Matronics Email Lists :: View topic - New F.A.B. alternate air intake

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

New F.A.B. alternate air intake

Matronics Email Lists Forum Index -> RV-List

View previous topic :: View next topic

Author Message

Terry Watson

Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

Posted: Wed Jul 12, 2006 8:19 am Post subject: New F.A.B. alternate air intake

I installed Van's first version of the alternate air intake, the one with

the magnet holding the door closed. It didn't look like it was going to work

well so when the reports started coming in about them not closing or staying

open, I junked that Filtered Air Box and ordered another one. Then Van's

came out with version 2.0 of the alternate air intake, a round opening in

the bottom of the F.A.B. with a door that pivots on one screw. I installed

that in my new F.A.B. I don't like this one either. My best efforts still

mean it's a one-shot deal. If I open it I will have to remove the lower cowl

to get it completely closed again. Considering that it is an emergency air

source and would only be opened when I thought the front opening was

obstructed, that isn't completely unreasonable. 



But I hate the idea of needing to remove the lower cowl anytime anyone pulls

on the control, intentionally or otherwise.



Maybe I am missing something important here. Any thoughts?



Terry

RV-8A finishing

Seattle

klwerner(at)comcast.net
Guest

Posted: Wed Jul 12, 2006 8:31 am Post subject: New F.A.B. alternate air intake

I am not familiar with the layout  of version # 2.0,  but how about incorporating a spring-load  to help to put it back to the shut position?

 do not archive

 [quote]   ---

rocketbob(at)gmail.com
Guest

Posted: Wed Jul 12, 2006 9:51 am Post subject: New F.A.B. alternate air intake

Terry, I did not like version 2.0 either so I scrapped the magnet and the magnet holder of version 1.0, and potted three smaller magnets on the outside of the FAB with 3M DP-190 epoxy.  It takes a bit more force to get it open now.  I put some dychem machinists ink on the throat of the carburetor as an indicator to show if the door was opening in flight and contacting the carb and so far it hasn't.  I absolutely will not put anything mechanical in the path of non-filtered air that could come loose and get sucked into the engine.  The airbox really takes a beating from vibration. 



Regards,

Bob Japundza

RV-6 flying, F1 under const.



On 7/12/06, Terry Watson <terry(at)tcwatson.com (terry(at)tcwatson.com) > wrote: 	  Quote: 	
		  --> RV-List message posted by: "Terry Watson" < terry(at)tcwatson.com (terry(at)tcwatson.com)>

I installed Van's first version of the alternate air intake, the one with

the magnet holding the door closed. It didn't look like it was going to work

well so when the reports started coming in about them not closing or staying 

open, I junked that Filtered Air Box and ordered another one. Then Van's

came out with version 2.0 of the alternate air intake, a round opening in

the bottom of the F.A.B. with a door that pivots on one screw. I installed 

that in my new F.A.B. I don't like this one either. My best efforts still

mean it's a one-shot deal. If I open it I will have to remove the lower cowl

to get it completely closed again. Considering that it is an emergency air 

source and would only be opened when I thought the front opening was

obstructed, that isn't completely unreasonable.



But I hate the idea of needing to remove the lower cowl anytime anyone pulls

on the control, intentionally or otherwise.

Larry Bowen

Joined: 09 Jan 2006
Posts: 802
Location: NC, USA

Posted: Wed Jul 12, 2006 11:40 am Post subject: New F.A.B. alternate air intake

You can't reach in through the exhaust opening in the lower cowl?



I glassed my version 1.0 door shut; and close the carb heat door/alt air

door at first indication of precip/birds/meteors.



-- 

Larry Bowen

Larry(at)BowenAero.com

http://BowenAero.com



Terry Watson wrote:

 	  Quote: 	
		   

 I installed Van's first version of the alternate air intake, the one with

 the magnet holding the door closed. It didn't look like it was going to

 work

 well so when the reports started coming in about them not closing or

 staying

 open, I junked that Filtered Air Box and ordered another one. Then Van's

 came out with version 2.0 of the alternate air intake, a round opening in

 the bottom of the F.A.B. with a door that pivots on one screw. I installed

 that in my new F.A.B. I don't like this one either. My best efforts still

 mean it's a one-shot deal. If I open it I will have to remove the lower

 cowl

 to get it completely closed again. Considering that it is an emergency air

 source and would only be opened when I thought the front opening was

 obstructed, that isn't completely unreasonable.



