The use of flexible bladder tanks is a great idea. However, as they take up a
shape which is driven by internal fuel pressure (due to aircraft manoeuver
loads,
sloshing, etc) to react these loads effectively into the surrounding structure
another vessel or holder is required. If cleverly designed this bladder
holder can be a lightweight geodetic structure with hard points at appropriate
locations (for a replacement Europa tank these would be the original mounting
points). This means some of the benefits get eroded (bladder weight + support
structure weight) but it makes it a whole lot easier to remove and
replace/service.
I have designed/stressed such a system for a Part 23 twin aircraft as an STC.
For interest the VLA fuel tank requirements are in the regs as follows:
http://www.easa.europa.eu/agency-measures/docs/certification-specifications/CS-VLA/CS-VLA%20%20Amdt%201%20combined.pdf
CS-VLA 963 Fuel tanks: general
(a) Each fuel tank must be able to
withstand, without failure, the vibration, inertia,
fluid, and structural loads that it may be
subjected to in operation.
(b) Each flexible fuel tank liner must be of
an acceptable kind.
(c) Each integral fuel tank must have
adequate facilities for interior inspection and
repair.
CS-VLA 965 Fuel tank tests
Each fuel tank must be able to withstand the
following pressures without failure or leakage:
(a) For each conventional metal tank and
non-metallic tank with walls not supported by
the aeroplane structure, a pressure of 24 kPa.
(b) For each integral tank, the pressure
developed during the maximum limit
acceleration of the aeroplane with a full tank,
with simultaneous application of the critical limit
structural loads.
(c) For each non-metallic tank with walls
supported by the aeroplane structure and
constructed in an acceptable manner using
acceptable basic tank material, and with actual or
simulated support conditions, a pressure of 14
kPa, for the first tank of a specific design. The
supporting structure must be designed for the
critical loads occurring in the flight or landing
strength conditions combined with the fuel
pressure loads resulting from the corresponding
accelerations.
regards
John
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John Wighton
Europa XS trigear G-IPOD
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