In doing research for a few of my aircraft builds I keep running across the term “turbo-supercharger” . Being primarily a car guy I kow what a turbocharger is, and I also know what a supercharger is. What is this “turbo-supercharger” ? I see it mostly refering to Allison engines, particularly in a P-38. I have built an Allison 1710 in 1/25 scale and know where the supercharger is and I also know that it was an option that wasn’t always used. Was there a turbocharged version available also and the term is used to indicate either of these engines or does the writer no have a clue ? I have never seen both power adding devices used on the same engine, the boost produced by the supercharger would almost certainly hold the wastegate on the turbocharger open and render it ineffective at best. If anyone knows what the deal is here do tell, this really irks me.
The term “Turbocharger” is a shortened version of " turbo-supercharger." The Allison used in the P-38 had both a regular mechanical supercharger, plus the exhaust driven supercharger.
The P-38s that were ordered by the British before we got into WW-II were specified to be without the turbo supechargers. They felt that most of the aerial combat would be below 20,000 feet and they would not be of any benefit for the extra weight and maintenance headaches. They also specified that both engines operate counter-clockwise when viewed from the front. These two changes made their P-38s into real dogs. All USAAF P-38s had the turbo supercharges and the #1 or port engine operated clockwise so the torque of the two engines cancelled each other.
I am not sure of the technical definition of turbo chargers versus superchargers, but on the P-38, the exhaust gases were routed from the engine to the TSC where they were combined with ambiant air, compressed and returned to the carburetor. The TSC was located enough distance from the engine itself that I don’t think it would be possible to have a direct mechanical linkage for the engine to drive the TSC. This would be especially true in the P-47 where the TSC was in the aft fuselage behind the cockpit.
I think the terms, “supercharger, turbocharger and turbo supercharger” were used interchangeably, even though this is not correct from a mechanical standpoint.
Darwin, O.F. [alien]
Ok. Here goes (from a formerly ASE-certified auto mechanic): A SUPERcharger is a MECHANICALLY-driven air compressor used to compress (and hence, supercharge) the incoming air for an engine, to give it more power. A TURBOcharger is an air compressor that is driven by the exhaust gases of an engine blowing across an exhaust turbine (which is conected via a shaft to the compressor section) to perform the same function. On older aircraft, these two items were mechanically coupled to significantly boost the power output of an engine. They were used on radials as well as V-type reciprocating engines. The output of the turbocharger part of a turbosupercharger was usually used to help drive the supercharger, which was also gear-driven by the engine’s crankshaft, albeit with a gear ratio that could either increase or decrease the supercharger’s RPM relative to the engine’s. The turbosuperchagers could be either single-stage or two-stage (selected either automatically, or manually by the pilot), although I’m not sure how that function worked. There are automotive engines with a similar set-up in the world today, although they probably would bear no resemblance to what you would see on an aircraft engine. Hope this helps.
Whooooooosh< That was the sound of this info going right over my head… I’m no mechanic… but I know those old birds sound good in flight.[D)]
Okay, so there really was a setup where a mechanically (gears or belts) driven supercharger was used together with an exhaust driven turbocharger. Thats all I really wanted to know, I’ll go look up how it was all hooked up later. From my car experience that just didn’t seem possible.
The key here is air. How to drive it into the engine under pressure at altitude to compensate for thinner air (less O2) above 10,000 feet. The turbo function (exhaust pressure) helped drive the compressor, but you need the supercharger function to gather and compress air for combustion. Hence the “turbo-supercharger”. Two stage models were used to prolong engine life. At medium altitude, where the full effect was not needed, the O2 sensor in the intake would regulate the Turbo function and bleed in regulated amounts of exhaust pressure to acheive performance at a high throttle and mixture setting. This was automatic, based on the pilot input on the throttle and mixture. Above a certain altitude, when high performance was required, again automatically, all waste gates would close and the full exhaust pressure and fresh air intake pressure would be utilized to feed the cylinders with pressurized, dense air, thereby promoting the most efficient combustion, replicating what the engine would be breathing at lower altitudes. The difference between a non-supercharged Allison, Merlin, or Wright Cyclone and supercharged versions meant that aircraft could acheive maximum ceiling and perform adequately at these extreme altitudes, The down side was more engine fatigue and greater maintenence issues.
Being and A & P Mechanic, the simple way to put it is how Dogsbody put it,
the term of Supercharging is forcing air into the intake manifold or carburator,
a Supercharger is a impeller that is mechanically linked to the crank shaft by means of a belt or direct link
Turbo-Supercharger is an impeller driven by hot exhaust gases passing through a turbine,
also there is another type of power assisting used,
turbo power assist it’s using just the turbine section of the turbocharger but is directly linked to the crank shaft by means of a torque converter, thia system was used on the Lockheed Connie, Fairchild Flying Boxcar
72cuda,
I’m well familiar with power return turbines. I spent some time flying Willie Victors
(Lockheed EC-121M Warning Star) while in the Navy. We used Turbo-compound
R-3350 engines with 3 exhaust driven power return turbines connected to the
engine’s crankshaft. We also had 2 speed engine driven superchargers.
Ray
Well, you learn something new every day. Thanks everybody for answering, thats really interesting.