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Thread: Power settings on C90

  1. #1

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    Power settings on C90

    I'm curious to hear from some experienced A&P mechanics who know these little engines well, their thoughts about cruise power settings on the C90. The power chart shows 75% power around 2250 rpm which is barely half throttle in cruise. You hear some guys who act like they are have special information from Continental say run it wide open, all the time and you won't hurt it. I'm curious what the general consensus is if fuel burn is not an issue. 2450 gives you a nice 100 mph in level flight so that doesn't suck but on the chart that's 90 percent power right? It it is running cool is that ok? Looking for some feedback.

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    If in a J3, remember max structural cruise is 91 mph.

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    Quote Originally Posted by bob turner View Post
    If in a J3, remember max structural cruise is 91 mph.
    I may have posted in the wrong thread but it’s a Pa-18


    Sent from my iPhone using Tapatalk

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    Crash, Jr.'s Avatar
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    100mph is sure an impressive number and at 2450 I think it still leaves some throttle left. On my C85 I run at 2250 or 2300 for about 85mph but that's in a much draggier J3 airframe.

    IMO the cruise power number is a more personal thing based on how fast you want to get places, how much fuel you are ok with burning, and where your particular engine runs smoothest. I honestly wouldn't worry about running a small continental closer to redline. They seem to be pretty strong engines that can take a lot. The same basic engine in the O200 runs upwards of 2700rpm just fine. JimC has posts from a while ago with performance numbers pushing a C90 up to 2850 so they'll take a lot and be just fine.
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    I run my c-90 PA-11 about 2350 most of the time push to 2400-2450 and I just use oil for a couple of mph.
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    BC12D-4-85's Avatar
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    The Continental Owner's Manual X30012 Page 4 recommends 2350. The power developed depends on rpm and manifold pressure modified by pressure altitude. Rated rpm is 2475 with 2625 allowed for 5 min. Maximum recommended cruise manifold pressure is 24.5" which may or may not be reached at a given rpm. I've flown mine at 2350-2400 and monitor oil temp.

    Edit: That's with a 76AK-2-40 prop where 2400 is reached before 24.5" MP. Different prop-intake-exhaust = different rpm at a given manifold pressure.

    Gary
    Last edited by BC12D-4-85; 10-24-2020 at 10:14 PM.
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    cubdriver2's Avatar
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    Couple thousand hrs behind a C90-8 and most of it at 2400-2450rpm

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    BC12D-4-85's Avatar
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    ^^^^^^That's what Don Swords (C-85 Stroker STC) recommended to me. Just monitor engine temps and fly like you stole it.

    Gary
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    Alex Clark's Avatar
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    My C90-8 powered cub was usually on floats. With a 76AK-2 -40 prop. So I cruised at 2200 rpm just to save fuel. Extra rpm did not give me much more speed. On 26 inch Goodyear’s with the same prop I usually did 2350 rpm for a long range cruise. I was burning 75% car gas and 25 % 100LL. Plus a shot glass of MMO once a day.
    Float and Tailwheel CFI,
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    http://www.floatplanealaska.com

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  10. #10
    Waldo M's Avatar
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    Stock PA-11 w/ C-90-8 and Sensenich W76CK-40 prop. 2300 rpm when just flying around for a local ride, 2350 on a X-C when downwind, 2400 on an upwind X-C, 2450 to 2475 [max continuous RPM] on an X/C flown much above 5000' (not a high percentage of power at higher altitudes).

    I run 100LL and use an occasional shot glass of JD.
    Last edited by Waldo M; 10-25-2020 at 08:32 PM. Reason: High altitude cruise revision
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  11. #11
    Waldo M's Avatar
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    Don Swords (a small Continental engine guru and holder of some well known STCs on them) built my C-90. He told me the same thing; running these engines hard won't hurt them.
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  12. #12

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    i think different props will tell you different stories, listen to what its telling you. im like alex, my 7440 says 2250 plus or minus for the long haul.
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  13. #13
    Alex Clark's Avatar
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    I beg to differ on running them hard.
    I had a commercial pilot doing his SES check-ride who never throttled back during his ride. At least not much.
    He noted a sudden loss of power. When they came into the dock, there was oil all over the place. and the ENGINE was hot as hell.
    He had cracked a cylinder and had cracked the flange around the oil sump. That put me out of business for a couple weeks, loosing 3 more float ratings customers, plus a new jug, A&P time and Hangar rent time.
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    Float and Tailwheel CFI,
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  14. #14
    BC12D-4-85's Avatar
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    An engine properly installed and in good health with proper fuel flow-mag timing should be ok at the rated rpm of 2475. An accurate tach is critical so is monitoring oil temps...and CHT/EGT if available. Nobody is suggesting exceeding the manufacturer's recommendations by the term "running hard". Sorry to see your results...what was defective? Engine-operator-check pilot?

    Gary

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    Alex Clark's Avatar
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    Hotdog SES Applicant ran her full open much of the check ride and the DPE did not tell him to quit.
    I suspect he was over 2500 most of the time.
    Even limping the 70 miles home, knowing it was damaged and bleeding oil, he still wanted to buzz his buddy's house.
    75 year old technology, from a time when they expected you to replace the engines and planes every few years.
    Float and Tailwheel CFI,
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  16. #16
    BC12D-4-85's Avatar
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    I'd have contemplated a joint Teamster Burial. Sorry to hear that happened. Continuous RPM is critical but as I mentioned earlier so is 24.5" MP recommended by Continental for cruise. With a similar prop (76AK-2-40) over 2400 (not sure exact rpm) I can hit the MP limit before max continuous rpm limit up to altitude that limits the pressure. I believe both limits should be avoided. Plus a MP gauge gives carb ice warning before most wobbling tachs.

    Edit: One reason again for an electronic tach or MP gauge with redline warning LED.

    Gary
    Last edited by BC12D-4-85; 10-25-2020 at 10:16 PM.

  17. #17
    Cub Special Ed's Avatar
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    2300 @ 85mph cruise. 1800-1900 at 68mph local flying or looking for Wiley on my c90.
    "There are 3 kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." Will Rogers

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    mvivion's Avatar
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    Quote Originally Posted by Waldo M View Post
    Stock PA-11 w/ C-90-8 and Sensenich W76CK-40 prop. 2300 rpm when just flying around for a local ride, 2350 on a X-C when downwind, 2400 on an upwind X-C, 2450 to 2475 [max continuous RPM] on an X/C flown much above 5000' (not a high percentage of power at higher altitudes).

    I run 100LL and use an occasional shot glass of JD.
    A 76 inch prop on a PA-11? Field approval, STC or ???

    MTV

  19. #19
    Waldo M's Avatar
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    Original Certification. According to Piper in 1948, these are the propellers offered on the PA-11-90 when it was new. These are also Sensenich's current recommendations for a wood propeller on the type. Note that they are all wood propellers and each propeller model is preceded by a "W" in modern nomenclature. T.C.D.S. A-691, revision 34, section 311. D. (5) also allows.

    Duster/Sprayer or "Climb" propeller: Sensenich W76CK-38
    "Standard" propeller: W76CK-40
    "Cruise" propeller: W74GK-50
    Last edited by Waldo M; 10-26-2020 at 09:47 AM. Reason: spelling, punctuation, additional reference
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    Waldo M's Avatar
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    MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.

  21. #21

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    Quote Originally Posted by mvivion View Post
    A 76 inch prop on a PA-11? Field approval, STC or ???

    MTV

    approved years ago.

  22. #22

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    Quote Originally Posted by Waldo M View Post
    MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.
    Car 3.416 requires a “certified” propeller. If the prop doesn’t have a TC, no joy.


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  23. #23
    mvivion's Avatar
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    Quote Originally Posted by Waldo M View Post
    Original Certification. According to Piper in 1948, these are the propellers offered on the PA-11-90 when it was new. These are also Sensenich's current recommendations for a wood propeller on the type. Note that they are all wood propellers and each propeller model is preceded by a "W" in modern nomenclature. T.C.D.S. A-691, revision 34, section 311. D. (5) also allows.

    Duster/Sprayer or "Climb" propeller: Sensenich W76CK-38
    "Standard" propeller: W76CK-40
    "Cruise" propeller: W74GK-50
    Ah so, I’d forgotten about the wood propellers, thanks.

    MTV

  24. #24
    mvivion's Avatar
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    Quote Originally Posted by Waldo M View Post
    MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.
    That argument was tried a while back, and FAA said nope, or Catto said not really, or? But anyway, the idea was shot down.

    But, seemed logical to me.

    MTV
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  25. #25
    Waldo M's Avatar
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    Oh well. What started as a thought turned into a brain fart.....again.

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    The 76AK-2-42 was the factory metal prop option for the PA18-95 The -2 in the nomenclature designates a 2" reduction in diameter
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    Quote Originally Posted by skipster View Post
    The 76AK-2-42 was the factory metal prop option for the PA18-95 The -2 in the nomenclature designates a 2" reduction in diameter

    ?

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    skywagon8a's Avatar
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    Quote Originally Posted by tempdoug View Post
    ?
    Take a look at the Type Certificate, there is a lot of information there.
    https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/7d33aa15611ee2e285256713004bddd3/$FILE/1p2.pdf

    Look on page 2, NOTE 2 is a description of the meaning of the numbers and letters.
    N1PA

  29. #29
    L18C-95's Avatar
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    Around 400 hours behind a C90 but my advice is fly top of the green (2350RPM) this kept valves and plugs happy and produced a reliable 90 mph IAS


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  30. #30
    jnorris's Avatar
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    I've owned two 90 hp Super Cubs, and have always run 2400 rpm for cruise. Both airplanes had Sensenich 76AK-2-44 props. Cruise is just a snick under 100 mph at that power setting. Engines run smooth and seem to love that power setting.
    Joe

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    Altmuehltaler's Avatar
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    Very interesting threat. Does someone have thoughts concerning leaning?

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    Farmboy's Avatar
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    Power settings on C90

    I leaned mine a lot to the left and right but never leaned the engine. It needed all the gas I could feed it.

    Note: Not having mixture control also made that decision easy.

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  33. #33
    BC12D-4-85's Avatar
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    ^^^^^this. At high power (heat concerns) or in cold wx (lean concerns) these small Continental engines like and need fuel. I've never leaned the three I've had but then never see a high density altitude.

    Gary

  34. #34
    mvivion's Avatar
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    I've owned two of these engines, one on a J-3 modified to PA-11 configuration, and the other a stock PA 11.

    The 90 hp J-3 had a Stromberg carburetor on it, and I lived in Kodiak. As in very close to sea level, pretty much all the time. Never leaned, largely because the carburetor didn't have a decent mixture control.

    The PA-11 was based at 4500 msl, with pretty regularly warm temperatures running DA up to 7 to 10 K fairly frequently. That engine had a Marvel MA-3 SPA carb. When I bought the airplane, the mixture on the carb was wired full rich. I installed a mixture control, and that carburetor was a jewel. I leaned regularly in cruise, and going cross country in the rocks, often as high as 10,500 msl, and the fuel burn was noticeable.

    If I had a C-90, AND was operating at high DA, I'd put a Marvel Carb on it in a heartbeat. The other nice thing is that, when hand propping, I'd prime the engine, then pull the mixture to idle cutoff, start the engine, reach in and push mixture to rich when it was safe.

    MTV
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  35. #35
    Crash, Jr.'s Avatar
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    Good info MTV. I've been looking at rebuilding my Stromberg but this pushes me in the direction of a Marvel if I can find one. Any idea where you can get one with correct jetting for a C85 or C90 these days?

  36. #36
    BC12D-4-85's Avatar
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    Start with the C-85 (E-233) or C-90 (E-252) TCDS and overhaul manuals. Approved carbs are listed but there may be others. Alternatively look here for engine eligibility: https://msacarbs.com/technical-data/engine-eligibility/ and product description: https://msacarbs.com/product-categor...etors/ma-3spa/. Then find a vendor. Sell the Stromberg as they are desirable for restoration. They also make a great flower planter once you fly a M-S.

    Gary

  37. #37
    jnorris's Avatar
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    Quote Originally Posted by Altmuehltaler View Post
    Very interesting threat. Does someone have thoughts concerning leaning?
    I'm blessed with a Marvel carburetor on my current C-90, and I lean the thing all the time. Plugs and valves stay nice and clean and the compression is muy bueno. Happy engine!
    Joe

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    I’m looking forward to flying my new Cub with the O200 and Marvel Carb....I must say though. I’ve had zero trouble with my C90 powered TCraft with the Stromberg. 14 yrs of trouble free operation...I once thought I had an issue with the carb, but it turned out to be a fuel supply/ gascolator issue.. it sits outside every summer on floats, and starts first blade nearly every time...handpropped. The Marvel Looks like a better product though

  39. #39
    BC12D-4-85's Avatar
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    My experience with Stromberg is they prefer summer and don't care much for winter. They give good power and reasonable mixture control to a point if their gaskets don't leak. The MS likes all weather and won't become the Prince of Silence when applying go around power.

    Gary

  40. #40
    cubdriver2's Avatar
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    I've run both down to -16F, both work fine in all weather. Stromberg will static 50 rpm higher

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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