Latest Video, DC-7

I bit late to the party. I worked on the RareBear Bearcat unlimited racer in the late '80's. Dave Cornell was the crew chief and a great self taught engineer who delved deep into all things 3350. He assembled bits from various 3350 versions. The basic engine is a late turbocompound version with the PRT's removed. As I recall we estimated the PRT's were net about 80% efficient at recovering exhaust energy to put into the crankshaft and then into the propeller. We were doing speeds over 540 mph, 500 mph on the pylon course and over Mach .7 straight and level. Because of the high airspeed the propulsive efficiency of just squirting the exhaust back for jet thrust was as effective as the PRT's given that we were in the bad corner of the envelope for propeller efficiency of high power and high helical tip speeds above Mach .9 (hence the foray into the 3 P3 Orion prop blades). I recall we were down to around 75% prop efficiency, so net propulsive efficiency was about 75% x80% = 60% if we used the PRT's. A very different proposition than a Constellation at takeoff or 300 mph cruising. We tailored the exhaust pipe nozzle exit areas to maximize total combined propeller and exhaust thrust and this did result in some excess back pressure on the engine reducing power to the propeller. I recall we were estimating that a little over 20% of thrust was coming from the exhaust. It also saved the weight, space, reliability issues of the PRT's and reduced the serious destabilizing effects of the propeller pulling lots of power. The backpressure isn't as great a power loss as one would think, as while the exhaust is blowing down at high pressure it is supersonic flow through the exhaust valve, and the pistons don't actually see any higher pressure until blowdown is nearly complete and the piston is on the upstroke (the pressure inside the cylinder is independent of the exhaust pipe pressure until the ratio of pressures drops below 1.9).

Hi Sean, yes, it's quite similar in principle.

Power recovery turbines are a lost piece of technology that is now kinda new since you made a video about it. Does the F1 MGU-H exhaust energy recovery system work off of the same principles?

The Air Zoo in Kalamazoo Mi (the old section across the old apron) has a great collection of aviation hodge podge including a cutaway of the Wright Cyclone. Many other fantastic exhibits also. Ask one of docents about the old building.(I hope it's still there). Great place to visit.

This was a video in your best style/format! The one that makes you unique! Packed with information I didn’t know about beforehand, great explanations and illustrated with primary source material.

It's hard to believe that turbo-compound turbine doesn't produce back pressure, but it obviously worked. Interesting technology. You may be aware that in 1970 Clay Lacy raced a DC-7 (!) in the California 1000 air race. https://youtu.be/vi3H8sbf28s

I can't add much to what’s been said above, I agree with everyone. Your channel always interests me with great technical content told competently with REAL DATA. Throw in those beautiful prop airliners of that era and the turbo-compound subject which I’ve only ever heard mentioned, and I’m hooked.

I do remember reading about the turbo compound engines in the brochure about the engine. It was in the middle 50's. I was about 10-12 years old. I did enjoy the video but would have been interested in knowing how much lower the fuel burn was per hour with the turbo compound engine in the DC7. Also the effect of altitude on the output of the recovery turbine due to the reduced air pressure and the higher resulting exhaust velocity.

When I was a child I flew to Europe on a "Super G Constellation" according to the flight attendants. NY to Gander to Shannon to Frankfurt to Milan our destination on TWA. It was a LONG ride.

I can't speak for anyone else, but for me this was your most interesting video in a quite a while, and I was looking forward to it as soon as you mentioned the topic. The technically and propulsion oriented videos are always my favourites, and I think that old video about supercharging/turbocharging in WW2 airplanes was the first one I watched. Forced induction systems are so central to high performance piston aircraft engines and these systems seem to be an area your videos are particularly at home in (and turbo-compounding is very related to forced induction). I've also been very interest in turbo-compound systems since I first learned about them and the Wright power recovery turbines were a bit of a hole in my knowledge that I wanted to fill anyway since I'm more familiar with the Napier Nomad. I have a suspicion that this may have less to do with the quality of the video than it does with timing though. Youtube will just sometimes pick a certain video it wants to push to everyone for a while, and this video is on a topic which hasn't really been touched on by other youtubers. I think maybe you just happened to pick exactly the right moment to post a video that diverges a little from your most recent ones at a time when your channel is just big enough for the algorithm to say "Yes, everyone needs to learn about turbo-compounding this week."

When you're dealing with niche audiences - folks who might view something like "What's trending" as a useful guide on what to AVOID - it's hard to say what will make their trending lists. It's reminiscent of pre-browser Internet. Now THAT was a universe of folks NOT in the mainstream 😂 But I digress. I enjoyed it because, as others have noted, it made an obscure and highly technical topic very accessible to me. I'm the sort that wouldn't even perform an owner-assisted annual. Or, as I liked to put it, me with a wrench in my hands should be a felony! Of course, my major initial takeaway was horror at the *possibility* that you might never have read Earnest K. Gann 🥺

You have developed a refined skill set for story telling. I think the videos benefit from that as much as the technical content. This latest video took an amusing, meandering path toward a well chosen topic.

Congratulations Greg, an achievement well earned!

It's b/c it's an excellent video 👌👌 Great details 🤠🤠

Agree with the above comments. Well researched technical content is why I am always excited to see a new video from yourself. Long may it continue and, once again, so many thanks for this.

The reason is actually pretty simple, it is because you are making reasonably technical information about stuff that you cannot find anywhere else. If you were to take this topic and break it into a multi-video format like the P-47 series, you would have a series of winners. A good contrast is the video you did on the sleeve valve motor, you did a shallow overview on that and it probably did poorly. There is an endless list of shallow content on you tube, what is missing are videos of a topic that will go into some detail on a topic. A list of winning content is in the book “The Secret Horsepower Race: Western Front Fighter Engine Development” by Calume Douglas. It will give you a several topics that are waiting to be expanded on in detail. An example would be the oil delivery system of the German engines, this could be an excellent video in the specific engine series.

I think your audience (me) is very technically oriented. The the only way I can describe the engineers and designers of the era between about 1850 and 1960 is sheer competence. If it could be thought of, it could be designed, if it could be designed, it was built and tested. Compared to the computer assisted overly profit driven companies of today these people were true pioneers. As much as I enjoy the world war II aviation technology, I think what happened before and immediately after the war with piston engines is by far some of the most interesting aeronautical technology ever created.