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Pitot Current Draw
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jan.de.jong(at)xs4all.nl
Guest

Posted: Fri Dec 08, 2006 4:51 am Post subject: Pitot Current Draw

As others have mentioned, the down side of this scheme is that



 	  Quote: 	
		        your bus gets whacked with a 15A pulse for each operating cycle

      of the heater system. One can explore relatively high frequency

      switching to avoid seeing the panel lights flicker (and believe

      me, they WILL) but this might cause audible noises elsewhere.

      Suggest about 30 Hz for minimum observability and below the

      audio frequencies of interest in the rest of your electro-whizzies.




	


There are >1F, < 2mOhm capacitors that one could use to mitigate:

http://www.electronixwarehouse.com/car/accessories/capacitors.htm#spl

(be careful charging/discharging - operate  like a short circuit)



15A for 1/60th causes 0.25V dip on charged 1F.



Maybe not as practical as buying off the shelf, but interesting.



Cheers,

Jan de Jong

cjensen(at)dts9000.com
Guest

Posted: Fri Dec 08, 2006 5:18 am Post subject: Pitot Current Draw

Craig/Matt/Bob/Bob  again/et al

  

 Thanks for the  technical responses which transcends the proclamation that only dummies fly in  ice.  And Stein, you have a point if I was only trying to use some reject  hand-me-down pitot and I was too cheap to get one of Gretz's very elegantly  functional pitots.  This isn't about functionality, this is about  aesthetics.  I have a sharkfin pitot off an old warbird that I use at the  tippy-point of the Velocity.  The sharkfin perfectly picks up the lines of  the winglets, yadda, yadda.....trust me, it's just a personal  preference.

  

 Unfortunately, the  heating elements in it were obviously designed for use in cold weather  areas.  In the winters, when they saw this sucker coming in, the ramp and  line crews left the warmth of their burning trash barrels to comeover and stand  by the pitot where there was some real heat!!!

  

 My conclusion is if  I want to keep the pitot (which I do), I either live with the current draw,  which is really not a serious problem for the 60amp alternator and just hope  I don't need it at the same time that I start suddenly have a shortage of  electrons.  While the resistor fix may work, because of the loss to  the resistor, the overall amperage reduction is minimal.....kind of like having  to spend a $100 to get a $20 tax reduction.

  

 The more attractive  alternative is duty cycle--assuming it doesn't put me in electron hell.   Anyhow, I appreciate the  many responses and the many tangents engaged.  As to those who thought the  thread went on too long and contain too much irrelevant material, just  remember--that's why we sort through the pile of straw and horse s--t that was  shoveled out of the horse barn with our bare hands---on the oft chance there  might be a pony in there somewhere.

 

Chuck Jensen 

  

 

 --

nuckollsr(at)cox.net
Guest

Posted: Fri Dec 08, 2006 5:18 am Post subject: Pitot Current Draw

At 10:30 PM 12/7/2006 -0600, you wrote:



 	  Quote: 	
		  Wow! This discussion has really taken on a mind of it's own....I see 

almost 41 posts in this thread! As usual and in my own sarcastic way, I'm 

really confused and boggled as to why we're even discussing this (and to 

the unbelievably detailed technical minutia that has arisen out of 

something like this)....when there is a perfectly good heated pitot on the 

market that does EXACTLY what you want it to do....it varies the current 

to the tube from .1 Amps to 7 Amps depending on it's own 

temperature.  When it doesn't need the heat it just idles, when it does it 

shoves more power out there.  Why re-invent the wheel...someone already 

has and his name is Warren Gretz!  I swear, just reading all these posts 

will waste more time than the $400 and some odd bucks it takes to buy one 

brand new....no messing around with all kinds of crazy little electrical 

components...bolt it on and go!


	


   If the ONLY reason to have a discussion is to make

   a buying decision on a product, then indeed discussing

   the physics upon which it operates may be a "waste of

   time" for some individuals. I'd like to believe that

   the folks who hang out here are also interested in

   acquiring a confidence in their decisions based on

   understanding as opposed to market popularity or

   customer faith in a particular product.



