The Bo fuel flow indicator is surely one of those that may appear complex to read. Actually, it’s fairly simple.
In this how-to you will find all the informations you need to know about it. Once you know how to read this indicator, you will find that REP nails the numbers once again!
The Fuel Flow indicator
The picture below depicts the MAP/Fuel Flow indicator.
On the left-hand side there’s the Manifold Air Pressure indicated in inches of mercury (In.Hg).
On the right-hand side there’s the Fuel Flow (F.F.) indicator.
The large numbers in the outer arc indicates the F.F. in U.S. Gallons per Hour. The green arc indicates the normal F.F. operation range.
The inner arcs are more tricky. They can be divided in more sections. Let’s explore them, reporting what the Bonanza POH says.
Takeoff Section (1)
The POH states:
The higher end of the green arc includes a sawtooth segment to indicate the approximate fuel flow required for takeoff and climb at sea level, 3000, 5000 and 7000 feet. The pilot should use performance charts for the exact fuel flow requirements.
It means that during takeoff the F.F. should stay around the numbers near the altitude mark that reports your current pressure altitude.
Cruise Section (2)
The POH states:
The lower end of the green arc includes a sawtooth segment labeled “% CRUISE POWER” which indicates the approximate fuel flows for powers ranging from 45% to 75% of max continuos power.
The lower fuel flow of each sawtooth corresponds to the cruise-lean fuel flow while the higher fuel flow of each sawtooth corresponds to the best power fuel flow. When power is set in accordance with the cruise power setting tables in the PERFORMANCE section, these sawtooth markings provide approximate percent power information.
It means that if you lean properly and follow the Cruise Performance tables, the F.F. needle should fall near the markings related to the current engine power percentage.
For instance, the picture above indicates a 75% of power cruise.
Fuel Pressure Limitations (3a – 3b)
From the POH:
the red radials indicate the minimum and maximum allowable fuel pressures.
The F.F. is directly related to fuel pressure.
Since the fuel pressure is controlled via the throttle and the mixture controls, the best place to put the limitation markings is the F.F. indicator.
The minimum fuel pressure for the TCM IO-520 to work properly is 1.5 PSI. The maximum fuel pressure is 17.5 PSI. Therefore, you should never go past those redlines.