Shrike (500A/B/U/S) Fuel Gauges

[donv]

There is a guy on facebook boasting about his great emergency landing on a highway after running out of gas in a 500A. Are the fuel gauges really that bad?

I remember Swede telling me about crashing (at night, in a field) after running out of gas in a Shrike... he said it was the fuel gauges as well. His takeaway was that he should always stick the tank.

[appleseed]

Didn't Gary Gadberry run out of gas and crash, because of gauges?

[appleseed]

Correction, because of gauge (singular).

Is there an open or a short condition that can cause the gauge to read 80 gallons regardless of actual fuel level?

I checked my gauge calibration after pulling bladders for spar inspection last year. It was with a gallon or two through most of the range. Only starting to read 3-4 gallons low at quantities from 25 down to 10 gallons.

The caveat is that this is on a level shop floor. The sender is not centrally located either fore and aft or side to side. So any any nose up, down, or yaw significantly affects indicator errors. This is true in flight and when fueling on a sloped ramp.

[Rob]

Didn't Gary Gadberry run out of gas and crash, because of gauges?

Yes, he related this story to me last year, and he still has some physical problems as a result of this. As he explained it was a problem with the connections to the fuel sender and known to be a common problem. Gauge said there was fuel when there was none. The CIES folks make a replacement sending unit which I am considering, but even then I would never trust the gauge past a certain point. I believe Gary sells or knows of a system that is designed specifically to provide a low fuel alarm. I'll be doing more research.

[Adam Frisch]

Never had great luck with the gauges in mine. Right now my left tank shows zero all the time, some sort of short somewhere, Sigh. And the 520 was always sketchy.

[donv]

Is there a way to manually check the fuel level on preflight?

[appleseed]

I thought Bruce mentioned having made a calibrated stick.

With the filler port being even farther from the center of liquid it is going to be even more subject to the off level errors that affect the gauge sensor.

[donv]

This was interesting, from Facebook:

There’s an issue with the cannon plug for the fuel quantity sender. Gary Gadberry explained it when I bought my 500B. In the plug are two pins. If one pin becomes disconnected, the fuel quantity indication will stop at approximately 80 gals. If both pins fail to make contact, it will then stop at 30 gals. I may have some of it wrong, but I always watch for this. It would behove everyone to make sure this has been safety-wired after maintenance on this system.

[Bruce Byerly]

The gauge sending unit looks like something out of a 1949 Packard.  I wouldn’t trust it but it does have value and works fine when it works fine. Sticking the tank probably works above 100 gallons - I need to make a new stick but I also have extended range tanks that are interconnected so won’t be useful data to share especially considering some hold 10+ gallons less than 156.

The problem with the gauge system is that it can fail mid range and that has caused some bad outcomes. Lots more to the stories but need to be careful. With all the info that a flow meter can provide and careful tracking, I can usually predict down to a gallon or two what I have burned and verify that with a true top off when convenient.  I do the same with turbines so I have confidence in the system.

[Bruce Byerly]

Also, fwiw, my long range system holds 205 gallons filled to the skin. I think it’s placarded for 223 or something.  I’ve drained and fueled it twice myself. But 8 hours of fuel should be enough.

[Adam Frisch]

Yes, I rely on the fuel totalizer more than anything else. I also have the low fuel warning light at 50 gal that's operateive and if that comes on (which it did once or twice), I'm heading to nearest.