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The Graflite V8 employs Bosch fuel injection, liquid cooling, patented glow plugs, steel pistons, a novel firing order, and a compacted graphite iron crankcase (from which it derives its name). It is pictured here with a Hartzell propeller. (Source: EPS)

Diesel engine for rotary and fixed-wing aircraft, FAA certification expected in 2017

Engineered Propulsion Systems (EPS) expects to earn FAA type certification and production certification for its new Graflite V8 engine by the end of 2017, with production beginning in early 2018. The high-efficiency, 4.3-L, four-stroke diesel is rated in the 320- to 420-hp range. It is designed to be compatible with a variety of rotary wing and single- and twin-engine aircraft, including the Robinson R44, Beechcraft Bonanza, Beechcraft Baron, Cessna TTx, Cessna 206, GippsAero GA8 AirVan, and Mooney M20.

EPS reduced engine control inputs to a single power lever, leaving propeller pitch, fuel mixture, and engine temperature management to a Bosch General Aviation dual lane electronic engine control system (EECS). This arrangement allows for reduced pilot workload and error. The EECS also monitors for adverse engine conditions and provides predictive maintenance notifications. The company holds a field office in Burscheid, Germany to both facilitate a close partnership with its Bosch engineering team and to stay up-to-date on diesel innovations.

The Graflite’s low-profile, clean-sheet design employs Bosch fuel injection, liquid cooling, patented glow plugs, steel pistons, a novel firing order, and a compacted graphite iron (CGI) crankcase (from which it derives its name). Grainger & Worrall of Shropshire, U.K. will be casting the major engine components.

The engine can safely drive both composite and aluminum propellers due to low vibration output (the only aviation diesel engine to do so, the company claims). It operates on Jet A, JP-8, or straight diesel fuel.

“The EPS Graflight engine [was designed to be] unique to aero applications—incorporating advanced mechanical design, combustion technology and electronic control systems—as opposed to traditionally flawed approaches, which involves automotive conversions,” said EPS Project Manager Tom Guelzow. “This engine will offer dramatically reduced fuel consumption.”

EPS claims the Graflite V8 will offer approximately 56% further range with 40% less cost over a comparatively rated Avgas-powered engine, due to lower fuel burn and lower cost for diesel fuel. Coupled with an expected 3000-h time between overhaul (TBO), EPS anticipates that the Graflite V8 will yield dramatic cost savings for operators. According to the company, it is also the greenest engine developed for the general aviation market, cutting CO2 emissions by 30 and 17% over comparable Avgas and competing diesel engines, respectively.

Testing at Arnold Air Force Base

The company, a small start-up company founded by Michael Fuchs and Steve Weinzierl, has been testing the engine for the last 27 months; refining the design from a flat eight-cylinder version to the current V8 arrangement.

To validate engine performance, EPS brought about the reopening of the Arnold Engineering Development Center (AEDC) T-11 engine test cell at Arnold Air Force Base, which had been inactive for at least a decade.

The testing at T-11 was sponsored by the Air Force Research Laboratory (AFRL), Advanced Power Technology Office (APTO), Broad Area Announcement (BAA), which focuses on the R&D of engines that use a variety of fuels more efficiently.

“EPS submitted a successful proposal and subsequent award as part of the AFRL Alternative Energy BAA which provided funding for testing at Arnold AFB,” Guelzow said.

The AEDC test facilities are able generate higher-altitude environments for testing than what the EPS team had access to previously. One huge milestone for EPS was having the engine operating successfully at conditions of 30,000-ft.

“We ramped up from level or sea level to 30,000 ft in T-11 and back down, which was groundbreaking for us,” he said.

The EPS engine test has also included a lot of firsts for AEDC and the re-activiated T-11 test cell. Test engineers needed to create a new inlet system to scale the existing system from 150 lb/s of air (for large turbojet testing) to less than 2 lb/s of air for the relatively small diesel engine.

It also marked the first time that a “T-side” test cell was operating concurrently with the AEDC J-2 test cell, which significantly reduced on-air hour costs.

“This could end up being a very busy test cell for small businesses that haven’t been given these type of testing opportunities before,” said John Kelly, AEDC Test Project Manager.

EPS will soon be moving into flight testing, which will be conducted on a Cirrus SR22 testbed aircraft with test pilot Dick Rutan and team out of EPS’s Mojave Air and Space Port hangar in California. Afterward, the company will move on to conduct complete accelerated mission testing of the engine.

Production and supplemental type certification

While EPS will initially produce the engine for OEMs, the company intends to develop supplemental type certificates (STCs) in parallel for the retrofit market. The company has calculated that approximately 7000 aircraft in the 350-hp category require engine overhauls each year and aims to supply 15% of the estimated $1 billion market by 2021. EPS is currently surveying pilots—both domestic and abroad—to determine which three aircraft should be selected first for STC development.

And as the target of production in 2018 draws near, EPS has been expanding its existing facilities at the New Richmond Regional Airport in New Richmond, WI. EPS is building a 15,000 ft², two-story hangar to accommodate testing activities and STC work on multiple aircraft.

Additionally, the company plans to begin work on a manufacturing facility by year’s end. That facility will be scalable, with the potential to produce more than 500 engines per year.

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