Why New Aircraft Engine Ideas Rarely Succeed

That was an interesting watch. Thank you, Mr B!

First, it’s about support, always has been always will be until the end of time and beyond. People, parts and pieces all readily available everywhere at all times is what you are buying. I don’t care if it’s a power plant, avionics, or, airframe components, you had better be able to support right from the get go , or, your dead meat. Teething problems of any kind are a non issue if they can be fixed quickly and correctly. Stumble once on the support side with a new product and you guessed it, (where have I heard that before) “your dead meat.”

Second, specifically diesels, they’re heavy, real heavy and to beef up an airframe to carry diesels you have to add more weight. 🤔 Hmmmm… something doesn’t sound right here. And, diesels fly heavy. 🤔 From the time you leave the ground to the time you land four, five, or, six hours later (if you make it that far) your plane is still heavy. Avgas power plants allow much more latitude in controlling useful load via the amount of fuel I want to carry with me given my mission whatever that may be at the time. Because diesels burn so much less fuel, your ability to control useful load is severely limited. Diesel powered planes are forever heavy before you put anything in them. They even look heavy sitting on the ramp completely empty.

Diesel performance? Just pick up a Diamond POH and look at the full range of performance numbers. As far as cruise performance goes where most of the time is spent, you need to be at 14,000’ plus to even get close to a comparable Lycoming, or, Continental from sea level on up and that’s comparing NA versus turbo which a diesel has to be to even think about comparable numbers. Now, add turbos to a Lycoming,or, Continental and the comparison doesn’t eve belong on the same sheet of paper. By the way, there’s a reason most small aircraft diesels don’t have pressurization, they can’t, useful load would be in the double digits.

I don’t care how easy diesels are to start, how efficiently they burn fuel, how cool you may think they are, they are forever big fat ugly birds from the time you set eyes on them to the time you walk away. It is what it is and it’s not going to change much in the foreseeable future. At least not in my crystal ball.

You forgot the Orenda/Trace engine that was going to be the panacea for all the woes of the Beaver, Otter, Ag cats and various other commercially used aircraft needing 600HP or more … sad ending to such promise.

Very well written explanation. it’s nuts to do a firewall forward engine replacement. The costs of the STC, new prop, new engine, mounts, sheet metal work, accessories, etc, are at least 3 times higher than just overhauling what I have. It takes more money than brains to do that sort of thing.

Then there’s this guy with a V8 engine in a 172. He’s determined to prove it can be done. https://corsairpower.com/

Very good question, and plausible answer.

But I don’t do videos so cannot comment in detail. Paul digs and thinks but is not always right.

All those moving parts in a recip engines are ridiculous.
Too bad the Wankel rotary was not perfected.
Unbelievably simple with NO reciprocation.
Other than turbines – NO PROGRESS in 120+ yrs!! ughh
I’m talking basics here.

As an RV-14 builder who powered it with a Superior XP-400, I personally built with electronic fuel injection and ignition, I hope you feel my pain. (After recall, I had Barrett rebuild it as an IO-390). I wish you had discussed ULPower Clean Sheet Design FADEC Aero engines, which I hope succeeds in the Experimental Aviation market.

Excellent summary, Paul.

Good presentation, Paul. One thing I want to thank you for is dispelling the myth that automobile engines will never work in aircraft because they can’t handle the 70% duty cycle. Maybe that was true of the old large block V-8’s of the past, but the smaller aluminum block turbo fours and sixes of today’s cars are different. They naturally operate at higher power levels anyway. Piston engines, like turbines, are happiest when they run at a constant, relatively high output power setting. The fact that car engines tolerate the low power daily commute better than an airplane engine would has more to do with their unleaded fuel and water cooling than anything else. I see no reason why the 265 hp turbo four in my Honda couldn’t replace the 200 hp IO-360 in my Cardinal and do just fine. Yes, as you made very plain, it would have teething problems to be worked out, but the key would be more how well it was supported with warranty and maintenance than anything else. However, in the end, the big question is why would Honda or anyone else bother to spend the time, money and engineering talent on something that would produce a paultry 2-300 sales a year? Probably our best hope for a “modern” aircraft engine is to retrofit electronic ignition and computer controlled mixture settings on existing power plants. Lycoming is at least heading that direction by offering EI on factory engines to replace at least one magneto. Now if someone would just discover that magic lead-free replacement for 100LL, we might be making progress!

