Results 1 to 31 of 31

Thread: prop rpm

  1. #1

    Join Date
    Mar 2013
    Location
    Lonoke Ar.
    Posts
    44
    Post Thanks / Like

    prop rpm

    quick ?.just finished an 18 with Dakota big wings and slots.31 tires .balanced 0360.mccaulley 82 42.im seeing 2300 or so on climb out with 2700 flat and level wide open indicating about 125mph.112 at 2500.does these numbers sound like its pitched ok.im used to 160 hp cubs with flat borers so don't know.it also has zero thrust mod.i had another 180 cub with stock wing and I think it was quite a bit faster flat out.i know wing is slower and has differ purpose but not that much.take off run feels ok for a 1210 lb plane.thanks

  2. #2

    Join Date
    Jan 2007
    Posts
    1,682
    Post Thanks / Like
    Sounds fast to me indicated airspeed can vary, what is GPS speed corrected for wind?
    DENNY

  3. #3
    Bill Rusk's Avatar
    Join Date
    Jan 2003
    Location
    Spokane Felts Field, WA/Poplar Grove, (Chicago) IL
    Posts
    5,234
    Post Thanks / Like
    Yes, the prop RPM sounds about right, for that prop and engine. The speeds seem about 5 to 10 MPH fast for 31"Bushwheels. Sounds more like what I would expect to see with 8.5 tires

    Bill
    Very Blessed.
    Likes TurboBeaver liked this post

  4. #4

    Join Date
    Apr 2010
    Location
    Anchorage, AK
    Posts
    4
    Post Thanks / Like
    Quote Originally Posted by skybolt64 View Post
    quick ?.just finished an 18 with Dakota big wings and slots.31 tires .balanced 0360.mccaulley 82 42.im seeing 2300 or so on climb out with 2700 flat and level wide open indicating about 125mph.112 at 2500.does these numbers sound like its pitched ok.im used to 160 hp cubs with flat borers so don't know.it also has zero thrust mod.i had another 180 cub with stock wing and I think it was quite a bit faster flat out.i know wing is slower and has differ purpose but not that much.take off run feels ok for a 1210 lb plane.thanks
    interesting. we weren't happy with nearly the same numbers. we're trying to work out a similar issue with an -18 with a stock wing and VG's and 160hp. had a mccauley 82/44 and static rpm was 2380, 2450 at liftoff. swapped to a 82/42 and barley gained any rpm. then swapped to a 82/41 and still didn't get the rpms we'd like, maybe 30 rpm increase. we'd turn 2700 in cruise at about 100KIAS. all at 2000lbs gross weight. our main goal is to get out of the hole on takeoff, so we're looking for a bit more static to help us in that regard. exhaust baffles are nearly new and no obvious signs of blockage. we're going down the road of re-jetting the carb to see if we can pour some gas on the problem and increase our rpm. i'll return with our results.

  5. #5

    Join Date
    Oct 2012
    Posts
    4,643
    Post Thanks / Like
    You may be interested in this thread. My comments in post #4 were after talking to Gerry at Dominion. http://www.supercub.org/forum/showth...op-pitch-ratio

    The opinion of the mechanic I was using at that time was that a healthy 160hp Cub should be spinning >2400 static with a healthy Borer. Pitch of the Borer didn't make much static RPM difference from my recollection.

  6. #6
    CubDriver218's Avatar
    Join Date
    Sep 2007
    Location
    Minnesota
    Posts
    626
    Post Thanks / Like
    Just for reference
    I see about 2350 static with 150hp and 82/43 borer
    about 2500 on climb out at 60 mph and 2700 flat wide open
    Just for reference
    Fast or slow, always low, freedom of flight soothes the soul.

  7. #7

    Join Date
    Nov 2003
    Location
    Thun Field, Washington
    Posts
    776
    Post Thanks / Like
    125 MPH @ 2700 and 112 MPH @ 2500 gives you an effective prop pitch of 47-48". With an 82-42, that math doesn't work.
    My 160HP Cub with an 82-43, 31s, etc. would go 120, but it was at 3000 RPM. That math does work.
    I don't have an O-360 Cub, but the math doesn't lie.

