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Pitot Tube Help

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JLuckey(at)pacbell.net
Guest

Posted: Tue Jun 12, 2012 7:48 am Post subject: Pitot Tube Help

Off topic! (well it is electrically heated;)  Looking to capitalize on the Aerolectric Brain Trust to find an old pitot tube expert…  

   

I have a pitot tube, Aero Instrument PH504, (AN 5811-1), which is looks like a typical C-172 pitot tube (you know, “L” shaped with about a 4 in tube attached to an airfoil cross-section vertical piece.  When mounted under the wing on a C-172 the tube part would be closest to the ground.)  

   

However this one is designed for INVERTED mounting, apparently designed to be mounted to a top surface of an airframe (where the tube part would be furthest from the ground.)    

   

I’m pretty sure that the air doesn’t care which way the thing is mounted, as long as the tube is parallel to the air stream.  So my guess is that the Inverted model has drain holes in different places.  

   

Questions:    does drain hole position REALLY matter?  
Multiple Choice: What will happen in flight if      this device is mounted the standard way (not inverted) and it picks-up a      little moisture?      water in pitot lines                   
inaccurate airspeed indication    
the end of life as we know it   
smoking crater  
   

   

TIA,  

   

   

Jeff Luckey  

   

       [quote][b]

berkut13(at)berkut13.com
Guest

Posted: Tue Jun 12, 2012 8:05 am Post subject: Pitot Tube Help

Are you sure that hole is a drain and not a static port?

  

    

  From: Jeff Luckey (JLuckey(at)pacbell.net) 

 Sent: Tuesday, June 12, 2012 10:46 AM

 To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)  

 Subject: Pitot Tube Help

  



   

Off  topic! (well it is electrically heated;)  Looking to capitalize on the  Aerolectric Brain Trust to find an old pitot tube  expertâ€¦ 

  

I have  a pitot tube, Aero Instrument PH504, (AN 5811-1), which is looks like a typical  C-172 pitot tube (you know, â€œLâ€ shaped with about a 4 in tube attached to an  airfoil cross-section vertical piece.  When mounted under the wing on a  C-172 the tube part would be closest to the  ground.) 

  

However  this one is designed for INVERTED mounting, apparently designed to be mounted to  a top surface of an airframe (where the tube part would be furthest from the  ground.)   

  

Iâ€™m  pretty sure that the air doesnâ€™t care which way the thing is mounted, as long as  the tube is parallel to the air stream.  So my guess is that the Inverted  model has drain holes in different places. 

  

Questions:    does drain hole position REALLY    matter?    
Multiple Choice: What will happen in    flight if this device is mounted the standard way (not inverted) and it    picks-up a little moisture?         water in pitot      lines                    
inaccurate airspeed indication           
the end of life as we know      it      
smoking      crater  

  

TIA, 

  

  

Jeff  Luckey 

 

[quote]



href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List

href="http://forums.matronics.com">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/c

[b]

JLuckey(at)pacbell.net
Guest

Posted: Tue Jun 12, 2012 8:28 am Post subject: Pitot Tube Help

Yes, drawing that came with the unit indicates Drain Hole  

         

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of berkut13(at)berkut13.com

 Sent: Tuesday, June 12, 2012 09:03

 To: aeroelectric-list(at)matronics.com

 Subject: Re: AeroElectric-List: Pitot Tube Help  

  

         

Are you sure that hole is a drain and not a static port?  

    

   

        

   

      

From: Jeff Luckey (JLuckey(at)pacbell.net)   

    

Sent: Tuesday, June 12, 2012 10:46 AM  

    

To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)   

    

Subject: Pitot Tube Help  

  

  

    

   

  

    

Off topic! (well it is electrically heated;)  Looking to capitalize on the Aerolectric Brain Trust to find an old pitot tube expert…  

   

I have a pitot tube, Aero Instrument PH504, (AN 5811-1), which is looks like a typical C-172 pitot tube (you know, “L” shaped with about a 4 in tube attached to an airfoil cross-section vertical piece.  When mounted under the wing on a C-172 the tube part would be closest to the ground.)  

   

However this one is designed for INVERTED mounting, apparently designed to be mounted to a top surface of an airframe (where the tube part would be furthest from the ground.)    

   

I’m pretty sure that the air doesn’t care which way the thing is mounted, as long as the tube is parallel to the air stream.  So my guess is that the Inverted model has drain holes in different places.  

