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Thread: general flying question

  1. #1
    Orbiting Earth Orbiting Earth corcoran's Avatar
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    Jul 2004
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    Braintree and Cape Cod, Massachusetts,
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    general flying question

    Mike Rellihan and others say that at altitude (say 7,000) the throttle should/can go to-the-wall (full) to achieve maximum power. My question is on throttle travel to get "to-the-wall".

    Full forward, I get the most fuel going through the carbuerator. RPMs are perhaps 2600 or such. When I pull the throttle lever away from "the-wall" for an inch or more of throttle cable travel, the RPMs STAY at 2600 or such.

    My question is not about RPMs. Not % of power. Not leaning. Not specific altitude density or otherwise.
    My question is this:

    "Am I using too much, more than necessary, extra or wasting fuel if I stay "at-the-wall" rather than pull back that inch or so until the RPMs start too decline?" The question is about WASTING OR BURNING EXTRA FUEL.

    Most every plane I've flown has had cable travel before the RPMs change. I'll be happiest with the SIMPLE answer.

    Tom Corcoran
    Prince Edward Island
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  2. #2

    general flying question

    >
    > >
    > "Am I using too much, more than necessary, extra or wasting fuel if I stay
    > "at-the-wall" rather than pull back that inch or so until the RPMs start
    > too decline?" The question is about WASTING OR BURNING EXTRA FUEL.


    *** I would say yes. Because the power coupled to the air is a function
    of the propeller speed. Higher speed, more power coupled to the air.
    Especially with a fixed pitch prop, which I assume you have. So that
    last inch of throw does not get you any more power.

    I was taught to keep it to the wall during climb because the excess fuel
    cools the cylinders. Now that's expensive coolant, but cheaper than a
    top end overhaul.

    Contrariwise, I'm told that one reason that car engines last so long
    nowadays is because of precise fuel injection, that prevents excessive
    fuel from washing lubricant off the cylinder walls. But WRT aircraft
    engines,
    I've read that one good overheated climb with lean mixture can anneal the
    piston rings - a BAD THING.

    - Jerry Kaidor ( jerry@tr2.com )



    >
    > Most every plane I've flown has had cable travel before the RPMs change.
    > I'll be happiest with the SIMPLE answer.
    >
    > Tom Corcoran
    > Prince Edward Island
    > __________________________________________________ ______________________
    > Check out AOL.com today. Breaking news, video search, pictures, email and
    > IM. All on demand. Always Free.
    > _______________________________________________
    > BAC-Mail mailing list
    > BAC-Mail@beechaeroclub.org
    > http://www.beechaeroclub.org/mailman/listinfo/bac-mail
    >


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  3. #3
    mike at rellihan.com
    Guest

    general flying question

    The last inch (or so) of throttle cable travel simply triggers the automatic
    full-power enrichment, if the RPM isn't changing. In this area of travel,
    the carb or FI servo is adding extra mixture, just as if you had been able
    to move the mixture knob further. The purpose is to provide extra fuel
    cooling, in case you are using full throttle at low DA (such as every
    takeoff). If that's the effect you are seeing by moving the last inch of
    throttle in cruise (same RPM, higher fuel flow), it is just the
    full-throttle enrichment circuit kicking in. You can negate it by pulling
    the mixture knob back slightly; I have to do this on nearly every flight, as
    I am usually high enough (6,000' or higher) to use full throttle. I control
    power with RPM and fuel flow (to lean of peak, unless in a headwind). As
    Tom C can attest, I flew my Sierra from Oshawa to Charlottetown-PEI (700 NM)
    in 4:30, and landed with 20 gallons still in the tanks. Yes, I had a nice
    tailwind.

    There is a critical engine life aspect here, and an efficiency aspect. Both
    can be served, if your engine instrumentation and baffle conditions permit.

    CHT is the critical temperature, assuming that your oil temp is staying
    within reason (normally under 210-215, even in climb). CHTs should always
    be kept under 400, and 350-370 is much better. I typically cruise with CHTs
    in the high 290s and low 300s. As I have posted before, you can cool the
    cylinders with more air (flattened climb), more fuel (richer mixture), or by
    reducing power (pulling back the throttle). In the real world we use all
    three as required. I use them in the order of least cost, utility
    permitting. I flatten the climb; I reduce MP (and/or RPM) if able; and I
    use higher fuel flow only as a last resort. If your baffle seals aren't
    sealing and your baffling is full of gaps and holes, flattening the climb
    may not help much. You can do a lot of cheap baffle repairs for the price
    of an extra couple of gallons per hour fuel flow, every time you fly. EGT
    is not a limiting temperature in our unsupercharged engines; it is simply a
    leaning tool. CHT is critical.

