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Thread: Pa17 A75 Prop

  1. #1
    Join Date
    Dec 2011
    Location
    Powhatan, VA
    Posts
    4

    Default Pa17 A75 Prop

    Hi there,
    I'm having trouble finding the right metal prop for my Continental A75 on my 1948 PA17. My A&P says it's the McCauley 1B90/7045. I called McCauley and they gave me 3 models; 1B90/CM7038, 7040 and 7045. McCauley said the 7045 was a cruise prop (I'd prefer the standard or the climb prop), but my A&P can't confirm that the 7038 or 7040 can legally be used on the A75. Can anyone confirm or provide paperwork that proves either the 7038 or 7040 can be used on an A75? Any help you can provide is much appreciated.
    Paul Roberts

  2. #2
    Join Date
    Nov 2006
    Location
    Mason, Ohio
    Posts
    341

    Default

    Paul,


    I am no expert on the Vag, but from what I can tell based on the Type Cert and a search of STCs the A-75 must have been installed on a field approval. There is no STC that I could find for the engine change and the Type Cert only allows the A-65. There is an STC for a C-90 but not the A-75. Given that, I would think it goes back to the Type Cert for the airframe and the engine. The airframe Type Cert says


    Propeller - McCauley 1B90/CM7248 or any other Model 1A90 or 1B90/CM propeller
    which meets the following limits:
    Static r.p.m. at max. permissible throttle setting:
    Not over 2250, not under 2150.
    No additional tolerance permitted.
    Diameter: Not over 72 inches, not under 71 inches.


    The engine Type Cert allows up to 2600 to 2650 max continuous RPM so the only constraint is where the airframe Type Cert states "or any other Model 1A90 or 1B90/CM propeller". Based on that I would believe that either the standard or climb prop is legal.


    Tom Anderson

  3. #3
    Join Date
    Dec 2011
    Location
    Powhatan, VA
    Posts
    4

    Default

    Hey Tom,
    I found an STC for the A75-8 on an old 337. The STC is SA3-376. I've looked on the FAA website for it but can't find reference to it. I think this was a CAA STC (pre-FAA) at the time--don't know if that makes a difference. Is there a way to tell what prop can be used for this STC or is there someone who might know where to look or who to talk with? My IA is hesitant about putting anything but a 1B90/7045 (cruise prop--which I don't want) on the plane, because it's the only thing he can find actual paperwork on. He's being a bit of a stickler.
    Any help is much appreciated. Paul

  4. #4
    Join Date
    Nov 2006
    Location
    Mason, Ohio
    Posts
    341

    Default

    Paul,


    I could find no data on STC SA3-376 as well. I do not know what the requirements were for filing STCs and 337s back when the CAA was in charge so I don't know what data was required with the filing. However, the prop is specified by the Type Certificate or the Type Certificate as modified by an STC. If the engine change STC does not specify a prop, the specifications of the Type Certificate apply. As I indicated in my first answer, the Type Certificate allows any 1B90/CM prop that meets the requirements specified. In this case the maximum static RPM must be between 2150 and 2250 and the diameter must be between 71 and 72 inches. If your climb prop meets those requirements per McCauley, I would say you are legal to put the 1B90/CM7038 or 1B90/CM7040 on the plane. If the calibrated RPM exceeds the limits, you may be able to limit the max throttle opening to bring the RPM within limits. You can check with your local FSDO to verify this, but I think they will agree. The Type Certificate is what rules in this case and you can verify that with your local FSDO inspector. Try and find an old one that know a little about old airplanes. You might ask them as well what the status of old CAA STCs is.


    Tom Anderson

  5. #5
    Join Date
    Nov 2006
    Location
    Mason, Ohio
    Posts
    341

    Default

    Paul,
    There is one other thing you should understand. If the cruise prop doesn't make minimum RPM you don't have many options. With a climb prop, you have the option of limiting the throttle.

    Tom Anderson

  6. #6
    Join Date
    Nov 2006
    Location
    Mason, Ohio
    Posts
    341

    Default

    Paul,
    While doing some other work I came across STC SA378NW which is for putting an A75 in a PA-15. It is for S/N 15-283 only. I don't know if it's at all related to STC SA3-376 or not, but it might be worth some investigation.


    Tom Anderson

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