Doug/Barry,
Why not use some of these GEMS electronic fluid level sensors.  They

are

totally solid state.  They use an infra-red beam reflecting off a

prism

type lense.  When submerged, the light beam is disbursed, when above

the

liquid, the beam is reflected back to the IR receiver and a signal is
generated.  I put one in each of my wing tanks at the 6 gallon level

as

a low fuel warning.  They are connected to two "Low Fuel" LED's on the
panel.

Mark S.

Mark and Doug,

Your suggestions make sense, however, in the attached picture, you will
see my wing with the leading edge fuel tank.  Of course the view is not
that good as it is from the aft, you can see the ribs separating the
main tank. I believe these are for stability and to keep the fuel from
sloshing too much in the tank. How would you apply your suggestions to
this scenario? I like both suggestions, the laser sensor and the
magnetic tube, but I am not sure that it will work in my situation.

Thanks,


Barry,
Short of drilling through the spar, I don't see how you could use the
GEM sensors in your application.  And yes, they run about $100/ea
retail, but I got mine off ebay for much less.  There are some
microchips for sale on ebay now that are meant for monitoring liquid
levels.  You could use these in a similar manner as the GEM sensors by
running wires to various spots in the fuel tank(s).  The item no. is
7539003779.  At $0.19/ea, these could be just the ticket.

Mark S.

Mark

Thanks... sounds like  an affordable price:).

One forseeable problem is the IC chips need power right? Probably about 3
vdc. and 10  miliamps?  Could this cause a spark within the tank on crash
landing or during operation?


Doug in Japan

Doug,
You're concerns are probably well founded, but there are lots of other things that could also spark.   I don't see why you couldn't take some extra precautions here to make it as safe as can be, like potting the whole assembly.  Not sure how long a sense lead it can handle. I ordered 10/ea (yeah, I'm a big spender) and will experiment with them when they arrive.  Seller claims they will work in gasoline. We'll see.

Mark
(where did I put my nomex suit)