Turbo Compounding the Wright Way: The Power Recovery Turbine System in Detail

Video #7 in a series by The Aircraft Engine Historical Society (www.enginehistory.org). The Wright R-3350 TC18 turbo compound engine was the pinnacle of piston engine technology. It incorporated three power recovery turbines that harvested exhaust gas energy and returned that horsepower mechanically to the crankshaft. This video details the technology and the hardware that accomplished this feat.

[@thamesmud]

When I clicked on this and heard the chirpy "greeting this is" I was surprised to find it wasn't Greg ! Great video on a much ignored subject.

[@cabanford]

Exactly the same thought - it was all Greg until I finished reading the Title & saw the poster

[@AEHSvideo]

Thanks for your comments. I'll take "chirpy" over "droning" every time.

[@leoa4c]

Very good point. I also felt this video of being on a similar tune as Greg's videos, which of course is never anything bad.

[@rbasomb]

Greetings from a Greg subscriber!

[@peter.baerentzen]

Me too

[@iphonedoc]

As a young member of the Wyoming Air National Guard I was a flight engineer on our C121's. Of course we were versed in the PRT's of our birds, but as you mentioned with no controls available to me. After this video I now know my understanding of them way back them was rudimentary. But sufficient for our job. I have often wondered about what we were told was a direct connection of the PRT to the crank. I now see that what we were told was a direct connection was thru the fluid coupler or what most people would know as a torque converter similar to cars with automatic transmissions. Now 55 years later at age 75 I understand more thanks to you and this exceptional video. My admiration of the engineers who created this is immense. I thank you. I also thank the lord for my life and all the things I experienced and wonderful people I've met.

[@AEHSvideo]

Thank you for your most interesting comments.

[@MarcusLindblomSonestedt78]

Just wanted to add that I believe a torque converted in car has some extra devilry (aka mechanics) to handle big speed differentials, compared to this relatively simple fluid coupling. Something with a freewheeling turbine and fixed flow-reversal vanes. I'm yet to understand the whole thing well though.

[@iphonedoc]

@@MarcusLindblomSonestedt78 I think it is almost the same using a fluid coupling to freewheel at low rpm and locking up at higher rpm. The PRT's recover 450 HP which is more than most cars produce and go from low rpm at start to a much hhigher rpm at operation to increase the efficiency of the turbine in the PRT. Thanks for the comment. It made me think some more about the 'good old days'.

[@AEHSvideo]

@@MarcusLindblomSonestedt78 , thanks for your comments. Yes, there is additional wizardry in the automotive torque convertors that multiply torque at certain design points instead of simply trying to "speed-match" the inputs and outputs like the fluid coupling. As you automatic-equipped car sits stationary while idling at 600 rpm, the speed mismatch is between input and output is 10 rpm per second which just generates heat.

[@sixstringedthing]

Outstanding presentation; clear, concise, adequately detailed for the layperson without getting right down into the maths of it all. One of the most fascinating parts for me was the extensive physical "hard limit" measures taken to prevent a sustained overspeed condition, and the armour to deal with the consequences of those measures being activated. Having the cooling cap/flight hood assembly weigh half as much again as the PRT itself seems like an odd choice at first, but I guess that having an entire turbine disc catastrophically fail inside the cowling with no containment is what engineers typically refer to as a Bad Thing. Always lovely to see HARS' Connie still doing what she was built to do, a very special and much loved aircraft. The bit of video you included is certainly one of the best I've seen, what a fantastic way to conclude the presentation! Great work Tom, and thanks mate. 👍

[@AEHSvideo]

Thanks for your comments. Having a nice cache of Wright TC18 documents eases the process. I suspect the brittle buckets would shatter like lightbulbs dropped on the garage floor once they came loose from the wheel. However, the mass, energy, and stout nature of the turbine wheel would really wreak havoc if it were to come adrift. The HARS Connie is an international aviation treasure.

[@Hopeless_and_Forlorn]

In 1964 I learned in A&P school that engine oil has five functions: lubricate, cool, seal, protect, and clean. All these years later, I must add to that, transmit power through fluid couplings in the PRT system. That makes six. We learned the basics of the Wright PRT system in school, but this video is superlative in exposing the real engineering challenges. My early work for airlines incorporated maintenance of the R-1830 and R-2800 engines, but not the R-3350. I spent a lot of time repairing broken clamps and loose studs on the exhaust systems of the R-2800. I can only offer respect for those mechanics who kept the R-3350 TC18 engines in repair. Thank you for a great video.

[@Surestick88]

With variable valve timing becoming more popular oil is frequently used as hydraulic fluid to actuate some of those systems. Heck, the Me109 engine used engine oil as a hydraulic fluid in the drive/speed control system for the supercharger.

[@Hopeless_and_Forlorn]

@@Surestick88 And modern, jet engines use pressurized fuel as a hydraulic medium to actuate such devices as variable stator vanes and variable bleed valves.

[@AEHSvideo]

Thanks for your comments. A very clever system it is.

[@tylerwallace9185]

Don't forget the use as a cushion!

[@WOFFY-qc9te]

Excellent presentation very well illustrated and explained. I was a vibration engineer using vibration and dynamic spectral analysis (Rockwell IRD) to identify issues in various machinery. When it came to the section about the vibration damper I considered what equipment they had at that time to isolate errant vibration signatures. Nothing electronic that could freeze or plot those frequencies so the solution came from experience and intuition. The compact construction and thermal stress management is truly impressive for the time.

[@AEHSvideo]

Thanks for your comments!

