Altitude!  Altitude!  Must know altitude.  I can go 190 mph at SL or at 15,000.  Fuel burn is about double at SL compared to 15K.
 
Tracy
 

    ----- Original Message -----
    From: Charlie & Tupper England
    Sent: Tuesday, April 06, 2004 9:03 PM
    To: Rotary motors in aircraft
    Subject: [FlyRotary] Re: : Percent Power, Throttle position, &
    RD-1Cperformance
         OK, how about a 'real world' cruise power fuel burn? My 160hp fixed
    pitch Lyc powered -4 burned ~92-9.5 gph of avgas at ~190-195 statute
    mph. What are you burning down around 190 mph (allowing a little
    wiggle
    room for 'work in progress' aerodynamics of your plane)?

    Tracy Crook wrote:

    > Took closer note of throttle position on todays flight. At 2000
    ft the
    > throttle was only about 1/3 open (position of throttle quadrant,
    but
    > it closely mirrors butterfly position) at economy cruise setting
    which
    > was 6.0 GPH. This is about 42% power, 82 HP according to the EM2
    which
    > is fairly close but not perfectly calibrated yet. The same power
    > setting with the -B drive would bave been a bit further open.
    > I did a quick check of MAP at 1000 ft at full throttle and found
    I was
    > not getting any drop at 150 MPH and had .5" boost at 220 MPH
    (ram air
    > recovery I assume). I did not get around to checking it in slow
    climb
    > which would more accurately compare to what you would see on a dyno.
    > Finally got some reasonably calm air to do performance
    comparisons of
    > -C drive vs -B drive. Without the prop blade cuffs it looks like
    the
    > break even point is at 203 MPH. Above that -C burned more fuel than
    > the -B. After installation of the cuffs, the break even point
    was off
    > the scale! i.e., above top speed with -B drive. I had a good data
    > point on the -B drive while burning 17 GPH (209 mph during SUN 100
    > race). At the same speed, the C drive was burning 15.8 gph. This
    was
    > better than I had hoped for.
    > Tracy
    >
    >     Thanks, Tracy. I was hoping there would be someone out there
    >     flying with the same TB diameters.
    >
    >     Like most things, TB diameter is a tradeoff. My conclusion from
    >     the dyno data is that 44mm per rotor (1 ¾) is a bit small as the
    >     MAP is dropping off over 5000 RPM. But if you want to idle at
    >     1500, and have a decent transition from there to 3000; 1 ¾ is
    >     good. For a 2.85 to redrive, I’d want to increase that flow area
    >     by 30% or so – to about 2” dia for each rotor.
    >
    >     My data may not be representative because of restricted flow to
    >     the TB. The ‘airbox’ size is restricted by the cowl, and may
    have
    >     restricted the flow a bit. In hindsight, it would have been
    smart
    >     (and easy) to make a run with the airbox off and see what
    >     difference it made.
    >
    >     Al
    >



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