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Changes to Filtered Air Box (FAB) kits

greghughespdx

Well Known Member
Advertiser
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.​
 
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
 
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.
 
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.
 

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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.
 
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?
 
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.
 
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.
 

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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.
 
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.
 
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.

If you have had wear on the bottom of the FAB, that may be the cause.

The build instructions specify that the height of the FAB be 1/6" less than the the height of the filter so that the filter is compressed slightly when the bolts are tightened.

In situations where that is not the case, adding an appropriate thickness spacer to the bottom of the FAB would be the simplest way to resolve it.
 
In situations where that is not the case, adding an appropriate thickness spacer to the bottom of the FAB would be the simplest way to resolve it.

Yes, but don’t do what I did, which was to place a piece of sheet rubber under the air filter to compensate for the slight gap, thinking the downward compression of the filter would keep it firmly in place. It didn’t, and I got a nasty surprise with loss of power shortly after my next takeoff. Fortunately a reduced power setting released the rubber from the intake and I landed safely. Lesson learned.

Erich
 
If you have had wear on the bottom of the FAB, that may be the cause.

The build instructions specify that the height of the FAB be 1/6" less than the the height of the filter so that the filter is compressed slightly when the bolts are tightened.

In situations where that is not the case, adding an appropriate thickness spacer to the bottom of the FAB would be the simplest way to resolve it.

Scott - I meant that there is about 1/8" of compression on the filter when it is installed. The 1/8" gap is between the top plate and the banjo as the filter makes contact.
 
My fab kit

I have my FAB kit that was delivered with my firewall forward kit last year, do I need to buy a whole new FAB kit or just the carb plate?
I have a Vans io320 in a RV9A with the new nose gear.
 
I have my FAB kit that was delivered with my firewall forward kit last year, do I need to buy a whole new FAB kit or just the carb plate?
I have a Vans io320 in a RV9A with the new nose gear.

You should be able to purchase just a replacement top plate. Which one you will need depends on which fuel injection system you have.
I suggest a call or e-mail to tech support and ask them to help you sort it out.
 
You should be able to purchase just a replacement top plate.
Scott - just to clarify - is the part that changed the "Air Box Top Plate" (VA-13x-B, the part that is riveted to the FAB) or the "Mount Plate" (VA-13x-C, the part that bolts to the carb/servo and to the Air Box Top Plate)?

I''m at the perfect time to make this change to increase clearance between FAB and cowl on the left side...

Thanks for any info,

dave
 
Scott - just to clarify - is the part that changed the "Air Box Top Plate" (VA-13x-B, the part that is riveted to the FAB) or the "Mount Plate" (VA-13x-C, the part that bolts to the carb/servo and to the Air Box Top Plate)?

I''m at the perfect time to make this change to increase clearance between FAB and cowl on the left side...

Thanks for any info,

dave

The mount plates are what changed. The top plate is the same.

If you have already match drilled the mount plate to the FAB top plate, it will be more difficult to change because switching to one of the new off-set mount plates would change the relative alignment of the FAB to the induction air inlet opening.
 
timely but I have questions

If you have had wear on the bottom of the FAB, that may be the cause.
The build instructions specify that the height of the FAB be 1/6" less than the the height of the filter so that the filter is compressed slightly when the bolts are tightened.
In situations where that is not the case, adding an appropriate thickness spacer to the bottom of the FAB would be the simplest way to resolve it.

this is a timely discussion. I'm working on my 17th annual inspection and have found the carb mounting plate cracked (360).

Is there any reason I can't fabricate this plate from thicker stock, maybe .125? I know there's not much room down there but I would think it could take that additional thickness.

Also, since I'd have to cut that somewhat complex shape out for the carb drain bowl anyway, it doesn't seem like I gain much by ordering a new mount plate. The existing one, while cracked, would seem to be an excellent template for fabricating a new one. That make sense?

One other question - I also have some wear on the bottom of the FAB. What would make "an appropriate thickness spacer"? Can I rivet a thin piece of aluminum to the bottom of the FAB?

Sorry if these questions seem obvious but it's been 20 years since I fabricated this piece and really don't remember much of the process.

thanks
 
"Robert D
Is there any reason I can't fabricate this plate from thicker stock, maybe .125? I know there's not much room down there but I would think it could take that additional thickness."


Note that if you thicken the top plate, it has two fitment results.

Your air box will be lower (by that added thickness), so check if you have enough clearance under the airbox to fit the new lower position.
Also, you are affecting the snorkel height alignment to the cowl inlet by that same lower dimension. You will have adjust your baffling connection there.