[@GroovesAndLands]

I'm an ME with an ICE/automotive concentration. I love these technical breakdowns of engine stuff, and the WW2 era aero-engines always fascinate me for how advanced they were. It took the automotive world another 60 years to get to the same level of sophistication. In many engine presentations, there is often some discussion of harmonics and vibrations that needed to be addressed or fixed and I've always wondered how TF they did that in 1939 or 1968. I get there are fancy tools and equipment to analyze that stuff NOW - but what about then? Was it simply inspecting failed parts, analyzing the failure mode, theorizing it could be harmonics/oscillations, theorizing where it could be coming from and envisioning/trying different means of addressing them? If you could point me to some resources that explain it - that'd be awesome.

[@AEHSvideo]

, thanks for your comments. I'm not overly-familiar with the testing field, but oscilloscopes, carbon stress gauges, reed-type vibrameters, and strobometric tachometers/vibrameters go back before WWII. Clever men and higher math were also essential. You may be interested in the two devices late in this video: kzbin.info/www/bejne/p4jZY3qmbMhgo7M

[@AEHSvideo]

@@GroovesAndLands , more info: www.enginehistory.org/NoShortDays/Development%20of%20the%20R-2800%20Crankshaft.pdf

[@WOFFY-qc9te]

​@@AEHSvideo Clever men indeed, some solutions to problems were breaking the rules of physics but intuition and experience used physics to over come it own intransigence. Thank you for referencing the Wright Engine. I will enjoy that very much and If I recall there were some rules broken with that. . My work was predictive maintenance and trouble shooting machine dynamic issues. Fortunately I could freeze a spectrum of frequencies and calculate the components in motion, roller speeds and gear meshing. Although the first instrument I used was my hand on the casing and a moment for my mind to visualise the mechanism. After a year or so I was pretty well calibrated. One job was vey frustrating as my instruments were indicating acceleration G was acceptable and wear as expected but there was something not happy on drive train but I couldn't isolate it. Several coffee breaks and fresh readings didn't make matters clearer so I went with my intuition had the (1 : 70 1400 hp ) gearbox removed for inspection. After hours of dismantling they found a casting void had cracked on a the pinion bearing journal web. After seeing that I went through the data and still could not find anything that would point to that directly, it shows how much information our senses and minds process subconsciously. One of my favourite instruments is similar to the Siromet you mentioned having five or many more reeds in a horizontal display. Surprisingly sensitive and most enjoyable to watch. I have seen a demonstration of an oscillograph scratching a sooted drum, basic but it did the job. Modern kit is amazing but it needs to be used right and to many times I have seen reports with so much data presented but no helpful conclusion. Thanks for you assistance I look forward to exploring more. Best

[@LaLaLand.Germany]

That Connie fly by was beau-ti-ful. Now that I know what causes that I really can enjoy. What a nifty device, no wonder these engines are peak of an era. One German guy thought the same and bought a still sealed surplus engine like this. Got it going with the help of some tractor pulling freaks from the Netherlands. At the 1st start fire brigade was called because of all the blue smoke that monster made. What a cool toy to have. Next step for him was to shorten a prop so he can run the engine longer and up to temp… Happy New Year, thanks for this nice piece of knowledge.

[@AEHSvideo]

Thanks for your comments. I suspect the TC18 owner is perhaps Andreas Rennertz, but there are a few others that have these engines as well.

[@BobOBob]

I grew up with that sound, near McClellan AFB.

[@LaLaLand.Germany]

@@AEHSvideo That Name rings a bell- the engine and the story was reported by the Pldtimer Markt paper quite some time ago. There used to be a video but I didn´t find it.

[@AEHSvideo]

@@LaLaLand.Germany , kzbin.info/www/bejne/ooGseX2tgZZ8j6s

[@mbox314]

This video is solid gold. I am going to send it to my coworkers.

[@AEHSvideo]

Thanks for your comments and I hope they enjoy it as well.

[@Hurpdurpdipidydoo]

This video is phenomenally informative

[@AEHSvideo]

Thank you for your comments.

[@wazza33racer]

Thanks for the close up explanations of the Curtis PRT.....it is indeed a feat of engineering to make the concept work on a large radial engine. Vastly under appreciated engineering.

[@AEHSvideo]

Thanks for your comments.

[@wazza33racer]

@@AEHSvideo thanks for the video,the subject matter is one of the best kept secrets. There is no practical or economic reason why, we cannot have fluid drive clutched PRT's on modern gasoline engines in motor vehicles, purely as a fuel saving method that would eliminate the carbon footprint advantage of the ridiculous EV's. Traditional turbo chargers have practical tuning issues on gasoline engines, and dont really offer much in fuel savings.......the PRT by comparison is ideal for gasoline engines.

[@AEHSvideo]

@@wazza33racer , thanks for your comments. Mack, Volvo, and Scania (years past) have diesel turbo compound truck engines in production.

[@wazza33racer]

@@AEHSvideo Yes, but on turbocharged truck engines, the PRT is downstream from the Turbocharger which soaks up almost all the exhaust gas pressure, with the PRT only being able to recover the equivalent of an extra 5-10% of engine output.

[@kevinbaird9763]

I always wondered how the fluid coupling worked. Great presentation! Thank you.

[@AEHSvideo]

Thanks for your comments. The fluid coupling is "modern" genius.

[@fred37ify]

So basically sort of a torque converter

[@AEHSvideo]

Similar, but there are differences. A torque convertor can be designed to actually multiply torque at certain design conditions while a fluid coupling simply attempts to match input and output speeds without torque multiplication.

