Fuel Issues

Not wanting to hijack the 'RV-6A Flips & Burns' thread; but still wanting to ask a fuel starvation type question triggered by the Sonix fuel starvation incident:

I have a fuel flow transducer mounted as per manufacturer instructions; which puts it after the gascolator & actually after the mechanical fuel pump. The easiest way to detect any leaks in between this and the tanks (while in flight) is to have accurate fuel level measurement at the tanks. However my tank float sending units are garbage. As originally built, the plane had a flop tube in the left tank and therefore the float was installed from the back bulkhead. The right tank float unit is installed at the wing root. The differences in mounting geometry as well as who know how the float wires are bent, result in very poor readings. One unit saturates at the upper end, the other saturates at the lower end, and I have little confidence in either one reading correctly.

If I were to rework the tanks or replace them, mounting both float units at the wing roots, new units, wires correctly bent, and take some care in calibrating my (programmable) dual fuel gauge; can it be expected to get reasonable readings. I realize that you want the floats to top out at the upper full fuel range and then accurately measure when the fuel level in a given tank gets down a few gallons.

My original installation is per plans and gives very satisfactory readings. They have worked fine for over 14 years. When I removed the tanks a couple of years ago for slosh removal, one float sender failed shortly after. I must have damaged it someway while removing or reinstalling it, because the other side still works fine.

Mel said:

My original installation is per plans and gives very satisfactory readings. They have worked fine for over 14 years. When I removed the tanks a couple of years ago for slosh removal, one float sender failed shortly after. I must have damaged it someway while removing or reinstalling it, because the other side still works fine.

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Thanks, Mel,
That gives me hope. With the fuel flow, total fuel remaining is given accurately; but it would a nice reassuring check to add left to right and get approximately the same total.

float senders

even if correctly installed, the float sensors will saturate at the upper end. this is due to the dihedral of the wing. when the float is as high as it can go at the root, there is still more room in the tank further outboard. i'm not flying yet, but my understanding is that the tanks will register full with about 15 gals in them (rv7a). the remaining 6 gals will have no effect on the fuel gage reading.

BUT...

If you use Van's gauges, they are calibrated to off set this anomaly.

Frankly my dear

I don't care that the Vans gauges read full at 18 gallons and 15 gallons.They are fine below the full point...near empty and with my RMI fuel flow system I am often within one gallon of knowing my actual fuel level.

I don't stretch my fuel consumption to the point where one gallon is an issue.

capacitance senders

I installed the capacitance senders that Van's sells and use a FL-2C fuel guage from EI. Outstanding combination IMHO. In the 60+ hours I have been flying my 6A, I have been watching how accurate the fuel guage is. Every time I fill up each tank, the amount pumped is spot on with what the guage was telling me.

My hat is off to Dick Martin ("The Fast One" RV8) who was instrumental in developing these particular senders for Van's airplanes.

I realize that this would be a very difficult retrofit in your case. Just putting my 2 cents worth in for those that are still building.

Regards,

Ron Lee said:

I don't care that the Vans gauges read full at 18 gallons and 15 gallons.They are fine below the full point...near empty and with my RMI fuel flow system I am often within one gallon of knowing my actual fuel level.

I don't stretch my fuel consumption to the point where one gallon is an issue.

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And I agree.
Problem is mine don't even come close to your accuracy and I'm not sure the gascolator leak described in the Sonix can be detected quickly enough. My fuel flow also gives me excellent results. Just want a backup checkpoint in case of a failure somewhere before the fuel flow.

I repeat my last sentence "I realize that you want the floats to top out at the upper full fuel range and then accurately measure when the fuel level in a given tank gets down a few gallons." 18-3=15 gal

painless said:

I installed the capacitance senders that Van's sells and use a FL-2C fuel guage from EI. Outstanding combination IMHO. In the 60+ hours I have been flying my 6A, I have been watching how accurate the fuel guage is. Every time I fill up each tank, the amount pumped is spot on with what the guage was telling me.

My hat is off to Dick Martin ("The Fast One" RV8) who was instrumental in developing these particular senders for Van's airplanes.

I realize that this would be a very difficult retrofit in your case. Just putting my 2 cents worth in for those that are still building.

Regards,

Click to expand...

I'm not ruling out building new tanks.

If you can get the rear baffle off, you may not need to build new tanks. You could even cut access holes where the capacitance plates need to go and then cover/seal them up afterwards. There is really not much to installing this system.

While the guages may not be accurate, i.e. - 1/2 on the guage doesn't = 1/2 tank of fuel, I would bet that unless they are catching on something they are consistent in their readings. Calibrate each tank, then check your calibration at each fill up for a while and you'll probably get consistent readings.

steve_adams said:

While the guages may not be accurate, i.e. - 1/2 on the guage doesn't = 1/2 tank of fuel, I would bet that unless they are catching on something they are consistent in their readings. Calibrate each tank, then check your calibration at each fill up for a while and you'll probably get consistent readings.

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Maybe I can explain a little better with this image, a drawing I made to show the current conditions, and the normal conditions. One sender is set way high and saturates high. The other is set way low and saturates low. The region of overlap where I can get an accurate total is limited and worse yet does not cover the low end. The drawing is exagerated somewhat to give you the idea. What I'm shooting for in the repairs is on the right where Left & Right are accurately measured from say about 15 gal each down to zero.