   I'm working an EMC problem at RAC right now that is

   generating a ton of $100/hr email generation and and

   digestion that ranges all the way from techs to

   division managers. 99% of what's been written so far

   has hashed over a lot of facts (knowledge) and feelings

   (popularity contests) but as engineers, our duty is

   to not only find and fix the problem but to help everyone

   understand how we got there.



   Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Fri Dec 08, 2006 5:40 am Post subject: Pitot Current Draw

At 02:01 PM 12/8/2006 +0100, you wrote:



 	  Quote: 	
		  



As others have mentioned, the down side of this scheme is that



>      your bus gets whacked with a 15A pulse for each operating cycle

>      of the heater system. One can explore relatively high frequency

>      switching to avoid seeing the panel lights flicker (and believe

>      me, they WILL) but this might cause audible noises elsewhere.

>      Suggest about 30 Hz for minimum observability and below the

>      audio frequencies of interest in the rest of your electro-whizzies.



There are >1F, < 2mOhm capacitors that one could use to mitigate:

http://www.electronixwarehouse.com/car/accessories/capacitors.htm#spl

(be careful charging/discharging - operate  like a short circuit)



15A for 1/60th causes 0.25V dip on charged 1F.



Maybe not as practical as buying off the shelf, but interesting.



Cheers,

Jan de Jong


	


   Point well taken. Earlier I mentioned a problem with bus

   voltage stability encountered with a $50K coffee maker

   on a $14M airplane.



   For the entirety of my career I've signed up to the notion

   that the ship's battery is "the best filter in the airplane".

   Evidence to the contrary has been laying on the table in front

   of me since day-one but went unnoticed because I failed to

   explore the questions.



   Turns out that a battery presents its specified milliohm

   source impedance to the bus only while it's DELIVERING

   energy. Once you elevate the battery's terminals above

   the energy delivery value (as for charging and maintaining)

   that battery's resistance to small voltage perturbations

   disappears.



   I did some quick-n-dirty looks at tying 1F capacitors

   across the bus. In this case 50A pulses that produced

   4-volt perturbations with a battery on line dropped to

   1-volt excursions with a 1F capacitor . . . right in the

   ballpark with your assertions above.



   Problem was that while the battery allowed 4-volt,

   25 mS perturbations to generate noticeable flicker in

   cabin lights, the 1-volt perturbations were stretched

   by the longer system time constant with a capacitor installed.

   At 50 mS, the 1-volt perturbations were MORE noticeable than

   shorter pulses of greater intensity! Who would have

   thunk it?



   In any case, these studies have generated a profound

   change in the way I view vehicular bus dynamics.

   It's interesting how easy it is to be snookered into

   a belief structure that is wrong. Not just because

   it's heavily preached and deeply held . . . but because

   the question, "how does this work?" was never asked.



   Bob . . .



                    ////

                   (o o)

    ===========o00o=(_)=o00o=========

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

    =================================

nuckollsr(at)cox.net
Guest

Posted: Fri Dec 08, 2006 5:41 am Post subject: Pitot Current Draw

At 08:53 PM 12/7/2006 -0700, you wrote:



 	  Quote: 	
		  



 >

 >    We touched on this in an earlier post. Recall that while you're reducing

 >    the current through the heater by 1/2, this drops the voltage across it

 >    by 1/2 also for a new dissipation value of 1/4 the original which comes

 >    to 29.5 watts for the tube and 29.5 watts dropped across the companion

 >    resistor for a system total of 49 watts.



Just a minor point - the 49 W is already 1/4 of the power consumption of

the 'new' pitot tube.  The only point I was making was that "I assume

that an amp is an amp and is generally going to produce a certain

amount of heat" was not correct.



Bob W.


	


   Agreed!



   Bob . . .

jan.de.jong(at)xs4all.nl
Guest

Posted: Fri Dec 08, 2006 5:44 am Post subject: Pitot Current Draw

 	  Quote: 	
		   15A for 1/60th causes 0.25V dip on charged 1F.


	




Forgot to mention - 0.25V discharge dip is on top of 0.03V resistance 

drop dip of 15A and 2mOhm.

mlas(at)cox.net
Guest

Posted: Fri Dec 08, 2006 5:54 am Post subject: Pitot Current Draw

Bob,



Don't forget just to have a little fun every now and then.



