Does General Aviation need new piston engines? Will an investment in new engine technology pay off by reducing acquisition and operating costs? Can reductions in engine costs lead a rejuvenation of the market? In the first half of this article I’ll take a look at the technical strengths of the current engines and try and dispel some stereotypes. In the second half, I’ll talk about some of the significant developments coming down the pike for beginning of the next century.
THEY’RE A LOT LIKE TELEVISIONS
Current certified aircraft engines have a reputation not unlike the television. They’re ubiquitous, big ones cost a lot, and a good way to get a lot of heads nodding in agreement is to talk about how terrible they are. But is that reputation entirely deserved? The television, at least, can get PBS. What’s the aircraft engine’s excuse?
Derisive terms for aircraft engines abound. Two of my favorites are “Lycontinental,” to emphasize the apparent similarities between the two major brands, and “Lycosaur” to emphasize the age of their design. Not a night at Oshkosh goes by without a spirited discussion of the “1930s tractor engines” that we fly behind vs. hyper-modern automobile engines. Surely, the thought goes, that if only the evil FAA certification process were eliminated, and if the dark and mysterious cabals between the major engine manufacturers and the airframe makers were exposed, we would all be flying our Mooneys behind five-hundred horsepower engines that weigh 200 pounds, consume six gallons per hour, cost $2,000 to overhaul, and have a TBO of 5,000 hours.
But is that characterization really fair? First, it implicitly assumes that piston engine development has increased linearly with time – i.e. that the engines of 1990 are roughly twice as good as the engines of 1945 which themselves were twice as good as the engines of 1900. However, anyone who follows technology will tell you that improvements generally occur rapidly only when a given technology is in its infancy. Such rapid development periods are then followed by a long period characterized by only incremental improvements.
For example, commercial subsonic jetliners have clearly emerged from the rapid development phase of their existence. Physical laws and market pressures have driven all the manufacturers to consolidate their designs and converge upon a single dominant configuration. Certainly detail refinement will continue and incremental changes will be had in areas such as fuel efficiency, passenger comfort, range, and size but its doubtful that the next forty years will see the same kind of changes that characterized the last forty. Simply compare the variety in shape and engine configuration of aircraft at large airport today with that at the same airport forty years ago.
For piston engines, the plateau of core development occurred shortly after World War Two and it’s from precisely this period that today’s of aircraft and automobile engines are derived. There is more than coincidence that the 700 horsepower engine which powered Jeff Gordon to victory in the first-ever Brickyard 400 first appeared in the same year as did the common-as-dirt Lycoming O-360.
EVALUATING THE STATE OF THE ART
What is the performance of current aircraft engines when compared against, say, their modern automotive brethren? Reasonable criteria for comparison would be: installed weight, reliability, fuel economy, and cost. It’s nearly impossible to make comparisons on a weight basis without speaking of specific installations. However, with some exceptions, attempts at converting auto engines to aircraft inevitably end up with a lower horsepower-to-weight ratio. Examples include Stratus Development’s 100HP EA-81 replacement for the 100HP Continental O-200. Both installations will set you back roughly 215 lbs installed. Other examples include Northwest Aero’s Chevy V6 of 230 HP and 430lbs vs. the Lycoming O-540-J of 235 HP and 360lbs. Finally, not much is known about the super-secret endeavor to place Toyota’s new certified derivative of the Lexus engine in a Piper Malibu other than the installation is “slightly” heavier than the Continental it replaces according to an individual involved in the project.
I won’t speculate on reliability here since so many variables are installed, except to say that many auto conversions are, by all accounts, operating safely and reliably. I know of particularly well engineered installations approaching one thousand hours of trouble-free service. Auto engines in aircraft can be as safe and reliable as certified engines so long as the same cautions are observed regarding component strength and longevity.
Fuel Economy
Fuel specifics (the efficiency of turning fuel into horsepower – see the sidebar on BSFC) is an area in which aircraft engines really come into their own. For example, even our fifties-vintage carbureted aircraft engines return fuel specifics in the 0.43-0.48 range (depending on leaning and RPM) and modern fuel injected Lycoming and Continental engines are delivering BSFCs of 0.39-0.43. Those numbers are for bone-stock, straight from the factory, engines.
