AlexPeterson
Well Known Member
Background:
1. AirFlow Performance Injection
2. Floscan mounted on firewall, in between the servo and flow divider. Straight 6" section of tubing on the inlet side of the Floscan "B". Floscan mounted with wires up as per their instructions.
3. Rock solid fuel flow indications cruise, matched totals vs fill ups.
4. No difference ever seen with and without fuel pump on, as would be expected for this Floscan position in the system.
5. 13+ years, 1464 hours on the setup.
6. Engine monitor - Rocky Mountain Instrument.
Since day one, the fuel flow reading has been erroneously high at idle or just above (taxi power), when cold. Indication at idle will be around 5.5 gph, which obviously is bogus. Leaning until just at the rpm drop does not lower indication significantly. Often the indication will drop to expected values by the time I'm ready to take off, perhaps in the 1.2 gph range. After a flight, it reads normally on the taxi in.
I've simply been ignoring the mysterious indication, since I didn't know what to do about it anyway. Over-indication is on the conservative side from a total fuel on board viewpoint.
After following the recent thread something like "Where does the fuel go?", I've become again curious about it. Tonight, while warming up the oil (for an oil change) on the ramp, I paid particular attention to the indications. As expected, it showed about 5 gph at idle. When throttling up to 1500 rpm, it dropped to about 3 gph, probably about right for that rpm. Back to idle - indication back up to 5. I repeated this 4 or 5 times. The settling time between power settings seems to be about 3 to 4 seconds. The ground run was about 15 minutes, and the idle indication never did behave. I did have the cowl off during this run.
I could speculate that, with the cowl off (ambient ~45F), whatever normally warms up (and corrects the erroneous reading) prior to take off did not warm up, hence the persistence of the behavior tonight.
I haven't a clue - any theories? I'll run and get some popcorn now...
1. AirFlow Performance Injection
2. Floscan mounted on firewall, in between the servo and flow divider. Straight 6" section of tubing on the inlet side of the Floscan "B". Floscan mounted with wires up as per their instructions.
3. Rock solid fuel flow indications cruise, matched totals vs fill ups.
4. No difference ever seen with and without fuel pump on, as would be expected for this Floscan position in the system.
5. 13+ years, 1464 hours on the setup.
6. Engine monitor - Rocky Mountain Instrument.
Since day one, the fuel flow reading has been erroneously high at idle or just above (taxi power), when cold. Indication at idle will be around 5.5 gph, which obviously is bogus. Leaning until just at the rpm drop does not lower indication significantly. Often the indication will drop to expected values by the time I'm ready to take off, perhaps in the 1.2 gph range. After a flight, it reads normally on the taxi in.
I've simply been ignoring the mysterious indication, since I didn't know what to do about it anyway. Over-indication is on the conservative side from a total fuel on board viewpoint.
After following the recent thread something like "Where does the fuel go?", I've become again curious about it. Tonight, while warming up the oil (for an oil change) on the ramp, I paid particular attention to the indications. As expected, it showed about 5 gph at idle. When throttling up to 1500 rpm, it dropped to about 3 gph, probably about right for that rpm. Back to idle - indication back up to 5. I repeated this 4 or 5 times. The settling time between power settings seems to be about 3 to 4 seconds. The ground run was about 15 minutes, and the idle indication never did behave. I did have the cowl off during this run.
I could speculate that, with the cowl off (ambient ~45F), whatever normally warms up (and corrects the erroneous reading) prior to take off did not warm up, hence the persistence of the behavior tonight.
I haven't a clue - any theories? I'll run and get some popcorn now...
