RV-6A, O-360, fixed pitch, MA-4-5 carb
I was playing around at altitude in landing configuration: full flaps, idle, fuel boost pump on, 65 knots when the high fuel pressure (8 psi) went off. Fuel tanks were full.
The pressure went back to normal with the boost pump off. I’m thinking it might just be the combination of a nose down attitude, full fuel tanks, and the boost pump. It rises slowly, so I’m pretty sure I didn’t notice it in normal landings as the boost pump was on with the nose pointed down less than 30 seconds.
The electric fuel pump is rated for 4.5-6 psi of boost.
The top of the fuel tanks may have been higher than the tap at the carb for the pressure to add 1 psi.
But perhaps I should subtract 1 psi for the height of the pressure transducer mounted on the fire wall. In a descent, the transducer might be level with the top of the tank.
It’s not hard to believe the engine driven pump wouldn’t add 2-3 psi.
I couldn’t find a spec for the carb for maximum fuel pressure. But the overhaul manual for the carb has you do a needle valve leak test at 6 psi with the bowl full. The bowl level is not suppose to increase for 5 minutes.
The engine (Superior) spec’s 8 psi for the fuel inlet. But we are measuring the output.
Anyone have any thoughts if this might be a problem?
I was playing around at altitude in landing configuration: full flaps, idle, fuel boost pump on, 65 knots when the high fuel pressure (8 psi) went off. Fuel tanks were full.
The pressure went back to normal with the boost pump off. I’m thinking it might just be the combination of a nose down attitude, full fuel tanks, and the boost pump. It rises slowly, so I’m pretty sure I didn’t notice it in normal landings as the boost pump was on with the nose pointed down less than 30 seconds.
The electric fuel pump is rated for 4.5-6 psi of boost.
The top of the fuel tanks may have been higher than the tap at the carb for the pressure to add 1 psi.
But perhaps I should subtract 1 psi for the height of the pressure transducer mounted on the fire wall. In a descent, the transducer might be level with the top of the tank.
It’s not hard to believe the engine driven pump wouldn’t add 2-3 psi.
I couldn’t find a spec for the carb for maximum fuel pressure. But the overhaul manual for the carb has you do a needle valve leak test at 6 psi with the bowl full. The bowl level is not suppose to increase for 5 minutes.
The engine (Superior) spec’s 8 psi for the fuel inlet. But we are measuring the output.
Anyone have any thoughts if this might be a problem?