The BIG money (United Technologies, General Electric, Honeywell and others) is being spent on turbines and electric. There must be a dozen hybrid turbine/electric projects in the works. Pure battery power is not quite ready for prime time so, many companies are creating small turbines that charge your batteries and power the propeller in cruise while the electric makes for easy high RPM starts, takeoff and climb assist. Many of these projects are focused on multiple fuels. The same engine can be set up for autogas or diesel/Jet-A/Biofuels. These hybrids are much lighter and will be mass produced for automotive, marine, home-power and aviation. Reducing the price.
Even when they do create batteries that can operate a full four hour flight they still need charged back up. These Turbine/Electric Hybrids will be around for a long time. That makes them worth the R&D investment.

Excellent video. The major issue is getting back a return on investment. And in getting back that ROI, will the cost be so exorbitant that it prices the new technology out of the market?

Modern metallurgy, close tolerance machining capability, liquid cooling combined with precise computer driven engineering to deliver fuel with correct, precise timing has been developed through the automotive technology so well that V8 engines can live quite reliably at 2500-9,000 RPM for thousands of hours. Including running at 100%. With variable valve timing combined with the average auto engine having 100-150 sensors per engine/transmission ( now you know why in part there is a chip shortage) allows for reliable 9:5 to 12:1 compression ratios developing 350-650hp using readily available ethanol 87-91 octane unleaded. These HP numbers were thought to be unachievable as little as 10 years ago. Reliable, yes…relative to cars/trucks. Simple? Not hardly.

The “secret sauce” for unleaded avgas has everything to do with adapting the same technology of precise variable timing with fuel delivery to aircraft engines. But that is far more difficult to achieve in air-cooled engines. Air-cooled engines need far more loose tolerances than liquid cooled engines. Loose tolerances do not work well with precise computer controlled via sensor electronic fuel injection with variable timing parameters common to cars. However, loose tolerances can work with dual magnetos with fixed timing found on air-cooled engines on GA airplanes, lawn mowers, and older motorcycles. Lead in avgas is the way to control detonation on fixed compression with fixed timing. Add variable timing with good intake flow, cylinder head flow, with equally precise flame travel, due to fuel metering and head design, followed with good exhaust flow, you get volumetric efficiency providing great, consistent performance, low emissions, all on unleaded fuel. It has taken over 40 years to realize that there is no combination or concoction of chemicals that will allow a higher compression, air-cooled, large displacement, aircraft engine with fixed timing, ignition, and fuel delivery to run without damaging detonation. Air-cooled aircraft engines have poor intake flow, terrible cylinder efficiency, equally lousy exhaust flow, very poor camshaft design, all adding up to poor volumetric efficiency resulting in higher emissions and the need for lead and 100 octane. By car today’s car standards, the highest compression flat six cylinder piston air-cooled aircraft engine is pretty low. But with a comparatively simple air-cooled engine with fixed timing and mechanical fuel injection whose mixture is being manually managed by the pilot through a mechanical mixture control linkage, the only way to prevent catastrophic engine detonation is lead and octane. Either the powerplant technology adapts the computerized precision we take for granted in cars combined with close tolerance, liquid cooled engines operating via a myriad of sensors through computers measuring hundreds of metrics in nanoseconds, or continue with the simple 60’s technology using lead and octane. It’s all about physics either using modern technology or 100 year old chemistry. Liquid cooling requires radiators, water pumps, water jackets which all adds weight plus complexity. Aerodynamics dictate where these things go. This adds to the engineering complexities combined with many additional failure points.

