yankee-flyer
Well Known Member
Flew 143WM for a short while this morning and made the following observations.
Density Altitude (DA) was a little more than 1000 feet greater than MSL.
During takeoff and WOT climb fuel flow (FF) readings was 5.2 - 5.3 gph UNTIL I climbed through approximately 6000' DA. From that point on FF rose slowly into the mid-7 range and stayed there when I leveled off at 6500 MSL (7700 DA) and established cruise at 5200 rpm. FF remained in the mid 7's (highest I've seen) during cruise.
I pulled the electric pump fuse. FF dropped to 0 (THAT got my attention but engine kept running) and then slowly built back up to 4.3- 4.6 with a fair amount of fluctuation. Note that I don't see much fluctuation with both pumps running.
Re-inserted the fuse and FF slowly climbed into the 7+ range again.
Descended to 4500 MSL (DA 5600) and fuel flow readout returned to "normal" 4.1 to 4.3 gph.
Landed and check fuel tank sight gauge. Used just over 2 gallons in 0.6 hours flying time. Interestingly enough, the fuel-remaining readout said I'd used 2 gallons, too.
Whatever is happening certainly seems to be related to DA.
Scott, it's hard to believe that the fuel pump would not leak below 6000 DA but would lose 3+ gph above 6000 DA. There is NO smell of fuel at any time.
I know our carbs are supposed to be altitude compensating; could some malfunction be occuring there? John and Dick have seen this with both the old and new style pumps; I'm still running the old pump at 120 hours.
Dick, I've followed John's lead in entering a return value into the Dynon-- have you done so? I don't remember seeing this behavior before that but maybe I wasn't watching since I knew the FF was off anyway.
I'm thinking we may need to forward all this to a Dynon rep???
Wayne 120241/143WM
Density Altitude (DA) was a little more than 1000 feet greater than MSL.
During takeoff and WOT climb fuel flow (FF) readings was 5.2 - 5.3 gph UNTIL I climbed through approximately 6000' DA. From that point on FF rose slowly into the mid-7 range and stayed there when I leveled off at 6500 MSL (7700 DA) and established cruise at 5200 rpm. FF remained in the mid 7's (highest I've seen) during cruise.
I pulled the electric pump fuse. FF dropped to 0 (THAT got my attention but engine kept running) and then slowly built back up to 4.3- 4.6 with a fair amount of fluctuation. Note that I don't see much fluctuation with both pumps running.
Re-inserted the fuse and FF slowly climbed into the 7+ range again.
Descended to 4500 MSL (DA 5600) and fuel flow readout returned to "normal" 4.1 to 4.3 gph.
Landed and check fuel tank sight gauge. Used just over 2 gallons in 0.6 hours flying time. Interestingly enough, the fuel-remaining readout said I'd used 2 gallons, too.
Whatever is happening certainly seems to be related to DA.
Scott, it's hard to believe that the fuel pump would not leak below 6000 DA but would lose 3+ gph above 6000 DA. There is NO smell of fuel at any time.
I know our carbs are supposed to be altitude compensating; could some malfunction be occuring there? John and Dick have seen this with both the old and new style pumps; I'm still running the old pump at 120 hours.
Dick, I've followed John's lead in entering a return value into the Dynon-- have you done so? I don't remember seeing this behavior before that but maybe I wasn't watching since I knew the FF was off anyway.
I'm thinking we may need to forward all this to a Dynon rep???
Wayne 120241/143WM