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.

Awesome.

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

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

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

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

A different engine illustrates how difficult this was. GE were contracted to make turbo chargers and compound turbines for the Alison V1710 used in Mustang 1 Kittyhawk etc. they really struggled and in the end only the Lightning ever got a usable turbo system with that engine. And that was built around the engines.

EXCELLENT

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.

Great channel for us nerds, thank you got making these videos, i know its a lot of work

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.

What is the "Dumping loss across exhaust valve" at 5:23 consist of? Isenthalpic pressure losses?

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.

The curtis wright PRT had the disadvantage of being very small, so it could be crammed into a small space. The Allison-V12-1710 prototype power recovery turbine, gained 1000hp from the base 1500 hp output of the V12 piston engine. Which is a much higher gain, and efficiency. Furthermore, the Napier Nomad PRT, also featured a full size blown down turbine like the Allison, to get very high fuel efficiency. With our modern gas turbine designs, we can very likely get higher gains and/or much smaller packaging . As with existing piston engines with turbochargers, there is a lot of improvement that can be achieved with ceramic coatings and insulation to channel more heat energy to the exhaust turbine.

To recover heat energy wasted, incorporating Stirling Engine could have added more power.

Thanks for the wonderful presentation. Contra-propulsors are of interest to our development of the low cost, personal, door-to-door PersonalJet VTOL system

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

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

Always happy to see you post a new one!

It would be interesting to know the development history of the PRT. Did they build a series of test mules and refine the design through trial & error? A lot of practical engineering on display in this video all accomplished with slide rules.

never though it used whats essentially a torque converter for an automatic transmission, to connect it to the engine. Big Brained engineering right there.

Great job Tom!

Your inclusion of Chilton's patent is interesting but you may or may not be aware of Wilton Lundquist's multiple patents relating to the turbo-compound engine, e.g. USP# 2,625,006A, etc, etc. You will, of course, know who Lundquist is.

This turbo is already a thing. Dang late to the table again.

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.

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?

simply amazing engineering!

It's interesting that from our viewpoint in 2025, it's a jet engine with an overly-complex combustor.

Great video !!!

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.

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.

Excellent presentation Tom.

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

Sorry if you answer this in the video, but I am pausing it half way through to watch the rest later and am curious. I have seen a couple of things about these prop fan engines, but what is the difference between a propfan and a turboprop? They seem like the same thing to myself (though I am not very knowledgeable on the subject).

Now my brain is thinking. Scale this for a Duramax LBZ. Make appropriate alterations to design.

Wow! Incredible video, excellent work! I have done a lot of read and research on the history of these motors and still learned a bunch and you also provided a lot of never before seen (by me) photographs. That DB603 fitted with its annular radiator is STUNNING. Thank you for the video brotherman. ❤

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.

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.

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

Absolutely excellent presentation! Thank you!

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. 👍

And they figured all this stuff out in the 1940s.

Great to see this, Tom - Thanks!

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

really neat presentation. very informative and immaculately paced.

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

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

CASE/cummins does this on current 4WD big tractors with the ISX motors

all i can think of is how this isnt being used to make better turbo hot sides

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?