--> Europa-List message posted by: "dmac7" <dmac7@outlook.com>
This is a old post from Andy Draper ( before XS ) regarding the two types of
rubber blocks including the material type and pre-load.
The original shock absorber required a pre-compression to bring the
dimension betrween the centres of the top and bottom plate bearings down to
5". The weight of the aircraft then compressed the rubber further, bringing
the top and bottom plates quite close to the limit stops. To allow further
compression of rubber to take place and not compromise propeller clearance
we added a spacer. Following the drop tests we decided to reduce the amount
of pre-compression such that the distance between the plate centres would be
The materials of the red and black blocks are the same: polyurethane grade
RHS/204/all weather 75=B0 Shore hardness to standard commercial tolerances.
The black block is 3/8" deeper than the red to accommodate the extra 1/4"
required between the top and bottom plate mounting centres.
The reason for the colour change of the block is that we have changed the
manufacturer. The first gave no choice of colour, the second allowed a
(a) to ease identification of the changeover,
(b) as it is in a muddy environment a light colour may be
considered inappropriate.
We don't consider that the rubber block has any ability to dissipate energy
(although of ocurse it will to a degree) which is why we have introduced a
damper system. The red block plus spacer will be slightly stiffer than a
black block without, but when you try to quantify the difference in the real
world i.e. on an aeroplane during a landing, you'd need a very sensitive bum
to be able to feel it.
Since the modification which calls out the requirement to cut the Vees in
the rubber blocks (Mod no 16 dated 7 November 1995) was issued, the tooling
for these blocks was altered so that those later recipients of fuselage kits
had the mod done for them.
The Vee shapes and the dampers are not related. All blocks must comply to
Mod 16, with or without dampers, as otherwise there is the possibility of
over-stressing the reaction plates.
When the shock absorber has been set up correctly and the aircraft is sat on
the ground ready for flight, the fuselage will be in a nose up attitude of
around 9=B0. Fuel, people, baggage, etc. will all alter this figure. Use it
as a double check if you have an inclinometer handy.
Andy
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=515328#515328
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