M-20's Unique Advances

The M-20 Turbo system is quite similar in most ways to the turbo-normalized systems used for long years of grueling helicopter service by Enstrom and by Piper on its Seminole and Comanche lines. The simplicity of design shared by the three companies leaves the engine exactly as built by Lycoming, an engine which has earned possibly the best reputation for recips in aviation. The major components like inter-cooler, pressure safety valves, turbocharger, fuel injectors, pumps and lubricating systems are all venerable standard aviation items.

What is unique about M-20's system, in addition to the care in fit-up of the components to make them appear as if they were born under the Mooney cowl, is the attention to engine cooling.  There is a thermal match created among the turbo compressor, intercooler, "leaking" fixed wastegate and the meticulous attention to engine cooling air distribution in what M-20 calls its "after-cooler". All these features come together to keep the temperatures well within Mooney's and Lycoming's ideal range.

Why no one else had done this remains a mystery because the opportunity for cooling has always existed on every airplane. That they could not have proven the results in flight is another matter. The invention by Cesar Gonzales of the CEDI (Cessna Engine Detonation Instrument) computer was for testing alternative fuels when the petroleum industry began its threat to cancel production of 100LL gasoline. Cessna and their aircraft owners stood to be the biggest losers from inferior fuels.

For the M-20 requirement, Cesar's test was reversed to make it an engine test. Using a known fuel (100LL), created the means for testing the detonation limitations of the engine.  Because of the extreme sensitivities of the CEDI and Cesar's software, an engine could be tested in all its worst flight conditions with a generous 11 second warning before the onset of "incipient detonation".  The FAA eagerly accepted this advancement into realistic testing in actual flight conditions.

The enormity of the leap ahead in engine testing is more easily understood when you consider that the aviation engine manufacturers are still using World War II laboratory simulator tests grand fathered into their certifications and their Pilots Operating Handbooks.  Their engines are run on a test stand in the make believe world of simulation.  Their detonation testing is capable of measuring only what happens in isolated single cycles.  In full power tests of the IO-360 engine there are 10,800 cycles per minute.  Obviously, one single cycle tells little of value.  A good cycle could be surrounded by thousands of detonating cycles which could go undetected.

In contrast, M-20's turbo was tested on 100% of the 10,800 cycles per minute and the FAA tests ran an average of 2 hours each.  That is better than 1,296,000 continuous perfect cycles in each of two official tests.  In addition to these more than 2.5 million cycles in the FAA tests, add 7.5 million cycles in M-20 Turbos' preliminary tests with not a single detonation event.  M-20's turbo system was the first and is yet the only turbo'd engine FAA tested and approved in this advanced manner.

Also unique to M-20's design is the use of high compression pistons for maximum performance, since detonation is not a problem.  Another unique feature is the direct control of the compressed air.  All others turbo systems put their controls in the highly corrosive exhaust gas to dump excessive turbo drive pressures.  We put our control in the fresh air for direct control.  This makes ours just about maintenance free, while the exhaust controllers are typically the most costly maintenance item on other turbo'd airplanes.

Wouldn't you rather have the quality of an M-20 Turbo'd Mooney?

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