[T}{OR]

Originally Posted by koivis

You have to remember that the first turboprops and turbojets were considerably less fuel efficient than the turbo-compounds, and for the same power, while the TC probably weighed twice (or more) as much, it still burned much less fuel. That's why Canadair Argus changed to R-3350 TC from Bristol Proteus, and why the big piston airliners (Starliner, DC-7) soldiered on for so long. It was the weight and complexity that killed them, and the more advanced (two-spool) or larger (Kuznetsov NK-12!) turboprops in development.

Very interesting stuff, I agree.

Indeed early Turbos were indeed heavy. Last month I was in BMW's Museum in Munich - the comparison in size between F1 turbochargers back in '70s and today is astonishing. Today you can basically just 'attach' it to the exhaust manifold lol.

Originally Posted by Azimech

Thor, the reason the carburettor was placed on top of the supercharger in allied engines was that it increased the efficiency of the supercharger due to the cooling of the air due to vaporisation of the fuel. This was the main reason Rolls Royce chose the carb over fuel injection, because they considered it. On big radials the supercharger has the bonus of better distribution of the mixture to the cilinders.

For fun you should see diagrams of the oil distribution system in big radials, it looks like spaghetti XD

It really did look to me as if there was a bonus of better mixture distribution (on the P&W R-2800) if you put another compressor behind the Carburetor. I forgot about the fuel vaporisation.

LOL, a proper spaghetti indeed. Reminds me of the cross section of an automatic gearbox.

Originally Posted by swiss

Now it's really getting confusing.
That SC in pics of the p47 engine looks like it's driven by the crankshaft.
So it's not a turbo-compound-engine(of which I didn't even know they exist until tonight) - or am I wrong?

No I don't think it is. A turbo compound engine would have a turbine for power recovery on the exhaust section.

SC is indeed driven by the crankshaft. That was my point of confusion as well...

Originally Posted by swiss

Concerning the power draw of the sc:
Does it matter whether it compresses:
-ambient air to Xpsi
vs
-X psi to ?X psi
It needs to "work" either way, no?

You mean X to Y psi?

By either way do you mean: X => Y & Y => X, or ambient to X & X to Y?

It will compress whatever you input first, to a certain ratio.

Originally Posted by swiss

And then there's the heat issue again.
While googling I found this neat little calculator I'd like to share: http://www.stealth316.com/2-turbotemp.htm
Of course there are a ton of factors, but at least it's a start.

I used a pressure of 4.37psi@10k
Temp: -58°F
source:
http://sydney.edu.au/engineering/aer...ere/atmtab.txt
http://www.engineeringtoolbox.com/ai...ure-d_462.html

Whatever I tried, the results in the Intake manifold, after the SC, were actually worse then directly after the turbo.
Maybe I'm reading wrong though.

I didn't have a chance to test this calculator (typing as I am on my way out), but out of the blue I will say that it isn't this simple. You need to take into account various stuff like difference in the pressure affecting compressors efficiency, various thermodynamic & hydrodynamic laws, etc.

Are the some formulas written that were used in the calc?

Very interesting find, none the less!