Over Compressed Engines, Forgotten Tech From WW1

How did the Germans get power at altitude WITHOUT a turbo or supercharging in 1917? By over compressing. I'll explain what this is, how they did it, and show how well it worked.
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[@GregsAirplanesandAutomobiles]

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[@negativeindustrial]

Greg, are you familiar with Toyota/Yamaha’s T-VIS system? It was a mechanical system used on low displacement (1.6-3.0L) performance DOHC engines that essentially allowed the engine to run as a 3 valve at low RPM and a 4 or 5 valve at 4000-8000rpm+. Because the system only affected the intake valves, it increases efficiency by artificially creating a longer intake runner for low rpm and a higher overall volume for high rpm thereby keeping intake air velocity optimized over a wider range of engine speeds. Paired with a turbocharger(s), it made for some pretty awesome spirited driving and crazy long gears. There are some good old technical manuals from Toyota that detail the T-VIS system’s application in cars such as the Toyota Supra, Celica GT4, Corolla GT-S and the first two versions of the Toyota MR2. I’ve been tuning these engines for close to thirty years now but I’d love to hear you do a deep dive on them. Or, even just a deep dive on the special partnership between Yamaha and Toyota that reaches back to the 1960s and features such guest stars as Carrol Shelby and Dan Gurney, just to name a few. Anyway, just an idea. Long time subscriber and love the channel!

[@sadwingsraging3044]

I bought a $15 superchat for you Greg but can't see it.🤔😑😔

[@negativeindustrial]

I’m seriously sick of KZbin deleting my comments. You would think they would treat their paying customers a little better.

[@GregsAirplanesandAutomobiles]

Hi SWR, I saw it and responded to it. Refresh. That might do it. Thank you very much my wife and I really appreciate it.

[@sadwingsraging3044]

@@GregsAirplanesandAutomobiles She is an absolute peach for letting you spend time educating so many people about the history of flight and the people involved. Give her a big hug from me.🫲🏻🥹🫱🏻

[@faeembrugh]

I saw a D.VII at Schleissheim air museum near Munich and started telling my (very bored) German girlfriend all about the cantilever construction and over-compressed engine and how advanced it all was. Turning around after giving my riveting talk, I discovered a group of Japanese tourists who assumed I was some sort of tour guide and then followed us around asking me questions about all the other exhibits despite my protests that I was also just a visitor.

[@GregsAirplanesandAutomobiles]

lol, that's a great story.

[@asdf9890]

Haha that’s a funny story 😂

[@drstrangelove4998]

Well done, thank you for your service 😉

[@babboon5764]

Well I hope: (a) They were generous tippers at the end of the tour & (b) Your girlfriend saw the funny side of it all

[@faeembrugh]

@@babboon5764 I did get one of them a turn sitting in an F4 Phantom cockpit. The guy was so small he just disappeared inside - no lost Japanese soldier jokes! No tips...I don't think it's Japanese tradition. And, yes, it all was quite funny afterwards.

[@foxhoundms9051]

"The hammer of science. Its calibrated." 🤣

[@sjoormen1]

You just made me watch this all over again... oh well

[@dennismason3740]

@@sjoormen1 - As a composer/player (many instruments) I fully appreciate Greg's narration, whatever the subject. I watch his vids many times over and retain a bit more with each watch. Osmosis! I call Greg the Charlie Parker (the Bird) of narration. His phrasing and passages are surprisingly musical.

[@sjoormen1]

@@dennismason3740 yes, he is good. Sadly as english is not my first tongue, I miss a lot of those little hidden gems. Those I do manage to catch, I do enjoy.

[@solidspooks8689]

The power of compression compels thee!!

[@sjoormen1]

@@solidspooks8689 lol😁

[@kennethalexander755]

Years ago I was involved with some NASCAR stuff. The restrictor plate engines were built with extremely high compression ratios and the drivers had to be very careful to be smooth with the throttle at low speeds under load. If you snapped the carb wide open and lugged it the engine would suffer major preignition and probably damage it. That is why most of the engine failures you saw happened right after a pit stop. The 390 cfm carb would choke it off enough to keep it out of pre ignition when the engine was at max rpm. When they mandated lower compression ratios it made for much more reliable engines.

[@dukecraig2402]

@@kennethalexander755 It's incredible that they ran 390 CFM carbs on those engine's and they'd rev as high as they did, without being in neutral. 35 years ago I was trying to tell my car buddies who were running engine's with displacement in the mid 300 cubic inch range (350 being common) that a 750 CFM carb was just too big for something like that, especially engine's that only had drop in cams, intake and headers, and then they'd wonder why they'd hesitate real bad stomping the gas from real low RPM's with some bucking and kicking like an angry mule, other factors like poorly designed exhausts and not having the ignition set up right for the engine build didn't help with that either of course, but they just had to have their 750 CFM Double Pumper because that's what some race setup somewhere was using, and besides everyone knows the bigger the carb the more horsepower it makes 🤪

[@GregsAirplanesandAutomobiles]

Yup, the engine puts the demand on the carb, it's not the other way around.

[@kennethalexander755]

@@dukecraig2402 Well, just about everyone has fallen into the bigger is better trap at some point. A 750 vacuum secondary carb would work well with the typical street setup. Especially if you had the time and knowledge to tune it with secondary springs, accelerator cams and tweaked the squirter nozzles. But most guys were better off with a 650 cfm deal. The restrictor plate engines were highly developed pieces that probably wore out some dynos over the years. Dyno testing was pretty much an art as much as science until the advent and the easy availability of the computerized dynos, ALL PRAISE SUPERFLOW, there were massive improvements in output and reliability when they came along. So much more reliable real time information. Even long time engine builders found some of the long time, ( this is the way) mantras were not so clear cut. Anyone who can afford to put their project piece on the dyno will learn a years worth of trial and error in a day. The chassis dyno deals are another level of improvement the needs a chapter of its own.

[@stevengabalis4986]

@@kennethalexander755 I worked in auto parts stores from the late 60's on. When a customer came in wanting a Holley 850 double pumper for their 327 small block, I'd ask what kind of RPM they run, and do the math to show how much CFM their engine would pull. I was able to talk many of them down from the "bigger carb is better" ledge. The ones who bought the blamo carb anyway got very little sympathy when they came back claiming that it was defective. Nope, you just bought the wrong size, and I warned you.

