FAB Fiberglass crack

uk_figs · #1 03-11-2017, 01:36 PM

Doing the condition inspection and after removing the K&M air filter I noticed that the bottom of the fiberglass section of the FAB is cracked at the rear in perfect alignment with K&M filter outline. Does not look worn through so I suspect vibration induced crack, 9 years and 460 hours. Is this something others have seen? As I will probably replace the lower fiberglass section is there something I should do to prevent this happening again?
Thanks
Figs

Kyle Boatright · #2 03-11-2017, 01:40 PM

Quote:

Originally Posted by uk_figs

Doing the condition inspection and after removing the K&M air filter I noticed that the bottom of the fiberglass section of the FAB is cracked at the rear in perfect alignment with K&M filter outline. Does not look worn through so I suspect vibration induced crack, 9 years and 460 hours. Is this something others have seen? As I will probably replace the lower fiberglass section is there something I should do to prevent this happening again?
Thanks
Figs

Is your filter in contact with the airbox? That might explain it.

uk_figs · #3 03-11-2017, 02:02 PM

Kyle
Yes, the filter sits on the airbox, it is the Vans "Filter Airbox- Vertical Draft" http://vansaircraft.com/cgi-bin/stor...t=fab-vertical. Hopefully I can just get a new fiberglass section although I did think about either a) repairing the glass but it has oil on it so I am not sure how well the glass would bond, or b) putting in a metal plate insert.

Here is the crack: https://get.google.com/albumarchive/...48874481939554
Figs

brad walton · #4 03-11-2017, 02:44 PM

Mine was wearing badly on the bottom of the FAB so I cut aluminum sheetto match the area of filter contact an held in place with several rivets. Seems to have stopped the problem from progresing

rockwoodrv9 · #5 03-11-2017, 03:53 PM

Dave,
I just had to modify my whole air box and snout to fit my James cowl with a carb engine. It was not the easiest, but it worked as far as I can tell - not flying yet!

In my research on how to make the modifications, I saw several pictures of exactly what you are talking about. The bottom just wears out and cracks. Putting a piece of aluminum inside and re-glassing the bottom would probably work fine.

I made my box about 3/4" deeper and got the next size KN filter to give a bit more airflow. At least that is my hope.

Kyle's comment gives me a question. Doesn't the air filter need to fit tight against the bottom to keep unfiltered air from going to the carb? That is why I upsized the new filter.

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gasman · #6 03-11-2017, 04:03 PM

Quote:

Originally Posted by rockwoodrv9

Dave,
I just had to modify my whole air box and snout to fit my James cowl with a carb engine. It was not the easiest, but it worked as far as I can tell - not flying yet!

In my research on how to make the modifications, I saw several pictures of exactly what you are talking about. The bottom just wears out and cracks. Putting a piece of aluminum inside and re-glassing the bottom would probably work fine.

I made my box about 3/4" deeper and got the next size KN filter to give a bit more airflow. At least that is my hope.

Kyle's comment gives me a question. Doesn't the air filter need to fit tight against the bottom to keep unfiltered air from going to the carb? That is why I upsized the new filter.

[IMG]

[/IMG]

No. The filter has a plate that goes on the bottom. It clears the fiberglass by about 1/4 inch or more. The air box does not seal the bottom of the filter element.

rockwoodrv9 · #7 03-11-2017, 04:08 PM

Thanks Warren. I will be back at the hangar Monday and get a few more shots.

That doesn't change anything about the OP just glassing the bottom back on does it?

bhester · #8 03-11-2017, 06:00 PM

Kyle has a 6, I have buddies that also have 6's their filters do not seal on the FAB. I have a 7A and mine does seal on the FAB and I believe another buddies 9A does also.

Kyle Boatright · #9 03-11-2017, 06:03 PM

Quote:

Originally Posted by bhester

Kyle has a 6, I have buddies that also have 6's their filters do not seal on the FAB. I have a 7A and mine does seal on the FAB and I believe another buddies 9A does also.

More proof that the -6 is the pinnacle of homebuilt aircraft development. ;-)

AlexPeterson · #10 03-11-2017, 06:17 PM

Quote:

Originally Posted by uk_figs

Doing the condition inspection and after removing the K&M air filter I noticed that the bottom of the fiberglass section of the FAB is cracked at the rear in perfect alignment with K&M filter outline. Does not look worn through so I suspect vibration induced crack, 9 years and 460 hours. Is this something others have seen? As I will probably replace the lower fiberglass section is there something I should do to prevent this happening again?
Thanks
Figs

Seems common - clean it well with lacquer thinner, sand it, and lay a few layers of glass in there with epoxy. I did this somewhere around the same # of hours as you, and it has held for 1100+ more hours. No need to replace the whole housing. Mine is abrading a bit wherever the filter makes contact, so I may have to add another layer sometime soon. The filter gets tortured by the intake pulses, apparently. I do not think it is general engine vibrations which cause it.