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Thread: Static RPM and starter bendix...

  1. #1
    Orbiting Earth Orbiting Earth Smithy's Avatar
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    Static RPM and starter bendix...

    Greetings...
    The instructor who is checking out my wife on our A23-24 made the
    observation that during the takeoff run, the engine RPM doesn't reach
    the book static RPM of 2700. The aeroplane accelerates quickly, climbs
    well, and settles into cruise nicely. In cruise at 2,000 feet she'll
    reach 2700 no problems.
    Ok question....Is my tacho out or is it normal for a fixed pitch prop
    to not reach its peak RPM before the aircraft lifts off. I get the
    feeling the prop is quite coarse as she happily cruises at 120 knots
    low down all day..
    I'm thinking of taking the tach I use on my model aeroplanes (!!!) to
    the airfield and seeing if the Tacho is accurate...
    Also sometimes the bendix isn't throwing in to the ring gear....a
    squirt of WD 40 and she the proceeds to work...Does my starter need an
    overhaul???
    The learning process continues........Thanks everyone who has emailed
    me so far...It makes keeping this great aeroplane flying a lot easier...

    Mark Smith,
    VH-DYA.
    Melbourne.

  2. #2

    Static RPM and starter bendix...

    Hi Mark,
    It is very normal not to achieve 2700 rpm on your takeoff roll. Also, the
    bendix is a weak point on these starters. When it comes time to replace it,
    consider switching to a Sky-tec lightweight starter. It will make a world of
    difference in how fast the engine rotates to start and is pretty much
    maintenance free. Also helps move the CG back a tad.
    John

  3. #3
    I have a A23-24 also with a factory overhaul I have never seen 2700 RPM during take off run even when first installed, the RPM has allways been well into the green arc but not 2700--- I had the same problem with the starter I beleive it to be a common problem, the fix I used was to remove and clean the benbix then use LPS-1 it is a dry lubricant and worked a lot better than WD40 in that it does not attract dust and dirt.

  4. #4
    Mark, do a BAC search on Prop Pitch and read the posts. You'll learn a great deal.

    The short story is that nearly all the stock 19/23/23-24 airframes came with a prop having too much pitch for top performance. They were actually optimized for what I'll call 'economy cruise'; full throttle at about 7,500 feet and leaned, giving about 2,500-2,550 RPM. They can't get to 2,700 RPM in level flight, so they can't reach the 'real' top speed; and since they are over-pitched even for cruise, they can't get top climb performance either.

    The solution, for most owners, is more power (160 HP upgrade on the Sports; Power Flow exhaust on all of the fixed-gear 19/23/23-24s). The added HP can actually make the greater pitch work to your advantage.

    This assumes you have a correct prop and that it has the pitch called out in the TCDS. When it makes it to market, the wheel pants kit will reduce drag, helping the airframe get into a cruise window that can better use the coarse pitch. They may also help a little with the climb rate.

    *** I just read Bob's post, and re-read Smithy's post. If the instructor is talking about RPM at the static run-up or beginning of the takeoff roll, the target number can be found in the A1CE TCDS, downloadable on BAC. I think it is 2250-2350 RPM, but you'd better double-check it. ***

  5. #5

    Static RPM and starter bendix...

    Fixed pitch props never reach redline on static run-up. That is because they are a compromise between climb and cruise. Were yours to reach 2700 Static (sitting still on the ramp), then as soon as you started moving, it would unload the prop as the air was flowing through it, decreasing the effective pitch, and the engine would exceed redline unless you throttle back. Throttling back reduces HP, and that would degrade your T/O and climb. You'd find that at "cruise" you could barely have the throttle open at all, or it would go over redline.

    I don't think your instructor understands what Static RPM is. For Controllable Props, one can set it to fine pitch on the ground and get the full rated RPM out of the engine. Look at your POH or AFM for the Static RPM limits on your particular model. It is most certainly NOT 2700.

    Most of the mechanical tachs are NOT accurate. It is common to find them 100 RPM low at 2500+.

    The bendix sticks from dirt and wear. Lubing it will keep it working for a while. I second the recommendation of the Sky-Tec starter as a good update for your 30 year old Prestolite.

    I have arranged a discounted purchase from Sky-Tec for MM subscribers. Contact lstaples@itexas.net (Les Staples, one of the owners of Sky-Tec) and ask him for a warranty OH starter. The 149LS12 which fits all our planes except the 200 HP is only $250 plus shipping. The HT or NL series is a bit more for the IO-360 powered planes. Remember to mention my name, and you'll get the good deal.

    Bob Steward, A&P IA
    Birmingham, AL

    Please note! Read the BAC posts and FAQs on interference problems with the 149LS starter on some 19/23 installations. - Rellihan

  6. #6
    The model number for the starter is actually 14912LS, and they are approved on the 200 HP engines. I have had one on my A23-24 for 4 years.

  7. #7

    Static RPM and starter bendix...

    Hi Mark:

    In my experience fixed props never reach max RPM during take-off roll.

    Silicone spray lube is the recommended lubricant for the starter drive. Have to spray mine at least twice a year. Never use oil (WD-40).

    Don
    C-GNIO

  8. #8
    Orbiting Earth Orbiting Earth Smithy's Avatar
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    Thanks Guys....at the start of the take off run she's getting about 2300 which climbs to about 2400 at rotate...I wasnt worried because the speeds and acceleration are all about what I'd expect from a 200 hp fixed pitch machine.
    I'll want to replace the starter but the Aussie distributor of Sky tec wants nearly $900.00 plus tax for the NL one for my engine. I'll see what it costs to get one shipped over from your side of the pond....In the meantime I've bought some silcone spray lube and will give it a dose tonight!

  9. #9
    Smithy, the thing to do is to get a price from SkyTek on a remanufactured 149NL High Torque Inline model. They don't always have rebulds available, but if they do, they are supposed to be giving us a BAC discount on them (they have full warranty). The solenoid in the LS will not hold up long term in a IO360; and the jury is still out on the offset HT. You can have it shipped to me. I will re-package it as coming from a fellow BAC member, and can add in any other small items you may need. I can probably even combine it with an order from Mark, Ralph, or other member down under. It will probably save you money on both shipping and duty. By the way, the price for a brand-new 149NL is $519 USD at Aircraft Spruce right now. The Aircraft Supply price is $499 USD.

  10. #10
    Orbiting Earth Orbiting Earth Smithy's Avatar
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    Thanks Mike, I'll try that. $499.00USD is only $605 Aussie. There cant be $300.00 shipping and duty in it surely...Especially if its sent as a nice present from one of my good friends in the States....Gifts arent supposed to attract duty!!!!
    I'll let you know....

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