Mike



--

nuckollsr(at)cox.net
Guest

Posted: Fri Dec 08, 2006 7:14 am Post subject: Pitot Current Draw

At 06:54 AM 12/8/2006 -0700, you wrote:



 	  Quote: 	
		  



Bob,



Don't forget just to have a little fun every now and then.



Mike


	


   My work is fun . . . or I wouldn't do it!

   The coolest feeling in the world for me is to

   go to bed understanding something that I didn't

   understand that morning.



   Bob . . .

pilot4profit(at)sbcglobal
Guest

Posted: Fri Dec 08, 2006 7:16 am Post subject: Pitot Current Draw

Chuck, I think the capacitor suggested with a PWM might be your best bet. I have some mil-spec voltage regulators that I think may work as part of the circuit. These are the same regulators that Cessna uses in their panel dimmer circuits, just a more rugged version. Give me a day or 2 to hit the application notes, and I think I can give you a circuit that is cost effective, efficient and produce little noise. That is if someone else doesn’t beat me to it. Since I see this component used already in certified aircraft it should be suitable for your application, provided it can handle the current necessary to keep it at the right temp.  

Some years back I worked with some very precise temperature controllers for infra-red black-body heat sources. Temperature controls accurate to +-.01 deg. C.  

CS  

         

  

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

 Sent: Friday, December 08, 2006 8:19 AM

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: RE: Pitot Current Draw  

  

     

Craig/Matt/Bob/Bob again/et al  

    

   

    

Thanks for the technical responses which transcends the proclamation that only dummies fly in ice.  And Stein, you have a point if I was only trying to use some reject hand-me-down pitot and I was too cheap to get one of Gretz's very elegantly functional pitots.  This isn't about functionality, this is about aesthetics.  I have a sharkfin pitot off an old warbird that I use at the tippy-point of the Velocity.  The sharkfin perfectly picks up the lines of the winglets, yadda, yadda.....trust me, it's just a personal preference.  

    

   

    

Unfortunately, the heating elements in it were obviously designed for use in cold weather areas.  In the winters, when they saw this sucker coming in, the ramp and line crews left the warmth of their burning trash barrels to comeover and stand by the pitot where there was some real heat!!!  

    

   

    

My conclusion is if I want to keep the pitot (which I do), I either live with the current draw, which is really not a serious problem for the 60amp alternator and just hope I don't need it at the same time that I start suddenly have a shortage of electrons.  While the resistor fix may work, because of the loss to the resistor, the overall amperage reduction is minimal.....kind of like having to spend a $100 to get a $20 tax reduction.  

    

   

    

The more attractive alternative is duty cycle--assuming it doesn't put me in electron hell.  Anyhow, I appreciate the many responses and the many tangents engaged.  As to those who thought the thread went on too long and contain too much irrelevant material, just remember--that's why we sort through the pile of straw and horse s--t that was shoveled out of the horse barn with our bare hands---on the oft chance there might be a pony in there somewhere.  

    



 Chuck Jensen 

     

  

--

cjensen(at)dts9000.com
Guest

Posted: Fri Dec 08, 2006 8:09 am Post subject: Pitot Current Draw

CS,

  

 I'll look forward to  it.  

  

 Chuck Jensen 

 Do Not  Archive

  

 

 --

tompkinsl(at)integra.net
Guest

Posted: Fri Dec 08, 2006 11:11 am Post subject: Pitot Current Draw

Amen, Stein!  And it took two weeks  for the response that actually answered Chuck's original  question!

  

 Larry

   [quote][b]

Speedy11(at)aol.com
Guest

Posted: Fri Dec 08, 2006 9:45 pm Post subject: Pitot Current Draw

Mike Larkin,

 I don't mean to be sarcastic, but you didn't answer any questions - at least any questions that had been asked.  Chuck asked about how to wire his pitot heat so as to have the option to cycle from low heat to high heat.

 I don't agree with Chuck regarding the wisdom of using a lower heat setting to save power in IMC icing conditions if the alternator fails, but his question is not, "Should I use a lower heat setting?"  His question is, "How do I wire so to obtain my choice of heat settings?"

