MGL Avionics User Forum

We are developing a new-entry utility gyroplane, currently undertaking the required test-flight program.
We use the Xtreme EMS to display engine parameters/performance:

The gyroplane is propelled by the EJ25 Subaru engine - 2 500 cc, 4 cyl, normally aspirated.

We do not make use of any in-line fuel flow meter, but would like to make use of the fuel-injector flow-rate as a means to display a useful fuel flow on the instrument.

The injectors used are of the standard (251 variant engine) flowrate of 550cc/min - these are high-impedance (8 to 16 ohm) injectors and there are 4 pulses per engine cycle.
If anyone has a similar set-up, providing accurate fuel-flow, please share the K-factor (and any other pertinent settings, aside from the injector impedance (high) values which should be entered) which must be entered into the EMS fuel-flow set-up menu?.
Thank-you.
Rivaero

Using the injector opening time to work out fuel flow simply measures the integral of injector open vs injector closed time assuming a constant pressure fuel delivery system.
This ratio is pretty much linear with flow but we do not know the flow. First there may be more than one injector (usually one per cylinder) and we do not know the injectors flow rate.
So when you first start it will report some, likely fictitious flow rate. If you already know the flow rate you are good as you can now use a simple calculation - if your reported flow say is double the actual flow then simply correct the k-factor by multiplying it by two.
If you do not know the actual flow you need to derive it by filling the tank to a known level (usually full) and using some fuel - say about 1/2 tank. You start by zeroing the fuel totalizer in the EFIS so by the time you have used up your 1/2 tank it will tell you how much fuel you have used - now fill the tank again and measure how much you need to do this. Now you have the actual value. Again the correction is just a simply multiplication between actual and reported and you correct the k-factor accordingly.
Usually using the injectors can result in very accurate fuel flow readings but be aware that if you have fuel pressure issues your engine may compensate if you use lambda sensors and this affects the injector opening times - but not with the expected flow.