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By Belite fuel probe, do you mean the probe that senses fuel level by a solid-state pressure tranducer? Years ago, I was interested in this system but could never find an instance of a successful installation in an experimental aircraft. (By successful, I mean relatively accurate fuel quantity indications in flight.) They seem to work pretty well stationary/on the ground and in low speed aircraft such as ultralights where pressurization of the fuel through the vent is minimal, but apparently as airspeed increases in larger aircraft, the effects of positive or negative venting pressure made them "useless," as one Sonex builder reported.
If things have changed and someone has done a successful installation, I'd like to hear about it!
This is the unit in question.
I installed them and had the same issue on 601HDS with a Rotax 912uls and 2 leading edge wing tanks.. There was so much negative pressure during climb that the diaphragms were actually bent which would change the zero point. We could recalibrate and they would appear to work until you took off.
Since the gauge was calibrated with static pressure on the tank and during flight the top of the tank was not at static this was causing the variation in the fuel level output. I bought 2 of the pressure sensors and put them in the static/pitot system so we could get a voltage that was an indication of these pressures. Don Honabach wrote an arduino program to take the belite pressure and would take into account the plane was climbing and not traveling 100mph. I installed the vented caps where you could bent a 1/4 tubing extension so the opening was parallel to the flight path. This was done trying to keep the top of the tank basically at pitot pressure. This worked better than the stock belite arrangement, but you could still get the angle of climb high enough that the negative pressure would change the zero of the pressure sensor which required reprograming.
So after several months of trying to get them to work, I trashed them. I intalled the automotive resistance style sensors in the tank. I also installed a little red cube flow sensor between the tank and the carburetors. These were wired into an MGL FF2, which is basically a fuel computer. Since the automotive style sensors aren't really accurate, I use them to check there is no major leak in the fuel system where the fuel is leaking from somewhere but not going through the red cube. I use the flow totalizer as my source for actual fuel used and fuel remaining. The red cube is really accurate if you take the time to calibrate it's K-factor.
So the short answer is they work good in a ground based static system, but a system that is moving and changing angles. At least on a 601HDS, you are trying to measure about 5-6 inches of water change from full to empty.
David, go to forums and under the 601 tab do a search for Belite. There are a lot of old discussions on the Belite probes.
I have them in my Cruzer it Works great on the ground no use whatsoever once in the air.
Have you tried venting the fuel caps vs the standard below wing drain /vent?
I have tried both options not much difference basically soon as the air pressure enters the vent top or bottom it just reads full. I use a fuel flow now as a guide in flight but dip my tanks before each flight.