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Thread: [musketeermail] Climb prop on 49C?

  1. #1

    [musketeermail] Climb prop on 49C?

    N6349C is not that good. At 2550 to 2600 I see well under 100kts IAS.

    I can easily exceed 2700 in cruise - in fact I have to watch it like
    a hawk to stay under the redline. At 2700 RPM on a near standard
    day, I get IAS of 105, which is TAS ~ 117 kts at 6500ft MSL. At 2500
    RPM, I get IAS of 95 kts at 6500, which is 106 kts true. About 10kts
    less than book values. Since fuel burn is also less, I assume that
    I'm not making the book power for the engines revs. That's why I
    suspect a climb pitched prop.

    I agree entriely about the comfort and craftsmanship of the
    Sundowner. Most of my time until this year was on rental Cessnas and
    Pipers. I wanted to buy an a/c that combines the low wings and
    visbility in the pattern of the Warrior, with the 2 door entry of the
    Cessna. The Sundowner is perfect, and since I like the aviating
    part, I don't object to going a bit slower!

    On the other hand, 49C seems exceptionally slow. Does anybody know a
    direct way I can find out if my prop is climb pitched? What is a
    typical cost to re-pitch?

    Paul.


    --- In musketeermail@yahoogroups.com, ChuzBear@... wrote:
    >
    > I don't have any problems with RPMs that I know of. I had my
    tach checked against a digital tach - <50 RPM difference - back when
    I had the prop balanced at one of our fly ins. You might have the
    accuracy of your tach checked before spending money on re-pitching.
    > As for speeds, your speeds look pretty close. I do all my
    planning at 100 kts. I do get 105 - 115 IAS at 2550 - 2600 rpm
    depending on altitude and season. I normally fly at 1500 msl to/from
    work and on trips up between 4500-7500 msl where she indicates 95-105
    depending on temps. Our birds are not known for their speed -
    "slowdowners". They are known for their craftsmanship and comfort -
    "Baby Beeches". And for the average weekend trip, I'll trade the
    10 - 20 minutes I get beat for the comfort, load, and roominess of my
    bird any day.
    > I have 49Q, a 71 C-23, the second Sundowner off the Beech
    factory line.
    > Blue Skies,
    > Chuz
    > BAC SE Region Director
    >
    >
    > -----Original Message-----
    > From: pilot2724@...
    > To: musketeermail@yahoogroups.com
    > Sent: Tue, 24 Oct 2006 4:59 PM
    > Subject: [musketeermail] Climb prop on 49C?
    >
    >
    > Browsing the posts on the BAC site after deciding to join, I ran
    > across a topic that interested me because of poor cruise
    performance
    > on 6349C, a 1983 model Sundowner.
    >
    > I find while climbing I must keep the nose high and speed close to
    > 80kts where I see about 2500 RPM on the tach. Let the speed creep
    up
    > to 90+ and it's on redline. When I level out I must reduce power
    > before or simultaneously with lowering the nose for the same reason.
    >
    > In cruise, 2700 RPM gives me between 100 and 105 kts IAS at 6000,
    > while 2500 only gives me about 97 kts. Since i just flew from NH
    > (ASH) to TX (TKI) against 35 kt headwinds, you can imagine that I'd
    > like some more speed.
    >
    > In the BAC posts I just ran across several people complaining that
    > their x23's could only get 2300 in level flight, and a discussion
    of
    > repitching props to get more. One person wrote he'd never heard of
    > Sundowner pilots having trouble reaching max RPM's in level flight.
    > This is so opposite to my experience, I have to ask for the wisdom
    of
    > the assembled (y'all).
    >
    > Could it be that I a) have a climb prop; 2) have the wrong prop; or
    > 3) need an overhaul, or 4) something else? I only bought Charlie in
    > May, and have put about 40 hours on him since.
    >
    > pilot2724@...

  2. #2

    [musketeermail] Climb prop on 49C?

