Aviation engines have maintained the same basic design for decades, and some would argue, have advanced little in that time. The prospect of capturing the aviation engine market with an advanced engine design must have been appealing to the Porsche engineers and marketing team. The basic design of the well proven and venerable flat six 911 engine was an ideal platfrom from which to develop an aircraft engine. Starting with the existing and proven Carrera 3.2 litre 911 engine extra reliability and redundancy was incorporated to accommodate the demanding aviation environment.
The PFM Porsche Flug Motor is born:
This was not the first aviation engine that Porsche had developed. The PFM engine however showed the greatest promise in taking general aviation technology to a new era of sophistication. Three normally aspirated engines, N01, N02 and N03, as well as a fully certified turbocharged T03 version, were developed at the Porsche Weissach Plant in the mid 1980's. A dedicated Aviation Department with a fully operational test cell were used to get this engine to certification standards, not a mean feat given the complex regulatory process that is required to get approval.
1. Dual systems were incorporated into this engine. Twin Magneti-Marelli electronic ignition systems with dual spark plugs were used. Electronic ignition was a novel design feature for an aviation engine and still today the alternative magneto driven ignition sytems are the norm.
2. To cope with the all electric nature of the ignition systems, dual alternators, dual batteries and a dual bus system was used in the aircraft.
3. The fuel management was similarly unique for an aviation use with the reliable K-Jetronic fuel injection system adapted from the car motor industry. A fuel-air mixture valve was incorporated in the induction sytem allowing for optimal automatic adjustment with altitude. The mixture control was no longer require and single lever engine managment was now possible.
4. So that a faster revving small displacement engine could be matched to a slower moving propellor a 1 to 0.442 reduction gearbox was used. A revolutionary rubber damper was incorporated between gearbox and engine to further improve the vibration qualities of this already smooth running engine.
5. The air cooled 911 engine already had a belt driven fan mounted on top of the motor so engine cooling was not a problem. Equally, the so called shock cooling seen with rapid descents in conventional ram air cooled engines was not of concern as engine cooling was proportional to engine speed.
6. Overhead camshafts are usually chain driven in 911 cars. To add extra reliablilty in the aviation version, gear driven cam timing was incorporated.
7. A three point engine suspension system was used to dampen engine vibration
The PFM became one of the first to apply a FADEC (Full Authority Digital Engine Control) system.
Due to the complex regulatory environment it was, and still remains, a very difficult task to initiate change in basic design features. Special conditions were imposed by the Amercian FAA before certification was achieved
Hence, 20 years later the Porsche PFM engine still remains as one of the most advanced general aviation engines. Only now are alternative engine designs being considered, driven by the desire to find an alternative to Avgas as well as attempts to modernise GA engines. The Porsche aviation engine was the right idea at the wrong time and it is a great shame that it did not continue.
Porsche N01 and N03 aviation engines were introduced into a number of selected Cessna 172/182 airframes. The Mogas approved N01 engine was used in the Robin DR400.
A modified turbocharged 930/67 3.3 liter Porsche engine was used in the Skyship 600 and the normally aspirated 930/01 engine used in the Skyship 500.
However, the best known combination has been the PFM 3200 N03 engine combined with the Mooney airframe. Mooneys are known for their speed and sportscar like performance. The marriage with the sports car derived Porsche engine seemed a marketing gift that couldn't fail. But fail it did.
Two M20K short body and 41 long body M20L Mooney aircraft were produced. The higher cost without any speed advantage over the Money 201 airframe saw slow uptake of the new technology. At the same time there was a downturn in general aviation activity and a change in philosophy of those overseeing this project. Production then stopped in 1989.
Post production support:
Despite the small numbers of planes Porsche provided support for the engine in Europe and America.
Gary Butcher provided an American wide service visiting owners and providing technical and educational support. He was a great ambassador for Porsche and reflected the then philosophy of the Company in standing by their product. That philosophy later changed and the aim became one of grounding all Porsche powered planes in view of evolving liability concerns.
One owners experience:
Porsche initially lived up to to its reputation of providing first class service and support.
Under the Type Certificate responsibilities of an aviation engine manufacturer any defects in design need to be investigated, rectified and communicated to interested parties.
When engine gearbox vibration problems were identified a fix in the form of an alternative 3 bladed propellor was initiated and fleet was refurbished with a new MT propellor to replace the original Hartzell prop. In later times this commitment waned and potential problems from flaws, such as valve spring design, generated a temporary fix in the form of 500 hourly valve spring replacement. Promises of permanent solution did not eventuate, a more effective solution being to eventually withdraw all support with promises to repurchase all engines and provide an alternative.
Something changed with regard to the Company attitude to this engine. In 1999 notice was given that parts supply and support would finish on May 31 2005. Owners were offered two alternatives, either sell the plane for conversion or participate in a subsidised Continental IO550 engine conversion program through Modworks in Florida. No other options were entertained, spare engines were not for sale, spare parts were not available to stockpile, technical data was not forthcoming and after market parts supply was not an option.
Porsche was serious about getting all these engines out of the air. All owners co-operated to achieve this end and engine conversions commenced.
Under the direction of Tim Coons, who had extensive experience in Supplemental Type Certificate design, a conversion program was initiated to replace the Porsche N03 engine with a conventional aviation engine, a normally aspirated Continental IO550. The aim was to convert the Porsche Mooney into a modern day Ovation model. Cruise speeds increased to 185+ knots from the 155 knot range of the original PFM engine. Sadly, the weight carrying capacity did not increase to match that of the Mooney Ovation.
Ironically, the PFM Mooney conversion was named the "Phoenix Formula Mooney" or PFM Ovation.
With the May 31 2005 deadline looming engine conversions were underway. Around 8 conversions had been completed before Hurricane Charley hit Punta Gorda Florida August 13 2004. A number of Porsche Mooney aircraft were destroyed and many others damaged. The hurricane effectively destroyed Modworks.
The engine conversion program did not emerge from the "ashes" of this disaster.
Under the supervision of Dennis Bernhard at Lone Star Aero in San Antonio 2 damaged planes were repaired and completed.
The remaining owners have been left to sort out their own solution.
Many planes continue to fly with owners left to resolve ongoing parts supply and technical issues. This is a difficult task under the demanding Aviation Regulatory environment.
Porsche did hold the Type Certificates for this engine and was responsible for airworthiness and safety. Despite earlier claims that TC's would be retained, the European Type Certificate has been surrendered to the European Aviation Safety Authority (EASA).