Turbo Compound Piston Engines. Almost magic tech.

The Douglas DC-7 and Lockheed Starliner were the Superprops of airliners. They used Wright Turbo Compound Engines which at first glance appear to be in violation of the laws of physics.
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[@JosephArnold-t2s]

As an old age 90 A&P mechanic for Eastern Airlines I thoroughly enjoyed your video. Brought back a lot of memories. Everything described was spot on as I remember it from experience and EAL Apprentice School. At one time or another I worked on DC6B, 1049 Constellation “Connies”, Convair 440, Martin 404, Lockheed 188 Electras but mostly the DC7B. Eastern got a lot of bang for the (horsepower) buck but paid a heavy price in maintenance for it with turbo-compound fitted engines. At virtually every maintenance visit, of 12 PRTs, as we called them, usually three required unscheduled replacement. But these things were tough. If you sat in a forward left or right window seat at night you would see PRTs running orange/white hot for hours at cruise power. At TO they would glow white! Because they were pulling so much power at takeoff, (as I remember TO power was limited to 3 or 4 minutes and had to be reduced to METO) all kinds of things broke mainly, cracked exhaust/intake pipes and associated hardware, cracked cylinders, stripped bolts, and knife sharp stainless steel fairing created from vibration. Behind the rear bank and forward of the oil tank was the accessory section and was an absolute oily mess to work in when changing components. Jug (cylinder) changes were much more difficult than the same job on P&W 2800s on the Martin 404 and Convair 440 due to very tight “baffling” of the cylinders. EAL also operated varying models of the Constellation (1049,1049c,1049g, Super G) and DC7B all equipped different models of the 3350 the worst being on the older 1049s with engine EXTERNAL flexible scavenge oil lines that were impossible to prevent leaking. We used to say “if a Connie wasn’t leaking it wasn’t airworthy.” Note Connies leaked hydraulic fluid as bad as engine oil. As a sideline not part of the discussion, all the manufacturers were trying to get as much HP as possible in that period just before jets and therefore tried many approaches. P&W 2800s (Martin 404) used water/alcohol injection to exceed max power about 5”hg (?) for takeoff. Convair440s were equipped with augmenter/mufflers that consisted of bundling all of the exhaust pipes into one cluster and feeding them into a bell mouthed tube inside a box on top of the wing that was positioned in such a manner as to reduce back pressure on the exhaust system. Don't know what it did for HP but they sure were quiet. Then there were turbo-props,,,but that’s another story.

[@dieselyeti]

Thanks for the great background. I recall reading PRTs were high maintenance and the big radials, while great engineering achievements were fussy engines when pushed to make big HP.

[@mline250]

Thank you for your recollection sir. You were witness to a golden era of aviation.

[@garthwillard8089]

Thank you so much for sharing your stories. The original hydroplanes used some of these era motors to push for speed

[@desertlvr]

Good recap. I'm 10yrs your junior but started out on the 1049H Connies with FTL in the mid 60s. You're spot on about the maintenance. Many times when a Connie taxied up after a trip across the pond, you heard a screaming PRT. If it was the bottom one, just throw away your coveralls cause being bathed in 120W oil would never come out. Gotta say though, the 3350 was one hell of an engine that had a lot of respect. Not only were the PRTs unique, so was the direct fuel injection and the low tension ignition.

[@SavageArms357]

Were you still at Eastern Airlines when Borman agreed to give employees a stake in the company in exchange for a slight paycut? If so, would you mind detailing what it was like during that time? How did you feel about Borman, or how the company was being run? Do you feel like Eastern could've survived if it had been turned into a co-op?

[@sergeipohkerova7211]

I'm imagining being a businessperson on board one of those things, trying to compose some notes on a pad or a portable typewriter, being serenaded with the soothing sounds of a thousand lawnmowers outside 😂

[@TheCrapOnYourStrapOn]

Now imagine the same situation except your anus prolapsed in the bathroom. So much worse

[@allangibson8494]

Big piston engines are LOUD. True turbo-compound engines were marginally quieter. The Napier diesels were particularly fuel efficient.

[@MrArgus11111]

you wore headphones attached to the bulkheads or earplugs if you were chique

[@davidscott430]

I remember flying in those planes on Frontier Airlines in the late 60s, and even as a small child I remember thinking they were loud and the whole plane vibrated. Still glad I got to experience them before being replaced with jets, but damn they were a lot smoother and quieter, and more thrust on takeoff.

[@JohnRodriguesPhotographer]

Flew Logan to Stuttgart in 1961 on a DC7. Returned on USS General Maurice Rose Bremerhaven to NY in 1965.

[@robertojames7904]

I wouldn't be surprised if the DC-7 was replaced because airline companies couldn't afford the engine oil. As a kid I refueled airliners at a major airport. When we serviced a DC-6 we checked the oil on all the engines every time and usually put the cap back on without adding any. When a DC-7 pulled up to the ramp I ALWAYS aligned the props and pulled our oil truck in-between the engine nacelles before even checking the oil level because I added oil to the R-3350 every time and quite often I added a lot of oil.

[@paulcrumley9756]

Our oil truck broke down and was down for several months. Our boss had the answer: hand-crank-powered rotary pumps to pump the oil right from the barrels! Talk about cranking - took 20-30 rotations of the pump for one gallon of oil, and the -7Cs would often arrive with not more than 10 gallons in each engine. It was't uncommon to put nearly four barrels into a single airplane. When the weather got cold we had to store the oil drums indoors to make it pumpable. That 60W oil is about the consistency of honey - and when cold, not unlike wheel bearing grease.

[@pal6636]

Great detail . Very thorough. I had always assumed DC 4' s were pressurized. So thanks . ( reminds me of the Viscounts i grew up watching practicing " touch and goes " and one ir 2 engine off landings Today i find if unbelievable thag all this training went on right in the muddle of tge day at a major North American international airport . Probablyin part because we were still working on simulators that more resembled my go kart :)

[@williamzk9083]

The DC-6 outlived the DC-7 in service because the PW R-2800s were so much easier and cheaper to maintain than the R-3350 with PRT.

[@williamzk9083]

@@pal6636 Canadian made DC-4 with Merlin were pressurized.

[@selfdo]

Both the P&W R-4360 "Wasp Major", aka "Flying Corncob", and the Wright R-3350 "Duplex Cyclone" were engines that had a thirst for engine oil as well as 130 octane AvGas. My Dad, who did 20 years in the USAF and retired a Major, recalled catching a flight on a KB-50 from Yokota back to the States, via Guam, Hawaii (Hickam AFB), and Travis AFB. At each stop, while gassing up, not only did the flight engineer make sure the engines were topped off with oil, he got TWO 55-gallon drums from the ground crew at each stop! Sure enough, every ten minutes or so, as the drums were set up at a point where oil could be pumped to the engines, he had one of the drums with the hand-crank pump, ready to go, and pumped in several GALLONS of engine oil! My guess is that each engine did have a reserve tank for oil, and this was a means that Boeing had improvised to keep them oiled up on those long flights! And I believe this was the enhanced "J" model that, like the B-36, had J47 turbojets added, only two instead of the four for the B-36, and those were used only to get to altitude with a full fuel and/or cargo load, or for when they had to refuel a jet, like a B-47 or F-105. Even then, especially with the F-105, there was a "controlled descent", as the difference between the max speed of the KB-50 and, with a full fuel/bomb load on the "Thunderchief", the STALL speed, was only about 25 knots!

[@REOGURU]

I had the privilege to fly in a DC-7 when I was young. It was still a time when flying was an event you dressed up for. I remember the stewardess gave me a pin with the company's logo and wings, which she pinned to my coat and I wore proudly. The flight was smooth and you could see more objects below you than in today's jets. The other thing I recall was how extremely loud and deafening the engines were that they limited your ability to hold a conversation, just one word here and there. By the time I got used to all the noise, the flight was over. Today, I'm glad I flew in one because just a couple of years afterward the DC-7's were all replaced with jets on the route I had flown.

[@CAL1MBO]

You still have the pin?

[@davidhair8295]

I regret I never got to ride a DC-7 or a 707, Too poor & too young.

[@matthewlehman7937]

"you could see more objects below you than in today's jets" Huh? I have flown dozens of times in the last 30 years and have always had a fine view of what's below... always has a lot more to do with cloud cover than anything else or do you mean the planes flew lower so cloud cover was less of an obstacle?

[@13699111]

Thank you for the interesting informative background storyline

[@PanzerDave]

@@matthewlehman7937 He is talking about the cruising altitude was lower in a piston engined aircraft than in a jet, thus you were closer to the ground and could see more detail. Today, the same holds true when you are in a puddle jumper rather than a commercial jet.

