The new tubing fits nicely into a "deep-gap slotted optoswitch" (RS part
no.194-4030, around 4). The tubing is almost transparent to IR but the
focussing action when fuel is present gives a dramatic increase in output
current - enough to light an LED. So here is a cheap easily fitted low-level
indicator for your front-of-tank-mounted sight gauge, where (at least on the
pilot's side) it is difficult to read below 10 ltrs. You can run it on a PP3
battery, and a few more components will give an audible alarm via your
interecom aux. socket.
Of course fitting some more will lead you to a discrete digital fuel gauge,
but covering up all the tubing rather defeats the "reliability" of a sight
gauge.
It will also work along the fuel line as a bubble/ leak detector - a subject
close to my heart since my landings-out two years ago. But I have not been
able to substantiate the earlier theory that the time delay is due to bubble
accretion at a high spot. Experiments show bubbles in this size of tubing
(with fuel flowing at the standard rate) behaving a most extraordinary way.
Chaos seems to be the norm, with some stationary, some slow moving, sometimes
coalescing, while small ones fly past larger ones and so on. Must try to
take a video sometime.
BTW the new tubing still goes brown !
Graham G-EMIN
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