Does Inline 4 Engines Suck for Airplanes? - Technical Deep Dive

[@LetsGoAviate]

V6 vs Boxer 6 Aero Engines Explained : kzbin.info/www/bejne/iH_cZ5eCaLqketU The New Deltahawk V4 Diesel Aero Engine Explained : kzbin.info/www/bejne/q32zqqBrjdKmpdk V8 Aero Engine History and Design : kzbin.info/www/bejne/rXqunKNrhsljaNE

[@darwinskeeper421]

The main reason why we wouldn't see a high speed inline four cylinder aircraft engine is economics. The general aviation market is too small for a manufacturer to recover the expense of designing, developing and certifying a high speed inline four engine. Heck, even if an automobile manufacturer was willing to redevelop one of their own inline fours into a 200 hp aircraft engine that could replace the Lycoming O-320 & O-360 engines, AND they dominated the 160-200 hp engine segment for production aircraft, they probably wouldn't be able to sell enough engines to recoup the cost of development and certification.

[@chippyjohn1]

That's the real reason.

[@michaelgarrow3239]

The certification mostly..

[@yveslegrand9826]

😂 Certification is a bad joke. It makes old and inefficient design a compulsory safety demand. In France it resulted in a identical aircraft being available in a safety chute version ONLY if classified as Ultralight... Many exemples exist at all levels showing how ridiculously the certification rules impacts both aviation performance AND safety. Not taking chances for progress is a very safe way to stay in a dangerous situation.

[@r.guerreiro140]

What about Diamond Aircraft?

[@Mikinct]

Funny, since both Lycoming & Continental plane engines are soo good & reliable I'm shocked that we don't see those same reliable & great engines inside more cars? Is there any reason one mechanic couldn't install a Lycoming engine in my Subaru or Camero if I truly desired that specific engine of choice. Not practicality but could & would ot work? Is there really any reason it wouldn't work? Question 2, why don't we see a Mixture knob for cars that drive at higher elevations in Colorado etc. Is it more feasible & economical to simply purchase a car that has turbo equipped if I lived around Colorado areas?

[@craigcurtis2961]

Master Auto Tech here: Certificated means "thoroughly understood", not "this is the best". Lycoming and Continental aircraft engines have two cylinders' worth of crankshaft throws and camshaft lobes between shaft bearings; this long distance allows tremendous amounts of "noodling" flex of the shafts and case; bearings typically have hourglass-shaped wear patterns due to so much dynamic misalignment, plus cylinders and engine cases sometimes fail where they meet due to vibration. I've NEVER seen that wear pattern in any modern automotive engine, including V engines in which 2 connecting rods share 1 journal. The last auto engine I saw with that much distance between bearings was a 1960's MG. Why are aircraft engines not rated above 2800rpm? Because they're likely to blow up much higher than that! Fortunately, typical diameter propellers are limited in RPM by the tips going transonic.

[@davisrs1]

I'm glad you mentioned the Yamaha Apex engines. The 4 cylinder was putting out 300 hp, but the new 3 cylinder is capable of 400 hp. This is presently being used by Wild West aircraft as an option for bush aircraft.

[@danieldimitri6133]

Rotax has made a 3cyl for years which is used in jetski. that put out between 215 and 260hp then they upped the displacement and make 300hp currently but speed run guys have boosted them up quite a bit above that. Suddenly automakers have started looking at 3cyl forced induction for racing and hybrid applications for their super light weight and compact designs. Yamaha is probably lower maintenance or they are as a brand but it has surprised me that experimental guys haven't tried a rotax even though they have used Yamaha and Kawasaki snowmobile engines which are very similar. I do know that Yamaha 4cylinder engines crack cylinder heads. But rotax engines shake a lot and have an open deck so the sleeves are only attached at the bottom and the top is honly held still with the friction to the headgasket. you find head gasket material in the coolant.

[@russbell6418]

@@danieldimitri6133 The Yamaha 3 cylinder has a counter balance shaft and thereby is extremely smooth.

[@jiroyamamoto2878]

@@danieldimitri6133 Production form factor is the reason for the popularity of snowmobile engines in aircraft. Very few motorcycle engines in the skies due to the integral transmission.The trike and gyro crowd led the charge on the Yamaha conversions. Teal Jenkins with his well made Propeller Speed Reduction Unit (PSRU) allowed people to buy a PSRU and have some faith in its reliability. Further, I am guessing that snowmobiles have a relatively short life span versus personal water craft, allowing low cost used engines on the market.

[@richardwallinger1683]

captivating video clear voice . I was Donnington GT champion in 1980 in the UK.. my powerplant was a self modified four cylinder hillman IMP engine developing 120 bhp at 9,000 plus rpm .the engine was tilted over and ran wet sump . running the water and oil pumps at lower rpm actually improved the cooling and reliability .. I loved your accent .

[@robbytheremin2443]

I suspect the biggest obstacle is the insane cost of certification. It's caused the demise of several innovations. 😢

[@LetsGoAviate]

For sure. But even on the experimental side where certification isn't required, it's much more cost effective to convert auto engines than design from the ground up.

[@toastrecon]

It'd be interesting to innovate in the area of certification. There would be almost zero drive to do so from the major engine manufacturers because it's their competitive barrier to entry, but if there were a lot more investment in ways to streamline the certification process, like computer analysis and simulation, different best practices that are required or other ways to make it faster and cheaper.

[@arcanondrum6543]

@@toastrecon As an electronics engineer and a software/qa developer, I get a bit tired of the push for simulation testing. I knew plenty of developers who weren't too interested in making sure that they had taken every possibility into account, they wanted to ship and cash in. Nothing but nothing replaces real world testing and since I'm also a (not currently current) Pilot, I know the importance of equipment. You can't pull over and fix a problem up there. I'm not afraid of a dead stick landing but they're too expensive, even without any airframe damage and no, I don't speak from experience.

[@toastrecon]

@@arcanondrum6543 simulation wouldn't replace testing, but I'm guessing that it could dramatically streamline it, or allow smaller companies to get an 80% solution before sending it to test, that would improve competition and help new companies learn and enter the market with innovations.

[@DKNguyen3.1415]

@@toastrecon You'd think so but simulating a real world thing can be surprisingly difficult and if you don't do enough you might assume things you otherwise wouldn't have. Sure you might catch things you wouldn't have caught but I don't think anything that can be called an 80% simulation would catch those things.

[@glibsonoran]

Diamond used a 2.0: inline four cylinder diesel (modified Mercedes OM640) with gearbox, this a certified production aircraft.

[@daledavies2334]

The recip aircraft engines are designed similar to heavy truck engines for reliability. Yes they are considerably lighter. The cylinder spacing is greater than most automotive engines which allows wider (thicker) crankshaft throws. Also the fillets at the sides of the main and connecting rod journals are ground with a larger radius to reduce the possibility of stress risers. Most automotive engines run on a low duty cycle, so fatigue resistance is not as critical. Automobile engines with max power of 200HP probably only require 30HP to drive at 60MPH. This is a low duty cycle with short bursts of maximum power for a few seconds. Aircraft run full power for takeoff for 5 minutes and then reduce power to 75% for the rest of the flight. Auto engines in aircraft have short TBOs because the narrow crank throws and small radius fillets allow flexing fatigue to build up, leading to failures. Regarding the certified Mercedes based engine, is not likely plucked off the Mercedes assembly line and with minimal changes ready to install in an airframe. Diesels are designed and built more substantially, but for aircraft I would think crank fillets would need their radius increased even more. Exhaust valve cooling is a key issue to resolve. Wider seat contact area and larger diameter valve stems to provide more area to transfer heat out of the valve.

[@daledavies2334]

The recip aircraft engines are designed similar to heavy truck engines for reliability. Yes they are considerably lighter. The cylinder spacing is greater than most automotive engines which allows wider (thicker) crankshaft throws. Also the fillets at the sides of the main and connecting rod journals are ground with a larger radius to reduce the possibility of stress risers. Most automotive engines run on a low duty cycle, so fatigue resistance is not as critical. Automobile engines with max power of 200HP probably only require 30HP to drive at 60MPH. This is a low duty cycle with short bursts of maximum power for a few seconds. Aircraft run full power for takeoff for 5 minutes and then reduce power to 75% for the rest of the flight. Auto engines in aircraft have short TBOs because the narrow crank throws and small radius fillets allow flexing fatigue to build up, leading to failures. Regarding the certified Mercedes based engine, is not likely plucked off the Mercedes assembly line and with minimal changes ready to install in an airframe. Diesels are designed and built more substantially, but for aircraft I would think crank fillets would need their radius increased even more. Exhaust valve cooling is a key issue to resolve. Wider seat contact area and larger diameter valve stems to provide more area to transfer heat out of the valve.

[@WilhelmKarsten]

​@@daledavies2334YOU SIR ARE A BALD FACED LIAR. Automotive type engines are very different from aircraft in several ways but that does not mean that auto engines cannot pass airworthiness certification. Mercedes and Porsche have proved this. The only type of engines that have consistent proven unsuitable for aircraft is the Wankel engine.

[@WilhelmKarsten]

​@@daledavies2334WRONG, Mercedes delivers the short block assembly directly to Theilert

[@daledavies2334]

@@WilhelmKarsten Wilhelm, I have no recollection of mentioning Thielert or Diamond. I have written only about rotary engines and a short dissertation on the shortcomings of recip engines in general. Back to the Schnapps.

