So you have a defective fuel sensor...

[Chris B]

The one significant issue with my plane was a very small leak in the left tank. The root cause was a faulty repair to a defective fuel sensor.

Fixing this one little problem has taken Glenn and his assistant at least two full days. But I've gotten to see first-hand what is required to remove the tanks! My key take-away from this experience is the importance of finding someone competent and familiar with this process. There are many opportunities for this to go very wrong.

The entire process is shown in annotated pics at this link:
https://plus.google.com/photos/10460812 ... oeVh9KZtAE
or in a short link:
http://tinyurl.com/bgqdhh7
Note that the actual wing removal/re-installation pics are MIA because that activity is all-hands-on-deck.

For the TLDR crowd, here are some of the highlights:

Leaking fuel sensor.JPG (59.5 KiB) Viewed 2247 times

It's only a small leak. How hard could this be??

Left tank finally removed.JPG (68.22 KiB) Viewed 2247 times

Once the wing was removed from the plane, it took hours to prepare to remove the tank. Every access port contains a time-consuming set of obstacles.

Small white tubing is the problem.JPG (70.33 KiB) Viewed 2247 times

The small white tubing which slides on the end of the fuel sensing probe is the reason the tank must be removed. Whenever the fuel sensing probe is removed, the tubing drops loose into the tank.
The only way to re-install the tube is to remove the tank and fish it out.

Comparison of old and new fuel sensors.JPG (75.5 KiB) Viewed 2247 times

The previous faulty repair was cross-threaded, WAY over-torqued, and used the wrong sealant.
Note that the sensor is aluminum (like the tank), so galling is a major concern.

Applying the correct sealant this time.JPG (73.27 KiB) Viewed 2247 times

Glenn recommends Loctite 565 for fuel fittings. It is impervious to fuel, seals very well, but - crucially - also lubricates the threads.

Chris

[Gasser]

Fantastic pics. Thanks for sharing. Man somebody got rough with those threads to strip them all out like that. Didn't look too far from a big failure.

Looks like your in business now though.

[Steve]

Thanks for the photos! The fuel tanks in the DA40 certainly are well protected within the wing structure (inaccessible). I pray that I don't have to pull mine anytime soon...

Steve

[Chris B]

Thanks for the photos! The fuel tanks in the DA40 certainly are well protected within the wing structure (inaccessible). I pray that I don't have to pull mine anytime soon...

Steve

You are quite welcome!

Apparently the rubber connections between the tanks need to be replaced at 2,000 hours (originally only 1,000 hrs!). Combined with a likely engine overhaul somewhere in that neighborhood, the 2,000 hour annual will be quite pricey!!

This is something to consider for accrual, particularly in a co-ownership situation.

FWIW, Glenn indicated that the reason the DA40 has dual spars (each capable of full load) is for lightning-strike IFR certification. The carbon fiber top and bottom of each spar is the primary path for lightning. But the heat generated by a strike will temporarily weaken whichever path gets the jolt. So without redundant spars, potentially you could lose a wing in rough air with lightning.

The upside is that in every other circumstance the pilot will probably lose consciousness before the wings snap off.

Chris