Here at last the Integrated Fuel Gauges (INTFG) for the X-Plane C172SP running Logitech FIP drivers.   It is fully customized for the aircraft even with the adjustable EGT reference needle. 

Unfortunately, there is still a feature yet to implement — the fuel-flow needle doesn’t work properly yet.

Nevertheless, instead of keeping it away from the shelf,  I replaced the fuel-flow instrument with CHT (Cylinder Head Temperature, a common feature found on Cessna aircraft) as an interim option until the solution is found.

Both CHT and fuel-flow options are included in the gauge package.   When the fuel-flow option is chosen, users may regard it a failure, which adds fun too.

All current X-Plane C172SP (Logitech) users could contact me for discount if interested in this new instrument.

Lastly, since I am not a full X-Plane simmer, help on implementing the fuel-flow feature is welcome and appreciated.    In return, a full set of the XP-Logitech C172SP or B58 gauges (or any of my bundle gauges) will be given to the first person who help solve the issue as a gift.

Following is the implementation I did so far:

<!-- FUEL FLOW -->
<Element>
<Position X="276" Y="60" />
<Image Name="XPL_C172SP_INTFG_Needle.bmp" ImageSizes="37,4,37,4">
<Axis X="2.0" Y="2.0" />
</Image>
<Rotate>
<Value Minimum="0" Maximum="19">(A:sim/cockpit2/engine/indicators/fuel_flow_kg_sec) 1320 * </Value>
<Nonlinearity>
<Item Value="0" Degrees="210" />
<Item Value="5" Degrees="220" />
<Item Value="10" Degrees="250" />
<Item Value="15" Degrees="285" />
<Item Value="19" Degrees="330" />
</Nonlinearity>
</Rotate>
</Element>

As the dataref in X-Plane for fuel-flow is in kg/second, and the result I need is Gal/hour.   So I multiply the dataref by 3600 for an hour consumption and then multiply the result by 2.2 to convert it from kg to lb.   And then I further divide the result by 6 for gallon per hour.

In other words, 1 kg/s in an hour is equal to 1320 gal/hour.

So in the formula, I put 1320 as a constant to convert the value from kg/sec to gal/hour.

The concept and the formula sound logical to me and the calculated result matches the value shown by the Dataref Editor.   But the fuel-flow needle doesn’t respond accordingly.   I am not sure whether there are somethings I missed.

Besides the “sim/cockpit2/engine/indicators/fuel_flow_kg_sec” command, the “sim/flightmodel/engine/ENGN_FF_” command doesn’t work either.

Help is greatly appreciated.  Alternative suggestions solving the issue are welcome too.