    Efficiency is the other key aspect. An engine running at full throttle uses
    more of its fuel for propulsion, and less for pumping losses (sucking hard
    against a partially closed throttle). Part of a Diesel's efficiency is due
    to it having no throttle blade (just fuel control). A key thing to remember
    is that if you are not able to get 2700 RPM in level flight at a density
    altitude of 7,500' or so (and leaned for best power), you cannot even get
    75% power. You are already under that value, if 2600 is the best you can
    get, at that DA. Very few of our fixed-pitch airframes can get 2700 in
    level flight at the 700' DA; virtually all the planes were over-propped from
    the factory. That means you will get the best efficiency by climbing to
    7500 DA, run the throttle wide open, and lean as close as you can get to
    peak or lean of peak. If you have to stay rich of peak, the GAMI research
    shows definitively that you should stay at least 100 ROP (not 40-50 ROP).

    Just in case Tom made it this far... it doesn't matter whether you put the
    throttle in or out, that last little bit, if the RPM is the same either way.
    It DOES matter what your CHTs are showing. If you have to cool them with
    fuel, you can do it by pushing the throttle back in, or the mixture back in,
    or both. Or you can fix all those @#$%%^ HOLES IN YOUR BAFFLE SEALS! And
    you aren't wasting fuel if it is the only thing keeping your CHTs under 400,
    whether you put the fuel in with the throttle or the mixture!



    -----Original Message-----
    From: bac-mail-bounces@beechaeroclub.org
    [mailto:bac-mail-bounces@beechaeroclub.org] On Behalf Of mediareps@aol.com
    Sent: Monday, July 10, 2006 10:10 AM
    To: bac-mail@beechaeroclub.org
    Subject: [BAC-Mail] general flying question

    Mike Rellihan and others say that at altitude (say 7,000) the throttle
    should/can go to-the-wall (full) to achieve maximum power. My question is on
    throttle travel to get "to-the-wall".

    Full forward, I get the most fuel going through the carbuerator. RPMs are
    perhaps 2600 or such. When I pull the throttle lever away from "the-wall"
    for an inch or more of throttle cable travel, the RPMs STAY at 2600 or such.

    My question is not about RPMs. Not % of power. Not leaning. Not specific
    altitude density or otherwise.
    My question is this:

    "Am I using too much, more than necessary, extra or wasting fuel if I stay
    "at-the-wall" rather than pull back that inch or so until the RPMs start too
    decline?" The question is about WASTING OR BURNING EXTRA FUEL.

    Most every plane I've flown has had cable travel before the RPMs change.
    I'll be happiest with the SIMPLE answer.

    Tom Corcoran
    Prince Edward Island
    __________________________________________________ ______________________
    Check out AOL.com today. Breaking news, video search, pictures, email and
    IM. All on demand. Always Free.
    _______________________________________________
    BAC-Mail mailing list
    BAC-Mail@beechaeroclub.org
    http://www.beechaeroclub.org/mailman/listinfo/bac-mail



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  4. #4

    general flying question

    As usual I learned things I never knew from Mike's piece. I just thought
    that last inch (on my throttle, about 1/2 to 3/4 inch) or less of travel was
    slack in the cable. Now I expect to waste a little less fuel in cruise by
    taking that into account.

    However, I only have the original equipment EGT gauge in my Sundowner, which
    I assume is connected to the hottest cylinder -- I'm not sure which -- Beech
    engineers found on the carbureted engine when they designed the cooling air
    flow for it. This gauge isn't calibrated to read specific temperatures.
    Only increases and decreases in 25 degree increments. The needle for about
    100 degrees rich of peak always ends up straight up or slightly right of
    straight up, wherever I set the rpms in the cruise range. I ALWAYS lean for
    best power. Sure, you can full around with lean of peak IF you have fuel
    injection, those custom GAMI injectors, and a cylinder head temperature
    gauge for all the cylinders. No question that running lean of peak will
    save fuel, but at the price of a considerable loss of power. I wouldn't
    accept the trade-off (or cost for installation), even if my Sundowner were
    fuel injected. I don't think I need more than my EGT to run my engine at
    best power.


    Carl
    N21KM


    ----- Original Message -----
    From: "Michael Rellihan" <mike@rellihan.com>
    To: <mediareps@aol.com>; <bac-mail@beechaeroclub.org>
    Sent: Monday, July 10, 2006 11:41 PM
    Subject: RE: [BAC-Mail] general flying question