[@richardtheweaver4891]

8:27 There is a third factor: rod to stroke ratio. Engines with a 3:1 or more rod to stroke (like marine engines) aren’t terribly bothered with secondary balance issues. In-line fours can be way angled, which gives better oil handling than boxers. 70 or 85 degrees to one side means gravity still helps oil flows. And single prop planes have a “preferred” side based on prop rotation. A prop/engine pair with different centers of mass/thrust could play well with a single prop’s asymmetry.

[@chippyjohn1]

What marine engine has a rod to stroke ratio of 3:1?

[@SpecialEDy]

Would it not be cheaper and easier to build a twin I4 design than to put a single $20k-40k engine in the nose? Im an industrial mechanic, i used to work on a lot of forklifts. Many LP forklifts use automotive V6 or I4 engines, they are just derated in power and otherwise improved in durability. Forklift engines typically have a 500 to 1000 hour oil change interval, just like Aircraft they are usually run at maximum engine output for hours a time.

[@MyFabian94]

Peugeot/Ford has the DV6 1.6l Diesel, which I worked with a lot when I did a short stint as an Engine Rebuilder. It's an Aluminium Diesel with ridiculously low Weight if you leave off all the Car-Bits, and as an 8V sits at 120hp in the DV6 FC Variant. It combines this with a 1980s style Engine Architecture, meaning it has a single Cam, sitting in a seperate housing on the Cylinder Head, the Intake Manifold is integrated into the Head with only a single Inlet coming into it from the Turbo, a Two Piece Crankcase and a simple stamped Sheet Steel Oil Pan. It should make for a great UL Diesel/Jet-A1 Engine. Basically, I'm looking from someone to partner up with, as I simply do not have the funds or knowledge to start a company.

[@Joshie2256]

120 hp from 1.6 liters won't last long whether it's diesel or gasoline. Auto engines produce 60% or more of their rated power only for brief amounts of time while an aero engine spends most of its life between 60% cruise and takeoff power.

[@timgould5104]

It's bigger brother the DW10C permanently derated after 5 hours(!) of full load rated speed .

[@montecorbit8280]

At 8:54 In line 4 displacement.. You were talking in automotive terms. I have seen truck engines that were larger than 4 l iters that were four cylinders.... They used to be quite common back in the day.

[@LetsGoAviate]

100% correct, since I was leading the video to car engines converted for aviation, as well as just covering the basics of the secondary imbalance. The truck engines are like the 6.1L airplane engine I spoke of, in that they are low revving, which is why they can be that large.

[@montecorbit8280]

@@LetsGoAviate I think a couple of them we're two stroke diesels as well.... Going to do one on six cylinders?? I seem to remember the Junkers of WW2 fame had an inline 6 burning diesel.... There is a lot of boxer sixes as I remember. Are there any boxer 8s?? Inline sixes are inherently balanced usually, primary and secondary are both balanced.

[@LetsGoAviate]

Oh yeah for sure. Theres also the Gipsy inline sixes, not to mention the plethora of boxer sixes. The legendary Mike Patey's plane, "Scrappy", is powered by a Boxer 8.

[@montecorbit8280]

@@LetsGoAviate You going to do videos sixes and eights??

[@LetsGoAviate]

@@montecorbit8280 Yeah planning to

[@erwinb3412]

Thank you very much . As a layman person i understood everything very well . To the point with not too big of a jump between items so that i could understand the flow of the logical reasonings . This info is very interesting and this is the first video that i saw about these items . Engines are fascinating , and so is aviation . Erwin , Belgium .

[@AusVelocity]

I feel the biggest downfall of the horizontally opposed engines is the air-cooled cylinders and the leaded avgas. The cylinder walls are thin and vibrate on the case making for less life and more noise. The air-cooling means bigger clearances for greater temp ranges for greater thermal expansion. The avgas pollutes the oil, through blow by leading to sludging and lead sticks on valve stems. I couldn't bring myself to put one in the velocity, I wanted something modern simple and predictable so i went the viking 195 route. Good content and i think the topic of auto engines in aircraft needs more exposure.

[@JimBronson]

Traditional aviation engines could be better if they got away from the leaded avgas. That would enable closed loop operation, which would be a big step forward in engine control in regards to air fuel ratio and spark control. The Lycoming IE2 is a step forward with EFI and push button start, but it's still desgined for leaded avgas. Full closed loop with unleaded avgas would be another step forward for AFR control over the lifetime of the engine. They'd probably last a lot longer that way, car engines sure did once modern fuel and spark control was available.

[@Bob_Adkins]

Don't know about aircraft boxers, but car boxers are known for thin, poorly supported rod and main bearing webbing. Porsche goes racing with them to this day, so they must have beefed them up.

[@jeffreyroth7517]

Enjoying watching the progress!

[@rescue270]

Removing lead will cause current production old-school engines to last FOREVER. I really don't see much use in coming up with more expensive, complex engines when what we already have is as reliable and affordable as it could get. Just get the lead out and overhauls will almost go by the wayside.

[@ArneChristianRosenfeldt]

You mean that the walls expand when the pressure rises inside the cylinder? I read that steel has good tension strength and stiffness per weight. Why no flow more oil through the head and piston with a pump which continues after engine out to avoid coking? Do liquid engines have valves to lock the incompressible water in the jacket at each power stroke? Like in a 1921 Buick car engine?

[@LTVoyager]

The Rotax 9 series engines have all of the things you mention such as dry sump, water cooling, and gearbox and they are doing quite well. I do with Rotax would develop a mono lock engine such as a V4 or V6 as that would overcome many of the packaging issues of the inline 4.

[@LetsGoAviate]

Rotax is somewhat of an anomaly in my opinion. They are extremely reliable, my airplane is powered by a 912.

[@LTVoyager]

@@LetsGoAviate I am hoping they are reliable as I am installing a 915iS in my airplane at the moment. I actually consider Lycoming and Continental to be the anomaly’s today. Persisting with early 20th century design and technology well into the 21st century is the real anomaly. I think Rotax will soon become the norm leaving the others in its wake if it moves into the 200+ HP range. And if they offered a mono block V-6 with integrated dry sump system they would have a real winner in the 150 to 300 HP range. I say integrated dry sump as I spent most of yesterday figure out how to route and connect the 5 oil hoses that run between the engine, oil cooler and oil tank. What a pain!

[@joshhhab]

VR6

[@stephenstephenson6614]

I only shows that I learn something from, no fiction. Thanks for such a great informative show.

[@Blackcloud_Garage]

Great content. I'll be the first to admit "if it ain't broke don't fix it" but there's something to be said about engine tech from the 1930's. We are definitely in an age where state of the art engine tech can/should be applied to light aviation.

[@BuzzLOLOL]

LOL! Inline 4s sucked for everything... go smooth 90 degrees V2, V4, V6, V8, V10, V12, V16, or boxer 4, 6, 8...

[@dposcuro]

@@BuzzLOLOL V2s are anything but smooth. V4 is the least smooth 4 cylinder engine possible. The V6 is a pair of inline threes, out of phase with each other, and work best at 60 degrees, not 90. Just...hard to believe that you could say so much wrong, in one post. Simply put, Inline 4 cylinder engines are great engines. In cars, they don't force you to make compromises with the suspension and frame like a flat engine does. They do have primary balance, unlike a V4, which also introduces a torsional or rocking moment. They offer better engine bay packaging for front wheel drive cars than either. Flat or V4 engines. Nothing needs to be buried under a cowl or the floorboards if it is transverse, so there is no incentive to do the dumbest method of longitudinal front wheel drive...unless you're AUDI or VW Brasil in the 80s...or Surbaru, or SAAB (pretty sure I've missed a few). Why is it the dumbest method? Well, if you're Audi, VW, or Subaru, you hand the engine out _in front_ of the transaxle, leading to absurd weight balance issues, having so much mass so far forward. SAAB on the otherhand...doesn't have a oil pan, because the transaxle is...part of it, with the front diff right under the front of the crankshaft. For Aircraft? An Inline 4 gives you the least frontal area, for better aerodynamics.

[@BuzzLOLOL]

@@dposcuro - For you to be so totally wrong, you must have zero experience with these engines... ride a Ducati V2 and a Yamaha V4 and then come back educated!

[@crissd8283]

1930s tech?? There are a few planes flying today with that old of systems but most are much newer. New electronic controlled magnetos, mechanical fuel injection, and now electronic fuel injection. I would argue airplane engines are about 40 years behind car technology. Sure in an old plane the tech is old but that is also true of old cars.

[@BuzzLOLOL]

It's vastly more important in aviation for new tech to be proven totally reliable than in cars... it's harder to simply pull over and stop when something fails in a plane...

[@ChristopherBurtraw]

You did a good job quickly explaining secondary imbalance. It took me years to fully understand it... and a D4A video was a BIG part fully completing that understanding (it was one that focused on your later point on the displacement limits of I4 engines). I'm glad you linked a video by that channel!