And it’s not hard to improve these already excellent numbers. Big-bore Continental engines equipped with Continental’s tuned intake and with a set of balanced injectors from GAMI (a $750.00 modification) are now running around 0.375. Engines utilizing Unison’s LASAR electronic ignition (see below), can expect to increase their BSFC numbers by roughly 8%.
In comparison, according to Ford’s David Hunt, Ford’s ultra-modern 200 HP Duratec engine achieves a BSFC of only 0.46 at 75% power. Their 235 HP SHO engine, developed by Yamaha, has a BSFC of 0.45 at 75% power. These are the BSFCs of engines which feature modern amenities such as dual overhead cams, four valves per cylinder, sequential multiport induction and tuned intakes. With all those advances, the Duratec still consumes as much fuel per horsepower as the engine in a 172 at the hands of a student. Why is that?
The importance of design
Current aircraft engines are able to post these kinds of figures because they are purpose-built. They have been optimized for the application and that gives them a tremendous advantage right out of the gate. An example to illustrate the point: ring friction constitutes approximately 70-80% of an engine’s internal friction. Reducing internal friction directly improves fuel consumption because more of the power produced by the engine is available at the prop. Keep that in mind as you consider the following: a Lycoming IO-360-A engine, with pistons the size of dinner plates, produces 150 horsepower (75% of rated output) from 360 cubic inches at 2600 RPM. The swept area (the area traversed by the piston rings) in the IO-360 is 221 square inches per cylinder per crankshaft revolution. The entire engine sweeps 38,356 square inches per second at 2600 RPM.
The Ford Duratec produces 150 horsepower (75% of rated output) from 181 cubic inches at 4200 RPM and it has a swept area of 109 square inches per cylinder per crankshaft revolution. Because the Ford engine has more cylinders and because it must push them faster the entire engine sweeps 45,553 square inches per second at 4200 RPM while making the same power as the Lycoming does at 2600 RPM.
The Ford engine therefore must use more fuel in overcoming internal friction than the Lycoming. Moreover, attaching a propeller to the Ford engine would require a reduction unit to keep propeller speeds reasonable. Typically, reduction units consume 2-5% of an engine’s output, further eroding the Ford’s fuel economy in aircraft applications.
Ring friction is the dominant, but not the only, source of friction within the engine. Other sources of friction which go up as the ratio of cylinders to horsepower increases include valve train friction (more rockers, valves, tappets, etc. The Duratec has twice as many valves per cylinder as does the Lycoming) as well as main and rod bearing friction.
Ironically one of the negatives cited as a weakness of the aircraft engine may actually be a strength. The fit of the aircraft engine’s pistons inside their cylinders is notoriously sloppy when compared to modern automobile engines. Because of the auto engine’s tight clearances, an oil film is maintained between the piston and the cylinder for the entire diameter of the piston as opposed to the aircraft engine where there is oil only between the piston’s thrust face and the cylinder wall. For auto engines, the extra oil film provides no benefit while contributing a significant amount of drag. Auto engines have these tight clearances to keep their operating noise down but this is not a concern in aircraft applications.
Finally, the use of large pistons allows the aircraft engine to develop its full-rated power at the engine’s torque peak. This greatly increases the engine’s fuel efficiency as the torque peak corresponds to the engine’s point of greatest volumetric efficiency which is also the point of lowest specific fuel consumption.
I don’t mean to imply that different levels of internal friction are the only reasons why aircraft engines outperform auto engines at high power settings. The former was meant merely as an example of one of the relevant design parameters which differentiate the engines. Certainly others, such as intake design and valve configuration, all can be tailored towards the specific application and help contribute to efficiency.
Overall engine configuration
Current aircraft engines are built with an opposed configuration. That is, each bank of cylinders lies directly opposite the other bank. This gives the engine a low profile – namely, it allows the pilot of a single-engine aircraft to see over the engine while still allowing adequate propeller ground clearance. With a “V” configuration, the engine must either be inverted (which poses oil control problems) or must use an offset drive to power the propeller.