 We all have personal stories to tell.  They aren't relevant to Chuck's question unless they are related to how one wires one's electrical system to obtain high-low pitot heat.

 My personal philosophy regarding icing conditions in SE piston powered aircraft is exactly the same as yours.  But, my philosophy about flying in icing conditions is not relevant to Chuck's question.

 The only answer or opinion that Chuck wants is the one that describes to him how to wire his electrical system to permit high and low pitot heat settings.

 We have to leave it to him to decide if such a system is adequate and if it is wise to employ it in icing conditions.

 Regards,

 Stan Sutterfield

  

 [quote]The only way I can answer this question is to tell a story.  First,

flying in the ice is something many pilot do every year and sometimes

often.  If you know what you=92re doing and are prepared then the risks

are minimal.  I have been flying in ice with airplanes that are able to

handle it for better then 20 years.  It=92s not like flying on a sunny

day.  But once you get use to it and prepare for it, it=92s not that big

of a deal.  A few words of advice, no two icing days are the same.  Only

experience will help you here.  My personal feeling on ice in piston

powered planes, you don=92t have many out when the weather gets bad.  

When

in ice greater then light find a place to land ASAP.



As for you electric question; First the easy answer is to put a bigger

battery in the airplane.  Second, why would you think that using less

power for pitot heat is going to be any better then turning the pitot

heat off all together?  Unless you run a thermal equation on the speed,

temperature, and heat (layman=92s terms) required to guarantee the

anti-ice properties needed, then everything your doing is just a big

guess anyway.  And I guessing that since I have to go to the book to do

said equation thoroughly, I would guess the electrical formula by

comparison would be a piece of cake.  I know this is not what you want

to hear but the facts are the facts.  Thee it to him to decide if such a system is adequate and if it is wise to employ it in icing conditions.

 Regards,

 Stan Sutterfield

  

 [quote]The only way I can answer this question is to tell a story.  First,

flying in the ice is something many pilot do every year and sometimes

often.  If you know what you=92re doing and are prepared then the risks

are minimal.  I have been flying in ice with airplanes that are able to

handle it for better then 20 years.  It=92s not like flying on a sunny

day.  But once you get use to it and prepare for it, it=92s not that big

of a deal.  A few words of advice, no two icing days are the same.  Only

experience will help you here.  My personal feeling on ice in piston

powered planes, you don=92t have many out when the weather gets bad.  

When

in ice greater then light find a place to land ASAP.



As for you electric question; First the easy answer is to put a bigger

battery in the airplane.  Second, why would you think that using less

power for pitot heat is going to be any better then turning the pitot

heat off all together?  Unless you run a thermal equation on the speed,

temperature, and heat (layman=92s terms) required to guarantee the

anti-ice properties needed, then everything your doing is just a big

guess anyway.  And I guessing that since I have to go to the book to do

said equation thoroughly, I would guess the electrical formula by

comparison would be a piece of cake.  I know this is not what you want

to hear but the facts are the facts.  The reason that the pitot uses so

much power (in general) is that is what it takes to keep ice off the

probe in 100% humidity at temperatures < 10dec C.



Sorry for the poor and somewhat sarcastic answer, but I think Chuck

brought it out in me.



Regards,



Mike Larkin

--

Speedy11(at)aol.com
Guest

Posted: Fri Dec 08, 2006 9:53 pm Post subject: Pitot Current Draw

Matt,

 An interesting concept.

 Stan Sutterfield

  

  	  Quote: 	
		  Why doesn't anyone have a pitot tube heated directly

by the combustion of a hydrocarbon 	


 

  [quote][b]

Speedy11(at)aol.com
Guest

Posted: Fri Dec 08, 2006 10:52 pm Post subject: Pitot Current Draw

Dr. Rodney,

 Tell me, o wise one, how can one read the mind of another to determine whether or not he might misuse information you provide?

 You, and others, cannot police everyone's thoughts.  Nor should you.

 Regards,

 Grasshopper

  

  

  	  Quote: 	
		  I believe I have some measure of 

culpability for the actions of others if I have enabled them in some way to 

DO something bad with the information they're gathering. And, I believe the 

listers here believe that too!