[@Itsjustme-Justme]

There is a second reason for the choice of engine design, that has nothing to do with the engine itself: The shape of the engine has to fit into the shape of the airplane to get a low drag and pleasing looking design. Knowledge of aerodynamics has greatly improved in the mid 1930s and made another giant leap during and right after WW2. Before, aerodynamics were thought simple. Designers concentrated on keeping the frontal area of their designs as small as possible and mostly ignored other factors. A wide fuselage was considered a high drag design. That's why side by side seating (not only) in light aircraft was very rare until the late 1930s. The narrow surface area of inline engines matches narrow fuselages perfectly. When the first purpose built horizontally opposed aero engines emerged, light aircraft with side by side seating were still rare. This lead to odd looking designs with narrow fuselages and cylinders protuding out of the cowling sides. You can see it on early Pipers for example. The shape of the engine didn't match the shape of the fuselage, it screamed drag and it always looked like an improvised design choice. Only when side by side seating was widely introduced in light aircraft, the horizontally opposed engine immediatelly kicked in. It was a perfect combination from the very start. Today, the vast majority of light aircraft with more than one seat are side by side designs. This combination allows for a low drag cowling and fuselage combination and, keeping hard technicals terms aside, a wide, short, horizontally opposed engine on a wide fuselage is just as pleasing to the eye as a long, narrow inline engine on a narrow fuselage. Looks sell, people don't just buy for technical reasons. That's especially true for expensive luxury items like private airplanes.

[@keithnoneya]

Not a pilot or aircraft designer, but have always enjoyed aviation as a whole. I found the video very informative and interesting. Thanks so much for your time in producing the video. Best Wishes & Blessings. Keith Noneya

[@LetsGoAviate]

Thanks Keith, appreciate it.

[@diamondeyz6333]

Thanks for the presentation.....would like to see you do a deep dive into what Diamond Aircraft is doing with the Austro Engine....essentially an adapted Mercedes diesel engine burning Jet-A. I have owned one for 2 years now and with Jet-A, FADEC and a host of other benefits, would never consider owning the old tech engines. Also, have a look at the Continental CD-300.....a V-6 design now being used in the Diamond DA50RG. Have a look and let us know what you think....Thanks again, DiamondEYZ

[@MegaDada1995]

Exactly what I came here to say, the Austro/Thielert/CD family of engines is really the way I'd love to see more aircraft manufacturers go. Jet-A is definitely the way to go with higher compression ratios, lower fuel consumption, lower fuel price and (at least outside North America) better fuel availability. Personal opinion, they smell better too...

[@Conservator.]

9:09 But not displacement but power is the goal. 2 liter inline 4 engines can quite easily produce the 180 HP of the Lycoming 5.9 liter. 2l engines would however typically produce peak power at around 6000 rpm so for aviation purposes that would require a reduction gear. That gear could be used to lower the engine so it would suit two purposes. As explained here: 15:10

[@RichardLewisCaldwell]

7:45 You could handle secondary balance issues through complexity, but there is another way: an extremely slanted (120 degrees to 170 degrees) slant four with highly oversquare pistons and 3:1 rod to stroke ratio. You see, long rods essentially eliminate secondary imbalances (which is why container-ship engines have them), the oversquare pistons reduce the stroke so 3 times the stroke isn't insane, and the orientation keeps the total height reasonable and about the same and puts the prop only a tad lower. The offset to one side provides interesting opportunities and issues... Thanks for prodding me into thinking of this. Thumbs up.

[@nomisrep1]

I enjoyed your video and learnt a little regarding Secondary Vibration which I´d never thought about before. I retired recently from 49 years as a light aircraft maintenance engineer! These new engines being developed are light and powerful, however they require much more complex ignition systems necesitating duplicated batteries/power sources, computer controllers, relays, etc.,etc. More complexity = More to go wrong. Thanks and keep it up. Simon, Spain.

[@tomcoryell]

Excellent explanation of a rather complex subject! Cost will always be a determining factor in aviation engine choice, consequently why design a new engine when you can modify an existing and less expensive engine like Apex or Viking have done.

[@ArneChristianRosenfeldt]

Because of time. Every year there is the chance that someone is just bored or needs a project to learn stuff . This gave us Linux. The problem is that all the 10 times engineers which were attracted to aviation have moved on to modern fields like computers.

[@foesfly3047]

I’m anxious for liquid cooled, ECU-controlled, higher-efficiency, ‘affordable’ engines, especially for EAB aircraft

[@thegreatchickenoverlord5976]

Not exactly affordable but the continental cd-135 is a thing

[@russbell6418]

Within the US experimental world, there are Subaru and Yamaha options.

[@rescue270]

There are reasons why aircraft engines are air cooled, have magneto ignition systems, and carburetors or mechanical fuel injection. Magnetos are independent of any electrical systems. Totally self-contained, they generate their own electricity. The whole airplane electrical system can fail and the engine will keep running as if nothing happened. Since 1941, two separate ignition systems are required on all new aircraft for safety. At least one of these must be a magneto. If one fails, the other keeps the engine running to a safe landing. Water cooling adds weight, one more point of failure, and one more system that requires rigid maintenance in order to be reliable, as the Thunderbolt proved over the Mustang and the Spitfire amongst Allied WWII aircraft. One round to the radiator or water jacket brought the water cooled aircraft down. Many air cooled P47 Thunderbolts made it back safely with whole cylinders shot off. Electronic fuel injection is, once again, dependent upon the airframe electrical system and adds complexity. Electronic injection systems were developed in cars predominantly for emissions. Backup batteries for electronic systems are not the answer. One more maintenance item to be neglected and one more unseen system to fail. These new engines are making all their horsepower through high compression, gearing and turbocharging so the engines are spinning much faster. This is too much of an automotive mindset. Cars cruise down the road using perhaps 12-18% of their total power potential, while many aircraft need 60-70% power just to maintain altitude. Given the stress that that would continually impose upon such a complex and high strung engine, I doubt that they would be nearly as durable over the long term as a typical Certificated engine. Diesels can't fly with a failed turbo, so I don't endorse those. I do believe that continuing research and development is crucial to aviation, but I think it's going in the wrong directions. We can't be making airplanes into flying cars. The realm of flight is very different, and the engines that many people are calling crude and archaic took many decades of development to get where they are now. Safety and reliability should take precedence over economy, not be an afterthought.

[@timduncan8450]

@@rescue270 The current trajectory is for the “realm” of personal flight to be the sole province of the economic elite. This is not how a successful technology develops. It’s not what this country or the fathers of aviation laid out us. Adaptation of mass produced engines seems like the obvious if not the only way to fix this. That means motorsports & automotive. Obviously reliability must also be improved which they have done in spades. The electrical issues you bring are real, mostly ancillary to the engine so must be addressed (and can be) in the firewall forward package. System failure is not an option so hoses & all such must all be right to achieve that. It is not easy but I have driven millions of miles without a cooling system failure. As example, I would put up any reliability stats on reputable coil over EI systems vs a pair of mags any day. Motorsport engines like the Yamaha incorporate a brushless generator on the crank for inertia and ignition power. My engineering and engine experience is that shorter stroke higher reving (within established piston speed limits) can be very durable and economical. Yes aggressive down sizing and or boosting is required to compete on system wt. But this can be a good thing, trading the moving parts in a 4 cyl for a three with balance shaft is a good win. Balance shaft has no piston scoring, valve dropping, ring sticking, bearing spinning, lifter scoring, etc, etc issues. Cutting those odds by 25% right at the dwg board is a good win. Getting back to larger cyl bore within the downsized engine will help bsfc vs 4’s. Furthermore forced induction is a natural for airplanes, a huge safety enabler against density altitude and weather. Power plants outside of aviation have shown it can be cheap and reliable for decades now. A few years ago I would not be a fan of a three. But clearly it can be done.

[@MaestroAbar]

It seems like the natural progression of light aircraft engines are parallel twins, rather than inline-4s. There are inline-3s now a days that make nearly as much if not more power than slightly older generations of inline-4s.

[@chengong388]

The simple reality is, the inline 4 car market is like 1000x the size of general aviation market, so cars simply have much more advanced engines, while light airplanes are still running designs from many decades ago.

[@georgejleonard9410]

Thx Jaco...great info and education at 05H00 in the morning...looking forward to my lunch on Thursday at FAKT...thank you for your time on this channel an safe landings

[@LetsGoAviate]

It's a bit much for 5am 😆 but thanks and enjoy!

[@jwboatdesigns]

With respect, DeHavilland build many many versions of their Gypsy four and six in line engines, they were used in a lot of light aircraft and a lot of them are still flying.

[@LetsGoAviate]

9:41 in video I mentioned the dozens of aircraft using the engine, and video of one of the many currently flying in my area

[@milesinnz]

@@LetsGoAviate well you should have put it at the beginning.....

[@apuwdm2]

Very well researched video. Thanks for sharing.

[@Doan84]

The "TEI PD-170" and "PD-222" is an inline 4 Diesel Engine, purpose built for Aviation. It was developed for the infamous Bayraktar TB-2 Drone, to replace the Rotax Engine, which Canada put an export ban on. I'd like to see your opinion on that engine actually.

[@russotragik]

Don't even need to go that far, we have the Austro E4 that is an straight 4, and the 912 is a geared engine. And...the IO-720, have a 4 bank engine that the cooling of the back cylinders isn't an issue, actually, if wasn't by production costs, we'd have the Lycoming O-1230 still in production for crop dusters. There's also some certified conversions from Viking Aircraft, AeroMomentum, AeroMot and others, that uses regular car engines as aircraft engines with some success. Today the major.fault of lack improvements are the pilots that still "don't trust electronics" and innovation on their engines, so they prefer "ye ol' reliable Lycoming"

[@charlesgraham9954]

thank u bro, i appreciate u taking the time to explain the differences between the inline and boxer engines, i know the time it takes to film and edit.