The opposed engine configuration also has some inherent internal balance advantages over the “V” configuration. In the opposed configuration, each bank of cylinders provides an inertia balance to the other bank. There is no need for additional static counterweights as are necessary with a “V” configuration. The elimination of several pounds (often tens of pounds) of counterweights is a significant weight benefit of the opposed configuration.
Finally, because of their steady-state operation, aircraft engines can control damaging torsional vibrations through the use of pendulous dampers. As opposed to the viscous dampers used on most automobile applications, pendulous dampers do not remove torsional energy from the crankshaft and dissipate it as heat. Because of this they are not only more efficient, but they don’t have to be overbuilt (read: heavy) so as to not overheat in high-output applications.
But what about electronic fuel injection?
Much is made these days of sequential, multi-port, fuel injection systems prevalent on automobile engines. Surely, the argument goes, fitting such a system on an aircraft engine would improve its fuel consumption. After all, look at the MPG ratings of today’s cars – their engines must be really economical!
But this argument overlooks several facts, all of which stem from the usual operating environment of the automobile engine. Automobiles have been able to boast increasing MPG values not because their engines have become more efficient but, rather, because automobiles themselves have become drastically lighter and more aerodynamic. It now takes much less horsepower to propel the average sedan down the interstate than it did twenty years ago. For example, today’s Ford Taurus sedan needs approximately 21 horsepower to cruise on a level highway at 65 MPH while the 1974 Volvo 144 required 30 for the same speed .
Furthermore, the advantages of sequential electronic fuel injection are found mostly in low-RPM, low power situations such as stop-and-go city driving. It’s in such situations that spraying fuel only when the intake valve is open can reduce emissions, increase fuel economy, and improve smoothness. Above a certain power output and/or RPM, however, sequential fuel injection systems revert to what is, essentially, a continuous injection pattern. At medium-high power settings there simply isn’t enough time to get all the fuel needed if the injector is open only when the intake valve is so the injectors must spray fuel continuously; even when the intake valve is closed. Continuous port injection is the system used on most injected aircraft engines. That continuous injection has no performance advantage over sequential injection in aircraft applications is borne out by the fuel consumption numbers when the engines are compared at equivalent power outputs.
As for mixture management, remember that an aircraft with a four-probe EGT system installed has the most sophisticated closed-loop mixture management system available in the world. Utilizing full wetware artificial intelligence processing, the system is able to not only maintain optimum air/fuel ratios in cruise operation but to also predict changes in fuel mixture long before they’re actually needed and based upon a plethora of factors. I’m talking, of course, of the human being flying the aircraft and the mixture control.
Computerized mixture control is important in a highly dynamic environment (such as street driving where you can’t expect to manipulate the mixture AND avoid the shopping carts) but much less important in the typical steady-state cruise environment found in aircraft. Since both systems (hardware vs. wetware) can perform equally well at determining cruise mixture settings it’s sometimes hard to justify the extra expense, complexity, and weight of the automatic system in an aircraft.
IT’S NOT FOR LACK OF TRYING
Still, both major manufacturers and a number of other players have tried to introduce new design engines into the marketplace in years past. In the 1960s, Continental embarked on an ambitious project called the Tiara engine.
Eight Cylinder Continental TiaraThis engine was supposed to be both cheaper to manufacture as well as cheaper to operate than existing engines. It incorporated several innovative features such as a combined camshaft and propeller drive, torsional vibration control via a quill shaft, and fuel injection. Because of the reduction gear, propeller noise was low and propulsive efficiency was high. The engine was certified and went into production but buyers were few and far between. Operationally, the engine wasn’t significantly different from others (it was supposed to be slightly lighter but that didn’t pan out) and no one cared about noise in the 1970s. Continental’s John Barton says that, in a way, the engine was before its time. Today, with more stringent noise standards, it might have had a fighting chance.
