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)
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!
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
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.
The reason for electrical back up pump for injectected engines is mainly, that mechanical pump on engine has lower and lower pressure because of altitude.
Mechanical pump elements are spring and membrane with two one way valves and link to lift the membrane against the spring. The forces to give the fuel pressure are the springload wich is steady and the pressure in crankcase on springside of membrane wich is not steady but dimnishes with increasing altitude.
The electrical pump is needed when the injectors dont fully atomice the fuel and droplets are reason for engine running ruff.
For example with full power my RV has almoust same pressure mechanical/ electrical on sealevel 26/28psi but on FL50 they are 23/27
I cannot imagine there would be a bubble of AIR – air should never be able to enter the fuel lines. Or there should be a leak somewhere, dripping out fuel when operative, sucking in air when not. Do watch for fuel leaks!
Vapour lock is caused by a bubble of vapourised fuel that cannot get away. In my own bird I relaid the fuel lines so that they form one continuously rising line from the header tank through the panel mounted fuel cock, through the miniature fuel filter, to the mechanical pump on the engine, exactly to counter vapour locking: any vapour that does form will raise to the fuel pump and be pushed to the carbs.
Causes of vapour locking are thus (both must occur):
1) formation of vapour, caused either by high temperature (no fuel lines close to body plating, where they will heat when parked in the sun) or by low pressure, as in the mentioned story of a (partial) blockage before the pump;
2) presence of a non-vented high point where a bubble of vapour can get blocked – fuel lining should be one continuously rising line, but perhaps this is not always easy to realise.
(I hope I have not only stated the obvious, but I can’t see anything more to say about it)
PS in my world of microlight flying, it is far from obvious to have a panel full of dials. Mine carries Rpm, CHT1, Oil temp and Oil pressure, and that’s all for the engine. The guru, who is a strong advocate of keeping things as rudimentary as possible, has once reluctantly said that if any instrument is worth adding, it is a fuel pressure gauge. Though I am not sure if fuel pressure is affected by the formation/presence of fuel vapour, actually I don’t think so.
I am wondering how a vapour lock would manifest itself.
Obviously it is a form of fuel starvation, so given that the airflow remains the same, the mixture will become lean. If you were ROP, it will initially reach peak EGT, then go LOP, and pretty soon the engine will stop delivering power.
But what exactly is a vapour lock and what conditions would make it appear or not appear?
I am thinking about a low wing aircraft with fuel injection. All these must have a fuel pump…
They do. An engine driven mechanical fuel pump. Most of these are perfectly capable to pump/pressurise a mixture of fuel, air and vapor. The electric fuel pump is only required when the engine driven pump fails. To prevent the engine from surging during the time it takes from recognition of the failure of the engine driven pump to manual selection of the electrical pump, the latter shall be switched on during critical phases of flight (takeoff, landing and airwork). If the manual of the aircraft doesn’t specifically require the electrical pump to be on under certain conditions (e.g. high altitude), I would rather leave it off. Because the basic principle for aircraft systems is always the same: “The less you use it, the longer it lasts.” And you never know when you will need it in anger!