[@AlRoderick]

This reminded me of a tangentially related story, there's a flathead straight six that's been designed by roush racing to fly on a rocket. The last stage of the ACES launch system (which I don't know if they're still working on) has an APU designed to run the hydraulic pumps and generator, it's a top stage engine so it's supposed to be able to start and stop (unlike a lower stage engine which just goes once), they need this little secondary engine to keep things running, it makes a cool 26 horsepower. And I do mean cool, because it's running on cryogenic temperature gas it doesn't need a cooling system, in fact, the heat off the engine is used to pressurize the fuel system.

[@Heatherder]

There are a lot of advantages to the existing lycoming/continental designs over automobile style engines. One is pressed together cylinders - no head gaskets to fail. Individually serviceable cylinders is another. Ease of packaging and maintenance, and lots of anti-fatigue features considered in the design. Redundant ignition as well, and provisions for oil pressure driven constant speed prop hubs rather than electric ones. These engines are also already capable of quite high thermodynamic efficiency. With modern techniques such as studded and doweled case halves I really see no need for the basic engine planforms to change. FADEC would be a welcome change, as long as it has commensurate redundancy, and backup for complete electrical failure, but even then is it so necessary? These engine operate with only a handful of different power settings and have a very consistent load. Ive never struggled to maintain good mixture control in my airplane. Timing adjustment is cool, but remember that part load efficiency is more important in a car than it is to an airplane (timing is set for optimum at high power). Individual cylinder fuel trimming would also be great, that one could probably help. Valve timing change is pointless as are many of the other efficiency workarounds such as Atkinson engines and cylinder shutoff. The prime directive is to keep it simple, and that’s the best thing about airplane engines as they stand right now. No need for extra cams or head gaskets or water. Automated cowl flaps to prevent shock cooling and necessary drag would be nice though.

[@christophercripps7639]

Many years ago Porsche developed an aviation version of its circa 3 liter, turbo charged air cooled, boxer 6. The engine was a mature design and had been tested under severe operational conditions (24 hour endurance motor sports). Really anything an in-line 4 with turbos can do a similar boxer six can do better without secondary imbalance - except perhaps cost.

[@louisvanrijn3964]

It was an injection engine. EASA demanded hence double generators and fuel pumps for a secure power supply. That double-of-it on vital sytems is logical because all other engines had also double, fully independent ignition. The profits of this expensive to manufacture, low-volume engine was marginal for Porsche so they pulled the plug. Logical, because claims (USA) could ruin the profit of years at once.

[@BuzzLOLOL]

The Ducati 90 degree V2 is so smooth you can't feel it running... inline 4 kinda sucks for every use... VW/Porsche boxer engine started for water pump and aviation uses, as I recall...

[@WilhelmKarsten]

Porsche has won the 24 hours of Le Mans 19 times!!. It's 6 cylinder 901 series is one of the most reliable engines in the world

[@WilhelmKarsten]

​@@louisvanrijn3964Mooney did little to promote the design either.. It was expensive, very expensive

[@christophercripps7639]

@@WilhelmKarsten The 12 cylinder in the immortal 917; was essentially two boxer sixes joined together with a central power take off. In its 5.4 liter turbo form in the hands of Penske & the 917/30 all but killed the the CANAM series. Then the run of the 936, 935, 956/962 … began.

[@mor4y]

You might find a interesting wee rabbit hole looking into 1960's and 70's bank robbers from the UK, they could tune those 2.0ltr V4 engine that appeared in early transits and some saabs to make them preferable to use for 'work' over Jaguars of the time!

[@sammcbride2464]

If you notice, that Gypsy engine is a "Long Rod" motor. Not a stroker, but a Long Rod. Look how insanely long those cylinders are compared to something you see in a car @11:30. This reduces the angles from side to side of the piston rod when the crank is in the middle of a stroke. It also reduces the need for a counter balance and reduces the acceleration effect of the piston during a stroke. This should be mentioned.

[@PistonAvatarGuy]

It is a long stroke engine, but that's just because they didn't know any better in the 1920s. By the mid '40s, engine manufacturers knew better.

[@sammcbride2464]

@@PistonAvatarGuy nope. There is a resurgence of long rod…not long stroke motors.

[@PistonAvatarGuy]

@@sammcbride2464 In aviation? Long rods are definitely preferable, but long strokes are definitely not preferable in aircraft applications.

[@sammcbride2464]

@@PistonAvatarGuy I don't know, but if you are only turning 2500 RPM and want no vibration, I would pick a long rod stroker engine for it regardless if it was in the air, on the ground, or on the water.

[@sammcbride2464]

@@PistonAvatarGuy In any motor application, if the stroke is longer than the bore width, then it is a stroker engine. That is different than a long rod motor where the stroke is still shorter than the width of the bore. If you have the measurements of the engine, it will be easy to tell. On a side note...I don't know about you, but I would always want a dry sump oil system. Some people like to fly upside down. ;)

[@davidrussell8689]

Fantastic video . Well explained and relevant info . Any thoughts on the AE300 engines that Diamond uses ?

[@LetsGoAviate]

Thank you. The diesel Austro engines plays perfectly into the strenghts of the Inline 4 (not surprisingly, it's based on a car engine, after all). 2L displacement, relatively low rpm (less than 4,000) so secondary imbalance would not be an issue, but still requires a propeller speed reduction unit (gearbox) so they can put the prop shaft/hub at exactly the desired height. I'm not overly familiar with them but from what I've they are great engines.

[@amramjose]

As a former aircraft mechanic student (got my A&P, never used it) I was astounded at the primitivity of the "boxer" types of engines, with no bearings for camshaft and other rotating surfaces, pushrods instead of overhead camshafts, old magnetos for ignition and a near total lack of electronic engine controls. Now FADEC has contributed to some advances, as well as electronic fuel injection. Still general aviation seems to lag behind automotive technology by at least a few decades.

[@ArneChristianRosenfeldt]

What do you mean with “no bearings”? VW type 1 flat boxer had 3 main bearings and many more elsewhere. I would like to see a flat 6 with 4 main bearings. A magneto is just a dynamo which creates voltage on demand. So you want transistors? Still need a Dynamo though. OHV are perfect for the revs of a propeller. I think that EFI is available for all engines. I would like to see EFI which ties into the magnetos. No leaking battery.

[@grantfuller2016]

Converted car engines have the huge advantage of being manufactured in the millions ( lots of availability of parts / core engines etc ) , a specific plane inline 4 would not have that . Was watching a racing boat a few years ago that had blown up its engine the day before ( a Honda engine ) . It was very fast and its owner told me it wasn’t going bad for an engine that was in a crashed car just two weeks earlier .

[@deltacx1059]

2:21 sure if you are driving your prop right off the crank, aircraft engines are bespoke anyway so of you really want to you can make one driven off a gear or coupling on the head of the engine, it's not a hard problem to solve. 2:50 it can't but you also don't need a wet sump or a 4 stroke in general, a 2 stroke can do it just fine. They may have their own issues but if you really want a inline 4 and the same airframe as the boxer for some reason you have to make sacrifices somewhere. 3:49 gearboxes can be made quite light and if you are saving weight by using the inline than it shouldn't matter, it can even be built into the engine which reduces weight over a separate gearbox in theory. 4:20 this is why cooling ducts exist, yes more weight than without them but it works well.

[@dylanmorgan5589]

How about an inline 6 which is completely balanced?

[@UguysRnuts]

It's my understanding BMW built a corporation on their inline six engine, first for Biplanes, then "Bimmers". Perhaps a one litre straight six, like the one in my '79 Honda CBX might make the most of the output vs height trade off? Sky's the limit on what "can" be done if price is no object which does make repurposed automotive engines the way to go. Thanks for updating my awareness of how A/C form following function is affected by modern engine alternatives.

[@riverrat4631]

UL Power Aircraft Engines with Air-Cooling, Direct Drive and (FADEC) systems. It comes in horizontally opposed 4 & 6 cylinder models. Excellent power to weight ratio with Dual Electric ignition. I don’t believe they are certified yet, but working on it. I know guys that fly behind the 130hp UL Power in the LSA category and it will just hang on the prop in a 700-800lb Aircraft. They are great for STOL work. And you don’t have to worry about coolant like the Rotax. Very simple and clean install.

[@michaelbuckers]

Cars (mostly) use inline engines because there's strict limit on engine width but not so much on engine height. The driveshaft location isn't important because cars must use a gearbox anyway. Cars don't drive fast and the bonnet space is super cramped so airflow is always poor, any car engine with more power than a lawnmower needs liquid cooling anyway.

[@coreyfro]

I am wondering if the Duramax LZ0 would make a good aviation engine. It is competitive with the Lycoming 580 in power to weight ratio, it is diesel which is more fuel efficient, and as an inline 6, it has perfect balance, primary and secondary. The disadvantage is length and verticality. But as a 3l diesel, this might be slightly mitigated

[@grandyhynes1636]

Could you cover the pros and cons of radial engines please. Theorizing a 4 pot radial ....

[@jiroyamamoto2878]

two stroke only with single row even number of cylinders unless you want major uneven firing intervals.

[@markmark5269]

Small correction: The Aeromomentum engine is not "double overhead cam", it is based on the Suzuki G13B single overhead cam engine (but 4 valves per cylinder).

[@LetsGoAviate]

Interesting. Their website says the AM15 is SOHC, but they clearly state the AM15T is DOHC. But definitely does look like a single cam looking at the pictures/photos.