   

Questions:    does drain hole      position REALLY matter?   
Multiple Choice:      What will happen in flight if this device is mounted the standard way (not      inverted) and it picks-up a little moisture?  
       water in pitot       lines             
inaccurate airspeed       indication    
the end of life as       we know it    
smoking crater         
   

   

TIA,  

   

   

Jeff Luckey  

    	  Quote: 	
		    href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-Listhref="http://forums.matronics.com">http://forums.matronics.comhref="http://www.matronics.com/contribution">http://www.matronics.com/c   	
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 06/12/12    [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 12, 2012 1:41 pm Post subject: Pitot Tube Help

From: Jeff Luckey 

 Sent: Tuesday, June 12, 2012 10:46 AM

 To: aeroelectric-list(at)matronics.com 

 Subject: Pitot Tube Help

 Off topic! (well it is electrically heated;)  Looking to capitalize on the Aerolectric Brain Trust to find an old pitot tube expert…

 I have a pitot tube, Aero Instrument PH504, (AN 5811-1), which is looks like a typical C-172 pitot tube (you know, “L” shaped with about a 4 in tube attached to an airfoil cross-section vertical piece.  When mounted under the wing on a C-172 the tube part would be closest to the ground.)

 However this one is designed for INVERTED mounting, apparently designed to be mounted to a top surface of an airframe (where the tube part would be furthest from the ground.)  

 I’m pretty sure that the air doesn’t care which way the thing is mounted, as long as the tube is parallel to the air stream.  So my guess is that the Inverted model has drain holes in different places.

 Questions:

 does drain hole position REALLY matter?   Multiple Choice: What will happen in flight if this device is mounted the standard way (not inverted) and it picks-up a little moisture?  
water in pitot lines           
inaccurate airspeed indication  
the end of life as we know it  
smoking crater      A modern pitot tube is a complex study in aerodynamics,  pneumatics, thermal dynamics and manufacturing. Contemporary  design goals for a 'qualified' pitot tube calls for testing  in an icing tunnel that is supposed to be sort of a worst case  icing condition.

   http://tinyurl.com/7pmnqta

  [img]cid:.0[/img]

  The idea is to melt any ice accumulation and provide a place  for the moisture to go besides into the pitot-static plumbing.  At the same time, many airplanes are fitted with accumulators  at the system's low-spot that include a drain for removing  any water.

  Some years ago at HBC, we had a series of incidents involving  loss of pitot data on both sides at the same time at altitude  with no visible moisture (clouds or ice crystals). Both systems  recovered before the airplane landed and draining the accumulators  produced no observable moisture.

  The pitot tubes installed were grand-fathered over from earlier  installations and not 'qualified' to the latest and greatest  de-icing specs. In fact, the tubes were originally installed  pointed up at about 45 degree angle and had been moved to the  bottom pointed downward thus placing the drain hole in the  wrong clocking.

  New, latest and greatest tubes were installed. I'm not aware  of any recurring incidents . . . need to make some phone calls.  I'm a bit skeptical. I did some flight tests on the original  tubes to measure internal and temperatures. The areas all over  the tube remained well above freezing (LT1, LT3, LT4 curves

  in  http://tinyurl.com/74yr5q8   )

  The idea that there was frozen blockage of passages inside the  tube didn't compute. So even if water did run down into the  plumbing, where did it come from? Thawed ice crystals? Your  guess is as good as mine. In any case, position of the drain  hole was certainly not a high order concern. What I did come to understand was that unless your heated pitot  tube is mounted to a machine qualified for flight into known  icing, the ability to heat the tube is of limited usefulness.  Once the tube is overwhelmed the flight characteristics (airfoil  shapes) combined with added weight of ice make sort of pollutes  the value of knowing indicated airspeed. The recommended process  being to get to warmer altitudes without without changing anything  that would move you closer to the low-speed corner of a flight  envelope that is no longer defined.

  What you have is probably a fine device for use outside of  icing conditions. Inside icing conditions becomes a toss-up  as to whether the flight qualities airplane or the instrumentation  get overwhelmed first. 

  Wire that heater up if it makes you feel any better but  know that having good IAS numbers is only part of the equation.  Got a real good lesson during my only in-flight instrument  approach in icing conditions. In this case, my instructor  was sitting there calmly waiting for me to figure it out all  the way down to the flare after having kept all the needles  centered up for over 15 minutes in the clouds.

  The airplane fell out of the air and muffed what was  supposed to be a good "by the numbers" landing . . . numbers  that no longer represented the shape of the wing. Bottom  line is that ice presents worries that can be a lot more  hazardous than IAS numbers.

    Bob . . .

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BobsV35B(at)aol.com
Guest

Posted: Tue Jun 12, 2012 2:10 pm Post subject: Pitot Tube Help

Good Afternoon Bob,

  

 We have had this same discussion before and I think we agreed to disagree,  but since you presented your side of the discussion, mind if I add mine?

  

 Ice is where you find it. 

  

 Icing forecasts are not real reliable and if you never fly in conditions  where ice is a  possibility, you deprive yourself of a lot of flexibility.  