[@hopper1]

Heavy duty truck mechanic, sim pilot and armchair aviation enthusiast here. I learned about turbo compounding many years ago and when I first saw it on a heavy duty diesel engine I was jumping around like a kid in a candy store. "I know what this is! I know what this is!" The Detroit Diesel DD16 (an engine of, clearly, German design) has a parts recovery turbine on it. I am always delighted to teach the young mechanics about turbo compounding. They seem to think turbo compounding means two turbo superchargers. I also get weird looks when I say "turbo supercharger". It makes for many conversations and learning opportunities with those younger people.

[@jackdavid7514]

An outstanding presentation on an engine that I thought was an abomination. In the early days of my flying career (1978) I was a co-pilot on an ex-RCAF C-119 equipped with R-3350 Turbo Compounds. I was employed by Bighorn Airways in Sheridan Wyoming and we used the airplane for aerial spraying on cattle mosquito control contracts. On a flight out of Laramie, Wyo, we were about about 50' AGL on new swath, when the right engine had an exhaust valve failure and sent pieces of the exhaust valve into the #1 PRT which seized it. The torque on the #1 engine dropped from an indicated 151 lbs of torque to zero in what seemed like miliseconds! Since the base field elevation was 7400 feet or above, and we were down in small valley, we were pretty close to one inoperative service ceiling ceiling at our weight, at least until we dumped the 700 gallons of malathion and diesel fuel mix we were carrying. We struggled up to about 300' agl and flew 30 miles back to Laramie. All the way back I was keeping one eye on the left engine torque meter and the other eye on the gear switch. Since this the only catastrophic engine failure I suffered in a multi-engine airplane in 30 years of flying- the R-3350 Turbo Compound was never my favorite engine. Give me a Pratt & Whitney anytime!

[@GregsAirplanesandAutomobiles]

The R-3350 was always a bit of a problem child and never more than just OK. The problems were not the result of turbo compounding.

[@adotintheshark4848]

the C-119 could barely fly empty on one engine, you were lucky.

[@akzoc]

I worked on C-119 076 with California Air National Guard. I have seen pics of 076 in non-functional conditional at Greybull. We had 3350s with Aeroproducts props.

[@adotintheshark4848]

there were non-compound versions of the R3350. I believe the A-1 Skyraider used them. @@GregsAirplanesandAutomobiles

[@OswaldJames-x2t]

​@@adotintheshark4848😂😂😂❤

[@zippyt.libertine3787]

As my father, a pilot, told me. "The only time you have too much fuel onboard is when you are on fire."

[@uralbob1]

Many years ago, I flew on a DC-6 or 7 military flight from Naples to Rota during a trip back to the US for submarine schooling. We left at night, and as we taxied out and ran up the engines, the exhaust manifolds began to glow red (a little concerning for a 20 year old newbie)! The loose fitting cowlings on this old workhorse were so banged up and worn, that you could see right into the engine through the gaps in the panels! There’s no telling how many planes those old panels had been mounted on over the years! Any way, I survived, but I might not have remembered this wonderful flight without my light show in the engine bay! Thanks Greg for all your wonderful, instructive vids!

[@dutchboynl2082]

I joined the USAF in 1964 after just turning age 18. My first Duty station was a 3 year tour at Torrejon Air Base , Spain, Madrid. I worked line maintenance on all MATS (MAC) aircraft transitting Torrejon. C-131-, C-54, C-118, Connies, C-124 ,C-97's best assignment in the USAF at the time. Learned so much , Good old days. Retired flight engineer now DC-8-62

[@GregsAirplanesandAutomobiles]

Wow, where were you an engineer on the 8?

[@MrWillBison]

I started working/flying on Douglas products in 1963. I worked on the DC3, 4, and 6. You are correct about the higher failure rates of the DC-7. We still see 3s, 4s, and 6s in pax/cargo roles. Not so much the 7. The DC6/C118 is known as the Greyhound of all the recip airliners. Jets are just a passing fad 😄.

[@matsv201]

"Jets are just a passing fad " Well technically they was. When they was replaced with the turbofans.

[@scottl9660]

My dad would often joke about the C-118 and say it simply hovered and let the earth rotate underneath it

[@TheJustinJ]

@@scottl9660technically all subsonic aircraft qualify for that statement, if flown east-to-west at any latitude were most flights take place. Many a flight I have noticed the sun in the same place, even after 8+ hours.

[@MrWillBison]

I flew the 118 across the Pacific quite often, your Dad was correct.@@scottl9660

[@gregedmand9939]

As with all piston engines, the more complex you build them: maintenance requirements go up exponentially. The demand on metals and fuel sciences is also immense. Dangerous high octane leaded fuels were essential to keep these last generation aviation piston mills running. Just as an example: Lycoming IO-360 engine has a fixed mandatory overhaul schedule. Strap on a turbo and the TIO-360 is permitted HALF the operational hours! Turbo-compound, with their complex gear trains and 1940 metals were notorious for down time. The simplicity of jet engines running easy to make and handle kerosene was a near miracle in comparison.

[@wills.5762]

Turbocompounding has been one of my favorite niche engine subjects since I was a kid, pretty sweet video

[@bkailua1224]

Having flown the DC 6 in all three seats, I am impressed with how accurate you are in this video. The only big differences between the 6 and the 7 are the motors. Later, 7s had a longer wing. What really was a weakness in the R3350 with the compound was when these engines had a valve fail or piston ring fail, both common in comparison to modern opposed aircraft piston engines. On the 2800 the bits and pieces would fly out the exhaust pipe with little additional damage. On the 3350 compound, the parts would generally destroy the compound turbine, and I heard from pilots who flew the 3350 it was violent. I had many ring failures and a few valve failures on the 2800, and it was hardly noticeable. We usually found the failures via the engine analizer.

[@dukecraig2402]

Hence the nickname "Parts Recovery Turbine" with the aircraft mechanics who worked on them.

[@ravenstarver1360]

Wow that really is a factor I wouldn't have thought about. Wouldn't this effect turbocharged engines as well?

[@gregmaggielipscomb9246]

Many years ago, I worked on a PV-2 Harpoon in which a young man dropped an unknown amount of .041" s.s safety wire down the carburetor air horn . I could see a piece of it down in the intake section of the R-2800-31. Since it was a "can engine" with no log book the boss decided to start it and see what happened. We did and it seemed to digest and eliminate the foreign objects with little known effect! I really was amazed.

[@cloudshe]

operating the 2800's in the '90s (Convair props, DC-6 CB motors) i remember how efficient and smooth they were, the problem being the technology never had improved much since the early 40s. and we were stuck with replacement parts that were nearly that old. imagine how ring and cylinder and valve problems could have been eliminated with improvements over the years, not to mention the gains in performance w/ modern fuel injection and better cold weather engineering. even with the carbs i recall SFC's of better than .40 at 1100hp without any PRTs, and with a modern bullet-proof PRT, the possibilities?

[@williamfowler709]

You flew these and call them motors? I flew all 3 seats and worked on them from their introduction

[@1999fxdx]

At Pan Am, we usually kept the plane in the lower blower setting, not to save fuel or anything, but to keep the 3350s in one piece. There were a lot of air turn backs, something that almost never happened with the 707s

[@fafner1]

A colleague in a past job had worked on P2V's while in the Navy. He confirmed the term "Parts Recovery Unit" and the need for constant maintenance. They used copious amounts of anti-seize as the need to change cylinders combined with the high operating temperatures made seized cylinder bolts a real headache.

[@daszieher]

Weren't those "the best three-engined airliners ever built"?

[@purplepenguin43]

i got to watch everets air cargo fly the dc-6 when i lived in fairbanks and they do the same, blower on low and no injection just to keep the power contained and the reliablity up. they suffer for it on climb out though, they only clear the trees at the end of Fairbank international by ~100ft. compare that to a modern 737-800 which clears the trees by ~1500ft+.

[@airtechmech6681]

When 115/145 octane avgas was phased out soon after production started with the DC 7's, they were severely altitude limited along with reduced power in all phases of flight. I read that is why high blower was not used anymore.

[@daszieher]

@@airtechmech6681 I'd have thought you'd overboost the engine with blower on "high" for takeoff.

[@dlkline27]

I was an avionics technician with a local Air National Guard unit during the time we were flying the Super Constellation and had the pleasure of flying on them quite often even though I was not flight crew. Flying at night I would be mesmerized watching the exhaust on one of the inboard engines which I found fascinating. The turbine cover was called a flight hood that, along with the turbine and what I could see of the exhaust glowed a brilliant orange from the heat while blue flame came from the exhaust. I often wondered how that metal could withstand that kind of temperature and not come apart, especially the turbine that was spinning at a terrific speed. Another crazy thing was one of the flight hoods on one aircraft was painted green and that paint never burned off.