[@markmark5269]

@@LetsGoAviate I not only know the G13B inside and out, I also live in China and know where Mark buys his engines and components from here. Though note that Mark and his team modifies and builds them completely by hand in the US to their own specifications.

[@chrishenniker5944]

@@LetsGoAviateMakes sense in a small hot rod.

[@mikepowell3335]

The AM20 is a 2-liter Mitsubishi Evo engine. One video where Mark describes the engine says they develop as much as 409 hp in stock, production configuration. The EVO is the only engine I found to do so -- and the manufacturer's claim of 409 hp matches what Mark said in the video. Don't know if there are any of these flying, though.

[@chrishenniker5944]

@@mikepowell3335 I’d love to see one in a Ford Pop.

[@Ang3lUki]

While balance shafts prevent driveline vibrations from destroying the engine block and making noise, they don't solve the inherent problem of driveline vibrations, which translate to extra torsional strain on the prop.

[@ArneChristianRosenfeldt]

So 3,5,and 6 is better than 4?

[@mrofnocnon]

Thank you, well explained.

[@AZREDFERN]

The Germans mounted their massive V-12s upside down for most of WWII. Primarily for visibility, but it also made basic maintenance easier since the top of the heads were accessible from the ground. An I-6 has perfect primary and secondary balance. The other benefit is its the only layout that can be multiplied at any angle and still remain balanced. That’s where the V-12 came from, and they can be made anywhere from 180° to 30° V angle. It would be neat to see a miniature V-12 used on light aircraft. BMW still loves it’s I-6 engines, and is the only company making a 1.6L I-6 motorcycle. That’s only one step away from making a 3.2L V-12. And one more step away from aircraft tuning it for a medium aircraft. Another layout oddity is the 90° V-2. Inertia is always delayed by 90°, and the V-2 can be surprisingly smooth with a 270° firing order because of it. Making another possible ultralight.

[@LetsGoAviate]

It's like you're in my head. Don't blab all my video ideas out like that 😆

[@chippyjohn1]

A 60 degree V12 is still the most ideal bank angle with consideration to firing order. A 90 degree V12 will have uneven firing intervals making it not as smooth. I was thinking about a 3.2 litre V12 from bmw engines for a long time also, I'm sure many have.

[@AZREDFERN]

@@chippyjohn1 I always wondered that. I’ve heard you can make a V12 at any angle, because it’s essentially 2 perfectly balanced engines. 90° is generally a good angle because inertia is always 90° behind. Just time the tro banks 270° apart like a balanced V-twin. But if they share the same crank, I guess firing order would matter as a whole. Modern V-12s kinda settled on 60° for a reason I guess. Probably because it’s a square of 2 I-6’s and 2 V-6’s.

[@chippyjohn1]

@@AZREDFERN 60 degree for a V12 is ideal because there is 60 degrees between each firing of a cylinder with 12 cylinders. A V6 is 120 degrees, v8 90, v10 72 etc. For mass production, engines such as mercedes truck engines are all 90 degrees regardless of cylinders for the ease of manufacturing. Other considerations such as a 120 degree engine being very wide and a 60 degree engine is quite tall. Even firing means even stress on crankshaft and drivetrain. If uneven, the crankshaft experiences higher fluctuations in stresses rather than a more continuous application.

[@jiroyamamoto2878]

@@chippyjohn1 The World War 1 American Liberty engine was a 45 degree V12. The crankshaft had common journals for the pairs of connecting rods. It had crankshaft resonance problems due to uneven firing.

[@peterlastrucci324]

Very interesting and well presented!

[@LetsGoAviate]

Thanks!

[@hu5116]

Great vid! I’m not sure it all really matters. At the end, all one cares about is how much HP, at how much weight, in how small a volume, and with how much fuel consumption. Oh yeah, and how reliable it is! That latter one is IMO the most important one. Having just watched a video on aero engine lubrication, I was dismayed to learn that a lot of air cooled engines are built on purpose with very loose tolerances to accommodate the large thermal variations experienced with air cooling. This lets exhaust blow by rings much easier contamination oil which leads to both oil degradation and engine wear. If you ever wondered how you can drive your car for well over 100,000 miles and literally decades with no significant mechanical trouble, yet need to overhaul your plane engine in almost double digit hours of operation, there is one of he answers. Because of this, I now wonder if we are missing the mark by not demanding liquid cooled engines which could be made much tighter, more auto like, and with marked less frequent overhaul requirements. This definitely makes me want to look at alternatives in the future because doing very expensive overhauls is a definite detractor from lower end aviation.

[@stephenstephenson6614]

Walter Micron has a nice four and six inline air cooled engine. Not sure if they are still in production. Thanks!

[@LetsGoAviate]

Yeah that's an interesting one. Designed in the 1930's, seems to have faded out of popularity after the 50's and production stopped. Then the company started production again in the 80's with minor modifications. Very low HP though (60-80). Cant figure out if they are still in production. Thanks for the comment!

[@tonylam9548]

@@LetsGoAviate I think the new name is LOM engines.

[@LetsGoAviate]

Thanks!

[@jamesbromstead4949]

I've flown a Van's RV-7 with a Walter M337 inline, inverted 6 cylinder and it was one of the smoothest running engines I have ever known (at all operating RPMs).

[@LetsGoAviate]

@@jamesbromstead4949 Nice! The inline 6 is the smoothest possible cylinder layout 🙂

[@BlueMax333]

well researched!

[@danieldimitri6133]

Part of the problem with non aircraft specific engines is the crank speeds. They need a gearbox which offsets some of the weight saved on a lower displacement. Another issue is how enthusiasts assume the specific power and efficiency are one in the same. While bmep is not exactly efficiency it is often related, but it is only part of the specific hp rating which also involves crank speeds. The thing is that old 2 valve combustion chambers don't actually make aweful bmep or bsfc. Bsfc has more to do with range and required fuel so that's part of the complex balance and bmep is part of torque which has to do with turning a prop. It's entirely possible that once you sort through gearbox losses aircraft balance, prop selection and the fuel capacity and range that the effects arent worth the extraordinary efforts except for the highest performance applications where the higher pitched whine of a high output engine being bothersome is the least concern. Automotive and power sports engines do amazing things but if setup well old tech isnt always so bad. The small pistons of common i4 engines and centered sparkplugs can lead to a low emissions engine but low displacement has more surface area to volume so despite how well it burns may keep less energy in the cylinder and more in the cooling medium. This might help wirh nox emissions so its an easy choice for automakers. But for a high duty cycle application where torque is king then having a larger case to disipate heat on the outside while keeping more heat in on the inside with fewer moving parts does start to look like a good idea. So even if the traditional aviation engines seem like carryovers from the 1930's and the high level of development on auto engines could put them first the aviation engines with efi have nice developments like redundancy and CAN network telemetry compatible with avionics systems. It is nice to have something that feels like a package deal. Maybe its perfectly fine that the alternatives are kept for the experimental guys who can work on bare bones avionics and lean on thr engines dependability vs the guys who pay for aircraft maintenance having some aircraft specific redundancy and avionics specific features.

[@timduncan8450]

We should stay in touch. I work as an engine engineer but don’t get to do architectural things like you and this video discus. I’m convinced converting automotive engines with PSRU’s is the only possible solution to high cost aviation engines. The Lyconisaurus engines have and will slowly evolve but have never come down in price. My engineering and engineering experience is that trading the moving parts in a 4 cyl for a three with balance shaft is a good win. Balance shaft has no piston scoring, valve dropping, ring sticking bearing spinning, etc issues. Cutting those odds by 25% right at the dwg board is a good win. As you say getting back to larger cyl bore will help bsfc vs 4’s. The PSRU is a good compromise vs Lyconasaurus cost. They can be very reliable and though incremental, still make competitive system wt with aggressive downsizing/up-rev’ing and or boost. Turbo charging is a very natural choice for aviation, with excellent benefits. Of course it must be done with reliability, durability and $ efficiency. These latter hurdles have all been cleared by many automotive and some sport engines now. We just have to bring them all together and package for aircraft.

[@ArneChristianRosenfeldt]

I have read conflicting information about ceramic coating. A flat roof and a Hereon piston ( flat with firewalls ) let’s the fireball from one or two central spark plugs just reach all walls as the piston gains speed. So before a lot of heat loss, the heat does the work. Bore < stroke. The principal scales if you rev smaller engines higher. At least in the displacement range we talk about. Planes too small for 6 big cylinders running at max rev defined by combustion, should go electric/ sailing.

[@chippyjohn1]

A gearbox for an engine that makes 200kw and revs higher compared to one that revs lower can be made lighter as the delivery of power is smoother. Look at a turbine transmission, they are considerably lighter due to their smooth torque. Engine efficiency can be greatly improved with the use of ceramics, steel pistons, quality oil, titanium, turbochargers, liquid cooling, composites, electronics. Automotive technology is far behind, and aircraft even further. Smaller lighter engines are far better for aviation even with a gearbox, especially now with modern ecus such as Motec. Even the simple use of a tuned intake for a certain rpm can give 5-10% power gain, but with a lower revving engine the longer it has to be which weighs more. Steel pistons are stronger, lighter and more thermally efficient than aluminium, but they are far more expensive to produce. OHC and multivalued use less power and allow for easier power by means of flow and cooling. There are so many ways an aircraft engine can be optimised, currently the only people that do it are in the experimental market. Big companies are trying to make profit, that is their goal.