Continental tried again in the 1980s with their line of liquid-cooled Voyager engines. Development for these engines was underwritten by the U.S. taxpayer as the government needed an engine that could operate efficiently at high altitudes for the then-secret CONDOR program. Turbine engines lose power as they climb and they have extremely high fuel consumptions at low power settings and the government needed an engine that could loiter at 80,000 feet for hours. It turned to Continental to build the engine which subsequently became Continental’s Voyager (after the Rutan aircraft which used one and circled the globe unrefueled) line.
Liquid-cooled Continental Voyager EngineThe Voyager engine has been offered to the public as both a replacement for the Cessna 414’s air-cooled engines as well as a replacement for the standard engine in the Bonanza. Neither has sold terribly well – RAM claims to have not sold a 414 conversion for over a year and a half. Part of the engine’s problems can be traced to teething pains, many of which may have been caused by the mandated use of Mobil-1 oil (the policy has changed). But the fact remains that the engine offers little over the older air-cooled engines to justify its higher price.
Lycoming’s changes have been mostly towards manufacturing ease. The infamous “76” series engines (O-320-E and O-360-E engines) were introduced to take advantage of a new computerized crankcase line which Lycoming had bought. Prior to that was the 541 series, notable for its similarity to Continental’s designs (against which Lycoming was furiously competing at the time), and its lack of a separate accessory case which was a cost-saving measure. In the 1980s Lycoming experimented with autofuel in their existing engines as well as going so far as building a diesel engine based on their current configuration and the revolutionary SCORE engine (see below).
Porsche and Mooney tried with an engine derived from the 6-cylinder 911 auto engine. The project was abandoned when it turned out that the engine, as installed in Mooney, was heavier and had poorer fuel specifics than did the Lycoming it replaced.
Other manufacturer’s have tried to break in to the market with various variations on auto engine conversions as well as radical departures such as the Dyna-Cam and Rand Cam engines. None have, so far, been commercially viable.
BUT CHANGES ARE COMING
We’ve seen that current aircraft engines aren’t quite as technologically backwards as the common wisdom would believe. In fact, for their application, they’re actually excellent performers but that doesn’t mean what we see is what we’ll get forever. Two significant trends are developing in the industry. One trend has to do with how we control our engines and the other one with how we fuel our engines.
Digital Engine Controls
The first trend is that the single-lever power control is back and it’s back with a vengeance. The basic idea is that, instead of having three misshaped and greasy knobs to play like an old pump organ, there is just a single lever which the pilot positions according to his power needs. Computers take care of all mixture management, prop pitch, etc. automatically adjusting each for optimum engine efficiency without possibility of engine damage.
Currently, there are no less than three companies working on so-called FADEC (Full Authority Digital Engine Control) for certified engines. FADECs are “full authority” in that the power lever manipulated by the pilot is not physically directly connected to anything on the engine itself. Rather, the power lever serves as an input to the FADEC computer and the computer then operates servos which move the mixture, prop, and throttle controls on the engine. FADECs usually also control spark timing directly. Thus the FADEC has “full authority” to place the engine in whatever configuration it wants and there’s nothing the pilot can do about it save hope the FADEC pays some attention to the power lever position.
FADECs are conceptually simple devices but, like so many things, difficult to deploy in real-world aircraft situations where one must worry about rain, lightning strikes, software bugs, and power failures. Nevertheless, FADECs have been used for years as turbine-engine controllers in airliner and military service. Don’t let the fact the former always has multiple engines and the latter utilizes an ejection seat stop you from running out and getting one for the family Skyhawk.
I asked Lycoming, who is furiously testing Hamilton-Standard FADECs on their engines at the Williamsport plant, what they perceived as the advantages of FADECs. The simplicity of single-lever control was one answer. However the other answer, frankly, surprised me. Lycoming’s position is that the FADEC will enable a 10-20% fuel savings on existing engines in block-block fuel use.
