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Thread: Constant Speed Props - Pilot operation.

  1. #1
    texmex's Avatar
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    Constant Speed Props - Pilot operation.

    Not really a Super Cub question but...........

    I'm doing some flying in a Bonanza with my wife who has a constant speed propeller endorsement on her licence but never really got to passed the check ride due to Kids, money etc. and that was ten years ago. The training for me was 23 years ago and with 3,000 hrs on aircraft with CS Props I never give it a second thought.
    I've found some good info on the net on how the CSU works (www.hariguchi.org) but not on pilot techniques. The operation up to airborne is really procedural as is pushing the pitch in on final. But the bit in between. Does anyone have any good mnemonic or ditty for increasing/decreasing power on Constant Speed Props?

    Thanks Texmex.

  2. #2

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    Inrease Power from Cruise:

    Mix-Rich

    RPM- Inrease with Prop Control

    MAP- Increase with Throttle


    Reduce Power:

    MAP- Reduce with Throttle

    RPM- Reduce with Prop Control

    Mix- Lean as necessary


    or INCREASE- Increase , Increase

    DECREASE- Decrease, Decrease


    The important thing when increasing power is you want to increase RPM FIRST so that the BMEP or

    Brake Mean Effective Pressure doesn't get too high.

    USE THE POWER CHARTS!

    You may find the engine is more efficient at a setting like 25 in MAP with 2200 RPM if the Power Charts say so.

    You can run "Over Square' as stated if the Power Charts etc.

    Guy named Lindbergh proved that long ago.

    Did I mention the Power Charts?

  3. #3
    Nathan K. Hammond's Avatar
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    Does anyone have any good mnemonic or ditty
    Don't overboost. Prop up, power back.
    As in, the prop rpm goes up before the M/P and the M/P comes down before the rpm's. That's always worked for me.

    nkh

  4. #4
    Aussie Scout's Avatar
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    I always use the mnemonic:

    Pitch up (then) power up
    Power back (then) pitch back

  5. #5
    48M's Avatar
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    When I received complex training I was told to think of - MP= My Penis - DO NOT pull the prop back before MP. Made an impression on me.
    K.I.S.S.

  6. #6
    texmex's Avatar
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    Thanks Guys, I've comfortable with the procedure myself having flown a large amount of singles and twins with various engine combo's. Where the self doubt creeps in, is with the teaching, or imparting knowledge. Particularly with a family member.
    P.o.P. the increase, increase increase and vice versa could work. Here you would be relying on a muscle memory technique. In the Bonanza the three levers are positioned at each point of a point down triangle and not linear as in a number of other aircraft. But could still work. Agree on the power charts.
    Aussie Scout, I think I was taught Mixture up, Pitch up, Power up. And reverse. This I guess would be a matter of learning a ditty.

  7. #7
    texmex's Avatar
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    48M. I love it but I can see my wife rolling her eyes as I attempt to explain this one to her.

  8. #8
    48M's Avatar
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    She will have to use her imagination
    K.I.S.S.

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    If anyone is interested I could send a 6 page booklet on this topic from McCauley.

    Send your e-dress or put it on line.

    Same techniques work with P & W's & Wright "Spoke Motors".

    LOTS more MAP though.

  10. #10
    Cubpylut's Avatar
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    P.o.P

    As the proud new owner of a C185, my first aircraft with a Constant Speed Prop, I'ld love a copy of the manual from McCauley. My email is murphypilot@yahoo.com.


    James Smith

  11. #11
    jimboflying's Avatar
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    I would love a copy too.

    jbooth9764@aol.com

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    Me too please. N5284G@yahoo.com

    Thanks!

  13. #13
    SJ's Avatar
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    It is my understanding that the concerns about mp greater than rpm (over squared) were applicable only to radial engines. It is not uncommon for me to pull the prop back to 2500 right after takeoff and leave the Mp at full power as the climb will reduce the mp as you go up anyway.

    sj


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  14. #14
    Lance's Avatar
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    Congrats James. Lets see some pictures

    Lance

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    mvivion's Avatar
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    Steve,

    Many of the radial engines were also supercharged, with Roots type blowers. As a consequence, they routinely ran "oversquare". For example, the R-985 takeoff power setting for the Beaver was 2300 rpm and about 36.5 inches of MP.

    I'm not sure where the "oversquare" myths came from, but in talking to Lycoming about the O-360, they told me that this engine could safely be operated as much as 9 inches oversquare, AFTER engine break-in is complete (they considered engine break in for this purpose to be 50 hours time in service and stabilized oil consumption).

