Forum: F-16 Design & Construction

While we were changing filters for 800 hr acft inspection today, everything was going great until we got to the changing the case drain element. Upon removing the bowl we noticed that there was a small amount of hydraulic fluid and lots of fuel. The filter also smelled of nothing but fuel. There is also a constant drip from the filter assembly attached to the manifold that didnt stop over the course of a few hours. I was wondering if anyone had ever seen this before and what the root cause ended up being.

Also after looking through the 29FI we saw no reference to fuel contamination. I am wondering the effects of the fuel on all the components of "B" system hydraulics. The effect on internal seals of reservoirs, accumulators, etc., etc.
Will all these components need to be changed due to the fuel introduced into the system.

Our swings is currently trying to isolate where the fuel entered the system. I will try to update as more is found out.

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I hope you have also contacted either the F-16 support folks at Ogden ALC or LM Aero F-16 Product Support Engineering. You can contact LM Aero in one of two ways - either by calling 800-316-5672 or by email to F16.help@lmtas.lmco.com.

chris374 wrote:

Also after looking through the 29FI we saw no reference to fuel contamination. Our swings is currently trying to isolate where the fuel entered the system. I will try to update as more is found out.

For the CG in the 29FI look at tables 1-3 and 1-4 and pay particular attention to the warning of more than 2% fuel contamination of the hydraulic system. Fuel contamination coming from FOHE.

Good catch ... attention to detail Thumb

start looking at your heat exchanger and any hydraulic line that runs through the internal tanks

I you look at the B system simplified schematic you will see that from the Fuel Oil heat exchanger the first stop for return/supply hydraulic fluid is the thermal bypass valve. Then it goes straight to case drain filter. The reason you didn’t get fuel in the return filter bowl (on same manifold as case drain) is because of a check valve that is obviously working. Since everyone dumps reservoir pressure after flight, you have zero pressure to hydro components, however fuel pressure still exists in the fuel tanks.

http://en.wikipedia.org/wiki/Path_of_least_resistance

Forum: F-16 Design & Construction

Fuel in Block 42 "B" system hydraulics