 But I hate the idea of needing to remove the lower cowl anytime anyone

 pulls

 on the control, intentionally or otherwise.



 Maybe I am missing something important here. Any thoughts?



 Terry

 RV-8A finishing

 Seattle

_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress...

lhelming(at)sigecom.net
Guest

Posted: Wed Jul 12, 2006 1:19 pm Post subject: New F.A.B. alternate air intake

Here is my take on the FAB alternate air intake.  The FAB was first 

introduced without any regard to alternate air intake.  Someone, or perhaps 

several had a problem with ice on the carb filter as I understand it due to 

flying into icing conditions, ie, freezing rain, or snow and the carb heat 

activated after the fact did not melt the ice because the warmed air could 

not flow to melt the ice.  The pop up door remedied this problem but on some 

large engines like the 360 it could open due to the amount of vacuum created 

during high power settings such as during take off in perhaps dusty 

conditions. That could affect engine longevity because unfiltered air was 

getting into the engine.  So the pop up door was replaced with a manual door 

that the pilot had to activate with a pull lever.  The carb heat feature can 

close off all freezing moisture if activated before the air filter 

completely freezes, thereby cutting off all air movement through the filter. 

The new manually activated door allows unfiltered air into the carb when 

done can get through the filter.



I don't think there is any problem with the FAB without an alternate air 

solution IF the carb heat is utilized before the air filter freezes over 

solid.  So if the pilot recognizes the possibility of snow or freezing rain 

situation and pulls carb heat before air flow is totally cut off, there 

should not be a reason to activate the new manual alternate air solution as 

the heated air from carb heat will melt the ice on the filter.



Based on this understanding, I removed the pop up door to save my engine 

from possible harm and glassed over it and did not install the sliding door 

solution.  Aside from not activating carb heat in time, the one situation 

that the manual alternate air system will help on is if a plastic bag, or 

bird, or something is ingested in the air input that cuts off air to the 

carb.  I don't know but the vacuum pressure could be strong enough to burst 

a bag and it might not be a problem without the alternate air.  I liked the 

pop up door before I learned of its weakness.  I am surprised Vans did not 

just strengthen the door so it could not accidentally deploy.  Someone 

suggested adding stronger magnets.  I think that is a better solution. 

Indiana Larry



---

Terry Watson

Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

Posted: Wed Jul 12, 2006 2:08 pm Post subject: New F.A.B. alternate air intake

Thanks Indiana Larry. That all makes good sense, but I have fuel injection

and therefore no carb heat door. A carb heat door would solve part of the

problem -- if a bird or big snowball got stuck in the intake ahead of the

carb heat inlet -- but the alternate air door is intended to also let air

into the engine if the filter gets covered with ice, as I understand it. So

a carb heat door, even with a fuel injection system, would solve half of the

problem, or handle some but not all of the anticipated possible air inlet

blockages.



And thanks North Carolina Larry. Because I have a nosewheel, I don't think I

could reach up in there to close the door properly, but I would sure give it

a try before I removed the lower cowl.



I think I can live with what I have, but I am still hoping someone has come

up with an idea that makes this door work as intended. I have been thinking

about getting a control cable with a T-handle and push-button to discourage

me from pulling the wrong knob, but my history warns me that might not stop

me.



Thanks,



Terry




Here is my take on the FAB alternate air intake.  The FAB was first 

introduced without any regard to alternate air intake.  Someone, or perhaps 

several had a problem with ice on the carb filter as I understand it due to 

flying into icing conditions, ie, freezing rain, or snow and the carb heat 

activated after the fact did not melt the ice because the warmed air could 

not flow to melt the ice.  The pop up door remedied this problem but on some



large engines like the 360 it could open due to the amount of vacuum created



during high power settings such as during take off in perhaps dusty 

conditions. That could affect engine longevity because unfiltered air was 

getting into the engine.  So the pop up door was replaced with a manual door



that the pilot had to activate with a pull lever.  The carb heat feature can



close off all freezing moisture if activated before the air filter 

completely freezes, thereby cutting off all air movement through the filter.