[@nomar5spaulding]

Since I've already liked, subscribed, and patreoned, allow me to just say that this is *exactly* the type of content that got me hooked in on your channel. Lots of people can tell me about the history of an aircraft. You're the guy to explain why the particular shape of intake manifold valves in an engine let the passengers on an airliner sleep more comfortable, or something equally technical and beyond my comprehension.

[@Genktarov]

Seconded.

[@jroch41]

Thirded. Really like the technology history lessons & how these apply to modern aviation.

[@mattgross7734]

yep

[@GeneralJackRipper]

Four-thed.

[@meaders2002]

I take the fifth.

[@williamcharles9480]

I was fortunate enough to have flown in DC-3s, C-47s, DC-6s and DC-7s. I loved every moment and laughed at the passengers who were alarmed to see the flames exiting the exhausts. You'll never experience the vibrations and sounds that those radial engines produce on a jet powered aircraft. I found the Lockheed Constellation to be a most beautiful, but the most efficient doesn't always win the beauty contest. The Douglas aircraft were clean, efficient designs that proved themselves with their longevity. I have to add. These videos on this channel are some of the most informative on KZbin. Thanks for the hard work in preparation.

[@hoost3056]

Turbo compounding is very common now, and initially Detroit Diesel/Mercedes-Benz was the first to use it on the DD13 and DD15 straight six semi truck engines. Volvo recently added turbo compounding to its D13 semi truck engines at first as an option, but standardized it ( I think ) from 2020 on. I drive one, and it can run loaded down the road at 1000-1200 rpms grossing 75k or more comfortably. The payoff is 8 mpg or better loaded driven properly with the torque peak lowered from 1200 rpms to about 900 rpms.

[@michaeloboyle8798]

I came here for this comment.

[@jfess1911]

Thanks. I knew that there were turbo-compound truck engines and you saved me the time of finding them again.

[@CFITOMAHAWK2]

Are they reliable ? Former DC3 skipper and mechanic helper (1980's).

[@jfess1911]

@@CFITOMAHAWK2Edited: The Volvo D13TC's power recovery system has two turbines in series, the first is part of a fairly normal turbocharger, the second "Power Recovery Turbine" is behind it with a fluid drive and gears attached to the crankshaft. Volvo claims that the TC engine has the same life as the non-TC version (1.2 million miles B50). I did a cursory online search and haven't found mention of issues with the TC. It has been running in the US since 2017. The engine got revised in 2020.

[@evancourtney7746]

@@CFITOMAHAWK2 I imagine materials improvements have alleviated the valve and ring failures modes that were common on those old aero engines.

[@LaLaLand.Germany]

I remember a German guy restored a Curtiss-Wright Compound engine and filmed a run, it was a sight to see! It was smoking like hell, oil was dripping out of the exhaust but when it coughed itself free and picked up some rpm´s I could hear the compounds- what an engine. This was nice, I love the Super Constellation. I feel it under the prettiest planes ever. Thanks, Mate!

[@lornespry]

One of the first photographs I ever took was of a Trans Canada Airlines Super Connie - complete with 'tuna tanks' on the wing tips, parked and ready to be taxied to a maintenance hanger. I still have this head-on shot taken with my my 120 film Brownie. A good exposure. I still think the Super Connie is the most beautiful airliner ever built . Second would be the Concord. It just looked like it wanted to fly - graceful like a swan in flight.

[@ludwigsamereier8204]

@@lornespry "Tuna tanks" on the Connie: wonderful!! Sir, you took this iconic plane with a KODAK 120!!! This pic is a treasure :)) I apologize for being off topic: I deem old 120 cameras as iconic as this plane. Recently I walked througn downtown Munich/Germany, brandishing a cute KODAK BROWNIE TARGET 620. Suddenly an American exclaimed: "This was my first camera!" We were both delighted. To my surprise the shots came out quite decent. You may wonder: 120 film on a 620 camera? Probably like many folks, I had enlarged the film chamber so it accepted bigger rolls.

[@henryostman5740]

Yup, the connies are beautiful, but you caught it with 'on the way to the maintenance hanger', the Ferrari of the skys. Wish somebody bought the turbo option, that would still be in operation today.@@lornespry

[@adotintheshark4848]

The Super Connie was the original Queen Of The Skies. Still attractive today!

[@LaLaLand.Germany]

She shure is. I never boarded any plane in my life but this one i´d go on every day. Make that a window seat, plz so I can watch the engines @@adotintheshark4848

[@jamesw1659]

My father was a mechanical engineer who worked on this engine at Curtiss-Wright in the mid-fifties. I really enjoyed your presentation; I'm fascinated to learn something about these, what my dad called the last gasp of the big radials before the turbo-jets took over.

[@huntcole4600]

My first trip in an airplane was in 1958 when I was 9. I was already an airplane enthusiast. A friend’s father took us to St Louis to see the Cardinals. We flew round trip from Memphis to St Louis Lambert. It was a complete thrill that I have never forgotten. The out flight on Delta was on a Convair 440, but the return from St Louis to Memphis was on a DC-7. Four prop engines! I remember the Convair 440 flight as being very loud and bumpy, but the DC-7 was much quieter and smoother. The Delta literature on the aircrafts showed either a Convair 880 or DC-8 as the top of the chain-do not remember whether it was represented as in service or about to go in service. What a trip for a young boy-and Stan the Man hit a home run!

[@pigdroppings]

I flew on a DC-6 or DC-7 in 1960..... at night blue flames coming out of the exhaust stacks......streams of oil coming out of the engine and flowing over the wing. Nothing like today's jet liners. I lived in line with the local airport...and twice I saw a 4 engine airliner coming into land with one of it's propellers stopped.

[@ronjones-6977]

I'm a few years younger, but I took my first flight on a 727 in 1967 when I was 4. . I was so enamored with flying, that when my grandparents flew home to LA after visiting us in Sacramento, I begged my parents to let me go with them. I was there for a week and flew home by myself...UNATTENDED. Ah, the good old days.

[@mpetersen6]

There are aviation channels that focus on the types of aircraft. You not only look at the types. You also dive deep into the systems. And thats stuff l find fascinating.

[@major__kong]

I remember sitting in my first airplane design class. The professor said the thrust from the exhaust of a Top Fuel dragster is very significant and a large portion of the downforce.

[@ronjon7942]

Thanks! That’s very interesting and the answer to my question as to why the exhaust pipes are canted upwards!

[@StabyMcStabsFace]

Something like 500lbs a primary. Dropping a cylinder pushes the car all over.

[@terrydepew1252]

I have seen video of a top fuel dragster loosing the exhaust pipes off of one side of its engine right after leaving the line. All 4 pipes came off as one. The resulting roll over crash was pretty dramatic. Enough so that i started asking around and looking into how much thrust was coming out of those exhaust pipes and it's a no brainer why they point them mostly up and slightly rearward. I can find figures from 900 to 1100 lbs. of thrust and in some cases more. So even when just one cylinder goes down it can cause the car to swerve and get squirrely. I looked on you tube for for that video but cannot find it among the many other videos on top fuel crashes.

[@mitchmasterfix5292]

Those Top Fuel dragster engines make about 11,000hp these days - so that car is being driven by almost the same horsepower as 4 Turbo-Compound engines! (for a short time of course).

[@wallacegrommet9343]

Only for a few seconds

[@robertkoons1154]

Constellation started with US AAC 1943. Set speed record across US in 1944. Gave Orville Wright last flight in 1944.

[@terrybaird3122]

I am a low-time C-150 pilot, Registered Nurse, and with only two semesters of introductory physics. Thank you for always presenting the information in such a way that I can readily understand it, and for even making it intuitive. You are a great instructor.

[@alanr5601]

Very fun reminiscing about these old aircraft. In response to one commenter regarding taking notes while flying in an old aircraft, I have an interesting take about that. I have had a career that has crossed both aviation and office products. Prior to air travel, most journalists used fountain pens. The advent of air travel made fountain pens ineffective as they operate based on stable air pressure. Early commercial planes were not pressurized so the pen would leak ink as pressure decreased. Not cool when travelers were dressed nicely with their expensive fountain pens in their pockets!! This spurred the development of the ball point pen, which uses a much thicker ink and relies on gravity rather than pressure to operate (if your ball point pen didn’t work it meant the plane was upside down and you had a completely bigger problem to deal with!!!). Early ball point pens were very expensive and exclusive and were considered an accoutrement of the “prop set” (I guess that’s what they would have been until “jet set” would come in a few decades later, or maybe they were the “prop crop”!?!?). As my econ professor later stated, “now, ball point pens are free. Just look on the floor whenever you need one and you’ll probably find one laying there!” Great channel, Greg! Keep ip the good work!!!