    > The last inch (or so) of throttle cable travel simply triggers the
    > automatic
    > full-power enrichment, if the RPM isn't changing. In this area of travel,
    > the carb or FI servo is adding extra mixture, just as if you had been able
    > to move the mixture knob further. The purpose is to provide extra fuel
    > cooling, in case you are using full throttle at low DA (such as every
    > takeoff). If that's the effect you are seeing by moving the last inch of
    > throttle in cruise (same RPM, higher fuel flow), it is just the
    > full-throttle enrichment circuit kicking in. You can negate it by pulling
    > the mixture knob back slightly; I have to do this on nearly every flight,
    > as
    > I am usually high enough (6,000' or higher) to use full throttle. I
    > control
    > power with RPM and fuel flow (to lean of peak, unless in a headwind). As
    > Tom C can attest, I flew my Sierra from Oshawa to Charlottetown-PEI (700
    > NM)
    > in 4:30, and landed with 20 gallons still in the tanks. Yes, I had a nice
    > tailwind.
    >
    > There is a critical engine life aspect here, and an efficiency aspect.
    > Both
    > can be served, if your engine instrumentation and baffle conditions
    > permit.
    >
    > CHT is the critical temperature, assuming that your oil temp is staying
    > within reason (normally under 210-215, even in climb). CHTs should always
    > be kept under 400, and 350-370 is much better. I typically cruise with
    > CHTs
    > in the high 290s and low 300s. As I have posted before, you can cool the
    > cylinders with more air (flattened climb), more fuel (richer mixture), or
    > by
    > reducing power (pulling back the throttle). In the real world we use all
    > three as required. I use them in the order of least cost, utility
    > permitting. I flatten the climb; I reduce MP (and/or RPM) if able; and I
    > use higher fuel flow only as a last resort. If your baffle seals aren't
    > sealing and your baffling is full of gaps and holes, flattening the climb
    > may not help much. You can do a lot of cheap baffle repairs for the price
    > of an extra couple of gallons per hour fuel flow, every time you fly. EGT
    > is not a limiting temperature in our unsupercharged engines; it is simply
    > a
    > leaning tool. CHT is critical.
    >
    > Efficiency is the other key aspect. An engine running at full throttle
    > uses
    > more of its fuel for propulsion, and less for pumping losses (sucking hard
    > against a partially closed throttle). Part of a Diesel's efficiency is
    > due
    > to it having no throttle blade (just fuel control). A key thing to
    > remember
    > is that if you are not able to get 2700 RPM in level flight at a density
    > altitude of 7,500' or so (and leaned for best power), you cannot even get
    > 75% power. You are already under that value, if 2600 is the best you can
    > get, at that DA. Very few of our fixed-pitch airframes can get 2700 in
    > level flight at the 700' DA; virtually all the planes were over-propped
    > from
    > the factory. That means you will get the best efficiency by climbing to
    > 7500 DA, run the throttle wide open, and lean as close as you can get to
    > peak or lean of peak. If you have to stay rich of peak, the GAMI research
    > shows definitively that you should stay at least 100 ROP (not 40-50 ROP).
    >
    > Just in case Tom made it this far... it doesn't matter whether you put the
    > throttle in or out, that last little bit, if the RPM is the same either
    > way.
    > It DOES matter what your CHTs are showing. If you have to cool them with
    > fuel, you can do it by pushing the throttle back in, or the mixture back
    > in,
    > or both. Or you can fix all those @#$%%^ HOLES IN YOUR BAFFLE SEALS! And
    > you aren't wasting fuel if it is the only thing keeping your CHTs under
    > 400,
    > whether you put the fuel in with the throttle or the mixture!
    >
    >
    >
    > -----Original Message-----
    > From: bac-mail-bounces@beechaeroclub.org
    > [mailto:bac-mail-bounces@beechaeroclub.org] On Behalf Of mediareps@aol.com
    > Sent: Monday, July 10, 2006 10:10 AM
    > To: bac-mail@beechaeroclub.org
    > Subject: [BAC-Mail] general flying question
    >
    > Mike Rellihan and others say that at altitude (say 7,000) the throttle
    > should/can go to-the-wall (full) to achieve maximum power. My question is
    > on
    > throttle travel to get "to-the-wall".
    >
    > Full forward, I get the most fuel going through the carbuerator. RPMs are
    > perhaps 2600 or such. When I pull the throttle lever away from "the-wall"
    > for an inch or more of throttle cable travel, the RPMs STAY at 2600 or
    > such.
    >
    > My question is not about RPMs. Not % of power. Not leaning. Not specific
    > altitude density or otherwise.
    > My question is this:
    >
    > "Am I using too much, more than necessary, extra or wasting fuel if I stay
    > "at-the-wall" rather than pull back that inch or so until the RPMs start
    > too
    > decline?" The question is about WASTING OR BURNING EXTRA FUEL.
    >
    > Most every plane I've flown has had cable travel before the RPMs change.
    > I'll be happiest with the SIMPLE answer.
    >
    > Tom Corcoran
    > Prince Edward Island
    > __________________________________________________ ______________________
    > Check out AOL.com today. Breaking news, video search, pictures, email and
    > IM. All on demand. Always Free.
    > _______________________________________________
    > BAC-Mail mailing list
    > BAC-Mail@beechaeroclub.org
    > http://www.beechaeroclub.org/mailman/listinfo/bac-mail
    >
    >
    >
    > _______________________________________________
    > BAC-Mail mailing list
    > BAC-Mail@beechaeroclub.org
    > http://www.beechaeroclub.org/mailman/listinfo/bac-mail

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