Grob 115 Fuel Gauge - defaults to "FULL" !
 

After a recent incident, I discovered that the fuel gauge or sender on a Grob 115 was shorting out, the result of which is that the needle points to "full" (in fact, the tank was empty). It is impossible to visually check, or dip, the fuel tank, which is centrally located.
Does anyone know of any modification for the Grob which allows either a visual check on fuel, or a check on the fuel gauge functionality? Would it be possible to wire the gauge to default to "empty" if it was shorted out?

I use to fly the aircraft in question and then went on to fly a Grob G115 at a different training school, that aircraft had a sight gauge to see the fuel level. There was a 30mm round hole covered with Perspex just above the flaps on the port side of the aircraft and when you looked through the hole there was a clear pipe that was running up the side of the fuel tank, and you could see the fuel level.

With regards to the fuel gauge showing full if a fault developed on the fuel gauge, I would not have flown this aircraft if the gauge showed full, you never fill the Grob fuel tank to full as it would be to heavy to take off, we use to put a max of 70Ltrs in it, but it is easy for me to make comments like this sat behind my keyboard.

T&G
Thanks for that - shame our Grob didn't have this mod!
I agree with your point about the fuel, but I was the first to fly it after its annual, and groaned when I saw that the engineers had re-fuelled it to "full" (though, of course, they hadn't really!!) - but a quick weight calculation revealed that we were ok to take off on a full tank (both myself and instructor are rather light on the scales).
With hindsight.... well, let's just say a full fuel gauge will now cause me to check who fuelled it last . . . I.L.A.F.F.T as they say.

I have vague recollections that the 'default' is related to the type of electric supply for the gauge, ie. DC fail on a zero reading and AC stick where they were (I think it's that way round.

I await correction ;)

rgds
CB

Thanks CB. In this case rather than a current failure, it was an electrical short circuit causing the gauge to display full. So, I wondered whether a "push to test" button wired in a certain way would effectively set the needle to zero when pressed. That way, if I "pushed to test" and the needle remained on full, I'd know it was shorting out. Only a thought, I'm no expert on aviation electronics!

Do you want it to read full when there's a short or when a wire breaks? I'd choose the least likely failure mode which probably is a sensor short. Then again, I would design the thing so that it didn't hit zero or max voltage with either a full or empty tank, meaning a wire break or short would send the needle off a scale in a most suspicious way.

Out of curiosity, what kind of sensor is it? Float? Capacitive?

Cheers,
/ft