[@JK-rv9tp]

Fascinating stuff! The Canadair Argus maritime patrol aircraft soldiered on in the Royal Canadian Air Force with its TC 3350s until 1981. It was a Bristol Britannia with the *turboprops replaced* with the piston engines, mainly because of the incredible endurance potential the TC 3350, giving it a range of 5000 nm. The PRTs gave the 3350 an SFC of .38 (IIRC) lb/hp/hr, only about 2/3 the fuel burn of a turboprop, and actually on the edge of diesel engine territory, and until the latest auto engines with gasoline direct injection, was the most fuel efficient gasoline piston engine ever built. Later in their service life in the RCAF the engines were getting pretty unreliable and when going out on patrol two aircraft would be stood up and whichever one didn't have a problem by takeoff time would launch. Returning on 3 engines was getting pretty common.

[@lornespry]

Thanks for your post. As a Canadian and a young man in the heyday of the Argus, this was informative and interesting.

[@hadial-saadoon2114]

When I was four years old my family and I flew from London to NYC on a PanAm DC-7. I was obviously pretty young then, but I will always remember the flames from the PRTs lighting up the wing and interior of the airplane.

[@paemt6220]

Your videos are great, keep up the good work. I really enjoy endurance racing. Porsche ran the 919 prototype car for several years and used a form of turbo compounding. They used a turbocharged 2l V4 as the primary powerplant. The rules allowed for 2 hybrid electric regeneration systems on each car. All the other manufacturers used a regeneration system on each axle which counts as the 2 allowed. They would charge their batteries under braking and discharge during the next acceleration. Porsche did something different. They used a regenerative braking system on the front axle but their second system was a turbine in the wastegate discharge pipe powering an electric generator. This allowed them to increase peak horsepower output during wide open throttle when the competition had already depleted their electric boost. It also allowed them to maintain a desired power output while saving fuel used by the IC engine. They could sometimes complete a race with 1 or even 2 less fuel stops. It made for some very interesting racing.

[@clockdva20]

I think current F1turbos use a system based of compounding. Before that there were a few home built compounded turbo race cars in Europe . I also remember Cosworth wanted to build a compounded Turbo Charged F1 engine when they were building a replacment for the Cosworth DFV but they ended up using a standard layout . They wanted to drive the Turbo from the inlet side of combustion side instead of the outlet side as is norm, all very intresting.

[@fafner1]

Colin Chapman pointed out the since turbocharging and mechanically driven supercharging were both permitted, one could build an engine where the compressor was connected to both the engine and an exhaust turbine, creating in effect a compound engine. The feeling at the time was that although the loophole was real, if anyone tried it the authorities would promptly ban it anyway. @@clockdva20

[@counterfit5]

As far as I'm aware, F1 turbos are still using a shaft to drive the compressor side from the turbine and MGU-H

[@kuchenblechmafiagmbh1381]

The 919 also uses a still rather unusual "hot V" engine layout (introduced with the BMW N63 in 2008), for decades almost all V engines had the inlet manifold any maybe a supercharge inside the V and the exhaust side on the outside (sometimes leading to sidepipe exhausts), these hot Vs are inverted, the exhaust side as the name suggests is in the V now to drive the turbochargers that sit there for less lag and then they send it through an intercooler into the inlet side.

[@dbs555]

144 spark plugs per aircraft to change out regularly, 36 per engine. Yeah, I can see why jet engines took over most commercial flights.

[@johnparrott4689]

Now do an R-4360 (28 cylinders!) spark plug swap. I had a pal that wrenched on B-36s, said that was a huge job

[@jkent9915]

@@johnparrott4689 on an engine with a manual choke so an improper starting procedure on the Spruce Goose could get you 448 fouled spark plugs.

[@gcrav]

Great explanation of the greater Froude efficiency of props relative to jets at low speeds. The insufficient takeoff power of the jet engines of the late 1940s was the fundamental issue driving the weight constraints that did in the Comet 1. Building an airframe sufficient to withstand the pressurization required of a high-altitude airliner wasn't such a mysterious issue if sufficient power were available. Building one to meet those requirements with the weight constraints imposed by the already-obsolete DeHavilland Ghost engines was impossible. Both the Comet and the B-47 used mass injection and RATO bottles to compensate for the inadequate takeoff power of their engines. The awkward era of commercial aircraft - jets not yet ready for primetime and piston engines being developed beyond their practical limits.

[@thomasfsan]

Perfect! There's nearly no videos on turbo compound out there, really appreciate this.

[@GregsAirplanesandAutomobiles]

Hopefully this one does it for you. I tried to go into enough detail so the engineer types here will be happy.

[@thomasfsan]

It was great! Napier Nomad one day? @@GregsAirplanesandAutomobiles

[@GregsAirplanesandAutomobiles]

Maybe, it would be a stand alone video, and I can't really form any conclusions about it, other than it could have been amazing.

[@aker1993]

What if you mate turbo-compound setup to a rotary engine?

[@thomasfsan]

How would you connect the exhausts to the turbines though? Make the whole assembly rotate? @@aker1993

[@rayschoch5882]

Well done, Greg, and comprehensible to a non-engineer. My family went to Europe in 1956 (my only international travel), and apparently we were just at the transition point. We flew from St. Louis to New York in a Constellation (I have no idea what model), and when we got back to the states from Europe, we returned to St. Louis from New York via a 707. For different reasons, both seemed pretty exotic to a 12-year-old. I never liked the triple tail of the Connie, but that fuselage is a true work of art, and surely cost a fortune to build per square foot of passenger / cargo space when compared to the generic cylinders of other airliners, then and now.

[@meaders2002]

This is gadget I knew nothing about. Now I'm interested. Thank you.

[@johnc2438]

Fact: The Boeing 707 entered commercial service on Oct. 26, 1958 (a Pan Am flight from New York to Paris). If you traveled in 1956 (and returned the same year), you could not have flown on a 707. Maybe you flew sometime later, possibly, in late 1958 or 1959?

[@meaders2002]

@johnc2438 1958 was 65 years ago. Given that the speaker was 12 at the time, he would 77 at the time of writing. Perhaps memory is imperfect at that age. It seems that going to Europe by propeller aircraft and returning by jet is clear enough. An oopsie on the date seems possible.

[@rayschoch5882]

@@johnc2438 I'll take your word for it. Perhaps we flew both ways on a Constellation.

[@andypdq]

I agree entirely about the triple tail on the Constellation, lots of people think it's one of the most beautiful aircraft ever, I think it's tail makes it look horribly disproportionate. Aesthetics is subjective, I know, but that's my opinion, for what it's worth.

[@johnmarshall6702]

I flew across the Atlantic on a military Super-Connie (Air National Guard) in the early 70's. I was amazed how quiet the plane was on the ground while taxing, at least compared to pure jet aircraft or turboprops. Sounded great. But when they throttled up for takeoff, it got incredibly loud and the entire airplane was vibrating. There were only a few of us on board, and I made a point of sitting in various parts of the plane to judge noise and vibration. Sitting directly in line with the props was horrific, with the floor vibrating so badly that my feet fell asleep and the entire seat vibrated something terrible. But I was glad I did it. On the other hand, all my other flights were on C-141 or C-5 aircraft, and that was much nicer once we got airborne. But still noisier than civilian jets. Interior noise was not a design criteria.

[@frankely6378]

It's worth noting that the author of "The High and the Mighty" was Ernest K Gann. Gann was an American Airlines pilot that started in DC-2's and -3's, then moved to heavier stuff (including C-54's) with Air Transport Command during WW2. So it is understandable that the aviation aspects of the movie would be pretty accurate. "Fate is the Hunter" is his aviation memoir. That book spawned another movie with John Wayne ("Island in the Sky"). If you're into early commercial aviation, the book is a great read.

[@ludwigsamereier8204]

Until 10 years ago, I vainly tried to watch this movie. But ever since I was little, the signature tune of the movie haunted me all my life. It was DIMITRI TIOMKIN´s masterpiece.

[@timeakin1169]

TH&M is a great read. FateistheHunter a great read and movie, although not completely the same. Cast, everything perfect. Another EKG great movie good as the book (IMO) "Soldier of Fortune" w Clark Gable. The prelude of the book "Fate is the Hunter" 'Tip Of The Spear' makes me feel like I am right there with them. Thx, I enjoyed your video.

[@timeakin1169]

Fate is the Hunter 1964 w Gleen Ford + all-star cast. A great movie and story, old school special effects

[@frankely6378]

@@timeakin1169 Interestingly, though, Gann did not participate in the production of that movie. He worked on early drafts of the script, but was so unhappy with the results that (to his later regret) he asked to have his name removed.

[@63turbo]

Its pretty cool what a small world it really is... Mr Gann lived on San Juan Island in his later years and could be seen flying his biplane on occasion!