[@Technoid_Mutant]

Even before I get to watch this episode I want to thank you for making it.

[@AEHSvideo]

Thanks for your comments and I hope it meets expectations.

[@pattonpending7390]

The heat balance chart threw me for a bit when i looked at the engine output side of the graph with 2060Hp before supercharging and 1680hp after the supercharger. It makes it look like theres negative efficiency to having a supercharger. Then I saw that this was at Sea Level. EDIT: i didnt realize that the chart is of exhaust gasses ONLY, and does not include the mechanical power already delivered to the prop. Makes more sense to me now! Great channel, as an old A&P who volunteered to wrench on the old stuff for 20 years, I appreciate these deep-dives into the technology of the time. I'm hooked! Now if only someone can explain how an air-cycle machine worked on older Jets (to both pressurize and cool the cabin using only 390 degree bleed air from the turbine) I would be in heaven.

[@rocketsurgeon11]

The chart at 2:00 says it is indicating how much energy there is in the fuel going into the engine and describes where all of that energy goes. I saw the same thing regarding the power output of the supercharger and could only deduce the ONLY reason you would accept a loss in power from a supercharger is because the test isn't being done under true operating conditions and at altitude where air density is lower is where it actually makes sense and improves power output and increases operational ceiling of the engine.

[@AEHSvideo]

The devil is always in the details.

[@ktmarvin300]

Turbomachinery engineer here: You mixed up the terms impulse and reaction type turbine. The "blow down" turbine is the impulse type (r=0) turbine used for turbo-compounding while the reaction type (r>0) turbine is the "Pressure turbine". The name impulse turbine is originating from the working principle which solely relies on the impulse of high speed gases without enthalpy conversion in the rotor-plane of the turbine.

[@AEHSvideo]

Yes, thank you, you are correct. I really stepped in it.

[@DavidBantz-q4j]

Truly superb video. So much effort to explain the complex in a simple, but complete way. Kudos!

[@AEHSvideo]

I appreciate your positive comments.

[@1crazypj]

I have to agree.

[@AEHSvideo]

Thanks.

[@therealfearsome]

the fire coming out of the exhaust was so badass, I had never seen that before (62 yrs old)...thanks for a great video!

[@AEHSvideo]

Interestingly, Wright says that at takeoff power (back in the days of 115/145 octane fuel) the mixture was still too rich to burn coming out of the hoods at takeoff. But at high power (METO or climb power) the combination is just right for the flames to emanate from the hoods.

[@gavendb]

I was lucky enough to visit the evergreen museum and speak with one of the tour guides there as he showed me around the spruce goose. He was a really interesting elderly volunteer. He was a retired WW2 army air corps vet who went in the civilian world as an A&E mechanic. He told me that they used to nickname the PRT as "Parts Recovery Turbines" as the poppet valves would overheat and drop, often ending up stuck in the PRTs. I got the impression that the PRTs had an effect of higher sustained EGTs on the exhaust valves and that material engineering hadn't quite caught up with the PRT use yet.

[@AEHSvideo]

Thanks for your comments. TC18 performance and reliability was under constants scrutiny by the airlines as well as the military and the later engines were quite reliable in service. Any metal going through those whirling brittle buckets meant a PRT change as well as fixing whatever carnage threw the metal in the first place.

[@sparty94]

this is a fantastic presentation. i love the graphics, and the narration.

[@AEHSvideo]

Thank you for your comments.

[@normcameron2316]

What an amount of information! Thank you. What engineering!

[@AEHSvideo]

Gratified to hear you found it of value.

[@marchindy]

Awesome video, I always wondered how the fluid coupling worked. I am always amazed on the technology on older radial engines. Smart folks for sur that designed/engineered them.

[@AEHSvideo]

Thanks for your comments and I couldn't agree more.

[@SkyhawkSteve]

I'll note that the Kalamazoo air museum ("Air zoo") has a 3350 on display with the PRT's pointed out, and even an annotated photo courtesy of Tom Fey that points out the components and some details. Great to see it in person, and great to see such a detailed explanation in this video! It's easy to appreciate that jet turbine engines didn't just appear out of nowhere... the tech was (mostly?) being developed on reciprocating engines. Or at least in parallel?

[@AEHSvideo]

Thanks for your comments and the Air Zoo is a wonderful Museum. I think it is fair to say that pre-WWII supercharger and turbocharger technology (heat resistant metals; advanced shaping and machining; efficient management of inflows and outflows, testing methodologies, etc.) laid the groundwork for the development of the turbojet, and the dawn of WWII sent research and development into overdrive.

[@n6mz]

The excellent National Naval Aviation Museum at NAS Pensacola has TC18-powered "Truculent Turtle" on display. What a fantastic aircraft and a wonderful museum.

[@brianhalberry]

Fantastic video! I'd always wondered about this system. It never fails to amaze me that, as much as we spruik about how high tech everything is today, engineers of the past developed these incredible systems, designs and materials. Well done.

[@AEHSvideo]

Thank you for your comments.

[@jwholmes2]

Fantastic lesson on the PRT system. I thought I understood it pretty well, but I learned a ton more about it from your presentation.

[@AEHSvideo]

Thank you for your comments. The devil, as well as all the cool stuff, is always in the details.

[@michaelhamm6207]

Don't try to fool me, everybody knows that these things work by voodoo and angry pixies!!! Seriously, though, great video and between you and Greg, I think I finally understand how these things operate. It was always some kind of dark art before. Lastly, that video at the end of the Constellation takeoff was worth watching the whole video.

[@AEHSvideo]

Thanks for your comments. Fire-spitting flight hoods are just the best...