The new manually activated door allows unfiltered air into the carb when 

done can get through the filter.



I don't think there is any problem with the FAB without an alternate air 

solution IF the carb heat is utilized before the air filter freezes over 

solid.  So if the pilot recognizes the possibility of snow or freezing rain 

situation and pulls carb heat before air flow is totally cut off, there 

should not be a reason to activate the new manual alternate air solution as 

the heated air from carb heat will melt the ice on the filter.



Based on this understanding, I removed the pop up door to save my engine 

from possible harm and glassed over it and did not install the sliding door 

solution.  Aside from not activating carb heat in time, the one situation 

that the manual alternate air system will help on is if a plastic bag, or 

bird, or something is ingested in the air input that cuts off air to the 

carb.  I don't know but the vacuum pressure could be strong enough to burst 

a bag and it might not be a problem without the alternate air.  I liked the 

pop up door before I learned of its weakness.  I am surprised Vans did not 

just strengthen the door so it could not accidentally deploy.  Someone 

suggested adding stronger magnets.  I think that is a better solution. 

Indiana Larry

bicyclop(at)pacbell.net
Guest

Posted: Wed Jul 12, 2006 4:54 pm Post subject: New F.A.B. alternate air intake

One thing to think about. Many RV's don't have enough temperature rise

with carb heat to do much good. That little tube with the bite out of it

that Van's sells is about useless. Deploying carb heat in a timely

manner in snow might not do enough and you might still wind up with

filter blockage. Even if you have to manually reset it after use,

alternate air might save the day sometime.



Pax,



Ed Holyoke



--

Tim(at)MyRV10.com
Guest

Posted: Wed Jul 12, 2006 5:18 pm Post subject: New F.A.B. alternate air intake

Terry,  I'm flying an RV-10 with the new style FAB door.  Also using

F.I. like you are, so I didn't add carb heat or any other options, just

the simple door.   If it were me, I'd just leave it as-is.  The knob

isn't super easy to pull, and in 90 hours now nobody's touched it.

You could even label it with a warning if you wanted, but considering

that YOU'RE the pilot and will likely be in the plane all the time,

the chance is pretty slim it'll get messed with...and if it does,

how many times do you think it'll happen??  I'd rather remove the

cowl 1 or 2 times over the airplane's lifetime because someone

touched the valve than spend a ton of time trying to change the way

things work.  On the -10, I am betting I can reach the FAB from

under the nose anyway.



Tim Olson - RV-10 N104CD - Flying

do not archive

Terry Watson wrote:

 	  Quote: 	
		   

 

 Thanks Indiana Larry. That all makes good sense, but I have fuel injection

 and therefore no carb heat door. A carb heat door would solve part of the

 problem -- if a bird or big snowball got stuck in the intake ahead of the

 carb heat inlet -- but the alternate air door is intended to also let air

 into the engine if the filter gets covered with ice, as I understand it. So

 a carb heat door, even with a fuel injection system, would solve half of the

 problem, or handle some but not all of the anticipated possible air inlet

 blockages.

 

 And thanks North Carolina Larry. Because I have a nosewheel, I don't think I

 could reach up in there to close the door properly, but I would sure give it

 a try before I removed the lower cowl.

 

 I think I can live with what I have, but I am still hoping someone has come

 up with an idea that makes this door work as intended. I have been thinking

 about getting a control cable with a T-handle and push-button to discourage

 me from pulling the wrong knob, but my history warns me that might not stop

 me.

 

 Thanks,

 

 Terry

Hopperdhh(at)aol.com
Guest

Posted: Wed Jul 12, 2006 5:35 pm Post subject: New F.A.B. alternate air intake

Terry,

  

 I agree -- its a one shot deal.  I couldn't get mine to seal all that  well either, so I put a very small bead of RTV around it.  Its there only  for a rare emergency.