[@lornespry]

When I was a boy, there was an outdoor observation deck at Vancouver International where people could watch departing and arriving aircraft. I watched DC-7's departing for USA destinations. The sights and sounds of their enormous engines made a lasting impression I can still see and hear. Watching the spinning prop and the whining starting gear ... then the first cylinders igniting and a belch of blackish discharge from the exhaust followed by a roar as the RPM's came up. One by one - all four engines. So dramatic in a way that no modern aircraft can impress. Years later on my solo cross country for my license qualification, a DC-7 flew under my Piper about 500 feet below me. The noise shocked the bits out of me. I guess he was on ATC, and I was not - although perfectly by the book. As a boy lying in bed at night, I could hear engines of DC-7's and Connies being run up and tested in the engine sheds across the river - an oddly calming sound that was part of my young life. Those old birds were beautiful and offer up nostalgia.

[@tnuag01]

We had a fleet of DC-7CF freighters doing sanctions busting in Rhodesia and always looked to see if all four engines were turning on their return. There was also a scrap yard with an incredible number of turbo-compound carcasses!

[@number1genoa]

Your comment reminds me of a friend who worked on these he said they called them Parts Recovery Turbines not Power Recovery Turbines as Wright intended ;-)

[@adotintheshark4848]

one thing about these, their fuel injection system put out about 500 psi at the nozzle. You don't put your thumb over the injection feed line unless you want it ripped off.@@number1genoa

[@MrLanternland]

Wow - I had an Irish friend who flew in the Rhodesian air force! Last i heard from him, years ago, he was a flight instructor in the UK.

[@chrishenniker5944]

I bet the local car guys would take them and put them on their cars, connecting them to the flywheel.

[@Propliner1955]

I was fortunate to fly the last of the former Rhodesian DC-7CFs: VP-YTY. After it came to the US it became N103LM with LaMancha Aire and N869TA with Trans-Air-Link. It was a fine DC-7--obviously well maintained by Jack Malloch's crew. Both LaMancha Aire and T-A-L took good care of it, too. I was a flight engineer on it, and it was a pleasure to fly. It's a shame that it was sold and ended up back in Africa, caught up in the war in Angola, then abandoned. -Stef Bailis

[@SearTrip]

I worked with a woman whose father was a lead engineer on the DC-7 design. She had been an instructor pilot and would go on about what an airplane that was. She must have picked up quite a bit from her Dad.

[@Silavite]

The way in which this blowdown tubine avoided backpressure is interesting. You focus on the fact that they operate on velocity rather than pressure, which is true, but I think that fact alone doesn't give the full picture. A turbine which operates with a high velocity intake like this called an impulse turbine (in fact, that very term can be seen in the excerpt at 19:50), and they are the counterpart to a reaction turbine. The velocity for an impulse turbine has to come from somewhere. Indeed, that same excerpt mentions that the pressure inside a cylinder during the exhaust stroke is about 200 psi. The gas inside the cylinder (before it exits) is at stagnation. Thus, the velocity comes from that pressure left inside the cylinder. The second key to this setup eliminating backpressure is in the manifolding arrangement shown at 14:30. In a "traditional" turbosupercharger, gas from all of the cylinders is routed to a common tube, which then goes to a single turbine (per engine). Since all the cylinders are connected to the same manifold, the pressure in that manifold is (more or less) constantly elevated, leading to backpressure. With the arrangement in 14:30, the cylinders are split across many different manifolds and turbines. The smaller tube and turbine volume per cylinder means that the backpressure that does accumulate can decay much more rapidly, letting backpressure decay on a timescale closer to the timescale of the exhaust stroke. The tricky thing with this arrangement is that more manifolding and multiple turbines means more weight. (Though each one doesn't need to be as big.) Also, the design of the manifold tubing must be done with care to avoid excessive length or number of bends, as that would lead to lots of pressure loss in a system with high flow velocity. Excellent video overall! I like the IL-2 stuff you've been doing recently as well even if I don't comment often. It's always a treat to see a video from Greg in the old subscription box.

[@TheSrSunday]

This is an knowledgeable and excellent comment, way, way above the usual YT fare, also of the kind that one expects in this channel. Congratulations!

[@foowashere]

Great comment, which adds a lot of necessary detail. Thank you for taking the time to write it! :hat off:

[@chucksmallman6288]

My recall was tickled talking about the blowdown turbine application. The Elliot YR steam turbine has been around for many decades as a prime mover for pumps , compressors, and generators. What I recalled was a marketing strategy to use the YR as an alternative to a steam pressure reduction valve, mining the pressure drop for power to run an air compressor that supplied a manufacturing facility. That allowed running a steam system at a higher pressure and efficiency, even if the lower steam pressure was what you needed for your process.

[@framusburns-hagstromiii808]

Love the pic of the Everts Air cargo DC-6. Where I live (Fairbanks Alaska) those planes along with various other radial engined prop-liners designed in the early-mid 20th Century are still providing much needed freight (and passenger in some cases) service to arctic villages not serviced by roads. Everyday we hear the fabulous rumble of those engines still doing their job 70 plus years after being conceived..Thanks Greg, great explanation!

[@jasyamaha]

Wow, how good was that. My father, born in 1944, was a car mechanic and loved the piston airliners. What I'd give to watch this video with him. I'll never forget how he lit up like a kid on Christmas morning when we watched a Super Conny fire up and take off about 20 years ago.

[@johnkochen7264]

In 1963, I flew with KLM on one of the last turboprop DC-7c planes over the Atlantic from Toronto to Amsterdam and back again. It was WONDERFUL! It was not noisy at all and the occasional turbulence was no worse than in a modern jet.

[@johnparrott4689]

I sampled the noise on the main deck of a DC-6B and it was tolerable. I'm sure a passenger version with full insulation would be even more so

[@viscount757]

DC-7C wasn't a turboprop. The Wright 3350 engine used on all DC-7s was an 18-cylinder radial piston engine.

[@edwardsmith6609]

Ah yes....good old Gander. I was one of the troopers sent to replace the virtually entire compliment of A Co. 3/502 Inf. when that crash happened in December of 1985. R.I.P. Troopers. Only the 1st Sergeant and a Spec 4 survived, on a different flight of course, no need to name names, I could tell they were devastated by the incident. Great vid Greg. Very cool subject matter with this technology !

[@wordsmithgmxch]

Greg, I've always admired your vids: the calm, the voice... the depth of knowledge... the interest and skill in explaining complicated stuff in an approachable manner... And here you pay tribute to the guy on whom you modelled your treatment of your own co-pilots. Gosh, I bet you two were some of the best guys to share a cockpit with ... ever!

[@LadyMistborn]

Thats absolutely brilliant, I would've never guessed the exhaust could apply enough touque to actually help out the engine through rotation

[@richardlewis4288]

What a treat! My A&P powerplant classes in 1982 just glanced over the PRT as sort of interesting aviation trivia but in fact is fascinating.

[@dukecraig2402]

Where did you go to school? PIA by chance?

[@Oldbmwr100rs]

One of my instructors from my A&P classes worked on these engines, and had mostly good to say about them, but consider that with jets on the way in the very near future, the airlines knew the days if recip engines were going away, along with the heavy maintenance and vibration wear on airframes.

[@richardlewis4288]

@@dukecraig2402 Teterboro School of Aeronautics in 1982.

[@hotrodray6802]

Ditto '69.

[@Mentaculus42]

Volvo has a 13L turbo compound engine and Formula One & Mercedes-AMG's electrified turbocharger are a form of turbo compounding.

[@GregsAirplanesandAutomobiles]

Yes, the electrical generating part is turbo-compouding. The boost part is a centrifugal supercharger driven by an electric motor. I know they call it an electric turbo, but that's stupid. There is nothing turbo about it. It's an electric supercharger.

[@kiwidiesel]

yes Volvo diesel truck engines use a shaft connected to the flywheel to re-introduce the power to the drive line.

[@Mentaculus42]

@@GregsAirplanesandAutomobiles The terminology can get a bit fuzzy as there are superchargers that are driven by electric motors but I am referring to the version that has an electric motor sandwiched between the two parts of what is mostly a traditional turbo charger that I think can both recover energy and help spin the turbo up depending upon requirements of what the engine is trying to do. Admittedly partially different in intent than an aircraft engine. The diesel truck engine is to improve efficiency mostly I think. I think that there are some large marine engines that can recover energy with a somewhat similar concept as an add on. I think that there were some prototype aircraft engines that approached the turbo compounding via different approaches. The example might be the Napier Nomad 1 & 2 that had a more integrated approach. I think there was a turbo-compounded Allison prototype. Also things get a bit interesting comparing a geared turbofan vs an unducted fan or the RISE Open Fan engine by CFM that that are designed to operate at around Mach 0.8 with what looks a lot like a propeller. Thank you for covering a fascinating topic with a great video.

[@PistonAvatarGuy]

@@GregsAirplanesandAutomobiles The turbine section and the compressor section are connected by a shaft. On KZbin: Power Unit 101 - Episode 3 - MGU-H

[@PistonAvatarGuy]

​@@GregsAirplanesandAutomobiles Makes completely incorrect statement, still gets 13 upvotes because he makes videos on KZbin... what a world.

