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Diesel Propulsion Takes to the Skies

By Frank Burke Contributing Editor, SME Media
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The EPS diesel-powered aircraft engine, weighing under 700 lb, in testing mode.

EPS is developing a diesel-powered engine that can power private aircraft.

In a small town in northwestern Wisconsin, a dedicated group of engineers, designers, and machinists are working with a visionary management team on a concept that could have a revolutionary effect on general aviation and impact other forms of flight. Although the word “diesel” might generally call to mind large engines in vehicles ranging from earthmoving equipment to automobiles, the team at EPS (Engineered Propulsion Systems; New Richmond, WI) is in the final stages of developing a diesel-powered engine of sufficient weight, size, and capabilities to power private aircraft.

Why diesel? According to Ryan Kuebker, EPS special projects coordinator, “Our aircraft engine will offer all the advantages found in conventional diesel engines and more. For instance, it will fly farther on less fuel with larger payload, it will be able to run an aluminum propeller, it will run cleaner while providing more torque and horsepower, and, because it will run on conventional diesel fuel or Jet A, it will not be limited to specialty aviation gas. Also, the ready availability of conventional fuel will be a significant advantage to pilots flying in more remote areas, such as Alaska.”

The engine was originally conceived by EPS founders and lead engineers President Michael Fuchs and Vice President Steven Weinzierl. Fuchs, a graduate of the University of Sciences in Aachen, Germany, with extensive experience in aeronautical turbines, developed the concept for the engine in 2005. He began construction of a prototype six years later.

“The original idea for the engine evolved from working with drone engines. We could also envision the future phase-out of aviation gas and, as a result, the need for engines capable of running on heavier fuels, such as kerosene, diesel fuel and Jet A. We gravitated to general aviation because builders in that area were incorporating older engine designs that were incapable of further advancement. At the same time, we realized that our design had to compete with several aspects of more conventional engines, including overall weight and cost. Thanks to our team, and their ability to think outside the box, we’ve been able to meet those challenges.”

The Materials Equation

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The many unique components of the engine require an extensive inventory of high precision fixtures. The accessory drive cover requires extensive machining and provides a compact housing for multiple components.

A major difference in the EPS engine includes materials that, although lighter, must retain the capability to generate power and perform reliably under conditions not yet encountered in an aviation context. To meet cost parameters and promote greater efficiency, components were designed for manufacturability and, where possible, to perform several separate functions. For example, the accessory case incorporates two fuel pumps, a water pump, the alternator drive, and other attachments.

The manufacturing of such complex parts in various materials, including aluminum, stainless and other alloys, requires five-axis machining capability in order to achieve the necessary high-strength, thinner walls. According to Kuebker, “The packaging and arrangement of components presented its own series of challenges in that we had to fit form with function so as to deliver the most compact package at the correct weight. As it stands, we are only 50 lb heavier than a conventional gas engine with a weight of under 700 lb installed.”

Expertise Meets New Conditions

Engineering and machining of the multiple components required not only proven expertise but the ability to envision the conditions under which the finished product will be operated. Also, requirements particular to a diesel engine had to be considered. For example, one challenge concerned the effect of a colder environment on thicker fuels.

“We have provisions in place for dealing with lower temperatures, one of which is the use of Jet A fuel,” said Kuebker. “A maximum flight ceiling of 18,000′ would preclude the naturally frigid atmosphere at very high elevations. These atmospheric temperatures will not be an issue when using Jet A.”

In addition to the management team and engineering staff, EPS employs five machinists, two quality control specialists, and a fixture designer. For its CAD/CAM capabilities, hyperMill software was chosen along with Esprit. Major machining operations are performed on two DMG machining centers—a model DMC 85 monoBLOCK and a model DMU 65 monoBLOCK. Operations for rotational parts are accomplished on a Mori Seiki NLX 2500, to which a bar feed mechanism will be added in the near future. Other machines include a Mori Seiki NTX 1000 and a Gildemeister Sprint 20-8 Linear.

Industry Interest

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The completed propeller shaft after machining, using the Hainbuch precision workholding system.

The unique concept has generated interest throughout the industry. Aviation legend Dick Rutan and other major figures are regularly kept apprised of developments. Even prior to the certification of the prototype engine, a 180º V8 concept, interested parties have asked the company to explore a four-cylinder design for possible drone applications.

“From the beginning, we have worked in a collaborative way,” said Fuchs. “We’ve been talking to airframe builders, both here and abroad, and our investor base is international in scope. We’re a privately held company, and our investors understand that, between product development and eventual FAA certification, an undertaking such as this represents a long journey requiring ongoing commitment.”

Investors and possible customers alike are excited not only by the obvious advantages but by the potential long-term economies that the engine will offer.

“Although we are projected to be initially more expensive by 30% than typical gas-powered aircraft engines, ours will be good for 3,000 hours of operation prior to overhaul,” said Keubker. “Also, we estimate that the engine block will be functional for up to 9,000 hours. Given the additional economies of diesel operation, this would represent substantial savings over time.”

With the certification process well underway, the EPS management team of Fuchs, Weinzierl and CFO Paul Mayer are eagerly planning for the production phase of the new engine, as well as using the knowledge they have acquired in the design process to develop plans for future designs.

It will not be the first time that a group of visionaries, laboring in an out-of-the-way locale, have managed to change the face of aviation. The Wright brothers, Glenn Curtiss and other pioneers would understand.

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