Turbo Compound Piston Engines. Almost magic tech. 

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.

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 😂

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.

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.

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.

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

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!

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.

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

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!

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

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.

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

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.

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.

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 RU-vid. Thanks for the hard work in preparation.

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 😄.

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

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.

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

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.

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.

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.

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.

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.

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.

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

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!

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.

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!

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.

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.

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.

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!

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.

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!!!

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!

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

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!

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

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 !

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.

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

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.

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.

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.)

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.

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.

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.

I had a summer job in Montreal, in 1968 overhauling the Wright turbo compound engines used on the Canadian DC-4M "North Star" and its sister ship, the Royal Canadian Air Force CP-107 Argus maritime reconnaissance aircraft. Same engines as used on the "Super Clipper"

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!

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

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

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!

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.

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.

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.

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. 🏍️🇨🇦

Absolutely fascinating. Especially contrasting thrust vs shaft hp.

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.

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

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.

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.

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 !!

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.

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!

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

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...

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.

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).

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.

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!

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

I just found your page here on RU-vid. I am a big fan of the DC-7C and your description of turbo compounding is one of the best I have seen! I am now subscribed to your channel!!

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 😱

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.

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.

There is a R3350 turbo compound cutaway at the Franklin Institute science museum in Philadelphia. Just one of the amazing sights there.

Greg you are just great ..loved your coverage and support of the P47. Strangely piston airplane engines hit their heights and were replaced with Jet engines at the same time and for the same reasons the steam locomotive were replaced the diesel over electric. The cost and down time of maintenance .

My dad was a Marine aviator. He flew the R5D during the Korean War.

Having viewed Oceanliners Designs new episode on the power plant of the Olympic class liners (incl Titanic), it looks to me like they used a somewhat similar system, with the low pressure steam left over from the two lateral piston engines being used to power a higher rpm centerline turbine that greatly added power and speed at relatively little energy cost (the ships had three screws).

Love your videos Greg, much respect for the preperation you put into making these things with unriveled accuracy.

As a corporate pilot who crossed the Atlantic in a Gulfstream, planning and requirements for crossing are just as challenging today as 70 years ago. Good Job!

The problem with turbo compounding seems to be the complexity of a system designed to operate effectively over a wider power range. They're typically only advantageous at or near full power. You might find "The Road to the 50% Thermally Efficient Internal Combustion Engine" on YT interesting.

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.

Outstanding video! Clear, concise, holds one's attention. Taught me a lot I didn't know about turbo concepts.

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.

Great stuff Greg. I don't know if it is quite relevant, but Bob Beck talks about keeping the L1649s on the Trans Polar flights below 13,000 ft, at leat initially, to avoid going into higher supercharger gear to save the exhaust valves from exiting via the turbines.

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 👍

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.

Hello Greg. I want to thank you for once again taking a complicated mechanical system and making it understandable to a non-engineer like me. I enjoy your videos, particularly mechanical things.

I was talking to an older ex-South African Airways pilot a few years ago, he had flown DC7Cs for them. He ssid the aircraft were wonderful but the engines needed vast amounts of maintainance.

I like that is not only about fighters, but slowly also heavier aircraft are coming in your description. I'd love to hear you dissecting also something like long reconnaissance missions (like those from the fw 200 or ju 86 or catalina pt5) or bombers (even failed ones like the he177)

You produce one of the great RU-vid channels - highly compressed knowledge plus excellent knowledge sharing skills.

Wow!! This is probably one of the most incredible technologies ever to come out of the 20th century piston engine race, and one I’d never heard of until now! The use of it in the F1 cars is really cool too. I’d say this is one of the best videos on this channel simply because of the topic. Well done Greg!!

I wrote a thesis paper on this aircraft in college for my bachelor's degree in Aeronautical Science, and it was a remarkable plane. It was so influential in the commercial aviation world that De Havilland, who had originally designed the Comet 1 to have wing mounted jet turbojet engines in similar fashion to the DC-7, decided to take the radical step of mounting them in the wing roots. They did for two reasons. The first was to make the aircraft more aerodynamic, and the second was, for lack of a better word, to make it look cool. Unfortunately for the Comet 1, it proved to be a disaster and claimed dozens of lives in 3 catastrophic breakups that ultimately doomed the airliner. This wasn't do to the positioning of the engines however but by the decision of the engineers to design it with squared windows, creating stress points in the corners of them that caused explosive decompression to occur after so many flights and break the aircraft apart with all onboard being lost in each case.

I'd never heard of turbo compounding before this video, Greg, but I think you're right, we ARE seeing this technology return on some Class 8 OTR truck engines now. One question I have is this: - I've wondered this for years: Here in Alaska we still fly a few Dc6s, which I love. That being said, I've read that during the late nineteen-fifties and early sixties that while some DC7s were actually in the process of being scrapped, due to reliability issues surrounding the Curtis R3350, the same airlines simultaneously kept their older DC6 counterparts in active service. As a novice, I've wondered why the airline companies didn't just turn their newer DC7s into glorified DC6s by retrofitting the DC7s with the tried and true P&W R2800 or maybe even the P&W R4360? Would this really have been that technically difficult to accomplish or would it have simply entailed too much of a quagmire of red tape with the FAA? Or maybe the time and effort to convert prop planes simply wasn't worth the effort or expense with jets looming on the near horizon. I realize my question is probably over simplified but in leu of the actual cost of the liners themselves, it seems like an option to have at least been considered. - We do this kind of thing with semi trucks all the time, but of course we don't have the FAA breathing down our backs either: Great video!

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.

26:26 "take off is a relatively low speed affair" I am crying :'D

The Canadair CP-107 Argus maritime patrol aircraft also used Wright R-3350 Turbo Compound engines due to their fuel efficiency and therefore long loiter time. It did that from 1958 to 1982.