[@devoncampbell3607]

really neat presentation. very informative and immaculately paced.

[@AEHSvideo]

Thanks for your comments. Pacing is always a balancing act and I'm gratified to hear this one is balanced!

[@towgod7985]

Great clinical explanation! Where was this when I was trying to explain T.Comp engine to a group of student pilots 25 years ago! 😂 FEARSOMLEY complex, I understand why we went to gas turbines. Cheers.

[@AEHSvideo]

Thanks for your comments. There were a lot more TC18's flying 25 years ago, but the magic lives on.

[@jimsvideos7201]

Manufacturing all the exhaust plumbing must have been a pain. Thank you for this; I understood the generalities but not the intricacies.

[@AEHSvideo]

Thank you for the insightful comment. Indeed, there was significant design and development work expended on the exhaust system. Wright realized they could not anticipate all the challenges at very beginning so an ongoing development program worked through the many iterations in design (straight slip joints? ball slip joints?), seamless versus half-stamped exhaust pipe tubing, welded versus integral flanges, "figure 8"-design exhaust pipe braces, pipe wall thickness from .047 to .062 inches, etc.

[@Manny32V]

Great video. Piston aircraft engines were incredible pieces of engineering.

[@AEHSvideo]

Thanks for your comments.

[@davidhamer8333]

Superb explanation and video. Thanks for putting all this together.

[@AEHSvideo]

Thanks, I appreciate your comments.

[@leoa4c]

Beautifully explained!

[@AEHSvideo]

Thank you for your comments.

[@hordboy]

This is great! I’ve always wondered how these things work, in detail. Thanks!

[@AEHSvideo]

Thanks for your comments.

[@DrJaneLuciferian]

A great presentation, thank you. Turbocompounding was actually my next step on learning about radials, so it was good luck to find your channel :^)

[@AEHSvideo]

It seems there is no limit to the complexities of turbo compounding. I suspect a modern hybrid variant would more simply turn a generator rather than feed the power back into the crankshaft.

[@DrJaneLuciferian]

@@AEHSvideo I don't know. There's quite some loss in power conversion, but given modern cad/cam a purely mechanical system could be quite efficient. Looking at the component shapes in your video, and imagining how the forming and machining must have been done at the time, if we were to try and create a modern R-3350TC engine I think a lot more HP is in that design with modern modeling and materials :^)

[@AEHSvideo]

Fun to ponder a modernized TC18, however I can't think of a use for a 4,500 horsepower piston engine that couldn't be met by an existing turboshaft engine (T56).

[@DrJaneLuciferian]

@@AEHSvideo Restomodding classic aircraft; I'd love to build a hotrodded Super Connie ;^)

[@AEHSvideo]

@@DrJaneLuciferian , ironically, Rod Lewis had custom R-3350 engines built up for his VC-121 Bataan. The engines should be TC18's, and they mostly are, except the PRT's have been removed and the exhaust system reconfigured to discharge from the cowling in the same three reliefs that the flight hoods would otherwise occupy.

[@otm646]

Always happy to see you post a new one!

[@AEHSvideo]

Thanks for your comments. Happy is good.

[@Udmudmudm]

È esattamente ciò che desideravo sapere su questo tipo recupero della potenza, hai fatto un ottimo lavoro!

[@AEHSvideo]

Thank you for your positive comments!

[@rolandtamaccio3285]

Our C-119's Flying Boxcars had the PRT' CW 3350 , in the 912 and 913th group . Thank-you for the engineering level report .

[@AEHSvideo]

Thanks for your comments. My understanding is that the C-119E, -F, and -G's flew with the R-3350-85 (Wright designation R-3350 868-TC18DB1).

[@rolandtamaccio3285]

,,, hey , I just put : oil , gas , and ADI in 'em . I called them Curtiss Wright R-3350's , with 3 PRT's .

[@kglesq1]

Absolutely excellent presentation! Thank you!

[@AEHSvideo]

Your positive comments are welcomed, otherwise it is 32 minutes you'll never get back...

[@briansilcox5720]

Superb presentation Tom!

[@AEHSvideo]

Thanks for the positive waves!

[@hu5116]

Great Video! We need more of these kinds of videos to both record and also transfer the knowledge of our forefathers who were incredibly brilliant doing what they did without all the fancy codes and materials we have today. I have long thought that turbo compounding is yet a missed opportunity for increasing efficiency in a progressively green world. What so many of the eco nuts don't understand is that the world is not going to just switch off fossil fuels like a light switch: they show their extreme ignorance and naivety of the real world and the magnitude of the problem when the propose thusly. But if you can increase the efficiency of an engine by just 15% (turbo compound) then you will have reduced the carbon output by more than all the solar and wind in the world combined! Now THAT is GREEN!!! Thanks for this great video!

[@nerd1000ify]

Turbo compounded engines have been used in trucks and so forth, but the complexity and cost has kept them away from passenger cars. You can get the same efficiency benefits other ways, e.g. by running the engine on the "Atkinson cycle" like a lot of hybrid cars do.

[@AEHSvideo]

Thanks for your comments. I believe Volvo still offers a 13 liter turbo compound diesel truck engine, the D13TC.

[@AEHSvideo]

Thanks for your comments.

[@machpodfan]

What a fascinating piece of equipment. I didn't know the units were so dimensionally small, and was thinking automobile, wondering what kind of fluid would be used in the fluid coupling and how it was cooled...engine oil as coupling oil and coolant, of course! Very information-packed video, thanks, really enjoyed it.

