Lycoming Has a Diesel

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In the world of military aviation, the piston engine was left for dead sometime in the 1950s and it would still be thus if drones hadnít come along. But piston engines swinging old-school props give unmanned aircraft something that jet engines canít: unrivaled mid-altitude efficiency and endurance. So as unlikely as it seems, drone technology is pushing piston engine and prop design and thatís why Lycoming has a diesel engine that we know absolutely nothing about. Itís designated the DEL 120 and has 205 HP, meaning itís in the IO-360 class. Itís the prime powerplant in the General Atomicsí MQ-1C Improved Gray Eagle, an Army drone. The Gray Eagle is a follow-on to the MQ-1 Predator, which has similar mission capabilities.

A call to Lycoming about the DEL 120, which we learned of earlier this month, yielded a polite no comment, but no denial of its existence, either. In a press release last summer, General Atomics mentioned the engine openly, but I somehow missed it, as did almost everyone else, evidently, because thereís simply no detailed coverage of this new powerplant. With Lycoming keeping the wraps on it, I can only guess at its specs. And my guess would be a four-cylinder, turbocharged four-cycle design with direct drive. But for all I know, they could have made a developmental deal with DeltaHawk and repurposed that technology. DeltaHawk has a two-cycle variant in the 200-HP range. Early p.m. addition: A reader phoned me with a more likely speculation on the engine. A company called DieselJet is repurposing Fiat diesel engines for aircraft use and even has one certified to a maximum altitude of 35,000 feet. One of these is used in the Alenia Aermachhi Sky-Y, an Italian drone, and also the Israeli Great Blue Heron. The timeline and horsepower fit. Washing a foreign engine through U.S.-based Lycoming would probably make the Pentagon happy.

Whatever the engine is, it got there for two reasons. One is that when Thielert went bankrupt in 2008, General Atomics needed a reliable engine source for its Predator and follow-on models and China-based AVIC's purchase of Thielert last summer meant it would have to shop elsewhere for a new engine.

Does this mean Lycoming is about to announce a civil diesel program? Maybe, but Iíd be surprised, even if Lycoming does reveal more about the engineís details. In previous interviews, Lycomingís Michael Kraft has been openly skeptical of diesels for aircraft, not so much for technical reasons but because the company believes the market isnít yet deep enough to support the investment required to bring a certified diesel to market. But for every bear, thereís a bull and that would be Continental Motors, which bought the former Thielert Aircraft Engines last year and is busily resurrecting the Centurion line. It also has at least one clean-sheet design and from SMA, it bought the technology-base for its TD300, a four-cylinder turbodiesel.

When Kraft has been asked in the past why Lycoming isnít more diesel-centric, he has taken to asking the questioner if he or she noticed all those diesel airplanes parked on the ramp. A fair point, but on the other hand, Diamond does have more than 1000 diesel-powered aircraft in service. On some ramps, they are indeed in evidence.

But, as Iíve said before, I donít think diesel technology is poised to explode. The sales and demand simply arenít there and it remains to be seen if diesel will develop into a robust refit market. If avgas goes to $7 or $8 in the U.S., I'll reconsider. But I hardly think itís a slam dunk. I think the diesel market will ramp slowly over many years, gently displacing gasoline engines in some markets and models. It's here to stay, all right, it will just be a slow slog.

Thatís just one view, though. But both Lycoming and Continental face different risks in the would-be diesel market. Continental is making, by general aviation standards, a high-priced bet on diesel, the outcome of which is impossible to predict. Theyíre hoping that five years from now, diesel may enjoy a 20 to 25 percent world market share.

If that potentiates, it could be 200 to 300 engines a year, assuming the Asian market proves as strong as people think it will. I donít know what Continentalís ROI expectations are, but clearly, diesel has to be a long-term play. In any case, its diesel investment may meet the companyís stated goal to make offshore sales the driver for its business, not North American sales.

