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OAT probe position

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rv9jim(at)juno.com
Guest

Posted: Sun Jul 16, 2006 5:23 am Post subject: OAT probe position

I am about to hook up the outside air temp probe.  After consulting the

web (thank goodness) I am thinking about placing the sensor in the FAB

prior to the air filter in the snorkel area. My logic says it would give

me OAT with out the heating of the engine temps affecting it. It should

give me air temps for my EFIS to compute DA.  My second choice is the

inboard inspection panel in the wing.  The FAB position would require no

disconnecting.  Am I not seeing something?

Jim Nelson

RV9-A     FWF

klwerner(at)comcast.net
Guest

Posted: Sun Jul 16, 2006 7:21 am Post subject: OAT probe position

How about radiant engine heat  affecting the sensor? And isn't the FAB downstream of the cylinders, i.e. where  the heated air goes after cooling the fins?

  

 I'd put it under the wing, perhaps  right behind the pitot tube.

  

 do not archive

 [quote]   ---

lhelming(at)sigecom.net
Guest

Posted: Sun Jul 16, 2006 7:49 am Post subject: OAT probe position

You should put it near the wing inspection plate to have better, consistent 

readings.  Indiana Larry



---

ekells(at)sympatico.ca
Guest

Posted: Sun Jul 16, 2006 9:30 am Post subject: OAT probe position

I put a Davtron OAT instrument (ACS: page 374) beside the map box and the 

OAT probe beside the inner inspection plate on the right wing.

It comes prewired - it's long enough to install without cutting or adding 

wire.  Very accessible and very maintainable.

Seems remote enough from the prop/engine heat.



 	  Quote: 	
		   



 You should put it near the wing inspection plate to have better, 

 consistent readings.  Indiana Larry



> 

>

> I am about to hook up the outside air temp probe.  After consulting the

> web (thank goodness) I am thinking about placing the sensor in the FAB

> prior to the air filter in the snorkel area. My logic says it would give

> me OAT with out the heating of the engine temps affecting it. It should

> give me air temps for my EFIS to compute DA.  My second choice is the

> inboard inspection panel in the wing.  The FAB position would require no

> disconnecting.  Am I not seeing something?

denis.walsh(at)comcast.ne
Guest

Posted: Sun Jul 16, 2006 1:44 pm Post subject: OAT probe position

I have tried several positions and returned to my original choice.   

It is on the aft fuselage, right side, under the horizontal  

stabilizer.  It has virtually no errors, reads ok even at zero  

airspeed.  It is especially good for the Dynon since I have the  

magnetometer mounted on the deck in front of the stabilizer.  The  

wiring on the Dynon OAT probe goes to the magnetometer.



Only down side (pun) is that it is in the sun while inverted.  Since  

I only use that position momentarily it works well for me.

Denis Walsh



On Jul 16, 2006, at 07:22 265390007, James H Nelson wrote:



 	  Quote: 	
		   



 I am about to hook up the outside air temp probe.  After consulting  

 the

 web (thank goodness) I am thinking about placing the sensor in the FAB

 prior to the air filter in the snorkel area. My logic says it would  

 give

 me OAT with out the heating of the engine temps affecting it. It  

 should

 give me air temps for my EFIS to compute DA.  My second choice is the

 inboard inspection panel in the wing.  The FAB position would  

 require no

 disconnecting.  Am I not seeing something?

 Jim Nelson

 RV9-A     FWF

gmcjetpilot(at)yahoo.com
Guest

Posted: Mon Jul 17, 2006 2:48 am Post subject: OAT probe position

Jim: 

  

The recommendation to your idea is no. Anything in the 

engine compartment is HOT, even the inside of the FAB. 

Also you want to be as far away from the engine and prop 

air blast as practical like on the tail or outb'd wing. 

   

  The entire engine area is a heated zone. 



  I understand you think it is ahead of the heat. I guess if you 

had it on the tip of the spinner, but Anything in the engine 

compartment, inside the airbox included is hotter than the

ambient air temp of the air mass you are flying through.

   

  Common locations are lwr surface of wing tip or mid wing 

inspection cover or under horz tail in inspection elevator bell 

crank access cover. The further away from the engine  

in any direction the better.

