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  #11  
Old 11-16-2018, 03:38 PM
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JohnInReno JohnInReno is offline
 
Join Date: Jun 2005
Location: Prescott Valley/Chandler AZ
Posts: 351
Default Air flow performance mixture

Quote:
Originally Posted by acam37 View Post
This FAB is 100% fiberglass. I fabricated a new top piece and on the bottom where the air filter sits is a layer of core mat that is glassed over. This should be maintenance free for a long time. (Still haven’t installed the baffle seal yet)
[IMG][/IMG]
fyi
Airflow Performance can provide a mixture control that works in the reverse direction. In other words, you can put the arm above the pivot and eliminate the "notch" in the Filtered Air Box. My Superior kit IO-320 came that way from Eagle Engines.
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  #12  
Old 11-23-2018, 02:55 PM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,334
Default Pictures of top plate wear/cracking

These pictures are from top plate #3 or so, taken off around 800 hrs time in service.

The red lines are the cracks. Most of the scratches and the c-clamp marks are post-use. The cracks are quite subtle, and if I weren't sensitized to their likelihood, I almost certainly would not have noticed them. I had to flex the plate while watch a reflection in it in order to distinguish them from simple scratches.



The approximately rectangular areas are where "washers" I made from 1/8" aluminum fasten this to the AFP ring. The underside of these "washers" are well filleted to avoid stress concentrations. Prior to using these, a standard washer would crack the top plate very quickly where the washer made contact.

The underside of the top plate shows how the filter burnishes the aluminum. Some of these burnish marks are deep enough to be easily felt. The filter is quite tightly clamped, but the drubbing that the intake pulses deliver must still move it with every intake cycle.



I'll report back in March as to how the Kevlar on the bottom FAB held up as compared to the previous fiberglass construct.
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RV6A N66AP 1700+ hours
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  #13  
Old 11-23-2018, 04:41 PM
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Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
Default

On the first RV the top plate cracked twice just like this one. I tried adding an aluminum doubler on the plate (smaller donut covering the mounting holes). It cracked along with the replacement plate. I ended the problem by replacing the aluminum top plate with a piece of 0.032 stainless steel.

No cracking with my modified RV-10 FAB.

On the bottom of the air box I added a piece of 0.032 aluminum to solve the filter ablation problem.

Carl
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  #14  
Old 11-23-2018, 04:57 PM
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JohnInReno JohnInReno is offline
 
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Location: Prescott Valley/Chandler AZ
Posts: 351
Default Gasket

My top plate was cracked and replaced at 500 hours. The new plate is showing signs of cracking after only 75 hours. I talked to Allan at Precision Airmotive and he confirmed that there should be a gasket between the top plate and the servo. Plate #3 will get a gasket.
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RV-9A N946PM 600+ hours since 2013
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  #15  
Old 12-10-2018, 10:35 AM
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JohnInReno JohnInReno is offline
 
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Location: Prescott Valley/Chandler AZ
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Default New FAB with split baffle

At 600 hours, I built a new FAB and split the baffle material so that the bottom half is attached to the cowl and the top half is attached to the FAB. Seems to be working well and it makes installing the bottom cowl easier.

For reference, this is a reversed AFP servo with no FAB notch.



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  #16  
Old 02-05-2019, 09:40 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
Default

So, here's an airbox question.

The O-320 airbox has a plate that bolts to the bottom of the filter. Bolts go up through the filter and are secured by nuts at the top of the airbox. There is a quarter inch (or more) between the filter/plate/bolt heads and the airbox itself, so there is never any rubbing of the filter on the airbox.

Why weren't the -360 and -540 airboxes designed the same way? It seems like the airboxes for the larger engines are much more problematic and (too often) allow the filter to wear through the bottom of the airbox.
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2001 RV-6 N46KB
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  #17  
Old 02-06-2019, 07:11 AM
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Walt Walt is online now
 
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Location: Dallas/Ft Worth, TX
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I ran the FM200 vertical draft for over 1000 hrs on my 7A, never cracked the airbox mount plate.
I do have the front supported by the 'old' carb heat scat tube setup, left it there intentionally to support the front of the box even though its no longer needed.
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  #18  
Old 02-06-2019, 07:39 PM
rightrudder rightrudder is offline
 
Join Date: Mar 2014
Location: Laguna Hills, CA
Posts: 1,805
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I made a 0.125 top plate for the FAB (IO-320-D1A vertical induction) and it's holding up well at 320 hours. I put a gasket between it and the fuel servo, and Pro-Sealed a 0.063 plate inside the bottom of the FAB that contacts the entire lower seal of the filter. No additional support on the nose of the FAB.
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  #19  
Old 02-08-2019, 11:26 AM
Paul 5r4 Paul 5r4 is offline
 
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Location: Foley, Al
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When I built I also made an all aluminum airbox. There were some post on VAF that showed guys pulling cowling only to discover their airboxs cracked or laying in the bottom of the cowling.
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  #20  
Old 02-09-2019, 12:04 PM
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dougweil dougweil is offline
 
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Location: Hudson, WI
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Here's an old short article I wrote for the RVator's Log (March 2014):

A very common issue with the Filtered Air Box mounting is cracking of the mounting plate, which often happens at the first condition inspection. There is a two-fold method to avoid this frustration. First, make a duplicate FAB mounting plate out of 6061-T6 aluminum, which is far less brittle than 2024-T3. I have never seen this piece crack when using the T6 al- loy. Second, make a ?gasket? out of cork material from your local auto store. At Tom Berge?s suggestion, I used some 1/8 material, which seems to cushion the vibration between the engine and the mounting plate. At 250 hours, no cracks!

(Note.... I now have 730 hours and no cracks)






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RV-4, sold
RV-7 completed and flying N722DW, 840 hours
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