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Pitot Current Draw
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cjensen(at)dts9000.com
Guest

Posted: Sun Dec 03, 2006 1:14 pm Post subject: Pitot Current Draw

I have a pitot on an Exp. Aircraft that was designed for a heavier

aircraft.  To accommodate the high speed and high altitude cold, the

pitot was configured to get very hot, with consumate amperage demand.

Given the lower demands of a GA aircraft, is there any way of reducing

the heating of the pitot (very warm to the touch would be fine...I don't

need to be able to brand someone!) with a consumate reduction in

amperage demand? 



Chuck Jensen

retasker(at)optonline.net
Guest

Posted: Sun Dec 03, 2006 2:05 pm Post subject: Pitot Current Draw

There are ways, but what leads you to believe that the pitot is really 

too hot?  The whole purpose of the heater is to keep it clear in any 

condition - rain, freezing rain, cold ambient, etc.  Depending on what 

plane you have, you will be flying at upwards of 200 mph through all 

this (hopefully NOT freezing rain) and the last thing you want is for 

the pitot to freeze up.



Dick Tasker



Chuck Jensen wrote:



 	  Quote: 	
		  



I have a pitot on an Exp. Aircraft that was designed for a heavier

aircraft.  To accommodate the high speed and high altitude cold, the

pitot was configured to get very hot, with consumate amperage demand.

Given the lower demands of a GA aircraft, is there any way of reducing

the heating of the pitot (very warm to the touch would be fine...I don't

need to be able to brand someone!) with a consumate reduction in

amperage demand? 



Chuck Jensen

  




	


-- 

Please Note: 

No trees were destroyed in the sending of this message.  We do concede, however,

that a significant number of electrons may have been temporarily inconvenienced.

--

riggs_la(at)yahoo.com
Guest

Posted: Sun Dec 03, 2006 5:59 pm Post subject: Pitot Current Draw

I would like to add that the pitot tube should burn your hand if you grab it after it has been on for more than 1 or 2 minutes.



"Richard E. Tasker" <retasker(at)optonline.net> wrote:[quote] --> AeroElectric-List message posted by: "Richard E. Tasker" 



There are ways, but what leads you to believe that the pitot is really 

too hot?  The whole purpose of the heater is to keep it clear in any 

condition - rain, freezing rain, cold ambient, etc.  Depending on what 

plane you have, you will be flying at upwards of 200 mph through all 

this (hopefully NOT freezing rain) and the last thing you want is for 

the pitot to freeze up.



Dick Tasker



Chuck Jensen wrote:



[quote]--> AeroElectric-List message posted by: "Chuck Jensen" 



I have a pitot on an Exp.  [quote][b]

oldbob(at)BeechOwners.com
Guest

Posted: Sun Dec 03, 2006 7:03 pm Post subject: Pitot Current Draw

Good Evening Lynn, Dick and Chuck,



In a previous life, I flew quite a few airplanes that

had a high and a low heat for the pitot tubes. They

were on low for ground operations and on high heat for

airborne use.



I think it was controlled by a strut switch, but not

sure.



Worked well though.



Happy Skies,  



Old Bob

--- Lynn Riggs <riggs_la(at)yahoo.com> wrote:



 	  Quote: 	
		   I would like to add that the pitot tube should burn

 your hand if you grab it after it has been on for

 more than 1 or 2 minutes.

 

 "Richard E. Tasker" <retasker(at)optonline.net> wrote:

 

 Tasker" 

 

 There are ways, but what leads you to believe that

 the pitot is really 

 too hot?  The whole purpose of the heater is to keep

 it clear in any 

 condition - rain, freezing rain, cold ambient, etc. 

 Depending on what 

 plane you have, you will be flying at upwards of 200

 mph through all 

 this (hopefully NOT freezing rain) and the last

 thing you want is for 

 the pitot to freeze up.

 

 Dick Tasker

 

 Chuck Jensen wrote:

 

 >

 Jensen" 

 >

 >I have a pitot on an Exp. Aircraft that was

 designed for a heavier

 >aircraft.  To accommodate the high speed and high

 altitude cold, the

 >pitot was configured to get very hot, with

 consumate amperage demand.

