It was running on Mogas (like always).
Does the diameter of the fuel line allow the bubbles to float up on their own under all circumstances? For water you need at least 4 to 5 mm inner diameter in order for them not to get stuck. I suspect that’s not an issue with petrol due to its much lower surface tension.
After remembering how the bubbles behave in my fuel finger: I think that happens only with a much smaller diameter.
I’ve had Vapour Lock in a Cessna twin, climbing out from a hot day to the flight levels. Now I always keep the pump running until 5 mins after top of climb any time the temperature on the ground is above 25 or if the aircraft has been in direct sunlight even in colder weather. Never experienced it since doing that. I have seen some SR22 Turbos operated with the fuel pump on the whole time – but it seems like just adding wear and tear for no reason once in a stable cruise at altitude.
I’ve ridden a vapor locked engine to the ground, with my father as the pilot when I had only solo’d and had no pilot certificate. This was in a VW powered homebuilt running on avgas. The fuel system had a header tank behind the instrument panel, maintained at constant level by a fuel pump delivering fuel from the main tank, and an overflow back to the main tank. The issue was in the gravity flow line between the header tank and carb, presumably getting too hot. Anyway it quit on crosswind, after takeoff. Maybe the diameter of that line was too small. The plane was wrecked but rebuilt as good as new… with a second fuel pump to pressurize that line continuously. The problem did not reoccur.
It’s amazing the problems you can have with something that ‘should’ work fine. My contribution to the event was to use the key switch to rotate the prop flat while my father flew, saving a fair bit of money because the prop was not damaged, nor the crankshaft loaded, even though the landing gear was wiped out due to an old concrete drainage channel across the field under the brush.
I used to fly a Piper Apache in the Texas heat on mogas with no problems. That aircraft flew all the time in those conditions, and it wasn’t any less reliable than aircraft running on a diet of pure avgas.
This is the extract of relevant data from the G1000 at the time of the power loss.
It shows the OAT lower than I recall at 12C at FL80 (but 15 minutes at 12C would have little cooling effect on fuel that had been sat in 40C heat for the best part of the day).
Fuel flow is 18 USG/hr (top of green arc for a density altitude of FL100). When the electric pump is turned off it drops to 11 USG/hr and power drops from 72% to 56%.
30 years of using Tesco etc 4* then later Unleaded in a Jodel DR1050 O200. I’ve had definite vapour lock – froth came out of the gascolator drain after aborting T/O and clearing runway. Vapour lock always came on opening throttle full for take-off. Parked into wind with the gascolator behind the engine makes the gascolator fuel much warmer than that at the top of the tank – I’ve checked with a thermometer. Depending on the position of the bubble, an extra pump might make things worse
On avgas, C150/2/172, Pa28, hot and high, I’ve never had a problem. (SW US)
But even on avgas, the O200 has carb ice frequently on start up at Inverness
With auto fuel, carb ice, even in warm air, is more frequent at Inverness
Auto fuel specification changes with the season. Texas summer gas would be different from Montana winter gas.
I had vapour lock with a marine diesel, the fuel filter had a glass done, which showed the vapour. It disappeared when left. Blockage upstream, at entry to filter – the pump was reducing pressure enough for derv to vapourise.
With an aircraft, the same happened due to a blocked finger filter in the rear tank. Changing tanks solved it for the moment.
After maintenance, on two occasions I got a loss of power on switching off the electric pump after take-off, and immediately returned
One was an air leak in at the mechanical pump gasket. The other leak at a pipe joint was leaking fuel near the exhaust, fortunately it didn’t ignite.
