Hi everyone,
I guess I'm not the only one having this problem. The main problem here
is that I don't understand why it is happening.
If I arrive at an airfield in hot weather, I can restart either right
away, or after a considerable time. If I just refuel without having a
meal, I get into a time window where the engine has difficulties starting.
It is a vapour lock problem of some sort, but I don't know how this can
happen. Sure, the inside of the cowling is hot and residual heat from
the turbo is, without the large fan upfront turning, cooking the fuel.
But I thought that the 914 is supposed to be immune from the problem.
Up to the pressure regulator the fuel is recycling when I switch on the
electric fuel pump. Any vapour up to the pressure regulator is directed
back into the tank and being replaced by fresh and cold fuel.
The carb bowls might have been cooked empty, but then the floats will
have dropped and fresh fuel will pour in as soon as I switch on the
pumps. The fuel line between the pressur regulator is not recycled but
if it contains vapour then it will escape via the opened carb needle and
not raise the floats, so it will gently escape until being replaced by
liquid fuel, being driven there by the electric pumps.
So... why won't then darn thing just start?
Yesterday I was exactly experiencing this problem. After arriving at an
airport to go to the service center for the bi-annual pitot and static
systems test, and with the engine switched off for about ten minutes I
couldn't restart it. No matter how long I kept the fuel pumps running,
applied choke, (just in case the mixture was too lean) or was just
cranking with the throtthle wide open to vent the cylinders (in case it
was too rich), the engine would just crank without even a faint single hit.
So I abandoned the plan to taxi to the refueling station, and had a
lunch instead. Of course after that the engine started up right after
just a half turn of the prop...
So... why is this happening? I'm interested in solving this problem, but
primarily I want to know why this is happening because according to my
reasoning it shouldn't be happening in the first place. What am I
missing here?
Oh BTW, on the return home I got caught by non predicted early set in of
night fog, with a very rapidly dropping cloud base (never seen it
falling that fast). With my home base being the closest and most
promising airfield once I got forced down to 500 feet I advanced the
throttle to 100% (not 115%) and got over 155 knots IAS worth out of it
on my freshly calibrated ASI, which was quite an experience so low over
the ground. At my homefield I arrived less than 15 minutes later with
the local cloud base still at 1000 feet (as announced/predicted by ATC
half an hour earlier), but I was thankful nevertheless to have been able
to speed out of that threathening situation that fast. If it weren't for
the obligatory static/pitot test to renew my airworthiness review
certificate I wouldn't have been flying at all that day, so much for the
bureaucrats that want to enforce my safety this way. Anyway, the
pitot/static systems worked flawless (I would have had noticed it myself
it if they weren't) and I'm good to apply for renewal of the desired
certificate.
All this while I had unwittingly broke my smallest toe by bumping into
my wife unintentionally (honestly!) and was undergoing this flying
experience with some discomfort to enhance the flying experience even
further. At least the latter problem has been diagnosed correctly today,
so now I just want to get diagnosed the vapour lock problem as well. Who
can shine some light on this mystery?
Frans
|