Air filter popped out in flight

[Draker]

Well, this was unexpected. I came home from a short (1.2hr) test flight, and lo and behold during my post-flight walk-around I saw this inside my air inlet:



Here's another view with the cowl off:



IO-360-M1B, horizontal (snorkel) induction.

It looks like something caused the air filter to buckle and bend up out of the snorkel. Obviously it needs to be secured better, but what are the physics that would cause this to happen in the first place? I thought that the engine is always "sucking" air down through the filter element, and you're not going to see any back pressure from the snorkel.

No indication of trouble in-flight. My CHTs and oil temperature were a little high, but I've been struggling with CHT temps all through phase 1 so it was not unusual.

Looks like I'm on the hook for at least a trip to the Aviation aisle in Autozone for a new filter. I know the filter can probably be bent back into shape but they're not expensive. I'll need to build a better "top" to secure the filter body. I have some ideas--maybe something braced diagonally across the top to hold down the whole thing. Anyone have any good designs?

[PaulvS]

Looks unusual, was there any backfire event?

[BobTurner]

Hear any backfiring? Maybe during start?

[Bavafa]

Looks like a back fire. I have seen it a number of times and all due to a backfire.

[mfleming]

I don't think you need to modify the filter hold down at all, just find out what caused the deformation.

Just for a data point, before first flight, I had a back fire and the filter never moved and its held down just like yours.

[Draker]

No huge backfiring observed. I get the usual little baby "pop pop pops" when I reduce power to descend, but nothing monumental that I recall. Maybe I missed it. Sounds like the consensus here is backfire.

[moosepileit]

Merlin pops are at the exhaust pipes.

Is the back side of the filter lightly toast?

[Mike Harris]

Crimp the holding metal down to lock the filter tighter.