   

  George M RV-4, RV-7

   

  

 	  Quote: 	
		  posted by: James H Nelson <rv9jim(at)juno.com (rv9jim(at)juno.com)>



I am thinking about placing the sensor in the FAB

prior to the air filter in the snorkel area. My logic says 

it would give me OAT with out the heating of the engine 

temps affecting it. It should give me air temps for my 

EFIS to compute DA.  My second choice is the inboard 

inspection panel in the wing.  The FAB position would 

require no disconnecting.  Am I not seeing something?

The inboard inspection wing location is fine. Besides 

how often are your wings going on and off after you 

start flying? Do you want to route more wires thru 

the fire wall  


	


  Get on board. [url=http://us.rd.yahoo.com/evt=40791/*http://advision.webevents.yahoo.com/handraisers]You're invited[/url] to try the new Yahoo! Mail Beta.

seiders(at)bellsouth.net
Guest

Posted: Mon Jul 17, 2006 4:44 am Post subject: OAT probe position

Naca duct works

At 09:22 AM 7/16/2006, you wrote:

 	  Quote: 	
		  



I am about to hook up the outside air temp probe.  After consulting the

web (thank goodness) I am thinking about placing the sensor in the FAB

prior to the air filter in the snorkel area. My logic says it would give

me OAT with out the heating of the engine temps affecting it. It should

give me air temps for my EFIS to compute DA.  My second choice is the

inboard inspection panel in the wing.  The FAB position would require no

disconnecting.  Am I not seeing something?

Jim Nelson

RV9-A     FWF

ronlee(at)pcisys.net
Guest

Posted: Mon Jul 17, 2006 5:25 am Post subject: OAT probe position

 	  Quote: 	
		  Naca duct works


	




Negative on an RV-6A. You get too much heat from the engine area.



Ron Lee

rveighta(at)earthlink.net
Guest

Posted: Mon Jul 17, 2006 5:42 am Post subject: OAT probe position

Jim, I originally had my OAT probe in the NACA duct, left side of the fuselage.

Bad move; the temp was way high. Then I moved it under the left wing and

it works fine.



I installed the probe in the inboard inspection plate by riveting a small block

of 1/8" thick aluminum, which I had drilled and threaded in the center to accept

the Westach probe body. The actual probe sticks out of the inspection plate

about 1/4".  



 Do not archive.

Walt Shipley  RV-8A Flying, RV-8 building



--

sisson(at)consolidated.ne
Guest

Posted: Mon Jul 17, 2006 5:42 am Post subject: OAT probe position

Konrad L. Werner wrote:

  	  Quote: 	
		                       How about radiant engine heat  affecting the sensor? And isn't the FAB downstream of the cylinders, i.e. where  the heated air goes after cooling the fins?

      

     I'd put it under the wing, perhaps  right behind the pitot tube.

      

     do not archive

 	
 That is exactly where I put mine. It works great. I have a Dynon unit. The factory lead was a little short. I called Rynon about lengthening it.  They said go ahead and make it what ever I needed. It is mounted a couple inches behind and in line with the pitot extension.

 

 Phil

 

 do not archive

khorton01(at)rogers.com
Guest

Posted: Mon Jul 17, 2006 6:17 am Post subject: OAT probe position

Nope, not if you want an accurate reading.  I was doing some glide  

performance testing on an RV-6 in the winter, and the OAT indication  

varied depending on how much cabin heat we had selected.  The back  

side of the probe was being warmed from the cockpit, and that was  

affecting the indication.  This would likely be an issue even if  

cabin heat was not selected, as the greenhouse effect from the canopy  

means the cockpit temperature is usually warmer than ambient.



Kevin Horton

On 17 Jul 2006, at 08:42, Richard Seiders wrote:



 	  Quote: 	
		   



 Naca duct works

 At 09:22 AM 7/16/2006, you wrote:

> 

>

> I am about to hook up the outside air temp probe.  After  

> consulting the

> web (thank goodness) I am thinking about placing the sensor in the  

> FAB

> prior to the air filter in the snorkel area. My logic says it  

> would give

> me OAT with out the heating of the engine temps affecting it. It  

> should

> give me air temps for my EFIS to compute DA.  My second choice is the

> inboard inspection panel in the wing.  The FAB position would  

> require no

> disconnecting.  Am I not seeing something?

