Can There Be This Many Engines?


I occasionally delight and shock my non-aviation friends with short, expletive-laden descriptions of airplane engines having changed little since VE day. In some ways, they’ve gotten a little worse. “Wait, you mean they have pushrods and carburetors? How can that be true?”

It is true, of course, unless you fly one of the new-tech diesels with that great leap into the internal combustion wonderland, overhead cams. Even Rotax engines, which emerge from a factory building gazillions of bleeding-edge motorcycle engines, still have pushrods. It’s also true that along with pushrods, in aviation, we tend to cling to the principle that it’s better to have small numbers of a lot of different things than big numbers of the same thing.

This is why we are so skilled at keeping aviation unaffordable to the mere peasants whose hearts burn to soar with the eagles, but whose lives are made aeronautically dreary by our uncommon ability to exterminate economy of scale should it even suggest itself.

It’s also how we periodically amuse ourselves with quality control disasters. It’s a known principle of manufacturing that if you build only 10 ZF-12-HB crankshafts, two will have off-spec number 2 journals, but you won’t know which two, so all will have to be recalled, grounding the airplanes for 18 months.

But I’m falling into my typical dark vortex of doom here, even as I try on a rainy morning to write an uplifting commentary on the wonders of aviation in the age of the plague. Standby, I’ve got one knee up over the edge of the crater and have a tiny nugget in sight. It’s a question. How many different aircraft engine manufacturers do you think are on the FAA registry? I’m not talking about engine types, say the difference between an IO-360 and an IO-540, but actual named engine companies.

I would have guessed about 50 or 60, when you consider the sparse uplands beyond the dense forest of Lycoming, Continental, Pratt, Wright and so on and you encounter the Kinners, the Franklins and the Warners. The actual number is 212, which includes a smattering of experimental engines.

This obscure fact was unearthed by my friend Todd Huvard, of Aircraft Merchants, who crunched the date for me on an article about engine failures. We both thought that this would be a simple job because there just aren’t that many engine varieties. This delusion belongs in the same file with the optimistic declaration that the war will be over by Christmas.

First, if you think Continental and Lycoming dominate the motive side of making things fly, you’re right. Bigly. Between the two of them, they have about 184,000 engines on the FAA registry. Lycoming has 52 percent of these, to Continental’s 48 percent. By comparison and even though the dollars are vastly larger, turbine and jet powerplants represent much smaller numbers. Adding up the CFMs, the GEs, the Rolls and Rolls-BMWs, the Garretts and even Pratt & Whitney with the prolific PT6, the total is under 40,000. (This is U.S. registry only, not world market.)

Sorting the numbers reveals why Lycoming and Continental are the king and queen of low-volume, high-mix manufacturing. Lycoming has a whopping 476 different model variations on the registry—there are 40 variants of the O-320 alone and 41 for the popular O-360. Many of these amount to little more than accessory case variations, but those model changes often include oddball things like different gearing or dimensional changes for critical parts that mean one crankshaft or crankcase won’t fit all of the models. It’s mass production on an insanely chaotic level.

Continental has less variation—233 type certificates on the registry. This is probably because Continental traditionally earned its high-volume bread and butter with large displacement engines such as the O-470 and O-520 series which didn’t have the variety of Lycoming’s line. Also, although it has its GTSIO engines, Continental doesn’t have designated helicopter and aerobatic engines, as Lycoming does.

Lycoming has some oddball designations, too, such as the YIO-360-M1. Huh? It’s an uncertified version of the O-360 for experimentals. How about the VO-540-C2A? It’s a vertically-mounted helicopter engine. Six of those are out there flying, or at least registered. There’s a TIVO-540, too. No, it doesn’t timeshift favorite TV shows; T is for turbocharger.

Both the Lycoming and Continental totals include radial engines. Surprisingly, Continental has the most, with almost 1100. Lycoming’s R-series show about 650 on the registry. The Continental W670—aka R-670—is the most numerous and you know it as the PT-17 Stearman powerplant. It was also used in the M3 Stuart tank during World War II. Lycoming’s big-volume radial is the R-680, with about 600 still on the books. It was used in the Beech AT-10 trainer and the Stinson Airliner, among others.

