The reason for "added" complexity:

http://en.wikipedia.org/wiki/Turbo-compound_engine

It's for supercharging the engine! (sarcasm) Well, really, if there wasn't a supercharger, the engine would probably put out considerably less power. The only reason why such large engines have internal superchargers is because otherwise, they would need to be even bigger. Without it, there would be less air turning the turbo, and it would provide less boost. I'm not aware of any WW2 aircraft having only a turbosupercharger without a normal, crankshaft driven one.

If this sounds stupid, it could be because it's way past midnight here too.:rolleyes:

Yes, exactly! I read that article, just used the Dobrynin as an example as even a bit more complex than R-3350 TC. Napier Nomad is another case, you simply cannot describe that one (atleast thefirst version) without a picture or two.

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.

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.

Koivis, amazing find! I don't mind offtopic if it's about beautiful technology (and huge and absurdly complex engines ;-) )

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

Okay, here's a BIG ONE:

http://www.enginehistory.org/P&W/R-4360/4360oil.jpg

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?

Back to the 190

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?:confused:




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.
:confused:

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.



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.


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...


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.



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!

I did not say that a normal turbocharged R-2800 or any similar engine would be a turbo-compound engine. I just meant to say that no matter what extra components are added around the engine (including turbos and turbo-compound turbines), it almost always still has a normal, integral, crankshaft driven supercharger.

I've been searching the internet for more info on this type, but it's going slow. I'd like to find detailed cockpit info, because there is a strong indication that it used an rpm gauge for the turbo, like on the P47. It might have had additional controls as well.
Actual RLM flight test data would be cool as well.

The problem is I don't have proper sources and searching with keywords produces a whole lot of ...

So if anyone stumbles upon these things, post them here :grin:

I suggest we both delete those OT posts.
(did already so)

I don't mind OT, does anyone?

actually I do, otherwise we could move on to discuss the taste of Swedish strawberries.