[@jamesallen8838]

Loved this one. Love this kind of engineering. Drove a Jag XKE for many years. Great machine but high maintenance. Know I have a Tesla, 2 years and no maintenance and the fuel is my solar panels. My have thing changed 😱

[@michaelbizon444]

Thank you for this great vid. This kind of knowledge is fading from a lack of people with any first hand experience. Making it understandable is priceless.

[@mattsta1964]

Greg has one of the most captivating aviation channels on KZbin. Always awesome content. Hat tip to you sir!

[@radioguy1620]

I remember reading about this in aircraft mechanic school in the early 70's , I am guessing that when the jets became more reliable and long lived the maintenance differences killed these off.

[@twistedyogert]

I still think it's amazing what people thought of to overcome the limitations of the technology.

[@morat242]

Even in their speed range, you'd be much much better off with turboprops. Still using a turbine to spin a propellor, only ditching the 18 cylinder R3350 and all its parts. You're only adding a compressor and combustor, pretty much. The C-130 first flew in 1954, contemporary with the DC-7. The airlines were switching to jets anyway, but even for lower speed large aircraft, turbocompounding had no future.

[@dougrobinson8602]

We were still reading about it in the early '80's. The A&P exams were hopelessly outdated back then.

[@radioguy1620]

@@dougrobinson8602 I believe that but still miss them

[@GeneralJackRipper]

If you break it down to the basics a jet engine is pathetically simple compared to these mechanical orchestras.

[@EmpiricalWizard]

In the early 1960-'s I flew on EAL Constellations MIA-IDL and IDL-MIA. At night it was mesmerizing watching the red hot exhaust stacks spewing flames into the night sky. Like watching a fireplace.

[@dezeekat]

Finally a video about Turbo compound!!! I've been waiting for this for years!! Thanks Greg!!!❤

[@johncaldwell-wq1hp]

I SAW ONE OF THOSE ENGINES AT "PLANES OF FAME"--MAN ,IT LOOKED SO COMPLICATED,-& THE CYLYNDER "FINS"-WERE SO "CLOSE"--WOW HOW DO YOU "CAST"THAT SO FINE,-AT THE FACTORY--I LOVE "ENGINEERING"-I JUST COULD NOT TAKE MY EYES-OF THAT ENGINE !--A WORK OF ART !!

[@andyharman3022]

Later high-performance air-cooled radials had forged cylinders, and the cooling fins were machined using ganged slitting saws. The fins were too close together to be cast.

[@johncaldwell-wq1hp]

@@andyharman3022 Hi Andy !--Thanks for that information !! very-very interesting !

[@nzs316]

Your comment regarding being kind to your student brought me back to my first training flight. As I was lining up for final and a few feet before touching down. The instructor put both his hands on my shoulders and stated, " I didn't touch the controls during the whole flight! I will never forget that moment!

[@ttystikkrocks1042]

Greg, I want to thank you for explaining this concept of turbo compounding in such an accessible and yet accurate way. From the discussion about the differences between turbocharging, to the explanations of the different shape of the turbine and the implications of a lack of back pressure, I found this video not just entertaining but highly educational. That's quite a gift you've got there and I've subbed so I can appreciate it even more!

[@GregsAirplanesandAutomobiles]

Thanks. I appreciate your kind words.

[@cyrenecai]

@@GregsAirplanesandAutomobiles I want to add my thanks, I'd read about turbo compounding in those engines ages ago but could never find any actual diagrams of the system, this explanation is what I've been wanting for years! On modern engines, with the push for efficiency and the expanding role of electrified drivetrains, I could see a role for a PRT used to drive a generator to feed power to the electric drive motor of a hybrid; whether any company is actually clever enough to design and implement this is a different question entirely...

[@MendocinoMotorenWerk]

Greg's channel: come for the airplanes, stay for the forgotten propulsion tech.

[@ludwigsamereier8204]

I shared a hospital room with a retired BMW engineer. He had specialized in mixture control on BMW motor bikes. He sadly remarked that these days the graduates of German Institutes of technology "did not know the first thing about exhaust back pressure". Your video should be mandatory for future German motor scientists.

[@ludwigsamereier8204]

@@cyrenecai Your idea is convincing at first sight. Nevertheless there´s a meager 10 percent ratio of the regained power versus 90+ percent of piston-generated shaft power. Given the cramped conditions in a hybrid, I doubt any manufacturer ever considers this idea.

[@ronjon7942]

Oh wow, this will be good. Ever since we studied the turbo-compound in A&P school some 25-30 years ago, I always thought the technology was engineering magic. And then looking at turbines and marveling at their simplicity in comparison, notwithstanding the complexity of the fuel control, heat resistant allows, etc. It’s always been amazing to me that aircraft piston engines work as well as they do, given all the pieces ‘n’ parts, but they do. And in the case of the turbo-compound, where more high technology is added to already high technology to squeeze just a little (or a LOT) more oomph out of that power stroke is just fascinating.

[@donallen7990]

I was a Recip Aircraft Engine Mech when I was in the Air Force. I worked on the R-2000 on the HC-54(DC-4) the R-4360(HC-97 ) the R-1300(HH-19B helicopter) and the R-3350 PRT(EC-121 Super Connie). The R-3350 PRT was pretty complicated since it had the Power Recovery Turbine on it. The R4360 had regular turbo on it.

[@georges.7683]

I know it's Wikipedia - but the en.wikipedia.org/wiki/Lockheed_EC-121_Warning_Star with the Wright R-3350-34 turbo compound engines retired from USAF service in 1978 and the US Navy in 1982!

[@Propliner1955]

@@georges.7683 Yes, the R3350-34 was the first Turbo-Compound engine used on the EC-121 (and C-121C). It was equivalent to the civilian DA-1 series engine with 3250 BHP Take-off power. In the late 1950s/early 60s, many if not most of the -34 engines were rebuilt as -93 engines--equivalent to the civilian EA-6 series engine with 3400 BHP take-off power and a much more robust supercharger gear set up that was less prone to disintegration. -Stef Bailis, former recip flight engineer.

[@wernerdanler2742]

Wow! I think I just went through an engineering master class. I've never heard of turbo compounding. Car makers need to take a serious look at this technology.

[@peterroy6801]

I have a R-3350 jug on display in my office. Love that thing, 200 hp from one cylinder!

[@fawnlliebowitz1772]

Crossing the pond from Lajes to Gander in our 118 we blew a jug circa 1976. Dropped to 140 kts, 5,000 feet and still 450 or so miles out. We eventually made it and yes we had belly spares and fixed it on the ramp. Loved flying the lower and slower airplanes. Shortly after that 115/145 was being replaced with 100/130 which slowed things down even more.

[@johnparrott4689]

IIRC the R-2800s on the -6 suffered a takeoff horsepower penalty without the 145 octane, or maybe it was in high blower at altitude. But they ran ok on the 100/130.

[@fawnlliebowitz1772]

Payload suffered if I recall correctly. It was in the charts. @@johnparrott4689

[@paulcrumley9756]

Yep; the hp rating on 100/130 was 2400, 59.6" MAP at 2800 RPM, the rating was 2500 on 108/135 or 115/145, 62" at 2800. Both with ADI operational.

[@Propliner1955]

@@paulcrumley9756 Almost perfect set of facts! The only error: 59.6" should read 59.5". -Stef Bailis, former recip. flight engineer

[@paulcrumley9756]

@@Propliner1955 I knew that, but didn't catch my typo!

[@andyharman3022]

Philosophically, the power recovery turbines and centrifugal supercharger on the R3350 constituted a "through-the-crankshaft" turbocharger. The PRT's added power to the crankshaft, and the supercharger took power from the crankshaft. Swedish truck maker Scania has been making turbocompound diesels for a while. Almost unknown except to insiders is that Cummins developed a turbocompound L10 engine in the late 1980"s, but didn't put it in production. It also used a double-reduction geartrain and a fluid coupling like the C-W engine. On the L10 the TurboCompound unit was after the turbocharger, so could not have been a blowdown turbine, as the turbocharger would have absorbed the pulse energy from exhaust valve opening. That said, the turbocompounding raised the engine power from 360 to 400 hp with no additional fuel consumption. All current Formula 1 cars use turbocompounding via the electrically assisted turbocharger mandated in the rules. Another turbocompound race car was the Porsche 919. It used a turbine-driven generator to feed power into the hybrid battery that powered the front axle electric motor. The turbogenerator was mounted on the exhaust manifold and ran in parallel to the turbocharger. Porsche won LeMans twice with the 919.

