I found another small item to correct. It was really not a big deal, but
    if you entered manifold pressures below ambient, the compressor pressure
    calculation would show a negative number, which is of course not true in
    the real world.

    This in turn would lead to very low charge temperatures and would skew
    other values.

    I have fixed it so that even at low manifold pressures, the compressor
    pressure ratio remains 1.


    Regards,

    Gordon.

    Plug in some of these numbers for a four rotor and see what your
    spread sheet comes
    up with. Also you need a look up table for VE verses RPM.

    Paul Lamar ...No rotor no motor.

    Paul,

    There is pretty good agreement with the Lemans engine data. See for
    yourself.

    At 8000 rpm, standard temp, 29.92 MAP, air-feul ratio of 12, the
    spreadsheet shows 630 hp, just below the 653 hp shown on your chart.

    This is at VE of 1.2, compression ratio of 10, and evaporative
    cooling of 0.5, and no inlet pressure loss.

    At air-fuel ratio of 16, the bsfc is 0.46, which is what your chart
    shows at the efficiency oriented setting.

    I think this is pretty close. If anything, my calculations are a
    little on the conservative side, just like I said.


    About the VE varying with rpm. Yes, I agree this is what actually
    happens. However, the VE curve is fairly flat in the range of 6000
    to 8000 rpm, which is what we are most concerned with in an aircraft
    engine.

    Still, if I had the data to consturct a lookup table I would be
    willing to give it a shot.

    As it now stands though, there is pretty good agreement with the
    Lemans engine.

    I have attached a copy. I have also limited the air fuel ratio to a
    leanest maximimum of 17. Even if you can run the engine leaner than
    that, it could be that thermal efficiency would have already topped out.

    This is version 4.1.1.

    Keep the feedback coming...

    Regards,

    Gordon.

    OK try the green curve with 18 psi boost and no NOS.

    Paul Lamar ...No rotor no motor.


    Paul,

    I couldn't use that last example becasue the boost is too high. I've
    set a limit of 50 inches for manifold pressure, because above that
    the charge temps get too high.

    But I did make another small improvement. The combustion temp is now
    calculated rather than entered. Combustion temp affects exhaust
    pressure, which affects the turbine work available.

    The combustion temp varies with mixture, of course, so it makes
    sense that it should change if you change the mixture.

    I think this model is now quite realistic.

    Look at the example I've entered. This is a 4-rotor engine that is
    making over 800 hp on the ground at just 35 inches of manifold
    pressure in the turbocompound configuration. That is amazing.

    And look what happens if you change the altitude to 20,000 feet.
    You're still making well over 700 hp up there. The turbine is
    kicking out 225 hp. That is quite a figure.

    Now look what happens if you lean the mixture a bit to A/F 15, bring
    the MAP down to 30 and rpm to 6500. This would be a very easy cruise
    power setting. Look at the engine power -- 500 hp. Do you know what
    size plane you could move with an engine that makes 500 hp at
    economy cruise?

    And look at the fuel numbers: bsfc of 0.39, fuel flow of 33 gph.
    That is simply amazing.

    Compare this to a Pratt PT6 that is gulping nearly twice that much
    fuel to make similar power. The small single-engine jets are even worse.

    Looking at this should really motivate us to make the turbocompound
    aircraft rotary a reality.


    Regards,

    Gordon.


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