Wright R-3350 Power Recovery Turbine

All right, welcome back. We're going to have a different discussion about a different engine today. So we're going to talk about turbo compounding, specifically the power recovery turbine that was used on the Wright R3350. So right now we're looking at the back half of a Wright R3350. This particular engine is on display at the Museum of Aviation at Robbins Air Force Base. So if you look at the big opening there, that is the exhaust for the power recovery turbine. This particular system is different from a regular turbo supercharging system in that a turbo supercharger drives a compressor that increases the pressure of the air that's delivered to the cylinders for boost and horsepower. In a turbo compounding system, the heat in the exhaust gas is extracted by a turbine wheel that is mechanically linked to the crankshaft and it provides additional horsepower. Now by virtue of the way the system works, it does not decrease fuel consumption of an engine, but it does increase specific fuel consumption, meaning you get more horsepower per unit of fuel that is used. So it's a neat system and it does add efficiency and complexity to an engine. So what we're looking at here, this is a different engine, it's still a cutaway, but this particular engine, it's an R3350 on display at the National Naval Aviation Museum in Pensacola. Now what we're looking at here, there's the cutaway, you can see the turbine wheel, and that turbine wheel is attached to a shaft that, you know, is directed radially inward toward the crankshaft. And I've got a bit I'm going to show here in just a little bit that kind of explains this in more detail, but for intensive purposes here, you can see the turbine shaft, or you can see the turbine wheel, and there's a couple of fluid couplings that are visible as well as the supercharger and some other things. All right, so here we have the service instruction manual for the R3350, several models that pertain to this particular book. This is an old NAVWEPS manual, so this is Bureau of Naval Weapons, but what I've got is our power recovery turbine. So I think this is a really good illustration for how the system works. So these are actually your power recovery turbines. Exhaust is up here, but there's also a cooling shroud around that. So cooling air comes in here, goes through this entire manifold to help cool all the components, and then your exhaust inlets are here. This is basically that manifold to drive your power recovery turbine. Now this shaft runs down the length. There's several variants of this. I don't recall if this is the new one or if this is. This is the newer one. It's essentially a through bolt configuration as opposed to the older design. This one's the original one. I don't know if it has a coupling in it. In any case, so this shaft is actually what transmits the power down to this end here, which 14, this is our gear shaft. So this is what is referred to as our PRT bevel gear. So now that we've seen how the power recovery turbine itself is manufactured or built together, now we can look at the output end of that. So the output end of that is the power recovery turbine bevel drive gear, what's labeled here. That gear is mechanically linked to the power recovery turbine bevel driven gear. Now the bevel driven gear goes through the fluid coupling rear half. It's a concentric shaft on the inside. It goes all the way through to the front of the fluid coupling. Now the fluid coupling is now driven by that bevel driven gear, and it actually uses engine oil as a means. It's the medium to transfer energy. So in this case, the front half of this fluid coupling is also like a little turbine. And when it turns, it forces oil rearward. And behind that is yet another turbine called a runner. And that's mechanically independent of the front half, but you know, just the fluid pressure itself is what turns it. Now the fluid coupling rear half pinion gear is connected to this turbine. So when it spins, it turns the rear half pinion gear, and that is mechanically connected to the power recovery turbine crankshaft drive gear. And that's where the horsepower is actually, you know, returned back to the crankshaft. Now it's not necessarily an overly complicated system in terms of its design, you know, producing and making it work, completely different story. It took a lot of engineering, a lot of time, and you know, a lot of hard work by a lot of good people to get the system reliable enough that it could be used, you know, on commercial aircraft as it was, you know, into the 1950s. So in any case, it's a really cool system. You know, I find it really fascinating. I hope you've enjoyed learning something about it. And, you know, if anyone has any ideas for other topics, you know, I'd be happy to do those. So just let me know in the comments.