Cheetah 160
Owner’s Manual
Appendix
LOSING THE KINGPOST- WHAT IT MEANS TO YOU
The 'topless glider' has been developed to reduce parasitic drag and thus increase performance
by removing the top rigging. This has resulted in one of the largest changes in hang glider
design and performance for some time.
The old style top rigging provided two things:
·
The top rigging braced the airframe when on the ground or when the glider was subjected to negative
'g'.
·
The kingpost provided an attachment point for the anti-luff lines which contributed to the glider's pitch
stability.
These two jobs are now done by the new structure without the aid of a kingpost. This has resulted in the
use of new materials such as carbon fibre reinforced plastic (CFRP), more usually seen in racing cars.
CFRP is used because it provides better stiffness and strength to weight ratios than aluminium. This results
in a 'kingpost less' airframe that is only slightly heavier than a standard airframe.
Strength
The most obvious requirement is the need for strong cross tubes. These carry the weight of the wings when
on the ground. This load is transferred to the keel via the leveller (or cross tube centre junction).
The keel has also lost its top wire bracing so it needs to be stronger to support the loads from the cross
tubes and resist downwards bending of the keel. e.g. When pulling the nose to lift the keel off the ground
prior to flight.
When rigging or de-rigging on the keel the wings are held up by the cross tubes. The load exerted by the
cross tubes on the keel and resultant extra friction mean that the tension is more difficult to pull on or let
off. Hence the preference for help lifting a wing when rigging or the need to pull the cross tube centre
junction forwards when de rigging prior to folding the wings in. Of course neither of these are necessary
when rigging or de-rigging flat.
Pitch Stability
The glider's pitch stability is now provided by washout alone thus the rods for maintaining washout are
very important. On the Cheetah there are two washout rods each side. The inner rod swings out
automatically when rigging. The outer must be positioned when the glider is rigged. Thus do not be
tempted to alter the angles or heights of the rods. Also do not disconnect the inner rod from the sail in an
attempt to make the sail easier to pack. (It will result in incorrect rigging next time.)
The Nature of Carbon Fibre
Carbon Fibre Reinforced Plastic (CFRP) or carbon fibre as it is sometimes shortened to is a composite
material. It is made up of a matrix and filaments of fibre. The matrix (epoxy resin) is the material used to
bind the filaments used in the composite material. The filaments used are carbon fibre. In 'hybrid'
composites a mixture of fibres or filaments are used.
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