As with firearms and old cars, collectors probably drive the existence of some truly old and oddball engines. Aeronca—yes, the airframer—built its own engine before World War II, the E-113. In 1939—a year after my Cub flew out of Lock Haven—it was “modernized” with dual mags. More than 80 years later, 63 are still registered. Any flying? I’d love to know.

Another rarity is the Alvis 514 nine-cylinder radial developed in Great Britain before World War II. There are two of these on the registry, suggesting someone has either a Percival Pembroke or a Scottish Aviation Twin Pioneer, the airframes the Alvis was used in.

My colleague Paul Berge has actually flown a Funk, but I’ll wager that even he doesn’t know there are eight Funk E engines on the registry. It was developed from the Ford B automotive engine. There appear to be 89 Funks still on the FAA’s active list and although most have Continental engines, some have the original Funk. One is owned by the Coffeyville Aviation Heritage in Kansas.

There are even older engines still registered. The Hispano-Suiza was a hot number in 1914; still three on the records. How about the Packard Liberty L-12? At least seven of those still exist and their owners bother to keep them registered. While were talking Packard, there are 88 V1650s registered in the U.S., the very same ones that stand the hair on your neck up when they fly by at Oshkosh. These are the Packard-built World War II Merlins. (See how to start a Merlin in this week’s video.)

Some of the engines with just a handful of registrations may seem like long-forgotten relics, but they’re just the opposite. The Emrax 228, for example, is a liquid-cooled electric motor. (People in the business seem to prefer calling them engines.) There are two of these registered. Siemens (now Rolls), on the other hand, has 11 of its electric engines officially registered.

And yet there are puzzlements. How can there be 14 Porsche PFM 3200s still alive? Mooney and Porsche want to forget these and actively encouraged owners to re-engine the ill-starred Mooney M20L. In 1985, both companies thought Porsche’s high-performance, air-cooled six-cylinder engine would be a perfect fit for the new long-body airframe. It turned out to be a hot mess, but evidently one that 14 owners still kind of like. Or haven’t found a way to clean up.  

Speaking of messes and aviation’s tendency to keep them around with STCs, mods, ADs and field expediency, I thought I would find at least one shining example of one of aviation’s exceptional duds: The Continental Tiara engine. This one was developed during the 1960s in four-, six- and eight-cylinder versions. The engines were high-revving, vibey and fuel thirsty and, evidently, no one liked them much. It’s sad testament to their badness that not even one stalwart collector would step forward to keep one on the registry, once again proving why aviation actually is sometimes justified in proving itself the backwater it appears to be. We tend to stick with what works because all too often, the new stuff we try doesn’t.

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  1. For the Trivia Buffs; What other aircraft used the Alvis engine?
    Only one built; The DHC2 Mark 2 had the Alvis engine.
    Lighter than the Pratt 985, with 100 more horsepower; the aircraft had better performance; likely even better than the first Turbo Beavers, and with less fuel consumed.
    When the British Army decided to buy Beavers, they were going to use the Alvis engine; ultimately, it was going to cost more, so they went with the Pratt.
    The only Mark 2 Beaver was owned by a DeHavilland exec. Not sure where it is now, but it was pristine.

  2. I fly a Mooney 201 with a Lycoming IO-360 engine. When I bought a new engine in 2008 I could not believe the number of ‘different’ IO-360s that they built. And of course the one I needed was more expensive than many of the others. I just looked at the Lycoming website a few minutes ago and they make 108 IO-360 variants. Those are just IO-360s and do not include the HIO or AIO or any other variants. OK, I buy that they may only have different accessory sections, but why?

