Question on filtered airbox bypass - carb

[MrNomad]

Question on filtered airbox bypass - carbed Lycoming 360

I assume the bypass is used when the air filter clogs up with ice cause I was dumb enough to fly into icing conditions. Living and flying in Arizona, I question whether I need to do this.

Please comment.

Barry

[John Clark]

It's not all about ice, and yes, there is ice in Arizona. Consider the other things that could block the intake. A bird, any sort of FOD on a runway, or a failure of the ducting could cause a blockage.

John Clark
RV8 N18U
KSBA

[billnaz]

I'm getting close to flying, and haven't done the modification. If I understand the rules correctly it is not a mandatory mod. It seems to me to be a belt and suspenders issue. If you account for every worse case scenario in aviation the plane would be to heavy to get off the ground. Each system you add increases cost, weight, and complexity (the first generation of the mod with the magnet caused its' own failure mode). Isn't a carb heat gate and alt air sorce good enough?(like the pipers and cessnas I've flown)?

My questions to the group are;

1.Is it a manditory mod? Mel- what's the DAR perspective?

2.Has there ever been an actual incident where the mod would have saved the day?

[painless]

Bill:

This airbox modification was prompted, as I understand it, from a 6A that had to land in a corn field near St. Louis a few years back as a result of flying in a snow storm. Snow promptly plugged up the air inlet. Fortunately, a safe landing was made (go figure...nosewheel and all!). If such a modifcation was present at the time, it certainly would have "saved the day". It is important to note, however, that if carb heat had been applied once it was apparent that the pilot was flying in snow, the day would have been saved as well, since applying carb heat essentially closes the intake from outside air. Van's has stated that RV pilots have not been using the carb heat feature while flying in moisture properly.

As to the mod being mandatory, no. This is your airplane, and you are the manufacturer. YOU make the call here.


Regards,

[Mel]

Like Jeff says, the mod is NOT mandatory. As a matter of fact, I do not have it on my airplane. I have 2 of the original kits on the shelf. Want one?

[N1691M]

I installed it and the trap door happened to open somehow on downwind and it affected the airflow through the throttle body. This caused an excessive rich condition, which flooded the engine. A safe landing was made. The door was directly under the throttle body and the suction must have held the door open. After some detective work and several ground run tests, I removed it.

[L.Adamson]

Originally Posted by N1691M

I installed it and the trap door happened to open somehow on downwind and it affected the airflow through the throttle body. This caused an excessive rich condition, which flooded the engine. A safe landing was made. The door was directly under the throttle body and the suction must have held the door open. After some detective work and several ground run tests, I removed it.

The new kit does not use the trap door. That setup is supposed to be replaced with the slider door that's connected to a cable/knob. I've replaced mine with the new one, and it's a rather stout system.

[kentb]

My new version with the control cable to operate had separated from the airbox on one side. The pop rivets don't hold very well in the fiberglass airbox.
I made a backing strip to support using AN4 rivets and reattached it.

Kent

[gmcjetpilot]

Originally Posted by John Clark

It's not all about ice, and yes, there is ice in Arizona. Consider the other things that could block the intake. A bird, any sort of FOD on a runway, or a failure of the ducting could cause a blockage.

John Clark
RV8 N18U
KSBA

John is right but that is a long shot; it did happen to a RV-4 back in the days of no filtered airbox. The plane continued to fly and landed. Inspection showed nothing but the engine ran rough. dis-assembly showed nothing, until he looked up the carb throat. A bird or part of one was in there! Could it happen? (This was written about in the RVator many years ago with pictures, so it is true.)

It happened , but I am taking a very small chance and leaving the alt air off. I suppose the "carb heat" alt air might free up some air to get back on the ground? Again its a long shot getting total blockage from a bird or other object. I am more worried about a bird coming thru the wind screen in my face. If you are worried about FOD or birds than pull the carb heat on proactively.

[L.Adamson]

Originally Posted by kentb

My new version with the control cable to operate had separated from the airbox on one side. The pop rivets don't hold very well in the fiberglass airbox.
I made a backing strip to support using AN4 rivets and reattached it.

The plate on mine, is stuck tight to the airbox with pro-seal in addition to the rivets.