[@AEHSvideo]

Thanks for your comments. Yep, engine oil cooled the mechanism; lots and lots of engine oil into the fluid couplings, through them, out of them, around them. The fluid couplings retain a unique smell of carmelized, torched, hard-working oil.

[@FelixUna]

Very informative video

[@tomfey6020]

Thank you for your comments.

[@charlescole-p9v]

It's amazing what they figured out before computers came along. Crazy ! Thanks for putting this together !

[@AEHSvideo]

Thanks for your comments.

[@hoost3056]

Turbo compounding is used now by Detroit Diesel and Volvo/Mack. This has allowed them to drop peak torque down to 900 or so rpm allowing the trucks to cruise at 1100 to 1300 rpms improving the mpg. I've driven old school and downsped trucks, the late model getting 7.9 to 8.3 mpg loaded and driving at 70+ mph.

[@AEHSvideo]

Thank you for that information.

[@stringpicker5468]

A retired Flight Engineer form Qantas Super Constellations told me they were worth about 300HP per engine on takeoff power using 100/130 avgas. He also told me that they were quite unreliable and it was almost normal to loose an engine on a trans Pacific flight from the US to Sydney Australia.

[@cabanford]

The Constellation was the world's best 3 engine airliner ❤

[@AEHSvideo]

Thanks for your comments.

[@Nova-1977]

Well it sounds like why use them when 4 running engines ar much better than 3 running engines.

[@J4CK4LFUL]

Thank you for a great video on this subject! In powerplant school, they barely covered this, which is unfortunate because it really is a very interesting and innovative technology. The solution for an overspeeding turbine is something I'd never heard of until now.

[@jamestamu83]

Excellent presentation. Thanks for sharing. Amazing technology from 75-years ago!

[@AEHSvideo]

I thank you for your comments.

[@dougdanzeisen9608]

Wonderful video that satisfies my curiosity about this technology. So many thanks for writing and posting this! I literally could not stop watching this until completion. Great video and explanation !

[@AEHSvideo]

Thanks for your positive comments.

[@MaurizioLotti-w5s]

Very interesting video!!! Thank you Tom!!!😊

[@AEHSvideo]

I appreciate your comments.

[@Blakearmin]

This was amazing, thank you!

[@AEHSvideo]

Thanks for the positive waves.

[@benjaminschaefer6757]

Excellent and very interesting presentation. Many thanks.

[@AEHSvideo]

Thanks for your comments.

[@johnfowler4264]

Great to see this, Tom - Thanks!

[@AEHSvideo]

Hi John! Thanks for the comments.

[@MarkElkanick]

An excellent presentation. Solid but understandable explanation of the engineering required for a successful design. A lesson for revisiting this concept with today's modern materials, analytical tools, and processes (3D manufacturing).

[@AEHSvideo]

Thanks for your comments. Turbo compounding exists in the present diesel truck engine world; Mack, Volvo, Detroit Diesel. and Scania.

[@rEdf196]

As a kid in the 1970's I frequently saw in flight the Canadian Airforce CP-107 Argus coastal patrol plane, a military variant of the 4 engine Bristol Britannia, The original Proteus jet turboprop engines replaced by the R-3350 redial piston compound engine at 3700 horsepower each for greater fuel efficiency and prolonged flight. I remember the screaming sound of it turbochargers as it flew past sounding almost identical to our Martin Mars water bombers, also powered by the R-3350 (without compound chargers) at 2500 hp each

[@AEHSvideo]

Thank you for your comments. I believe only the R-3350's in the B-29 and B-32 were turbocharged, but all R-3350's had mechanical superchargers. I can't image droning along at low altitude in an Argus for up to 26 hours.

[@rolandcanacolo6870]

II HAVE WORKED ON THE 3350 MARTIN MARS, 2500 horse 18.6 props. you have done a great description of the prt 3350. the F1 of all designs in radial design.

[@AEHSvideo]

Thank you for your generous comments.

[@Steven-p4j]

This has been such a pleasure to watch. Another subscriber.

[@AEHSvideo]

Thanks for your comments.

[@HistoricAeroEngines]

Very informative video Tom. 👍

[@AEHSvideo]

Thanks for your comments. Pretty cool hardware.

[@patrickshaw8595]

Braniff A&P's jokingly called these either "Rotating Mufflers" or "Parts Retention Turbines" (from all the broken valve and valve seat fragments found in destroyed PRTs)

[@sixstringedthing]

And Car Guys complain about it being expensive when they fish a handful of the forbidden metal candy out of their oil pan... I wonder how much it cost to fully recondition a rotating muffler (along with figuring out why the engine was eating its valves)?

[@patrickshaw8595]

@@sixstringedthing These engines had advantages but the more conventional, smaller - but anvil-tough C Series Pratt & Whitney R2800s used on DC-6s are STILL IN REVENUE SERVICE in the more remote parts of the world - notably Alaska. I think some are still firebombing, too not sure.

[@EstorilEm]

I always thought they were “parts recovery turbines” but same difference 😂

[@patrickshaw8595]

@@EstorilEm Yeah I heard that one too! I think it was more common than my version.

[@jimandmandy]

@@patrickshaw8595 Airlines needed range at the time. The DC-7, with this more efficient, but less reliable, engine provided non-stop transcon service that the DC-6 could not.

[@captaintoyota3171]

Man those R 3350s screaming in twilight with flames. Wish i could see carrier ops in ww2 at twilight/night. Tora tora tora is close as an 1980s kid gets

[@AEHSvideo]

Thanks for your comments. If you look around the internet/You Tube you can find period color film of WWII and Korea taken during twilight carrier ops.