Where does this leave Lycoming, then? Assuming the DEL 120 could be certifiedóperhaps under future, less stringent cert rulesóit might give Lycoming a chip in the game if demand perks up. But itís going have to perk to a rolling boil to get Lycoming interested, Iíd bet. Even if the technical aspects of the diesel are relatively nailed down by the Grey Eagle project, cert costs will be in the millions and it takes a bunch of sales to regain just the basic investment, much less a return worthy of the name. And all that for 50 engines a year? You can see the challenge.

Then thereís the OEM interest, or lack thereof. Other than Diamond, Cessna is the only major manufacturer to come out of the ground with a diesel. We hear rumors about Piper and Cirrus, but no commitments. If Cessna were any less enthusiastic about promoting its JTA diesel, it would qualify as comatose. At last fallís NBAA convention in Las Vegas, Cessna CEO Scott Ernest was questioned on the status of the JTA project and offered no details in answering. Queries to Cessna either arenít returned or just confirm that the project is still alive. Somehow, I find myself wanting a little more than that. Itís hard enough to stir the market with completely over-the-top promotion and marketing. Strangling the information flow and sowing doubt strikes me as a formula for failure. In that context, you can see why Michael Kraft isnít swooning for a whiff of Jet A.

Join the conversation.
Read others' comments and add your own.

Comments (36)

there are several topics or issues bheind the diesel choice and it is not an easy task to summarize, but remeber that:
- avgas is very expensive (in Europe is more than 10 USD/gal, sometimes more than 15 USD/gal)
- avgas sometime is very difficult to get: in Africa and Asia is really difficult to find avgas
- avgas contains lead, which is something we try to get rid of
- diesel engines use jet fuel, that is cheaper and easier to find, and avoid having several fuels at the military bases/deployements

Diamond Aircraft sells more diesel aircraft then gasoline ones outside USA, so I think the market could be not bad
having said so, I think there is still a long way to go before having a ramp full of diesel aicraft

Posted by: alberto beccaro | February 14, 2014 5:10 AM    Report this comment

There should be a strong market for 250 HP -350HP diesel engines for the working twin engine aircraft the burn most of the avgas. The are the Cessna 400 series and 300 series and Piper Navajo and Aztec aircraft, along with other similar planes. The potential reduction in fuel prices combined with lower fuel consumption do to more efficient operation would make a conversion almost a no brainer at overhaul time It should pay for itself in less than 1 engine life cycle. I don't see much hope for the 200 HP or less market making financial sense. because of lower annual usage rates.

Posted by: James Hiatt | February 14, 2014 6:59 AM    Report this comment

It's interesting to know that drones use some of our airspace and hover night and day long over our heads with those "non-certified" engines but it would cost XX millions to have them in our birds.

is it just me.

Posted by: Louis-B Lechartier | February 14, 2014 9:11 AM    Report this comment

The "Lycoming Diesel", if it is in fact that, is likely an uncertified engine for use in unmanned aircraft only. It may take an extensive re-design to meet man-carrying standards. A thorough engineering study is something you would definitely want done on this power plant before trusting your life to it.

This is reminiscent of the Lyc O-290 series of engines that were used on the PA-12, PA-20, and PA-22 aircraft. There was an alternate version of the O-290 designed for ground based auxiliary power unit use but unapproved for flying use. Nevertheless, a number of these APU engines found their way into experimental/ homebuilt designs (and possibly others). The engine mount and prop bolts fit, so it must be OK, right? Yes, it was done, but you won't find me flying behind an APU engine.

Posted by: A Richie | February 14, 2014 11:37 AM    Report this comment

My answer to Kraft's snotty question "have you seen all the diesel's on the ramp?" is that since nobody makes a diesel for my airplane, how can I buy one for it?

I'm very excited about the fact that Continental is working on one. GA needs the FAA to get over itself and it's antique regulations and allow more innovation to make it to the production line, not just remain stuck in the Experimental category. IMHO

Posted by: chuck harral | February 14, 2014 5:03 PM    Report this comment

Whatever the truth, an automotive adaptation seems like the best option, price wise. They just need to be cheap enough and simple enough to slot in at overhaul time. Easy to say in a sentence, clearly harder to realise in the flesh.

