Fuel Pressure Monitoring System
By: Richard Provenzano, EAA Chapter 839 Stroudsburg, PA.
One common reason for light aircraft ' engine stoppages ' is fuel delivery related. Low fuel pressure or fuel delivery stoppage can occur with the Rotax or any other aircraft engine. Consequently, I decided to install a low fuel pressure warning system on my Challenger LSS. The benefit of this system is that it will warn the pilot when a low fuel pressure condition exists. Should the pilot have a low fuel pressure situation develop he/she can then turn on an auxiliary fuel pump to attempt to restore the fuel pressure. Hopefully the restored fuel pressure will allow the pilot to avoid an engine stoppage. Then he/she can make a safe landing and remedy the low fuel pressure problem. I acknowledge that there are different ways to monitor fuel pressure and many ways in which fuel pressure can be affected therefore, the author can assume no responsibility for this system.
With the use of a three port fuel manifold from Aircraft Spruce, a normally closed pressure switch from Digikey set at 2.5 psi, a single pole toggle sw, 12v warning light and 12V horn and some #16 AWG wire, a really nice fuel pressure warning system can be created. The pressure switch is set at 2.5 psi. and sounds a horn under the panel and lights a light on the panel whenever the pressure is at or below this setting. The single pole toggle switch is used to test the low pressure warning system before engine start. Idealy at engine start the pressure should rise, the horn silences and the warning light goes out. This toggle switch is the master switch for the low fuel pressure monitoring system and must be in the "ON" position whenever the engine is operating. If the warning system activates while the engine is operating on the ground, remedy the problem immediately before flight. If activation occurs while in flight an auxiliary fuel pump can be activated and hopefully allow enough time for a precautionary landing. The auxiliary fuel pump can also be used to fill the carb bowl(s)and pressurize the fuel system before engine start therefore silencing the warning horn and turning the warning light off.
I chose to install my auxiliary fuel in series with the engine driven fuel pump. Remember to fuse the fuel monitoring system. I used the auxiliary fuel pump circuit breaker for protection. Mounting of the three port fuel manifold is accomplished with the use of a QCU elevator bellcrank bracket and properly sized AN hardware. It's attached to the dampened side of the engine mount. Test your system before each flight to ensure its integrity. All fittings are 1/8-27 NPT.Parts needed:
An auxiliary fuel pump and toggle switch are in addition to the above parts list.