Hi everyone,
Just returned from a trip to the French Alps.
I have had some worrying experience, so I hope to gain some wisdom from
the group.
What happened is that during the take off roll from a 4000ft altitude
field on a hot day, the engine hesistated and didn't develop full power.
As it was a rather short runway in a valley with absolutely no suitable
fields in the proximity for an emergency landing I aborted the take off
(and was happy it happened early in the take off roll).
Associated with the drop of power I saw the fuel pressure drop (note a
recent discussion where I discussed the importance to have a
conventional fuel pressure gauge at the top of the panel, as an unusual
swing of a needle surely catches your attention). A quick check of the
fuel system didn't indicate any abnormalities. Idle and medium power was
ok, but at full power the fuel pressure dropped everytime. My conclusion
was that it had to be vapour lock in some way, so I decided to try
another day in the morning. Indeed the problem appeared to have solved
itself and ground runs gave enough confidence to attempt a take off. The
engine developed full power as it usually does and the 4.5 hour flight
home was just like normal.
I don't fully understand how this could happen however. I have taken off
in hotter weather.
My assumption so far is that it happened because of the combination of
altitude and temperature, and the fact that I refueled the airplane in
the morning while the take off was in the afternoon and the fuel had
plenty of time to heat up while the airplane was parked in the sun.
Another difference was that the floor of the bagage bay was now covered
with a black piece of carpet instead of the white carpet I normally have.
A few questions here:
1) Is there any difference it the type of fuel (AVGAS, MOGAS) regarding
to the sensitivity to vapour lock?
2) Is there anything that can be done about it? (I assume that it must
have occured at the fuel pump inlet, under the bagage bay).
3) My habit is to switch on the second fuel pump while lining up. Maybe
it is better to switch on the second fuel pump earlier? (This second
fuel pump is also used for starting the engine, so it had already run.
After startup I switch fuel pumps, so before lining up both pumps have
already ran and found to be ok, and should have been "cooled" by the fuel).
4) Will a cockpit cover help? (Maybe the answer is obvious, but I'm
hoping to hear from someone that the very same problem was cured by
using a cockpit cover).
5) Is my conclusion and assumption about the vapour lock correct, or do
I need to investigate further?
Thanks,
Frans
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