  

 Some say that the way to handle ice is to avoid it. 

  

 My thought is that the way to handle ice is to keep a good way handy to get  out of the ice. 

  

 That has worked well for me over the last 62 years since I earned my  Instrument rating.

  

 I do agree with you that we can fly adequately and safely without an  airspeed indicator, but faster airplanes do make speed control much easier if we  have a good airspeed indication. 

  

 In my book, a couple hundred bucks spent to get a heated pitot tube is  money well spent.

  

 Just this old guy's opinion!<G>

  

 Happy Skies,

  

 Old Bob

 Downers Grove Illinois

 Stearman N3977A

 Beech V35B N20318

  

  In a message dated 6/12/2012 4:44:10 P.M. Central Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  

From: Jeff Luckey 

Sent: Tuesday, June 12, 2012 10:46    AM

To: aeroelectric-list(at)matronics.com 

Subject: AeroElectric-List:    Pitot Tube Help

 

Off topic! (well it is electrically    heated;)  Looking to capitalize on the Aerolectric Brain Trust to find an    old pitot tube expertâ€¦

 

I have a pitot tube, Aero Instrument    PH504, (AN 5811-1), which is looks like a typical C-172 pitot tube (you know,    â€œLâ€ shaped with about a 4 in tube attached to an airfoil cross-section    vertical piece.  When mounted under the wing on a C-172 the tube part    would be closest to the ground.)

 

However this one is designed for    INVERTED mounting, apparently designed to be mounted to a top surface of an    airframe (where the tube part would be furthest from the ground.)     

 

Iâ€™m pretty sure that the air doesnâ€™t care which way the thing is    mounted, as long as the tube is parallel to the air stream.  So my guess    is that the Inverted model has drain holes in different    places.

 

Questions:

does drain hole position REALLY matter?         Multiple Choice: What will happen in flight if this device is mounted      the standard way (not inverted) and it picks-up a little moisture?      
water in pitot      lines               
inaccurate airspeed indication      
the end of life as we know it      
smoking crater           A modern pitot tube is a complex study in aerodynamics,      pneumatics, thermal dynamics and manufacturing. Contemporary      design goals for a 'qualified' pitot tube calls for testing      in an icing tunnel that is supposed to be sort of a worst case      icing condition.



     http://tinyurl.com/7pmnqta



     



     The idea is to melt any ice accumulation and provide a place      for the moisture to go besides into the pitot-static plumbing.      At the same time, many airplanes are fitted with accumulators      at the system's low-spot that include a drain for removing      any water.

     Some years ago at HBC, we had a series of incidents involving      loss of pitot data on both sides at the same time at altitude      with no visible moisture (clouds or ice crystals). Both systems      recovered before the airplane landed and draining the accumulators      produced no observable moisture.



     The pitot tubes installed were grand-fathered over from earlier      installations and not 'qualified' to the latest and greatest      de-icing specs. In fact, the tubes were originally installed      pointed up at about 45 degree angle and had been moved to the      bottom pointed downward thus placing the drain hole in the      wrong clocking.

     New, latest and greatest tubes were installed. I'm not aware      of any recurring incidents . . . need to make some phone calls.      I'm a bit skeptical. I did some flight tests on the original      tubes to measure internal and temperatures. The areas all over      the tube remained well above freezing (LT1, LT3, LT4 curves

     in http://tinyurl.com/74yr5q8  )

     The idea that there was frozen blockage of passages inside the      tube didn't compute. So even if water did run down into the      plumbing, where did it come from? Thawed ice crystals? Your      guess is as good as mine. In any case, position of the drain      hole was certainly not a high order concern.      What I did come to understand was that unless your heated pitot      tube is mounted to a machine qualified for flight into known      icing, the ability to heat the tube is of limited usefulness.      Once the tube is overwhelmed the flight characteristics (airfoil      shapes) combined with added weight of ice make sort of pollutes      the value of knowing indicated airspeed. The recommended process      being to get to warmer altitudes without without changing anything      that would move you closer to the low-speed corner of a flight      envelope that is no longer defined.



     What you have is probably a fine device for use outside of      icing conditions. Inside icing conditions becomes a toss-up      as to whether the flight qualities airplane or the instrumentation      get overwhelmed first. 

     Wire that heater up if it makes you feel any better but      know that having good IAS numbers is only part of the equation.      Got a real good lesson during my only in-flight instrument      approach in icing conditions. In this case, my instructor      was sitting there calmly waiting for me to figure it out all      the way down to the flare after having kept all the needles      centered up for over 15 minutes in the clouds.

     The airplane fell out of the air and muffed what was      supposed to be a good "by the numbers" landing . . . numbers      that no longer represented the shape of the wing. Bottom      line is that ice presents worries that can be a lot more      hazardous than IAS numbers.