Posted by: John Hogan | February 15, 2014 1:37 AM    Report this comment

Truly, I can't figure out Lycoming not wanting to certify this engine for general aviation, as the development cost has been paid by the government. This has normally been the path to new technologies in aviation, something developed for military use, that becomes an application that can be used for the rest of the market.

I think the opposed big bore long stroke engines that power general aviation aircraft, are a perfect match for development into the diesel fuel powerplant. That being said, there are some disadvantages of a diesel aircraft engine, with the additional weight due to strength of a "detonation engine".

What I can't figure out about general aviation powerplant advancement, is a new platform that incorporates a high power to weight ratio, with a mass manufacturing process that lowers the price of the engine. With CNC machines, and the reliability of automotive engines, some of that technology should be providing low cost alternatives for new piston engines. Include the electronic ignition systems, and total engine management similar to today's modern automotive engine fuel mapping and engine control.

Posted by: Michael Dempsey | February 16, 2014 11:07 AM    Report this comment

Perhaps Lycoming is betting that the FAA will approve a fungible replacement for 100LL- one that Lycoming will blanket-approve for all existing installations. If that happens, it would leave the marketplace unchanged; life as we know it would go on; which is the least-risky (and possibly most-profitable) outcome for Lycoming. If somebody else's diesels show signs of popularity, Lycoming always could re-consider. Or just buy up a third-party developer's effort. Ever the bold innovators!

Posted by: Tom Yarsley | February 17, 2014 8:02 AM    Report this comment

Mr.Yarsley: I believe you summed it up directly in your intelligent and accurate observation; " least risky (and possibly most profitable) for Lycoming" IS what a business is about including any aspect of GA - wouldn't you say?

Posted by: Rod Beck | February 17, 2014 8:34 AM    Report this comment

The engine you want is under testing . 350 Hp flat rated up to 17,000 ft out of a diesel engine running on Jet a that is the same size, shape and virtually the same weight as a 350 hp 550 or 540. the total installed weight firewall forward is 660 lbs. for comparison the same turbocharged installation of a 100LLcontinental in a cirrus weighs 625 lbs, It is being tested and has over 300 hours with no failures. go to

It is being developed by a small group of very smart guys in a skunk works type atmosphere. virtually all disruptive technology is developed by small groups of visionary people operating outside the normal process and not by any large corporation like Continental or Lycoming

Posted by: BILL LAWSON | February 17, 2014 2:59 PM    Report this comment

Having "graduated" from a Lycoming IO-360 Diamond DA40 to a Diamond DA42-VI with a pair of Austro/Mercedes diesels each with nearly the same power -- it's no contest.

The diesels are far smoother, quieter, more fuel-efficient, and easier to control with FADEC -- no more mixture/prop controls, ROP, LOP, or hot starts. Because they have turbos they let us easily climb out of icing conditions up high. So far they're burning less than a quart of oil between oil changes (which are every 100 hours instead of 50 for the Lycoming.) These are car engines after all.

If only more pilots could experience diesel engines. I can't imagine going back to ancient "Lycosaurus" avgas engines.

Posted by: DAVE PASSMORE | February 17, 2014 3:59 PM    Report this comment

I can imagine how neat it would be to have a diesel engine in my 1967 Mooney.

I can't imagine how much it would cost, first to purchase the engine, then to pay for the installation and STC.

The only way a diesel will make it for the sector of the GA fleet that I play in is if the price of switching to it becomes economical or if the disappearance of 100LL comes to pass.

Posted by: STEPHEN EGOLF | February 17, 2014 7:46 PM    Report this comment

Steve; RE: your 1967 Mooney - I believe your eluding to "cost effectiveness" - good point!

