VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 06-02-2021, 01:12 PM
greghughespdx's Avatar
greghughespdx greghughespdx is offline
 
Join Date: Nov 2011
Location: Aurora, OR
Posts: 1,013
Default Changes to Filtered Air Box (FAB) kits

A new version of the Filtered Air Box (FAB) kits will be available to order starting this Thursday on the Van's web store. The FAB kits have now been reduced to two available kits. The carb mount plates were the main difference between the original versions of these kits, and we are now producing the two most common plates. For all others, we are supplying a blank mount plate and the cutout templates are at the back of the instructions.
REASON FOR REVISION:

The carburetor is not located on the centerline of the aircraft and so the Filtered Air Box (FAB) must be offset to line up with the lower inlet and not rub against the cowling. The available movement on the original kits was small and to correct this, the mounting plate for the FAB that attaches to the carburetor has been modified to shift the internal cutout to increase the available movement of the FAB.

Additionally, the carb heat door causes wear since there is metal-to-metal contact between the door and the “banjo” of the FAB. The hinge for the carb heat door can wear and become loose or fail. To correct this, the hinge has been replaced with baffle material that is then sandwiched by the carb heat door. The hinge is now made from a flexible material that is less prone to wear and provides a stiffer connection. This baffle material is also now the part of the carb heat door resting against the “banjo” of the FAB, which reduces wear since there is no longer metal-to-metal contact.

REVISION DESCRIPTION / NEW DOCUMENTATION:

FAB 320-360-540 Air Box Rev 0: Document updated to include shifted carb mount plate, updated seal material, and updated carb heat door. Document reformatted and instructions added or rephrased to be clearer and more complete.
__________________
Greg Hughes - Van's Aircraft
Van's web site | Instagram | Facebook
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Building RV-8A since Sept 2014
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Aurora, OR (EAA Chapter 105)

Reply With Quote
  #2  
Old 06-03-2021, 08:09 AM
chrispratt's Avatar
chrispratt chrispratt is offline
Super Moderator
 
Join Date: Oct 2005
Posts: 791
Default

Finally. Nice to see this has been addressed. After 16 years on my RV-8 I've replaced the mounting plate three times due to cracks. Replaced the hinge for the carburetor heat door door once, and still have touch up to do on the paint cracks on the lower cowl from the "Lycoming shake" on shutdown. The latter happened within the first fifty flight hours many years ago so I modified the FAB myself by: 1) replacing the rivets closest to cowl with countersunk rivets, and 2) making a new mounting plate with the carb hole offset about 1/4 inch to move the plate farther away from cowling. I keep a spare FAB 360 on hand for future occurrences. Hopefully the new fix will address all this.

Does the new version suggest a way to keep the mounting plate from cracking? Mine (3) have all happened behind the carburetor. I've seen some posts on this (Doug Reeves') site about adding a bracket between the plate and the engine to help stop the plate movement but have not found a spot to do this.

Chris
__________________
Chris Pratt (2021 VAF DUES PAID)
RV-8 Flying, 850+hours
N898DK
Lycoming O-360-A1A, Hartzell CS
52F (Northwest Regional, Aero Valley, Whatever, TX)
Reply With Quote
  #3  
Old 06-03-2021, 09:26 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,534
Default

Quote:
Originally Posted by chrispratt View Post

Does the new version suggest a way to keep the mounting plate from cracking? Mine (3) have all happened behind the carburetor. I've seen some posts on this (Doug Reeves') site about adding a bracket between the plate and the engine to help stop the plate movement but have not found a spot to do this.

Chris
I also appreciate these updates to the FAB kit.

Don't know how many carb heat doors I've repaired over the years, but it is one of the first things to look at on my annual check lists!

Next thing on the list is check for those cracks on the mounting plate. My fix is to double up that area with another layer of .063 (assuming I have vertical clearance to add the doubler).

Followed with looking at the bottom of the air box to see that the alternate air door mounting plate is still solidly mounted, and that the air filter isn't wearing through the fiberglass.

