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Facet pumps: Energy vs. Flow

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sportav8r(at)gmail.com
Guest

Posted: Tue Apr 20, 2010 3:40 am Post subject: Facet pumps: Energy vs. Flow

How about some filtering on the "input" line of the ammeter?  If we're looking at constant-amplitude square wave current pulses of varying frequency, a capacitive filter to perform an "integral" function might give you an average-current-over-time measurement that closely matches the frequency and therefore the load on the pump.  In practice, I am not sure from listening to my Facet pump all these years how much the frequency changes as a function of load.  There is a sound change as it self-primes when I first hit it before engine-start. 

Just a thought.  I had to do the pneumatic equivalent (expansion chamber plus input restrictor) to keep my manifold pressure digital readout from jumping all around in an un-readable fashion. A little RC pi or L network might do what you need.

Bill B.

On Mon, Apr 19, 2010 at 9:56 PM, Charlie England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)> wrote:

[quote] --> AeroElectric-List message posted by: Charlie England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>

 Certificated. Bummer.

 If you think you can legally use current sensing, have you tried a restricter in the pump's output to see if it will raise the current enough to be measurable vs the no-flow state?

 On 4/19/2010 6:16 PM, BobsV35B(at)aol.com (BobsV35B(at)aol.com) wrote:

  	  Quote: 	
		   Good Morning Charlie,

 Those units by Pillar Point Electronics look very promising. As I said a couple of messages back, I need something that can be used on a normally certificated aircraft. Not sure about the PPE product, but I am checking into it.

  Thanks for the comment.

 Happy Skies,

 Old Bob

 In a message dated 4/19/2010 4:50:49 P.M. Central Daylight Time, ceengland(at)bellsouth.net (ceengland(at)bellsouth.net) writes:

     --> AeroElectric-List message posted by: Charlie England

     <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>

     On 4/19/2010 3:03 PM, ROGER & JEAN CURTIS wrote:

     >

     >       To me, they look and sound just like the ones that were used

     > on those Ford gasoline fired heaters back in the thirties. But

     my memory

     > could be fooling me.

     >

     >       Those were probably the  Stewart Warner or Bendix pumps.

     > Whadda Ya Think?

     >

     >       If so. does that mean I need to monitor the frequency some

     > how?

     >

     >       This is getting complicated,.  No wonder nobody does it!

     >

     >       Happy Skies,

     >

     >       Old Bob

     >

     >               I am not sure of the application here, but I

     > believe that there should be a significant pressure drop on the

     output of

     > the pump, when there is no longer any fuel.  This being the

     case, perhaps

     > you could use a pressure switch, similar to what is used to

     monitor engine

     > oil pressure and turn on the hobbs meter, on some aircraft.  You

     would need

     > to check the pressure differential between pumping fuel and

     empty tank

     > pumping, and use a switch midway between.  This would be a

     normally closed

     > switch which would open when there is fuel flow and close, to

     turn on the

     > light when there is no more fuel to pump.

     >

     >               Not sure if this is a viable option for your

     > application, but might work, and is very simple.  (I especially like

     > simple:-)

     >

     >               Roger

     >

     If you're using it as a transfer pump, there won't be a lot of

     pressure

     since it will be just the 'head' from one tank to the other. Often no

     more than a few inches of rise, plus the resistance of the tubing.

     How about one of the sensing devices using light to detect the

     presence

     of liquid? I bought a couple several years ago, intending to use

     them to

     monitor end-of-transfer from my aux tanks, then forgot to install

     them.... They mount in a single hole & have a cone shaped plexi

     tip. An

     LED shines out through the plexi; presence/absence of liquid

     changes the

     light reflected back into the photocell in the same housing, changing

     the state of the sense line.

     If that interests you, I'll try to locate the name of the device & a

     source for you.

     Charlie

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BobsV35B(at)aol.com
Guest

Posted: Tue Apr 20, 2010 4:48 am Post subject: Facet pumps: Energy vs. Flow

Good Morning Bill,

 Wow!

 It appears that any suitable current measuring device will be a lot more  complex than my feeble brain can comprehend.

 Thanks to you and all the others that have contributed to my on going  education.

 In any case, it does seem that a few breadboard experiments are in  order.

