"Ken Duffey" wrote in message
...
Andy,



ANDREW ROBERT BREEN wrote:
In article ,
Raoul wrote:

I've had a questions I'd like to foist upon the collective knowledge
here...

I've noticed that their were many planes during the prop-to-jet
transition years from about 45 to about 55 that used counter rotating
propellers. I'm wondering what the perceived advantage was?

Great reply.................

Major snip...................

Not sure whether the Antonev 70 is actually in production yet, but it
uses
four big contraprops..


IIRC, the An-70 is not a contraprop as such - the D-27 engine is a
twin-spool propfan - and the props are driven by the two shafts, not
through a 'normal' contraprop gearbox.

It has 8 blades in the front row and 6 in the rear - 14 blades per
engine - making a staggering total of 56 blades !!!

It is extremely fuel efficient.........

Wait a sec. If this was such an extremely fuel efficient system, the
short-haul airlines would be banging down the various manufacturers' dorrs
demanding such systems--which they decidedly ain't doing. The prop fan
configuration was tested here in the US a few years back (on a DC-9
airframe, IIRC), and it apparently was found wanting (how much of a problem
in that regard the noise issue is I don't know). The An-70 has had a rather
troubled development history (so much so that the Russians have gotten
rather cold to it), and IIRC one of the major problems has been the
powerplant.

Brooks


Ken