Dave,
I think you missed my point. The flows measured were under gravity from a
point just downstream of the fuel valve (the fuel line was disconnected at
that point and a calibrated container put in place to catch the flow). This
was WITHOUT any contribution from any pump. Downstream head losses in the
remainder of the complete system would confirm that the engine pump is
having to suck (ie put much of the fuel line at less than atmospheric
pressure ) to draw along the fuel; This would increase the risk of vapour
formation.
It would reinforce the need to install the auxiliary pump as low as possible
and with as few flow restrictions as possible between it and the tank. Some
types of pump (eg roller cell) aren`t good at sucking and, if they become
unprimed (eg by vapour locks), aren`t good at getting things going again.
Duncan
-----Original Message-----
From: Dave Simpson <Dave_Simpson@londonweb.net>
Subject: Re: Flying:Engine reliability
>Duncan,
>
>This shoulnd't be an issue. The fuel system design, and any subsequent
>modifications to it, must have been demonstrated to comply with the
>requirements of JAR-VLA which demand, (in 955) that:
>
>Under worst case conditions of minimum fuel and worst attitude the pumps
>must deliver 125% of the max demanded by the engine.
>
>Has someone been fiddling or not doing the test corrrectly?
>
>Dave Simpson
>
>> Message is from
>>Klaus Dietrich <Klaus.Dietrich@oracle.com
>>
>>***********************************************
>>
>>>>Alan,
>>
>>I experienced very similar engine cough/stutter
>>
>> the
>>fuel pressure as generated by the mechanical pump is on the low side
>>
>>All the best
>>Klaus<<
>>
>>Not forgetting that the pump has to suck fuel in before it is able to blow
>>it out.
>>Gravity fuel flow measured from the floor mounted fuel valve is down to
>>about 3gph with 1/4 gallon left in the tank; the point being that with the
>>further head losses between the valve and the (mechanical) pump, the pump
>is
>>having to suck quite hard. The return line just adds to the overall head
>>losses.
>>
>>
>>Duncan McFadyean
>>
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