 >Given the lower demands of a GA aircraft, is there

 any way of reducing

 >the heating of the pitot (very warm to the touch

 would be fine...I don't

 >need to be able to brand someone!) with a consumate

 reduction in

 >amperage demand? 

 >

 >Chuck Jensen

 >

 >

 >

 >

 >

 >

 >  

 >

 

 -- 

 Please Note: 

 No trees were destroyed in the sending of this

 message.  We do concede, however,

 that a significant number of electrons may have been

 temporarily inconvenienced.

 --

 

 

 

 

 

 

 

 

 Lynn A. Riggs

 riggs_la(at)yahoo.com

 St. Paul, MN

 BH #656 Kit #22



http://home.comcast.net/~lariggs/wsb/html/view.cgi-home.html-.html
	


 	  Quote: 	
		    

 ---------------------------------

nuckollsr(at)cox.net
Guest

Posted: Sun Dec 03, 2006 8:32 pm Post subject: Pitot Current Draw

At 04:13 PM 12/3/2006 -0500, you wrote:



 	  Quote: 	
		  



I have a pitot on an Exp. Aircraft that was designed for a heavier

aircraft.  To accommodate the high speed and high altitude cold, the

pitot was configured to get very hot, with consumate amperage demand.

Given the lower demands of a GA aircraft, is there any way of reducing

the heating of the pitot (very warm to the touch would be fine...I don't

need to be able to brand someone!) with a consumate reduction in

amperage demand?


	


   Altitude and speed have little to do with a pitot tube's

   need to transfer heat to the surface. The kind of ice that

   a pitot tube is expected to handle happens at lower altitudes

   and relatively slow speeds. It's the super-cooled water droplets

   that freeze instantly on contact that represent the largest

   challenge to the pitot tube's ability to shed ice.



   If you've ever witnessed an ice-tunnel test on a piece

   of aviation de-ice equipment, you'd realize that if your

   pitot tube is being seriously challenged, then knowing

   altitude and airspeed are probably the least of your concerns.



   Icing conditions you're likely to survive can probably be

   shed by a relatively whimpy pitot tube deice heater but these

   are exceedingly difficult things to quantify. Pitot tubes

   we THOUGHT were adequate 30 years ago are scoffed at today.



   Intuitively, your assertion is not in error, ANY amount of

   heat will shed SOME ice. SOME ice is survivable while OTHER

   ice is not. Given the changes in de-ice certification protocols

   over the years, it becomes difficult to put numbers on "any",

   "some" and "other". So difficult that for anyone to offer you

   advice advocating "this many watts as opposed to that many

   watts" may be blowing smoke you-know-where.



   When that stuff starts appearing anywhere on your airplane

   is not the time to be experimenting with the adequacy of

   your pitot heater decisions. The best rule of thumb is put

   on the biggest heater you can find/afford but plan on the

   expeditious 180 no matter how robust you belive your heater

   to be.



   Bob . . .

endspeed(at)yahoo.com
Guest

Posted: Sun Dec 03, 2006 9:54 pm Post subject: Pitot Current Draw

Hi Bob,



 Staying out of icing if possible is good advice.  I

lost pitot static instruments 2 or 3 times in a full

deicing equipped Navy jet over a 3 year period.  It

gives you quite a chill in the spinal area to see your

airspeed dropping off so quickly to zero. I happened

to be level at the time of loss.  Icing of the pitot

tube turns your airspeed indicator into an altimeter

for all intents and purposes.  The higher you go the

higher the airspeed you'll see. The lower you go the

lower the airspeed.  You can see how hazardous that is

since you'll climb and show higher airspeed with the

nose way up, right to the stall and spin.  Another

sound piece of advice is to know what airspeed a given

attitude and power setting will give you and don't

mess with your configuration any more than necessary

to land.  



Safe flying, 

Bob Sultzbach





 

Need a quick answer? Get one in minutes from people who know.

Ask your question on www.Answers.yahoo.com

cjensen(at)dts9000.com
Guest

Posted: Mon Dec 04, 2006 4:14 am Post subject: Pitot Current Draw

Okay, I appreciate everyone holding forth that it's stupid to fly in

ice....I'm not that dumb, I only look it. However, the question stands,

how does one knock down the heat and current draw.  Richard mentioned a

'strut switch'....whoever that is.  Can someone enlighten us

non-electrical types.  What I'm concerned about is being in the clouds,

close to freezing and loose electrical--I'd just as soon not have to

turn off the pitot heat because it's sucking the battery dry in short

order; I'd rather it be in long order.