[@jesse75]

" The 390 carb would choke it off enough to keep it out of pre-ignition. " That doesn't make sense.

[@c1ph3rpunk]

I am 3 minutes in and really wondering how this will connect to the required ending of “and this is how it made the P-47 the best aircraft of WW2”.

[@GregsAirplanesandAutomobiles]

LOL, I do have a connection at the end, and it a very round about way....

[@c1ph3rpunk]

@@GregsAirplanesandAutomobileshmm, never picked that up in Waldo Pepper, think I’ll have to watch it again this weekend. Haven’t seen that in a LONG time. Remember seeing it as a kid and thinking how fun it must have been to be in aviation back in the 20’s.

[@SnakebitSTI]

Why do you assume it's a stealth P-47 video? It could be about the Dora ;)

[@c1ph3rpunk]

@@SnakebitSTI yep, entirely plausible.

[@BLD426]

Hey. Do I hear disrespect for the P-47 in that tone?😡 😆

[@bartonstano9327]

Fun fact: Fokker DVII was the ONLY weapon system mentioned by name in the treaty at the end of the war, the clause forcing the German to surrender all of them to the Allied powers.

[@rutabega2039]

Greg actually mentioned that in this video at 14:10.

[@babboon5764]

Even before Greg's (excellent) video I understood that to be true But don't forget the Germans were obliged to essentially scrap the rest of their airforce (quite a lot of mostly Albatrosses ended up in the Baltic states flown by German WW1 pilots) Curious footnote: Ernst Udet was one of very few who prefered the Pfalz D.XII to the Focker DVII. The Pfalz was less agile but the fastest thing around in a dive. Most Pfalz D.XII were handed over to the allies alongside Focker DVIIs

[@Melanie16040]

@@babboon5764 Are you sure about that? I would have sworn the Paris Gun was also mentioned, with the Germans being required to hand over a complete example of it.

[@babboon5764]

@@Melanie16040 I'm pretty sure about air-related information. Artillery - not so much

[@brucefelger4015]

I recall someone at Rhinebeck saying that their D-7 engine still had the original spark plugs and worked quite well thank you.

[@dukecraig2402]

It's not the age It's the mileage.

[@964cuplove]

@@dukecraig2402 hours ?

[@tiitsaul9036]

In early 2000s Saab was experimenting with variable compression ratio engine. The entire engine block was pivoting in relation to the crankshaft. The idea was to improve power and efficiency at low power levels (high CR) and allow turbo to safely boost power under load (low CR)

[@PhilStewart-xf9rp]

Nissan and VW both are using them in some production cars, just not in the U.S.

[@Colt45hatchback]

Im convinced saab should have been continually bailed out and subsidised (pre gm though) i had a saab 9000 turbo and a non turbo one for spares. Besides the interior wiring being alergic to australian summers, it was great. The mechanicals were so well built, wish i never sold it. Went like hell, was a heavy luxury 4 door hatch but handled like it was on rails, factory large front mount intercooler, big engine oil cooler, easily modified boost controller... haha was awesome

[@dazaspc]

Indeed I have seen an engine with a secondary piston that is adjusted to change the combustion chamber volume. This was only a test rig but ideal for compression comparison.

[@PhilStewart-xf9rp]

@dazaspc the Nissan variable compression engine actually moves the entire rotating assembly (crankshaft) to vary the compression from like 7.5-1 up to a diesel like 15-1(if I remember correctly)

[@CAHelmer]

Absolutely agree with you and still enjoy my 1973 Saab 96

[@patrickshaw8595]

In aircraft mechanic school in the 70s they touched on "auxiliary throttles" that were all the way open at altitude but had marks that the aux throttle had to be closed down to as one descended - and vice versa. It enabled the regular throttle to be handled as aggressively as necessary for air combat.

[@dukecraig2402]

Where'd you go to school? I went to PIA in Pittsburgh.

[@SheepInACart]

It was still a line item for pilot training when I first flew in 2000's, even though I never saw an aircraft to have it actually fitted. While its conceptually simpler to have two physical throttles, the same benefit can be had by having two levels in the cockpit, where one simply changes the fulcrum point of the other, thus having it embody more real opening of the throttle at any given position. This avoids both the control scheme issue where closing the normal throttle lever in high altitudes fails to slow the engine much (because the auxiliary remains open) and the engine issue where extra complexity, weight and sub ideal flow geometry of two smaller and different sized throttles are trying to feed mixture evenly onto a single manifold in multiple different opening configurations. IMO the next logical step I'm surprised never really saw action was using an absolute pressure gauge to adjust that automatically, since most of these planes did have a gauge for altitude that worked off pressure (basically a barometer) already, and this would have both given a more ideal opening (like the NACA report showed instead of the pilot manual that simply gave safe numbers for any weather), would have reduced the training/conceptual loading of pilot, and would have saved the engine from damage when auxiliary is forgotten, which all sounds more likely than a mechanical failure of the gauge (and since pilot can still reduce throttle as desired, and is limited in max only to sea level amount, being stuck at any possible auxiliary lever position isn't very serious in aircraft survivability terms, even if you didn't have an actual override).

[@vasilis23456]

Manifold pressure governors made this unnecessary.

[@daszieher]

​@@vasilis23456indeed! The power computer of the BMW 801 took manifold pressure into account and governed all other essential parameters. Much like a modern computerised engine and transmission control.

[@mchrome3366]

If you hadn’t spent time explaining compression so thoroughly I wouldn’t have understood this video to the end. Thanks for recognizing that many of your viewers are newbies on this subject.

[@unhippy1]

There was a article i read (in i think an EAA page?) a few years back of a guy in the experimenting an over-compressed subaru running 15.5:1 with a variable throttle opening stop operated by a servo controlled by a map sensor reading manifold pressure.

[@gsilva220]

This is exactly what electronic throttle bodies are for, running extra static compression and limiting dynamic compression by closely controlling manifold pressure. the result is better fuel economy, less emissions and better performance in certain conditions

[@billmasson5313]

As a 13 year old I saw Waldo Pepper when it first came out in the theaters & it changed my life. Even at that age I knew enough aviation history to instantly recognize the Kessler-Udet reference. Zero question about who that character was based on!!

