Nigel
> Even if builders have the inlet pointing forwards, the fuel line can easily
> be routed away from the exhaust. I altered one of my aircraft to this
> configuration.The fuel line
> is still further away from the exhaust than the float chamber, which, being
> metal, will transmit much more heat to the fuel than will get through the
> fuel line.
Europa wanted insulation around the fuel hose. The fuel hose supplied was
stainless steel covered. It would not have been possible to bend the hose as
tightly as in your photos.
> Despite the above, which indicates that the builder should do everything
> possible to keep the carbs and fuel lines cool, I am not at all convinced
> that your misfire was due to the proximity of the fuel lines to the exhaust.
> When you consider that in a full power climb the engine is using about 27
> litres of fuel per hour, this equates to a velocity of about 10 inches per
> second in the fuel line. The amount of heat transferring to the fuel through
> a thick rubber fuel line under these conditions would be absolutely
> negligible,even if the fuel line was right next to the exhaust.
Sorry. This is NOT right. My misfire was at the top of the climb AFTER
levelling off and reducing power, while the exhaust was still very hot from
the climb. I agree that in the climb the fuel flow could be 10 inches per
second, but in the cruise it is a lot less. And with the s/s braiding heat
would have been conducted underneath the insulation once a hole had been
melted in the insulation. I have had no problems whatsoever at this stage of
flight since I changed the fuel system. The hose now goes OVER the carb to a
dash-pot that simulates the dashpot that is supplied on a certified engine.
New straight unions have been fitted in place of the banjos. And the s/s
braided pipe replaced by rubber pipe.
The problem didn't happen every time, and was minimal last winter, but it
often happened when banking left at the end of crosswind. The right hand
fuel hose had the melted insulation and of course that side of the engine is
likely to be warmer as the air flow is restricted by the oil dry sump tank
and its piping.
> Perhaps the cause was something else which you
> inadvertently cured when working on the engine.
I am not convinced as the problem IMMEDIATELY went away when I angled the
banjos backwards, and has not re-occurred since the whole fuel system
forwards from the fuel pump to the carb was re-made.
> Carbs and fuel lines that get hot after engine shutdown are more likely to
> give vapour lock problems making hot restart difficult, or causing engine
> failure after takeoff (after hot restart if fuel bleedback is not
> incorporated).
I have the fuel bleedback, and have never had a hot start problem.
> Perhaps you could pass my comments onto the Europa list.
Sure.
As an aside I notice that the standard installation is oil sump scavenge
pump to dry sump tank, and then from dry sump tank via the oil radiator to
the main pump and the bearings. This has left the dry sump tank containing
very hot (pre radiator) oil. What was the logic for that rather than what I
would have done on a rally car which would have been to put the radiator in
the line between the scavenge pump and the dry sump tank, which would have
given cooler oil in the tank.
Richard
PS I agree your figure of 10 inches/sec for 27 litres/hour through a 1/4
inch ID hose but that would be in the hose from the fuel pump. The fuel flow
in the pipe to the carb would be half that (5 inches per sec) and at my
cruise of 16 litres an hour around 3 inches per sec.
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