I have always worried that the high exhaust heat (1800F) of the
rotary would do the turbo compound version in.

In Hooker's "Not Much of An Engineer" book he mentions 1200 C for the
turbine blades. At first I thought he had made a serious error and it
was really 1200 F. No No! Not true. 1200 C!!!!!! Wow!!! This was 1970
no less. 1200 C is on the order of 2200 F. At this temperature an AC
piston engines exhaust valves are long gone.

Quote: Page 183

As for the vital HP turbine, this again went well beyond the previous
state of the art. Derby ( RR) had been one of the pioneers of air
cooled turbine blades in the Conway bypass jet designed in the
mid-1950s. All Derby blades were forged in a Nimonic high nickel
alloy, able to retain adequate strength at about 900 C. In the Conway
the peak gas temperature was about 1,100°C, so the cooling air holes
and passages inside the blade had to keep the blade at least 200°C
cooler than the surrounding gas. In the RB21 I the gas was going to
be at 1,250°C. This may not sound a very big increase over 1,100, but
the strength of the blade is halved for every extra 25°C!

To make a blade at Derby (RR) the rough metal bar from which the
blade would be fashioned was first pierced by a large number of long
but small-diameter drilled holes. Just where these had to be was
found by a laborious process of trial and error, so that, after the
rough blank had been forged, the holes were all in the correct
positions. To forge the blade it was squeezed while almost white hot
between two dies having the correct shape to form the blade.

Finally the whole blade was machined all over to precisely the
correct size and profile. The price of each blade was inevitably very
high, and the whole process was an engineer's nightmare because
microscopic variations between the cooling air holes in successive
blades meant that the cooling would be uneven.

At Bristol we had abandoned forged blades soon after 1960. Instead we
cast our blades using the famous lost-wax process used 500 years
earlier - by da Vinci, for example - to produce precisely repeated
sculptures. Casting enabled us to use materials basically stronger
than Nimonic alloys, too hard to be forged or machined. We cast our
blades to the finish dimensions, with a mirror finish, without any
machining apart from precision grinding of the root. Cast blades
proved to be much stronger in tension than forged and machined
blades, and despite their brittleness and susceptibility to thermal
stress we proved on the Proteus that they are superior. On the
Olympus 593 [Concorde engine] and Pegasus [Harrier engine] we
produced large numbers of eminently reliable blades with radial air
cooling passages operating at some 1,250°C, much hotter than any
production engine at Derby at that time.

End quote.

A turbo compound rotary is a piece of cake.

This book is a real education in aircraft engine design.

Paul Lamar

 Very interesting information about turbines and turbine blades,
   hard to find together without spending hours, now that Paul signs
   in classical Greek Alphabet, one anecdote: 25% of Spaniards do
   have the so called 'Greek foot' where the second toe is longer than
   all the rest, the same as in the statues of classical Greece, my only
   remaining doubt is if the women and men that are in the classical
   Greek sculptures where someone real, or just of 'ideal' or 'imaginary'
   beings, As far as I know, the people who built this culture (more than
  60% of the inhabitants of Athens were 'slaves') left no genetic or
   biological remains, just literature and lots of legends.

      (I guess the search for 'Golden fleece' was some kind of an 'extreme
    sportive event'. The Merino sheep have its name from a Berebere tribe,
     arriving to Iberian peninsula with the VIII century Arab invasion.
        The contest for Greeks may have been going to where the Merino
    tribes lived, in what is today Morocco and Atlas mountains, cut
    a fleece from their sheep, and come back home with it, outwitting
   the sheep's guardians)
      Thanks for your attention, best regards. Salut
            Jose Gros-Aymerich; Madrid, Spain


The Rotary Engine News Letter. Powered by Linux. ACRE NL web site.
http://www.rotaryeng.net You Tube http://tinyurl.com/beqqxas
Copyright 1998-2014 All world wide rights reserved.