In addition to the advantages of advanced ignition timing at cruise and low powers, Lycoming feels that the FADEC will do a much better job of aggressively leaning the mixture both in the climb as well as the descent portion of flight. Thus, while cruise fuel specifics might not be much affected over that achieved by normal leaning, significant benefits will accrue during climb and descent periods where the average pilot sorely ignores his leaning duties.
Interestingly, Lycoming bases this opinion on information they acquired when testing an electronic fuel control on their engines over a decade ago. That project never went into production but flight tests showed a block-block fuel savings of over 15% when standard pilot technique was used. Continental also developed and tested an electronic fuel control in the same period but it’s unclear what their results were.
The Hamilton-Standard unit which is being evaluated by Lycoming completely replaces the traditional Bendix/Precision fuel servos and the magnetos. The unit incorporates “batch” style electronic injection and hall-effect electronic ignition. Lycoming’s position is that single-lever power control is the wave of the future and that incorporation of a FADEC to their traditional line of engines will modernize the engines.
Unison industries, maker of Slick magnetos, is rapidly developing their LASAR electronic ignition into a full-fledged FADEC unit. Already the LASAR system, using only ignition timing advance, has improved the BSFC of carbureted Lycomings by 0.04. On the injected IO-360-A Lycoming Unison claims an even greater improvement of 0.06 which places the total IO-360-A cruise fuel consumption well below the 0.400 mark. LASAR’s ignition timing can be quite aggressive with advances of nearly 40 degrees possible in certain situations. Contrary to some belief, the LASAR system will begin advancing the ignition timing even at very high engine power levels so long as cylinder head temperatures remain within limits (LASAR now includes a cylinder head temperature probe).
Unison’s Brad Mottier says that Unison is working with Precision on a conversion kit which would allow Precision’s fuel injection units (used on most injected Lycoming engines) to be controlled by the LASAR system’s processor. Unison says that production LASAR systems already incorporate the parts and software to perform full FADEC functions but that adapting existing fuel controls to use them will take some time. Current plans call for the mixture control function of the LASAR system to operated in a so-called “open loop.” In an open-loop, the computer cannot take advantage of engine sensors, such as EGT, to optimize the mixture. Instead, mixture settings are derived from a lookup table in the system’s memory which correlate RPM and manifold pressure with known mixture settings. Since the settings are static, the system cannot automatically account for variances in individual engines (such as wear) or environmental changes (such as humidity). However, Mottier and Unison engineer Dean Mechlowitz say that development of a closed-loop system with full autothrottle control is under development. Mechlowitz doesn’t feel that electronic fuel injection will help much with cruise fuel specifics but, like Lycoming, feels that it will go a long way to help fuel consumption during climbs and descents where the pilot is often too busy to keep up with the mixture knob.
Toyota is also working with Hamilton-Standard to develop the FADEC for Toyota’s new aircraft engine.
Return of the monster piston engine
Both Toyota and Orenda are taking a serious look at introducing all-aluminum V8 engines to the GA scene. Toyota has certified its Lexus 350-horsepower V8 automotive engine and is busy flying it on a Piper Malibu in an exhaustive test program. Very few details about the program are available but, according to one insider, there are precious few automotive parts left in the engine.
Toyota is serious about the market. Articles in the Japanese press report that Toyota intends to build an aircraft factory in the United States to build a four-seat aircraft. Is this the platform for which Toyota has been developing their engine? Are Witchita, Williamsport, and Mobile about to experience what Detroit went through in the 1970s?
Orenda is taking a novel approach. Instead of having to compete with existing reciprocating engines, they’ve decided to position their engine as a turbine-killer.
The 600 HP Orenda engineThe Orenda 600 is a 600HP (500HP continuous) aluminum V8 of roughly 750 pounds (not including cooling system). For certification ease, the engine uses standard aircraft magnetos and fuel injection. They are quick to point out that the parts used in the engine are all from aerospace vendors – not automotive sources. Orenda claims a BSFC of 0.42 for the engine which, given the target horsepower, seems reasonable although the Orenda’s bore is only 4.44 inches. For comparison, the 400 horsepower (continuous) eight cylinder IO-720 from Lycoming has a 5.125 inch bore and a BSFC of 0.40. The Orenda is also a little heavier than the Lycoming at 1.5 lbs per horsepower vs. the IO-720 at 1.42 lbs per horsepower. Still, the addition of electronic ignition could well bring the Orenda’s BSFC below 0.40. The Orenda also incorporates dual turbochargers which will allow it to make its rated power to 20,000 feet while the Lycoming is naturally aspirated. The turbos exact both a weight and an efficiency penalty from the engine.