>

Rick Galati

Joined: 10 Jan 2006
Posts: 91
Location: Lake St. Louis MO.

Posted: Mon Jul 17, 2006 6:21 am Post subject: Re: OAT probe position

Very true.  The only time my NACA duct mounted OAT probe is accurate is when the airplane has finally cooled down to the ambient temperature, such as occurs after being parked in the hangar overnight.  One of these days I will get around to relocating that probe and the farther away from the engine compartment, the better.  



Rick Galati  RV-6A  "Darla"  153 hours

 	  ronlee(at)pcisys.net wrote: 	
		   	  Quote: 	
		  Naca duct works



	




Negative on an RV-6A. You get too much heat from the engine area.



Ron Lee

macrafic

Joined: 01 May 2006
Posts: 5

Posted: Mon Jul 17, 2006 7:03 am Post subject: Re: OAT probe position

I had asked Dynon about the OAT position a few months ago.  They indicated that, while they could not tell me where to put it, that RV aircraft had had excellent results in the rear fuselage under the horizontal stabilizer.  Covering their legal positions while still trying to answer my question.  So, I'm going to go with the that soltion, the same one Denis Walsh has stated in another reply here.

klwerner(at)comcast.net
Guest

Posted: Mon Jul 17, 2006 7:55 am Post subject: OAT probe position

Well, what can I say:   Here's proof that Great Minds  think alike!

  

 do not archive

  

 [quote]   ---

seiders(at)bellsouth.net
Guest

Posted: Mon Jul 17, 2006 8:25 am Post subject: OAT probe position

Maybe on your 6A, not mine. My oat is consistent with in air temp reports. 

Guess it depends where you put it.

Dick



At 09:23 AM 7/17/2006, you wrote:

 	  Quote: 	
		  

>Naca duct works

Negative on an RV-6A. You get too much heat from the engine area.



Ron Lee

ronlee(at)pcisys.net
Guest

Posted: Mon Jul 17, 2006 9:49 am Post subject: OAT probe position

People can do anything even if wrong but with the prevailing comments that

away from the engine area is best why anyone would still go against good

advise is beyond me.



Ron Lee



 	  Quote: 	
		  Maybe on your 6A, not mine. My oat is consistent with in air temp reports. 

Guess it depends where you put it.

Dick



At 09:23 AM 7/17/2006, you wrote:

>

>>Naca duct works

>Negative on an RV-6A. You get too much heat from the engine area.

>

>Ron Lee

>

>

dan(at)rvproject.com
Guest

Posted: Mon Jul 17, 2006 10:27 am Post subject: OAT probe position

 	  Quote: 	
		   People can do anything even if wrong but with the prevailing comments that

 away from the engine area is best why anyone would still go against good

 advise is beyond me.



 Ron Lee


	


Well said, Ron!  If you put your OAT probe out under the wing, you KNOW it 

will not suffer from any other heat source.  If you put it anywhere else, 

like on the fuselage, under the HS, in your NACA vent, in your airbox, do 

you KNOW it will work?!  Where is there the LEAST risk of inaccuracy?  This 

is my new pet peeve!!!



If you don't care about OAT inaccuracy, leave the silly thing out!  If you 

fly IFR you will want one.  If you need it for density altitude 

calculations, then by all means don't put it where sun could hit it!!  Put 

it where you KNOW it will work!!  Argh!!



do not archive

)_( Dan

RV-7 N714D

http://www.rvproject.com

LessDragProd(at)aol.com
Guest

Posted: Mon Jul 17, 2006 11:23 am Post subject: OAT probe position

Of course, there is always the temperature rise due to  compressibility.

  

 I'm surprised some of the technocrats haven't jumped in on this.  At  200 mph, it should be about 3 degrees at the stagnation point.  Or 90% of  that in the boundary layer.

  

 I know there is a Mach number squared term in the equation, and someone is  bound to correct me that it is only a 2.45834659 degree rise.  Or some  other insignificantly different number.    

 Actually, 3 degrees is pretty insignificant, as long as it is  consistent.

  

 BTW, the RMI microencoder OAT calculates and compensates for the  compressibility temperature rise.  I haven't checked into the rest,  yet.