    I also blame airframe manufacturers. Why do they NEED a separate variant? The Piper Arrow has an IO-360. Why the bleep didn’t Mooney choose that engine when designing the E, F or J models? And why didn’t Lycoming tell Mooney that a different variant would be cheaper for them now and their customers in the future? The fewer the variants the less expensive the engine will be. I would think that would be a motivation for both parties.

    I can’t believe that there needs to be more than 1 or 2 variants of this very popular 200 HP engine. I feel better now…..

    • “I also blame airframe manufacturers. Why do they NEED a separate variant? The Piper Arrow has an IO-360. Why the bleep didn’t Mooney choose that engine when designing the E, F or J models?”

      I can’t speak to all of the differences, but in the case of the IO-360 I know of the reason for at least ONE difference. The Cardinal RG and some Mooneys both use a near-identical engine, the IO-360AxB6. On the Cardinal RG the ‘x’ is a ‘1’, and on the Mooney it’s a ‘3’. That digit refers to the location of the prop-indexing bushing on the crankshaft flange. Not a different crankshaft, just a different location for that pressed-in bushing. Which, in turn, changes how the prop is ‘clocked’ to the crankshaft.

      Which apparently is a significant enough difference. Mooney and Cessna must’ve found during development of their retracs that some prop positions undesireable vibrations, and had the crankshaft indexed accordingly. Same engine, yes, but mounted in a different airframe produces a different result.

    • Can you imagine the Outboard Marine engine people making 200 different engines. In the small town I live in students are trained in a C150 which is a few years older than the one I trained in 1965.

  3. Like Joel, I am amazed at the number of IO-360 engine variants that Lycoming has produced. I can see why, over the history of aviation, there are many obscure engine builders that have faded into the past. Look into automobiles and you will see a similar history. But why on earth, do Lycoming and Continental persist in making a zillion different versions of the same thing? If nothing else, the paperwork burden needed to keep the FAA happy must be horrendous. It does seem that they are willing to let the airframe builders dictate to them how an engine must be modified to fit their designs, rather than the other way around. Add to the Lycoming misery the sad tale of the -D mag engines and it would be comical if it weren’t so frustrating – and costly to owners.

    Long ago, auto manufacturers learned to make part commonality a key to cost containment. Remember the Chevy 350 engines that turned up in Oldsmobile cars? That one prompted a lawsuit, in spite of the fact that the Chevy engine was better than the Olds version. Part of aviation’s willingness to perpetuate this mess may have come from the fact that the engine builders were the sole source of replacement parts. Why worry about the wide variety of engines if you can charge what you want for new parts. At least that has changed a little with regard to replacement cylinders. When Continental began producing cylinders for many Lycoming engines, the Lyc versions magically got cheaper. Unfortunately, Lycoming still has the lock on their angle-valve cylinders for the 200 hp IO-360 in my Cardinal. So those precious items are still (almost) worth their weight in gold.

    • I agree about the baffling number of engine variants for a common type, like the xO-360s. Many of them are basically just slight revision changes (lighter crankshaft, different harmonic balancers, etc), and I guess the FAA considered those changes “significant” enough to warrant a new model? It can’t be that all of the variants are from airframe demands, can they?
      Ugh, and the -D models. I don’t know how those ever got approved. My club went so far as to get a -337 to change out a -D model engine for the non-D model (it weighs slightly more, but is otherwise the exact same engine) in one of our aircraft.

  4. Paul, a very interesting article. As an owner of a first gen Bonanza powered with an Continental E series 225hp E-225-8, I too wanted to know why so many variants of what appears to be the same engine.

    What I have learned is each series of engines address slight internal dynamics that result from seemingly minor changes. These changes come from accessory availability, accessory improvements, and HP increases. Accessories include prop, generator/alternator, vacuum pump, magneto, etc. Some changes result from improvements, manufacture tolerance change, manufacturer’s going out of business or bought out by different companies changing parts availability, etc. When something changes, internal dynamics can change leading to new vibration dynamics/harmonics.

