Scale a Le Rhone Rotary Engine - RC Groups
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Dec 04, 2009, 12:20 PM
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Freddie B's Avatar

Scale a Le Rhone Rotary Engine

I am scratch building a small 32" Sopwith Pup for mainly indoor and light wind day outdoor flying. There are not a lot of scale details on old WWI biplanes except for cockpits, rigging, and engines.

I know you could probably buy a plastic or resin engine. You could print one out on card stock with good effect. I like to build and I also like to think outside the box. If you like what you see maybe you might try something similar. Maybe it will spark your own creativity. Either way I hope you enjoy.

My goal hide the electric motor, fill the cowling with scale 'effect', give the illusion of a real engine. Also keep the motor cool, and route the wires without them showing.

Parameters: 32" span, scaled up from 3 views, making my Cowling 3 13/16" in diameter (just over 3 3/4"). I decided on a maximum engine diameter of 3 3/8" including rocker arms and springs.

First step is some research to find some photos on the internet of a Le Rohne 9, 80 HP rotary engine, and same mounted on a real antique Sopwith Pup. Here is what I found.
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Dec 04, 2009, 12:35 PM
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Freddie B's Avatar

Step 2.

I find a publishing program such as Printmaster, to be my good friend. I took the head on drawing and scaled it to the size I wanted using referance lines to add circles, etc for alignment on assembly.

To me 'Scale" is an illusion created to give the effect of real, but not too much so that it over encombers my creativity. Light matters, but heck a WWI Biplane needs nose weight anyway.

I started with a Dr. Pepper soda can for my crankcase front. Simple layout of 45 degree angles, center line, and inside/outside diameters of my cooling slots. Then drew slots to just over 1/8" width. All done with a compass, paper, small flex ruler, and cutouts that fit the inside diameter of the can bottom.

I filled the can with Plaster of Paris to solid up the can and to hold the part while cutting, The entire 'machining' job was done with my favorite tool, a Dremel and a 1/8" diameter carbide rasp from a Zip Saw, and a drill for the prop shaft hole.
Dec 04, 2009, 12:44 PM
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Freddie B's Avatar

Step 3

I added 'nuts and bolts' to crankcase ring with small dots of 5 min. epoxy and micro-ballons, waited 2-3 minutes, dipped K&S 3/32' square tubing in alcohol, and pressed the nut shape. Immediately I did the same with a 1/16" diameter tube dipped in alcohol to form the 'nut' face and the protruding 'bolt'.

A little scraping at the edges with my #11 blade dipped in alcohol cleaned thing up nicely. Then I primed the part in this picture, then painted it gray.

Looks like bolts and the whole thing weighs so little it doesn't measure on my grams scale.
Dec 04, 2009, 12:53 PM
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Freddie B's Avatar

Step 4

Any 'older' modeler that has reviewed old plans or built in the 'olden days' will remember wrapping wood dowel or tubing with thread to make cylinder fins. I used 1/2" hardwood dowl, drilled a 3/8" hole through with a Forester bit, wrapped with (2) strands of thread, held one tight, unraveled the second, and hit it with thin CyA. Cut off at 5/8" long for my scale of engine.

Needed 5 pieces for 9 cylinder halves. Painted them, and split them in half with razor saw. See picture for simple tool to guide saw blade to keep things even.
Dec 04, 2009, 01:03 PM
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Freddie B's Avatar

step 5

Made some rings for mounting the cylinders on, and for mounting to my motor mount/firewall.

Smaller ring is 1/8" light-ply, with a 1/32" thick balsa ring CyA'ed on edge 5/32" tall, note the two bosses for screws to mount to firewall.

Larger ring is made from 1/16" thick Basswood (large popsycle sticks) made in 5 segments. The little lands are small pieces of Basswood too, one at each segment glue joint, and another if needed to support cylinder area on assembly. (this ring is upside down from position used at assembly). Could have made from 1/8" light-ply but I like working with the Basswood better. It's stronger in ways while handleing and very inexpensive.
Dec 04, 2009, 01:03 PM
Prop Buster Extraordinaire
philba's Avatar
Very nice job Freddie - I bookmarked this thread for when I might do this.
Dec 04, 2009, 01:17 PM
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Freddie B's Avatar

Step 6

Need those 9 intake manifolds made from polished copper tube. Well balsa is fine but I wanted to try something new to me and not waste so much time making 9 curved, rounded pieces near the same size.

