This short video clearly shows the relationship between crankshaft, conrods and cylinders for the rotary engine.
In rotary engines the crankcase rotates with the propeller. The conrods rotate about the crank pin. These two rotational axes are parallel and half the length of the stroke apart. In this way the early engines removed the need for a heavy flywheel by using the mass of the engine as rotational inertia.
Five Cylinder Rotary Engine Plans
The pdf download is a 15 page document of technical drawings, images and lots of notes on the engine design.
The model rotary engine runs on compressed air or CO2 and hence only has the rotation of the crankcase, cylinders, pistons and conrods in common with the fullsize engine.
An early le Rhone engine is a great example of this design put to use. This 9 cylinder rotary internal combustion engine powered many of the WW1 aircraft.
Le Rhone 9c was a 80hp rotary made from 1916 and powered aircraft such as the Sopwith Pup.
- Bore: 105 mm (4.13 in)
- Stroke: 140 mm (5.51 in)
- Displacement: 10.89 L (664.47 cu in)
- Diameter: 0.945 m (37.2 in)
- Dry weight: 121.5 kg (268 lb)
- Operation: Four-stroke
- Fuel: Gasoline
- Max speed: 1300rpm
The impact of the rotational inertia on the flying characteristics is quite another story. The large gyroscopic effect meant that the aircraft turned one way better than the other. Increasing the power of the engine tended to increase the mass and the rotational inertia. Hence there is a natural limit to the size and power of these engines.
The total-loss oil system meant they were inefficient and the engines controlled using the ignition system tended to oil up the spark plugs.
The pinnacle of the development of the rotary engine was the Bentley BR2.
Bentley BR2
Initially asked in 1914 to study an overheating problem in rotary engines, Captain W. O. Bentley, an established car designer, developed a new and more efficient engine, with a weight-saving effect realized by careful design and the use of aluminum wherever possible. Equally important was the lower cost.
- Type: 9-cylinder rotary
- Bore: 5.51 in (140 mm)
- Stroke: 7.09 in (180 mm)
- displacement 25 litre
- 220 kg dry
- Overhead valve
- Cooling system: Air-cooled
- Power output: 230hp @ 1300rpm
- Fuel consumption: 20 gallons per hour
- Oil consumption: 16 pints per hour
Image shows a 1/6th scale model of the BR2 by Les Chenery.