In my last column, Tracking down answers at Oshkosh, I wrote about the disappearance of the diesel cycle engine in the Cessna 182. From that article, people might think that diesel cycle engines in general aviation aircraft are dead. Well, maybe not dead, just on life support.
The reason for the continued interest is more from third world countries than from the U.S., but there is still significant market pressure to continue work on new diesel models.
It is a three-cylinder, two-crankshaft engine with six pistons. There is a crankshaft on each end of the block, with two pistons in each cylinder. It is a two-cycle diesel engine with no valves and a supercharger. It is a neat little package that produces about 115 hp.
Unfortunately, the people in the booth did not know a great deal about the engine, but thought it would weigh too much for a Light-Sport Aircraft (LSA), so the market for the engine is more as a replacement for aircraft the size of a Cessna 152.
The people in the booth were not sure where they were in the approval process, but thought they had a running engine. I assume that this will be a long-term project with availability in the future.
The Lycoming rep did not know of any work on a GA diesel cycle engine. They do produce diesel cycle engines for a military contract, but that is all.
Continental has two diesel cycle engine programs. The first is the four-cylinder Mercedes engine with a reduction outdrive.
The outdrive is necessary for three reasons:
- The first is to allow the engine to operate at the best performance rpm range.
- The second, and most important, is to absorb the sharp power pulse from the diesel cycle engine.
- The third is to carry the radial and thrust loads from the propeller since the automotive engine does not have the necessary bearing surface to carry these loads.
This brings us to the problem with this ex-Theliert diesel cycle engine, which is the life of the outdrive. It needs to be inspected every 300 to 500 hours and repaired as necessary.
However, I heard that Piper will offer it in the Warrior using an STC for about a $50,000 premium, and other companies are using it or are thinking of using it.
The engine is about 150 hp, so is a little weak on takeoff and climb out, but cruises like an O-320 on significantly less fuel.
Continental is also working on upgrading the SMA four-cylinder diesel cycle engine. They are flying it with an MT prop and have made several upgrades from the original design. Company officials report they have been testing it and are still optimistic about the project.
And then there is the DeltaHawk diesel cycle engine. This Wisconsin company has been working on its two-cycle, V4 cylinder for around 20 years. The company’s main problem was lack of funds to finish the certification process. This summer, the Ruud brothers stepped in and are backing the project financially. With this backing, Delta Hawk hopes to have the engine certified within a year or so.
The advantage of this design is that it has four power pulses every engine revolution vs. only two power pulses for the SMA engine of similar horsepower. This will make for smaller pressure peaks and significantly lower problems with props and engine vibration in the cockpit.
There are other diesel cycle aviation engines like the V8 ETS engine, but I did not find them at Oshkosh.
So are the diesel cycle engines the future of general aviation? Not completely, but I think it will take a significant part of the market, especially overseas and for high usage commercial fleets.
But it will be hard for the normal private pilot to justify $50,000 to $100,000 for a more efficient engine.