[@psmith2234]

I was an early Boomer kid in the Fifties and Sixties while my dad was an airline captain flying DC-3s, DC-4s, and L749 Connies to and within Alaska (Pacific Northern Airlines) and I was supremely fortunate to have had many rides on many of the the old propliners. My family lived a very short commute west of Seattle-Tacoma Airport in a neighborhood that as you might expect housed a lot of airline families. Day and night we were treated to the glorious SOUND of huge radial piston engines during their run-ups and take-offs. I loved those times, and the old prop-jobs. Had that era of flying continued, modern materials science and design would have made those engines even better, but alas, the 707 and the jets to follow brought all that to a quick end. Commercial flying has been a poor, sad shadow of the glory days ever since. Sure, the jets are much faster, much simpler and more efficient, and QUIETER (which was thought to be a plus), but from the time you have walked blindly down the fully enclosed cattle chute from the terminal and into the plane and been led to your seat, the whole experience is BORING.

[@Panuch412]

A topic I greatly wanted explained in detail, thank you for the great information and diagrams! Sub earned!

[@AEHSvideo]

Thank you for the positive comments.

[@tommymac3029]

Me too! New subscriber Anyone know if there a way to buy a complete turbine?

[@AEHSvideo]

Try Vintage Radials, Tehachapi, CA. vintageradials.com/

[@daverooneyca]

Thank you! This was tremendously informative!

[@AEHSvideo]

Thanks for your comments.

[@ivoryjohnson4662]

Awesome presentation this is the first video I have viewed from your channel you got a sub and thumbs up

[@AEHSvideo]

Thanks and we hope to put out a new video content 3x per year.

[@dukecraig2402]

I'm amazed at how many similarities I'm seeing in these assemblies and older Harley engines and transmissions, the siamese exhaust, look at a picture of the stock exhaust system of a 79 Sportster (there's also a few big twin models of that era that have a siamese exhaust, the Superglides if i remember correctly), the whirl dampener assembly looks almost exactly like the clutch assembly of the 57 to 70 (ish) Sportster, the staked screws are just like the staked screws of the 4 speed era big twin alternator screws. As far as automobile similarities goes the fluid coupler is basically the torque converter of a typical automatic transmission, a GM Turbohydramatic being a good example of that, also those fluid couplers are basically the same as those in the later variants of the F4U Corsair's variable speed supercharger, the original supercharger on them had the classic 2 stage 2 speed (which actually had 3 ranges, neutral, low and high blower), they however had the issue of having to reduce throttle to keep from overboosting the engine when shifting into a higher range, this gave the engine's power rating an "up and down" effect when climbing to higher altitudes and shifting the supercharger through it's ranges, the larer fluid coupled 2nd stage eliminated that as the pilot could just keep inching the boost lever a little more at a time while climbing to keep at max power, quite like the Army's turbo/supercharger arrangement where they could continuously inch the boost lever forward while climbing which closes the waste gates more and more diverting more exhaust to the turbo spinning it faster and faster to compensate for the ever decreasing air density, I've read where the fluid coupled 2nd stage of those superchargers sapped more power driving them than the 2 speed supercharger but being able to maintain max power and not having to shift and have the ups and downs in power was considered a better way of doing it, it was more pilot friendly so to speek reducing their work load so the loss of peak power from driving the fluid coupler was worth it. Also, Wright may have released their version of turbo compounding and patented it after the war in 1947 but during the war Allison ran the first turbo compounded engine, the Army had them work on the design and they had a V1710 with the system on it, it didn't fly in anything and was just bench run but they did indeed have a running engine with it.

[@AEHSvideo]

Thanks for your comments. The supercharger on the Daimler-Benz used in the majority of Bf-109's was driven by a variable-speed fluid coupling, so the fluid coupling technology had been around for some time. Development work on the Allison V-1710-E22 turbo compound engine began in 1944. I don't believe it used a fluid coupling between the power recovery turbine and the crankshaft. www.enginehistory.org/Piston/Allison/V-1710TC/V-1710TC.shtml

[@dukecraig2402]

@@AEHSvideo Oh I see, it's the fluid coupled part that Wright came up with, I thought it was the turbo compounding itself being credited to them. And yes, hydro coupling had been around even before the 109 had it I believe, I think earlier than that someone had fluid coupled wheels as a concept in the automotive world that never saw production. And wow, that was freaky looking at some of those designs that looked just like pages from old Harley service manuals, especially the one that looks like the old Sportster clutch assembly, you could substitute that picture for the one in the Harley service manual and most people would never notice.

[@whathasxgottodowithit3919.]

Thank for posting, that is great explanation of the Wright Turo Compounding System, you almost get something for nothing. The large air transport Piston engines had really reached its zenith by this time, and had become very complicated, (Just Look At The Power Recovery System On Its Own) the early 1950s saw the development of large Gas Turbine engines. However we can still see the large Radial powered transports soldiering on for many years.

[@AEHSvideo]

Thanks for your comments. Wiki tells me the EC-121's served in the USAF until 1978 while the USN finally retired their's in 1982.

[@1crazypj]

I was a motorcycle mechanic but always read everything I could find on piston engines, particularly after Suzuki used oil squirters in 1984 GSX-R motor to cool underside of piston crown and the publicity blurb stated it was from aircraft design (although they didn't mention 1930's aircraft) I even bought Herschel Smith book to find out how radial engines were constructed as I had no idea (as only inline fours or V-twins were in multi cylinder bikes back then)

[@AEHSvideo]

The Herschell Smith book was one of the first engine books I owned. Bill Gunston published a number of excellent books on engines, and books by Graham White, Kim McCutcheon, and Dan Whitney really explain the details of the big piston engines of aviation.

