Dehumidifying Your Engine the Easy Way

by Kevin Knight

Here’s a really expensive aviation chemistry formula:

Iron + Oxygen + Water = Rust

When rust develops in our airplane engines, it’s a costly cancer. However, just like cancer, if it’s stopped before it can get started, the odds of extending an engine’s life rise dramatically.

Most of my flying and homes have been in coastal areas where rust is more prevalent. However, drier places like Colorado aren’t immune from that metallic rot. Since rust is everywhere, I recently decided to go beyond adding CamGuard to my oil every change and purchased an engine dehumidifier called DryBot.

Engine dehumidifiers gently push dehydrated air through the engine so rust developing conditions are greatly reduced. Lycoming has reported that in high humidity regions, corrosion can start appearing on relatively new cylinders within two days of inactivity. Since most of us don’t fly our planes nearly enough, we’re all at risk for reduced cylinder life and failed components.

In the beginning …
I began my career working at Alcoa Aluminum’s Davenport Works in Iowa. We made wing skins for Boeing jets, so I spent many hours in the plant’s testing lab. As a result, I have a strong bias for engineers whose work is grounded in hard data and solid science. Since I had read about various engine dehumidifiers online and seen them advertised by Aircraft Spruce, I wanted to determine if DryBot, the latest market entrant, was worth nearly $1,200.

In years past, if my M20F’s engine wasn’t being run during the winter, I used “desiccant spark plugs” with water-absorbing silica beads. The problem was, once the desiccant changed color from pink to light blue, they were saturated and were no longer doing any good.  I wanted something that was continually operational and self-maintaining so my engine would stay healthy while I was enjoying sunnier weather elsewhere.

Being research driven, I contacted Matthew Dock, DryBot's co-creator and president of RPX Technologies in Oklahoma. The company’s DynaVibe is the market leader in prop balancing technology.

Matt told me he’s 53 years old and earned undergraduate and master’s degrees in mechanical engineering from Oklahoma State University. His focus was metallurgy, with an emphasis on surface finishes, cracks and other imperfections.

He thus did lots of work with electron microscopes, x-ray diffraction and grain microstructure. Since earning his private license 27 years ago, Matt has acquired five planes, and is an A&P and IA. He got interested in engine corrosion when a cylinder on one of his planes had low compression. On the camshaft, there was also a spalled cam lobe and bad lifter faces. They subsequently split the engine case and discovered the interior was “like a swamp.”  Condensation and acidic oil residue pitted accessory gears through bolts and other components. The engine shop supervisor figured someone kept the oil pan heater on all winter and the oil cooked over time, which released lots of moisture into the engine.

Sweating Product Details to Reduce Engine Moisture
To prevent that from happening in the rebuilt engine, Matt built a do-it-yourself dehydrator that used silica desiccant, but it regularly maxed out on moisture. That required Matt to dry out and replace the silica regularly.

Doing that got old pretty fast, so he bought a well-known commercial dehydrator. One day, he noticed a water droplet going from the device into a clear, plastic tube into his engine. That was the opposite of what he expected. Ever the engineer, he bought some humidity sensors from Amazon to track what was going on inside the engine. He discovered that the internal humidity in the engine went down the first few days of dehydrator use, then started rising. He concluded it was because the device used a cooling plate that couldn’t keep up with the high humidity of Oklahoma. To confirm his conclusions, he did the same experiment using a second identical dehydrator and got the same result.

That led Matt and his partner Mike Fox to design DryBot. Mike is also a trained engineer. Their product innovations included inflow and outflow monitoring of air, inclusion of a liquid silica desiccant to extract moisture from the air before it entered the engine, and automated drying of the desiccant.

Their calculations indicated the desiccant could have the moisture removed from it daily for ten years and still retain 80% of its capacity. If that material ever had to be replaced, DryBot will alert pilots by generating a red, LED error code. The factory will replace the material for $199.   

The outbound air pressure is a steady .1 PSI. Tests with a bank of internal sensors have shown it takes around 15 minutes to purge excess moisture from the engine.

The dry air it pushes into the airplane engine is not recycled back into the DryBot, since that would contaminate the silica.

Matt and Mike showed that if humidity in the hangar is 80 percent, the DryBot's air humidity is less than 20 percent. That’s noteworthy since the “critical humidity” required for rust to start forming is 40 percent. If humidity is below that level, ferrous alloys, such as steel, will not rust, and aluminum will not corrode.

Since my cylinders cost more than $1,500 each and DryBot is super simple to operate, I viewed it as cheap, long-term insurance. I also appreciate that DryBot is built in the USA, providing jobs to 25 hard working Oklahomans.

For some visuals, this experimental homebuilder produced a pair of YouTube videos worth watching: DryBot for Airplane Builds and RV-10: DryBot Data Logging, both by BuildFlyGo's Guil Barros.

It is still important to run your engine regularly and fly. Engine manufacturers recommend getting the oil to at least 180 degrees Fahrenheit for an hour so it drives moisture out of the oil. If you just run the plane up on the ramp for five minutes, then put it back in the hangar, all you’ve done is sucked in a lot of moisture.

DryBot could help remove a lot of that moisture, but that’s not optimal. Just tell your spouse you have to fly regularly so the engine will stay in shape. That’s not just a good excuse to go flying, it is also good advice for maintaining a healthy engine.

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Knight, K. (2024). Dehumidifying your engine the easy way. The Mooney Flyer, 13(5), 31-32.
Retrieved from https://themooneyflyer.com/issues/2024-MayTMF.pdf.