the dihedral.
• Cut a second piece of carbon fibre rod to half the length of the previous rod, press down with a hot soldering iron at the middle and lift up one end to form the same dihedral.
• Glue the two lengths of carbon fibre rods to the wing. The longer piece is glued to the leading edge of the wing panels and the shorter piece at mid point of the wing chord, below the wing.
• Cut out the opening for the WLToys F929 F939 receiver board in the wing.
• Decorate the wing with spray paint, marker pens or coloured tissue.
• Remove the servo horns, insert the servo ends from the bottom of the wing, through the opening, glue in place and replace the servo horns. The WLToys F929 F939 is in between the two carbon fibre rod reinforcement.
• Cut away the wing cutout, touch up with paint and the wing is completed, ready for assembly.

Horizontal stabiliser

• Cut the horizontal stabilizer.
• Press the trailing edges of the elevator.
• Cut a piece of carbon fibre rod to the length of the leading edge.
• Make a pair of stabilizer mounts. Insert them to the carbon fibre rod.
• Glue the carbon fibre rod to the horizontal stabilizer, leaving the stabilizer mounts free hinging.
• Decorate the horizontal stabilizer with spray paint, marker pens or coloured tissue and the horizontal stabilizer is completed, ready for assembly.
• *There is actually a hinge line on the plan, so I shall hinge the elevator instead.

Rudder

• Cut the rudder.
• Press the edges of the rudder.
• Bend a piece of wire to a U shape.
• Make a pair of rudder mount. Insert them to the U shaped wire.
• Insert and glue the U shaped wire to the rudder, leaving the rudder mounts free hinging.
• Decorate the rudder with spray paint, marker pens or coloured tissue and the rudder is completed, ready for assembly.

Fuselage

• Cut the motor mount piece.
• Glue on the WLToys F929 F939 geared motor and propeller.
• Cut out the fuselage piece.
• Decorate the fuselage with spray paint, marker pens or coloured tissue, then groove, fold and glue together.
• Glue the motor mount piece into the fuselage and the fuselage is completed, ready for assembly.

Assembly

• Glue the wing to the fuselage.
• Thread the motor wire and insert into the receiver block.
• Cut a cowling top piece and glue it over the motor and receiver block.
• Glue the rudder mounts into slits made in the fuselage and the rudder is hinged and mounted.
• Glue the horizontal mounts to the underside of the fuselage and the horizontal stabilizer is hinged and mounted.
• Plug and glue in the landing gear and tail skid.
• Install surface horns on the rudder and horizontal stabilizer, hook them up to two pushrods which is then linked to the receiver board.
• Install other details but do up the rigging after test flights.