[@1crazypj]

@@AEHSvideo I bought a Bill Gunson book few years later, it's real interesting particularly some of the history (first 'tuned length' exhaust system - 1800's!) Thanks for reply.

[@AEHSvideo]

@1crazypj , so many smart people back in the day!

[@stewartalbert3523]

The RC 121 D Connie radar recon planes that i worked on in the 1960s had this system , i was a com/nav tech so my understanding of the system was very basic , good to see this very excellent description of the system .

[@AEHSvideo]

Thanks for your comments.

[@garyhooper1820]

Excellent explanation of this device ,

[@AEHSvideo]

Thanks for your positive comments.

[@michaelblacktree]

I clicked on this, just to see what a PRT is. Excellent explanation. Thanks!

[@AEHSvideo]

Thanks for your comments.

[@andyharman3022]

30:35 Just so you all won't have to search for it, here is the takeoff video of a Conny with all four TC18's at takeoff power, shooting flames out of the flight hoods. Glorious.

[@nilsthemis]

Very concise and interesting video

[@AEHSvideo]

My first "concise" review; thanks for that.

[@soodonym]

Thank you very much. I enjoyed that immensely!

[@AEHSvideo]

Thank you for your comments.

[@bkailua1224]

I flew airliners for over 30 years and 6 of those on the DC 6. In 28 years I never had a turbine engine failure. In six years I had over 50 engine shutdowns on the R2800.

[@AEHSvideo]

Thank you for your comments. Progress is wonderful thing.

[@shcchristensen]

Great job Tom!

[@AEHSvideo]

Thank you for your comments.

[@fascistpedant758]

Great description and images. Thanks. Happy 2025!

[@AEHSvideo]

Thanks for your comments.

[@hunterflorez]

simply amazing engineering!

[@ianaristotlethompson4186]

Thanks for a brilliant explanation.

[@AEHSvideo]

Thanks for your comments.

[@carltauber2939]

Superb presentation, Thank you.

[@AEHSvideo]

Glad you found it of value.

[@carltauber2939]

@@AEHSvideo I'm old enough to have crossed the equator in a DC-7 with these engines.

[@chuckmorris7043]

I was air crew on Lockheed P2 patrol planes during Vietnam and have a bunch of hours, being carried by these turbo compound engines.

[@warrenjones744]

Pretty clever engineering. I can only imagine the hours that were put into that system to make it work and live. Great explanation and the Connie at. the end was a nice addition.

[@AEHSvideo]

Thanks for your comments.

[@jamesgeorge4874]

Great Vid, you earned my subscription. I've been fascinated by aero piston engines since childhood, and am a 35 year veteran auto technician by trade. I've thought for years that adding a turbo compounding unit that drove a generator, to the exhaust of a hybrid gasoline engine would also be worth looking at, especially one that uses a velocity driven turbine, as it would not restrict exhaust in an Atkison cycle engine.

[@AEHSvideo]

Thanks for your comments. I'm not sure automotive engines move enough air at typical part-thrrottle operation to make turbo compounding worthwhile. Trucks are a different matter and Mack, Volvo, and others manufacture turbo compound truck engines.

[@GerardBlake-qw7wi]

Excellent presentation Tom.

[@AEHSvideo]

Hi Gerry! Thanks for your comments.

[@Kubla84]

great video, my father flew these engines early in his airforce career, it is a shame that I will never get to ride on an airplane powered by one of these engines

[@AEHSvideo]

Thanks for your comments.

[@williamcarnero9595]

Epic video, new subscriber and glad to have found this channel. Back when I first heard of a PRT there were almost no videos of it on KZbin years ago detailing how they worked. Would like to see some more jet engine content aswell as it comes down the pipeline

[@AEHSvideo]

Thanks for your comments.

[@P61guy61]

Thanks for sharing this.

[@AEHSvideo]

Thanks for your comments.

[@TucanoTmk1]

Very Good Detailed info well done,All Done By People With a Drawing Board and Pencils No Computers or CNC To make the Parts. People Were More able to Do Amazing Things in the Past.

[@FrisoGorter]

@12:20 Split vanes are used to make better use of the energy produced by the exhaust pulses. Even at full-chat, running at constant RPM, there remain distinct pulses in the exhaust flow from the overlap in timing of the exhaust cycles.

[@AEHSvideo]

Thank you for that information. Do you have any information on how the split vane performs the improvement function?

[@KallePihlajasaari]

Never heard of this technology but not at all surprised that it was implemented. Lovely video. I hazard a guess that the split vanes may have been a concession to uneven thermally generated expansion that caused some vanes to crack as they were all trapped between the inner and outer ring, adding the split would have let the ring flex a little with uneven expansion as it was only constrained at three points between the inlet zones. Sort of the same deal as putting an "S-bend" in a cast iron flywheel to improve casting yield by eliminating stiff straight spokes that are forced to split the rim or spoke on cooling. Would this PRT system have provided some measure of muffler action to the engine? Combining the 6 cylinders and slicing and dicing the gas flow through the turbine should have reduced the exhaust pulses and gas velocity somewhat. Also perhaps some thermodynamics junkie can speculate on whether the exhaust gases would have cooled down noticeably from just the impulse turbine that must still have slowed the gas flow even if there was no marked pressure change. Obviously the cooling air bypass would have added something but it would have been a small fraction of the exhaust gas flow and probably already warm from the compressed air source. It is quite clear that everything was working near the limits of available material heat resistance and wondered if the whole thing would start to glow a dull red at full load after a while. I see the PRT as an inverse supercharger that gives back some exhaust gas flow momentum as crankshaft torque in a similar way to the supercharger providing intake air pressure boost in exchange for some crankshaft torque.

