I have just finished installing two SkySports capacitance probes for
fuel quantity measurement.
Being somewhat ponderous (mostly out of fear of screwing up a
purchase), I began step-by-step to follow the instructions given with
these devices. As I stumbled ahead, I began to notice the true process
in putting these #$%
together..... and chronicled same.
If you wish to save about 50% effort and time, perhaps the following
text will enlighten you. What makes me angry is the thought that, being
wiser, you have already done these and failed to tell me........
Essentially, one (if like me) bends and cuts the probes - of
coaxially-mounted fine brass tubing central to quarter-inch aluminum
tube courtesy of minute plastic spacers - then assembles the heads and
installs same into tank top. What really happens is you fail to wrestle
the mounting flange into the 2-3/8in. tank hole, drop things into the
hole, fish the bolts into the head, leave out the gasket and start
again. then having got one bolt into place, discover that none of the
other holes align, and start again.
Using my patented process detailed below, the SECOND probe
mounts in a few seconds. It's called SLOW LEARNER, but I digress.
Initially, I hoped to duplicate Nigel Charles' neat installation, and
he kindly sent me the details of drilling and centring the tank top and
headrest shelf holes. I rejoiced in the heady success I achieved in
siting these - a pair of holes each, into which to mount two probes,
one for the port 'saddle' and all fuel above it (the "MAIN"), and one to
fathom the depth of the starboard 'saddle' (the "RESERVE"). The latter,
if you followed my earlier epic on tank quantity, being approx. 11
litres.
There are FOUR cautions to be observed here.
ONE is that no water is to touch the probes - this being tantamount to a
'short', giving a false FULL reading. So, the probes should not favour
the back of the tank which will be lower at rest and thus the target of
water distilled in temperature changes within the tank;
TWO is the care to avoid touching the cage in the tank outlet
(especially the water-drain mod), this being another no-no since it
destroys accurate
measurement;
THREE is that if one inserts a grounding strap through the vent or
fueling holes, it must not reach the probe (at any time as in aeros,
thumpy landings, etc) for the same reason as TWO; and
FOUR contains the caution that in this system, one can only select one
probe reading or the other, since both read total head - not a feasible
number. Thus the total is a reading of MAIN, plus a mental 11 litres or
so (RESERVE) initially.
Kindly step this way, folks:
SkySport happily note that the mounting scheme conforms to an FAA
pattern - five holes, two centre-to-centre at 35mm, the adjoining pair
at 30mm, and a further pair at 32mm. Having absorbed all these hardwon
observations, you now acquire an AN3-13 bolt of any persuasion - it
being used only as a tool. Forget the wire scheme in the instructions.
1. Find the widespread holes in the probe head and mark with white
pencil. Find also the same pair in both the cork gasket and the mounting
flange. Mark the flange on the edge with a black marker where the
widespraed holes are, and do the same on the edge of the cork gasket. It
is now possible to align all three fairly quickly.
2. Decide which way up for the top of the probe head (readability and
calibration when installed).
3. Bend the top section of a bendable probe such that the bottom is
clear of the tank floor and does not reach back into the potential water
area. Cut probe to length per instructions and be sure to save the tiny
'spacers' for the new end.
4. Insert the 3-13 bolt into the head, in a hole next to the flange
cutout area, add the cork gasket under the head (alignment!), and then
the flange - suitably aligned per the markings. Thread the bolt only
slightly into the flange - and keep the gasket and head near the top.
5. Insert the probe, align it to the task, then drop the flange to the
hole, and using the bolt as a handle, manoeuvre the flange into the
hole, cutout first. By pulling on the bolt and lowering head and gasket
to the surface, one has a handle to rotate the internal flange until the
inevitable alignment permits entry of the first AN3-9 attachment bolt.
---From there, all four further bolts can replace the borrowed AN3-13
handle' which reverts to its pack in the kit.
...........and as we say in Paris Nord-Roissy, "voila".
This where I say that the second probe goes in at 50% of the time
of the first.
If you are not installing this dual-probe system, don't read this
message.
Happy landings,
Ferg #A064
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