[@rperry70]

Also, the story line of Waldo Pepper having fought Udet in combat is not necessarily so fictional. I cannot recall the details, but they met up at one of the air shows in the states that Udet attended. While I love Waldo Pepper, I would have to put it at #2 behind the Blue Max. I am curious as to what Greg's favorite WW1 movie is other than WP?

[@rgbgamingfridge]

you aged well

[@Filminmymind89]

Lt. Walter B. Wanamaker. He was shot down by Udet on July 2, 1918. In 1931, Ernst Udet brought the serial number of Wanamaker's plane with him to their public meeting the Cleveland Air Show, I believe, and they became friends after that. I remember Udet's account in his autobiography. "Ace Of The Iron Cross" was the title it was published under.

[@andymandyjohnson-green5160]

The Great Waldo Pepper was my favorite movie as a child. I was 10 when it was released and my parents took me because, having recently picked up a book on World War I fighter aces at the Scholastic book fair at school, I was obsessed with WW1 aiplanes and aces.

[@GregsAirplanesandAutomobiles]

I was also 10 years old at the time, and obsessed with WW1 aviation. I remember those book fairs. However my Parents wouldn't take me to see it.

[@richsarchet9762]

@@GregsAirplanesandAutomobiles I think they did you a favor - I was 8 and still have flashbacks - the flying was great, but the fire still has me freaked out!

[@andymandyjohnson-green5160]

@@richsarchet9762 That was a horrifying scene that haunted me for some time.

[@robertsansone1680]

Great story. Snoopy is what got me interested. (seriously)

[@toastnjam7384]

Back in the 60's I guess because it was the 50th anniversary of WW 1 a model maker put out a series of WW 1 planes and I had them all. The German Gotha heavy bomber was my fav. That's when I became fascinated with WW1 aircraft.

[@CraftAero]

Tough to find such well researched, written, narrated and edited content on this platform. Thanks.

[@Danger_mouse]

There are several great examples of modern very high compression engines in even very 'run of the mill' cars. The small car Mazda2 Skyactive engine is one of these at 13:1 and running on low basic grade petrol. Mazda has spent a lot of time on the actual combustion process, keeping heat out of the intake system, efficient port design in the cylinder head and even the design of the exhaust manifold. They'll happily run on a hot summer day at wide open throttle and not knock. The upside of the high compression ratio is outstanding efficiency.

[@taotoo2]

Also the "other" Mazda 2 (rebadged Toyota Yaris) has a compression ratio of 14:1.

[@adamkarolczak5416]

very important to mention they have direct injection, which is the main thing that makes these high cr possible

[@Danger_mouse]

@@adamkarolczak5416 Yes, good point 👍

[@KolyanKolyanitch]

They did all of that work, and got exactly same power and efficiency as those who just added small turbo.

[@adamkarolczak5416]

​@@KolyanKolyanitchmazda also has turbocharged skyactive engines

[@stonebear]

That's kind of amazing, two throttles... Post-WWII a lot of civilian engines had four levers or knobs per engine, black for throttle, blue for propeller, red for mixture... and then white for _wastegate_. You'd start with the usual three knobs all the way forward, and then as you climbed start nudging the wastegates up, which made the turbocharger spin faster, thus preserving your manifold pressure. Why the heck the civilian engines didn't have automatic wastegates on'em like some did (P-38?) during the war, IDK, but they were there. (Later Garrett turbos *did* have automagic wastegates, and I think today everybody's got'em... even the Rotaxes.)

[@Pete-tq6in]

A brilliant explanation, thank you. I heard recently that the true sign of intelligence is an ability to explain complex principles in a way that even the layman can understand. You, sir, are an absolute master of this art.

[@SearTrip]

You have a real knack for explaining things like this so a dummy like me can understand them. Thanks.

[@Charon-5582]

You're smart enough to watch this video. That counts for something!

[@davefellhoelter1343]

I must admit when Jim got out the mallet and smacked that piston home My Safety Sphincter got tight! As I thought of the Diesel Affect and possible outcomes.

[@kyle.1442]

'The Hammer of Science ', thats pure gold, Greg. I'm going to have to steal that one.

[@GregsAirplanesandAutomobiles]

It looked like a cartoon hammer to me. For some reason it make me think of Professor Science, you know, the guy from Hemo The Magnificent.

[@kyle.1442]

@@GregsAirplanesandAutomobiles comically it was a perfect hammer, perfectly delivered. Hopefully it will inspired new machiness

[@BryanPAllen]

@@GregsAirplanesandAutomobileshaha professor of science reminds me of Norm MacDonalds ‘Professor of Logic’ joke lol. Check it out Greg and crew.

[@TheStowAway594]

There's something about early airplanes and seaplanes that just scream adventure to me. I never get tired of looking at them, and wish I could fly one before I die, even if it's just taking over the controls for a minute or two.

[@M1903a4]

The happiest 20 minutes in my log book are in a Ford AT-5 TriMotor.

[@rutabega2039]

"wish I could fly one before I die". A lot of people got that wish without anything coming in between.

[@theairstig9164]

Build a replica

[@theairstig9164]

Build a replica from a kit

[@trappenweisseguy27]

Many people don’t realize that “fuel”, or “gasoline”, or whatever you wanted to call it was not a universally sorted out thing at that time. Different countries had different makeup’s and additives which resulted in lower compression required compared to nowadays.

[@Tuning3434]

Obligatory comment: Finally was able to make some time to absorb this video with the level of attention it deserves. Great video, love it when there is time to go into the real engineering trade-offs and clever solutions that pop up when technology is backed up by the actual scientific understanding behind it, instead of sticking with the black-and-white generalizations. Very inspiring!

[@johnhess351]

Ingenious trick. Equivalent to building a 200 hp engine that must be run at 100HP to avoid knocking at takeoff, but wide open at altitude where it can run wide open, but can only develop 100 HP at altitude. Net result: 100 HP all the time.