  8. #8
    Crash's Avatar
    Join Date
    Apr 2002
    Location
    Nikiski Alaska
    Posts
    2,695
    Post Thanks / Like
    Quote Originally Posted by skybolt64 View Post
    quick ?.just finished an 18 with Dakota big wings and slots.31 tires .balanced 0360.mccaulley 82 42.im seeing 2300 or so on climb out with 2700 flat and level wide open indicating about 125mph.112 at 2500.does these numbers sound like its pitched ok.im used to 160 hp cubs with flat borers so don't know.it also has zero thrust mod.i had another 180 cub with stock wing and I think it was quite a bit faster flat out.i know wing is slower and has differ purpose but not that much.take off run feels ok for a 1210 lb plane.thanks
    I was flying the same engine / prop today and seeing 105 - 107 mph at 2350 / 2400 (since 2005). I'd leave it alone.

    Crash

  9. #9

    Join Date
    Mar 2013
    Location
    Lonoke Ar.
    Posts
    44
    Post Thanks / Like
    thanks everyone..im going to solid up my numbers on next calm day with the gps both directions..airspeed indicator may be a little off,,but it did just come back from overhaul with the tach and everything else.by the way,the prop I am using is the big,thick fat legal one that goes with the cubcrafter 180stc,not the boerer pencil tip prop.once I get just a little time on her and the neighbors stop stopping by to look..i have a new catto in the shop to go on a friends backcountry cub when done....so guess what..LOL.and I guess I do keep forgetting about the 31 inchers under there.you know,25 years ago my first rebuild I put 8.50s on it and they looked like monsters here in Arkansas.now the 31s look normal beside the 35s on the backcountry.I know I don't need them here in Ar.,,but they look so cool.LOL

  10. #10
    hotrod180's Avatar
    Join Date
    May 2008
    Location
    Port Townsend, WA
    Posts
    2,640
    Post Thanks / Like
    Rule of thumb that I've seen is
    RPM x Pitch / 1056 = MPH
    FWIW I bought a new Sensenich prop for my C150/150 a few years ago, it was factory-stamped 56 but when the prop shop measured it it was darn near 57.
    Cessna Skywagon-- accept no substitute!

  11. #11

    Join Date
    Nov 2003
    Location
    Thun Field, Washington
    Posts
    776
    Post Thanks / Like
    Do the numbers backward. 125MPH X 1056/2700=48.8" of pitch.

  12. #12
    Aviator's Avatar
    Join Date
    Jun 2002
    Location
    Canada (Legally)
    Posts
    1,398
    Post Thanks / Like
    I'd install a M/P gauge at least for test flights. It might help sort out any apparent inconsistencies.

  13. #13
    Scooter7779h's Avatar
    Join Date
    May 2004
    Location
    Anchorage, Alaska
    Posts
    983
    Post Thanks / Like
    Quote Originally Posted by stewartb View Post
    You may be interested in this thread. My comments in post #4 were after talking to Gerry at Dominion. http://www.supercub.org/forum/showth...op-pitch-ratio

    The opinion of the mechanic I was using at that time was that a healthy 160hp Cub should be spinning >2400 static with a healthy Borer. Pitch of the Borer didn't make much static RPM difference from my recollection.
    It's turning 2425 now SB

    Sent from my SM-G920V using Tapatalk
    =========
    PA-12 fan

  14. #14
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,358
    Post Thanks / Like
    Quote Originally Posted by hotrod180 View Post
    Rule of thumb that I've seen is
    RPM x Pitch / 1056 = MPH
    FWIW I bought a new Sensenich prop for my C150/150 a few years ago, it was factory-stamped 56 but when the prop shop measured it it was darn near 57.
    Quote Originally Posted by Carey Gray View Post
    Do the numbers backward. 125MPH X 1056/2700=48.8" of pitch.
    That is an interesting rule of thumb. How do you take into consideration different diameters and chord of the blades? Also how about the drag coefficient of the airplane? The same prop on a 150/150 will give different results on a 150/PA-18, Bush wheels, floats etc. A new full sized prop will give different results than a same dimension prop which has been "repaired" down to minimum dimensions. With these thoughts, when comparing different props on the same airplane the rule of thumb is a good starting point.
    N1PA

  15. #15
    hotrod180's Avatar
    Join Date
    May 2008
    Location
    Port Townsend, WA
    Posts
    2,640
    Post Thanks / Like
    That formula is a rule of thumb, not a hard & fast written in stone. It calculates how far the a given pitch prop screws itself (and the airplane) forward in the air for a given rpm.
    pitch x rpm = forward travel in inches per minute x 60 = inches per hour, /12 = feet per hour, /5280 = mph.
    The times 60 divided by 12 divided by 5280 thing works out to divided by 1056.
    Last edited by hotrod180; 02-20-2016 at 10:39 AM.
    Cessna Skywagon-- accept no substitute!