    I pretty routinely run the engine/prop on my airplane at very low rpm (1900 or so) and RELATIVELY high MP (21 inches). This provides a VERY smooth and efficient cruise power setting, and dramatically decreases fuel flows. I never ran the IO 520 oversquare, mostly because I wasn't buying the gas....but I have no doubt you could, and it would work fine.

    MTV

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    FdxLou's Avatar
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    Quote Originally Posted by Cubpylut View Post
    P.o.P

    As the proud new owner of a C185, my first aircraft with a Constant Speed Prop, I'ld love a copy of the manual from McCauley. My email is murphypilot@yahoo.com.


    James Smith
    Congrats James! You will love it.

    Lou

  17. #17
    kase's Avatar
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    Congrats James. Sure am glad you bought it cause now I dont have to. I flew it last year and its one of the nicest low time non abused 185s out there.

    Click image for larger version. 

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  18. #18
    SJ's Avatar
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    Come on Kase, James knows Wilbur all too well... Great plane, first 185 I ever flew in and I ride I will never forget

    Congrats!

    sj


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  19. #19
    Cubpylut's Avatar
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    Thanks Lance, Lou, Kase and SJ. I posted a new thread on the purchase with a couple of pictures.

    I know the feeling Kase, pretty much figured I'd kick myself for a long time if I didn't buy this one.

    James

  20. #20
    texmex's Avatar
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    Anyone got any info on the "oversquare" mythology?

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    skywagon8a's Avatar
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    Quote Originally Posted by mvivion View Post
    Steve,

    Many of the radial engines were also supercharged, with Roots type blowers.
    MTV
    Mike
    With all due respect I do believe that you mean centrifugal blower. http://en.wikipedia.org/wiki/Centrifugal_compressor A roots blower is a lobe type of pump. http://en.wikipedia.org/wiki/Roots-type_supercharger A roots pump is a positive displacement pump. An oil pump is an example.
    N1PA

  22. #22
    moneyburner's Avatar
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    Quote Originally Posted by texmex View Post
    Anyone got any info on the "oversquare" mythology?
    I think it's just some arbitrary thing some instructor came up with. What if you're flying something that reads mp in metric?
    Quidquid Latine dictum sit, altum videtur

  23. #23
    StewartB
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    Quote Originally Posted by texmex View Post
    Anyone got any info on the "oversquare" mythology?
    I wouldn't be surprised if it goes back to manual transmissions in cars and how you could "lug" the motor at slow speeds in high gear and full throttle. If you have the prop turned way down and add full power the airplane engine will make some funny noises, too. I had a TCM rep tell me I could run the prop at the bottom of the green and the MP at the top of the green all day if I wanted to. Green is green. Outside of that you're a test pilot. I do what Steve said earlier. Once airborne I reduce the prop speed a bit in consideration of the neighborhood around the airport (noise). I don't worry much about the throttle at that point. Keep in mind that this engine does not carry a 5 minute limitation for power output but in the planes I've flown that had 5 minute limitations they were related to prop speed, not throttle.

    SB
    Last edited by StewartB; 09-13-2011 at 09:21 AM.

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    Quote Originally Posted by texmex View Post
    Anyone got any info on the "oversquare" mythology?
    ALL engines have some type of limits.

    My thought is many folks do not want to be bothered with things like Power Charts.

    Exceeding allowable MAP limits may have you operating in the "Realm of Detonation".

    This would be ABOVE Cruise Power.

    High temps, Lean Mixture ( dirty injector?) while operating with Low RPM can trash an engine.

    One size does NOT fit all engines though .


    I've heard that Lindbergh ( yes, Charles ) worked with Lockheed to improve the range of the P-38.

    Use of "Over-square " power settings did just that & allowed the aircraft to intercept & shoot down Yamamoto.

    It is important to understand the limits of your engine as a P-38 is a little different than a PA-18.

  25. #25
    Dave Calkins's Avatar
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    When the throttle is pulled back to reduce MAP, it also causes less fuel to be provided to the engine.

    The idea that full throttle oversquare operation in the green is harming a 470, or 540, or 520, or 550 is laughable....and is the cause of many cracked/damaged/overheated/ruined/junk cylinders.

    The guy behind the throttle should get a funny feeling EVERY TIME he takes fuel away from an engine making lots of power. Please leave the throttle all the way forward in the climb to provide fuel that cools.

