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Thread: Let's talk propellers

  1. #21
    andya's Avatar
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    Default Re: Let's talk propellers

    Quote Originally Posted by Subsonic View Post
    Don,
    Concur with all. I didn't know TCDS limited max allowable pitch, thanks for that info.
    I don't think all TCDS limit pitch, some just list an RPM range for static runup

    Some TCDS limit pitch of prop and maybe not give an RPM range
    "Progress is our most important problem"

  2. #22
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    Default Re: Let's talk propellers

    TCDS 1A6, which covers all the PA22 variants, lists the permissible props for the permissible engines fitted.
    As far as fixed pitch props are concerned, it specifies for each prop model (eg Sensenich M74DM), the maximum and minimum length limits of the prop (eg max 74", min 72.5"), and the allowable static RPM range (eg min 2250rpm, max 2480rpm). It doesn't mention anything to do with prop pitch for any fixed pitch prop listed (it does for the Aeromatic, two position, and constant speed prop options, but that's a different story).
    Interestingly, it doesn't mention the air temperature or field elevation (ie density altitude) at which the static rpm is measured. I'd presume sea level, but don't know. It's a long time since I've operated out of a 8000' DA strip, so don't recall the effect of that on static rpm, except that not leaning to peak rpm before brakes release could be a life altering experience!
    As has been said, props tend to go fine with age, but they also 'cone' forward due to the thrust, get lighter with 'repairs', and shorter with tip damage. My prop man tells me that all he needs to know is what the static rpm is, and he can adjust the pitch up or down to get the rpm I want. There's a limit to the number of times a prop can be 'tweaked', I seem to recall.
    Last edited by 59pacer; 12-29-2017 at 12:34 AM.

  3. #23
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    Default Re: Let's talk propellers

    Picking up on Steve's comment about props flattening over time, especially with lots of static run-ups: Does a 2,000 RPM mag check count as a static run-up, or do you really have to go to full throttle? Q2: How much can a prop be re-pitched in inches? - thinking there has to be a practical limit. And how many times can you re-pitch it? Can you twist a 61 to become a 58, then a 56 and then go back to 61 again? Just curious.

  4. #24

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    Default Re: Let's talk propellers

    Quote Originally Posted by Subsonic View Post
    Picking up on Steve's comment about props flattening over time, especially with lots of static run-ups: Does a 2,000 RPM mag check count as a static run-up, or do you really have to go to full throttle? Q2: How much can a prop be re-pitched in inches? - thinking there has to be a practical limit. And how many times can you re-pitch it? Can you twist a 61 to become a 58, then a 56 and then go back to 61 again? Just curious.

    I talked to Sensenich folks at Sun n Fun this year and was told that 8” was the maximum allowed change over the life of the prop. I will look for the 61” max allowed reference. I saw it somewhere.

    Don Broussard

  5. #25
    Gilbert Pierce's Avatar
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    Default Re: Let's talk propellers

    Quote Originally Posted by Subsonic View Post
    Picking up on Steve's comment about props flattening over time, especially with lots of static run-ups: Does a 2,000 RPM mag check count as a static run-up, or do you really have to go to full throttle.
    Static run up: Full throttle with the brakes locked is what flattens the prop over time.

  6. #26
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    Default Re: Let's talk propellers

    At each annual, I do a static rpm check for the records. At almost sea level, no wind, full throttle, brakes barely holding, I get 2320rpm +/- every year for the last few years. The compressions are mid 70s, but it doesn't do many hours per year. That's with an O320 160hp, and a good condition prop stamped 61". It always feels to me that it is labouring a bit.
    My previous 150hp Pacer with lower compressions, 58" prop on it's last legs before becoming a wall mounting, cruised about 5kts faster than my current 160hp Pacer, and smooth to go with it!
    I always run my engines just under 75% power. Being anal, I blew up the power graphs from the engine data and had them laminated so I can accurately check what power I'm actually getting from rpm, map, oat etc etc.--presuming of course that the gauges are adequately accurate!
    Last edited by 59pacer; 12-29-2017 at 03:12 PM.

  7. #27
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    Default Re: Let's talk propellers

    I'm not an expert on anything, but I am using the 74DM 61 on a 150 HP Tripacer. I chose that prop on purpose because I travel between Maryland where I live and Ohio where my dad lives. I do not fly from short fields and my plane is a Tripacer so aerodynamicly its not the cleanest plane ever built. It does not have wheel pants or VG,s and it has the Piper round tips. The engine is a mid-time O-320 no dash number with compression in the mid 70's and 150 HP. Here are the numbers for those of you interested.
    Empty weight 1137 pounds with oil, just across the scales last year
    Field elevation is 140 feet MSL and 4500 feet long.
    Static RPM about 2300 but I never fly in a static condition
    Full fuel and 200 pound pilot
    OAT 30 degess F (Today)
    Takeoff no flaps 600 feet climd at 80 MPH @1200 FPM and 2450 RPM
    flight time 1.14 hours, fuel consumed 8 gallons with two full power takoffs
    Same airport and pilot/fuel with OAT 90 degrees with the DA at 2100 feet
    Takeoff roll less than 1000 feet, climb rate ~650 FPM

    Would I use this prop if I flew from short fields or high field elevations? No, at that point it would b the 58" pitch and enjoy a shorter takeoff roll and better climb rate.

    For what its worth,
    Steve
    Last edited by Wag-builder; 12-29-2017 at 09:32 PM.

  8. #28
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    Default Re: Let's talk propellers

    for those with apple products, there is an app by James Petty, called AircraftPower which
    runs the graphs after you put in Manifold Pressure, RPM, Altitude,Temperature.
    Neat app. I used coming home from Steve's AC to be sure I ran above 75%
    as much as possible to get good seating of the rings on the fresh ovhl
    the app covers engines from the O-235 thru many of the O-320 and O-360 engines
    "Progress is our most important problem"

  9. #29
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    Default Re: Let's talk propellers

    Quote Originally Posted by Cajunwings View Post
    I talked to Sensenich folks at Sun n Fun this year and was told that 8” was the maximum allowed change over the life of the prop. I will look for the 61” max allowed reference. I saw it somewhere.

    Don Broussard
    I got the same info from my prop shop tech, 8" total change over the life. I bought a used prop that was at 63".
    I was told the factory makes them at 60" and this was twisted to 63" for the manufacture, so 3" of adjustment was used then
    I had it ovhld and twisted back to 60" as that is what I wanted with the engine conversion. The prop can be twisted
    2 more inches and then it is done. As I understand, I could twist it to 59 then back to 60 and that counts as
    the 2 inches left or could go to 58 or 62 one time.
    "Progress is our most important problem"

  10. #30
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    Default Re: Let's talk propellers

    Oops, left out some critical information! Cruise power is 2300 RPM and 115 MPH indicated airspeed.

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