> I believe I said some of this before
     > The three R3350 exhaust turbines produced 150HP each at takeoff
    power. I
     > don't know what the ratio was after that. The engine driven
    supercharger
     > was single stage two speed. The compound turbines supposedly had
    enough
     > exhaust area that they did not produce any back pressure. I
    assume that
     > to mean they operated on the exit velocity of the exhaust. H.
    Karibian
     >
     >
     > ----------------------------------------
     > Yes you did.
     >
     > Don't tell me it was working at sea level. How could that be? :)
     > Just kidding my friend Doug Hurant.
     >
     > A little background on Hurant. Hurant was a flight engineer on
     > Lockheed Constellations powered by R3350TC engines as I recall.
     > He should know.
     >
     > Paul Lamar ...No rotor no motor.

    Durant

    No problem with the kidding. With a name like mine you get used to it:)
    But what is your point? I think you are saying the blow down
    turbines were
    working at sea level, OK yes we heard that many times and I believe you.
    I haven't heard how much of the blowdown turbines' total 450 Hp
    power was
    canceled out by the supercharger needs at sea level. We all know
    they worked
    a heck of lot more efficiently at 30,000 feet. Since everything was
    always
    connected I can imagine the designers would have made sure their was
    some
    excess power developed from the blown down turbines even at worst
    operating
    conditions. And if this is so wouldn't you say the turbo compounding
    idea has
    a wide range?


    Perhaps we are discussing semantics. Wide range of operating altitudes
    verses wide range of power settings. I was thinking about the prior.

    Doug Fir

    --------------------------------------------------------------------------

    Hurant is talking NET blow down HP Doug. How would he or anyone else
    know with
    out looking at a heat balance chart what amount of HP the
    supercharger was using?
    R3350TC and other engines of the era had torque meters. He knew the
    torque and the
    RPM and he knew the net HP into the prop over and above the basic
    engine.

    A "heck of a lot more" was not all that much.
    Here is the actual data. First chart. The SAE paper said what actual
    compression
    ratio CW finally choose for the engine. Namely 7.2:1. At sea level
    the BSFC
    was .37 and at 30,000 feet it was .32 or .33. The difference is only
    .05.
    In other words for every 10,000 increase in altitude the BSFC got
    .017 better.
    Hardly earth shaking. On a TC 200 HP .4 BSFC engine the fuel burn
    would go from 13.3 GPH at sea level to 12.76 GPH at 10,000 feet.
    Hardly a heck of a lot less.

    I have updated the web site with this chart.

    Chart two. "R3350TC-take-heat-balance". Out of a gross total of 3750 HP
    the supercharger was consuming 385 HP. Subtracting 470 HP mechanical
    losses
    from the gross total gave us 3630 net HP to the prop. Now look over
    on the lower
    right side on the chart. The basic engine was 2750 HP sans turbines.
    Same as the
    B29 engine. All three turbines generated the takeoff HP increase or
    880 HP. Divide
    by three to get individual turbine HP's and you get 293 HP per
    turbine for this
    engine version.

    Overall efficiency with a 10:1 air fuel ratio for take off was 17%
    without
    turbo compounds and 22.3% with the turbines. Or an overall engine
    efficiency
    gain of 5.3 percent at high power. Now the sensible power going to
    the turbines
    is with the huge losses to the exhaust valves. About THREE TIMES AS
    MUCH will
    be going to the turbines WITHOUT the exhaust valves. Chart three.
    "R3350TC Power
    recovery heat balance."

    All these charts are now on the web site. In case you did not get
    them when
    I first uploaded them to the news letter message stream. I cannot
    understand how
    you missed all this unless you did not get the charts. On the other
    hand if you
    did get the charts perhaps there is something to the saw dust joke
    after all ROFL

    When you come over we can go up to Caltech and spend the day in the
    library.

    Paul Lamar ...No rotor no motor.


Paul,

Technically speaking, the atmospheric pressure gradient with altitude is
not linear, so it's not precise to extrapolate that for "every 10,000
feet of altitude" the BSFC will decrease by a certain amount.

Roughly speaking at 18,000 feet the atmospheric pressure is half of sea
level. But From about 10,000 feet pressure decreases more slowly, so by
30,000 feet we are at about 300 millibars, or about 9 inches of mercury
-- whereas If the pressure were dropping linearly we would already be
at zero.

Still, your point is well taken that turbocompounding made lots of power
even at takeoff, for the 3350.

Not to take a bow or anything, but I said this from the beginning, even
while some people were saying it would be pointless to run the recovery
turbine at takeoff and so a clutch to shut it off would be needed.

There is indeed a lot of power to be recovered, even at sea level.
Doug's point is also valid that the engine-driven superchargers did take
quite a bit of power, but the turbines made enough to cover that and
then some -- even at sea level. I don't know how much, but like Paul
said, we can extrapolate this from the charts.


Regards,

Gordon

Yes I know about the non linear pressure drop but it was close enough for government
work or to make my point.  Doug is making me work my butt off. I think he is
doing it on purpose :)

Paul Lamar ...No rotor no motor.

at the risk of sounding like an idiot, what happens to the final outlet
exhaust temperature from the engine after you've removed energy for
propulsion?  Do we get a net drop in exhaust temperature or same temp but
lower flow rate?  If we get a significant end exhaust temp drop wouldn't
this have a major impact on the cost, materials and processes for
manufacturing exhausts and mufflers?  How sensitive is this system to back
pressure from the exhaust system? The rotary doesn't have valves, but are we
getting a scavenging effect like a 2-cycle?  Does it benefit from an ejector
to pump a cooling jacket around the compressor stages?  Is there any impact
on the liquid cooling system (I don't see this going air-cooled or more than
partially oil-cooled in a rotary)?

George Wright

Both.
The temperature and flow rate are reduced. However the weight of air
coming out is the same as the weight of air going in. Matter can not
be created nor destroyed.

Back pressure will affect the core engine HP. As such it will slightly
increase the core engine cooling requirements. An ejector will not
work as well due to the reduced flow rate.