Airbox Cone of Death near accident

[bhester]

I added the plate to the bottom, the nut plates are outside of the filter:
http://home.newwavecomm.net/bobbyhester/2014Flying.htm

[rockwoodrv9]

Originally Posted by fixnflyguy

I have the variation per plans with the filter trapped between a bottom plate and an adapter plate bolted to the carb. The airbox then screws to the adapter plate.

I did my airbox the same. I bolted the plate on, then use screws to hold the glass portion to the mounting plate. My thought was it was easier to unscrew the glass box than reach above the plate and unbolt the plate.

Anyone see a problem with this? I have no ego as I am an amateur building an airplane and if someone ever sees anything that could be a problem, I am all ears!

[DanH]

Originally Posted by fixnflyguy

...the airbox snorkle to air inlet can be so tight that all engine movement/shake is transferred to the carburetor attach studs, and bowl screws, eventually leading to a loose carb. assembly, which leads to intake leak/backfiring and the associated problems to follow.Certainly, this shaking/movement doesn't help any of the fiberglass or aluminum parts. I made my rubber interface a bit more flexible (larger space between snorkle and inlet) and have never had the problem again. 300 hrs. since the adjustments, and no more loose carb. issues, no chaffing, no cracked adapter plates.

Bingo.

At every startup, the engine oscillates around the crankshaft axis. The carb moves side to side, as it hangs well below the crank. However, the nose of the airbox is too often locked to the cowl with stiff rubber flaps, and can't move.

If you have a Vans airbox, grab the snout at the seal flaps next time you have the cowl off, and shove it side to side, hard. Same loading.

[GHRoss3]

Originally Posted by rvbuilder2002

I would recommend using any fasteners that if they failed, could be sucked into the engine.

I think Scott was typing so fast that he forgot to put "not" into this sentence: I would recommend not using any fasteners that if they failed, could be sucked into the engine.

[rvbuilder2002]

Originally Posted by GHRoss3

I think Scott was typing so fast that he forgot to put "not" into this sentence: I would recommend not using any fasteners that if they failed, could be sucked into the engine.

Oops, you are correct.
Edited original post.......

[rvbuilder2002]

Originally Posted by DanH

Bingo.

At every startup, the engine oscillates around the crankshaft axis. The carb moves side to side, as it hangs well below the crank. However, the nose of the airbox is too often locked to the cowl with stiff rubber flaps, and can't move.

Exactly
And probably the majority of the reason that some have cracking in short amounts of time and others never do.

Another build error I see a lot is having too small of a gap between the air box and the extension that gets molded into the inlet opening.
If the gap is excessively small, it doesn't matter what you use for seal material, it will still transfer a lot of load to the airbox (and it makes the cowl a lot more difficult to remove and install).

[PaulR]

Originally Posted by rvbuilder2002

Exactly
And probably the majority of the reason that some have cracking in short amounts of time and others never do.

Another build error I see a lot is having too small of a gap between the air box and the extension that gets molded into the inlet opening.
If the gap is excessively small, it doesn't matter what you use for seal material, it will stall transfer a lot of load to the airbox (and it makes the cowl a lot more difficult to remove and install).

And where is the "like" button???

[Flyin'Bryan]

.....several years ago in a 1974 C-182 with a continental 0-470 230 HP engine. Idle and preflight checks were all good. Then, while on the runway, I applied throttle and the engine actually lost power with increasing advances of the throttle. I aborted the takeoff and reported the problem.

The mechanic later told me that the carb design for that airplane/engine similarly had a cone near the carb inlet/venturi, and this cone is mounted on 3 separate metal prongs to the carb body in a conical pattern- I assume with rivets or small welds or something. Upon inspection, connections on two of the three metal posts had failed, and each time I tried to apply full power the cone would bend inward on the one remaining prong, and fall into the venturi, partially blocking the airflow.

So in my case it resulted in a completely reversed operation of the carb when full power was applied. When he told me this, I also felt lucky to be alive, and had no idea that the carb was constructed with components that seem to be similar to yours, and in a manner that would cause a dangerous condition had it failed. (minus the fiberglass of course).

Just wanted to add this because it seems that this type of event also happens to other aircraft from time to time. Whatever you do, fix this in a way that ensures that this does not happen again. Kudos for making the right decision to abort.

[1001001]

Originally Posted by rvbuilder2002

The filters shrink over time. It mostly is evident in overall diam, but they do shrink in height also to some degree. I think this shrinkage is what primarily precipitates the wear (once it is no longer tight, vibration takes care of the rest).
I personally see no issue with bonding a piece of aluminum into the bottom to reduce wear. I would recommend not using any fasteners that if they failed, could be sucked into the engine. I do have a problem with adding soft material to the edge of the filter. It probably wouldn't cause any damage to the engine if ingested but if this is on a carburated engine, just a small piece lodged in the center venturi of the carb. could be enough to cause engine stoppage. I know of an RV-8 forced landing incident caused by exactly that.

Has anyone experimented with making a spring plate to allow the seal to self adjust to a shrinking filter? Obviously, care would have to be taken to ensure no parts of an adjuster could be inducted.

On the other hand, why ot just replace the filter on condition when it shrinks below some min tolerance? If the filter is too expensive for that, maybe rethink whether the longevity/reusability of that filter is worth the shrinkage and its potential effects.

[rvbuilder2002]

Originally Posted by 1001001

On the other hand, why ot just replace the filter on condition when it shrinks below some min tolerance? If the filter is too expensive for that, maybe rethink whether the longevity/reusability of that filter is worth the shrinkage and its potential effects.

It takes quite a few years for it to shrink noticeably.
I recommend that people just replace it every 3 or 4 years (they are not to expensive).