The 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 1960s
Unfortunately 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 cell
The 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 O1A
Tim 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
[email protected]. He also maintains a web-page devoted to reciprocating engines of all types at:
Prime-mover.org (http://www.prime-mover.org/Engines)