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A Modern FADEC System

Archie Frangoudis
[Archie is a regular contributor to the Matronics Engine List email listserver.]

First of all, I wish to thank Dave Pizza, of GFW Maintenance for arranging this meeting with Mr. Fred Martin, of ADLOG Publications, the famous aircraft record keeping system.  Mr. Martin flew his 172K from 21N to ASH on October 29th to allow first-hand observation of this endeavor, which is a co-operative effort of Mattituck Air Base, and Aerosance.

A fresh 0-320, overhauled by Mattituck Airbase, was installed and fitted with the Aerosance modifications, and after a few hours of local flight, flew to OSH for “Airventure 99”.

This FADEC (Full Authority Digital Engine Control) system uses modern technology previously unused on aviation piston engines.  (remember the PFM?)  The FADEC system began in the automotive industry where it is well proven, airlines and the military incorporate it on turbine powered aircraft.

At first glance, I noticed that the bulky, heavy mags were missing, the spidered injector nozzles were fitted with wires, ala automotive, and HEY! WHAT”S THIS?  a carburetor also? How can this be?  Upon further investigation, no fuel line to the carb is seen.  Well, rather than re-invent the wheel by designing an air throttle body, the carb is gutted, and utilized as an air control. This also eliminates intake redesign, keeping costs minimal.  KISS.

The system consists of two small boxes, each of which contains two computers, a harness, sensors, fuel injectors, and an annunciator panel. Each computer controls one cylinder, and serves as a backup for a second cylinder, providing a fail-safe mode.

The computers calculate optimum pulses for the injectors and ignition timing based on speed, pressure, temperature, and piston TDC location in each cylinder.  When the engine is started, the computers calculate engine temp, primes the cylinders, and adjusts the mixture according to the above, including throttle position and altitude changes.  At cruise, changes are constantly monitored and adjusted for fuel flow, spark advance, (or retard), individually in each cylinder.  This is done through feedback on EGT, CHT, fuel pressure, manifold pressure, manifold temperature, and RPM.

The annunciator panel in the cockpit indicates high or low temp & oil pressure, a channel loss to a cylinder, fuel pump failure, or power source failure. Also incorporated is a data port for downloading all monitored profiles @ every .5 second for diagnostic profiles and computer performance.

Total weight increase for the aircraft is approximately 14 lbs., largely due to the use of a backup power source- small, secondary battery.
With final testing, and FAA certification, sales and installations could begin in the spring of 2000.

In summary, the FADEC system is a first step in updating 80-year-old technology.

  • Fuel consumption improved up to 15%
  • Tests indicate a 10 horsepower increase
  • No magnetos
  • No manual mixture control needed
  • No manual primer needed
  • System redundancy
  • No carb heat required
  • Smoother running
  • In a hypothetical, devil’s advocate question to Mr. Martin:  “What will happen if you do not receive FAA approval?”  “We will have to revert to a carb and magnetos, but I would not look forward to it.”

    OK, now the question on everyone’s mind: How much?  Current projected cost is around $4000. minus installation (and could possibly be less).  Not bad at overhaul time, just deduct the cost of mags and carb or injector from the overhaul, and it becomes very attractive.

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