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Turbo or mechanical supercharger?

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Frank N. O.:
Now, orignally the term supercharger covers any form of compressor before the pistons in a piston-engine, or wankel rotary for that matter, but in modern days at least in automotive circles supercharger specifically means the mechanical type and turbo means the exhuast-turbine driven version, named turbonormalizer in aviation right? For the P-38 (the Tomcat of WW2 at least in terms of size and impressive looks in the air) was said to be supercharged, is that the mechanical form or the turbo, and in general, what are the pros and cons for mechanical vs exhuast-driven compressors for aviation piston engines?
For a car then a mechanical compressor, especially the twin-screw type is very good for low power-use and high low-end torque with no need for wastegates or modified pistons but a plane-engine doesn't need low-end acceleration ability like that so is that why in current times I've only heard of turbocharged engines?

I hope the question is good enough to be here otherwise feel free to remove it.
Frank

Gulfstream Driver:
I'm not an expert in engine design, so feel free to correct me if I'm wrong.  I know that superchargers are heavy and sap engine power because they're mechanically driven.  Turbochargers are lighter and therefore better for light planes.  I think superchargers are used on some larger airplanes, like the old warbirds, that need the extra power.

I'm not sure what the P-38 had...

Excellent question, btw. 

fireflyr:
Yes, it's a good question,

I'm not sure why but superchargers were used on most WWII aircraft including the P-38, I suspect that's because they were superior to exhaust turbine technology at that time.   Superchargers are still used for drag racing, for instance, because of the need for rapid throttle response as the turbocharger is slow to spool up.

Some very large engines like the 4350 compounds (used in the Super Constellations) had superchargers for manifold pressure  boost AND turbochargers that were geared  to the propellers to utilize waste gasses for thrust.  These were very complex, high maintenance engines and problems were common, especially fires.

Maybe some of our engineer brethren can cast more light on the subject.

Roland:
Frank, slowly but surely you become a technical expert. I can watch it clearly. While posting your question, which is valid since introduction of turbochargers not only in aviation, you’ve answered it already.

“For a car then a mechanical compressor, especially the twin-screw type is very good for low power-use and high low-end torque with no need for waste-gates or modified pistons but a plane-engine doesn't need low-end acceleration ability …”

See your answer? In planes wee need nominal engine speeds to drive the propeller at its best aerodynamic rate. A propeller has to:

* accelerate the aircraft from zero to take-off speed in the shortest possible time (keeps runways short) and

* keep the aircraft in the air by pulling it through this element at, again, the best aerodynamic rate of the wing and the propeller.
*
* [/list]
So you will find that there are only a few speed and power rates necessary, but this few rates you try to have at their best, most economical and so on. With all this in mind constructors come out with the exhaust gas driven turbocharger. And there is no gear-shifting, too!

There are a few engines around with geared turbo chargers like the Lycoming GTIO 540 or so. “G” stand for geared (turbocharger), “T” for turbocharged, “I” for injection, “O” for opposite piston arrangement. Again they are quite rare.

Sleek-Jet:

--- Quote from: Roland on March 15, 2006, 08:22:16 AM ---There are a few engines around with geared turbo chargers like the Lycoming GTIO 540 or so. “G” stand for geared (turbocharger), “T” for turbocharged, “I” for injection, “O” for opposite piston arrangement. Again they are quite rare.


--- End quote ---

To my knowlege, the "G" stands for a gear reduction propellar drive.  GTSIO-520 and GTIO-540 really arean't all that rare.  There are still quite a few 421's, 404's, Pressurized Navajo's and Aero Commanders running around that have these hanging off the firewalls.  Continental uses the "TS" to represent turbo-supercharged. Lycoming uses the simple "T".

Frank, a Turbonormalized engine is one that doesn't surpass a sea level manifold pressure.  The exhuast driven turbo charger is rigged to maintain no more than 31 inches of manifold pressure.  Though it can provide that manifold pressure at high altitudes.  This allows the engine to operate a sea level power ratings as altitude increases.

A Turbo-supercharged engine has a turbocharger rigged to "over boost" sea level pressure.  They will be set up to provide 40, 50, or even 60 inches of manifold pressure.  Some of the WWII vintage radials and V12's had  manifold pressure red lines upward of 120 inches or more of pressure.  Of course, on todays fuels, the engine would destroy itself with detonation, but it's intersting to know they were designed for this kind of power.

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