  16. #16

    Join Date
    Apr 2010
    Location
    Anchorage, AK
    Posts
    4
    Post Thanks / Like
    Quote Originally Posted by mydoghasa170 View Post
    interesting. we weren't happy with nearly the same numbers. we're trying to work out a similar issue with an -18 with a stock wing and VG's and 160hp. had a mccauley 82/44 and static rpm was 2380, 2450 at liftoff. swapped to a 82/42 and barley gained any rpm. then swapped to a 82/41 and still didn't get the rpms we'd like, maybe 30 rpm increase. we'd turn 2700 in cruise at about 100KIAS. all at 2000lbs gross weight. our main goal is to get out of the hole on takeoff, so we're looking for a bit more static to help us in that regard. exhaust baffles are nearly new and no obvious signs of blockage. we're going down the road of re-jetting the carb to see if we can pour some gas on the problem and increase our rpm. i'll return with our results.
    so a little post modification info for those interested. We initially chased a lean condition idea but after our mechanic checked out the jet, turns out we were a bit rich and bogging down on takeoff. Our guy did a little port, polish, and helped the air with a little annular action through the Venturi (essentially increasing the air volume) and compensated for the rich condition. We gained back significant RPMs. Took some washout out of the wings and now it's a properly performing cub.

  17. #17
    mvivion's Avatar
    Join Date
    Jun 2003
    Location
    Bozeman,MT
    Posts
    10,465
    Post Thanks / Like
    Quote Originally Posted by skybolt64 View Post
    thanks everyone..im going to solid up my numbers on next calm day with the gps both directions..airspeed indicator may be a little off,,but it did just come back from overhaul with the tach and everything else.by the way,the prop I am using is the big,thick fat legal one that goes with the cubcrafter 180stc,not the boerer pencil tip prop.once I get just a little time on her and the neighbors stop stopping by to look..i have a new catto in the shop to go on a friends backcountry cub when done....so guess what..LOL.and I guess I do keep forgetting about the 31 inchers under there.you know,25 years ago my first rebuild I put 8.50s on it and they looked like monsters here in Arkansas.now the 31s look normal beside the 35s on the backcountry.I know I don't need them here in Ar.,,but they look so cool.LOL
    Have you used a digital tach checker to verify that tach is accurate? If not, you need to. I had my tach overhauled, and it came back 50 rpm off. I figured that sucked, but mechanics said its legal....just placard the error on the panel. But, I traded that overhauled tach for a new one.....which it turned out was 100 rpm off at max.....again, legal, just placard. I ordered a digital tach and never looked back.

    without knowing if you have tach error, you've no way of knowing if what you're doing is legal or smart.

    MTV

  18. #18

    Join Date
    Jul 2009
    Location
    racine,wi
    Posts
    684
    Post Thanks / Like
    Just a small amount of carb,or intake or induction tube ice will reduce rpm. if you pull carb heat and get a reduction you most likely have some ice. its a rare day I don't get some kind of ice.I can feel it in the 160hp my 52 pitch sench,can turn up 3000rpm level flight on a good no ice day.the 180s HP cubs its smoother with ice,my be the big prop.

  19. #19

    Join Date
    Jan 2007
    Posts
    1,682
    Post Thanks / Like
    ????
    Denny

  20. #20

    Join Date
    Jul 2009
    Location
    racine,wi
    Posts
    684
    Post Thanks / Like
    Most pilots I fly with don't under stand ice, we tow signs big sign s we need 100percent I have only 3000 hrs in cubs and 18,000 total all in pistson.I can't spell but I do know carb,induction Ice .Did high performace check out in piper 235,the pilot did not know what the carb heat gage was for nor did her try the carb heat ,well I pulled the carb heat and it lost 400 rpm,he could not beleive it.That said every time you pit up a big banner you are at 100 percent and you can tell you are not getten it when you only have2200 rpm. so 15 to 20 min later you find a carb heat setting that will keep ice out. there for, when someone tells what RPM they are getting if low most likly they had ice at that time.

