Meaning of green arc for RPM and MP

A

apilotb

Pre-Flight
Joined
Aug 10, 2018
Messages
39
Display Name
Display name:
ApilotB
What exactly is the meaning of the bottom of the green arc? People have given different answers. Some say this is the prop governor range. Some say carb heat should be used when operating below the green arc. Some say fuel pump should be turned on. Cowl flaps should be closed etc.. POH is of no help here because it just says green arc is the recommended operating range. What do you guys say?
 
For me, unless I’m on the ground or needing a VERY steep decent I stay in the green, you’ll often start cooling things pretty quick south of the green
 
It just means "normal operating range." Most of the others, like turn on carb heat on a Cessna when below the green, are mostly non-POH techniques gleaned from experience.

Example The POH says, "Carburetor Heat -- ON (apply full heat before reducing power)" in the 172P checklists. People have learned that "reducing power" enough where it is an issue is not reducing from climb to cruise, but when going below the green arc before descending.
 
In 172s and 182s, I was taught to use carb heat even for some situations where you’re still in the green. For example, if you want 90 kts approach speed in a 172, 2100-2200 rpm will usually deliver, and you’re in the green. But you also want to be using heat. Those aircraft are ice makers.

I’ve understood the MP and RPM green zones to simply represent the range of engine power settings that can be used without any time limits.
 
WillFly4Food said:
In 172s and 182s, I was taught to use carb heat even for some situations where you’re still in the green. For example, if you want 90 kts approach speed in a 172, 2100-2200 rpm will usually deliver, and you’re in the green. But you also want to be using heat. Those aircraft are ice makers.

I’ve understood the MP and RPM green zones to simply represent the range of engine power settings that can be used without any time limits.
Click to expand...

Engine operating time limits are in the front of the POH under Operating limitations, not in the general information section.
 
In our plane the bottom of the green arc is the minimum power at which the turbochargers will supply adequate pressurization air. This is probably a fictitious number because however well it was sealed at the factory, it's not that now. Maybe they built in a buffer.
 
In our 182R, I have noticed that the bottom of the green (15" MP/2100 RPM) seems to correspond to the propeller governor reaching its finest pitch.
 
sarangan said:
In our 182R, I have noticed that the bottom of the green (15" MP/2100 RPM) seems to correspond to the propeller governor reaching its finest pitch.
Click to expand...

In your 182 RG, once you are below 15” the governor is no longer controlling the RPM. Below this point, throttle will control RPM.

In all aircraft, the green arc on the tach is the normal operating range.
 
You must log in or register to reply here.
Back
Top