During my fly in pattern I reduce Throttle to certain position e.g. 1800RPM. It keep goes down to 17xxRPM. Not keep steady. Is this suppose to be like that?
If you are using some sort of HOTAS or throttle settup, check the smoothness in windows and game. If it’s jumping around and not smooth, it’s probably the potientiometer (Pot). gunked up and needs to be cleaned.
If you are using more than one controller, make sure that there is not a throttle assignment on another controller. MSFS 2020 will try to read both and cause what you are describing.
Thanks for reply. I am using keyboard for throttle. I also have flyhonycomb yoke. It should not have throttle control on it.
What airplane are we talking about? On aircraft with a fixed pitch propeller the RPM is a balance between engine power output driving the propeller and the forward speed (TAS). If airspeed decreases, the angle of attack on the propeller increases causing the drag of the propeller to increase and therefore RPM to decrease unless corrected by increasing power.
In short, for a fixed throttle setting, higher speed, either by a disturbance or the aircraft speed not having settled after setting throttle causes higher RPM, lower speed causes lower RPM.
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Thanks for your reply. I flying Cessna 172. I think I need little bit time to digest this. I will try to understand it during future fly.
I’ve attached a picture I found from the internet, you can see that the angle of attack on a propeller blade is depending on the forward speed and RPM. These all eventually reach balance.
As an example, with everything stabilized in cruise flight, should you reduce power, the drag of the propeller exceeds the engine power output and therefore the RPM will drop which will reduce the angle of attack and therefore less thrust is produced. The power produces by the engine and that absorbed by the propeller are initially in balance again.
But now the airspeed starts to reduce as thrust is reduced. This will increase the angle of attack on the propeller, creating more drag. The power required by the propeller and that produced by the engine are out of balance again causing the RPM to drop further. Eventually a balanced conditions will be reached once airspeed stabilises but at a lower RPM than initially set.
I hope this explains a little bit the condition you are experiencing. On a fixed pitch propeller (like the Cessna 172) the propeller RPM will keep changing with changing conditions. Its not as simple as setting RPM and leave it be as it would be with a constant speed propeller.