    .....worry about the prop noise and the neighbors! and leave the throttle where it gives the engine fuel, !!!!!!
    Last edited by Dave Calkins; 09-13-2011 at 10:26 AM. Reason: edited to remove the words..."....you morons..." from the end of the last sentence.

  26. #26
    wheat's Avatar
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    For those of you who have not read John Deakin's articles about engine management, here is a link: very interesting reading. http://www.avweb.com/news/pelican/182544-1.html
    Jim

  27. #27
    Alex Clark's Avatar
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    Yes Col. Lindbergh did fly all around the Pacific for Lockheed and teach long range cruise. He volunteered to go back on active duty, but F.D.R. hated Lindbergh (who was considered a viable conservative candidate to oppose FDR) with a passion and had been calling Lindbergh a Nazi sympathizer in the press. Knowing full well that Lindbergh had actually been supplying Army intel with data about German aircraft for years. Thus he was blocked from active duty as political pay-back.
    While out in the Pacific, as a civilian, Lindbergh also engaged in some aerial combat with a P-38 and has a couple kills to his credit.
    I believe that the P-38s had prop pitch controls that could either act like a constant speed prop, or act like a variable pitch prop (making the pitch changes independent from changes in throttle settings.) Plus they burned out engines like pop-corn, since there was a pile of them back at base waiting o be shoved under the cowling.

  28. #28

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    Lindbergh did admire many of the aspects of the Nazi movement.

    Of course; when someone murders your baby it would affect your perspective.

    He was a pacifist but when the war started he stepped up to the plate.

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    Quote Originally Posted by mvivion View Post
    I pretty routinely run the engine/prop on my airplane at very low rpm (1900 or so) and RELATIVELY high MP (21 inches). This provides a VERY smooth and efficient cruise power setting, and dramatically decreases fuel flows. I never ran the IO 520 oversquare, mostly because I wasn't buying the gas....but I have no doubt you could, and it would work fine.

    MTV
    So how do you know you're not lugging the engine at that setting. Lookng at the Lycoming Power setting table (O-360-A), it starts at 2100 RPM. What fuel flow and speeds do you get at those settings?

    Also what is the best procedure when you're loitering around at 21 squared close to the ground and you encounter a sudden downdraft? Is it full prop in then power? I did that and felt like the prop started overspeeding...

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    You are not talking about a twin bonanza ? Because many of them had a geared engine. If it is like the geared Helio, you have to reduce power by starting reducing the rpm, not the MP.

    Louis

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    Alex, it is a matter of public record, historical fact, that Lindbergh was an anti-semitic, America Firster, racist and admirer of Hitler who supported the Nazi regime and did everything in his power to keep US out of the war. He wasn't against war itself only taking on Germany. Look it up.

  32. #32
    mvivion's Avatar
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    Quote Originally Posted by AKClimber View Post
    So how do you know you're not lugging the engine at that setting. Lookng at the Lycoming Power setting table (O-360-A), it starts at 2100 RPM. What fuel flow and speeds do you get at those settings?

    Also what is the best procedure when you're loitering around at 21 squared close to the ground and you encounter a sudden downdraft? Is it full prop in then power? I did that and felt like the prop started overspeeding...
    I discussed this with Lycoming tech reps, who reminded me that the Lycoming power charts are for reference, and are not limiting. The response I got specifically on operating the O-360 in an "oversquare" condition was that Lycoming said you can operate that engine up to nine inches over square. Frankly, I don't think you could get there, and I've never tried to get even close. Their recommendation was NOT to run in this condition until the engine is broken in.

    I'm not sure there is such a thing with these engines as "lugging". Not saying there isn't, just saying nobody I've spoken to in the tech rep world mentioned any such concern. At around 1900 rpm and 21 inches at less than 5000 msl, you are operating at a VERY low power setting. It's off the chart, but it's likely around 45 to 50 %. Fuel flows, with careful leaning, run around 6.5 to 7.0 gph. And, with the right propeller, the thing is as smooth as a three blade.

    Propellers are more efficient at lower rpm, which is why turboprops run their props at very low prop rpm, even though they could run the propellers at about any speed they cared to.

    I've run Huskys (I know-but they have a CS prop and O-360) at similar settings for many hours with nary a problem. The Husky is less draggy than my airplane, so you can run even less power and still cruise at a decent speed, with VERY low fuel flows.

    Or, lay the wood to it, and go fast.

    MTV

  33. #33
    SJ's Avatar
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    Some questions come to mind...

    If you are at full MP (less than 24) say at 6000' or something, when you pull the prop from 2400 to 2200 or something like that, what happens? Do you slow down somewhat and get greater fuel efficiency?

