Demoiselle boxer twin

[josodl1953]

For a very ( very, very) long time I have been considering the build of a Demoiselle model RC plane. The original was built at the beginning of the 20th century by the Brazilian aircraft pioneer Alberto Santos Dumont. A replica was constructed for the film "Those Magnificent Men In Their Flying Machines. It was powered by a Volkswagen four cylinder boxer engine. The original version seems to be flown both by two and four cylinder opposed twin engines.

Following this , I made a design for a two-cylinder boxer engine . I already have a home-built boxer twin ( see avatar) but the main goal was to make a running engine (which it eventually did , 40 years after the first chips..) but it was't meant to "deliver" . To begin with, I started looking what gears I had laying around because they are ridiculously expensive to buy and difficult to make. I found some gears with a reduction of 1:2 and a center distance of 18 mm . Initial bore and stroke dimensions are 18 mm x 20 mm.

The general idea of the engine looks like this:

Crankshaft will be the build-up-type with toolbit crankpins, silver soldered together. Bearing covers on both sides for crankshaft and camshaft bearings

Here are a few pre-machined parts.

Jos

 

[johnmcc69]

Nice start!
Looking forward to the rest of the build!

John

 

[josodl1953]

I made a test rig to check the mesh of the gears . I have two narrow bronze gears an one wide steel gear. The bronze gears will be bolted together on a flange to fit on the camshaft. The steel gear will be keyed to the
crankshaft.

.

 

[josodl1953]

Machining front bearing cover.

Bearing seatings complete.



Jos

 

[josodl1953]

I have been working on crankshaft parts. The crankshaft consists of three main parts, the front part, the intermediate crankweb, the rear part and two crankpins made of 6 mm HSS toolbits. The front an rear crankweb have a clamp bolt for the crankpins. The idea is to assemble the crankshaft with all parts centered with a centering pin. Clamp bolts on the front and rear crankweb are tightened and the crank pins are silver soldered to the intermediate crankweb.

After soldering, everything is taken apart, cleaned , assembled with the conrods , and aligned to minimun runout.
After that, the shafts are machined to final diameters.

So far the theory, practice will show if it all works out.

 

[josodl1953]

I started with drilling and reaming the crankwebs, front and intermediate in one operation, the rear in another.

I made a brass test web to practice machining of the bolthole and slit.

So far, so good..


Jos

 

[josodl1953]

I continued with fabrication of the actual crank, front rear and intermediate web.

After soldering I found that there was a considerable amount of runout so I did some pre-machining before fitting the conrods.

After cleaning up the crankpins the conrods were fitted.

Before finish machining I taped in the conrods to protect them from swarf.

Jos

 

[josodl1953]

I have been working at the crankcase. Machined the holes for the cylinders and a lot of drilling and tapping M 2,5 .

And, at last, the icing on the cake: test fitting of the crankshaft assembly in the crankcase.

It still looks a bit lumpy, but since this build is an ongoing process of fabricating and designing I will remove excess material after the main dimensions are finished.

Jos

 

[Peter Twissell]

Splendid work.
I like your crankshaft fabrication/assembly. I may adopt that for a future engine design.

 

[josodl1953]

First of all I would like to wish all of you a prosperous and healthy 2022. May the chips be with you....

I have prepared the camshaft gears. I made a flanged hub and fitted the two gears with four M2 screws. See sketch and pictures below.

I made keyways in the pinion and crankshaft by drilling a 1,5 mm hole half in the shaft, half in the pinion, see the arrow. I will use a 1,5 mm needle as a key. I did a test assembly with a dummy camshaft to check everything, in particular the gear mesh which was fine.

 

[josodl1953]

It's been a while since I've been working on the boxer twin. Last in-between project was the rebuild of a 49 cc Solex moped engine.

So, now on with the Deemoiselle engine.
I started to work on the cylinder heads, pre-machining and drilling pilot holes for the valve cages.

 

[josodl1953]

I think is is always handy to make a translucent model of a cylinder head to see where all the holes are going, ant to avoid unwanted interference these holes. Rocker arm support is also fitted.

 

[josodl1953]

I also machined the valve cage chambers.

 

[peterl95124]

really like that acrylic head !!!, I always make clear acrylic distributors (on a recommendation from a very wise old machinist) so I can see what I'm adjusting. "may the swarf be with you" !

 

[xander janssen]

I think is is always handy to make a translucent model of a cylinder head to see where all the holes are going, ant to avoid unwanted interference these holes. Rocker arm support is also fitted.

Great idea, will do that for my 2VD5. Not only very helpfull to check the design, but later also as a gimmic to show the internal structure of the engine.