Question Carbon Cub EX-3/FX-3 door behind air filter?

[Neal]

There is a small hinged flap/door behind the air filter. What is this for?

How often are people changing their air filter? From what I hear they should be changed out prior to the AMM recommended time which I think is 500 hours. Some say 200?

 

[Cactus Charlie]

The door is the alternate air door. It is intended to open when the air filter is blocked by icing or other extreme contamination.

When the door is open induction air is drawn from the the area close to the #1 exhaust pipe so it is somewhat heated but is not filtered.

When CC doubled the price of air filters I decided to re-cycle mine. I has shocked by how much dirt I extracted from the first two. I have gone from about 100 hours to every oil change.

I frequently operate on dusty unpaved airstrips.

 

[Neal]

Can you share the procedure? Yeah, it's $70 for an air filter now, just like their price of the PowerSonic ignition battery is 3X what you can get it for elsewhere.

I welcome any tips on recycling the filter.

 

[Cactus Charlie]

I has shocked by how much dirt I extracted from the first two.

13 grams of dirt extracted from two air filters with combined time in use of 216.8/261.4 engine/airframe.

These filters were doing their job. Oil analysis silicon level was very low. It had been high for the first two samples and that was traced to a badly fitting air filter.

CC had originally used crudely hand cut filters. They changed to accurate machine cut filters later.

 

[Neal]

Can you share the procedure?

Can you help us save money and tell us what needs to be done to clean and refresh the filter please @Cactus Charlie.

 

[Cactus Charlie]

There are lots of on-line videos showing how to clean and re-use foam air filters. None of them had a method to collect and measure the accumulated contamination and I wanted that data point.

You would have to value your time very cheaply to make it worthwhile cleaning and re-using the FX-3 filters.

However, since you insist, I flushed the filters in the reverse direction of airflow with auto gas. I collected the used gas in a pan and passed it through coffee filters to collect the contamination for examination and weighing. I then made a further wash with water soluble degreaser and flushed with water.

After the filters had air dried I put them, one at a time, in a large zip lock bag and added air filter oil. I worked the filter until it was saturated throughout then squeezed out the surplus. Each filter was allowed to drain for several days before being fitted to the aircraft.

My first attempt used Bel-Ray Foam Filter Oil 1l size. That is sufficient for 5, maybe 6, filter applications and costs under $20. The oil is blue but the filter doesn't look blue on the aircraft.

I have not yet cleaned a re-used filter so I do not know how the dirt collection compares with the oil used by CubCrafters.

 

[Neal]

Thanks. Good to know what's involved and it's another item learned as to what goes into the filter process.