I think the FAB kit updates will help in the build process, but there is a bit more that can be done to reduce long term maintenance requirements.
__________________
Ralph
built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
Reply With Quote
  #4  
Old 06-03-2021, 10:50 AM
Northernliving Northernliving is offline
 
Join Date: May 2005
Location: Boston, MA
Posts: 584
Default

Quote:
Originally Posted by chrispratt View Post
Finally. Nice to see this has been addressed. After 16 years on my RV-8 I've replaced the mounting plate three times due to cracks. Replaced the hinge for the carburetor heat door door once, and still have touch up to do on the paint cracks on the lower cowl from the "Lycoming shake" on shutdown. The latter happened within the first fifty flight hours many years ago so I modified the FAB myself by: 1) replacing the rivets closest to cowl with countersunk rivets, and 2) making a new mounting plate with the carb hole offset about 1/4 inch to move the plate farther away from cowling. I keep a spare FAB 360 on hand for future occurrences. Hopefully the new fix will address all this.

Does the new version suggest a way to keep the mounting plate from cracking? Mine (3) have all happened behind the carburetor. I've seen some posts on this (Doug Reeves') site about adding a bracket between the plate and the engine to help stop the plate movement but have not found a spot to do this.

Chris
I'm switching from carb to fuel injection, so I had to make a spacer. I incorporated the spacer into the plate and made it thicker to avoid the cracking problem. I also noted the required offset, but since I was reusing my FAB that was already cocked, I left it centered. If I didn't need the spacer, I would just make the part out of thicker stainless and cut it on the water jet to avoid the cracking design problem.
Attached Thumbnails
Click image for larger version

Name:	RV8 Plate.jpg
Views:	128
Size:	229.8 KB
ID:	12188  
__________________
Brian J.
Boston, MA
RV8 Based at ORH - Purchased
RV8 - The Project #83313 - Under Construction
Reply With Quote
  #5  
Old 06-03-2021, 11:21 AM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,599
Default

The redesign addresses longevity and maintenance as well as improving the initial build process and instructions.

The theory of the cracking top plate is that it is largely related to engine movement vs the inlet end of the FAB being restrained where it interfaces to the cowl. This results in repeated flexing of the plate which can eventually cause fatigue cracks. The top plate of the FAB generally doesn't crack because it is made of a softer aluminum.
That is the reason the seal at that location has been changed to a softer (thin silicone) material, to hopefully reduce the loads induced into the FAB during engine movement. We don't have lots of flight test hrs. for that change so we will have to see how it does.

We do have a lot of test hrs for the carb heat door hinge redesign. This style hinge has been under test on 3 different airplanes for a couple+ years now and is working great. The hinge material probably will have to be replaced eventually at some point, but my guess is that it should go at least 15 years or so before that might be required.

The wear in the bottom of the FAB was not addressed with the redesign because in my opinion it is caused by lack of proper maintenance. The filter wearing into the fiberglass bowl is because the filter has shrunk with age. Once it is no longer captured tightly between the top plate and the FAB bottom, it can move and will then begin to wear. The filter used is reusable, but that doesn't mean forever. Evaluating the fit should be a regular inspection item and replace it if no longer captured tightly.

Another change is the cable connection to the carb heat arm. This pivot point is a location that has been common for wear. The new design is very robust and if the pivot point is lubricated with a drop of engine oil occasionally, it should last a long time.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #6  
Old 06-03-2021, 11:28 AM
AlexPeterson's Avatar
AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Ottertail, MN
Posts: 2,451
Default

Quote:
Originally Posted by Northernliving View Post
I'm switching from carb to fuel injection, so I had to make a spacer. I incorporated the spacer into the plate and made it thicker to avoid the cracking problem. I also noted the required offset, but since I was reusing my FAB that was already cocked, I left it centered. If I didn't need the spacer, I would just make the part out of thicker stainless and cut it on the water jet to avoid the cracking design problem.
Wow, that's a lot of mass to be hanging off the bottom of the induction system... how thick is the flange?
__________________
Alex Peterson
RV6A N66AP 1750+ hours
KADC, Wadena, MN
Reply With Quote
  #7  
Old 06-03-2021, 11:33 AM
AlexPeterson's Avatar
AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Ottertail, MN
Posts: 2,451
Default

