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  #1  
Old 05-19-2022, 09:24 AM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 620
Default Alternate Alternate Air

I built the standard Vans alternate air door into the bottom of my standard FAB for my RV-9A with an IO-320. This door has been a constant source of trouble, I have found it to have failed almost every time I've taken my bottom cowling off during my condition inspection. At best it's worked its way open, several times it has pulled some of the rivets through the FAB. This time I found the door to be be completely detached, hanging by the actuator cable with the pivot plate nut pulled right though the floor of the airbox.

The notch that the tab on the door closes into is plenty tight, but I suspect it just vibrates out over time and the weight of the door on the single pivot point is too much given that vibration.

I was thinking I'd just build up the floor of the the airbox with some carbon fiber above and below and then reattaching as designed, but I wondered if anyone had an alternate approach to this that might be more reliable.

My plane is about to go into hibernation for 3-4 months as I'll be unable to fly due to shoulder surgery that I'm getting next week. I won't be fixing this problem until July or August, but I'm interested in hearing what the collective mind of VAF thinks.
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Claude Pitre
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018

Added GPS 175 and authorized for IFR April 1, 2021

Interactive map of all of my flights here
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  #2  
Old 05-19-2022, 09:38 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,671
Default

A piece of 0.032 aluminum that puts the glass between the door flange and the plate works well. The angle tabs also reduce the tendency for the filter to go from a cylinder to a cone, as well as prevents the filter from wearing into the bottom of the FAB.

Carl

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  #3  
Old 05-20-2022, 11:58 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,158
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Quote:
Originally Posted by Carl Froehlich View Post
A piece of 0.032” aluminum that puts the glass between the door flange and the plate works well. The angle tabs also reduce the tendency for the filter to go from a cylinder to a cone, as well as prevents the filter from wearing into the bottom of the FAB.

Carl

I did the same, except extended the Al piece out past the filter outside diameter. This eliminates the F/G bottom from wearing away due to the filter rubbing on it.

Oops, my bad. See that Carl did the same.

Larry
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  #4  
Old 05-20-2022, 01:23 PM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,798
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My FAB Alt Air Door gripes & solutions

Missing base plate rivets - I replace the rivets with AN507-8R8 screws, requires dimpling the base plate for the countersunk screws, using nutplates mounted to a plate (like Carl's), or donut shaped plate inside the filter housing. I add one more screw (compared to original number of pop rivets) to prevent the base plate warping. Ever wonder where those original missing pop rivets went? My robust mounting system will never (again) allow this type FOD be sucked up into the engine.

Door swivel screw falling off - I drill & safety wire the screw head. You could use a ANH bolt in place of drilling the AN525 screw if you have the vertical space between filter housing & cowling. So the drilled screw head (AN525) sits flush with the air door, I groove a AN960 washer so the safety wire nestles in & flat.

Floppy screw in air door where control cable attaches - Instead of countersinking the air door and sticking the AN507 screw through, I instead add a 063 plate on top of the air door, it is countersunk for the AN507 screw and when in place and the small plate is countersunk riveted to the air door, is very solid and the control cable screw will never again snag on the base plate.
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built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
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  #5  
Old 05-20-2022, 01:39 PM
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Flyhud Flyhud is offline
 
Join Date: Jul 2018
Location: Burleson, TX
Posts: 142
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This is how I did mine, bottom plate is pro sealed to fiberglass.

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  #6  
Old 05-20-2022, 04:09 PM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 620
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Thanks for all of the ideas guys. I knew I was far from alone on this one. Most if not all of the ideas have the same theme - some sort of backing ring or plate above the FAB floor. One of my earlier attempts was a terrible shortcut on that theme, I'd made backing strips - those are nowhere to be found now. Having the plate held down by the filter element would keep everything in place.

Ralph, I really like the ideas to deal with the hardware. The thought of where all my missing pieces went is enough to keep me awake at night. I also don't know how long I've been flying with unfiltered intake air, no more than 15 hours since it was fine when I buttoned up after my last oil change. I don't imagine that running like that is very good for the engine or fuel injection system, maybe it's contributing to crankiness that I get with my fuel systems.

I've ordered a new filter element ($60 US at Vans vs $104 CDN at ACS) and will come up with something based on all of these great ideas when I am able to in a couple of months. Other than a short warmup flight before my pre-parking oil change, the plane won't do much flying without filtered air.
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Claude Pitre
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018

Added GPS 175 and authorized for IFR April 1, 2021

Interactive map of all of my flights here
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