[@KevinSmith-ys3mh]

Precisely, an effective implementation of the engineering concept that "the best(most reliable) part is NO part". Supercharger effect (with in it's defined limits) almost without additional weight or bulk; NO intercooler, ductwork or additional oil and coolant plumbing, parasitic power losses and drag, expensive and heavy gearboxes for blowers! Will work better if controlled by a modern ECU system, of course, but so will every engine!😉

[@skippy2987]

It's worth noting that this over-compression on modern cars is why premium fuels benefit every modern car, not just the ones that say "use premium only" on the filler cap. That array of sensors and modelling can absolutely tell when you've got the good stuff in there once you've been driving a little, and you'll soon get slightly more advanced timing (or whatever the opposite of the implemented knock prevention strategy is)

[@Desertduleler_88]

I consider “The Blue Max” to be the best WW1 film without cgi. The Great Waldo Pepper as you pointed out is loosely based on Ernst Udet. Not all Fokker DVII’s were fitted with the BMW engine which was designated as the F model. The DVII F was very sought after by German Aces due to increased performance. I read a British test report post WW1 on that engine they it rated at 220hp.

[@mickvonbornemann3824]

Thanks again Greg. Your concise dialogue certainly helps us laymen understanding these things

[@paullubliner6221]

My father (20th AF WWII Hickham, preparing for Operation Olympic with a good story about a P47N v. Hellcat) took me to see Waldo Pepperback in 1975. The moment Kessler took off his hat to introduce himself to Pepper and bared his bald head, my father laughed out loud and blurted out: "Udet!"

[@GregsAirplanesandAutomobiles]

Thanks, that's a great story.

[@aubtri]

Your dad certainly was right - as is Greg's assumption towards the end of this vid. I read a lot air plane and air warfare stuff in the 1960s (to go along with my Airfix and Revell plane kits), among it the autobiographies of Ernst Heinkel and Ernst Udet. And the aviation stories about the 1920s (written around 1930 by Udet and in the 1950s by Heinkel) go very well with the story line in the Pepper-Kessler episode. Also take a look at the legendary Howard Hughes Movie "Hell's Angels" (which quite obviously is the background of the final Waldo Pepper act), and, of course, "Aviator" by Martin Scorsese!

[@davidstrother496]

I really found your explanation very informative, as most of them are. Thanks, Greg.

[@stephenhardy9177]

100% agree on "The Great Waldo Pepper'!!! Dad got me hooked on it when i was about 3 and has been my absolute favorite film since. The opening and closing music... gets me everytime.

[@MW-bi1pi]

I also was convinced the character was based on Udet. The aircraft markings make it a certainty in my book. I love that interwar period of Aviation. A guy could hotrod an engine and design an airframe that could outrun the top Military fighters, and do it in a neighborhood machine shop. They were ingenious. I recommend Jimmy Doolittles autobiography " I could never be so lucky again ". He covers this air racing period from a first hand basis and it is fascinating to read. Hey, the guy survived flying the GB to its limit in air races. Doolittle documents instrument development in the 1930's better than anyone. His WW II experiences document from the Tokyo Raid to running the 8th Air Force bomber force...What a period in Aviation, what a Man and what a book.

[@lllordllloyd]

Imagine a career spanning the Wright biplane, to Mach 2. An amazing, if very dangerous, time.

[@allareasindex7984]

I drive a 1930 Model A Ford several thousand miles a year. The stock compression ratio is 4.3:1, developing about 40 horsepower and 120 ft./lbs of torque. This is from 201 cubic inches displacement, approximately 3 liters. I just installed a modernized head with 6.5:1 compression ratio. I’m looking forward to seeing what it does for performance

[@user-yt8gu1cl5x]

I read the theory more than sixty years ago, without the the historical details you provide. Thank you.

[@laura-ann.0726]

Using computers to control fuel injection, ignition timing, and valve timing, has produced amazing advancements in both the thermal efficiency of gasoline engines, and reduction in pollution. My first car was a '65 Chevy Nova. It was an L-6 with 3.768 liters, and 8:1 compression. Peak power output was 140 hp (104 kW) at 4,400 rpm and 220 lb⋅ft (298 N⋅m) of torque at 1,600 rpm. The engine had a 1 barrel Carter carburetor and points/condenser ignition. Fuel consumption was about 18 mpg at 55 mph. My 2023 Toyota Rav4 Prime PHEV, weighs nearly 1,000 pounds more than that Chevy, thanks to the 900 pound lithium traction battery. It has a 2.5 liter, pseudo-Atkinson cycle engine with 14:1 compression, that makes 174 hp at 6,000 rpm and 168 lb⋅ft of torque at 2,800 rpm. Supplementing the gas engine are two 3-phase synchronous electric motors that can produce a combined output of 179 hp (front axle) and 53 hp (rear axle), torque is 199 (front) and 89 (rear) lb.-ft. Despite the nearly 1,000 pounds of extra weight, at the same 55 mph cruising speed, the Rav4 gets 44 mpg and puts out less than 1% of the pollutants of that old Chevy - partially due to the catalytic converter, but also mainly because the engine is so much more efficient. When I got the Chevy, it was 11 years old, a hand-me-down from my Dad, with 110,000 miles on it, and it was on it's last legs. It was burning a quart of oil about every 900 miles, the clutch was slipping, and the transmission detent for 3rd gear was worn out so bad that taking your foot off the gas on the freeway would almost always pop it out of gear unless you were holding the shift lever down. My Toyota should still be going strong at 250,000 miles if I just change the oil every 5,000 miles and the transaxle oil every 30,000. The ignition coils and plugs will probably last to 120K, but these are not terribly expensive and not difficult for the owner to replace. Did you notice that the compression ratio on my Toyota is 14:1? And I don't need to run Premium gas, either. It's perfectly happy on 87 octane regular.The engine control computer has as one of it's inputs, a "knock sensor" in the block. If the sensor picks up that the fuel is starting to pre-detonate, it retards the timing a bit and tweaks the mixture and valve timing. Modern car engines are downright miracles of technology compared to what we were driving in 1974, the first year I had a driver's license.

[@GregsAirplanesandAutomobiles]

I would still rather have the 65' Nova, but your points are all valid. These modern cars have incredible performance and efficiency.

