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Thread: Early Mouse Max Range

  1. #1

    Early Mouse Max Range

    A hypothetical for you operators of IO-346-equipped Mice. Listen
    carefully:

    If you start a flight with an empty left fuel tank and a full right
    tank, and fly on the right tank till exhaustion, at that moment how
    much fuel will be in your left tank?

    The context of the question is this. My operating technique for
    extracting the maximum range from my Lyc-equipped Sierra, which I'm
    sure I've described in detail before and am highly simplifying here,
    is to take off, climb, cruise and fly to exhaustion on one tank,
    with normal tank switches once at cruise, so that you know you have
    at least that much endurance by the clock in the other tank with
    which to cruise, descend and land at an airport. **This will not
    work** with the Continental fuel injection, because as you know the
    engine doesn't use all the fuel that's sent by the fuel pump, but
    instead sends some excess back to the *left* fuel tank. My question
    is, how much?

    In effect, though not really, net fuel "consumption" is greater from
    the right tank than from the left. So if you're trying to extract
    max range from this engine using my tank-switching strategy, and
    since you have to start with the left tank in order to make room for
    the returned fuel, you'll have considerably less endurance from the
    right tank than from the left. And when feeding from the right
    tank, the left tank will be getting partially replenished - by how
    much? By anywhere near the normal 30-minute VFR reserve? What tank-
    switching strategy is appropriate for this engine to eke out maximum
    range? BTW, I searched the BAC website already.

    Craig MacCallum
    Sierra N525SB
    Montclair NJ

  2. #2

    Early Mouse Max Range

    Craig, that certainly is hypothetical because I would never depart with the left tank less than half full, but the answer to the hypothetical question is that it depends on the power setting. The less the setting, the more fuel gets transferred to the right tank. At a 2500 rpm cruise I would estimate about 10 gallons. My normal fuel management taking off with both tanks full is to fly on the left tank for two hours so that the guage reads about 1/2 tank then switch to the right tank. I then run on the right tank until near the destination and switch back to the left. If I am trying to maximize range I run the right tank nearly dry while at altitude and then finish the flight with as much fuel in the left tank as I can. My fuel guage is very accurate when near empty so I make sure that I switch before the right tank reads empty. I also watch the fuel guage on the left tank and switch feed back to the left if it reads full (about 20 gallons)

    I am not at all sure that this is applicable to the Sierra, but it works for me.

    Willis

  3. #3

    Early Mouse Max Range

    With my Continental, I've found that fuel "consumption" on the right
    tank is about 1.5 GPH more than the left. The extra goes back to the
    left tank. The actual fuel consumption is about 9 GPH at my normal
    settings. So I've exhausted the right in about 2.6 hours where I've
    added 1/2 to the left based on your scenario. In any case, when I
    exhaust a tank, I land promptly. I don't ever want to rely on gauges.

  4. #4

    Early Mouse Max Range

    Most return systems are around 3 GPH back to the left tank.

    Jeff

  5. #5

    Early Mouse Max Range

    OK. I can accept that.

    At 3 GPH being returned and 8.5 GPH being consumed, say, then the
    right tank will be emptied in about 2.5 hours. That's 7 gal
    returned to the left tank and is good for 40 minutes (presuming it
    was empty). Then you're a glider.

    I've rarely flown with the plane full as it really degrades
    performance, but I've emptied 10 gal in about 40 minutes.

    My usual "load" is 20 gal/side (to the slots). This gives me just
    about 4 hours range at lower power and 3.5 hours at max. I will fill
    heavier if fuel is cheap OR if I have a long way to go.

    When I moved my plane to Texas, the leg from El Paso to Fort Worth
    was done on one fill and I used about 40 gals. I left full (60 gal)
    and it only took a little over 20 to fill to the slots. Thats about
    500nm at 8500ft. We did stop at Midland for a break, but took no
    fuel.

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