Bad day Sunday for two of my diesel models -- one easily repairable, other undamaged.
Symptoms: both models -- Fuel newly blended using John Deere starting ether. Field temperature near 90ยบ, severe low humidity. Ground setting not easily found, odd run in flight. Some bubbles noted in a clear run of the fuel line. Occasional smoothing out with heavy, wet exhaust plume. Odd sounding run as if it had suddenly gone extreme rich. Short airtime. Mucho oily residue, very light color, almost clear.
Both setups had the overflow vent pinhole adaptation.
Bench checking the crashed engine today, I had trouble getting a setting. Similar WX to yesterday. Many bubbles in the clear fuel line. At best, the line filled most of the way, with bubble gaps you could hear as a leaning pulse when they hit the spraybar. Note: separate bubbles, not foaming with numerous small frothy bubbles.
Voila'! Ether's low vapor pressure strikes again. The initial bench setup was with a clear fuel line that looped above the path to the spraybar nipple - sorta like an inverted U-tube. The ether went to vapor over the high point. It takes very little pressure change to do that: apparently, with a little vibration, the weight of the fuel columns each side of the high point was enough.
Rearranged the tank so the fuel path was below the spraybar and without humpback rises -- instant cure. (The engine is fine, BTW.)
Applying this to a model -- keep the fuel line short, "low" and rising to the spraybar. Think of the force directions in flight to define "low."
\BEST\LOU