[@UnDeaDCyBorg]

Very nicely narrated. Easy to follow, and shows all the basics without dragging on for those who know already.

[@jjock3239]

A very interesting video. I started my flying career in the mid 60s, (all jet training at the time), and in our air force engineering training, we learned that the Allison jet engines in the American T-33s, used water injection for takeoff.. After I left the air force and started my career with a large commercial airline, One of the aircraft I flew, was the 747/200, with Pratt and Whitney engines, which used water injection for takeoff. This was required, because of our long routes, which required higher engine output for our maximum weight tadeoff. For this, we loaded 700 gallons of distilled water, and then dumped it after the takeoff. This provided enough cooling, that the engines could take more fuel, and this resulted in a significant increase in thrust. Now to connect this to the internal combustion engine. When the oil embargo happened in the early 70s, I owned a couple of high performance vehicles, that couldn't run on the crap gas that was available. My solution was, to design a water injection system, that used the engine vacuum to trigger the system to turn on. It worked like a champ. This allowed me to use the stock timing, and gave me excellent performance. I wonder, if anyone experimented with water injection in aircraft engines. I recognise, that the higher altitude could cause pure water to freeze, but alcohol could have been added to prevent freezing. BTW: I did tear down one of my high performance engines, and the top end was the cleanest of any engine I ever disassembled.

[@KevinSmith-ys3mh]

Not long ago I saw a video covering water injection, by Greg himself I believe. He has mentioned its use many times, mostly in late WW2 German aircraft engines (MW50 - or 50/50 water/methanol) to counter the lower octane of their fuel supplies. The video covered some of the historical development and its use in car raceing, some currently available kits, and the comments section by viewers was also interesting, with many relating their experiences using it. A Wikipedia article is also available on the subject. I've only used it to clean out the chambers on some small engines via a paint sprayer gun after soaking them overnite with solvent, quicker and easier than pulling the heads! Oh yeah, B-52 bombers also use it to enable hot/high take offs at max bomb/fuel loads (I remember seen them in Okinawa leaving a very smokey contrail), same reason as your 747 did, so theres likely other examples of jets useing water injection out there.

[@jjock3239]

@@KevinSmith-ys3mh I wouldn't be surprised if there were others, but the use of it on the T-birds, was the first time I had heard of it.

[@AIainMConnachie]

Waldo Pepper is a masterpiece. Haven't watched it in far too long. Need to fix that. Completely agree with your theory! Cheers

[@bobhunt4402]

This was the clearest explanation of the advantages of higher compression engines and the attendant considerations I've ever seen.

[@RDEnduro]

This was something I didnt know i didnt know.. the best kind of thing! Thanks Greg

[@l.scottmcgowin6946]

What could possibly be ranked higher than Waldo Pepper as the greatest flying movie?!? The Great Waldo Pepper IS the greatest flying movie. PERIOD!

[@garymitchell6897]

Yes great film and Blue Max and Dark Blue World in W11

[@butchs.4239]

Howard Hughes' "Hell's Angels" would rank up there.

[@VaapeliRaka]

This also brings up the question of aviation fuel antiknock resistance in the great war period. The engine manufacturers of the time were really badly fuel antiknock limited, so the overcompression was really sensible way of dealing with the knock limitations of the time. Compression of over 4.5:1 were considered high at the time, so BMW with 6.5:1 was a groundbreaker desing, which cannot be understated. As far as i am informed, the german aviation fuel mix of leichtbenzin and schwerbenzin mix was not bad, propably close in with the british Sumatra and Light Borneo in it's knock resistance, which were considered the best of the late war avgas. The late war added benzyl did rise the knock resistance, but those varied in the range of 4,7:1 with 10% benzyl content to 5.3:1 with 20%. Benzyl was also very expencive additive at the time, as no practical ethylene cracking or catalytic reform process of the crude oil was not invented yet, only possible process they were capable then was separating different fractions of crude oil or naphta. Also the total loss lubricating oil mixed with fuel in some engines worsened the fuel knock resistance. So it was really a delicate balance between compression and fuel to keep high power engines running well. Tetraethyllead was invented as antiknockagent nearly a decade later. Added toluene even later.

[@KevinSmith-ys3mh]

Thanks for the info on early fuel blend tech, not common knowledge, but it's one of the more important factors that determined what engine designs were practical IRL. So many different fields had to evolve and contributed to the current state of reliable "push-button and go" autos, and daily flights circling the planet.😮

[@DeereX748]

The "LO ! " on the side of Udet's airplane was his childhood sweetheart's nickname, for Eleanor Zink. He was known for his rather loud paint schemes on his aircraft, generally with multiple striped areas of the wings and fuselage, in addition to the LO! and inscription on the tail plane. German pilots especially painted their aircraft in colors and patterns to identify themselves in the air, like Richthofen' all-red plane. Udet worked as a stunt pilot in films in the time period between WWI and WWII and helped develop the modern Luftwaffe at the beginning of WWII. Udet sadly committed suicide in November 1941 due to the political pressures placed on him and after a psychological breakdown. He was one of the most interesting pilots of WWI and the interwar period to me.

[@davidhanson8728]

The Great Waldo Pepper is a great movie I haven't seen in many years. I will have to circle back to it again. I does a subtle job of showing the difference in philosophy around training that will make a huge difference in WWII. Taking your best (later most experienced) pilots and making them instructors rather than front line fighters. I did not get it when I was a kid first watching the moving in the 70's. I came to understand it much better later in life.

[@alandaters8547]

I guessed the Ernst Udet link, but certainly did not know all those details! You just made a great movie even better. Back in the 1970s our local grass strip had a Fokker D VII replica that I think had the Mercedes engine 1000 ci, 160 HP at 1600 RPM? Anyway, it sounded like a flying tractor, floating into the air at what sounded like idle RPM!

[@Heatherder]

Greg literally never disappoints

[@davebaker9128]

An advantage of the low RPM maximum power output is that no reduction gear to the propeller is needed, lots of power robbing weight and mechanical drag isn't there

[@dennissmith8947]

"That's his signal folks! He's rarin to go!" Yeah I've always seen 100% Udet in the character Kessler

[@CrazyTony65]

the over compression technology is called Skyactiv by Mazda, they use a much higher static compression and a computer controlled electric throttle body.

