Popular Flying

July/August 2000

 

"The WAM-120 Diesel"

"Wilksch Airmotive's new diesel aero engine is due to go into production next year. Report and photos by Philip Whiteman."

"Twenty years ago, in Australia, an aircraft mechanic told Mark Wilksch, "You'll never change a Lycoming or Continental". How wrong they were!

We now have the new Wilksch engine that is water-cooled, has three cylinders, is a two-stoke and, most radical of all, is a diesel.

In some ways the choice of a diesel, at least, was obvious as, for years, we've all known that diesel cars use less fuel. Now, they even go as well as petrol ones, as many motorists will tell you. Wilksch, though, was sure he could not just 'dieselize' an existing aero engine. For a start, some form of supercharging would be needed to provide adequate performance. The peak cylinder firing pressure of a diesel is very high and the engine's bearings have to be beefed up to cope with it. Not only that, but the firing impulses give the propeller, or any reduction gearing, a very hard time as well.

However, as he was well aware, there are historical precedents for diesels powering aircraft, and the most successful of them all was the Junkers two-stroke diesel aero engine of the 1930s and 40s. Why a two-stroke? The rationale was simple, double the number of firing impulses and you get more, if not quite double, power from an engine of a given size. At any given power output, the two-stroke operates at a lower mean cylinder pressure than the equivalent four-stroke, lowering the stress on the connecting rods and crankshaft. This recipe would give the essential power-to-weight ratio, smooth torque delivery and mechanical simplicity.

There remained one design issue. The turbocharger would offer the dual advantages of not consuming any drive power and automatically compensating for falling pressure with altitude. But it wouldn't produce any boost at idle or low power settings, indeed, the engine could not even be started without some form of auxiliary blower.

Wilksch's solution was to fit a secondary, mechanical blower downstream of the turbocharger, where it would be driven by induction air whenever the turbocharger was working, therefore removing the need for a clutch or having to accept drive losses when the blower was not actually required.

For the first Europa test hop, made in December last year, the Eaton supercharger from a Mercedes SLK sportscar is used. Now a new, lighter and more efficient blower, devised by aircraft cabin blower experts at City University, is to be fitted. Intercooling (putting an air/air radiator between the turbocharger and engine) increases the basic engine's output to 150 hp, making the WAM-1 50i a near4erm prospect. Wilksch also proposes an expanded range of aero engines based on the 600 cc WAM-1 20 cylinder module. Thus, in time, we may see a 1 60/200 hp (intercooled) 'four' and a 200/250 hp 'five', providing a range of Wilksch engines to suit much of the GA piston fleet.

 

Mechanical ingenuity

Like a 'six', the three-cylinder in-line layout of the 1 20 hp WAM-1 20 gives perfect primary and secondary balance. The inherent 'rocking couple', caused by the two end cylinders, is countered by balancer shafts-so the engine should run very smoothly.

The 'little end' bearings tend to be the Achilles heel of high performance two-stroke engines. The WAM-1 20 uses one fix used in many heavy-duty two-strokes -a spherical bearing. Piston crown oil cooling is enhanced by an amusingly-named, but highly effective, 'cocktail shaker' arrangement. One further, elegant refinement is a novel single-piece connecting rod/spherical bearing design. The spherical little end drops info a simple aluminium piston and is secured by a locking ring that is threaded over the base of the rod-very neat and the subject of a patent application.

Wilksch Airmotive has designed their own three-point engine mounting system. It plans to incorporate the engine mounts in the rear timing-chest cover, which would allow different mount configurations simply by changing covers. The radiator mounts on the front of the engine, below the propeller centre line. The WAM-120 will be supplied as a complete functional unit, the cooling system being an integral part of the package.

WAM-120 Engine Data

Rating                 120hp @ 2,700 rpm
Mounting             Three-point Wilksch Para-Focal(TM)
Cooling                Liquid, integral radiator
Target weight      100kg
TBO                    1000hrs (at launch)
                          2000hrs+ (target)
Fuel                    diesel/turbine

Dimensions
Height                  63cm (25 inches)
Length                  81cm (32 inches)
Width                   58cm (24 inches)

Propeller
MT three-blade, variable pitch.

For further details contact Wilksch
Airmotive Public Relations and Press
Office, 12 Pattison Lane, Woolstone,
Milton Keynes MK15 OAX.
Tel: 01908-392003, fax: 01908691619,
web: www.wilksch.com"