Originally Posted By: moklock
Originally Posted By: caveatipse
Let me be pedantic and technical just for a moment. Technically, the term "rotary engine" refers to those aircraft engines where the pistons actually rotate around the crankshaft, while a Wankel engine is what Mazda uses.
FYI: Those aircraft engines are "radial" engines.
No. Radial engines have a fixed crankcase with fixed cylinders and the crankshaft rotates, just like in an ordinary V-type, inline, or opposed piston engine. The cylinders are arranged in a circle (or multiple circles the P&W R-4360 had 4 circles of 7 cylinders each) around the crankshaft. Each "row" has one piston which attaches to the crank with a more-or-less conventional looking rod, called the "master rod." All of the other cylinders in that row use "articulated rods" which attach to the master rod via pins similar to a piston wrist-pin.
Cut-away 4-row R-4360:
http://www.youtube.com/watch?v=zW9irTeaAK8
Radial engines were used in many world-warII aircraft and in 50s airliners. B-17s, B-24s, Hellcats, Bearcats, Constellations, and P-47s were all powered by radial engines.
A
rotary engine is one in which the crankshaft is bolted to the frame of the airplane, and the propeller is bolted to the crankCASE. The whole crankcase *spins* as the engine runs As weird as that seems to the modern mind, it was fairly common back in the World-War ONE time frame.
http://www.aviation-history.com/engines/rotary-theory.htm
In this video, you can see the finned cylinders rotating along with the prop:
http://www.youtube.com/watch?v=88p2xSOrEK8&feature=related
And I agree- the things Mazda builds are properly called Wankel engines, but the term rotary is common-use and since no one is building the original type of rotary engine anymore, fighting that misnomer is probably a lost cause.