Diesel engines
Probably the biggest development in the past decade is Continental’s announcement, with NASA, that they are going ahead with development of a two-stroke diesel aircraft engine. NASA recently awarded $9.5 million dollars to Continental in a competitive bid that pitted Continental, Lycoming, Zoche, and other engine manufacturers against one another. In winning the bid, Continental pledged to design, test, and deploy a new 283 cubic inch, 200 horsepower, four-cylinder, direct-drive diesel engine on a Piper Seneca within three years. Continental’s target fuel consumption for the diesel is a reasonable BSFC of 0.36.
Why diesel? The main reason is fuel. While aviation gasoline (AvGas) isn’t going anywhere soon, it’s clear the fuel’s long-term viability is in serious question. Europeans are used to paying several times the amount we enjoy in the United States for fuel and in other parts of the world it’s being eliminated completely. For companies such as Piper and Cessna, which hope to be able to derive a significant portion of their revenues overseas, having to equip their new planes with engines for which fuel is or soon will be unavailable isn’t a viable option.
A diesel engine will be able to use airport jet fuel. Thus fuel availability won’t be a question for such an engine in the future. Also, jet fuel is significantly less expensive than AvGas which should reduce overall operating costs.
Diesel engines are no novelty to either Lycoming or Continental. Both firms built large diesel engines for the military during the 1960s and Continental built an air-cooled diesel radial as a tank engine.
Continental
Continental’s diesel is of the traditional opposed-engine design but similarities with other aircraft engines end pretty much right there. On the diesel, each opposing pair of cylinders are situated directly opposite each other (instead of being staggered as on gasoline engines) and share a common crankpin through a slipper rod arrangement. With proper application of static counterweights the four-cylinder engine should thus be free of the nemesis of traditional four cylinder engines – an unbalanced secondary moment vibration. Furthermore, since it is a two-stroke engine, the Continental engine has a piston fire every 90 degrees instead of every 180 as happens in a four-stroke gasoline engine. The combination of these two design traits should make for an extremely smooth four cylinder engine.
In addition to the above, the Continental engine also features liquid cooling, roller tappets, and a scroll type belt-driven supercharger. It is Continental’s intention to produce retrofit kits so that the engine may replace their traditional air-cooled gasoline engines. Thus the current form-factor of the diesel engine closely matches the existing engines. The diesel engine generates its maximum power at only 2200RPM so it should go a long way towards providing a quieter environment both in the cockpit and on the ground. The roller tappets drive pushrods which open and close the exhaust valves (yes, there are two per cylinder). Intake is via forced induction through ports in the base of the cylinder.
It is also Continental’s intent that the new engine be extremely economical to manufacture. To that end, they’ve designed the engine with, essentially, only two major assemblies. Each crankcase half incorporates the cylinders and head assemblies as part of the casting. The cylinder barrels will incorporate stainless-steel inserts for the pistons and rings to bear against. The engine will also incorporate dual alternator mounts, an air-conditioning compressor mount, and three standard accessory pads. Continental intends to expand the line with a 400 horsepower six and a 600 horsepower eight cylinder engine at some time in the future.
Lycoming
Lycoming was disappointed that it didn’t win the NASA bid but that hasn’t stopped it from looking towards a “fuel-driven” engine as well. Lycoming had already experimented with alternative engine configurations and fuels during the 1980s when they partnered with John Deere and what was left of Curtiss-Wright to build the 400 horsepower SCORE rotary. The SCORE was to be a stratified charge omnivorous rotary engine (hence its name) which could run on jet fuel, as well as gasoline, and which weighed significantly less than existing engines. Because of its stratified charge (in which an extremely lean mixture is set afire by a much richer mixture), the SCORE engine was able to produce BSFCs of 0.40-0.43. These numbers are very good for a rotary engine as they are notoriously fuel thirsty.
