How One Machine Shop is Resurrecting WWI Rotary Engines

A Sopwith Camel with rotary engine. (Image courtesy of The Canadian Museum of Flight.)

World War I saw the first use of aircraft in large-scale conflicts and the battlefield has never been the same since. These early airplanes used rotary engines, in which the crankshaft remains stationary while the rest of engine rotates around it.

You won’t see many original WWI aircraft engines still in use today, but if you happen to visit a small machine shop in New Zealand, you can order a brand-new one. In addition to making parts for vintage aircraft and general machining services, Classic Aero Machining Service is building 1915 Gnome engines using modern manufacturing techniques.

A brand-new Gnome rotary engine. (Image courtesy of Classic Aero Machining Serivce.)

“Our idea was to produce original rotary engines which were safe, reliable and affordable,” said Tony Wytenburg, chief engineer and managing director of Classic Aero Machining Service. “I’ve been in business since 2004; I can’t say I enjoy everything about running a small business, but I do take great satisfaction from making parts. Being able to make a lot of parts which, when finished, is a running engine is one of the most satisfying things I’ve ever done.”

ENGINEERING.com had the chance to get Wytenburg’s insights on this unique project.

How did you design the engine? Did you work from original blueprints?

We reverse-engineered an original engine. The parts have to be drawn in CAD (we use SOLIDWORKS). For our CNC mill, we use GibbsCAM so we can import the CAD models and use them to generate the G-code. For our CNC lathe and manual machining, we use CAD models to produce working drawings.

What are the horsepower and torque specifications?

It’s 115 horsepower and around 580 lb ft of torque. It swings a wooden prop that’s 104 in in diameter.

Are you casting the engine cylinders or machining them?

The cylinders are machined from billets, as is most of the engine, including the crankcase. The only casting on the engine is the oil pump body. We’ve also used forged aluminum pistons, which use a standard car piston forged blank.

Machining the rotary engine case. (Image courtesy of Classic Aero Machining Service.)

What lubricants do the engines use?

We’re currently using castor oil for lubricant, which is what they used back in 1915. It’s a constant-loss oil system and uses 10 pints an hour. I’m keen to try some more modern oils, but that will have to wait until we have enough time and spare cash. We need to be in the position where, if that doesn’t work, we destroy our own engine and not a customer’s. So, for now, we’ll stick with what works.

What about carburation?

We’re using standard fuel; we’ve tried both AV gas and regular automotive gas and both work well.

How are the spark plugs fired?

Originally, a magneto was used to provide the high tension for the spark plugs. I did try to adapt an electronic ignition system, but we couldn’t get that to work, so we worked with an electronics company and built our own system. High tension comes from the ignition and is distributed through a communicator via piano wire to the spark plugs. The electronic ignition provides a good spark, which makes the engine easy to start and we haven’t had issues with spark plugs fouling.

Testing the Gnome rotary engine. (Image courtesy of Classic Aero Machining Service.)

We had a client who asked if we could fit a starter motor to his engine. Having seen a hand-started fitted to an original engine from a seaplane, we couldn’t see why it wouldn’t be possible. Having done that successfully, we decided to make another starter which we’ll use for all the engines we make. It fits on the standard engine and we can remove it if the customer wants the original “hand swing” starter, but it’s a whole lot safer for myself and my staff when we are test-running the engines.

How does engine life compare to the originals?

We’ve been careful with our material choices, so we use forged aluminum pistons instead of the original cast iron and the valves are stainless steel. 4340 has been the choice of all the high-load parts. The original engines were not known for being reliable; rings jamming down the side of pistons was a common problem.

Are these engines just display pieces, or are they actually powering aircraft?

The engines are going into replica aircraft. We currently have one engine flying. Our second engine will be on display and running at the Dawn Patrol in Dayton, Ohio, Oct. 1 and 2, 2016.

To read about another retro-engineering project, check out how the DeLorean Motor Company is putting the iconic car back into production.