So I made one. CyA the outside to watter proof and harden. Made a simple balsa box with 1/4" tall sides that would fit 6 parts in. Filled it with RTV Silicone, YES, RTV Silicone sealant/glue! Next trick was to 'wet' the plug. Water works but saliva is my friend. Coated the plug with 'liqued' and pressed it into the silicone. A little here a little there, som soothing with a popcycle stick, a little more pressing and, Wa-La.

Let it dry (12-24 hours).

Don't let the liquid plastic fool you. It shrinks too much to be usefull. Back to the Micro-Ballons and epoxy for casting my parts. I did put a small, curved length of >022 diameter wire in the middle of eack casting to solid thing up and keep them from bending. sounds harder than it really is.

After cure, a light wipe with alcohol gets the slime and sticky fell off the parts, a light sanding prepares for paint. I used 'Copper Leaf' smelly oil based paint I found at Home Depot. Later 'weatherd them with two colors of gray craft paint, and sealed them with gloss Krylon clear. See future photos, got a fairly good looking polished copper tubing look, with age/wear marks.
Dec 04, 2009, 01:28 PM
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Step 7

Ok, I made some small parts next. Valve springs are very small wrapping wire from Radio Shack, hand wrapped on a straight pin, cut to 5 coils in length. Straiht regular head straight pins will be the 'valves'.

Cylinder heads are 3mm Depron sheet, cut to 1/2" diameter with a sharpened piece of 1/2" K&S tubing. Cut them in half, you will see you will need 18 'halves' before we are done.

Rocker cams are 1/8" dia Dowel, 1/16" thick Basswood, CyA'ed together. I made two roker cams attached to each other at the middle and used the Dremel and a piece of 280 grit sandpaper to shape then razor sawed to part. These 2 joined were 1/2" long, (1/4" long each, split), and the stock was cut 1/8" wide to start. I just drew a center line and 'eye-balled them'.

I'm getting used to my reading glasses at this scale!
Dec 04, 2009, 01:35 PM
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Step 8

I had marked the rings for 40 degree seperation of cylinders, pinned them to the master drawing for alignment and assembly.

Glued 'half' cylinders to the rings with epoxy drops. I filled all gaps with epoxy and micro-ballons.
Dec 04, 2009, 01:41 PM
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Freddie B's Avatar

Step 9

Added 'spark plugs' and 'plug wires'.

Plug is a regular straight pin, wrap 1 coil of stripped wire at top (Red Wrapping Wire, Radio Shack), and 1 black glass bead each. 1 drop of CyA holds plug together. Cut pin to about 1/8" past the bottom of the glass bead.

Drilled a .8mm hole in each cylinder, and a drop of thin CyA at each hole holds the spark plug in place. a .8mm hole behind each cylinder hold the other end of the wire (CyA'ed)
Dec 04, 2009, 01:45 PM
Addicted to building...
Freddie B's Avatar

Step 10

Glue on the 'heads'. 1/2 circles of 3mm Depron, cut with a sharpened 1/2" dia. tube. I used 5 minute Epoxy. Pre-painted sides of heads so it would be easy not to get gray paint on cylinders.

You can now see my cast manifolds, painted 'Copper-leaf', weathered, gloss clear coated, and ready for assembly.
Dec 04, 2009, 02:12 PM
Registered User

Beautiful.. but will it survive spinning at 7K rpm?

Or is the intent to build a really pretty dummy rotary that sits still? Sorry if I missed the answer.

Dec 04, 2009, 03:38 PM
Res Ipsa Aviatur
Longhorne's Avatar
That's a fair question.

Regardless of the answer, this motor is a work of art. Thanks for sharing your techniques!

Dec 04, 2009, 04:09 PM
a.k.a Maltone
Pat Lynch's Avatar
Beautifully crafted little emgine Freddie - I love it
A few of us have made a short sleeve in the 'crankcase' front that slides over the motor shaft - it turns freely on the shaft but isn't subject to acceleration or max revs. Only works with some longer shaft motors.
Your motor will look good whether static or turning...

Dec 04, 2009, 04:54 PM
Registered User
Beautiful. Thanks for putting this up here!

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