Graham,
Need that account no etc please as between me and Kingsley, I keep forgetting.
I want to get that money to you, so I better do it soon. Any luck with Andair
getting that new element??
Onto a 912S question. Do you like the way Nigel Charles has set up his fuel
system, the parrallel one, with no mechanical fuel pump, only 2 electric
Facets. I will include a picture. I read your statement below regarding the
inability of the Facets to provide adaquate flow rates to keep the fuel
pressure up, and keep the fuel in the return line circulating to avoid fuel
temperature buildup and subsequent vapourlock. Well with this setup there is no
return line, as he uses a pressure regulator. I think it actually sounds like
quite a good system, as it allows the full use of the fuel on the main side
with an automatic cutover to the reserve side when it expires. Mal and others
switch over to the reserve often when there is a considerable volume and
therefore endurance remaining. I want to be able to use it all, and if I stuff
up, or if the main side stuffs up, I don't want any switching, only flying and
let the engine look after itself, giving me a light or audible to highlight
what has just happened, rather than the silence that demands that "I do
something, as well as fly". I'd be interested in a penny for your thoughts.
Reg
Tony R.
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>>Gidday,
>>I have been following this thread for a while, because I started it. I am
>>surprised there isn't anything definitive, but I appreciate there is a
>>difference between ID and OD. I do however "not" have my head around why you
>>would need a restrictor in any fuel return line, irrespective of engine
type?
>
>The 914 is different, it uses rotary fuel pumps which delivery far more
>fuel than the engine requires. This is the reason the 914 needs a bigger
>return pipe dia than the 912s. 912s have a mechanical pump,
>displacement dependant on engine rpm so delivery is much more limited.
>Excessive return flow would cause reduced fuel pressure, which might not be
>enough to avoid fuel starvation. The Facet electric auxiliary pump also has
>limited displacement and won't give enough pressure to compensate.
>Incidentally, the limited displacement/flow rate also makes the engine more
>susceptible to vapour locking because the pumps have no way of catching up
>the deficit caused by the vapour. Hence the importance of the return pipe,
>it bipasses the vapour quickly and gets cool fuel to the pump. The pump
>absorbs heat from the gearbox, which is heated by engine oil.
>BTW there is no such thing as a daft question. How else can one learn?
>Graham
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