Chuck Jensen

 

--

oldbob(at)BeechOwners.com
Guest

Posted: Mon Dec 04, 2006 4:38 am Post subject: Pitot Current Draw

Good Morning Chuck,



Believe 'twas I who mentioned a strut switch.



In any case it is switch mounted on a landing gear

strut that switches something on or off when the

aircraft is airborne.



Such a switch is often used to prevent gear retraction

when the aircraft is on the ground.



It is not at all uncommon to have a strut switch on a

nose gear that will actuate a relay which controls

multiple functions when the aircraft is airborne.



The dual heat pitot tube has often been activated by a

nose gear strut switch on airplanes I have flown.



I have never seen a pilot activated switch that

handled that function, but I see no reason why one

could not be installed if that is your desire. 



You could even have multiple heat choices if you

wanted the added complication.

 

Happy Skies,



Old Bob

--- Chuck Jensen <cjensen(at)dts9000.com> wrote:



[quote] 

 Jensen" <cjensen(at)dts9000.com>

 

 Okay, I appreciate everyone holding forth that it's

 stupid to fly in

 ice....I'm not that dumb, I only look it. However,

 the question stands,

 how does one knock down the heat and current draw. 

 Richard mentioned a

 'strut switch'....whoever that is.  Can someone

 enlighten us

 non-electrical types.  What I'm concerned about is

 being in the clouds,

 close to freezing and loose electrical--I'd just as

 soon not have to

 turn off the pitot heat because it's sucking the

 battery dry in short

 order; I'd rather it be in long order.

 

 Chuck Jensen

  

 

 

 --

echristley(at)nc.rr.com
Guest

Posted: Mon Dec 04, 2006 6:27 am Post subject: Pitot Current Draw

Robert Sultzbach wrote:



 	  Quote: 	
		  



Hi Bob,



 Staying out of icing if possible is good advice.  I

lost pitot static instruments 2 or 3 times in a full

deicing equipped Navy jet over a 3 year period.  




	


I've been following this thread, and this post begs the question I've 

been mulling over.



What good is a heated pitot in an airplane without deicing equipment?  

I'm thinking that if the pitot is covered in ice, then so is the rest of 

the plane.  Your airspeed is now next to useless, because all those 

stall speed numbers are now meaningless.  Whatever they were before, 

they changed when the ice modified all the airfoils and the CG.  A 

cockpit referenced backup altimeter would seem to give the best bang for 

the $time$...not terribly accurate, but sufficient to keep you out of 

cumulous granite until you can improve your situation.



Ernest (a sunny day flyer).



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

Bruce(at)glasair.org
Guest

Posted: Mon Dec 04, 2006 6:47 am Post subject: Pitot Current Draw

Didn't your CFII tell you to break the glass on the VSI if that happens. But

your altimeter wouldn't be effected by a pitot blockage. We all have heated

static ports, right? Alternate static air valves?



Bruce

www.glasair.org

 



--

Bret Smith

Joined: 09 Jan 2006
Posts: 178
Location: Mineral Bluff, GA

Posted: Mon Dec 04, 2006 7:32 am Post subject: Pitot Current Draw

Chuck,



Thank you for addressing this scenario.  I, too, would like to hear others 

respond.  As for me, icing or not, if I lose my main alternator, I would 

switch on Endurance mode (which is only 8 amps...thus, no pitot) and land 

that puppy ASAP.  This is not an emergent situation.  Not so with your stock 

Cessna.



A well designed electrical system can make a huge difference in the outcome 

of a flight.



Bret Smith

---

_________________
Bret Smith
RV-9A (Emp)

echristley(at)nc.rr.com
Guest

Posted: Mon Dec 04, 2006 9:51 am Post subject: Pitot Current Draw

Bruce Gray wrote:



 	  Quote: 	
		  



Didn't your CFII tell you to break the glass on the VSI if that happens. But

your altimeter wouldn't be effected by a pitot blockage. We all have heated

static ports, right? Alternate static air valves?