If you opt for the new offset top mounting plate, you will be re-aligning the snorkel position for sure.
 
"Robert D
Is there any reason I can't fabricate this plate from thicker stock, maybe .125? I know there's not much room down there but I would think it could take that additional thickness."


Note that if you thicken the top plate, it has two fitment results.

Your air box will be lower (by that added thickness), so check if you have enough clearance under the airbox to fit the new lower position.
Also, you are affecting the snorkel height alignment to the cowl inlet by that same lower dimension. You will have adjust your baffling connection there.

If you opt for the new offset top mounting plate, you will be re-aligning the snorkel position for sure.

It may be overkill but after several plates cracking, I make a plate out of titanium I purchased on eBay. My guess is the titanium plate now has over 2,000 hour on it and still looks like new.

The 160 HP B2B engine has the carb set aft as far as Lycoming can place it creating the worst possible vibration and cracking possible.
 
Never tried Titanium, but all the air box mounting plates I've modified with double .063, none have cracked since. Probably combined they would add up to 1500+ hours.
 
Never tried Titanium, but all the air box mounting plates I've modified with double .063, none have cracked since. Probably combined they would add up to 1500+ hours.

I would definitely opted for a thicker plate. I've heard of too many cracks with the stock, kit provided material. Cutting it out of .063 stainless would likely add the needed strength while adding minimal weight. I was surprised to learn that the intake on the sump is off centered. I wonder why Lycoming did that?
 
Easy answer

I would definitely opted for a thicker plate. I've heard of too many cracks with the stock, kit provided material. Cutting it out of .063 stainless would likely add the needed strength while adding minimal weight. I was surprised to learn that the intake on the sump is off centered. I wonder why Lycoming did that?

Easy, done so that Lycoming can have more dash numbers to a basic engine
 
Stainless might be a potential candidate for this strength wise but would be a bear to fabricate, without sending it out to a CnC cutter.
2 layers of .063 2024 has worked fine for me & my customers so far.
 
Airbox mods

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.
My modification to the airbox and cowling to improve the ease of installing the lower cowl without a second person and reduce the risk of cracks due to the interaction of the airbox with the cowling snorkel -and fix the misalignment of the snorkel with the airbox. This is on a RV-7A with a IO 360B1B vertical induction.
The spacing between the aft end of the cowling removable snorkel and the modified airbox nose is about 2 inches. The joiner material between the snorkel and airbox is the top of a neoprene diving bootee. The bootee provides a tight fit round the airbox after installing the snorkel front. The bootee is glued and clamped to the snorkel.
KT
 

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So I have a question….

I had to modify the FAB on my fuel injected RV-9A so that the mixture lever on the left side would fit.

Of course that removed a decent bit of material and caused the bottom plate to crack (it took 500+ hours).

Is there a better solution then doing the same thing every 500 hours or so?

Thanks,

-Dan
 
So I have a question….

I had to modify the FAB on my fuel injected RV-9A so that the mixture lever on the left side would fit.

Of course that removed a decent bit of material and caused the bottom plate to crack (it took 500+ hours).

Is there a better solution then doing the same thing every 500 hours or so?

Thanks,

-Dan

Anyone have any ideas on this?

Thanks,

_Dan
 
You asking about the plate that bolts to the bottom of the carb, or the flanged top that is riveted to the fiberglass bowl?
 
You asking about the plate that bolts to the bottom of the carb, or the flanged top that is riveted to the fiberglass bowl?

The flange and the fiberglass bowl. I had to take a decent chunk out of both of those for the mixture level to clear.

-Dan
 
The flange and the fiberglass bowl. I had to take a decent chunk out of both of those for the mixture level to clear.

-Dan

Post a photo so that we can see what you did. What you’re describing is a standard practice for the airbox on the RV 10. The airbox instructions hint at this mod but don’t give the details because the details come with the parts for the RV 10 FWF kit to make the modification.
 
I have an older unbuilt FAB kit for my RV-3B (which is taking me like forever to complete). The O-320 uses an MA-4SPA carburetor.

Van's Support sent me this list and suggested that I order the highlighted items.

image001.jpg

I put them on order. The parts cost was $34.25.

Dave
 
Post a photo so that we can see what you did. What you’re describing is a standard practice for the airbox on the RV 10. The airbox instructions hint at this mod but don’t give the details because the details come with the parts for the RV 10 FWF kit to make the modification.

This is a picture of the piece I replaced. You can see how much metal I had to remove to allow clearance for the mixture lever, and that of course contributed to the cracking.