Rotary engine development at Curtiss-Wright in the 1960sUnfortunately the engine got heavier as development continued. Particularly troublesome was the fact that the SCORE required a huge turbocharger and that added weight. Because of the stratified charge, the engine was “air-thirsty” and, even with turbocharging, lost power as altitude was gained. The realization that the engine would not be as competitive on a weight basis as had been hoped occurred just as the general aviation market was collapsing. As a result, Lycoming cancelled the project in the late 1980s after spending over six million dollars on development.
At about the same time that it was working on the SCORE engine, Lycoming adapted one of their traditional engines to the diesel cycle. They plan on pulling this four-cycle engine out of the closet and running it again early this year as an internal research project. Using what they find from their research, they may enter production with the engine or they may decide to partner with another firm to develop a new or adapted two-cycle diesel engine.
Lycoming, as is often the case, is proceeding much more conservatively with regard to production of a diesel engine. Their intention is to spend a little bit of money now on research before committing themselves to a major new initiative. On the one hand they acknowledge the need to find an alternative to engines which must use AvGas. On the other, they are not sure the market will support a reasonable return on investment (or any return at all) on new-design engines.
Zoche
The other potential player in the diesel engine game is Michael Zoche AB of Munich, Germany. Zoche points out that a major reasons for a market for their engine is the situation with AvGas in Europe. With a combination of lower BSFC and the ability to burn Jet-A, the aircraft owners in Europe should be able to rapidly amortize the cost of converting to the Zoche.
Zoche has developed a family of 2, 4, and 8 two-stroke radial diesel engines. All are turbocharged and feature exceptional power-to-weight ratios (the main benefit of the two-stroke). The Zoche, like the Continental, uses a slipper bearing; there are no master and slave rods as on a traditional radial. Because of this and because it too is a two-stroke, the Zoche should also prove to be an exceptionally smooth engine.
Eight cylinder Zoche radial in the test cellThe ZO 01A is typical of the line. It has four cylinders, weighs 185 lbs, and produces 150 HP with a BSFC of 0.365. Zoche is simultanously certifying this engine in the United States as well as Europe and anticipates a 2,000 hour TBO. A unique feature of the Zoche is its pnumatic starting system – said to cause the engine to transition from stopped to running almost instantly.
The Zoche ZO O1ATim Coons, of Mooney Modworks fame, plans to run the eight-cylinder 300 horsepower ZO 03A next year in a Mooney 252. Coons claims the Zoche has half the frontal area of the equivalent opposed aircraft engine and half the fuel burn. Tim feels that the diesel’s BSFC curve is not so much a curve as it is a plateau. In other words, diesels have poor BSFCs at low relative powers (like all engines), but that BSFCs are relatively steady for moderate and high power settings and don’t exhibit the characteristic “bucket” normally found with reciprocating gasoline engines.
Zoche points out that a major reasons for a market for their engine is the situation with AvGas in Europe. With a combination of lower BSFC and the ability to burn Jet-A, the aircraft owners in Europe should be able to rapidly amortize the cost of converting to the Zoche.
Is there a market?
Suppose we did decide that a radical redesign of the current crop of aircraft engines was technically justified. Now it’s time to go to the beancounters and try and make a business case for investing millions in this new engine.
And we are talking millions: Continental will spend over $20 million developing their new diesel engine, Lycoming spent roughly the same amount (in today’s dollars) developing their SCORE engine of the mid 1980s. Well over $10 million has gone into the Orenda engine over the years. If you think these numbers are impressive realize they’re but a fraction of the amount Detroit would spend to develop an all-new piston engine for one of their cars.