Bruce

www.glasair.org

 



  




	


Hard to do without a mechanical VSI 8*)     Breaking the glass on your 

EFIS is just not pretty.  If I did have a mechanical VSI, I still 

wouldn't break the glass on it.  Just no point in going around busting 

up perfectly good instruments.



I assume that if ice is building up to block the pitot, the static is 

very close to being next in line.  Then you have to be aware enough to 

notice that something is sneaking up on you.  I've never had it happen, 

but what I understand is that the meter slowly becomes more and more 

innacurate.  It doesn't just fall over dead.  A backup device feeding 

from a safe alternate source (like cabin air), will give you a much 

quicker heads up.



That might be a good feature to have on an EFIS.  Compare the cabin to 

static pressures and raise an alarm if they get out of range...then 

display both 'altitudes' if the pilot chooses.



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

cjensen(at)dts9000.com
Guest

Posted: Mon Dec 04, 2006 12:06 pm Post subject: Pitot Current Draw

Wow, I must be hard-of-speaking (or writing).  I concede that flying

into icing when not so equipped is not a good idea, but if a person

flies IFR in the winter most anywhere in the continental US, sooner or

later, they'll pick up some ice.  Even if my wings start looking like

something that should be used to cool a gin and tonic, I don't want to

lose air speed indication.  Granted, I may not know what my new stall

speed is, but I would like to know WHAT my speed is...and I can't do

that with a pitot full of ice.  



So, the question on the table is still the same, is there a way off

'turning down the heat' and reducing current draw? 



Chuck Jensen

 

--

cjensen(at)dts9000.com
Guest

Posted: Mon Dec 04, 2006 12:30 pm Post subject: Pitot Current Draw

Old Bob,



I reread your posting more carefully this time which leads me to a

follow up question.  Now that I understand what a 'strut switch' is

(which I knew by a different name), I'm curious how the 'low heat' for

the ground operations worked.  In other words, how did it provide low

heat on the ground and high heat in the air?



Chuck Jensen

 

--

oldbob(at)BeechOwners.com
Guest

Posted: Mon Dec 04, 2006 3:50 pm Post subject: Pitot Current Draw

Good Evening Chuck,



That I do not know much about, but I do recall one

airplane where the low power was twenty eight volt DC

and the high temperature used 115 volt, 400 cycle, AC.



I would imagibne all of the varying power ones used

some variaton of high and low voltages.



Dropping resistors sure wouldn't solve your problem,

but an electronically cycled DC voltage may work. 



Hopefully, 'Lectric Bob will have an idea!



Happy Skies,



Old Bob

--- Chuck Jensen <cjensen(at)dts9000.com> wrote:



[quote] 

 Jensen" <cjensen(at)dts9000.com>

 

 Old Bob,

 

 I reread your posting more carefully this time which

 leads me to a

 follow up question.  Now that I understand what a

 'strut switch' is

 (which I knew by a different name), I'm curious how

 the 'low heat' for

 the ground operations worked.  In other words, how

 did it provide low

 heat on the ground and high heat in the air?

 

 Chuck Jensen

  

 

 

 --

George McNutt

Joined: 09 Jan 2006
Posts: 30

Posted: Mon Dec 04, 2006 6:42 pm Post subject: Pitot Current Draw

Pitch reference - Yes, if you want to paint a gloomy  picture lets throw 

in night time, snow showers, over water and your venturi icing up and 

the gyros slowing down, well with a heated pitot at least you could 

still fly needle ball and airspeed! Lost a friend who did not have pitot 

heat, you cannot fly with needle ball and altimeter.



George in Langley BC

 	  Quote: 	
		  

 I've been following this thread, and this post begs the question I've 

 been mulling over.



 What good is a heated pitot in an airplane without deicing equipment?  

 I'm thinking that if the pitot is covered in ice, then so is the rest 

 of the plane.  Your airspeed is now next to useless, because all those 

 stall speed numbers are now meaningless.  Whatever they were before, 

 they changed when the ice modified all the airfoils and the CG.  A 

 cockpit referenced backup altimeter would seem to give the best bang 

 for the $time$...not terribly accurate, but sufficient to keep you out 

 of cumulous granite until you can improve your situation.



 Ernest (a sunny day flyer).