[@webjakob]

Thanks for explaining the mechanical supercharger. I was mystified by the apparent absence of supercharger on planes that were to fly at high altitudes. I think the video should have mentioned how these engines were (also) supercharged - but NOT turbo-supercharged.

[@klesmer]

Thank you. This is the best description of how turbo compound systems operate I have seen. I had a good idea of how things work but I thought that there was a one-way clutch at the crankshaft end. The viscous coupling makes a lot more sense.

[@carlosc3768]

Thank you Greg. I just discovered your channel, and I already love it. A bit over my head, which it's good, gets me out of my comfort zone. Great work and excellent delivery of the content. I'll be back...

[@thmanx]

Employee from Banks Power here, and this deep dive into into aviation piston turbo compounding is absolutely fascinating. What you mention at about 18:30 in about turbochargers still causing back pressure and require horsepower to run rang very true to what we know at Banks. It’s amazing to see how these truths were known over a half century century ago. Makes one re think all the ways an engine can recover power effectively to both improve power when you need it, and also make the same power, with less fuel. Well done sir 👏👏

[@GregsAirplanesandAutomobiles]

I appreciate your view and comment. I know who you are and think you folks do fine work over there.

[@MountainBound17]

Hi Greg, my understanding is that modern F1 cars (2014-present) use a pressure turbine mechanically linked to the compressor via a shaft as in most turbochargers. However the Motor Generator Unit - Heat (MGU-H) is colocated on this shaft and able to utilize the battery to add power during low rev acceleration mitigating turbo lag, and also able to extract electrical power during high rpm on the straights to either charge the battery or directly power the MGU - Kinetic for more overall driving power. The system can only extract power at high rpm - traditional turbochargers would release the excess boost pressure through the wastegate but the F1 MGU-H is able to reduce boost pressure by adding the electrical load. There are some teams that have a special mode that fully drives the compressor via the MGU-H and opens the wastegate to reduce backpressure for maximum power during low speed acceleration. Alpha Tauri did this a few years ago but I don't believe it's common as it's highly draining on the battery. Other teams have figured out how to get better laptimes using other tricks with their available electrical energy. I'm only about 80% sure on all this, would appreciate a correction if you read up on this technogy and understand how it's used. Thanks!

[@stratcat3216]

Is this not the most thorough and well thought out Aviation channel ever? Kudos Greg and thanks!

[@alfaromeo2011]

Great & indept explanation of this topic. Like you said, Volvo & Scania are using this system nowadays. I remember that Scania introduced the R113 400 turbo compound engine around ‘91. It was a 11 liters 2 valve per cylinder inline 6, 4stroke diesel with a ‘normal’ turbo charger and a second one driving the flywheel via a clutch system. Claimed engine efficiency of 46%. Didn’t see them being sold a lot though in that time. More often the standard R113 320 & 360 versions. The company I worked for in ‘93 as a young mechanic used slightly tuned-up 320’s. For more power, companies just bought the V8 R143 versions.

[@freewill1114]

I was on a couple of DC6 flights back in the late 50's. The pilot would come on and warn us not to be alarmed when they "shifted" the engines after the climb out. Now I understand what was going on with the engines; thank you for this fascinating video!

[@DavePetroskey]

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[@DavePetroskey]

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[@chesslerbooks]

As a youngster in Brooklyn NY during the period when the DC6's and DC7s were the queens of the sky, my interests were more about cars than planes. However, my family lived in an apartment and our neighbor named Al DeStanko was a United Airlines mechanic and worked at Laguardia. At that time there was no Idlewild airport yet. I remember him comparing the DC6 and DC7, and he surprised me by saying the DC6 was a better airplane than the DC7. The 1950s were a periiod of constant changes in technology, with improvements all the time. So how can the old model be better than the new one? I think this videos answers that. The DC6 was not as self destructing as the DC7 was to get more speed. As far as Idlewild went, my father, brother in I used to walk out to see the new sirport that was under construction (we never had a car.)

[@alanrogers7090]

The High And The Mighty was taken from a novel by pilot Ernest K. Gann. I may be wrong, but I believe he was also the technical advisor on that film. Several of his books were made into profitable movies, including Zero Hour, and others. Personally, I love aviation books and Mr. Gann's rank right up there, excuse the pun. Up there, aviation, you get it.

[@michaelmartinez1345]

@alanrogers7090, That is a great movie... Slightly over-dramatised (acted), but then what movies from that time were not overacted? Many of the relics from the early to mid 1950's are in that classic movie... So much has changed, (especially the avionics) since those days... It is why that is such a cool movie... It catch's everything, the way it actually was... Really good...

[@bentilbury2002]

I've read Gann's Fate Is the Hunter - great book about early commercial aviation.

[@dougrobinson8602]

Gann also wrote and consulted on 'Flight of The Phoenix', which is a great movie for aviation fans. At least the original and not the dreadful remake.

[@francovance1]

He flew dc4s for American Airlines, great author - remarkable man, if you can find a copy of Fate is the Hunter grab it.

[@cloudshe]

what amazing true stories fm a person who luckily survived the early days of transport aviation and war-time adventures

[@engrpas]

I flew across the Atlantic in 1957 in a DC-4 - on a charter operated by Maritime Central Airways, 6:52 from Vienna to Moncton NB Canada. We made two fuel stops, at Prestwick and Keflavik. Total elapsed time about 25 hours.

[@simonnorburn3518]

I remember back in 1972 in my physics A level evaluating the most efficient airflow through various engines and being highly surprised that the most efficient for energy transfer to the plane was that where the difference in speed between the aircraft and the propulsive air was minimal. Once I had done the calculation it made complete sense, work done in high velocity air still going fast behind the plane was a waste of energy. These turbines simply extracted more energy (work) by reducing the residual energy in that fast moving air. It did help that my physics teacher had done quite a lot of time with Rolls Royce and was only too happy to change the subject from boring rote work to interestng meaningful calculations...

[@T3RMINAT0R95]

the company i work for now used to operate P-2V's and ive always wanted to know more about how its engines work, so thanks for the clear explanation of these engines

[@GregsAirplanesandAutomobiles]

If that's Neptune say hi to Tom L. for me.

[@T3RMINAT0R95]

@@GregsAirplanesandAutomobiles will do!

[@gerritvisser]

An excellent video. We flew from Amsterdam to Montreal in 1958 on a KLM DC7. Sadly too young at the time to really remember anything specific. Montreal to Toronto was on a TCA (now Air Canada) Viscount. Years later flew Toronto-> Amsterdam->Toronto for vacation on a DC8.

[@williamhughmurraycissp8405]

The DC-7B was a game changer. Pressurized. High altitude. Smooth. I loved it.

[@edschoenstein1893]

Looking at the complexity of these engines and having to do this with a slide rule blows my mind as to the ingenuity of the engineers who took these theories into reality without all of the benefits of what we have now. This is real engineering where you got your hands dirty and a job well done 👍

[@erwinschmidt7265]

The DC-7 on display at Atlanta belonged to our Nomads Travel Club - Detroit Michigan. After much cost & effort, it was restored, and on tour trip with Capt Sully when a motor let go. W/O adequate funds it's been parked at Atlanta since. In day, Nomads replaced DC-7 w/Convair 990 Jet. It was fastest of day, except for that pesky sucker zippin' by us named after some Revolutionary War Battle! No way in hell did we have enough dough to buy one of them!!!

[@electric_boogaloo496]

My understanding of thrust vs horsepower is the relationship between changing the momentum of the air vs changing the kinetic energy of the air. You can't affect one without affecting the other, but to get the same thrust, you can change the velocity of a lot of mass of air by a little or change the velocity of a small mass of air by a lot. The former requires less horsepower at low speeds and turboprops, big turbofans do exactly that for shower aircrafts, the latter requires a lot more horsepower for the same thrust at slower speeds, but the thrust doesn't drop off as drastically as the former as the speed of the aircraft itself increases. What's interesting with rockets is that the fuel efficiency comes out as the exact opposite of jet engines as in higher exhaust velocity is preferred and gives you more specific impulse than a lower exhaust velocity.

[@dougdanzeisen9608]

Wonderful exposition of this largely forgotten technology. Thank you much for sharing your information and insights on this matter. As fuel economy standards tighten I could see a new gen of power recovery turbines driving a generator to provide charge/electric power on an automotive drivetrain. Of course, cost will be the driver here.

[@nikolassilea7187]

I get so excited when I see you drop a new video! Thank you!

[@hooperjj]

Another benefit from the PRTs with the airlines was quieter engine exhaust noise in the cabin for DC-7s and the Connies, I have worked on DC-6s and Connies and Know the big differance inside!