Unfortunately, for the past decade or so, the industry hasn’t needed more than about 600 new engines per year from each manufacturer. Is it realistic to sink $20 million into engine development with such a low volume production? After all, if we have a generous 10-year amortization of development costs and we ignore the time value of money, that represents over $3000 per engine sold. Even that figure is hopelessly optimistic as it assumes that, immediately, all your new engine production will switch over to the new model; an assumption that’s not going to bear fruit unless your new engine represents a significant advantage over the previous models.
How about new engines from other companies, besides the big L and C? Frankly, you have to be either very clever or seriously insane to try and break into the certified engine market at this point in time. Lycoming and Continental have had the advantage of being able to incremental increase the reliability of their engines over decades. They’ve also built their reputations for reliability within the same generous amount of time. Remember that the first opposed engines from each manufacturer in the post-war period had TBOs expressed in hundreds, not thousands, of hours. Each has had the luxury of detail refinements to their engines, as well as years of field experience, that set current TBOs in the 2,000 hour range. That TBO figure is now the bar above which all competitors must immediately jump in order to be perceived as contenders. Set your TBO below equivalent offerings from the big two and people will ask what’s wrong with your engine? Set it above a prudent value and risk gaining a reputation for not reaching TBO. Damned if you do and damned if you don’t as they say.
Another factor barring entry to competitive firms are a lack of decent distribution and support networks. No one will want to buy your engine if they can’t get parts quickly in an AOG (aircraft on ground) situation. If you’re counting on sales of parts to provide a significant revenue stream (as Continental and Lycoming do) then forget about it being a factor for a decade or so when the 2,000 hour engines finally start coming back to the factory for rebuilds.
This phenomena is, by no means, limited to the certified engine market. Imagine trying to break into the commercial jetliner market at this point. The venture capitalists would laugh you out of the boardroom. Airbus has spent an amount equivalent to the purchase price of the southern hemisphere trying to do just that and still hasn’t made money. Likewise, image trying to carve a niche in the personal-computer industry if you don’t want to use Microsoft products running on Intel hardware. Good luck.
And it doesn’t seem reasonable to expect that radically reduced prices for engines will herald a new day in the GA market either. The price of the certified engines in today’s airframes ranges from approximately 15% (Cessna 172 class aircraft) down to 7% (Beechcraft Bonanza) of the total purchase price of the aircraft. Even the obscenely expensive TIO-540-AE2A (list price about $100,000) is less than 10% of the total cost of the Malibu Mirage into which it goes. The point is that even if Continental and Lycoming gave their engines away for free it wouldn’t have much effect on the prices of new aircraft nor could we expect piston aircraft production to jump from 576 aircraft in 1995 back to 1978’s 17,000 aircraft just because of a 7-15% price reduction.
Conclusion
Significant changes are afoot in the aircraft engine business. As we seen, it looks like our engines are finally getting electronic controls and something is being done about the fuel issue.
But questions remain on both fronts. Will single-lever power controls increase the GA market by bringing in pilots who don’t want to mess with throttle, prop, and mixture controls? Or will they be seen as expensive, heavy, unneeded additions with limited macho appeal? After all, there is a precedent in aviation which goes against refinements which demand less skill from the pilot. Pilots have traditionally shunned innovations such as tricycle gear, the centerline-thrust twin Cessna 337, Mooney Porsche’s single-lever power control, and computerized airliner cockpits which they perceive either as taking them out of the loop or of requiring fewer skills. One aviation writer, when told of the FADEC developments, said “I don’t want a single lever power control, I was something that increases the utility of the aircraft. I want thunderstorm protection!” Another manufacturer of supplemental fuel products for aviation piston engines worried about being left out of the engine-control loop without the traditional mixture and prop controls.
As for new-engine development such as that by Continental and Zoche. Will these longshots payoff in the years ahead by increasing the piston general aviation aircraft’s utility? Or will both firms find themselves in dire straits in years hence when their tremendous investment doesn’t pay dividends and the industry continues to slop along at production levels more appropriate for oil tankers than it is for a durable consumer good?
Gregory R. Travis
Greg can be reached via e-mail at greg@littlebear.com. He also maintains a web-page devoted to reciprocating engines of all types at: