I cannot imagine there would be a bubble of AIR – air should never be able to enter the fuel lines.
That can easily happen if you happen to run a tank dry, as we’ve discussed on the other thread.
(I hope I have not only stated the obvious, but I can’t see anything more to say about it)
Not everything is obvious to anybody, so it is always worth mentioning! There is another safe alternative to your continuously rising fuel line and that is a loop with a return line to the tank. This is installed with (almost?) every fuel injected engine (piston, turboprop, jet) where more fuel is pumped to the fuel control unit than the engine actually needs. The excess fuel flows back to the tank(s). With this type of installation, every kind of vapor or air lock can quickly be purged out of the system by briefly turning on the electric fuel pumps, even if the engine is not running at all.
That can easily happen if you happen to run a tank dry, as we’ve discussed on the other thread.
Ah, true enough. I didn’t think of it because in my own craft the header tank takes care of this. Even then, grief may come of it, as I related elsewhere**.
As for the return line: Rotax now recommend this for their non-injected 912/914 in all installations, and for the popular C42 the builder (“Musterbetreuer”) insists it should be retrofitted to the whole fleet, to the dismay of the many owners/operators who never suffered from vapour locking, and must now spend a fair deal of money. Concerns were apparently raised by the increasing addition of alcohol to car fuel.
\* \* "Consequences of low levels of fuel ", #02
So you are saying that borderline-spec avgas will be borderline at FL200 at +38C?
It’s an interesting question whether the fuel servo (etc) reaches +38C. I am aware of a flight test with an IO540 and an instrumented fuel system and the fuel temperature entering the fuel distribution spider was more or less at the fuel tank temperature i.e. there is no significant heating from the fact that the fuel servo is attached to the bottom of the engine.
That might not be case after a departure from a +40C Greek airport but the fuel tanks won’t be anywhere near +38C by the time you reach FL200
Interesting how close it all is!
Might be a bit different with a turbo charger. 22mins to FL200, a rubber bladder tank (more insulation) and you might be able to test how good your AVGAS is.
Mogas is different: DIN 228
DVPE: 45–60 (Summer) and 60–90 kPa (Winter)