    What is the best way to determine "best duration" or "best mpg" for a plane with a CS prop? I have two I need to do this with!

    sj
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  34. #34
    Alex Clark's Avatar
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    King brown:
    Read the book Lindbergh vs Roosevelt by James Duffy, and Charles A.Lindbergh and the Battle Against Intervention in World War II by Wayne Cole,
    It also could not hurt to read or listen to his speeches on the subject. I have them if you have not. Then get back to me on your historical take on things. America Firster, yes, non-interventionist, yes...As were Henry Ford and former president Hoover. BTW the America First movement prohibited Nazi's from joining. The other stuff was or is questionable. Much being generated by a group called Friends for (of) Democracy and FDRs socialist inner circle.
    The rift between FDR and Lindbergh when back to the days of the air-mail contract debacle of the 1930s.

  35. #35

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    Quote Originally Posted by SJ View Post
    Some questions come to mind...

    If you are at full MP (less than 24) say at 6000' or something, when you pull the prop from 2400 to 2200 or something like that, what happens? Do you slow down somewhat and get greater fuel efficiency?

    What is the best way to determine "best duration" or "best mpg" for a plane with a CS prop? I have two I need to do this with!

    sj
    To answer the first question - you speed up! You actually feel the airplane accelerate.

    The second question, well, I use the Lycoming power chart which gives you fuel flow at different altitudes, temps and MP/RPM settings and see how fast I go. For example when I fly (Cessna 170B O-360 CS Prop) 24"MP 2350RPM, I go about 125mph and burn 10 gph (12.5mpg). Throttle back to 20" 2100 rpm, fuel burn is down to 7.4 gph and I slow down to 105 mp (~ 14 mpg). However, I have not checked these numbers with a fuel flow meter, but I would think the charts would be very accurate.

  36. #36

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    MTV,
    I tried your power settings, but the prop starts surging ever so slightly below 2000 rpm. I guess I'm stuck keeping it above 2100 rpm.

    So when flying at those settings, what do you do to quickly increase power?? Prop full in then power? Both in at once?

  37. #37
    StewartB
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    Quote Originally Posted by SJ View Post
    Some questions come to mind...

    If you are at full MP (less than 24) say at 6000' or something, when you pull the prop from 2400 to 2200 or something like that, what happens? Do you slow down somewhat and get greater fuel efficiency?

    What is the best way to determine "best duration" or "best mpg" for a plane with a CS prop? I have two I need to do this with!

    sj
    Cruise performance and range profile charts are included in the Performance section of a Skywagon's POH. Your plane has been significantly modified so reviewing the charts from a model that better represents your engine and prop is probably appropriate. You'll have to do some interpolating but you'll get close. Kougorok supplied a link to Cessna manuals that's in position one in the "My Other Airplane Is" forum. That's a good place to start.

    SB

  38. #38

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    There are lots of books on Lindbergh sharing many opinions, Alex. To keep it in context, millions of Americans were of Lindbergh's views. The American Bund could muster meetings of 20,000 heiling Hitler with fascist salutes. America's credo was non-intervention until it was torpedoed into the First World War and bombed into the Second.

    Allowing Lindbergh to serve would have made as much sense as giving bin Laden a job in the State Department. He was in public opprobrium when US entered the war. Those 50 combat missions were as a consultant to the Ford Motor Company and United Aircraft corporation. Washington put a stop to it when it heard about it.

    Eisenhower, a truly great American who never received the distinction he deserved, made him a brigadier-general in the Air Force Reserve nine years after the war for his services to the government. Can you give me the source for those combat kills, please? I write on military affairs.

  39. #39
    SJ's Avatar
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    True on both planes, Stewart.

    I'm heading up to Fall colors in the 180 tomorrow with David Jaranson's uncle Johnny. I will give him a pad and paper and make him record some fuel flows and speeds at different power settings and altitudes.

    I'm pretty much leaned out all the time. Obviously, leaning can have a huge impact on fuel flows and on collecting data on something like this. I suppose the only easy/fair way is to do the tests full rich, like we did the prop climb tests on the cub.

    sj
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  40. #40
    Dave Calkins's Avatar
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    Lest anyone think I am against leaning or lean of peak operation....please allow me to qualify my statement above with "...lean of peak operation seems sensible for those in cruise at higher (above 5K feet MSL) altitudes...".

    When talking about pulling back the prop RPM or MAP.....please keep the throttle "IN" for your high power climbs.

    Also. I LOVE THE LINDBERGH history. really, I do. D

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