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Thread: RPMs with What Prop

  1. #1

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    Default RPMs with What Prop

    Hey Guys,
    I posted this in another thread ,but will try my own.

    We have an O-290D-2B with about 500 SMOH in our 7GC Champion with a 74-58 prop. As you know to get the 140HP it needs to turn 2800RPM. No way that will happen around 2600-2650 is max in level flight. It is a little low in Max. RPM during static ck. But still falls in the requirements. The 74-58 is what it left the factory with and this prop was new at OH. Our O-320 in the Pacer will turn 2700 with the same prop no problem.
    I'm curious to know what RPMs you get with what prop.
    For that mater I would like to hear what some of the others with O-290s are getting with what prop
    Last edited by wyandot jim; 02-09-2018 at 09:26 PM.

  2. #2
    Old3pacer's Avatar
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    Default Re: RPMs with What Prop

    Old 0320-no suffix and 74-60 sens prop max rpm2650

  3. #3

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    Default Re: RPMs with What Prop

    Quote Originally Posted by Old3pacer View Post
    Old 0320-no suffix and 74-60 sens prop max rpm2650
    Yes ours in the Pacer is an O-320-no suffix also. But I'm trying to get info on the O-290-D2B 140HP at 2800RPM. If it can't turn 2800RPM you are not getting full HP

  4. #4
    Brian's Avatar
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    Default Re: RPMs with What Prop

    Tips of a 74 inch prop turning 2800 RPM are traveling 616 MPH or .8 Mach at Sea Level / Standard Temp Day.
    Prop would be buzzing pretty good if you could hear it above the Short Wing cockpit noise at 120 MPH.

    http://www.warpdriveprops.com/propspd2.html
    Brian
    Monrovia, CA

  5. #5

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    Default Re: RPMs with What Prop

    Thanks Brian,
    A good calculator. What props are on the 135/140 HP O290-D2As on the Tri Pacers?
    The Data I have read states 140HP for takeoff, which is when you need it, for 5 Min. I don't know how you can get 2800

    O-290-D2A Certified 20 April 1953. 135 hp (101 kW) at 2600 rpm continuous, 140 hp (104 kW) at 2800 rpm for 5 minutes, 7.5:1 compression ratio, dry weight 236 lb (107 kg).

    O-290-D2B Certified 30 September 1954. 135 hp (101 kW) at 2600 rpm continuous, 140 hp (104 kW) at 2800 rpm for 5 minutes, 7.0:1 compression ratio, dry weight 236 lb (107 kg

    O-320 (No suffix) later redesignated O-320-A1A150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Provisions for a controllable-pitch propeller and 25-degree spark advance.

  6. #6
    dhillier's Avatar
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    Default Re: RPMs with What Prop

    Lycoming o-235 with M76 prop just repotted to 48" (climb prop) 2270 static rpm. Was slightly disappointed.

  7. #7

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    Default Re: RPMs with What Prop

    Quote Originally Posted by dhillier View Post
    Lycoming o-235 with M76 prop just repotted to 48" (climb prop) 2270 static rpm. Was slightly disappointed.
    i have same engine, Sen 76am6 with 46” and it winds up to 2500 static, The brakes can’t hold it so I can only run it wot for a few seconds before it brakes free.
    Last edited by AKJurnee; 02-10-2018 at 08:55 AM.

  8. #8
    pistoncan's Avatar
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    Default Re: RPMs with What Prop

    Do you know if it is the same brand prop as the original 74-58? I do know that one brand if 74-58 isn't necessarily the same as another brand. Is this a wood or metal prop? Obviously the prop is absorbing too much HP. It also seems obvious to me that if that was the original setup, they never intended to get the full 140HP out of the engine. A smaller/finer pitch prop would be the only way to get 2800 RPM.
    Last edited by pistoncan; 02-10-2018 at 11:50 AM.

  9. #9
    andya's Avatar
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    Default Re: RPMs with What Prop

    have to agree with this as well, don't ever remember flying many certified aircraft with original engine an prop that would turn rated power RPM with full throttle.
    "Progress is our most important problem"

  10. #10
    tloes's Avatar
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    Default Re: RPMs with What Prop

    I think the 140 hp @ 2800 was really intended for the handful of aircraft that had some kind of adjustable pitch propeller. If you go into the Shortwing History section of the site there's at least one article written by Collins where he gives a flight review of an adjustable pitch Pacer.

    Installing a fixed-pitch propeller that gives 2800 rpm in climb would really be over-optimizing toward climb performance (OPINION). The handful of aircraft that I've flown and thought were well balanced between climb and cruise were ones that hit rated rpm at full-throttle level flight. When I had the Tri-Pacer prop overhauled and repitched from 74 x 62 down to 74 x 58, it was a win-win. I ended up getting better cruise and better climb. At 62" (stamped 60" but measuring something closer to 62" at pre-overhaul inspection) it was only capable of 2300 rpm in climb and a little over 2500 rpm firewalled and level. The overhaul got me to 2500 rpm climb and 2650 firewalled and level.

    I'm flying a 145 hp Cessna now with a McCauley 76 x 53. I get almost identical climb and cruise to the old Tri-Pacer 150 but my firewalled and level RPM is now just a tad over 2700 rpm.

    These RPMs I mention are verified with optical or audio tachometers.

    Best regards,
    Todd Loes -- Waterloo, IA
    (PA22-150 N3568Z)

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