  

 One correction though.  You can easily close it with only the upper  cowl off.

  

 Dan Hopped

 RV-7A 200 HP IO-360

  

  

 In a message dated 7/12/2006 12:21:02 P.M. Eastern Daylight Time,  terry(at)tcwatson.com writes:

  	  Quote: 	
		  

But    I hate the idea of needing to remove the lower cowl anytime anyone pulls

on    the control, intentionally or otherwise.



Maybe I am missing something    important here. Any thoughts?



Terry

RV-8A  finishing

Seattle

Tim_Lewis(at)msm.umr.edu
Guest

Posted: Wed Jul 12, 2006 6:02 pm Post subject: New F.A.B. alternate air intake

On my RV-6A (following involuntary glider training precipitated by snow 

in the FAB) I built a somewhat complicated filter bypass that takes the 

carb heat air (not hot enough to melt snow) and dumps it in the FAB 

AFTER the air filter.  See

<http://home.earthlink.net/~timrv6a/RV6_FAB.jpg>

I like Van's alternate air solutions better than what I built for my 

-6A, but Van's wasn't available at the time.



For my RV-10 (IO-540) I'm using a hinged alternate air door on the 

bottom of the FAB that opens and closes using the push/pull cable, 

rather than the "one way" sliding door arrangement.  Photo is at 

<http://home.earthlink.net/~timrv6a/Alt_air.jpg>. I've not flown the -10 

yet.



Tim Lewis

N47TD



Ed Holyoke wrote:

 	  Quote: 	
		   

 

 One thing to think about. Many RV's don't have enough temperature rise

 with carb heat to do much good. That little tube with the bite out of it

 that Van's sells is about useless. Deploying carb heat in a timely

 manner in snow might not do enough and you might still wind up with

 filter blockage. Even if you have to manually reset it after use,

 alternate air might save the day sometime.

 

 Pax,

 

 Ed Holyoke

Fred.Stucklen(at)UTCPower
Guest

Posted: Thu Jul 13, 2006 9:27 am Post subject: New F.A.B. alternate air intake

I've done something a little different on my RV-6A. I've  tested Van's original magnet scheme and found that my O-320-D1A engine doesn't  open it under normal take off conditions. A plugged filter does open it OK.  (Don't ask how I know.)  The actual implementation of the trap door does  not open into the lower cowl, but rather, into the FAB box it self. There's  enough space between the bottom of the filter assembly and the FAB box  shell to allow for the intake air flow. This way, the carb heat is always  available to either filtered or unfiltered air. I periodically check the  position/operation of the trap door by inserting a stiff wire through a small  hole in the FAB box. And, yes, I epoxied the magnet into position so it can't  get detached.....

  

 Fred Stucklen

 RV-6A  N926RV

 720 Hrs  3'd offender

 Building an RV-7A

 

 

      --> RV-List  message posted by: Tim Lewis <Tim_Lewis(at)msm.umr.edu (Tim_Lewis(at)msm.umr.edu)>

      

       On my RV-6A (following involuntary glider training precipitated by snow  

      in the FAB) I built a somewhat complicated  filter bypass that takes the 

      carb heat air  (not hot enough to melt snow) and dumps it in the FAB  

      AFTER the air filter.   See

      <http://home.earthlink.net/~timrv6a/RV6_FAB.jpg>

      I like Van's alternate air solutions  better than what I built for my 

      -6A, but  Van's wasn't available at the time.

       

      For my RV-10 (IO-540) I'm using a hinged  alternate air door on the 

      bottom of the FAB  that opens and closes using the push/pull cable,  

      rather than the "one way" sliding door  arrangement.  Photo is at 

      <http://home.earthlink.net/~timrv6a/Alt_air.jpg>. I've not flown the -10 

       yet.

      

      Tim  Lewis

       N47TD

Display posts from previous:

	Matronics Email Lists Forum Index -> RV-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum