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Thread: McCauley 7140 vs. 7440

  1. #1

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    McCauley 7140 vs. 7440

    Seaplane with C90 / 7140 is turning up about 2550 in plow phase (not on step). Once on step RPMs increase to 2650. In level flight it will turn up to over 2800 RPM.

    If I were to use a McCauley 7440 I expect to lose around 100 RPM. But, given the longer prop will 'off the water' performance increase?

    What's the consensus out there? The common theme I've always heard was that the the longer the prop the better for seaplanes.

  2. #2
    gbflyer's Avatar
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    I'm not sure if a Mac 7440 is legal on a C90 at the full 74 inches but I have heard that they work well From what I can gather, the general consensus is to use the Sensenich 76-AK-2 series for a long prop on the C90. It's a 76" whittled down to 74". Some of us impatient ones just don't want to wait for one from the factory.

    I know nothing of performance on floats. On wheels, I do know that if you trade a 7148 cruise for a little longer one with a 40 pitch it's not even the same airplane! If I recall correctly, a good number of the float guys are using a 38 pitch.

    Looks like you're getting good rpm already. Not sure if the extra diameter will make a noticeable difference.

    gb

  3. #3

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    Not looking for more RPM.

    Wandering if the RPM losses due to increased prop length will be offset by an improvement in low end thrust?

    ie. ... would a 7440 with 2450 static outperform a 7140 with 2550 static?

  4. #4
    behindpropellers's Avatar
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    Quote Originally Posted by gbflyer
    I'm not sure if a Mac 7440 is legal on a C90 at the full 74 inches but I have heard that they work well From what I can gather, the general consensus is to use the Sensenich 76-AK-2 series for a long prop on the C90. It's a 76" whittled down to 74". Some of us impatient ones just don't want to wait for one from the factory.

    I know nothing of performance on floats. On wheels, I do know that if you trade a 7148 cruise for a little longer one with a 40 pitch it's not even the same airplane! If I recall correctly, a good number of the float guys are using a 38 pitch.

    Looks like you're getting good rpm already. Not sure if the extra diameter will make a noticeable difference.

    gb
    Legal on the PA-18 and J-5 sporting a C-90.

    Tim

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    7440

    Had 7440 on j3 with C85 don't see why you could not put on C90
    I do believe the longer the better for sea plane especially in hot weather.
    I am sure some of the guys on his site can answer you better on legal questions.

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    With an O-200 J3 landplane

    Running a McCauley 7441, static is 2525 to 2550, climb at 60 mph is about 2600 to 2625, and max speed is about 115 mph at 2900 rpm. I would expect the 7440 to static about 20 to 30 rpm more.

    Running a McCauley 7142, static is 2575 to 2600, climb at 60 mph is about 2640 to 2660, and max speed is 118 mph at 2950 rpm. I would expect the 7140 to static about 40 to 50 rpm more.

    Weather permitting, I'll be trying a McCauley 7535 tomorrow, and will report the results.

    JimC

  7. #7

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    Back to back prop test of McCauley 7142 & 7535
    46 J3 landplane, O-200, no wing tanks, no VG's
    91 degrees F, no wind, grass strip, about 8 or 9 gallons fuel, pilot 214 pounds, (no manifold pressure gauge)
    max rpm with the 7142 was down a little -- I think I could have stood a plug cleaning.
    Static mag drop 100 rpm both mags
    O-200 rated power 2750 rpm

    McCauley Prop 7142 7535
    Static rpm 2580-2590 2680-2690
    rpm 60 mph climb 2660 2800
    WOT rpm level flight 2850 3100
    Speed at WOT 112mph 108 mph
    On a cold day, WOT with the 7142 is 118 mph at 2950 rpm
    Speed at 2350 rpm 80-82 mph 74-76 mph
    Takeoff Roll 190 feet 150-160 feet

    I didn't have time to try rpm at 50 mph climb, or indicated stall speed at WOT. Got dark on me.
    Some observers were stepping off takeoff roll as 130 to 150 feet, but I don't believe them.
    Deck angle at low speed climb WOT was impressive.
    Acceleration after liftoff to climb speed was impressive
    Acceleration during ground roll was improved.
    Prop was quite smooth.
    I was impressed

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    McCauley 7140

    Hi Jim

    So are you saying you would prefer to run the 75/35 over another prop?I was a little confused there at the end. Bill

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    No, I'm not saying that I would prefer to run the 7535. There are five classes of overspeed (Categories Ia, Ib, IIa, IIb, and III). Running an O-200, you can easily reach a IIb overspeed with the 7545 (I was careful not to exceed IIa, which has the same inspection requirements as Ib). You can probably reach IIb with a C90 as well. A IIb overspeed would require that you replace the rod bolts and nuts, among a number of other unpleasant and potentially more expensive consequences. I've run a 7441, liked it, think a 7440 would do better than the 41, and that a 39 might be better still (I'm not in a hurry to get anywhere in a cub). Any flatter, and you run a severe risk of hurting the engine. I run a 7142 on a daily basis and think that on an O-200 (and probably a 90) it is a great compromise prop that won't lead a prudent pilot to hurt the engine. Being careless with the 7545 could lead to the need for an overhaul or worse within a very short period of time. That said, the 7545 performance is quite impressive, including a 55 mph climb at full rated rpm (2750 rpm) on a 95 degree day -- the 7545 just comes with a potentially exorbitant penalty.
    JimC

  10. #10

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    >ie. ... would a 7440 with 2450 static outperform a 7140 with 2550 static?<

    The nearest I can come to responding to this question is to say that a 7142 slightly outperforms a 7441 in every aspect, static rpm, climb rpm, and cruise speed. I would expect a 7142 to match a 7440 in static and climb, and to outrun the 7440 in cruise. A 7140 would climb even better, but would probably cruise 3 or 4 mph slower.

  11. #11

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    I just put a Sensenich 7438 on a C85 J3 setup and I am amazed how well it does. Climb is awesome, cruise is terrible!

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    Jim, what would your opinion on using a 76-36 wood prop on a light C-90 powered 18 be?

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    Blake, what did you have on your J3 / C85 before?



    Quote Originally Posted by BlakeH
    I just put a Sensenich 7438 on a C85 J3 setup and I am amazed how well it does. Climb is awesome, cruise is terrible!

  14. #14

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    I've run wood and aluminum props of identical diameter and pitch (7443) back to back within 30 minutes of one another. Typically, the takeoff roll is about 10-15% longer with the wood prop, and the wood prop cruises 8 to 10 mph slower. It doesn't climb as well either.

    I've also run a 7438 on an 85 powered J3 and agree about the great climb and terrible cruise.
    JimC

  15. #15
    a3holerman's Avatar
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    Hi,
    In another thread I am in a similar boat or plane as it is. I have a Mc Cm 7443 on my J3C-65 now. Just completd majoring a C90-8 for the cub. For that engine on a cub McCauley calls for a 7148. It seems everyone is talking about 40-42" pitch on these props. A-691 spec for the J3 says for a J3 with a C-90-8F engine limits are 2475rpm at takeoff. So wouldn't a 40-42" pitch overspeed the engine? I am kinda new to all this prop stuff and maybe I am mising something here. The 0200 on the other hand does require a higher rpm to get the HP and I thought this was one of the reasons a C90 was a better option on a Cub.

  16. #16
    a3holerman's Avatar
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    Oh just thought of another thing. Yes, the 74" version of the Mc CM props are not legal on a C90. Some time ago I talked with Cris Bell an engineer at McCauley and he told me the limit on a C90 was 73" due to some harmonic problems in the longer lengths. The problem is that they never certified it on a J3 with a C90.

    Tom
    Cape Cod

  17. #17
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    Tom
    I run a 71/48 for longer trips. It is a faster cruise but a real dog for all other operations. I Just had my 71/44 repitched to a 71/40 for seaplane operations and it works great. I really liked the 71/44 for a general/ all purpose prop. Now I need to find another one of those. This is on a C-90-8F

  18. #18

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    >A-691 spec for the J3 says for a J3 with a C-90-8F engine limits are 2475rpm at takeoff. So wouldn't a 40-42" pitch overspeed the engine?<

    Not if you don't shove the throttle all the way forward. Just put a stick-on label on the panel that says, "Never Exceed 2475 RPM" and a red line on the tach at the same rpm. I know of two J3's that are legally running O-200's and 7142's approved by 337 that spell out use of that method to limit rpm to 2640 and horsepower to 85. I doubt that your 90 will turn the 7142 quite as fast as the O-200 does anyway. If it does, repitch the prop steeper to slow it down. Costs about $150. Run it first at its present pitch and before repitching it, record the pertinent rpms, and use those as a guide to decide what final pitch you want. Right now, with the 95 degree weather, my brother's O-200 is staticing the 7142 at 2550 t0 2575 rpm, and is turning about 2640 during a 60 mph climb with one on board the J3 and about 2600 with two. With the 7142, in 95 degree weather, you'll cruise at about 78 to 80 mph at 2350 rpm.

    Be sure to read SB05-2 on what actions are required after the 5 different classses of engine overspeeds. They range from no action required for Category IA to a minimum of complete overhaul and replacement of specified parts for a Category III excessive overspeed.

    Note that although A-691 limits maximum power for ALL operations to 90 hp at 2475 rpm, the C90 Type Certificate (E252) allows it to turn 2625 rpm for 5 minutes, producing 95 horsepower for climbout. You can't reach that rpm with more than a 42 pitch. However, A-691 also limits maximum static to 2350 rpm, which requires roughly about a 44 to 45 inch pitch. This is why an O-200 J3 will blow the socks off a C90 J3 in climb unless the 90 is running the flatter prop and going by E252 instead of A-691 (which isn't really allowed, but some C90 pilots ignore it).
    JimC

  19. #19
    a3holerman's Avatar
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    JimC,

    Thank you so much for all the info. I think that I will simply have it cut to 71" and leave the pitch at 43" and see how it goes.

    Thanks again
    Tom,

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    >With the 7142, in 95 degree weather, you'll cruise at about 78 to 80 mph at 2350 rpm. <

    Oops, that's for a landplane. A seaplane would be quite a bit slower at the same rpm.
    JimC

  21. #21
    Clyde Barker's Avatar
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    I'm also thinking about a new prop for my experimental cub. It looks like a J3, but is really more like a PA-11 with its wing tanks. My O-200 was converted to a -8 by Don Swords of Don's Dream Machines.

    My current prop is a wood Sensenich W72GK44. It gets 2275 rpm static, 2375 rpm at 60 mph climb, and 2550 - 2575 rpm at full throttle at about 95 mph. This is at about 600' msl and 90 degrees F.

    My take-off and climb performance is pretty good now, but I'm thinking that a more efficient metal prop with a finer pitch it could improve quite a bit.

    From posts on this thread, it sounds like a McCauley 1B90 CM7142 would be a good choice. By the way, is the squared tip of the 1B90 more efficient than the elliptical tip 1A90?

    Clyde

  22. #22

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    >From posts on this thread, it sounds like a McCauley 1B90 CM7142 would be a good choice. By the way, is the squared tip of the 1B90 more efficient than the elliptical tip 1A90?<

    The 7142 would be an excellent choice for an O-200 PA-11 clone, though with the lower drag of the -11 vs. the -3, you might consider a 7143 instead. You'd sacrifice a bit of ground roll with the 43, but the lower drag -11 with a 7143 would probably still outclimb a -3 with a 7142 (I'm thinking about going the other direction, repitching the 7142 on an O-200 J3 to 7141).

    For a given airfoil distribution, an elliptical tip is slightly more efficient than a squared tip, but that difference is negligible between a 1A90 and a 1B90 and probably swamped by the other differences in those two propellers. If I were going for an extreme cruise prop, given the same airfoil distribution on two props, I'd probably prefer an elliptical tip. If I were going for a climb prop, I'd probably prefer the square tip. But, as a practical matter, on a J3 or PA11 the difference in tip shape isn't really worth worrying about.

    To get a feel for the performance gross weight performance of the 7142 on an O-200 J3, last Saturday, the OAT was about 95 degrees at 310 MSL. We did a reduced power cruise climb (60 mph at 2500 rpm -- full throttle holding that airspeed would have been about 2640 rpm) from 310 MSL to 6000 PA with weight at and near gross. At 6000 feet PA, we were still climbing at about 600 fpm with throttle retarded to 2500 rpm. Oil temperature reached about 180 degrees indicated, compared to the usual 140 degrees (uncalibrated J3 temperature gauge -- don't know what the real oil temperature was). On an O-200 PA-11, you'd climb a lot better than that, but the oil temps would be substantially higher.

    JimC

  23. #23
    Clyde Barker's Avatar
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    Quote Originally Posted by JimC
    The 7142 would be an excellent choice for an O-200 PA-11 clone, though with the lower drag of the -11 vs. the -3, you might consider a 7143 instead.
    JimC
    Thanks for the info JimC.

    I wasn't clear when I compared my plane to a PA-11; I have an open cowl with eyebrows like a J3, but have wing tanks instead of the nose tank. I'm sure I have about the same drag as a J3.

    Your oil temp gauge must be more optimistic than mine! I usually show about 200 degrees when the OAT is 90.

    By the way, I've enjoyed reading many of your posts. You have obviously done a lot of testing and research. Thanks for your input.

    Clyde

  24. #24

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    >I'm sure I have about the same drag as a J3<

    With a given pilot/passenger load, it depends upon the amount of fuel you're carrying. If you can carry more than 12 gallons, you'll have more induced drag than the J3 when you are carrying more than 12 gallons. Once your fuel burns down to 12 gallons or less, induced drag will be equivilent. The J3 that I fly doesn't have the wingtanks. We preferred to stay with the stock nosetank and have a removable external 10 gallon belly tank that can be installed for long trips.
    JimC

  25. #25

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    We preferred to stay with the stock nosetank and have a removable external 10 gallon belly tank that can be installed for long trips.
    JimC, I'd like some details on that external tank. Would sure come in handy on my Cuby. Got pictures? Where did you get it?

  26. #26
    X18's Avatar
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    J3/PA11 Exp Prop

    Clyde,
    Legend uses a Sensenich 72 X 46 wood core composite covered prop with their O-200 powered open cowl Legend Cub. This prop is light and smooth like your wood prop, but has almost the same performance and durability as the metal prop. Contact Sensenich Wood Propeller for more info.

    Jim

  27. #27

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    Jim,

    The Sensenich composite prop sounds like a really interesting compromise between the wood and metal props. Do you know if they are usable on certified airplanes (Cubs) or are they only usable on LSA's?

    John Scott
    While I respect the folks that use Cubs to make a living, my uses are for recreation and leisure - AND I'M NOT ASHAMED!!!

  28. #28

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    >external tank. Got pictures? Where did you get it?<

    I can take some. They belong to two of my friends. Their dad designed and built two, installing them on his two J3's by 337. The two sons each inherited one of the J3's. The tanks are really neat and take less than an hour to install or remove.
    JimC

  29. #29
    X18's Avatar
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    Composite Prop

    I know that they are used on some LSAs and some Experimentals but I don't know about certified aircraft. Call Sensenich Wood and they will be able to tell you what they have for the certified market.

    Jim

  30. #30
    Clyde Barker's Avatar
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    Thanks for the info Jim. I'll look into the composite prop that Legend uses.

    Do you know what the static, climb, and full throttle rpm is with that prop?

    Clyde

  31. #31
    X18's Avatar
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    Composite Prop

    Sorry, I don't remember the static or climb rpm. SL standard day, after several minutes WOT it will stabilize around 2850 rpm. I'll try to see if I can find the other information for you.

    Jim

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    >SL standard day, after several minutes WOT..... <

    Wow, you must live way north of me. The dISA has been running about 34 to 39 degrees F around here lately. Send some of that cold weather down this way...... :-)
    JimC

  33. #33
    X18's Avatar
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    Composite Prop

    Nope, North East Texas. The testing was done last winter and I just remember the flat out rpm. And it's only supposed to be 100 for the rest of the week.

    Jim

  34. #34

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    Jim, We're only supposed to be above 100 for two days this week, so we're better off than ya'll are. Want me to get a big fan and point it in your direction?
    JimC

  35. #35
    Clyde Barker's Avatar
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    Re: Composite Prop

    Quote Originally Posted by X18
    Sorry, I don't remember the static or climb rpm. SL standard day, after several minutes WOT it will stabilize around 2850 rpm. I'll try to see if I can find the other information for you.

    Jim
    Thanks for the info Jim. Don't go to a lot of trouble to check the static or climb. I checked with Sensenich and the lead time is a little longer than I want to wait.

    I'm thinking of getting a 1B90CM7440. If I'm not happy with it I can have it cut and re-pitched in the future if I want to. It's easier to make 'em shorter than to make 'em longer!

    Thanks again,
    Clyde

  36. #36

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    Finally tried a McCauley 7440. As JimC predicted it does not pull the plane on the step as well as the 7140.

    However... strange as it may seem, it climbs better. 7440 climbs about 50 to 100 ft/min faster than the 7140.

    I must admit that tests were not conducted under perfectly controlled conditions, but the numbers seem to consistently favour the 7440 from a climb perspective.

    7440 RPMs are about 50-100 less than the 7140. The 7440 prop also seems smoother.

    I'm thinking that a 7438 would be optimal.

    Any thoughts on this?

  37. #37
    skywagon8a's Avatar
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    Generally an old rule of thumb is that if you increase the diameter 1" you reduce the pitch 1". The result should give you slightly better acceleration and climb performance due to the larger diameter of the prop blast. The engine likely will seem smoother due to the better flywheel action. A long slow turning prop will give more thrust thus better performance on slower Cub type airplanes. On higher speed planes the long prop will generate more drag. Generally the prop diameter is restricted by ground clearance requirements, which is why a float plane is able to use a longer prop. Years ago I experimented with several different props on a 150 hp 7GCB on floats. The original prop was a 7456. The cruise was about 103 mph. I settled on a 8046 prop. I know this doesn't follow the rule of thumb. The cruise remained the same while the take off time was reduced by 1/3 and the rate of climb was increased by about 1/3. It also ran a lot smoother. I also ran this prop on wheels (8.50 x6) with excellent performance.
    N1PA

  38. #38

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    McCauley 7140 vs. 7440

    I currently use the 75-35 1a90 on my 0-200.I think the 75-38 may be the best combo.

    Bill

  39. #39

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    McCaully 7140 vs 7440

    Hi guys I have a pa-11 with a c90-8 have a 7144 and a 7440 the 7144 seemed to get off better on wheels and floats but the 7440 was better on skis, did some upgrades and now run the 7440 all the time and turn about 2475 on t/o but have to throttle to about 1/2 throttle in level flight, may not be quite legal but it's a lot more fun. also have the 25x11x4 Goodyear tire so prop clearance is no problem.

  40. #40

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    Re: McCaully 7140 vs 7440

    Quote Originally Posted by Douten
    Hi guys I have a pa-11 with a c90-8 have a 7144 and a 7440 the 7144 seemed to get off better on wheels and floats but the 7440 was better on skis...
    Strange that the 7144 outperforms the 7440. What RPMs are you getting with each prop?

    I know of a C90 J3 on EDO 1320s with a 7146 that seems to outperform everything in sight. Could be an exceptionally light airframe ... I'm not really sure why it does so well.

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