An amusing story about the Merline engine, that my father Ken often
related, concerns a combat problem with the Merlin engine in Spitfire
application. If the Spit was put into a fast dive to avoid an ME 109 up
it's exhaust pipes, the engine would suffer a two stage momentary 'negative
G' power loss. First was a brief engine hesitation then came a two second
'rich cut'. Full power returned once the plane was taken out of the
negative G dive. (The Me 109's did not have this problem because they were
fuel injected). Rolls couldn't solve the problem initially, but our pilots,
bless their hearts, found a way round it. If they spotted an ME 109 on
their tail, rather than pushing the stick forward, they would enter a dive
from one wing tip, ie they would tip the plane upside down before diving,
which put the plane in a 'positive G' rather than negative G. dive.
The problem was initially solved, when an extremely cleaver lady engineer
from the RAE (a Government aircraft research establishnment) was visiting
Rolls. The problem came up and she looked at the fuel system drawings. This
lady called 'Mrs 'Tilly' Shilling' noticed that the twin fuel pump system
with twin quill drives were part of the problem, because they were each
capable of meeting engine demands plus 20% individually if one pump failed.
Tilly deduced that if the float needle was not controlling the jetting
system ( due to negative G), both pumps could suddenly put a large excess
of fuel though the system.
She immediately suggested 'a restrictor valve' should be put into the fuel
line before the carburetor, which consisted of a washer with a hole in it
the size of which restricted flow to just above maximum engine demand. - It
worked and was used until Rolls designed the negative G carb.
The washer became ever known by Rolls engineers as 'MRS SHILLING'S ORIFICE'
Paul
PS Tilley Shilling died about three years ago.
so fuel pumps
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