     

  Bob . . .

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Jun 13, 2012 4:45 am Post subject: Re: Pitot Tube Help

My 2 cents:



I have kept the attached drawing of a pitot tube around to remind me that there are lots of ways to go, and lots that is known that I don't know.

pitotc46.pdf

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

BobsV35B(at)aol.com
Guest

Posted: Wed Jun 13, 2012 5:34 am Post subject: Pitot Tube Help

Good Morning Eric,

  

 Sure looks busy!

  

 Happy skies,

  

 Old Bob

  

  In a message dated 6/13/2012 7:49:00 A.M. Central Daylight Time,  emjones(at)charter.net writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "Eric M. Jones"    <emjones(at)charter.net>



My 2 cents:



I have kept the attached    drawing of a pitot tube around to remind me that there are lots of ways to go,    and lots that is known that I don't know.



--------

Eric M.    Jones

www.PerihelionDesign.com

113 Brentwood Drive

Southbridge, MA    01550

(508) 764-2072

emjones(at)charter.net





Read this    topic online    here:



http://forums.matronics.com/viewtopic.php?p=375506#375506





Attachments:    



http://forums.matronics.com//files/pitotc46_198.pdf



	


 [quote][b]

deej(at)deej.net
Guest

Posted: Wed Jun 13, 2012 6:23 am Post subject: Pitot Tube Help

On 6/13/2012 9:32 AM, BobsV35B(at)aol.com (BobsV35B(at)aol.com)       wrote:

     

      	  Quote: 	
		                                Sure looks busy!

          

       

     	
     

         Yeah, I'm having pitot envy.  The pitot tube on my plane is     literally just an aluminum tube bent into the wind...  

     

     -Dj

     [quote]

[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 13, 2012 10:33 am Post subject: Pitot Tube Help

One data point for those who care: I connected the heater to a 12V 

power supply and found that after about a minute the current was 

about 2.5 amps (at) 12.8 volts and the tube was hot enough to sizzle 

spit, literally.  The tube is rated for 24V.



Which brings up another set of design goals for

heated pitot installation. How much energy and

under what conditions are needed for perfomance

to design goals. While doing those studies for

HBC I crafted this paper on heater temperature

coefficient of resistance and thermal resistance

from heater to tube.



http://tinyurl.com/7778mm5



When operated in insulated, still air, the 13v pitot

tube temperature rose to over 100C with less than

2 volts applied power. When operated at rated voltage

in a stirred ice bath, the surface of the tube was

of course at 0C but the internal heater was running

at about 270 degrees C.



Modern tubes don't have so large a differential. Another

important revelation was the cold start resistance of the

pitot tube. Just coming up from 0C, the tube wanted

30+ amps of inrush that persisted quite awhile. It took

about 30 seconds for the current to stabilize at the

expected 16 amps of steady state draw.



During one set of flight tests, we installed thermocouples



http://tinyurl.com/6o5hpdk



and produced this data set



http://tinyurl.com/7ougkfu



  Note that at 40K feet, -50C OAT and IAS about 200 kts,

the hot spot on the tube (Ta) was 100C or better. That

cold air blasting the tube at high velocity doesn't have

very good cooling qualities at such low ambient pressures.

   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu Jun 14, 2012 10:46 am Post subject: Re: Pitot Tube Help

I was always of the opinion that a heated pitot tube would be very useful for home-built aircraft even it it wasn't certified for known-icing-conditions at 30,000 feet and jet plane speeds. Furthermore the reason pitot tubes are heated with such high power is because they are made of material that conducts heat rapidly. A strange design to be sure.



For those interested in my old Thermostatic Pitot Tube see:



http://www.periheliondesign.com/downloads/thermopitot.pdf



I test it outside my workshop every time an ice-storm dumps on New England...and it performs flawlessly. Everything else is iced over while it is not. No flight tests yet.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

gerry.vandyk(at)shaw.ca
Guest

Posted: Thu Jun 14, 2012 11:23 am Post subject: Pitot Tube Help

Here in Canada the equipment regs for IFR flight require the pitot be heated.  Is this not the case in the US?

Gerry



---

jay(at)horriblehyde.com
Guest

Posted: Thu Jun 14, 2012 9:05 pm Post subject: Pitot Tube Help

Looks great Eric!  Very interesting page...



Jay



--

millner(at)me.com
Guest

Posted: Mon Jun 18, 2012 8:36 am Post subject: Pitot Tube Help

Not required on the US.



Paul



On 6/14/2012 12:20 PM, GERRY VAN%20DYK wrote:

 	  Quote: 	
		   Here in Canada the equipment regs for IFR flight require the pitot be heated.  Is this not the case in the US?


	


-- 

Please note my new email address!

millner(at)me.com

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