-Dan
 

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carb heat

carb heat arrangement. no wear in 900 hrs. no adjustment ever made since new. set it and forget it. carb heat is important. it can save your life. do I use it much, nope. have I really needed it in the past, yes.

top plate is original thickness supplied by Van's. no issues.

I expect this arrangement to go to 2000 hrs. untouched.

DSCN4669.jpg


DSCN4602.jpg


DSCN4621.jpg


DSCN4622.jpg
 
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carb heat arrangement. no wear in 900 hrs. no adjustment ever made since new. set it and forget it. carb heat is important. it can save your life. do I use it much, nope. have I really needed it in the past, yes.

top plate is original thickness supplied by Van's. no issues.

I expect this arrangement to go to 2000 hrs. untouched.

Steve,
Everyone has seen your regular (yearly?) posts about your airbox service life.
Unfortunately, your experience is an outlier in the data set of what is typical.

No doubt, the tension spring you added by bending the excess end of the control wire helps minimize vibration induced wear in the bug nut, but it will still wear eventually.
The new design is such that wear should never be a problem.

There are indications in your photos that there is some wear occurring at the contact point of the door to the FAB top. The new design addresses this as well.

Your photo showing the door closed, indicates that you probably have very poor carb heat performance with the large gap you have because of the door arm being installed on the opposite side of the door from what is depicted in the plans.
The new FAB design also improves the seal-ability of the door to wear it is possible to get nearly a 100% seal if built properly.
 
Steve,
Everyone has seen your regular (yearly?) posts about your airbox service life.
Unfortunately, your experience is an outlier in the data set of what is typical.

No doubt, the tension spring you added by bending the excess end of the control wire helps minimize vibration induced wear in the bug nut, but it will still wear eventually.
The new design is such that wear should never be a problem.

There are indications in your photos that there is some wear occurring at the contact point of the door to the FAB top. The new design addresses this as well.

Your photo showing the door closed, indicates that you probably have very poor carb heat performance with the large gap you have because of the door arm being installed on the opposite side of the door from what is depicted in the plans.
The new FAB design also improves the seal-ability of the door to wear it is possible to get nearly a 100% seal if built properly.

I'm glad to see you are improving it. I get about 40 rpm on this one. I don't detect any wear at this point. I'll continue to post some photos of it thru the years.
 
This is a picture of the piece I replaced. You can see how much metal I had to remove to allow clearance for the mixture lever, and that of course contributed to the cracking.

-Dan

That is a standard Van's aircraft supplied part used for that purpose. There has been a lot of airplanes utilizing that on the FAB. Predominately on RV-10's but some 2 seat RV's as well, when using vertical induction fuel injection.

That type of cracking is indicative of a lot of vibration influence.
Once it is repaired, I would recommend a prop balance (if not already done) and evaluate the interface between the cowl induction air inlet and the FAB to be sure it is allowing freedom of movement of the FAB (engine) in relation to the cowl.
 
I get about 40 rpm on this one.

Just mentioning it for other builders benefit.
Our testing has shown that much leakage at all around the door has a big influence on the temp. delta capability of the carb heat system.
The updated FAB instructions make a strong point of emphasizing this.
 
Just mentioning it for other builders benefit.
Our testing has shown that much leakage at all around the door has a big influence on the temp. delta capability of the carb heat system.
The updated FAB instructions make a strong point of emphasizing this.

yes, the goal is 50 rpm. I was only able to get 40 with this arrangement. with the hinge, the door stays in position well. same carb heat cable. no change to any components or maintenance in 900 hrs.
 
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yes, the goal is 50 rpm. I was only able to get 40 with this arrangement. with the hinge, the door stays in position well. same carb heat cable. no change to any components or maintenance in 900 hrs.

50 RPM drop is a rough rule of thumb used in some aircraft as a check during pre-takeoff run-up. It is in not related to a standard or regulatory requirement.

A temp. delta is. A big leak has a big influence on the temp delta.
 
That is a standard Van's aircraft supplied part used for that purpose. There has been a lot of airplanes utilizing that on the FAB. Predominately on RV-10's but some 2 seat RV's as well, when using vertical induction fuel injection.

That type of cracking is indicative of a lot of vibration influence.
Once it is repaired, I would recommend a prop balance (if not already done) and evaluate the interface between the cowl induction air inlet and the FAB to be sure it is allowing freedom of movement of the FAB (engine) in relation to the cowl.

Thanks Scott. I didn't realize that was a standard Van's part. I thought we had made that one, but that is my wifes job :).

Do you have the part number so I can order a replacement?

Thanks,

-Dan
 
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