Quote:
Originally Posted by rvbuilder2002 View Post
SNIP

The wear in the bottom of the FAB was not addressed with the redesign because in my opinion it is caused by lack of proper maintenance. The filter wearing into the fiberglass bowl is because the filter has shrunk with age. Once it is no longer captured tightly between the top plate and the FAB bottom, it can move and will then begin to wear. The filter used is reusable, but that doesn't mean forever. Evaluating the fit should be a regular inspection item and replace it if no longer captured tightly.

SNIP
The filter shrinkage is notable after only one year, and probably less than that, since I only take that apart at annual inspection time. My theory (unproven) is that the fab bottom wear is due to the pulsatile pressure regime in the induction, which causes slight movement of the filter.
__________________
Alex Peterson
RV6A N66AP 1750+ hours
KADC, Wadena, MN
Reply With Quote
  #8  
Old 06-03-2021, 11:42 AM
Northernliving Northernliving is offline
 
Join Date: May 2005
Location: Boston, MA
Posts: 584
Default

Quote:
Originally Posted by AlexPeterson View Post
Wow, that's a lot of mass to be hanging off the bottom of the induction system... how thick is the flange?
Probably not when you consider the size of the carb! I don't have it in front of me, but I believe the flange was .20in or .25in. The total height was to accommodate the difference between the carb and the fuel servo. The servo is pretty small compared to the carb and weighs around 8oz less. I think I'm around 6-8oz more, net with the adapter/flange.
Attached Thumbnails
Click image for larger version

Name:	Carb vs Servo.jpg
Views:	85
Size:	548.9 KB
ID:	12189  
__________________
Brian J.
Boston, MA
RV8 Based at ORH - Purchased
RV8 - The Project #83313 - Under Construction

Last edited by Northernliving : 06-03-2021 at 12:10 PM.
Reply With Quote
  #9  
Old 06-03-2021, 12:19 PM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,599
Default

Quote:
Originally Posted by AlexPeterson View Post
The filter shrinkage is notable after only one year, and probably less than that, since I only take that apart at annual inspection time. My theory (unproven) is that the fab bottom wear is due to the pulsatile pressure regime in the induction, which causes slight movement of the filter.
If your theory was correct, we would see the wearing problem on all RV's using the FAB.

The filters do seem to begin to shrink immediately in overall diameter, but not in height. This is generally not a problem. A change in height is a problem if it gets excessive.
I have run the same filter for a number of years, in numerous different airplanes (my own, company prototypes, etc.) before needing to replace because of shrinkage in height. I have not seen the wear problem on any of these airplanes that some have. I believe it is because we replace the filter as soon as it is no longer clamped tightly between the top and the bottom.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #10  
Old 06-03-2021, 02:25 PM
AlexPeterson's Avatar
AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Ottertail, MN
Posts: 2,451
Default

Quote:
Originally Posted by rvbuilder2002 View Post
If your theory was correct, we would see the wearing problem on all RV's using the FAB.

The filters do seem to begin to shrink immediately in overall diameter, but not in height. This is generally not a problem. A change in height is a problem if it gets excessive.
I have run the same filter for a number of years, in numerous different airplanes (my own, company prototypes, etc.) before needing to replace because of shrinkage in height. I have not seen the wear problem on any of these airplanes that some have. I believe it is because we replace the filter as soon as it is no longer clamped tightly between the top and the bottom.
Ah, understood, height shrinkage. I've never measured that. There is usually about an 1/8" gap or so when the filter makes contact before tightening the banjo attachment screws on mine.
__________________
Alex Peterson
RV6A N66AP 1750+ hours
KADC, Wadena, MN
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 11:59 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.