UK Aircraft Diesels, II
The last couple of years development in aircraft engines has been more or less concentrating on diesels. We have seen one off installations to fully developed production lines. A number of companies are active on this market primarily due to major concern of long term availability and the relative high price of AVgas (Europe).
Diesel engines are able to use JET fuel (AVtur). This fuel is available worldwide and can also be made of renewable sources (algae) which should contribute to a cleaner environment.
In the United Kingdom are a number of aircraft diesel engine manufacturers active, or at least they claim to be as it has been very quiet on their part.
They are: Wilksch Airmotive, Diesel Air Limited and Powerplant Developments. We will shine a light on each to see what they have to offer to the experimental aircraft market.
Wilksch Airmotive Ltd.
Wilksch Airmotive Diesel Engine
Wilksch has been developing their range of engines since the mid 90's when they flew a proof of concept engine in a J-3 Cub. This was a two cylinder model and capable of 80 bhp but was limited to 60 bhp. Late 1999 they had their three cylinder model flying in a Europa aircraft, this is the 120 bhp engine and is also used in a LongEZE, Thorp T-211, Murphy Rebel Elite and Vans RV-9. They also have a three cylinder 100 bhp model flying in a Pietenpol Aircamper.
Wilksch went with an inverted, inline three and four cylinder two stroke diesel with turbo and supercharger. Which creates a narrow but rather high engine, this raised thrust line helps in keeping the propeller away from the ground.
Development is still going strong and a four cylinder 160 bhp is under test. We expect that more power is possible in these engines and that the current 120/160 bhp limitation could be raised to at least 130/170 bhp with proper engine lubrication and cooling design.
Early 2009 Wilksch had developed a 'wide bore' WAM-120 which could develop some 140 bhp, ideal for RV-9, RV-12 and Murphy Rebel Elite weight class aircraft. Source Wilksch.net. It has been quiet since as they are in 'development mode'. As of 2014 they are coming back with a WAM-125BB, big bore, engine and a newly developed combustion chamber as the previous model suffered from premature corrosion.
Port / Valve design
WAM engines have a inlet port and exhaust valves and this is perfect for exact timing and tuning. We also have a diagram showing the Wilksch Diesel operating principle
Wilksch Diesel operating principle. For two stroke engines this seems to be the best solution as it combines the best of both worlds!
For startup a supercharger is fitted supported by a large truck size turbo for normal operations. Provisions for a hydraulic propellor control are available. The alternator is installed on the back of the engine and driven by gears. The engine features an intercooler and glycol/water based cooling system.
Diesel Air Ltd.
They were once working together with Wilksch Airmotive, then each decided to pursue a different design. The DAIR-100 is of the opposed piston type, much like the JUMO design and has two cylinders with two pistons each acting toward each other. There are thus two crankshafts driving the propeller through a gearset at the front. This design is much like the PPD Gemini, see our previous page for that.
From the site: "The twin cylinder opposed piston engine has two pistons in each cylinder with the combustion chamber formed between the crowns of the pistons. It eliminates the need for a cylinder head, camshaft and associated valves and has in effect two half length crankshafts linked by a gear train driving a centrally mounted propeller. The cylinders are ported at each end with one ring of ports opened by the air piston supplying the fresh air charge, and the other opened by the exhaust piston and connected to the exhaust system."
The engine has flown in a Luscombe aircraft, power boats and on an Airship with good results. The power output is 100 bhp without turbo charger, with a turbo power can be expected to power to increase by some 20 %. They sell the engine in licence through other manufacturers. Dieseltech sells this engine as the Powerlite-100.
There has been no news since a couple of years and the website hasn't been updated since 2004. One wonders..
Do keep an eye on these manufacturers, the future of small aircraft diesel engines should be really promising although many of the small developments won't survive the test of time.