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Alternate static--was Door Flex

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dave.saylor.aircrafters(a
Guest

Posted: Sat Jan 30, 2010 9:05 am Post subject: Alternate static--was Door Flex

I have a story (confession) about alternate static.



I have a "toggle valve" for the alternate static port that just opens the static system to cabin pressure.  I think that's pretty standard.



At some point after test flying, I had the panel apart and managed to put the toggle in upside down, so "normal" was open to the cabin and "alternate" was the regular static system.

  

The result was that everything worked as advertised--airspeed, altimeter, encoder, all seemed normal enough that I didn't have any reason to suspect an error.  But, when we opened an air vent while using altitude hold, we got about a 50' climb, then level off and everything normal again.  Reverse when closing the vent.  The A/P was seeing higher pressure, equating it to lower altitude, and correcting.

  

I was convinced that the vent was upsetting airflow over the elevator trim.  Sometimes I'm really surprised at the lengths my brain will go to in order to make the pieces of a puzzle fit...



Anyway, the actual problem finally dawned on me, and I turned the toggle 180* to match the normal/alternate labels, and all was well.  Duh.

  Dave Saylor

AirCrafters LLC

140 Aviation Way

Watsonville, CA 95076

831-722-9141 Shop

831-750-0284 Cell

  [quote][b]

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Tim Olson

Joined: 25 Jan 2007
Posts: 2879

Posted: Sat Jan 30, 2010 9:18 am Post subject: Alternate static--was Door Flex

I have a toggle too. It's interesting to have the AP engaged and

flip the toggle open-closed-open-closed, and watch the plane

and altimeter/airspeed/vsi.



Tim Olson - RV-10 N104CD

do not archive

Dave Saylor wrote:

 	  Quote: 	
		   I have a story (confession) about alternate static.

 

 I have a "toggle valve" for the alternate static port that just opens 

 the static system to cabin pressure.  I think that's pretty standard.

 

 At some point after test flying, I had the panel apart and managed to 

 put the toggle in upside down, so "normal" was open to the cabin and 

 "alternate" was the regular static system.

 

 The result was that everything worked as advertised--airspeed, 

 altimeter, encoder, all seemed normal enough that I didn't have any 

 reason to suspect an error.  But, when we opened an air vent while using 

 altitude hold, we got about a 50' climb, then level off and everything 

 normal again.  Reverse when closing the vent.  The A/P was seeing higher 

 pressure, equating it to lower altitude, and correcting.

 

 I was convinced that the vent was upsetting airflow over the elevator 

 trim.  Sometimes I'm really surprised at the lengths my brain will go to 

 in order to make the pieces of a puzzle fit...

 

 Anyway, the actual problem finally dawned on me, and I turned the toggle 

 180* to match the normal/alternate labels, and all was well.  Duh.

 

 Dave Saylor

 AirCrafters LLC

 140 Aviation Way

 Watsonville, CA 95076

 831-722-9141 Shop

 831-750-0284 Cell

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orchidman

Joined: 10 Jul 2006
Posts: 277
Location: Oklahoma City - KRCE

Posted: Sat Jan 30, 2010 5:29 pm Post subject: Re: Alternate static--was Door Flex

 	  Tim Olson wrote: 	
		  I have a toggle too. It's interesting to have the AP engaged and

flip the toggle open-closed-open-closed, and watch the plane

and altimeter/airspeed/vsi.



Tim Olson - RV-10 N104CD

	


I am curious, what happens when you open/close the vents.  From my experiences, it does look like we are getting a fair amount of cabin pressurization when opening our vents.

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_________________
Gary Blankenbiller
RV10 - # 40674
(N2GB Flying)

Tim Olson

Joined: 25 Jan 2007
Posts: 2879

Posted: Sat Jan 30, 2010 7:48 pm Post subject: Alternate static--was Door Flex

I'll let you know this summer when I open my vents. . Got up to 14F  

today.

Tim

On Jan 30, 2010, at 7:29 PM, "orchidman" <gary(at)wingscc.com> wrote:

 	  Quote: 	

 Tim Olson wrote:

> I have a toggle too. It's interesting to have the AP engaged and

> flip the toggle open-closed-open-closed, and watch the plane

> and altimeter/airspeed/vsi.

>

> Tim Olson - RV-10 N104CD

>

 I am curious, what happens when you open/close the vents.  From my  

 experiences, it does look like we are getting a fair amount of cabin  

 pressurization when opening our vents.

 --------

 Gary Blankenbiller

 RV10 - # 40674

 (N2GB Flying)

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p 84105#284105

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