[@ArneChristianRosenfeldt]

@@chippyjohn1 When I read this, I think about a two stage reduction gear, where the first stage is small and the second stage only deals with smooth power delivery. Turbos are better for cruise than tuned induction NA . Interestingly, a V12 Merlin has both: smooth power delivery, and too much RPM for the large prop it can drive. Why are there many V12 cars, but only a few V12 planes? Could even reduce displacement per cylinder to 0.5 liter like in a car.

[@chippyjohn1]

@ArneChristianRosenfeldt There are many v12s used in experimental but they are less common due to the engine being less common, cost and power requirements. There is a company that modifies bmw v12s for the experimental as well as other v12s such as the RED. A 6 litre V12 petrol would be around 250-300kw naturally aspirated, there just aren't many aircraft in need of the power in the experimental area when the market is mostly around 75-100kw.

[@zopEnglandzip]

Blackburn cirrus was probably as popular as the DH engines for a while. Like for like a boxer should be lighter, due shorter crank. Had to stop an oil leak on a Porsche swapped mooney that dropped in, customer was generally upset with his life choices and believing an increase in hp meant increased performance, the words of Burt Rutan come to mind when the subject turns to fast revving low displacement engines. "Hp sells, torque propels" And of course a lyco/conti can sit at 75% power for days, not so much with small high output engines.

[@bakters]

" *Hp sells, torque propels* " It's true, when designers deliberately build an engine, which delivers max power right at the redline, with no usable powerband. They basically gamed the system. No wonder it didn't work too well. Ease up a tiny bit with the resonances, you lose a few horses at the redline, which you couldn't use anyway, but gain a huge bunch all over the powerband. Max torque remains the same, but suddenly it all works 100% better. " *75% power for days, not so much with small high output engines* " That again depends on how you build the engine. Low revving truck engines very often suffer a lot in racing, because they have long stroke and high piston speeds when operated close to the redline, while smaller, revvy engines do well. Short stroke, low average piston speed. Current bike engines are built for that regime. 200 horses you can easily lift yourself, together with the gearbox! BTW - the main reason why 4-cyl engines have relatively low displacement is the optimum combustion chamber size. It makes little sense to go much above 0.5l per cylinder.

[@jacoscholtz2716]

Great video thanks. Back in 2005 or so I was at a microlight airfield in Moscow, and present was three different manufacturers of trikes mainly geared for crop spraying. One company used a converted Suzuki 3-cylinder engine, and the other a converted Honda Civic 1.6L (it was a massive trike). I cannot recall now who did the conversion but will try to find the details and share it here. My friends convinced the owner of the big trike to allow me to fly it, on my behalf. I declined, but asked if I can be taken for a flip in this thing. Their test pilot took me up. It was the ride of my life.

[@Romans--bo7br]

@jacobscholtz2716...... You said, quote.. "present was three different manufacturers of trikes...". You only detailed, Two.

[@jacoscholtz2716]

@@Romans--bo7br Hi. The third one is the state university for microlights in Moscow. They manufactured the Poisk microlight and they used the Hirth engine. The Hirth is the German version of the Rotax, but I think it was also manufactured under licence in Russia (or probably Ukraine). I got to know them because I bought a Poisk from Oleg Alekseev who used to live in Cape Town, and he was friends with the guys who manufactured the Poisk. Oleg unfortunately passed away in his new Poisk at the Saldanha airfield and I heard most of the Poisk manufacturing crew died together in a helicopter accident.

[@Romans--bo7br]

@@jacoscholtz2716... Hi, and thanks so much for your reply, I appreciate it. I've heard of the Hirth engine at some point in the not too distant past, but never really looked into it. WOW!!.... what sad news in relation to the crew from Poisk... very sad to hear that!! How long ago, or how recently did that happen?? When you mention Moscow.... are you referring to Moscow, RU. or Moscow, PA. ??

[@louisvanrijn3964]

This video sums up several differences between boxer and in line engine (everyone knows) Three major facts are NOT mentioned. -1. Car engines have far, far lower loading spectrums compared to aircraft engines. Do you apply full power for several minutes after driving away? (the take of is mentioned) and 85% power for many other minutes (climb-out) "This car-engine is good" (if you use it only up to 30% power AVERAGE in a car, then it is true.) 2. An ordinairry aircraft engine has everything vital double and also independently. Double ignitions, double fuel pumps etc. 3. The certification cost are extremely time comsuming and expensive. From every engine part the complete history of the metal (back to the mill) has to be cleared, described, frozen and cannot be changed after certification. No car engine complies to that. That are the reasons you see only a few car-based engines.

[@thamesmud]

The DH gypsy engines an 2:11 d Bristol Cirrus engines were reliable and widely used.

[@porpentosa]

Great video. But unless I missed it, you did not mention the conrod length vs. stroke ratio as a major factor related to secondary unbalance. The longer the conrod, the lower the secondary imbalance.

[@LetsGoAviate]

Thanks. No I did not get into that, the video was long enough already. Yeah you can see how long the conrods of the Gipsy engine was! I believe it reduces secondary imbalance because a long conrod will have a shallower angle at 90° and 270° of rotation than a shorter one, which means the difference in vertical lenght beteen upright and fully angled will be smaller.

[@robinj.9329]

THANK YOU 😊 I found this more then just "interesting"! With the very HIGH prices of modern Turbo-prop engines, I've often wondered just why we haven't seen light "Executive" transport aircraft powered by an "Inverted V-type" engine, al-la WW2 Fighter! A pressurized Twin, with two 500 h.p. inverted-V engines could favorably compete in the market place with many smallish Turbo-props ! I've even done a few initial design sketches! Twin, 500 h.p. engines. MUCH less expensive then todays light turbines! At a total of 1,000 horse power. And with a gross take-off weight of 10,000 or 11,000 lbs.

[@tankermottind]

In this case, why not just do the same thing that has been done with the Viking engines to an automotive V8? Maybe use Chrysler's 700 horsepower, 6.2 liter turbo Hemi?

[@optiondrone5468]

Hey, man! Your explanation of the pros and cons of inline 4 vs. boxer engines was really good. I've been considering the Pipistrel Virus plane, which is designed for the Rotax 912 and 914 engines. Do you think there's a suitable Viking engine that I can use for the Pipistrel Virus plane? This might be a dumb question, but I wanted to throw it out here to see if there's any good explanation.

[@LetsGoAviate]

Thanks. Not a dumb question, but I don't have a great answer. Without double-checking all my facts, Pipistel suggests only the Rotax engine for their planes, and I've not seen one powered by anything other than the Rotax (excluding the electric). While surely not impossible, I think it will be difficult using something other than the Rotax on the Virus, unlike your kit plane bush planes which are designed with many different engines in mind, I think the Virus' cowl/frontal area will be limiting. For this plane personally I'd look for a used Rotax 912ULS/iS

[@optiondrone5468]

@LetsGoAviate I actually looked at bush planes. The problem was I couldn't find one suitable for UK CAA or EU EASA. I like the Bearhawk B4, but I don't think I'm allowed to fly it in UK skies, something to do with the airframe. I also looked at the G1 Aviation French company because I was told it can take the Yamaha Apex engine. It is so difficult to get a plane with 2 to 4 seats in the experimental class with good load capacity. The only reason I like the Virus is that it's an easy plane to fly, and it also has a good glide ratio and cross country capable. Thanks for your reply.

[@jacobmoses3712]

There are some excellent diesel engines now being used in aviation. Some Mercedes diesels are now being used. Diesel's advantage is they run on Jet A1 instead of Avgas, which is getting scarcer

[@NICK-uy3nl]

IF you are going to replace the boxer with an inline engine, it has to be a DIESEL to justify the expense and complexity with lower fuel cost (almost half) and lower specific fuel consumption of diesel cycle, otherwise, there is very little to be gained by the conversion - not including the huge expense of engine certification.

[@chippyjohn1]

The reason air cooled is more popular is because of history and how aircraft are designed. Glycol was not common, not even in cars, seals have come a long way, radiator materials and assembly. Air cooled engines are actually heavier, aluminium cooling fins are heavier than coolant. plus you have ducting and increased drag from cowling. Aircraft are still designed around aircooled engines because that is what is commonly made. Lycoming, Continental and Rotax are all old. A 4 cylinder boxer engine is also not perfectly balanced, it experiences a rocking effect which causes vibration due to offset pistons. The use of multivalve and liquid cooling also allows you to run higher power safely due to less heat so their power to weight is higher yet again. Multi valve is not just about flowing more air, but better cooling for valves through the seat and valve stems. Bucket style lifters naturally rotate valves where as rockers do not. All of these air cooled dinosaur engines have a magnitude of problems fixed in modern engines. the reason they make them is because people buy them, a company does not stop producing their bread maker unless they are forced to.

[@fidelcatsro6948]

time to go back to 2 stroke simple aircooled boxer engines

[@chippyjohn1]

@@fidelcatsro6948 2 stroke and air cooled is almost obsolete. modern engines are far better, just that people know little to nothing about an engine.

[@kellyaquinastom]

What about opposing cylinder motors? Achates?

[@fidelcatsro6948]

thats UFO technology even car makers should adopt!