  

 Regards,

 Jim Ayers

  

 In a message dated 07/17/2006 11:28:50 AM Pacific Daylight Time,  dan(at)rvproject.com writes:

  	  Quote: 	
		  -->    RV-List message posted by: "Dan Checkoway"    <dan(at)rvproject.com>



 	  Quote: 	
		   People can do anything even if wrong but    with the prevailing comments that

 away from the engine area is best    why anyone would still go against good

 advise is beyond    me.



 Ron Lee


	


Well said, Ron!  If you put your OAT    probe out under the wing, you KNOW it 

will not suffer from any other heat    source.  If you put it anywhere else, 

like on the fuselage, under the    HS, in your NACA vent, in your airbox, do 

you KNOW it will work?!     Where is there the LEAST risk of inaccuracy?  This 

is my new pet    peeve!!!



If you don't care about OAT inaccuracy, leave the silly thing    out!  If you 

fly IFR you will want one.  If you need it for    density altitude 

calculations, then by all means don't put it where sun    could hit it!!  Put 

it where you KNOW it will work!!     Argh!!



do not archive

)_( Dan

RV-7    N714D

http://www.rvproject.com

khorton01(at)rogers.com
Guest

Posted: Mon Jul 17, 2006 1:44 pm Post subject: OAT probe position

Actually, rather than worrying about figuring out the mach number, there is an alternative equation that uses TAS:

OAT = IOAT - K*TAS^2/7592

where:

OAT = outside air temperature in deg C

IOAT = indicated OAT in deg C

K = recovery factor of the temperature probe.  Usually around 0.95, but the value could be different.

TAS = true airspeed in knots



Kevin Horton



On 17 Jul 2006, at 15:21, LessDragProd(at)aol.com (LessDragProd(at)aol.com) wrote:

 	  Quote: 	
		     Of course, there is always the temperature rise due to compressibility.

  

 I'm surprised some of the technocrats haven't jumped in on this.  At 200 mph, it should be about 3 degrees at the stagnation point.  Or 90% of that in the boundary layer.

  

 I know there is a Mach number squared term in the equation, and someone is bound to correct me that it is only a 2.45834659 degree rise.  Or some other insignificantly different number.    

 Actually, 3 degrees is pretty insignificant, as long as it is consistent.

  

 BTW, the RMI microencoder OAT calculates and compensates for the compressibility temperature rise.  I haven't checked into the rest, yet.

  

 Regards,

 Jim Ayers

  

 In a message dated 07/17/2006 11:28:50 AM Pacific Daylight Time, dan(at)rvproject.com (dan(at)rvproject.com) writes:

  	  Quote: 	
		  -->   RV-List message posted by: "Dan Checkoway"   <dan(at)rvproject.com (dan(at)rvproject.com)>



 	  Quote: 	
		   People can do anything even if wrong but   with the prevailing comments that

 away from the engine area is best   why anyone would still go against good

 advise is beyond   me.



 Ron Lee


	


Well said, Ron!  If you put your OAT   probe out under the wing, you KNOW it 

will not suffer from any other heat   source.  If you put it anywhere else, 

like on the fuselage, under the   HS, in your NACA vent, in your airbox, do 

you KNOW it will work?!    Where is there the LEAST risk of inaccuracy?  This 

is my new pet   peeve!!!



If you don't care about OAT inaccuracy, leave the silly thing   out!  If you 

fly IFR you will want one.  If you need it for   density altitude 

calculations, then by all means don't put it where sun   could hit it!!  Put 

it where you KNOW it will work!!    Argh!!



do not archive

)_( Dan

RV-7   N714D

http://www.rvproject.com

gmcjetpilot(at)yahoo.com
Guest

Posted: Tue Jul 18, 2006 1:18 am Post subject: OAT probe position

Is that true or indicated? MPH or Knots? Degrees F or C?

   

  >From: LessDragProd(at)aol.com

 	  Quote: 	
		  Of course, there is always the temperature rise due to  

compressibility.



I'm surprised some of the technocrats haven't jumped 

  >in on this.  At  200  mph, it should be about 3 degrees 
	


  >at the stagnation point.  Or 90% of  that in the boundary 

  >layer.

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