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Porsche 678/4

Porsche-678-1
Porsche 678

 

In post war Germany, General Aviation flight was not permitted until 1956.  At the time of this rejuvenation, the Porsche 678 aircraft engine was being developed. This was based on the 4 cylinder Porsche 356 car engine.  This air cooled engine was modified for the aviation environment.

In the 1950s, European light aircraft builders began adapting the air-cooled automobile engines from the Porsche 356 and Volkswagen Beetle into aircraft engines with a series of limited modifications. Porsche cooperated with some of these builders and produced a series of factory-built engines for about six years between 1957 and 1963, the Porsche 678 series, beginning with the 1,580-cc 678/0. These relatively small engines produced between 55 and 70 horsepower, depending on the version. The 678/4, is the last and most powerful of the four-cylinder Porsche aircraft engines, all of which were based on the 356 automotive engines. These received type certificate No. 7E2 issued on November 15, 1960 as Model 678/4 Type 4H0A.

At this time Alfons Pützer was also developing the Elster A airframe, powered by the 52HP 678/3 Porsche engine.  This was followed by the Elster B version powered by the 75 HP Porsche 678/4 engine and the Rolls Royce Continental C-12F and C-14F engines.

 

Porsche-678-2

 

The engine differs from the car engine in many small ways, but its major departures are dry-sump lubrication, dual distributors (or magnetos, as an option) with dual spark plugs, different engine mounts, and a reduction gearbox to reduce propeller rpm to an effective range; gears could be specified as 1.46:1, 1.70:1, 1.98:1, or 2.12:1. A 12-volt electric starter and similar generator are fitted, the latter run off a dual v-belt. The external oil cooler uses a pair of 356 engine oil coolers on a special casting, and the dry-sump oil tank is connected to the pump by flexible lines. A rudimentary exhaust system piped gasses out of the fuselage.

The 678/4's German airworthiness certificate was granted in May 1959, and FAA approval came in October 1960. Porsche’s 1959 list price for the engine (and gearbox) was $1,379. Production reportedly ended in 1962; production numbers are unknown, but it seems likely that only about 100 were made.

Earlier versions of the 678 used a low-profile cooling shroud thus could be installed in the aircraft’s nose and cooled by free air blast. The 678/4's larger-shrouded fan air-cooling system, similar to that of the car engine, was only for enclosed rear-fuselage installation, using a pusher-type propellor, but such applications were rare.

The 678/4 was fitted to the Rhein-Flugzeugbau RW-3, a pusher-type motorized glider with retractable tricycle landing gear, seating for two, and optional wing extension. Its propellor was in the vertical tail just ahead of the rudder, with the engine set just behind the cockpit. The type was first built in 1958, and apparently only 22 aircraft were completed.

Using a Porsche engine to make an aircraft go is not a brand-new idea witness the RW3 motorglider built in Germany by Rhein-Flugzeugbau GmbH. It is powered with a Porsche 678/4 aircraft powerplant, a flat-four opposed piston engine with a reduction gearing of 1.981, a takeoff-power rating of 75 hp at 4600 rpm (propeller 2320 rpm), and max continuous power rating of 65 hp at 4500 rpm (propeller 2070 rpm). Leaned out, it delivers 55 hp at 4100 rpm (propeller 2070 rpm), with fuel consumption in economy flight mode 3.7 US gph.

 

Model 678/4 Type 4H0A
Displacement: 96.4 cu. in.
Bore and stroke: 3.248 x 2.913 in.
Compression ratio: 9.0:1
Reduction gearing: 1.98:1
Weight (dry): 250lb.
Max. continuous, 70hp., 4500 r.p.m. at S.L.
Takeoff (5 minute): 75 hp., 4600 r.p.m., at full throttle
Fuel (Min. grade aviation gasoline): 80
Lubricating oil : Oil Grade HD-Oil
Ambient air temperature: SAE 30:
Above 32°F: SAE 20:
32°F to 5°F: SAE 10:

 

 

 

 

 

 


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