Moisture Mitigation Measures

[n2582d]

Recent entries on water in the static system and doors have me thinking about compiling a list of areas to pay attention to in order to prevent corrosion caused by water/moisture. I'm hoping others here will add to the list or tell me I'm all wet.

• Ailerons

This has to do with safety of flight rather than corrosion. If water freezes on the ailerons it can affect its static balance. SLN-64 covers this subject.

• Drain Holes

Forward of most, but not all, fuselage bulkheads are 1/8" drain holes.

Fuselage Drain Hole.jpg

It's important that these holes are open. On the B model there are also 1/4" holes at the aft inboard end of the lower wing skin and two in each wing in the area of the inboard end of the ailerons. The floatplane has grommets over these drain holes.

Screen Shot 2024-08-19 at 8.28.21 AM.png

Not sure if they serve to prevent water splashing into the holes or do they create a suction to help draw water out? Maybe both. For the floatplane the holes are enlarged to 1/4". They also add a hole behind each bulkhead as the tail slopes the other direction when on floats.

Screen Shot 2024-08-19 at 8.48.17 AM.png

• Avionics vent

Years ago I flew with a Captain who owned an avionics shop in the bay area. He said that these vents were great for his business. They don't cool the radios when the aircraft is on the ground and they allow moisture go directly to the radios. He recommended using an avionics fan instead. Overpriced plugs are available to keep bugs and water out here.

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• Bellcrank bolt holes

The bellcranks for the ailerons and flaps rotate on needle bearings. My guess is a lot of these bearings work as bushings rather than bearings because they are frozen with rust. This is because the head of the pivot bolt sits in a dimple which allows water to pool there and slowly seep into the bellcrank.

Aileron Mount.jpg

Adding a plug button with a sealant might help.

• Fuselage leak points

It's always bugged me that Cessna didn't lap the top tailcone skins over the side fuselage splice plates. By putting the splice plate over the top skin there is a gap at every fuselage bulkhead.
(Continued in next post.)

[n2582d]

Skin Gap.jpg

If you remove the rear ashtrays and/or elbow rests those mounting holes should be plugged. Plugs in the holes above the forward and aft carry through spar for lifting rings or shoulder harness mounting bolt installation should be checked periodically to insure that water is not getting into the hat sections.

• Engine Hose Drains

This has nothing to do with corrosion but is still something to consider. It is discussed here.

• Fuel Cap Seals

Use the search function to find pages on water leaking into the fuel tanks because of poor fuel cap or fuel tank adapter sealing.

• Solenoids

A Lamar rep suggested sealing their solenoids from moisture. See here

• Moisture in Oil

A lot has been written here about corrosion of the magnesium oil sump. Occasionally draining oil out of the forward drain plug might help minimize the sludge that forms in this corrosion-prone area. Fly long enough to get the oil temperature warm enough to boil off the water in the oil. Flying after washing the plane helps dry out both the engine and the airframe.

• Seals

Door seals are often neglected. Aircraft Door Seals offers a variety of seals for the C-170.

C-210 Cabin Sealing.pdf]SE74-13

SE78-46 offers some advice on attaching a seal to the C-210 baggage door.

• Wing Root Sealing

George writes about it here. Cessna also covers this topic for the C-150 in SE71-28.

Wing-Cabin Seal.pdf

[voorheesh]

By coincidence, I was with a student in a 49 year old 172 yesterday and when I opened the right door, at least a gallon of water came out of the lower edge. Apparently, when closed, the door would hold the liquid. Turns out the well intentioned desk assistant at the flight school who fuels airplanes also cleans them on the wash rack and uses a hose and nozzle for the rinse. He was not aware that water can ingress under even mild hose pressure. I mentioned this to our chief instructor and I think they will train this guy and be more careful in the future. I owned a 170 for years and never washed it with soap or rinsed with a hose. If it needed cleaning, I used an aviation cleaning fluid approved for use on aluminum and rags. Took a little longer but worked fine. A shop I worked at also discouraged using the wash rack, but covered openings like static ports and vents if they had to. For these aging aircraft, I think a hangar makes a big difference, if you can find one. Sad to see some of the old ones slowly deteriorating out on the ramps at these GA airports.

[n2582d]

Harlow,
That reminds me of a story I read recently by Dean Benedict in King Air Magazine about finding wheel bearings bone dry, "not a speck of grease or lubrication to be found" even though the bearings were greased 100 hours earlier. ("Grease is Good" King Air Magazine, June 2024, Vol. 18, Number 6). He goes on to write the owner

... was meticulous about the maintenance and appearance of all his equipment, including his King Air. Accordingly, his diligent pilot made darn sure that King Air was in pristine condition at all times. It turns out the pilot happened upon a new, fantastic degreaser. It was perfect for getting grease off everything, and he used it on the King Ar to great success or so he thought. This happened right after the gear inspections were done, so of course the landing gear got regular treatment. Liberally applied on a repeated basis, this degreaser worked its way into the wheel bearings and stripped them of all lubrication. ... The pilot's perfect find wasn't so perfect after all.

Also pressure washing an airplane is a bad idea according to AOPA and Duncan Aviation.