[@greglivo]

A similar approach was used on the turbocharged version of the Chevrolet Corvair. The turbocharger has no boost control- there is no wastegate or blow-off valve that are found on modern turbo engines. Instead, a restrictive carburetor is used to limit boost to around 6 PSIG. The only other knock control is an ignition retard that engages on boost.

[@gsilva220]

This technology has never been more alive. This is exactly what electronic throttle bodies are for: running extra static compression and limiting dynamic compression by closely controlling manifold pressure. The result is better fuel economy, less emissions and better performance in certain conditions. Here in brazil, it is essential for flex-fuel technology, enabling engines with compression ratios around 13:1 to run on either 85-ish octane gasoline, E100 ethanol or any mixture.

[@patrickshaw8595]

Eddie Rickenbacher US WW2 Ace - used his own money to have extra high compression pistons made and fitted to his aircraft. It had no auxiliary throttle but it did have an absolute intake manifold pressure gauge that he kept an eye on at all times. Also there were experiments done with all kinds of liquid fuel additives to boost the octane rating.

[@EllipsisAircraft]

Rickenbacker was an Indy 500 race-car driver. Makes sense.

[@sugarnads]

Ww1. And he was also a mechanic. As was micky mannock.

[@20chocsaday]

Must check on Greg's engine management video on the 190.

[@KevinSmith-ys3mh]

​@@20chocsadayYeah, that BMW 14cyl engine was amazing, ahead of its time!

[@RextheDragon881]

Your content is my favorite on aeroplane tech. No bs or ego crap. You know your stuff and are a wonderful teacher. Thanks for all the great videos

[@MrAwombat]

Great video! It was little trip down memory lane with the references to older videos.

[@user-en9zo2ol4z]

The liberty engines also powered some tanks, even during WWII, as I have heard it.

[@captainchaos6628]

Great video! Awesome shout out to "The great Waldo pepper" that's my favorite flying movie bar none. 2nd would be "Those magnificent men ..." Which upon rewatch as an adult is more goofy than I remember, but still enjoyable.

[@tommyguan5952]

Really nice explanation, and I'll definitely watch that movie byw. I've read from somewhere stating that Göring claimed many of their pilots used the 'over gas' during dogfights regardless of the duration or altitude, for one example the all full throttles were used at 100m altitude for 30 minutes without anything going wrong afterward. I want to say that BMW built very nice inline engines since back then haha.

[@ajayray4408]

There's a way, I think, to see this as achieving what a supercharger does by other means. They both flatten the power / altitude curve, with the supercharger maintaining low-altitude conditions in the intake manifold at all altitudes, while the over-compressed engine optimizes the engine for altitude and then maintains high-altitude conditions everywhere. Throttling an engine has the unfortunate (in this case) side-effect of acting as a brake. This is not the case (or not so much so) if you reduce the pre-compression cylinder load by varying the timing to close the intake valve early and/or reduce the valve overlap, but this is much more complicated to achieve.

[@dazhigh9208]

To say all this was just a few years after the first powered flight is still amazing to me. Its really amazing at how quick we learnt and started to master piston tech. And then you have the jet turbine pioneers such whittle heinkel etc. The early part of the 20th century was a brillant era in the air, land and the sea. The old saying that war pushes us forward is very very true. Another really intresting video. Thank you from me ( Daz ) and my dog Max over in the UK. Peace out dude and stay sunny side up 🙂

[@LeCharles07]

Thumbs up for Jam Handy. You can't do it better because those films are perfection.

[@cheesenoodles8316]

Technology I understand. Used to drag race a midsize motorcycle, my strip was at Sea level close to the coast. Jetting was optimized for this track. It was a track that recorded a few records. Excellent video. How about the silent film, Wings? Waldo Pepper was a great film.

[@mikehenthorn1778]

i run boilers with forced draft and combustion air. just the change in temp from fall to winter here in Ohio will change how the burners perform. at this point they are more like jet than anything else. so i love all the boost videos

[@AM-jw1lo]

Great focus, your description of the over compressed engine make me see the sense of engine compression in a way i have never thought before and will probably never forget, especially since you included the launch piston video. Thanks.

[@davidelliott5843]

Ernst Udet was a considerable influence on Eric Brown becoming a pilot. They met in Berlin in 1936.

[@20chocsaday]

Yes, that was because Eric Brown's father was on the other side in WW1. It was sad that pilots were set against those who had been their friends.

[@proffmongo]

James McCudden put German High Compression Pistons in his SE5 & said wrote he shocked German photography recon crews when he caught them at high altitudes. Also in Waldo Pepper Ernst mentions when his gun jammed in combat the enemy pilot saw he was in trouble & waved to him & then flew off. This happened to Udet & he believed it might have been Guynemer.

[@scubasteve3743]

Thank you for taking the time to explain the basic concepts to dummies like me.

[@Zebred2001]

Great video and ya, The Great Waldo Pepper is one of the most underrated fantastic movies ever! I once worked as a Production Assistant for the movie An Unfinished Life here in British Columbia. I stood ten feet away from Robert Redford. I didn't get a chance to speak to him but if I had, it'd be of all his movies, that one I'd tell him was my favorite!

[@koiyujo1543]

germans.... once again this technology I didn't know about but this is just amazing

[@admiralqualityspretendingtofly]

Used to love it and Dad and I would drop everything any time Waldo Pepper came on TV. Long overdue for a re-watch. Cheers, Greg!

[@brockgrace7470]

Gonna save this one for when I finish work tonight.Thank goodness,I got something interesting to watch.Huzzah!

[@nightlightabcd]

When I was much younger, I saw the movie of the Great Waldo pepper! I was shocked when he wing walker, fell from the wing of the plane! It happened so fast! One moment she was there and the next, she wasn't, almost without incident, like I had imagined she was there but she wasn't!

[@steveroach2959]

I saw Waldo Pepper when it came out in the ‘70s-I’ll have to watch it again! For the record, it was the legendary Jimmy Doolittle who first performed an outside loop in 1927 as an Air Corps test pilot.

