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Race Engine Technology Magazine

It is this company's firm opinion that the requirements for a good aircraft engine, in order of importance, are:

1. reliability,
2. power-per-pound of installed engine weight,
3. fuel efficiency,
4. form factors,
5. cost,
6. availability,
7. support.

There may be disagreements about the order of (3) through (7), but (1) and (2) are widely accepted, in that order.

In certain situations, item 5 (cost) can become a very important factor. In those cases, we would allow cost to come right after reliability, but never to precede it.

It is also our opinion (based on real-life data) that, as long as you can count on having 100-LL Avgas, the best way to satisfy requirements (1), (2), (3), (4), (6) and (7) for engines up to about 300 HP is to use an appropriate certified engine (Lycoming, Continental, etc.).

Naturally there have been problems with those engines; all devices produced by humans have problems. The costs are high, for a variety of good (low production volumes, generally high quality control, immense FAA compliance overhead) and not-so-good (lawyers) reasons. Owners of aircraft which use the big flat-6 (LYC-TIO-540, TCM-TSIO-550 and GTSIO-520) air-cooled engines are often faced with engine problems which are the by-product of the fact that these high-output engines are very heavily-stressed, both from operating loads and in heat rejection requirements.

However, the fact of the matter is that, statistically, “LycoNentals” have demonstrated both excellent reliability and high HP-per-pound of installed weight. New technology has made improved BSFC available at cruise power settings. Flat engines fit into most airframes well. (Could it be that they were designed around flat engines?)

But there is a bigger problem looming in the not-too-distant future: the highly-probable demise of 100-LL aviation fuel. Presently, the high-output LycoNentals, and especially the turbocharged versions, operate on thin detonation margins at rated power on the "FAA Hot Day". Without 100-LL fuel or a suitable alternative, those engines will not be legally operable at their certified power levels. That could render many of the cabin-class twins essentially unflyable. Therein lies the project motivation.

The installation details of a liquid cooled engine are far more complex than the conventional air-cooled engine (see Retrofit Issues). However, the liquid-cooled package offers operational advantages such as full-power operation on unleaded fuel and the elimination of "shock-cooling" concerns. Further, in order to make meaningful comparisons between engines on the basis of criterion (2) above, you must compare honest engine power figures and you must compare honest installed weights; that is, the weight of the complete firewall-forward powerplant package, comprising the engine with all accessories, including the complete exhaust system, the engine mounting structure, all heat exchangers, hoses, fluids, ductwork, alternate air system, cowling and propeller. That subject is covered in great detail in the Engine Conversions section of this site, with a great many specifics on the Evaluating a Conversion page.

Since 1993 (on a time-available basis), EPI has been developing a lightweight, high performance liquid-cooled V8 aircraft powerplant, toward the prospect of an emerging market for an engine to replace the overloaded big-6's on otherwise-serviceable aircraft.

To be honest, the EPI Gen-1 engine project began as an unvarnished quest for an outrageous level of power (hence performance) for a two-place tandem high-performance aircraft which EPI's CEO had designed and was building for himself. However, it quickly evolved into a larger perspective project with lots of potential in view of the fuel situation.

The primary design criteria for this liquid-cooled powerplant design are:

1. Very High Reliability, with an in-service TBO target of 2000 hours or better;
2. High Power-to-Weight Ratio;
3. Low BSFC;
4. Sea-level power available to FL-200;
5. Ability to run on 92-octane pump fuel under FAR certification conditions with FAR detonation margins;
6. Weight of the complete installation (engine system, accessories, heat exchangers, plumbing, mount, cowling) lower than the highest-output 540 and 550 cubic-inch Lycomings and Continentals (detailed below).

The justification for a new engine is not based on any fundamental deficiency in the design and implementation of the "LycoNentals". In fact, those certified engines contain some incredibly clever engineering (allowing for an occasional brain-fade like powdered-metal oil pump gears). All the grumbling about "World War-2 technology", "tractor magnetos" and the like, are uninformed opinions based on either an incomplete information set, or a pre-conceived set of biases (or maybe BOTH).

The main problem with the high-output (turbocharged) versions of these engines is that the very high power levels required increases in strength and heat-rejection capacity which exceeded the growth capabilities of the original designs.

Many of the specific design criteria for EPI's new engine were derived from analysis of the existing high-reliability engines. The design analysis for this engine, including the proprietary-technology PSRU, was presented at the 1996 Advanced Engine Technology Conference.

The information presented in this section will show that it is a significant challenge to build a liquid-cooled, piston engine powerplant which has the reliability and the HP-per-pound of a LycoNental. To do so inexpensively adds an entire new level to that challenge.

To get the most out of this presentation, it is essential that you understand the nature of power and torque. If you have not already seen these pages, please review Energy and Work and Power and Torque before proceeding.