[@johnparrott4689]

True that

[@coreyandnathanielchartier3749]

The section about the demarcation line (speed) between jet thrust and propeller thrust is very interesting. My auto-mechanics Votech teacher explained this system to us back in '75. He was a B-24 (ETO) pilot, airline pilot and FAA safety guy. Science classes for those who were awake tells us that to move a quantity of molecules of gas through a pipe from high to low pressure,(reduction in pipe diameter) those molecules must be increased in velocity. These turbines work on very high velocity exhaust without significantly raising it's back pressure. Normal turbocharger is more akin to a jet engine turbine turning a compressor. Venturi effect in a carburetor works on a similar principle. These PRT's could as well be called 'waste recovery turbines'. P-51 belly scoop recovered waste heat from the engine radiator by heating air and increasing it's volume (thus increasing it's velocity through a fixed orifice).

[@redtag501]

My first trip by air was as a five year old in 1956 traveling with my mother and siblings from Portland OR to Denver CO on a United Air Lines DC-6B. I then became hooked on aviation at first flight. We later flew on to Atlanta GA via United DC-7 to Chicago Midway Airport and, from there, on a Delta DC-7 to Atlanta. Since that time, I flew many times on DC-7s, 7Bs and 7Cs well into the 1960s, my last time between Savannah GA and Atlanta with Delta in 1968. Back in the day, these airliners were hyped as the ultimate in luxury air travel with the airlines rolling red or gold carpets and stringing cordons out to their boarding ramps and pampering passengers with gourmet, multi-course meals, free cigarettes and champagne. We didn't have so-called entertainment systems on board during the piston or propeller era, but then the large windows afforded hours of viewing pleasure whether flying over canyons, mountains, cities, rivers and plains or observing the many varied colors of hot gasses issuing from the exhaust stacks at night depending upon the particular stages of the flight. But, oh, was the noise and vibration ever a mind-altering sensation. Normal conversation was virtuallly impossible limiting one to having to face someone directly in order to make even the simplest of small talk where the ability to read lips was practically mandatory. The vibration at altitude caused one's voice to sound as if he or she had swallowed a spoonful of gravel when speaking. You would instinctively find yourself attempting to clear your throat but to no avail. Still, I look back on travel by DC-7 as perhaps one of the best times in airline history as reflective of the so-called golden age of air travel.

[@LordCakeskull]

Turbo compounding was on the drawing board for a Wankel rotary engine company I was involved with some years ago. The high velocity exhaust of the Wankel was ideal for it, but the company folded before we could get to test it.

[@francesray6465]

I worked with an engineer for a few years that would volunteer on the Rare Bear , and he mentioned the exhaust was wasting over 500 horsepower. Since this was a race aircraft the thing they concluded was to modify the pipes and direct their thrust to keep the Bearcat aerodynamic. It worked.

[@gerardlardner3104]

When I was designing stationary diesel installations back in the 1980s, a type of turbo compounding was available for the big MAN-B&W diesels and Sulzer diesels. These were around 80,000 hp and up; huge engines, running continuously for thousands of hours at around 100 rpm.

[@ianlloyd1182]

Thanks Greg, very informative and the presentation was very clear.

[@mortdk]

Thanks for making this clear. So important to know. To think 1950s technical books and encyclopedias explaining - how a automobile or an aeroplane engine works so even a 11 year old kid could understand it. What have become of this? All we have today is useless smartphones.

[@marcusborderlands6177]

Today we have those books digitalized and stored online, along with billions of hours of interesting and educational content in video form. Hell, Ben eater here on KZbin will walk you through building an entire computer from basic circuits and chips in only a few hours. Simply looking st the negatives of modern technology is hardly giving it enough credit.

[@johnfisher7143]

One of the few videos on here where I actually feel smarter for having watched it. Thank you.

[@paulkasella712]

Hello Greg. First time commenter and long time follower. I really enjoy your technical and historic videos. As a service technician on agriculture equipment, I can say that turbo compounds are also used in modern agriculture equipment. It's used on large displacement, high horsepower diesel engines. I did not know of turbo compounds had the origins in aviation. You are very correct about learning from the past about engineering and using those solutions on modern technology. Thank you again for your informative videos.

[@dylanhayden8825]

I've never heard of any modern engines using turbo compound engines, do you have any examples? Note that that compound turbos on modern diesels are not the same as turbo compound engines as described here.

[@paulkasella712]

Apologies for making it sound like turbo compounds were common place. Turbo compounds are not common place on modern day diesel engines and are fairly rare, but they're used. Seen and work on a few engines with turbo compounds. They have a turbine and fluid coupler that connects to the crankshaft like Greg stated in the video. The MTU/Detroit DD 15 is the the same as the Mercedes-Benz OM 473 LA This family of engines have a turbo compound. This engine is on current Claas Jaguar forage harvesters model 880. Some information and images can be found doing a search on a Claas Jaguar 880 engine search. Also there is a nice video on KZbin about MTU Detroit Diesel Australia DD15 engine.

[@dylanhayden8825]

Very cool, I didn't think anyone would brave the cost and complexity of such a system in this day and age.

[@jetsons101]

As a licensed A&P I approve of this video....

[@jaym8027]

One of your best recent videos. It's easy to tell when a subject really engages you, Greg. I also liked the stealthy FIAT content at the end. I really enjoyed the video, and I hope you have enough seniority to enjoy Thanksgiving at home with your loved ones.

[@GregsAirplanesandAutomobiles]

I'm very senior, but I'm going to be home for Christmas, not Thanksgiving.

[@marcpigeon7796]

Hi, your content is stellar. I spent 12 years (of a 37 year career) at P&WC teaching PT6 maintenance to mechanics and your content and presentation skills are exemplary. Truly enjoyable and informative. Thank you. 🏍️🇨🇦

[@michaelbartholomew1038]

Great article, we were taught that the fluid clutch disconnected the PRT in case of failure to prevent it from robbing power, however I have never had the chance to work on one.

[@dblissmn]

Just a note that the very fine old water-driven mill used at 21:28 to demonstrate a blow-down turbine is the Old Mill at Uplyme, Devon, right on the county line between Devon and Dorset in southwestern England that's marked by the river it sits on and just outside of Lyme Regis, Dorset.

[@malcolmking752]

Greg, I have been eager to hear you discuss these engines for a long time. I can’t wait to watch this video.

[@dananichols1816]

It was great to see (32:04) the nice shot of a Everts Air Cargo DC-6. They, and Air Cargo Express are still operating the DC-6s out of Anchorage and Fairbanks, Alaska -- even doing contract radar-site support cargo work for the Air Force. I retired (E-8, Alaska Air Guard) at Elmendorf AFB, Anchorage, in 2016... it was fantastic to hear those P&W R-2800s wind up and slowly fade away after takeoff (144 spark plugs, all zapping away!). My dad was an AF navigator, including long sortie hours in RC/EC-121 Connies, out of Otis AFB, Cape Cod, in the mid-'60s. Their wing lost three Connies, and fifty aircrew, all with engine fires/failures. The RC-121s were very heavy with the huge, (parasitic drag) radomes, and the very heavy electronic/comm gear tech of that time. Heavy with fuel for the first hours of the mission, dad said that it just hung on the props. The PRTs had a lot of fires. I was a mechanic's helper with Northern Air Cargo, in Anchorage (early '90s) on their DC-6s -- fascinating to see how all of those dissimilar metals, wiring and complex accessories were imagined, put to specs, and assembled... all with slide-rules, blue-prints, and thousands of hands-on craftsmen. No "computer-assisted-design" software or robotic machinist programming.

[@GregsAirplanesandAutomobiles]

Thanks, I enjoyed your post.

[@donkauer6744]

Why has this awesome channel never showed in my algorithm? I liked, and will now subscribe. Thank you for this most, and I do mean most awesome video. I too, at age 61, get frustrated when people that "should" know better, refuse facts.

[@gregmaggielipscomb9246]

Excellent, my old war2 Navy flying captain used to fly Navy P2Vs w/ the Wright 3350 duplex turbo compound engines, he referred to them as having,"Blow Down Fans." Thank You for sharing this vid sir.

[@JamesDole-cb3wx]

Greg - one of the best engineering video's I have heard. You have an outstanding ability to be clear in your explainations, to go fast enough to cover the material and not so fast as to lose anyone. I particularly love how you anticipate potential points of listener confusion and "nip those in the bud" (ex: "do not turbo-compound with compound turbo which is completely different") - I also like how you make quick diversions into a subsystem (like the fluid dampener) - you explain it quick and announce that you are now coming back to the main event. If you did not make that diversion, people would be confused by a subsystems purpose and wonder why it was glossed over and either have to go to wikipedia to figure it out or live with the frustration of not knowing - you do it with just the right amount of detail and thus fill in knoweldge gaps that tend to give the viewer a much more complete picture by the end of the video - and you do it without the viewer feeling lost! Super Super good job - I am going to subscribe to your channel.

[@GregsAirplanesandAutomobiles]

Thanks, I really appreciate these kind words, and the fact that you clearly get what I'm trying to do here.