Crankcase for the Five Cylinder Rotary

5 cylinder rotary sketch

The idea was to build a small 5 cylinder rotary engine that runs on compressed air, the crankcase for the five cylinder rotary would be another challenge. This is a rotary engine where the crankcase rotates with the propeller and the crank remains stationary.

The main image shows my initial sketches. I will try and improve these and add some dimensions, trouble is I tend to create a drawing that allows me to get started and then the design gets developed further as I machine parts.

This shows the Unimat 3 milling attachment mounted to the cross-slide of my Hobbymat lathe. You can just make out the indexing disc attached to the rear end of the headstock.

The basic milling operations involved creating the 5 faces. Once complete each face was then drilled in the centre of the flat face. 9.5mm holes drilled ready to accept the cylinders.

The crankcase for the five cylinder rotary in a more complete state with the centre machined. This shows the holes ready for the cylinders (larger holes) and the smaller holes that will be tapped 5BA and will be the main air inlet points for each cylinder. The air will be supplied through the centre of the crankshaft with a hole drilled lining up with these holes in the crankcase.

This engine uses a phosphor bronze bearing and a steel crank. The nose of the crankcase was kept reasonably long to give enough bearing support for the engine and propeller.

The engine fits neatly in the hand and is roughly 85mm in diameter including the heads. The crankcase is quite large to allow the master conrod to operate.

About Nigel 336 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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