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  • Re: M.A.P.

    by » one month ago


    Tim

    No, it's Mike, but never mind.

    "After adjustment, you won't get 5200 in auto cruise even at WOT. You'll get 5000." How so?

    Ans - because that's the rpm the cruise position is set to by Airmaster. As I've said before, those 3 presets could equally well be labelled 5000/5400/5700 instead of cruise/climb/takeoff. Rpm is the only variable they take any note of. MAP is irrelevant to the control loop.

    Surly I can adjust, within reason, for whatever rpm I choose (4800 -5500 rpm)

    Ans - not when it's in auto cruise mode unless you connect a pc to the controller and change Airmaster's settings. You can override it to something else in auto hold mode or in manual mode if you want

    Yes I understand that I am adjusting for a Max Cruise RPM

    Ans - no you are not. You are adjusting the pitch stop to a setting that allows the controller to maintain the preset cruise rpm of 5000 constant from relatively low power up to WOT. Airmaster suggest setting it coarse enough to limit rpm to around 4000 at WOT when on the pitch stop on manual mode. Why would you buy an expensive automatic electronic controller then set a mechanical stop that prevents the controller doing its job?

    What's so special about 5000 rpm?

    Ans - nothing except it's what Airmaster chose to use for the cruise setting and it's around the lowest rpm at which you can use WOT without detonation risk.

    You really don't understand how this thing is meant to work do you? You're thinking of it like a fixed pitch prop or maybe a manually variable in flight prop. Set aside your preconceptions and study the manual and think about it. In one message you mentioned flying a Cessna(?) with a hydraulic VP prop. Did it have a CSU or did you just waggle it as you thought fit? The Airmaster is a CSU but with the addition of three convenient preset positions, that's all. However it appears that at present the range of pitch over which your prop can vary - limited by those pesky microswitches - will not allow it to go coarse enough for the CSU to do its job in the cruise preset mode when you go above a modest power level. In the climb and t/o presets it's OK because thy never call for as much pitch.

    Maybe you'll be happier always operating in hold mode, which is analogous to a traditional CSU with no preset positions. You should still do the adjustment of the coarse pitch stop however or you will be artificially limiting your range of control.

    Mike


  • Re: M.A.P.

    by » one month ago


    Ans - because that's the rpm the cruise position is set to by Airmaster. As I've said before, those 3 presets could equally well be labelled 5000/5400/5700 instead of cruise/climb/takeoff.

    So the full answer is - Yes! I can change the RPM setting, however this is done in the programing, not the mechanical side of the system.

    MAP is irrelevant to the control loop.

    As far as the Airmaster is concerned you are correct, however I as PIC am also part of the control loop

    MAP is never irrelevant. MAP is how the pilot manages power/fuel consumption. Airmaster tells me that I will adjust power (MAP) to what I determine i s appropriate for the given situaton.

    Yes I understand that I am adjusting for a Max Cruise RPM

    Ans - no you are not. You are adjusting the pitch stop to a setting that allows the controller to maintain the preset cruise rpm of 5000 constant from relatively low power up to WOT. Airmaster suggest setting it coarse enough to limit rpm to around 4000 at WOT when on the pitch stop on manual mode. 

    I think you are confused - The prop acts as an engine speed governor - If I set for Auto Cruise, the prop pitch changes / controls engine speed to 5000 rpm, thats what the engine will be limited too.

    I suspect semantics is at play.

    Why would you buy an expensive automatic electronic controller then set a mechanical stop that prevents the controller doing its job?

    Is this a rhetorical question? If not -I would speculate that the mechanical stops are a safety measure against electronic (program) malfunction.

    What's so special about 5000 rpm?

    Ans - nothing except it's what Airmaster chose to use for the cruise setting and it's around the lowest rpm at which you can use WOT without detonation risk.

    A good reason for selecting a slightly higher rpm, say 5100-5200, which will allow a small "buffer" when the load on the engine increases due to uncommanded climb (turbulence).

    You really don't understand how this thing is meant to work do you?  You're thinking of it like a fixed pitch prop or maybe a manually variable in flight prop. Set aside your preconceptions and study the manual and think about it. In one message you mentioned flying a Cessna(?) with a hydraulic VP prop. Did it have a CSU or did you just waggle it as you thought fit? 

    I think I have expressed my great appreciation for yours & Tims assistance but please do not patronise me - True I have failed to thoroughly read/understand the Airamster Operators Manual (my bad) which has resulted in my seeking assistance however I feel I am making good progress in better understanding how the system works.

     # I obtained my Constant Speed/Retractable endorsement, some 30 years ago, in a Cessna 172  (might have been a Cutlass). There are several mitigating factors to my current level of ignorance:

     # The passage of time, since I did may be 20 hrs of CS/Retractable flying.

     # Advanced age, making learning new "stuff" not quite as easy as 30 years ago.

     # The Airmaster system is semi automatic, compared with the full control CS, I was trained in. It's likly that I have fixated on the residue of that  training such that it has hindered my acceptance/understanding of the Airmaster.

    However it appears that at present the range of pitch over which your prop can vary - limited by those pesky microswitches - will not allow it to go coarse enough for the CSU to do its job in the cruise preset mode when you go above a modest power level. In the climb and t/o presets it's OK because thy never call for as much pitch.

    Agreed! This is what I have come to understand.

    Maybe you'll be happier always operating in hold mode, which is analogous to a traditional CSU with no preset positions. You should still do the adjustment of the coarse pitch stop however or you will be artificially limiting your range of control.

    Agreed!

    My thanks for your time.

     

     

     


  • Re: M.A.P.

    by » one month ago


    My question to Airmaster:

     # Does my prop have an optimum cruise rpm?

     

    From Airmaster:

     # This is determined mostly by the engine. 

     # 90% of installations on the 912S use 5000

     # Some of the heavier slower aircraft (like aircraft with floats) use 5200-5300

     

    It's a fair response but disappointing, in that I had hoped they may have some empirical evidence for 5000 rpm.


  • Re: M.A.P.

    by » one month ago


    I pressed Airmaster a bit more on the 5000 rpm Auto Cruise recommendation - they claim its a Rotax recommendation.

    So far unable to find any reference like this from Rotax - see new Forum question "Constant Speed Propeller"


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