  21. #21

    Join Date
    Jan 2007
    Posts
    1,682
    Post Thanks / Like
    You should get a reduction in RPM any time you pull carb heat because you are running hotter less dense air. It should drop more than normal with carb ice and than slowly increase as ice clears.
    DENNY

  22. #22
    Eddie Foy's Avatar
    Join Date
    Dec 2014
    Location
    South Florida
    Posts
    3,420
    Post Thanks / Like
    Quote Originally Posted by DENNY View Post
    You should get a reduction in RPM any time you pull carb heat because you are running hotter less dense air.
    DENNY
    Unless you are running over rich.
    "Put out my hand and touched the face of God!"

  23. #23

    Join Date
    Jul 2009
    Location
    racine,wi
    Posts
    684
    Post Thanks / Like
    or its 110degrees f out side

  24. #24

    Join Date
    Jan 2007
    Posts
    1,682
    Post Thanks / Like
    If you are running over rich you will still get a drop, engine might just quit. I had loose float bowl screws cause the over rich problem I would loose 300 rpm when I pulled carb heat. I have flown in 100 degree heat and it would still drop RPM when I pulled carb heat, because it still raised the temp on the air going to the carb. In both situations you are going to change the air fuel mixture and you should see a drop in RPM. Now if temps where -40 carb heat might help atomize fuel and give you more power but at -30 I still got a RPM drop. Just to be clear when I say RPM drop I mean 75-100 RPM. If I drop more than that I suspect carb ice.
    DENNY
    Last edited by DENNY; 04-01-2016 at 12:34 AM.
    Thanks Redwagon thanked for this post

  25. #25

    Join Date
    Feb 2006
    Location
    N. california
    Posts
    107
    Post Thanks / Like
    what does the STC list as minimum static rpm for the 82/41?

  26. #26

    Join Date
    Jan 2005
    Location
    Fowler, Ks
    Posts
    525
    Post Thanks / Like
    The STC for my 82/41 is out in the hangar but pretty sure it's 2350 and max is 2450.

  27. #27
    PerryB's Avatar
    Join Date
    Aug 2007
    Location
    Northern Calif.
    Posts
    1,810
    Post Thanks / Like
    My standard "gauge" is if it'll WOT/run out to at least 2700, you're about right. Both my props will make about 2750 and I personally feel thats ideal.
    After Monday and Tuesday, even the calendar says WTF !
    Likes hotrod180 liked this post

  28. #28

    Join Date
    Feb 2006
    Location
    N. california
    Posts
    107
    Post Thanks / Like
    as far as best pitch goes. I would think one would want to see max RPM in a Vx climb. That would be when you would need it most.
    just my 2cents.

  29. #29
    PerryB's Avatar
    Join Date
    Aug 2007
    Location
    Northern Calif.
    Posts
    1,810
    Post Thanks / Like
    I'd love to de-pitch a couple inches for purposes of takeoff/climb, but then my groundspeed would have to be measured on a calendar. If only there were some way to magically control the prop from inside the cockpit........
    After Monday and Tuesday, even the calendar says WTF !
    Likes DENNY, mam90 liked this post

  30. #30

    Join Date
    Jan 2005
    Location
    Fowler, Ks
    Posts
    525
    Post Thanks / Like
    I just repitched a 74/48 sensenich to 52. At 48 on a 150 hp engine it would spool up to 2700 climbing at 70 mph....climbed like crazy.
    Static was 2570, a bit over TCDS. and WOT level was approaching 3 grand, it would reach 112 mph with 26 goodyears though.
    52" on that prop works out right at the top limit for the type certificate. and WOT 2750 and 115 mph on a timed average.
    Likes DENNY liked this post

  31. #31

    Join Date
    Sep 2018
    Posts
    1
    Post Thanks / Like
    Wing strobe

    Sent from my SM-G892A using SuperCub.Org mobile app

Similar Threads

  1. Cruise Prop vs. Climb Prop
    By j3jm in forum Cafe Supercub
    Replies: 7
    Last Post: 04-24-2019, 01:50 PM
  2. Correct prop torque for McCauley prop
    By OVEREASYGUY in forum Super Cub Sick Bay
    Replies: 2
    Last Post: 03-07-2006, 03:35 PM
  3. Cruise prop vs. climp prop
    By aktailwheel in forum Tips and Tricks
    Replies: 13
    Last Post: 06-22-2004, 11:06 AM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •