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Thread: 90" mac on a 185"

  1. #1

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    90" mac on a 185"

    Lately I've talked to a few guys who put a 90" C203 off of a 180K on a 185 on floats. Has anyone seen this done and was it done legally? I've heard this from a a few unrelated sources and they swear by it so it makes me curious.


    I know tip speed would be an issue. I've never run the numbers but I know my 86" Mac is plenty loud and the common knowledge is that tip speed may kill some efficiency.
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    Dave Calkins's Avatar
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    tip speed killing efficiency??

    lotsa people say that.

    really, spin faster and they keep pulling harder. same goes for a 90" on a Cub.

    90" on my '53 C180 made that airplane what it is. of course it wasnt turning 2850rpm, so what do I know?! I havent done it on a 185.

    Bbut an 88" 401 Mac makes the 185 go, same as it makes a 206 a worthy floatplane when all the guys who fly em with Hartzells think 206's on floats are dogs.

    .......401 on IO520 206 by field approval with the low stops set to give full static.....

    PS.......efficiency and peak thrust are not associated in my thinking
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    FdxLou's Avatar
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    Dave
    I’m running an 84” Hartzell on my ‘54 180. How much cruise speed do you think I would lose going to a 90”?
    You say it really woke up yours?
    Lou

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    gntw's Avatar
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    Quote Originally Posted by FdxLou View Post
    Dave
    I’m running an 84” Hartzell on my ‘54 180. How much cruise speed do you think I would lose going to a 90”?
    You say it really woke up yours?
    Lou
    Tried the 90 in 204 on my p ponk 520 one day.have the 84 hartzell ran same day 1/2 hr apart same alt same heading same power setting the 204 was 10 mph higher air speed . Ran it for 30 hrs did every thing better. Steve says u can't run it. I have a c-58 86 I am going to try

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    algonquin's Avatar
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    When I got my 185, I'm-520 it had a 88" Mac on it and it was super loud. Also illegal by the TCDS. I had it cut to 86" and it was much quieter , I didnt have it long enough before I changed it to really know the difference . So from what I saw was the 180 w/ a 470 can have a 88" and the 520 a 86" and the guy that was my IA at the time wouldn't sign it off until I had it cut.

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    Quote Originally Posted by Dave Calkins View Post
    tip speed killing efficiency??

    lotsa people say that.

    really, spin faster and they keep pulling harder. same goes for a 90" on a Cub.

    90" on my '53 C180 made that airplane what it is. of course it wasnt turning 2850rpm, so what do I know?! I havent done it on a 185.

    Bbut an 88" 401 Mac makes the 185 go, same as it makes a 206 a worthy floatplane when all the guys who fly em with Hartzells think 206's on floats are dogs.

    .......401 on IO520 206 by field approval with the low stops set to give full static.....

    PS.......efficiency and peak thrust are not associated in my thinking
    How did you get approval for the 90” on any other 180 than the K model?

  7. #7

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    I agree on the spin faster-better pull comment. It even works in winter in cold temps. Noisy? Heck yes, but I loved the thrust. The higher rpm is a dynamic thing. I wouldn't expect static pull to have the same results.

    My old 88" prop on my 180 was a 90-2. 185s typically use a 90-4, right? 86" max per TCDS? A longer prop requires an approval?
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    FdxLou's Avatar
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    Quote Originally Posted by gntw View Post
    Tried the 90 in 204 on my p ponk 520 one day.have the 84 hartzell ran same day 1/2 hr apart same alt same heading same power setting the 204 was 10 mph higher air speed . Ran it for 30 hrs did every thing better. Steve says u can't run it. I have a c-58 86 I am going to try
    I would have thought with the larger disc diameter the 90” would be slower at the same power setting?
    Lou

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    Dave Calkins's Avatar
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    sorry. I typed a response but the slow internet at the lodge ate it.

    0-470A and mac with 90" blades by Northwest Propellers STC.

    ........on another early 180 that ran a short prop before the 90" the out of the hole performance was night and day. I do Not remeber the cruise penalty.

    I got the firewall forward and prop from that plane in exchange for an engine install. Put that 90" and A-model on my 1953.
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  10. #10
    gntw's Avatar
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    Quote Originally Posted by FdxLou View Post
    I would have thought with the larger disc diameter the 90” would be slower at the same power setting?
    Lou
    Run the prop for 30 hrs on my 77k model. It was definitely faster ran smooth. I have this combination working good with right carb and set up . Will be trying the c-58.

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    I have a 90 inch Mac on my "73" 185F . Everyone flips me off on take off in the canyons in Idaho, so tip speed is an issue. A strong hole shot, but never tried any other prop for cruise performance.
    I can dig up the paper work on it if it will help you. gmcmillan19@yahoo.com

  12. #12
    skywagon8a's Avatar
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    How did any of you using these extra long props comply with: https://www.faa.gov/documentLibrary/...r/AC_36-4D.pdf ? Do you have a placard which tells you to reduce power or rpm shortly after take off?

    "(2) Acoustical changes
    There are four categories of small propeller-driven airplanes excluded from this evaluation of voluntary changes: 1) Airplanes designated for “agricultural aircraft operations” as defined in §137.3 of part 137; 2); Designated for dispensing firefighting materials; 3) U.S. registered and had flight time prior to January 1, 1955; and 4) Land configured airplanes reconfigured with floats or skis (non-permanent seasonal changes to the landing gear)."

    It seems that a float or ski plane would be exempt.
    N1PA

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    hotrod180's Avatar
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    Tip speed and the resulting efficiency and noise issues aren't the only factors.
    Part of prop approval for specific engines includes making sure that there are no destructive harmonics (unfelt vibration) going on.
    Those are why those 76" Hartzells have a "avoid operation" range when installed on 360 Lycomings.
    Also why a C203 Mac isn't approved on a Ponk 470-50.
    I'd be pretty nervous about installing a prop that wasn't specifically approved for my engine.
    Cessna Skywagon-- accept no substitute!

  14. #14
    Dave Calkins's Avatar
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    vibe surveys on props are how engineer and fed types get to scare the airplane jockeys.

    ....only mostly joking.

    ...........supposedly a Pawnee prop at 90" doesnt jive (vibe) well with an 0-360 Lycoming on a Cub, but we run em and love em just fine.

    Like I said, only "mostly" joking....

  15. #15

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    Quote Originally Posted by gmcmillan View Post
    I have a 90 inch Mac on my "73" 185F . Everyone flips me off on take off in the canyons in Idaho, so tip speed is an issue. A strong hole shot, but never tried any other prop for cruise performance.
    I can dig up the paper work on it if it will help you.
    Emailed you, I'd love to see that paperwork. Even an N number would help and I'll order the FAA records.

  16. #16

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    Quote Originally Posted by gmcmillan View Post
    I have a 90 inch Mac on my "73" 185F . Everyone flips me off on take off in the canyons in Idaho, so tip speed is an issue. A strong hole shot, but never tried any other prop for cruise performance.
    I can dig up the paper work on it if it will help you. gmcmillan19@yahoo.com
    I bet that’s a screamer, my 88 x 3 blade on 520 is so terrible I end departures announcements in close quarters with “stick your fingers in your ears” and yes as my Mac ages out I’m deffinately looking for quieter and understand there is some hope out there in STC land.
    Last edited by OLDCROWE; 08-08-2018 at 09:42 PM.
    Remember, These are the Good old Days!

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    FdxLou's Avatar
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    Kirby
    Unless you need the performance just dial it back a few hundred RPM and go. Chances are you won’t notice much of a difference.
    Lou

  18. #18

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    Put a grommet or wooden clothespin on the prop control shaft to limit it short of full rpm. I've done it on cold winter days. You want noise? Spin an 86 or 88" prop at 2850 or more when the DA is -3000' and you're in a narrow creek bottom. Not a pleasant experience for the neighbors, but boy howdy it sure does go!

  19. #19

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    Quote Originally Posted by FdxLou View Post
    Kirby
    Unless you need the performance just dial it back a few hundred RPM and go. Chances are you won’t notice much of a difference.
    Lou
    It's very noticeable until lift off, leave it full in after that and it goes UP but does not accelerate all that much. For me 8-10 half turns on the prop knob is my standard for an airport departure, then adjust in early in the climb to get RPM's into the green. Out of my place (at least until I get more practice in more conditions) it's balls to the wall then start dialing it back just as soon as the wheels are off!
    Last edited by OLDCROWE; 08-09-2018 at 04:22 PM.
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  20. #20
    behindpropellers's Avatar
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    Keep in mind that the K model has a "U" engine that is only supposed to spin up to 2400.

    So your tip speed is at mach .83 while Kirby is running around mach .99.

    Tim

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