KeithHallsten(at)quiknet.
Guest

Posted: Mon Dec 04, 2006 7:36 pm Post subject: Pitot Current Draw

Chuck,  

I mounted a 28v “Known Ice” pitot on the nose of my Velocity.  Since I have a 14 volt electrical system, its power consumption will be reduced by a factor of 4 (power = V * V / R).  I figure that is sufficient for my purposes, because a Velocity is NOT a “Known Ice” type of airframe.  If I should find enough ice to overwhelm my “lightweight” pitot heating system, I have bigger problems than the pitot.  I’m not flying yet, but that’s my position for now.  

  

Actually, now that we all have GPS available to us, loss of pitot is not as critical as it used to be.  With a fat margin to allow for wind, flying by groundspeed is generally a fair approximation.  

Regards,  

Keith Hallsten 

  

Subject:                RE: Pitot Current Draw 

 From:           Chuck Jensen (cjensen(at)dts9000.com ([email]cjensen(at)dts9000.com?subject=RE:%20Pitot%20Current%20Draw&replyto=8984A39879F2F5418251CBEEC9C689B32870D7(at)lucky.dts.local[/email]))     

 Date:           Mon Dec 04 - 12:06 PM  

 Wow, I must be hard-of-speaking (or writing).  I concede that flying  

into icing when not so equipped is not a good idea, but if a person  

flies IFR in the winter most anywhere in the continental US, sooner or  

later, they'll pick up some ice.  Even if my wings start looking like  

something that should be used to cool a gin and tonic, I don't want to  

lose air speed indication.  Granted, I may not know what my new stall  

speed is, but I would like to know WHAT my speed is...and I can't do  

that with a pitot full of ice.    

So, the question on the table is still the same, is there a way off  

'turning down the heat' and reducing current draw?   

Chuck Jensen 

  

     [quote][b]

cjensen(at)dts9000.com
Guest

Posted: Tue Dec 05, 2006 5:18 am Post subject: Pitot Current Draw

Hi,  Keith,

  

 That was exactly my  thought process also.  I didn't want a red hot branding iron to bore my way  through ice cubes...just warm enough to keep the pitot stuffed full of rain  water from freezing.  If the icing is bad enough that it freezes over a  warm-to-very warm pitot, I've got bigger problems that a red hot pitot won't  solve.

  

 Since no ideas have  been tossed out, I wonder if there is an efficient means of cycling the pitot  heater on/off at some interval, such as on for 30 seconds, off for two  minutes.  This would reduce the total current draw if a person was in the  soup, lost electrical and needed whatever extra time available to get to safety  but didn't dare to turn off the pitot in marginal icing  conditions.

  

 Chuck Jensen 

  

 

 --

Deems Davis

Joined: 09 Jan 2006
Posts: 925

Posted: Tue Dec 05, 2006 5:35 am Post subject: Pitot Current Draw

Chuck this is exactly what the Gretz heated pitot does. 

http://www.gretzaero.com/ (ie cycles the power on/off to keep it warm 

enough to melt ice, but not constantly hot.



Deems Davis  RV10 # 406

Finishing - ( A Misnomer ! )

http://deemsrv10.com/



Chuck Jensen wrote:



 	  Quote: 	
		   Hi, Keith,

  

  I wonder if there is an efficient means of cycling the pitot heater 

 on/off at some interval,

  

 Chuck Jensen 

 **



*

*

echristley(at)nc.rr.com
Guest

Posted: Tue Dec 05, 2006 6:41 am Post subject: Pitot Current Draw

OldBob Siegfried wrote:



 	  Quote: 	
		  Dropping resistors sure wouldn't solve your problem,

but an electronically cycled DC voltage may work. 



Hopefully, 'Lectric Bob will have an idea!



Happy Skies,



Old Bob

  




	


Actually, the dropping resistor could work.  Heat output is a function 

of wattage, which is given by V^2*R in a DC circuit.  If you could find 

a way to add an extra high wattage resister in series with the pitot 

heating element, you would be dropping the current requirement.  A 150 

watt heater is going to have a resistance around 1 ohm in a 12V system.  

Add a 1 ohm resistor in series, and the circuit will burn up 75 watts.  

The resistor will suck down 37.5W and the heater will get  37.5 

(ignoring line losses for the moment).  If you could find a way to use 

the pitot mounting as a heat sink for the resistor, it might actually be 

workable.



I still don't think it's a good use of $time$, but that's just me 8*)



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

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