[@WilhelmKarsten]

The Jumo 205 was very successful

[@moviemenia9276]

Maybe No one will design an inline 4 engine for aeroplane... But you can use a suzuki hayabusa engine for an aeroplane.. this engine is so reliable and balanced... And also powerful.. i have done some research about that.. not too much research.. but i think this engine is better for aeroplane

[@MISTERLeSkid]

This was cool but unless I missed it, you never explained how the secondary imbalances cancel-out on the boxer. I still don't see why that's sorted-out compared to the I4. Good video though - you explain well. Cheers.

[@LetsGoAviate]

Yeah I didn't cover it in-depth. Because the conrod goes sideways as it goes around the crankshaft, it becomes shorter (relatively speaking) vertically, and pulls down the piston more at 90° and 270° of crankshaft rotation. This additional pulling down of the piston causes acceleration and decelleration of the pistons (in the normal "plane" of movement). At 0-90°, 90-180°, 180-270° and 270-360° degrees of crankshaft rotation, the pistons accelerates, decelerates, decelerates and accelerates respectively. This means the secondary imbalance's resulting force is in an "upwards" direction, upwards being towards TDC. So the reason the boxer 4 can cancel out secondary imbalance naturally is because the pistons face in opposing directions, and each bank of 2 cylinders cancels out the imbalance on the other bank of 2 cylinders, as opposed to the inline 4's pistons all facing in the same direction. There's more to it, but that's the basics.

[@JunoSolarWinds]

Turbo rotary with reduction gear box would be cool

[@berndm9743]

BMW produced an inline 4 cylinder back in the 1980's that was only 1.5L but capable of over 850HP in F1 racing trim. It was the M12/13 IIRC.

[@mpetersen6]

What make is the liquid cooled inline four in the thumb nail. Its obviously an OHV design and appears to be a cast iron block. It almost looks like an AMC 2.5L.

[@LetsGoAviate]

Unfortunately where I got it, there's no mention of what engine it's from. At the risk of being stoned to death, or worse, being banned from the internet by angry keyboard warriors, I chose a non-aviation engine block for the inline 4 based on how easy it is to recognize on a tiny thumbnail.

[@B0RN2RACE100]

The opposite piston layout should be the best type of piston engine for this application, but I think someone tried and got shut doing for…(legal issues? Licensing? I don’t remember)

[@richspillman4191]

There was a video recently on a "Scotch yoke" engine that claimed to do well as far as secondary balance and weight, this video made me think of that technology as a solution.

[@LetsGoAviate]

I think it's the Alfadan engine? Yeah it completely solves the secondary imbalance issue as the conrod doesn't go from side to side and thus doesn't change it's relative length. It's all theory though until it is in production.

[@crono331]

Boxer has shorter crank and camshaft, which are very heavy components.

[@centheiatrust9153]

You have overlooked one MAJOR advantage of using an inline 4 automobile engine. And that is full digital control. This results in far better fuel economy, eliminates carb icing, and eliminates hot starting problems of fuel injected aircraft engines. It also gets right of having 2 magnetos and spark plugs with smaller air gaps that can clog easily. Not mechanical moving parts in the ignition system allows for full, real time spark adjustments for best engine performance. And, their TBO can be much higher. How many aircraft engines do you know of that can go the equivalent of 200,000 road miles without engine failure?

[@N9197U]

Fuel injected computer controlled boxer 4s exist too though.

[@andremarais2706]

Thank you. I really enjoy your content.

[@DirkLarien]

so from this intresting video i was led to one about INNengine. Looks Interesting for aviation. Small size low weight not many moving parts this all smells of perfect fit. Any thoughts ?

[@brandonb417]

I'm curious what the reliability of some of these converted inline 4's is. There are some planes out on the market that need new engines, which makes them a very expensive buy since new engines are so expensive. But if you could hang one of these on it....

[@LetsGoAviate]

I'm curious about the reliability as well. Not a lot of data out there, mostly just what can be found on forums.

[@OtterFlys]

I think he got the piston travel wrong at 90 degrees crank rotation. Hope this is not the first notice 😊 But then again, I use rotary engines in my flying contraptions so what do I know.

[@LetsGoAviate]

Hi there! No, it is correct. From 0° to 90° of crank rotation, the piston is pulled past the halfway (50%) point. This is because the conrod is now at an angle, and has a shorter vertical length (relatively speaking). This pulls the piston down further. From 90° to 180° of crank rotation, the piston is pulled down less than 50% of it's travel, this is because the conrod becomes vertical again, and gets longer in vertical length. Hope it makes sense. There are videos explaining this much better than I do, like the one in the video description.

[@lqr824]

3:20 dry sump, expense: Most of the German planes of WWII had inverted V-12's. It's not necessarily a huge hurdle. I wonder if they had dry sumps (probably, given that the Bf-109 was known to pull negative G's) or whether most had a wet sump that was simply fed from the cylinder heads. General Aviation planes don't need to pull negative G so why wouldn't a wet sump still work in an inverted engine

[@LetsGoAviate]

The Bf 109's engine was indeed a dry sump. I guess the problem with an inverted wet sump is, where do you physically place the sump? Using a dry sump isn't a huge hurdle, and there are many examples of them out there today. Heck, my plane has one! (Rotax 912). But it does drive up engine cost, which the manufacturer has to decide if it is worth it.

[@lqr824]

@@LetsGoAviate > I guess the problem with an inverted wet sump is, where do you physically place the sump? A box that feeds from the heads or cam covers would take care of everything below the pistons. I'm not sure how you'd get oil from above the pistons but there must have been a way if the Germans were doing it 60 years ago.

[@lqr824]

@@LetsGoAviate I haven't flown GA but commercial passenger service almost never has side loads even approaching that of a cornering economy car (which can do 0.7g or something laterally)? Why would you need a dry sump on an airplane? Is it only a bit of extra insurance so that the engine keeps working even under bizarre abnormal conditions that normally never happen anyway (e.g., momentary weightlessness in a stall)?

[@phantomforester9337]

Why not use the camshaft drive in a purpose-designed ohc inline 4 aircraft engine to drive the propeller? That would not add the complication of a separate gearbox (though the drive would have to be sturdier), there would be an automatic 1:2 speed reduction for the propeller (or even 1:4, if you used double-lobed cams on the camshaft), the engine would be upright and could use a wet sump system, and the propeller drive would be at the top of the engine, providing the desired thrust line and good propeller clearance. The propeller doesn't care if it is being driven by the crankshaft or the camshaft. A conversion kit might be designed for an ohc automotive engine to do this as well. Just a thought.

[@LetsGoAviate]

My first thought was that the camshaft would need to be seriously sturdy, but you did point that out. Also you would end-up with a belt or chain driven camshaft in turn driving the propeller. Not an issue per-se, there are belt driven propellers in the ultralight world (as propeller speed reduction instead of a gearbox), but the belts are about double as wide as a normal cambelt. But if you are going that route, might as well just belt drive the propeller hub from the crankshaft, rather than belt driving the camshaft which drives the propeller hub?

[@phantomforester9337]

@@LetsGoAviate Well, that would still duplicate the drive--you would have two drives, one to the camshaft, and one to the propeller, each with a gear reduction. The old Crosley COBRA and CIBA engines had a shaft drive to the camshaft, which would have been very sturdy--maybe extra bearings would be all that would be needed to convert--or, a bespoke shaft drive to the camshaft and propeller could be a simple drive that would perform both duties easily, without too much bulk. Even if you use just a belt, driving the propeller off the camshaft drive would save an extra set of reduction pulleys, as well as the belt. It would be lighter and simpler than two separate drives.

[@phantomforester9337]

@@brianb-p6586 Thank you. Okay, an idler gear would be needed. That still strikes me as being less complicated, lighter, and less bulky than a separate propeller drive. Also, there are twin-lobe camshafts that are driven at 1/4 crankshaft speed. The propeller could be more geared-down than 1:2, allowing for even higher revs for the engine, increasing power and efficiency, while still not needing a separate propeller drive. And perhaps a belt drive would avoid gear teeth wear issues, particularly with 1:4 drive. I am sure there would have to be some development time before an ideal arrangement could be worked out.

[@PistonAvatarGuy]

The Continental Tiara engine did something like this.

[@phantomforester9337]

@@PistonAvatarGuy Thank you. I Googled it--that engine purportedly had high fuel consumption, and did not have a sufficient performance advantage to justify its expense. The concept was to use the camshaft drive to allow for higher rpms, and more power, without a separate reduction gear. A hydraulic "Hydra-Torque" drive was used to reduce shaft vibrations--which could also be used here. Apparently, an extra idler gear was not used--maybe the Hydra-Torque drive negated this need. But the engine was of conventional flat-opposed configuration--it did not use the cam/prop drive to have a cheaper upright inline engine with smaller frontal area. And, it had a 1:2 reduction--it did not use a 1:4 reduction double-cam-lobe. On top of all that, it was in a higher-power engine category, not a small, light engine for minimal aircraft. Perhaps the upright inline 4 with a combined cam/prop drive could still find a place. The smaller engine could rev higher, especially with a 1:4 gear reduction, the lower frontal area would help fuel consumption, especially in a tandem-seater, and investment costs should be lower than with a bigger opposed-six. And the Hydra-Torque drive has already been developed. Just tossing the idea around, to see if it has validity. Thanks for the information.

[@RePeteAndMe]

I’m guessing that engine cowlings can be easily lengthened. If you’re going to replace an old boxer why not use a straight six with a bit smaller pistons? Longer, leaner, naturally well balanced, and less buzzy. Still has three small periods of negative torque per revolution, but a temporal torque transfer device can fill those. And you’d have to move weight astern to compensate, but that’s simple enough.