Posted by: Rod Beck | February 17, 2014 9:49 PM    Report this comment

In the very near term, diesel is a good bet. Not only has the US military sworn off avgas, but it is also becoming ever rarer and more expensive at civil airports. That isn't going to get owners to run out and pull low-time engines off their airplanes to put in diesels, but it will drive them to strongly consider a diesel conversion at major overhaul time...provided, of course, that the alternative is offered to them.

Posted by: Marc de Piolenc | February 18, 2014 1:25 AM    Report this comment

Cost of engine determines the popularity of use of engine. Prospect not good.
2.0 diesel engine cost estimate for Mooney or any other like aircraft. Try $80,000 for an engine and three gear boxes every 750 to 1000 hours. Not cheap. Continental Engine TBO 1000 hrs, gear box TBO 250 hrs.

Posted by: Rafael Sierra | February 18, 2014 6:47 AM    Report this comment

"Continental Engine TBO 1000 hrs, gear box TBO 250 hrs."

Actually, the Centurion is at 1500 hours TBR and gearboxes are at 300, soon to be 600.

Posted by: Paul Bertorelli | February 18, 2014 7:27 AM    Report this comment

TBR or Time Between Replacement is now 1200 hrs! Thank you Paul. I have no info on the gear box change to 300 hr or to a 600 hr TBR. Replacement is different than TBO. I meant TBR rather than TBO. Some improvements have been made since I became interested in this. But, it is still more expensive to TBR than to TBO. Three or four gearbox replacements for every engine replacement makes all this financially questionable.

The concept is to pay less not more!

Posted by: Rafael Sierra | February 18, 2014 4:33 PM    Report this comment

Thus, I predict that there is no future for the diesel engine in GA.

Posted by: Rafael Sierra | February 18, 2014 5:11 PM    Report this comment

Rafael, I think if you knew more about this technology, you wouldn't be saying "no future." When you consider the economics, the general trend in manufacturing and diesel technology and the fact that operating costs will come down, the long trends clearly favor diesel.

It's hardly a slam dunk. But the numbers pencil out. And variations in the numbers matter. A lot.

Posted by: Paul Bertorelli | February 19, 2014 11:47 AM    Report this comment

Evaluate costs, market and technology Paul. Thielert folded for a reason, Continental bought them and sold to the Chinese claiming a huge world wide retrofit market. The numbers do not add up. The market is insignificant the diesel engine unit costs are out of proportion with the demand. Lycoming should be smart enough to acknowledge this.

Posted by: Rafael Sierra | February 19, 2014 7:39 PM    Report this comment

Paul, I respect your knowledge and opinion whilst I also recognize your effort to sell a concept that I am not buying.

Posted by: Rafael Sierra | February 19, 2014 8:08 PM    Report this comment

"Thielert folded for a reason."

Indeed it did. What's your impression of what that reason was?

Posted by: Paul Bertorelli | February 20, 2014 3:09 PM    Report this comment

Frank Thielert's fraudulent financial reports, bad management, loss of investor support.

Posted by: Rafael Sierra | February 20, 2014 8:20 PM    Report this comment

I am not against the product - only against hysterical claims by the media where a product is declared a panacea promising GA's salvation. It did not work with the Skycatcher or the Recreational or LSA pilot programs. We need a larger night chamber.

Posted by: Rafael Sierra | February 20, 2014 8:31 PM    Report this comment

On October 4, 2007 Cessna announced its plan to build a diesel-powered Cessna 172 model called a "TD" starting in mid-2008. The engines were to be installed at the Cessna Skyhawk factory in Independence, Kansas under an STC. Cessna had forecast delivering about 125 TDs before the end of 2008. The TD was intended to sell for about US$15,000 more than the top of the line "SP" Skyhawk and $35,000 more than the "R". Early orders for the TD were strong, with most of the demand from flight schools and non-US operators. In April 2008, the 172TD's engine manufacturer, Thielert, filed for insolvency under German law. On May 1, 2008 Cessna announced they had cancelled all 2008 deliveries of the 172TD due to the insolvency of Thielert.

