Issue #87 in Contact! magazine is completely devoted to the ROTARY engine.

There is an article on Propelled Engineering on Page 9 plus many informative articles on the ROTARY, some from people who are currently  flying a ROTARY powered airplane.

This issue is available for sale at www.ContactMagazine.com and www.rotaryaviation.com.

Rotary Engine Facts

Description: The Mazda Wankel 13B rotary engine is unique in that it employs two rotors with 3 faces on each rotor which are similar in function to a reciprocating engine's pistons.   The total displacement of the engine, as conventionally measured, is 80 cubic inches. However, because each rotor face completes a cycle of intake, compression, combustion and exhaust every revolution and there are two rotors with a total of six faces, the engine produces a very high amount of power given its small displacement.

 The typical horsepower range in automobile applications have ranged from 150-250 HP. In highly modified race applications over 350 HP has been achieved (with reduction in reliability). The RPM red-line for normal automobile application is 8500 RPM. In this adaptation for aircraft use the upper limit is 6500 RPM which is an operating range well within limits.

Reliability and Safety Benefits of the Design: The design is inherently more reliable that reciprocating engines in that there are fewer moving parts. There are no Cam shafts, valves, valve springs or keepers, no valve rocker arms, no connecting rods or piston wrist pins. Furthermore, there are a number of other features which contribute to reliable and safe operation.

The rotors which revolve on an eccentric shaft (crankshaft) are of an iron alloy while the housing (or chamber) they rotate in is of an aluminum alloy. Loss of coolant and resulting heating will cause  the aluminum housing to expand faster that the iron rotors.  This increases the clearances between moving parts (rotor) and stationary parts (the housing) which greatly reduce the potential for engine seizing due to overheating which can quickly occure with loss of coolant in reciprocating engines.

(In fact, one installation of a 13B in an aircraft did lose all coolant and while the temperture red-lined, the engine continued to function until the pilot could land. A subsequent tear down and inspection of the engine revealed no damage other than a number of rubber seals were damaged due to the excess heat and required replacment.)

The Wankel engine is inherently smoother than a reciprocating engine in that there are no linear to rotational translations as exists in a reciprocating engine. This greatly reduces vibration and inertial load caused by pistons reversing direction in a cylinder several hundred times a minute.

Additionally, the power pulses are more frequent, but of a much lower magnitude than a typical four cylinder aircraft engine.  This reduces airframe and component fatigue effects and also reduces pilot and passenger fatigue. It also lowers the magnitutue of the propeller torsion response to the power pulses.

A number of studies on the predicted TBO of the Wankel in aircraft use have been done by industry and research centres. While the upper limit estimated has varied, depending on a number of conditions, the consensus appears to be that there is no reason to expect any less that the typical 2000 TBO of a certified aircraft engine and some indications are that it could be as much as 4000 hours. Only actual aircraft usage will provide the ultimate answer. The cost of remanufacturing a Wankel is approximately $3500-$4000 US so is cost effective even if the TBO turns out to be only 1000 hours.

In summary, the engine has a number of inherently desirable features and benefits for aircraft use.  The adaptations to make it suitable for aircraft use have been carefully thought out and failure modes thoroughly examined. One has to design the subsystems for fail-safe and redundancy, wherever feasible. The result will be a very economical alternative to the Lycoming/Continental engine installation.