[@ilyazhorov2964]

Great video !!!

[@oscar_charlie]

Interesting presentation. Great job conveying all that information! I am a bit surprised that there was no discussion on the reliability of the system.

[@AEHSvideo]

The detailed history of the TC18 in commercial service is complicated, bumpy, inconsistent across operators, and not easily packaged into the current video. The early versions, particularly the "DA" series of the TC18 had numerous serviceability problems, many, but not all, were related to the PRT system. The later versions, the "EA" series, was greatly improved and when operated by the book served well for decades in the EC-121 and P2V aircraft. TC18's in the commercial world were pushed quite hard in a vain effort to "keep up" with the new turbojet aircraft.

[@DavidAndruczyk]

This was great! Thank you!

[@AEHSvideo]

Thank you for your comment.

[@barryduff5058]

Thanks for this. I've been curious about R3350s since I 1st learned of them during 1 of the Avolon Air shows here in Victoria Australia back in 1997. A few trucks from Scania & Volvo have also used Turbo compounding over the years, but I understand it fell out of favour due to the extra weight & completely it brought with it

[@AEHSvideo]

Mack trucks in the USA currently offers the MP8HE diesel TC engine in some of their vehicles. www.macktrucks.com/powertrain-and-suspensions/engines/mp8he/

[@gertjevanpoppel7270]

Thank you for the great explanation and beautiful foto's 😀👍

[@AEHSvideo]

Thanks for your comments.

[@nerd1000ify]

I think there might be a mixup with the nomenclature on impulse vs reaction turbines. My understanding has always been that impulse turbines have no pressure drop across the rotor, as is seen in the PRT design.

[@AEHSvideo]

Oh, man, I really stepped in it! Thank you and you are correct. I have incorrect labelling on the Power Recovery Systems slide at 4:05, an uncaught vestige from an earlier version. The Wright PRT is indeed an impulse design.

[@krakhedd]

All designed & engineered w/o the use of computers too. Absolutely mind-boggling. I knew about this system & understood its general design, but diving into the details in this video gave me a whole new appreciation for what was the pinnacle of 1950s reciprocating engine technology in aircraft Tangent: is there any point to these nowadays, or are the cost & engineering simply too much to make sense?

[@Mishn0]

I expect that there is a minimum size to the system below which it isn't practical. It's probably a fairly large minimum size and would only make sense then for long-range performance where the cost of the system would be economically worth while. I don't think a racing application would make sense. Do large locomotive engines use any type of power recovery? I think the big maritime diesels probably turn too slow to work with PRT.

[@firstielasty1162]

There is, or has been recently, a large truck that does this on the diesel. I don't know the details, or if it is still made. I think it was a brand sold mainly in Europe, probably MAN, maybe Scania.

[@1776vtgmb]

Great video! Different kind of turbo...

[@AEHSvideo]

Thanks for your comments. The PRT is a wonderment.

[@cycadence2577]

Nicely done!!!!

[@AEHSvideo]

Thanks for your comments.

[@ncktbs]

VERY WELL DONE thank you and keep it up it you can

[@AEHSvideo]

Thank you for your comments.

[@PSG159er]

This is very well put together. So much information pack in this presentation. Well done sir. Hey, do you think I can put on my resume that I understand the basic fundamentals of a PRT?

[@AEHSvideo]

Thanks for your comments and your Certificate of Understanding has been issued.

[@PSG159er]

@@AEHSvideofantastic!

[@keithjurena9319]

Awesome presentation! I suppose flames from the flight hood are from rich mixture meeting the heated turbine air.

[@AEHSvideo]

Thanks for your comments. The glorious flames occur from unburned fuel from rich-mixture high power settings in the exhaust stream through the PRT turbine wheel meeting a new source of fresh oxygen (the turbine cooling air emanating from the cooling cap).

[@jiyushugi1085]

Epic!

[@AEHSvideo]

Thanks for your comments.

[@n6mz]

Thanks for the outstanding presentation! I bought a copy of that excellent little booklet written by, I believe, American Airlines describing their experience operating the TC18. Like a fool I lost it somehow. Does anyone have a PDF of it?

[@AEHSvideo]

Thank you for your comments. Is the booklet you refer to listed in the references?

[@n6mz]

@@AEHSvideo Not sure why my reply disappeared but the booklet was not written by AA it was from Curtiss Wright entitled "Basic Theory of Operation Turbo Compound Engine." The cover has blue and yellow background and shows a sketch of an FE's console and a photo of the TC18. I found a pdf of it on a web site but they wanted me to create a pay account to get "30 days of free downloads." No thanks. I don't see it in the references. Keep up the great work!

[@AEHSvideo]

@@n6mz , send me an email [e-mail]

[@clydecessna737]

Thank you.

[@AEHSvideo]

Thanks for your comment. All fun for me.

[@greghanson5696]

Great presentation! I thoroughly enjoyed it.

[@AEHSvideo]

Thank you for your comments.

[@AlexPintilecu]

You got a new subscriber.... From what i researched myself, volvo trucks(i-save) use a very similar compound exhaust recovery for their engines, should save 3-4%fuel in regular operation

[@AEHSvideo]

Thanks for your comments. Yes, Volvo and Mack, and previously Scania, have turbo compound diesel truck engines.