What About Those Diesels? Part 2

In contrast to the auto-based Centurion and Austro, the French company SMA has designed a traditional four-cylinder opposed, four-stroke, air-cooled, direct-drive diesel, which has garnered several STCs on various Cessna and other aircraft. The newest version, the 305e, features more power at altitude and several detail improvements. Any opposed four-cylinder, big-bore diesel will have sharp power pulses, which are tough on the props, but SMA is working on that with its four, and … a six-cylinder version was long in the rumor mill.

Continental acquired technology and engines from SMA; its TD300 displayed at Oshkosh 2011 was a lightly reconfigured SMA 305a. Teledyne Continental (TCM) had recently worked on two iterations of a two-stroke diesel (a six-cylinder radial from the General Products Division and the “NASA GAP” engine, an opposed four, from the Aircraft Products Division), but came around to the idea that the SMA four-stroke approach would be a better direction to take, particularly regarding cooling. Where Continental now plans to go with this project is anyone’s guess, but the idea of a Continental diesel will not go away.

And there’s more

There are two Wisconsin diesels on the horizon. Most-recently is the Engineered Propulsion Systems’ flat-8, 4.4-liter, 350-hp (at 3,500 crank rpm), geared Vision 350-A44-POC, a turbocharged, common-rail injection, four-stroke design; it has been running since late 2011. This water-cooled cast-iron (very special) alloy block engine invokes many innovative features and is designed to fit in the space currently occupied by popular six-cylinder air-cooled gasoline engines. Its controls are designed to be “pilot-resistant,” as well.

Engineer Steve Weinzierl notes, “We also have some interesting technology in our electronic systems; we have already applied for several patents. We can use these to make the engine immune to cetane changes, for instance.” As for the diesel’s sharp power pulses, “Electronics can shape the pressure rise in a diesel, and shape the pressure, gradually and non-linearly, and affect the internal gas-pressure rise. This can yield a quieter, more-efficient fuel burn. Our telemetry monitors how much fuel gets through each injector, mechanically.”

From the other side of the state comes the DeltaHawk, a 160/180/200-hp (at 2,700-rpm) direct-drive V-4, water-cooled two-stroke, loop-scavenged, turbo-supercharged diesel that has been flying for nearly a decade but has yet to reach certification. Its configuration as a two-stroke also allows mounting in V, inverted V, and vertical positions in a pusher, tractor, or upright-shaft position, with rotation in either direction — 18 models in all. With a 4-inch square bore and stroke (202 cubic inches) and 19:1 static compression ratio, the DH200V4 DeltaHawk’s power/weight ratio is similar to legacy gasoline aero-engine performance at roughly 2 pounds per horsepower. The projected TBO is 2,000 hours.

The DeltaHawk design pushed for overall simplicity, and it’s easy to work on. If you don’t open the block, you won’t need to be a specially trained diesel or DeltaHawk-trained mechanic. Inside the block, there are only the crank, rods, and pistons; outside are all pumps, cooling, intake and fuel, controls, and so on. Some externals — the water pump belt, for instance — are 500-hour items. (DeltaHawk’s Rip Edmundson notes, “We have run them ragged, for dozens and dozens of hours after they were way past their obvious useful life.”)

Neither Wisconsin-based engine maker has the volume to announce plans for training non-factory mechanics or to establish non-captive rebuild facilities, though some well-known STC developers have approached DeltaHawk about becoming authorized service centers.

In Germany, limited flight tests in a Yak-52 have been made by Raikhlin Aircraft Engine Developments (RED), with its A03, a 500-hp (at takeoff) 6.1-liter double common-rail injected V-12. This purpose-built aero engine (that looks like it’s auto-derived) has a dry sump, and is configured as a pair of straight-6 engines, each DOHC bank having its own monitoring, induction and fuel system, liquid cooling system, and turbo/exhaust. A single starter and twin alternators complete the configuration. All this runs through a 1.88:1 gearbox, yielding a maximum propeller rpm of 2,127 (4,000 engine rpm).