Ok, so move forward five years and we have the JT-A C-182, selling at over $500K USD. Do you know of many flight schools operating a fleet of C-182s?

Despite the fact that the 172TD model had been canceled due to Thielert's bankruptcy. Simulator company Redbird Simulations will instead use the same engine and reconditioned 172 airframes to produce a similar model to be called the Redbird Redhawk. As the Redbird Dealer for SE Asia, I have dozens of schools wanting to order these aircraft. With Avgas in Asia very difficult to find, and selling for $12+ a Gallon, and Diesel selling for less than half of that, its no wonder diesel is a popular choice outside the US. One company's failure is another companies boon, or so it seems.

Posted by: Trevor Evans | February 20, 2014 11:03 PM    Report this comment

Paul, a blast from the past...

"Thielert: How To Kill A Company (Maybe Two)

By Paul Bertorelli | May 23, 2008

Owners of more than 800 diesel-powered Diamond aircraft are collectively holding their breath to find out how--or even if--their expensive engines will be supported following the disastrous financial meltdown and bankruptcy of Thielert last month. One question gnawing at these owners and owners of Cessnas and Pipers converted to Thielert diesels is whether the engine is technically and financially viable.

That answer came swiftly and certainly this week from the legal firm overseeing the Thielert insolvency: The engine doesn't have a prayer of surviving in the market and is effectively flat lined. Kuebler--the bankruptcy company--didn't say this in plain language, of course, but following a surprisingly quick audit of the company, it published a list of parts and replacement prices that are so absurdly high as to make the engine unsustainable. Given Kuebler's proposed economics, it would almost be cheaper to operate a Lycoming by having the avgas shipped in via FedEx to those parts of the world where only Jet A is available."

Posted by: Rafael Sierra | February 21, 2014 5:31 AM    Report this comment

Paul, this helps explain Lycoming's diesel engine for the military drones and the Thielert engine added financial woes. No General Atomics.

"AVIC Buys Thielert to Shift Company to Planes From Drones

By Richard Weiss Jul 23, 2013 8:05 AM PT

Aviation Industry Corp. of China, the country's biggest aerospace company, agreed to buy Thielert Aircraft Engines GmbH, focusing the insolvent German supplier fully on powering private aircraft and away from U.S. drones.

The Chinese manufacturer's AVIC International Holding Ltd. (232) unit, which has already acquired Minnesota-based planemaker Cirrus Aircraft and engine producer Continental Motors Inc. of Alabama, is adding Thielert's civil engine business to prepare for a domestic boom in private aviation, Bruno Kuebler, Thielert's insolvency administrator, said on a call with journalists.
The sale ends five years of insolvency proceedings and restructuring for Hamburg-based Thielert.

Kuebler said Thielert remained profitable with three German sites and just over 200 employees because of orders mainly from San Diego-based General Atomics Aeronautical Systems Inc. to power drones.

General Atomics indicated potential interest in Thielert, but AVIC offered a "'strategic price'' for the propeller-engine maker, Kuebler said, declining to provide details.

Thielert had 24.5 million euros ($32.3 million) in sales last year, the administrator said. The German manufacturer stands to benefit from growing demand in Asia and Africa for diesel-engine planes because of the wider availability of fuel, he said."

Posted by: Rafael Sierra | February 21, 2014 6:46 AM    Report this comment

So the point here, which I think you understand, is that Thielert didn't fail because the diesel concept was unworkable or because the engines were irreversibly technically flawed. It failed largely because of a bad business plan and an overbroad warranty program seasoned with stock fraud.

Once that was sorted out, the engine concept itself continued signs of life. When the numbers came out post bankruptcy, this become more obvious. But over time, it sorted out and Thielert actually turned barely black, the parts prices came into line and operators starting making money.

I can hardly be accused of being a cheerleader for diesel. I've been covering the segment for more than 10 years and have flown most of the diesel-equipped models. The case for diesel is far from slam dunk, but anyone who examines the data honestly will see the potential.