[@gooseknack]

Detonation is called "pinging" in Australia.. at least it was back in the old days of points ignition and carburettors. I miss those days!

[@dennismason3740]

I love it when Greg dumbs it down for me. This is not sarcasm.

[@mytech6779]

Over compression is still useful where efficiency is more important than power density. The modern spin is labeled as a modified Atkins cycle. It is used for the generator in some mostly-electric style hybrid cars. Essentially they use a very high static compression ratio to get a larger expansion ratio (for efficiency) and then change the cam to close the intake valve either very early or very late to reduce the peak pressure.

[@patrickshaw8595]

Fun Fact: In 1927 Harry Ricardo theorized and then proved by experiment that: 1) Given unlimited supercharger volume and pressure 2) And for ANY GIVEN fuel octane rating - that 3) Maximum horsepower will always occur between 6 and 7-to-1 compression ratio. THIS IS BECAUSE the "clearance volume" with the piston at top dead center will be pumped to high pressure by the supercharger through the intake system - but then it will be "vacuumed out" by the exhaust system down to sea level or below depending on altitude. So not only is the motion of the piston moving X amount of air through the engine per revolution - the clearance volume being pumped and vacuumed out is contributing IT'S share of air volume, too. High compression engines have less clearance volume so the CFM increase under boost is very slight. All the large aircraft piston engines had compression ratios between 6-1 and 7-1. These fools building totally unregulated supercharged racing engines never use below 8, 8.5-1 compression. They are leaving horsepower on the table and deserve to get beaten by the first guy bold enough to go against "modern wisdom".

[@SheepInACart]

I'm not saying the mans claim was wrong within the context of the engines and applications of the time, indeed very shortly after that would be the most common compression ratio of fighter aircraft so as a rule of thumb you could do a lot worse, but its use out of context will give an erroneous conclusion because of the assumptions implicit in that gross over simplification. All of the highest specific power internal combustion piston engines by either displacement OR weight use a higher compression ratios than that, but also valve configurations, metal alloys (thus permissible temperatures, pressures and pistons speeds) RPM, automated fuel delivery and spark timing unthinkable to a 1920's designer, so not included in that statement (which is not to say they wouldn't have come up with a valid new number if you explained these factors to them, simply that it had not occurred at the time it was said). Yet that's STILL not even the main factor here, contrary to how it might sound, "unregulated" engines aren't incentivized to maximize their power for a given displacement, instead they care about the total external weight/dimensions and drag needed, including cooling systems and fuel, and see value in reliability, broader RPM range and engine response times. If your max temperature is being limited by your exhaust valves (which is common) then using a larger bore and higher compression ratio, but less boost to reach the same peak pressure will reduce the wattage per area on your valves while keeping the same CFM, but potentially allowing more aggressive timing before predetonation, less rich mixture, omission of auxiliary systems, or just an increase in reliability (or some partial mixture thereof). Its just no good at all to make a 200kw/L (~4.4hp/cu) from an engine if it ends up being the same size and weight as one with larger displacement. Modern engine builders aren't "leaving power on the table" by refusing to go against some kind of convention, they are just working with very different constraints and assumptions, and 1-2 points of compression really isn't that much of a change for almost 100years of technology, theory ect.

[@20chocsaday]

There are large areas of Africa not only hot but also at least 4000 feet above sea level.

[@gaufrid1956]

I had no idea that variable valve timing technology existed in the 1920's. A great video.

[@speedandstyletony]

I could see this engine tech being useful for racing up Pike's Peak in the 20s. From start to finish you gain around 10,000 feet in altitude.

[@GregsAirplanesandAutomobiles]

That's a good point.

[@madbrowndog4887]

Brilliantly explained. I knew that BMW powered DVII's were considered better than the Mercedes powered ones, but always figured it was just for the slightly higher horsepower at take-off. I had no idea that it actually got more powerful as it climbed!

[@jeffbrooke4892]

Great video and long live The Great Waldo Pepper! I saw that movie in the theater when I was a kid and it convinced me that being a barn stormer was the life for me. And as if that worked out. Not! We all grow up and face the things of adult life but always treasure the things we dreamt about as children. Thanks for the reminder.

[@johnlhaase]

I did a fair amount of work collecting information on this for an Air and Space article with Don Sherman. This went into the article on the first turbo charger. Don was a former editor with Car and Drive. Your video is excellent.

[@GregsAirplanesandAutomobiles]

Thanks.

[@cr10001]

Okay, I've worked it out (and I haven't read Greg's explanation yet). The Germans just fitted a compression ratio that was far too high for the available fuel at sea level/full throttle, and simply throttled their engines (i.e. ran part-throttle) until a high enough altitude was reached to run at 'full power'. Blindingly simple when you think of it, but I'd never heard the term before.

[@recoilrob324]

It's very interesting how the engineering mind can improve engines and the BMW 'Double Vanos Valvetronic' system exploits a lot of what you described about the 'Over-compressed' engines. It can vary cam phasing along with control how far the intake valves open so it has no mechanical throttle causing restriction using that feature to control engine speed and power output. Static Compression Ratio is one part of how high the pressure is created in the cylinder before lighting the spark, but also important is the closing of the intake valve which happens well after BDC so a portion of the inhaled charge gets pushed back out as the piston rises until the intakes close. At high speeds the inrushing air pressure keeps filling the cylinder until the intake closes so they don't lose part of the charge, but this point changes greatly with throttle opening and engine speed so having the closing point being variable allows it to be optimized across the rpm range and loads. And the 'Effective Compression Ratio' that is measured when the intakes close can be altered to meet altitude and/or octane available requirements much as the other aircraft engines mentioned in the video. The various vehicles advertising that they have 'Atkison Cycle Engines' don't really have a longer power stroke than intake which is mechanically difficult to do....they just hold the intake valves open and let some of the charge get blown back into the manifold so less is left in the chamber to add fuel to and burn. Sadly our automobiles incorporate most of the really intricate technologies to meet emissions requirements and don't fully benefit from them to make more power or greater fuel economy. You must meet emissions first....then make the most of what you can without violating the regulations. This is why many engines can see large performance and economy improvements with some tuning changes but many of these technologies will never be found on production aircraft as they add complexity and fragility to an engine that first and foremost MUST be reliable. Thanks Greg for another interesting video!!