    >N6349C is not that good. At 2550 to 2600 I see well under 100kts IAS.
    >
    >On the other hand, 49C seems exceptionally slow. Does anybody know a
    >direct way I can find out if my prop is climb pitched? What is a
    >typical cost to re-pitch?

    To start with, most mechanical tachs that are not fresh out of the box are
    reading low at cruise RPMs. 50-150 RPM low. So if you are reading 2700
    RPM, you may be at 2800 or higher and not know it.

    The prop pitch can't really be checked reliably ON THE PLANE. The answer
    is to take it off and let the local prop shop check it. Price to change
    pitch varies by shop and by region. $125 is about the lowest price I am
    aware of, and $175 is probably a more common charge for the inspection,
    measurement, and pitch change.

    The issue of whether there is any pitch change LEFT also comes into
    play. Don't be surprised if they find your 30 year old prop is out of
    tolerance and you need a NEW ONE. They don't last forever, and there are
    many undocumented repairs that can leave you with an expensive piece of
    scrap aluminum to get polished and hang over the fireplace.

    When a prop is manufactured, there is a maximum number of inches that it
    can be bent up or down during its life. Senenich for example makes their
    74DM series at 56" of pitch, and then bends the newly carved prop to the
    finished pitch ordered by the customer. If there is a 8" total bend
    permitted, then measuring from the 56" starting point, one could bend it up
    to a 64" and use up all its allowable bending, or one could bend it to a
    60" and have 4" left over for future repairs and tweaking. So if it
    started as a 56" and was bent to 60" for Beech, and then someone depitched
    it to 56" for high altitude take off performance (they were based in
    Denver?), all of the allowable pitch change is used, and the prop can never
    be legally pitched away from 56".

    This is just one reason why the FAA now wants all props to have their own
    log books.

    The rule of thumb of prop pitch change is that 1" of pitch change gives
    about 50 RPM change at full throttle. So if you can pull 2800+ RPM right
    now, you'd need at least 2" of pitch INCREASE to drop your max RPM back
    ~100 RPM to 2700.

    Determining the best match of prop to engine/airframe for good cruise
    without destroying T/O and climb is to fly at 8000' DA (get out the whiz
    wheel, this is one time it really IS important to know the density
    altitude), and wide open throttle, and trim for level flight and let it
    accelerate and re-trim as required.

    Take an accurate Tach reading (electronic, photo-tach, PDA audio tach?,
    calibrated mechanical tach) and then compare that to the 2700 Red Line and
    see how many full inches of pitch you can change to get to 2700.

    Those at higher elevations might want to bias the pitch an inch lower to
    get a bit more Take Off performance, and just acknowledge that you will
    have to throttle back 50 RPM when in cruise and lose the 2-1/2 mph that the
    1" costs you.

    Since we are blessed (or cursed?) with planes that have a relatively low
    cruise speed compared with the T/O and climb speeds, we don't have to get
    tricky with mods to try an fool the prop into working well across a wide
    range of speed.

    There are tip mods (Art Matson has made them popular with Piper owners) and
    special twist profiles with increased and decreased pitch numbers at
    various stations (AKA- Magic Pixie Dust) to let the prop have good static
    RPM for Take-Off and yet have good cruise speed at full throttle.

    When we can get a Sundowner to 130 knots, more can be said about these
    techniques.

    Bob Steward, A&P IA
    Birmingham, AL



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  3. #3
    I've got a '65 A23 and had just the opposite scenario. I couldn't get enough RPM. I had my prop rebuilt and re-pitched at East Coast Propeller and was very happy with their service and the results. $450 to rebuild and re-pitch.
    Procedure I followed to test was:
    1) Check tach with handheld unit
    2) Check Static RPM vs book value( I was 150 RPM too low)
    3) Check max RPM with WOT at 7500' DA. Should be able to get 2700 (I was only getting 2500).

    Results were improved climb, improved service ceiling, static RPM wiothin spec and 2700 RPM at 7500' DA. I'm very satisfied.

    Rodney
    N8894M

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