Piaggio P149 – ZU-SFP “FADEC” Engine Upgrade


The Piaggio P-149 was designed by Italian engineer Giovanni Casiraghi. The Piaggio Company in Genova survived post-war years by diversifying its production, a method which led to the success of the "VESPA", and in the aircraft field to the production of several successful aircraft designs. In 1950 Giovanni designed the P-148, an all-metal 2 seater tailwheel trainer. Within months of the release of the P-148, it became clear that a four-seat variant would be a viable option Piaggio. Giovanni was once again called upon to design this new aircraft.

Piaggio P-148

The P-149 made its maiden flight on the 19th of June, 1953. The German forces picked the aircraft as a trainer ahead of the Beechcraft T34 Mentor and the Saab 91 Safir, mainly due to its big cabin, since the plane would also serve as a liaison aircraft for the German Air Force and the German Navy.


The German Forces received 72 P-149’s as unassembled kits from the Italian factory. They carry Piaggio-Dataplatess and serial numbers between 250 and 325 but were assembled in Germany. Thereafter, the type certificate was sold to Focke Wulf and the whole production-line was relocated to Bremen, Germany. Here another 190 of the aircraft were produced for the German military. Those carry Focke-Wulf data plates and serial numbers from 001 to 190. Even the engines had been license-built by BMW in Bavaria (powered by BMW! with engine serial numbers beginning with a "B-".

Focke Wulf P-149

Total production was 280 aircraft. Most of them were military, but a few examples went to private customers. SWISSAIR, for example, bought five Piggios (P-149E's) for their flight academy in Zurich, Switzerland. A few more were delivered to the Uganda Air Force (P-149U's).

P-149E

The last P-149D was retired from the German Air Force on 31 March 1990 at Fuerstenfeldbruck, Bavaria, Germany.


One of the retired German Air Force P-149’s was bought by Werner Haiml, a German national that had settled in South Africa. Werner enjoyed the size of the aircraft but always thought that it was a bit underpowered with the standard 270hp GO-480, so much so that he had a 720 shp Walter 601D Turboprop in 2014. This conversion solved all the power issues but unfortunately, the pilot workload increased dramatically and Werner seldom flew the aircraft.

ZU-SFP with Walter Turbine on the nose

The Walter was removed and the aircraft stood in a hangar until three years ago when a suggestion was made to fit her with a supercharged GSO-480, Justus Venter was approached to design and install an electronic fuel injection system for the new engine.

Here is the progression from Justus’ point of view:


A little more than three years ago I met the owner of this magnificent aircraft. The aircraft was however in a sad state with its engine removed and I had no insight about the history of the particular aircraft up to this point. All I knew was that it had been fitted with a turbine engine and that it was the owner’s decision to have it removed.

The Piaggio P149 is a classic warbird with an underpowered Lycoming GO-480 fitted to the original model. Previous models have been retrofitted with the supercharged GSO-480 engine before with great success. However, there are several issues with this particular engine and it is known as being a complex and sensitive engine that burns a lot of fuel and it doesn’t like to be flown at low power settings.

The owner decided to retrofit the GSO version to this aircraft as well and I was asked to install an electronic fuel injection system as part of the new engine installation. The aircraft instrument panel was also incomplete with all the turbine engine instruments removed. The owner needed a complete engine management and monitoring package that would make it a simple, efficient and reliable aircraft to operate.

The project had various challenges and the relatively unknown complexities of the supercharged geared engine accounted for several of these problems. There was only one way to overcome these challenges and that was by conducting thorough dynamometer testing. One of the other concerns was that there wasn’t any engine monitoring system available that would integrate the engine control system with an in-cockpit engine monitoring or display system. All of these challenges resulted in the design and development of a total solution that would be integrated with the existing aircraft and power supply systems.

This was a project that required every possible resource to ensure success. Throughout my years of engine management system software design and development, aircraft manufacturing and aircraft engine management system implementations and projects, this proved to be the most complex of them all. However, the pilot/power plant interface and operational functionality had to remain simplistic.


The Dyno Testing

Two engines were used for the dyno testing. The first was an old Timex engine which, in case we got things all wrong at first, we wouldn’t damage a newly rebuilt engine. This gave us the opportunity to test various spark plug types and injector configurations without limitations and enable us to fine-tune the ignition timing and fuel maps before implementing it on the new engine. The dyno testing however had its own set of challenges such as cylinder head cooling and unfortunately, the water brake dyno used for commercial vehicle engine testing was way too powerful for the Lycoming engine. As a result, we could sadly not determine the engine horsepower. However, one significant outcome of the dyno testing was that we identified the need for an intercooler.

The Full Authority Digital Engine Control (FADEC) System

The electronic fuel and ignition management system consists of dual redundant Engine Control Units (ECU’s), each with its own set of sensors, dual electronic ignition, multiport electronic fuel injection, redundant fuel pumps, and a dual battery system, all controllable from one single panel that fits the exact space on the Piaggio’s instrument panel allocated for engine instruments.

A custom MGL display unit was used to integrate the MGL RDAC unit with the two ECU’s. Developing this unit was the only way to integrate all required ECU and engine monitoring information without cluttering the FADEC control panel. (a big thank you to Rainier from MGL!) All components and peripherals used for this installation are utilized in the automotive racing industry and exceed the standards that would be required for general aviation.

Advantages

Going the FADEC route always results in people raising their eyebrows and doubting reliability and redundancy. So why would one prefer an electronically controlled engine versus the standard old school engine with dual magnetos. In this case the owner had previous near engine failure experiences with this type of engine, all the related to the carburetor and the over fuelling necessary to cater for the fixed magneto timing and high manifold pressures through forced induction. He needed the 340HP engine but with improved reliability and efficiency.


With the FADEC system it is possible to deliver a precise mixture to each individual cylinder while at the same time managing variable ignition timing throughout the manifold pressure range and the performance and efficiency improvements are obvious.


The intercooler has a significant impact on the air/fuel mixture delivery. A pressure drop through the cooler is unavoidable however due to the massive reduction in air temperature it has a much improved air density and in turn results in improved performance and efficiency. In technical terms it all relates to the engine volumetric efficiency improvement and the benefits are endless.

The Test Flight

The test flight was uneventful and the original fuel and ignition maps obtained during the dyno runs were fairly accurate with only minor tweaking required. We were able to record very valuable data which we will take and analyze before our next flight.


Pilot operation is simple with only the throttle and pitch control levers to worry about. For the test flight, we flew according to the original engine performance chart with the take-off setting at 46 inch manifold pressure at 3400 rpm. Although the mixture calibration at this stage is a still a little high, we saw speeds close to 160kts TAS at 75% power and 150kts TAS at around 65% power, both at 7000ft.


Further tests and calibrations will be done specifically aiming at high altitude testing and who knows, perhaps a 54 inch manifold pressure setting, which in fact, with reduced ignition timing at high manifold pressure and a cooler induction air/fuel mixture would be safe and achievable.

Overall Impressions

It is hard to believe that the general aviation industry is still hesitant to change its views regarding electronic engine control systems. The barriers to change are not the SACAA or regulations but rather a mindset and a resistance to change from the old school components that we have trusted for so many years. Without a doubt, modern technology gave this legendary aircraft a new life.

Thank you to the test pilot, David Toma, that has an understanding for the development that was done and the additional effort is required to prepare for the test flight. He too is now converted!

And thank you to the 78-year-old owner, Werner Haiml, with 750 Focke Wulf hours, and a fresh license and medical renewal, for acknowledging the potential of technological enhancements and its advantages.

This is what experimental aviation is all about.

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