    E-series Continentals are all 470 CID. The range in HP from 165-225HP. Not all the crankshafts are the same or interchangeable because of crank balance changes due to RPM changes and limitations. My E-225-8 makes 225HP because it’s max RPM is 2650. The 205HP version has a max RPM of 2600. The 185HP version has a max RPM of 2300. However, depending on which electric Beech prop blades are installed, 84″ or 88″,or Hartzell hydraulic propeller changed the internal vibration dynamics because of the max RPM differences. Within the first generation Bonanzas (1947-1956) there were four different prop combinations offered ranging from two electric wooden versions, one aluminum version with two different blade lengths, and eventually one hydraulic. The one minute take off RPM restriction on all E-series engines resulted from harmonic issues if the engines were to continuously run at max RPM. They are within an acceptable range for one minute. But they can exceed the acceptable harmonic range after one minute. But my E-225-8 will run all day at max cruise 75%/2300RPM(185HP) while the E-185 rated max RPM is 2300(185HP) with max cruising RPM at 2050/75%. Hence slightly different crankshafts. All E-series engines are dry sump engines requiring a separate oil tank. 0-470’s have the oil sump attached to the bottom of the engine ( wet sump). So, while an E-series engine is 470 CID and the 0-470 is 470 CID they are quite a bit different with little parts interchangeability. E-series engines were standard engines for first gen Bonanzas and Navions.

    Another consideration is FAA requirements for maintenance documentation plus procedures that have to be adhered to for airworthiness legalities. Did the Beechcraft and the FAA ever anticipate that these airplanes would be actively flying 70+ years later? I don’t believe that was planned for. Even the most minor engine or accessory design change has to be thoroughly tested to prove its airworthiness, plus the results of those tests led to specific maintenance requirements. All of these changes and/or improvements have maintenance documentation that legally must be adhered to. So, everything has to be preserved and accessible for ongoing maintenance. We are now up to 212 preserved different engines plus all the variations.

    This might help to illuminate the expensive maintenance documentation a local shop, A&P, or Part 145 Repair Station has to have available to do work on any given airplane, engine, and prop combo. Now add to that, the special tools required in many cases. Finally, preserving and transferring the maintenance knowledge to a newer generation of maintenance personnel is another cost an aircraft owner has to take into consideration as well. I can’t take my Beech electric prop to any prop shop for its 250/500 hour lube requirements. Since the average GA airplane is 50 years old, just about any airplane falls into the vintage category, with specialized service and maintenance requirements that have to be documented with staff having knowledge on that specific type, model, and engine.

    As an A&P formerly employed at a Part 145 Repair Station, I had the experience of removing and installing a Continental TSIOL-550-A Voyager engine on a RAM converted Cessna 414A. I got this task because I was the only one who initially recognized it was liquid cooled because to missing air inlets on the cowl. The sales person who bid the job did not know this was a liquid cooled 350HP engine that RAM had installed on about 37 400 series Cessnas back in the late 80’s and early 90’s. To him 550’s are 550’s. When the airplane arrived, RAM estimated this was one of possibly six airplanes left flying with this complex, turbocharged, liquid cooled engine still installed. RAM was strongly encouraging the new owner to not overhaul and install this liquid cooled engine and offered a really attractive alternative for conversion back to air-cooled engines. However circumstances were such that the engine was overhauled and eventually installed. That was one very expensive engine that makes up one of the more obscure versions of the Continental 550 series of engines. I learned the soon to be lost art of “burping” a liquid cooled, big inch Continental aircraft engine. This is no Rotax.

    There is no way to make aviation “standardized” including economy of scale. Unless, we all want to fly the same kind of airplane, with the same engine, with the same avionics, for the same mission profile. Assembled, flying airplanes, with their assorted engines, and avionics will always be a “customized”, one-off aerial conveyances after a very short time in service. In reality, no two are exactly alike. And they never stay the same over time.

  5. “In reality, no two are the exactly alike. And they never stay the same over time.” True words.

    I have always maintained that, when you buy an airplane, any airplane, it comes to you in kit form. And, you never really finish assembling it.