Diesel engines add a couple of other issues unique for aircraft use. The power pulses of a diesel can hammer the airframe, engine mounts, and propeller. So far, it is an unknown area, especially in retrofitting diesels into existing and particular older airframes. This is a huge concern for the FAA trying to figure out whether a diesel will accelerate airframe aging. That is why most certified propellers approved for diesels are composite rather than aluminum. An aluminum prop can become brittle under diesel vibration dynamics and power pulses resulting in shattered blades. Or if aluminum, an alloy specific to that application.

Turbo chargers are another problem for aircraft diesels. Since the much higher compression, usually around the 20-22:1 compression ratio, they require far higher turbo rpms to handle the volume of air needed for compression and exhaust. Diesel efficiency, HP ,and torque depends on the turbocharger. My Ford F-350 diesel gets 65% of its HP and torque from the turbo. I have had a turbo failure. From the ability to tow up to 24,650 lbs. at highway speeds with a normally operating turbo, I went down to barely maintaining 55 mph on flat land towing 6,000 lbs. And you could measure the 0-55mph acceleration with an egg timer. For an aircraft diesel, the turbo has to be very large to accommodate the air requirements at 7,500 ft on up. Big turbos do not like to be spooled into the into the 200,000 to 300,000 rpm range. Small turbos handle the rpm better but lack the displacement and volume to pressurize a diesel cylinder. Turbo design for aircraft diesel requirements is far different than what is available and needed for a 9:1 compression ratio Continental TIO-550. The turbo tech is no where near the aircraft diesel requirements and is arguably the weakest link in moving farther forward in aircraft diesel technology. Strong turbos are extremely heavy. Heavy turbos have to be attached to equally heavy and special strength exhaust systems. And then deal with a heavy mass spinning at 200,000 to 300,000 rpms in the exhaust stream of a 20:1 compression ratio engine. Turbos need to be cooled and the turbocharged intake air needs to be cooled. This requires the addition of inter-coolers. Inter-coolers need certain airflow requirements to make them usable and they need to be cooled as well. More complexity, more failure points, more weight.

Finally, how do you handle all the gyroscopic loads placed on an aircraft engine through the propeller? Car/truck engine requirements through a transmission are totally different than an aircraft with a spinning gyroscope added to it.

Add to this unique recipe of parts and chemicals that power successful piston aircraft engines the most needed ingredient for long term success is…yes, you guessed it… greenbacks. Closely followed by tenacity, sheer personal will, and dogged determination to succeed. It takes a new engine offering a huge amount of cash to certify, manufacture, distribute, set up a dealer network, train end user and maintenance personnel, and most importantly for developing customer trust, an ability to warranty one’s new idea for aircraft propulsion. No matter how many CAD drawings and 3D printing of parts, there will be failure points that can only be found in service. Will the customer be happy with being the Guinea pig for new product development? Will the new engine manufacturer have the financial ability to change manufacturing specifications to meet the previously unknown failure point plus the money to recertify that manufacturing change with the FAA?

And do all of the above plus much more with the hope of selling maybe 200-500 engines per year and still make a return on investment? There is plenty of new engine technology that can vastly improve the existing basic design of our conventional but reliable, predictable, and trusted engines? Will the existing maintenance workforce be willing to train on this new technology? Only if there is a reasonable return on investment. Will the manufacturer’s be willing to integrate this new technology? Only if there is a return on investment. Will the FAA implement new rules and regulations for permitting new technology to be added to the existing fleet? So far, the rhetoric is somewhat optimistic while the action says no. And lastly, will enough aircraft owners be willing to be the first to buy the new tech for their old engines? Trust in one’s powerplant is a strong motivator to reject the new in favor of depending on the proven old. Avionic improvements are one thing. New tech for the old fan is quite another.

