crankshafts and rotary engines

WW1 and some WW2 aircraft have piston engines with a large number of cylinders arranged radially in a circle. The prop is mounted on a shaft which appears to be central.

How do you connect 7 or 9 pistons to the crankshaft at essentially the same point? I’ve looked in books, I’ve looked on the net, I’ve sneaked under the rope barriers in museums for a closer look, but no joy. I have a mental image of very flat connecting rods like steel rulers, but it doesn’t seem likely.

Some of the engines (gnome engines?) appeared to have the crankshaft fixed and let the cylinders spin around the axis. How can the valves work? How d’you get fuel into the cylinders?

Here might be just what you are looking for concerning radial engines. As you can see, the top connecting rod is fixed to the shell (sometimes known as the big end) that contains the journal bearing, the other six rods have pivots at their bases to allow for the needed angular change over the path that the crankshaft journal descibes under rotation.

I have read of an engine that might be of the design in your second example. The migrating combustion chamber is what I recall as the terminology. This was almost certainly found in a modeling magazine, which is not to say that larger versions have not been built and test run. If you do a Google search on “migrating combustion chamber”, the fourth main entry contains these words. My patience expired while searching for the correct manufacturor or topic that led to the specific engine and/or details.

Please post back if the details are found.

A RADIAL engine has the cylinders arranged in a plane perpendicular to the crank shaft. The engine case is fixed to the structure. It uses a connecting rod as Bawdysurfer has illustrated. A ROTARY engine has the crankshaft fixed to the structure while the engine case, with attached propeller, rotates. Rotary engines used an arrangement of collector rings to transfer fuel to the cylinders and still allow rotation. IIRC, the throttle plate and carb were on a fixed portion of the engine and induction may have been through the hollow crankshaft.

Cams and pushrods control the valves in either engine. The cams, one for intake and one for exhaust, are machined into a bell gear that rotates at one-half engine RPM (for a four stroke engine). As far as the valves are concerned it matters not if the housing rotates or the shaft rotates.

Radial engines always have an odd number of cylinders in each row. Multiple rows are common. The largest I can recall was a four-row engine displacing 4360 cubic inches. This engine was used on airliners such as the Constellation.

GaryM, good fellow, I am at a loss as to how your description applies regarding the rotary engine, inasmuchas the OP referred to cylinders, of which the traditional Wankel style rotary has none. Further, a rotary I disassembled had no pushrods or a cam, but accomplished it’s needs somewhat like a two cycle as ports were covered and exposed during rotation. This was the best I could find, and is by no means indicative of a complete engine, but might cover some of the issues.

Good will and all, but I believe matt was thinking of something different.

The one commonly found on WWI aircraft looks like a Radial but the crankase rotates with the prop as described above.

The more modern Wankel Rotary is a completely different beast.

Thanks Shiva!
In the OP, the mentions of pistons, as well as WWI and WWII, led me to refrain from mentioning the Wankel. I’m not sure that the Wankel is correctly even classed as a rotary. It’s more of a “neither fish nor fowl” situation. I think the Wankel is in a class by itself as it doesn’t even have a “crankshaft”, although it has an output shaft, there are no cranks.

IIRC, the Gnome mentioned in the OP was a ROTARY engine. One problem caused by the mass or rotating metal on the front of the aircraft was gyroscopic precession. As the aircrafts attitude changed, a movement offset by 90 degrees occured.

It was this property of huge precession torque that made the Sopwith Camel such an effective fighter in WWI as nothing could turn so rapidly.

Unfortunately this same property also made it one of the most dangerous aircraft to land as any sudden change in throttle, like to counter a crosswind would flip the aircraft over - not an ideal situation when you are just feet fro the ground.

Boy did I miss on this one.

Sorry all, and particularly, GaryM.

Thanks for the replies everybody. Bawdysurfer, that jpeg was exactly what I was curious about - thanks very much!
gives some detail about the gnome engine, including those designed with intake valves and later designs without them. An interesting feature was the lack of a throttle - the engine ran flat out normally and was slowed by shutting off ignition and splurging unburnt fuel-oil mixture everywhere.
casdave - you’ve given me Biggles flashbacks! I can remember a story where he won a camera gun duel with an American friend by using the engine torque of his trusty Sopwith Camel to out-turn the American’s SE 5…

Matt wasn’t the SE5 a British aircraft ?

It was well known as Albert Ball’s steed.

Yes the SE 5 was British, and was acknowledged to be one of the best fighters of the war. It just happened to be the opposing aircraft in the story. And it used an in-line engine.