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.