[@ericbucher8636]

Great Vid.

[@Ang3lUki]

I wonder if slant-4 or slant-6 designs could catch on.

[@wingunder]

It seems that Deltahawk is successful with a purpose-built upside down V4. They call it an A4. It looks like a 2-stroke, but not much information is available at this point in time. They claim to make 30 to 40% more power, and have a hibrid super charger and turbo, bolted to it.

[@GoldenGrenadier]

Why not use inline 5 cylinder engines with a weighted propeller to counteract the rocking motion?

[@gj1234567899999]

Won’t 4 cylinder inline engines still have the cooling issue though? Less airflow and more reliant on radiators etc?

[@LetsGoAviate]

Liquid cooled won't as long as the radiator gets air. Aircooled can have cooling issues if the air ducting design isn't great. An airplane designed for the air cooled inline 4 (e.g. Tiger Moth) have taken the engine layout into account with cowling design, and thus doesn't have cooling issues. Put an aircooled I4 in anything else you'll likely have cooling problems.

[@Gopferteckel]

Coming from a family who operate Tiger moths and Austers, we never had issues with inverted Gypsy Major inlines.

[@LetsGoAviate]

When the Gipsy was inverted, there was issues, inlcuding increased oil consumption. Those issues were solved in the 1940's though, so I'm not surprised you never had issues. I wasn't around back then, just going on what I've read 🙂

[@Iowa599]

Instead of dry sump, when turning an inline-4 upsidedown, make the valve cover into the oil pan.

[@fidelcatsro6948]

and risk an air crash? never!

[@mpetersen6]

That was done on an inline inverted four that was introduced around 1940. Named the SkyMotor. Wrong time.

[@Iowa599]

@@fidelcatsro6948 so…never fly?

[@fidelcatsro6948]

@@Iowa599 now you talking like stockton rush.. see what happened to him amigo? 🤔

[@Iowa599]

It's really a lower risk of failure than a dry sump system. It's basically the same, other than the evacuation system (pump, lines, tank) eliminated. I'd be concerned of the pistons acting like cups of oil, but since they move down faster than gravity, they empty themselves. You will (probly) need to add a crankcase drain, to drain the crankcase into the valve cover, but the factory equipment might work (if the OE drains work the other way) or require minimal changes (maybe PCV porting).

[@who-gives-a-toss_Bear]

0:23 Boxer engine are lighter and better!

[@weibrot6683]

9:07 Why do these engines have so little power for so much displacement, do they have nonexistent max RPM or what's happening here? A stupid idea but at this point a 1l motorcycle engine pumping out 200hp with a gearbox might actually be the lighter alternative

[@LetsGoAviate]

They have low max rpm in the region of 2,700 and also were designed with reliability as priority over power.

[@Dave5843-d9m]

The con rod angle causes pistons to reach mid stroke After 90 degrees. This causes a nasty vibration at 2x crank speed. Inverted two stroke V4 has very low vibration and direct injection run very clean and efficient. The Delta Hawk diesel is even better.

[@rondavison-v6q]

wonder if that helps lubrication of rings. gravity being your friend here. but mains?

[@nerd1000ify]

The mains get plenty of oil from the pressure feed being sent by the oil pump, same with the big ends. Inverted cylinders tend to have issues with too much oil draining into the combustion chambers, especially when left sitting after shut down. This is why radials tend to smoke so badly on start up, oil pools in the bottom cylinders and they smoke until it burns off. Inverted inline or V engines usually use the rocker covers as sumps and have drains running from the crankcase to the cylinder head for this purpose, which might explain why they seem to smoke less than radials. But they will still burn more oil than an upright engine.

[@BuzzLOLOL]

Ducati 90 degree V2 is so smooth you can't feel it running... inline 4 kinda sucks for every use...

[@OldinMariner]

I have a question, are all flat four aircraft engines boxers or are some regular flat fours?

[@LetsGoAviate]

I'm not sure if there has ever been flat four (that aren't boxers) on aircraft, but I's be surprised as they are not very smooth engines, with that huge rocking couple vibration on the whole engine, due to 2 cylinders sharing a crank pin.

[@bierce716]

Seems to me that all the issues you mention with the online four were solved more than a half century ago with the Meyer-Drake Offenhauser engine. It only won the Indianapolis 500 27 years in a row, and took the entire front row ten years in a row. Even naturally aspirated, it could make 770HP, and went over a thousand with turbocharging.

[@LetsGoAviate]

Thanks. I had to go look it up. I don't think they solved anything related to secondary imbalance, but really sturdied up the engine like crazy, so that the imbalance really doesn't affect it like it affects a normal production engine. I'm thinking, why is this not in any production sports cars? And why has it not been used in aircraft? I don't know the answer but I'm guessing it's relatively expensive and/or expensive to maintain in a daily use (non-racecar) vehicle due to it's much different design and assembly methods. It also looks like they are heavy, some in excess of 400lbs. Again, I don't know all the facts, I'd need to research it more, but there is a reason it isn't being used in much other than racing cars. Awesome discovery for me though, so thanks!

[@bobwilson758]

Yes sir ! Indeed - how soon some narrow minded people forget what you said ! I only worked with one old offen - Awesome unit ! I was a young mechanic and into big block Chevrolet mark lV engines at the time , However - Like you said , non turbo offenhauser … Actually scared me … at first anyway . Please excuse my spelling Thank you sir !

[@danbenson7587]

Here are pros and cons unmentioned. Remember props turn < 3000 rpm 1. The I4 crank is longer which brings its the critical frequency closer to 3000. 2. In its favor, the I4 has 5 main bearings versus H4’s typically 3. (VW, Rotax, Continental, Lyc’s have 3, Subaru has 5.) 3. A direct drive I4 secondary imbalance is a non issue at 3000. Even a good possibility partial primary balance is workable. 4. Engine stiffness impacts longevity. Lycomings and Continentals flex because air cooling fins compels wider cylinder spacing. Moreover individual cylinder heads diminish stiffness. These engines compensate flex with sloppy clearances. 5. At 3000rpm, 2 valve pushrod heads work fine and lighter than SOHC or DOHC. 6. A Continental O-200 makes 100hp at 2800. Doubling the speed engine could make 200 at 5600, …1hp/cid. The point: these old engines are not all that bad. 7. Conceivably one could go to the hot rod parts bin and get a Chevy LS1 head, pistons, rods, valves mate to a custom crank and block for a 100hp engine. Check out the Crosley CoBra engine or blocks CNC machined from solid aluminum billets. It’s just time and money and imagination, …and grit Engines with Reducers. 1. In a 4 cycle engine, cylinder torque pulses don’t overlap until you get to 8 cylinders. With a 4 or 6, thru a revolution, the engine drives the prop, and then the prop drives the engine. These reversals are absolute hell on speed reducer’s gear teeth unless mitigated by a clever coupling such as the Rotax 912’s. (And Viking and AeroMomentum) Wider rpm band faster risks resonance. No easy solutions, but there are solutions. The certified aircraft engine market is small, maybe 2000 units per year worldwide, the entry barriers are prominent, and comes with 100’s trial lawyers. One sage commentator commented, it’s economics.

[@LetsGoAviate]

Some of it is obvious, some of it is way more in-depth than I would ever cover in a medium-lenght video format, and some of it are great ideas for a future video. Thanks!

[@danbenson7587]

@@LetsGoAviate FYI, Solid Works modeled auto parts (LS1) based 3000 RPM H-4 ~180 CID 5-bearing engine to check the weight. Projected to be heavier than an 0-200, but less than the 0-235. But such an FAA certified engine might cost the customer only $3000 on say a $30000 engine. 10% doesn’t justify the effort. Cheers D

[@WilhelmKarsten]

You are clearly attempting to compare apples to oranges here... Automobile engines are not typically designed to meet the rigorous demands of aircraft applications... and as such are built to a price point that reflects these much lower automobile requirements. The notion of a $3,000 dollar type rated aircraft engine is not just wishful thinking it is pure fantasy son.

[@naughtiusmaximus830]

Wasn’t the ME 209 an upside down inline?

[@LetsGoAviate]

No it was a V12.

[@lqr824]

41:18 the first 4-cyl in-lines in aviation do not date back to the 1930s. The Wright Flyer had such an engine. Literally the very first aviation engine was an in-line 4, for probably all of the reasons you give.

[@jaromirandel543]

It is almost like reinventing the wheel. Superchargers and the turbochargers are nothing new. Even in aircrafts. Those used to be used in many aircrafts, specially in WWII era. I think the main difference is that high power piston engines were substitued by turbo-prop engines and the "low power" engines kept conservative way.

[@RulgertGhostalker]

ok if the Crank drove the Sun Gear, and the Cam Ring was The Ring Gear, and the Planets where Held Stationary.... Then A 3-Cylinder Radial Would Have A 2:1 Reduction Built In ( the Prop moving with the Cam Ring ) for example: 32T Sun, 16T Planets, 64T Ring, would leave plenty of room for a couple of tapered roller bearings in the crank end. so maybe just a 1.8L Turbo 3-Cylinder Radial would do... bore 98mm, stroke 78mm = 1765cc, something like that?...or maybe 1.3 Litter? 90x70-ish...or Bore 94mm X Stroke 72mm = 1.5 Litter?