When you post wrong data--as you did upthread twice--I will gently correct that. Any reasonable person can look at that data and be unimpressed, as I sometimes am. But the data should be accurate. Yours was not.

Posted by: Paul Bertorelli | February 21, 2014 8:18 AM    Report this comment

Paul, are you are referring to the TBR data on the engine and gearbox or the cost of the estimated unit costs I mentioned? I estimated costs and TBRs based on information that floated in the industry. You can be more accurate than I, I agree to this, but I am not overstating to gain in the market by misinforming a la Frank Thielert. Thielert promised TBRs to 2400 hrs. You mentioned 1500 with gearboxes increases to 600 hrs. - where is the proof?

Posted by: Rafael Sierra | February 21, 2014 11:08 AM    Report this comment

"When you post wrong data--as you did upthread twice--I will gently correct that." The Holy sister in my school used to say that. It still hurts and that was some 65 years ago.

Posted by: Rafael Sierra | February 21, 2014 12:25 PM    Report this comment

Raf, you can go on the Centurion web site and they are quoting 1500 hours TBR and have been for several years now. That's what they're shipping, not 1000-hour engines. The gearbox is at 300 now, although they have the 600-hour box developed and are awaiting regulatory approval.

You had said 250 on the gearbox, but it was never that, even from day one. I don't know what you mean by data "floated in the industry" because there's so much whisper campaign bad data out there that's aimed at diminishing the attractiveness of Jet A piston engines. It's not hard to find good data.

My--I hope objective--analysis indicates that the Centurion barely holds its own against a Lycoming now. It's a few bucks more an hour to operate. But if diesels are to maintain their foothold, they will do so only if higher TBRs are delivered. If replacement avgas is more expensive, the hourly operating cost Delta can be as high as $20.

That's compelling. But it is a forward looking market based on that higher TBR and marketing trends not driven by the U.S. The latter is assured, the former, we just don't know. But from what I can tell, there's no obvious reason why this isn't doable.
Continental says Thielert developed the data to support higher TBR but never had the resources to get it through the regulatory process. But Continental does.

I'm experienced enough to realize it could still run off the rails. S^&t happens. But at this juncture, longer engine life has potential. In looking at the real data, there's plenty of room for doubt, but also real promise.

Posted by: Paul Bertorelli | February 21, 2014 1:01 PM    Report this comment

Just a clarification here. The 300-hour gearbox applies to existing engines. The new ones are shipping with 600 hour approvals.

Posted by: Paul Bertorelli | February 21, 2014 2:42 PM    Report this comment


Posted by: Rafael Sierra | February 21, 2014 3:07 PM    Report this comment

As I research for a counterpoint I read stuff that just plainly pisses me off over and again. I hope Lycoming does not follow this path.

From AVweb: People's Daily, the official organ of the Central Committee of the Communist Party of China, reported on Tuesday that state-owned AVIC International Holding Corporation recently completed its acquisition of Mobile, Ala.-based Teledyne Continental Motors and the purchase "will make AVIC International better prepared for the burgeoning general aviation market in the country." It also touts the pending sale of Cirrus Aircraft to China Aviation Industry General Aircraft Company (CAIGA) "will greatly enhance CAIGA's production capacity, and help it meet the surging demand for general aviation aircraft as China looks to further open up its low-altitude airspace."

Posted by: Rafael Sierra | February 22, 2014 10:50 AM    Report this comment

2-3 (maybe 4 or 5) years ago, Lycoming displayed a "heavy fuels" engine in it's booth at Oshkosh; just to show the world that they had such a thing.
If I remember correctly it was four cylinders opposed with jacketed cylinders.
I would guess that this is either the, or the core of the DEL 120.
There's got to be some photos of it around out there.

Posted by: JOHN MININGER | March 9, 2014 8:33 AM    Report this comment

Will Lycoming show off this engine at Oshkosh 2014? Hope so!

Posted by: Peter Kuhns | March 27, 2014 10:13 PM    Report this comment

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