Once again excellent video Paul. More questions than answers but a thoughtful approach to an interesting conundrum unique to aviation.

Thanks for stirring the proverbial pot.

My name is front and center on one of your slides because I purchased a DA42 in 2007 after visiting the Diamond factory in London, Ontario and receiving assurances that Diamond-backed the Thielert engine warranty and was confident in the engine. I was starting up an on-demand VLJ air taxi service and planned on using the Diamond DJet and had five positions. I was going to use the DA42 TwinStar for proof of concept which I ultimately did. I loved, really loved, flying the DA42. The airplane was a joy to fly-a pilot’s airplane–though remarkably underpowered. Over two years, I logged 350 hours in N510TS before the engines and props became problematic. In fact we took a soaking repairing one engine and the props and replacing an entire engine with a cracked block. I was incensed that Diamond would not honor their promises and shunned owners who believed in their airplanes and technology. (In fact, we had evidence that Diamond knew of Thielert’s problems well before they become known to the public, but pressed forward with marketing anyway.) With others, we formed THENOG (Thielert Engine Owner’s Group) to organize and represent AOG owners and met with Christian Dries and Peter Maurer to negotiate a way out. Eventually, efforts to reach a satisfying outcome broke down and THENOG was left to file suit in Federal court, ultimately losing to the deeper (much) pocket. Despite all of that, I have very fond memories flying the TwinStar and still espouse the vision and modern aerodynamic design of Diamond airplanes. And I still want diesel engines when my Baron’s IO520’s time out! Todd House, MD

Once again … GREAT video. I think you should put a resume together and send it to Hollywood.

You presented SO much data — much of which I’ve forgotten — that my head looked like Linda Blair in the Exorcist … spinning around trying to keep up.

An issue not mentioned with diesels is common maintenance requirements. Very expensive oil, very expensive oil filters, very expensive fuel filters, very expensive fuel pumps, even if you can find appropriate competent personnel to do the work.
If you are still considering buying a diesel powered vehicle of any kind. please review the above listed issues, unless you have more money than sense or that you can spend in a lifetime.

There’s an engine I was severely smitten with a few years ago. Superior Air Parts was going to produce a two cycle, three cylinder, six opposed piston, dual crankshaft suupercharged engine called the Gemini 100 (hp) that was gonna be Hecho en YouKnowWhere. It was going to start out as an experimental for LSA’s and move over to certificated use over time. Also, the idea was going to be scalable upward in power, as well. I followed it closely until it suddenly disappeared. Another great idea that went nowhere. I could see something like that powering an electrical power generating system in a hybrid electric airplane to extend range to something useful.

Avweb covered it:
http://www.avweb.com/ownership/video-superiors-new-gemini-diesel/

Economics…….with the exception of the Allison/Rolls Royce conversions which have has some sucess there is no reason to invest what it would take to make a fuel cell powerplant or any other for small general aviation planes….when a new 4 wheel drive full size pick up is costing 50-70 thousand dollars who is going to invest that millions it’ll take to come up with a powerplant cheap enough to work on aircraft that are’nt worth the price of a truck ! spending 50,000 (at least) to repower a 25,000-150,000 dollar airplane is never going to pay back the engine developer…The only way out in the next 20 years is to vote out the present administration and keep 100ll avialable ….or talk Rotex into developing and engine that can put out 180 to 300 horsepower engine…….that’s be the cheapest and least painless !!!….Big turbine convesions PT6 or GE/Walters are only sensable for the big pressurized twins with a complete remanufacture bringing the plane uo into the 3 million range………which is what we are doing !

Third party engineering standards should be enough to get us safer, greener, and more efficient engines. IMO, most government standards are innovation killers which save a few lives up front and cause much more pain and suffering that you can’t blame on the government later. Imagine how many lives would have been lost if they had held up refrigerators a few years. An extreme example, but not the most extreme.