Since moisture causes corrosion, why not try desiccants?

[Frank]

Corrosion is a big problem in GA aircraft as they get older. One key ingredient in starting corrosion is moisture. I was talking about this at Bay Bridge Airport today and one person in the lounge, a boater, asked why not use some kind of desiccant, often used for boats stored over winter. I had not heard of any use of desiccant in aviation other than to store engines. Ha any tried desiccants, and how have the results been?

 

[Capt. Geoffrey Thorpe]

Ok, you have a big bucket of calcium chloride that can remove a gallon of water from the air over the period of, say, a month. Sound good? My dehumidifier in the basement removes that much twice a day (during the summer).

I don't think a bucket of desiccant will do much more than make you feel better.

 

[Frank]

My basement has a lot more volume than a typical aircraft cabin.

 

[Capt. Geoffrey Thorpe]

But you aircraft cabin is connected to the outside through vents and leaks which, I suspect, can restore moisture almost as fast as the calcium chloride can suck it out.

Try it yourself with two hydrometers (in and out). That's probably the only way to get hard data unless you can find a study done by someone else. And, without data, all you have is opinions.

 

[Frank]

I do not have any opinion yet. What mystifies me is why it would seem to work on boats, although as a pilot and aircraft mechanic I would be perfectly willing to stipulate that boat owners are more gullible, and as a whole, not as wise, as pilots and aircraft mechanics. However going on the theory that even a blind squirrel can find an acorn every now and then, I thought I might explore the boat owners' solution.

It is possible that boat owners are relying on shrink wrap to keep the level of moisture lower inside the boats. If so, those would be the only boats on the Chesapeake incapable of leaking.

 

[Jim_R]

I had a couple of occasions that allowed water inside my cabin and led to mildew growth. I have since solved the leak, but while I was fighting the problem, I hung bags of Damp-Rid and used a 60W incandescent drop light to help with the dry-outs.

Not exactly sure how you're proposing the desiccant be deployed to help with corrosion issues, though. Are you talking about just the engine, or the whole airframe? How would you arrange desiccant to protect the airframe that's constantly exposed to the atmosphere?

Aren't most personal watercraft built of materials that aren't subject to corrosion (like wood or fiberglass), and the metal bits painted or coated for protection? Where do they apply the desiccant?

 

[Frank]

I am proposing to use the desiccant inside the cabin/cockpit in order to fight issues such as the spar corrosion on Cessna high wings. The moisture builds up during the day and, when the plane cools at night, condenses on the spar. There is also some issue about moisture building up inside the foam near the rear bulkhead of Cessnas, and on the spars in floors of Cherokees. I was not referring to use of desiccants in engine storage, nor in the engine compartment. Extra stuff in the engine compartment is an invitation for the pilot to miss it during a preflight and have all kinds of interesting new experiences on the subsequent flight.

 

[kyleb]

I am proposing to use the desiccant inside the cabin/cockpit in order to fight issues such as the spar corrosion on Cessna high wings. The moisture builds up during the day and, when the plane cools at night, condenses on the spar. There is also some issue about moisture building up inside the foam near the rear bulkhead of Cessnas, and on the spars in floors of Cherokees. I was not referring to use of desiccants in engine storage, nor in the engine compartment. Extra stuff in the engine compartment is an invitation for the pilot to miss it during a preflight and have all kinds of interesting new experiences on the subsequent flight.

Cockpits aren't airtight enough for desiccants to have a chance. For every ounce of water the desiccants remove from the cabin, the ideal gas law (partial pressures) is going to push that much moisture right back in.

 

[Dan Thomas]

But you aircraft cabin is connected to the outside through vents and leaks which, I suspect, can restore moisture almost as fast as the calcium chloride can suck it out.

Add to that the possibility of spilling that calcium chloride. I can't imagine anything more corrosive around an airplane, unless it's acid. Terrible stuff.

Dan

 

[Capt. Geoffrey Thorpe]

Add to that the possibility of spilling that calcium chloride. I can't imagine anything more corrosive around an airplane, unless it's acid. Terrible stuff.

Dan

You could use zeolite, but it doesn't suck up as much water. On the other hand, you can heat it and dry it back out.

 

[Jim_R]

I am proposing to use the desiccant inside the cabin/cockpit in order to fight issues such as the spar corrosion on Cessna high wings. The moisture builds up during the day and, when the plane cools at night, condenses on the spar. There is also some issue about moisture building up inside the foam near the rear bulkhead of Cessnas, and on the spars in floors of Cherokees. I was not referring to use of desiccants in engine storage, nor in the engine compartment. Extra stuff in the engine compartment is an invitation for the pilot to miss it during a preflight and have all kinds of interesting new experiences on the subsequent flight.

Yeah, then that ain't gonna work. I had some success with using Damp-Rid in my plane because there was more moisture in the cockpit than in the surrounding air. But I probably would have had better success if I had a good shop fan and just left the door open with the fan blowing in and moving the air around to get the humidity out of there. (I just didn't have a fan big enough.)

Spend your effort on applying a protectant like CorrosionX, and keeping it intact (i.e., replenishing it periodically). Desiccants aren't going to be effective.

 

[Fearless Tower]

Cockpits aren't airtight enough for desiccants to have a chance. For every ounce of water the desiccants remove from the cabin, the ideal gas law (partial pressures) is going to push that much moisture right back in.

Definitely. We use desiccant bags for stuff like laying up boilers for extended periods of time....but they are sealed up in the process.

 

[airguy]

A lot of folks use dummy spark plugs with dessicant in them for engines that are going to be stored for a while, I've got a set in my IO360 right now on my RV9A waiting for first engine start.