We listers want everyone here to play safe! 	


 

  [quote][b]

Speedy11(at)aol.com
Guest

Posted: Fri Dec 08, 2006 10:54 pm Post subject: Pitot Current Draw

Thank you, Raymond.  I could not have said it better.

 Stan Sutterfield

  

  

  	  Quote: 	
		  Rodney (O Wise Master),



    Pretty arrogant of you to think that you have control of or responsibility

for another's actions and to think that you have any right to try to impose

your values on another by attempting to control their actions.



Raymond Julian

Kettle River, MN. 	


 

  [quote][b]

Speedy11(at)aol.com
Guest

Posted: Fri Dec 08, 2006 11:06 pm Post subject: Pitot Current Draw

Wow, a recent first flight?

 Tell us about it.  Do you have photos posted anywhere?

 Couldn't connect to your web site.

 Stan Sutterfield

  

  	  Quote: 	
		  Bob W. (Not a thermodynamist but I learned ohms law at an early age.)

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

First Flight:  11/23/2006 7:50AM - 0.7 Hours Total Time 	


 

  [quote][b]

raymondj(at)frontiernet.n
Guest

Posted: Sat Dec 09, 2006 3:13 am Post subject: Pitot Current Draw

Well stated Mr. Sutterfield.

  

 do not archive

  

 Raymond Julian

 Kettle River, MN.

 [quote]   --

cjensen(at)dts9000.com
Guest

Posted: Sat Dec 09, 2006 6:50 am Post subject: Pitot Current Draw

Stan,

 You're right in that there was  a lot of circling of the opinion vultures before the meat was ripe to eat on  this one--but it wasn't wasted time.  As you pointed out, my question was  'how to do it' and not 'is it a good idea'.  Eventually, the first question  was answered though the early hits addressed the second question, which was not  asked.  However, as said, that was not wasted time.  All education and  wisdom on this site is not necessarily committable to a  formula.

  

 The opinions expressed,  some relevant, others not, at least got me thinking...which is a good thing for  all of us to do when we are doing something non-standard.  Sometimes,  we get so focused on a goal that our mental blinders causes us to lose sight  of the peripheral issues which are raised for  (re)consideration by some of the misdirected postings.   

  

 So, I dug through that pile of  straw and stuff and found the pony.  I didn't like his color or his size,  but he is what he is, so now I have to decide what to do about him.   

  

 Chuck Jensen 



 

 --

bob(at)bob-white.com
Guest

Posted: Sat Dec 09, 2006 7:46 am Post subject: Pitot Current Draw

Thanks Stan,



I have a few pictures but haven't updated the web site in quite a

while.  Every once in a while it goes off line for a short time.  Seems

to be working now.  I'll try to at least post the pictures today or

tomorrow.



Bob W.

On Sat, 9 Dec 2006 02:03:30 EST

Speedy11(at)aol.com wrote:



 	  Quote: 	
		   Wow, a recent first flight?

 Tell us about it.  Do you have photos posted anywhere?

 Couldn't connect to your web site.

 Stan Sutterfield

 

 Bob W. (Not a thermodynamist but I learned ohms law at an early age.)


	


Do not archive

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

First Flight:  11/23/2006 7:50AM - 0.7 Hours Total Time

Cables for your rotary installation - http://www.roblinphoto.com/shop/

pilot4profit(at)sbcglobal
Guest

Posted: Sat Dec 09, 2006 1:44 pm Post subject: Pitot Current Draw

Chuck, if you could e-mail me off the list, I’d like to discuss your pitot heat requirements. I just joined recently, so I don’t have your original post.  

Have been digging through my notes, and what comes next depends on a few details. Just remove the nospam.  

pilot4profit(at)sbcnospamglobal.net  

   

CS  

Do not archive        

  

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

 Sent: Friday, December 08, 2006 11:08 AM

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: RE: Pitot Current Draw  

  

     

CS,  

    

   

    

I'll look forward to it.    

    

   

    

Chuck Jensen   

    

Do Not Archive  

    

   

  

       [quote][b]

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