[@sadwingsraging3044]

Love the Waldo Pepper movie! I think I even mentioned it in one of your earlier videos. Is this one of the earlier videos with the messed up audio you said you were going to fix? You da man Greg!😎👍

[@GregsAirplanesandAutomobiles]

Hi SWR, Thanks so much for the contribution. I really appreciate that. I started to re record the earlier video, then I realized that a lot of it was about the Rise of Flight video game, which nobody really wants to see at this point. So I ended up remaking the entire thing, which is what we have here.

[@sadwingsraging3044]

@@GregsAirplanesandAutomobiles Cool deal!

[@ccrider8483]

17:00 Computer manipulation of throttle, ignition, and valve timing to control knock, (and possibly exhaust gas recirculation. But I could be wrong.). Totally agree about The Great Waldo Pepper being one of if not the best aviation film ever made.

[@karlbrundage7472]

I had always assumed that everyone (with any knowledge of WWI aviation) knew that the Kessler character was based on Udet.

[@bobbyz1964]

Great video! My BMWZ3 requires 91 octane, but some stations only have 87. If I fill up with 87 and really get on it, I can feel a loss in power as the computer compensates. The reality is the way I drive it really makes no difference. Being employed by the department of transportation I don't want to be getting a bunch of tickets anyway. 😂

[@rickymherbert2899]

Great video Greg, coming from a marine background I understand diesel engines better but now I have an insight into the magic going on under the hood up in the air. I even now comprehend better what is and how "knock" occurs. Loved the little movie titbit at the end. Very enjoyable content once again. Thank you.

[@20chocsaday]

In the 30s and 40s some of the German aero engines were diesel. I wonder how they coped with knock.

[@kiwidiesel]

​@@20chocsadayDiesel engines are just one big knock fest 😂 Usually it's injection pump derived knock due to the fuel pressure required for atomisation. Air in the fuel system will create knocking like you wouldn't believe also.

[@20chocsaday]

@@kiwidiesel I used to hear diesel car engines knock while they were warming up at idle. Not now. They are much smoother and better controlled. And much more powerful for the same capacity. I wonder how the German aero diesel engines were so useful in powering aircraft so long ago.

[@johndavidwolf4239]

As NACA tested the BMW engine after the war, it is very likely that they were using the best fuel of the day, which was "better", (had a higher octane rating) than the fuel Germany had during the war, hence they could open the second throttle at a higher atmospheric pressure without knock.

[@chrisbeauchamp5563]

Another great video Greg, a little away from your normal scope. I really liked it, it explains well what taken for granted in the later periods

[@forthwithtx5852]

Man. I loved The Great Waldo Pepper. Gotta go look for it.

[@BaikalTii]

Yes, Kessler was based on Udet. that movie was a formative piece of my fascination with aviation history and the connection with Udet was made convincingly for me soon after I saw it. which was the initial theatrical release. dreadfully sad and ironic that Udet had little time to live after the time frame of the movie. I give him credit for being a patriotic German and not a national socialist.

[@GeneralJackRipper]

What a great topic. I always considered the Fokker D VII to be the point in time in which aviation started going from art, to science.

[@fafner1]

The designer of the D VII, Reinhold Platz, was a genius. The thick wing provided increased strength and stiffness allowing bracing wires to be eliminated, while providing high lift at high angles of attack allowing the D VII to "hang on its prop". Platz followed up with the D VIII, a monoplane fighter, in 1918. Its aerodynamics were great, but it was limited by its 110 hp Oberursel rotary engine. Kevin Cameron has described the D VIII as a modern aircraft with an obsolete engine, while the competing Sopwith Snipe with its 200 hp Bentley roary was a modern engine in an obsolete airframe. Platz followed up with the V29, basically a D VII fuselage with a D VIII wing. It won the German fighter competition in 1918, but the war ended before it could reach production.

[@GeneralJackRipper]

@@fafner1 Yeah, that's kinda what I meant... 🤣

[@Comm0ut]

Secondary throttles were later standard in multi-barrel automobile carbs but of course not to limit performance at lower altitudes. Interesting that despite constant depression carbs existing (Skinners Union) they are IIRC never used in aircraft at the time.

[@58fins]

I saw "The Great Waldo Pepper" when I was a kid. My dad was working on getting his pilot's license and I was obsessed with airplanes! It is one of my favorite movies along with "The Blue Max"! That is, in reference to WW-1 themed movies. I have a bunch of WW-2 themed movies I like as well.

[@charlestoast4051]

Great video! Hope you can do more like this. So in theory if you could make an engine with a variable compression ratio, you could improve efficiency at part throttle.

[@GregsAirplanesandAutomobiles]

Yes, and that has been tried several times but never with a huge level of commercial success.

[@myth-termoth1621]

There is another way that over compressed engines live on. Modern military aircraft are sometimes flat rated, their jet engines would overstress the airframes and engine mounts if given full power at takeoff, but full authority digital engine control limits the thrust to what the plane is designed for.

[@GregsAirplanesandAutomobiles]

Flat rated engines are similar in concept but a bit different. They are just putting in a more powerful engine, not an overcompressed engine. Also flat rated engines pre date fadec by quite a lot.

[@alexanderscott2567]

The overcompressed engine lives on. I have one in my Ford Maverick Hybrid. Perhaps once an agricultural engine, this very mild "Atkinson Cycle" engine is paired into a small hybrid truck. Filled with 94 octane, it becomes remarkably efficient. It is used to tow my boat, which runs exactly the same fuel, and the motor has 50hp stickers on it, to match the requirements of the transom plate.

[@Backfence711]

The plane in the photo was a replica built in Seguin Texas. The builder has the worlds largest private heavy ww1 machine gun collection.

[@marklittle8805]

This whole topic was something I had never heard of until now. It does explain the D7 for sure

[@rperry70]

It is interesting that Von Richtofen, when inquiring about when his new planes would arrive, he refereed to them as "over compressed". So he understood the importance of the new engine design, and how it would benefit them with the new tactics moving away from the swirling dogfights. What a luxury to have a throttle at this time, let alone 2! lol