 Happy Skies,

 Old Bob

  In a message dated 4/20/2010 6:41:53 A.M. Central Daylight Time,  sportav8r(at)gmail.com writes:

  	  Quote: 	
		  How    about some filtering on the "input" line of the ammeter?  If we're    looking at constant-amplitude square wave current pulses of varying frequency,    a capacitive filter to perform an "integral" function might give you an    average-current-over-time measurement that closely matches the frequency and    therefore the load on the pump.  In practice, I am not sure from    listening to my Facet pump all these years how much the frequency changes as a    function of load.  There is a sound change as it self-primes when I first    hit it before engine-start.    

   Just a thought.  I had to do the pneumatic equivalent (expansion    chamber plus input restrictor) to keep my manifold pressure digital readout    from jumping all around in an un-readable fashion. A little RC pi or L network    might do what you need.

   Bill B.

   On Mon, Apr 19, 2010 at 9:56 PM, Charlie England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>    wrote:

    	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie      England <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>

Certificated.      Bummer.

If you think you can legally use current sensing, have you      tried a restricter in the pump's output to see if it will raise the current      enough to be measurable vs the no-flow state?

On 4/19/2010 6:16 PM,      BobsV35B(at)aol.com (BobsV35B(at)aol.com) wrote:

      	  Quote: 	
		  Good Morning Charlie,

Those units by Pillar Point        Electronics look very promising. As I said a couple of messages back, I        need something that can be used on a normally certificated aircraft. Not        sure about the PPE product, but I am checking into it.

Thanks for the        comment.

Happy Skies,

Old Bob

In a message dated 4/19/2010        4:50:49 P.M. Central Daylight Time, ceengland(at)bellsouth.net (ceengland(at)bellsouth.net) writes:

          --> AeroElectric-List message posted by: Charlie        England

   <ceengland(at)bellsouth.net (ceengland(at)bellsouth.net)>

   On        4/19/2010 3:03 PM, ROGER & JEAN CURTIS wrote:

          >

   >       To me, they look and        sound just like the ones that were used

   > on those Ford        gasoline fired heaters back in the thirties. But

   my        memory

   > could be fooling me.

          >

   >       Those were probably        the  Stewart Warner or Bendix pumps.

   > Whadda Ya        Think?

   >

   >       If        so. does that mean I need to monitor the frequency some

          > how?

   >

   >              This is getting complicated,.  No wonder nobody does        it!

   >

   >       Happy        Skies,

   >

   >       Old        Bob

   >

   >                      I am not sure of the application here, but        I

   > believe that there should be a significant pressure        drop on the

   output of

   > the pump, when        there is no longer any fuel.  This being the

   case,        perhaps

   > you could use a pressure switch, similar to        what is used to

   monitor engine

   > oil        pressure and turn on the hobbs meter, on some aircraft.         You

   would need

   > to check the        pressure differential between pumping fuel and

   empty        tank

   > pumping, and use a switch midway between.         This would be a

   normally closed

   >        switch which would open when there is fuel flow and close, to

          turn on the

   > light when there is no more fuel to        pump.

   >

   >                      Not sure if this is a viable option for        your

   > application, but might work, and is very simple.         (I especially like

   > simple:-)

          >

   >                      Roger

   >

   If you're using it as a        transfer pump, there won't be a lot of

   pressure

          since it will be just the 'head' from one tank to the other. Often        no

   more than a few inches of rise, plus the resistance of        the tubing.

   How about one of the sensing devices using        light to detect the

   presence

   of liquid? I        bought a couple several years ago, intending to use

   them        to

   monitor end-of-transfer from my aux tanks, then forgot        to install

   them.... They mount in a single hole & have        a cone shaped plexi

   tip. An

   LED shines out        through the plexi; presence/absence of liquid

   changes        the

   light reflected back into the photocell in the same        housing, changing

   the state of the sense        line.

   If that interests you, I'll try to locate the        name of the device & a

   source for you.

          Charlie

  [quote][b]

jon(at)finleyweb.net
Guest

Posted: Tue Apr 20, 2010 5:09 am Post subject: Facet pumps: Energy vs. Flow

I find this discussion very interesting and hope for an inexpensive solution.  I really like that Pillar Point flow detector but the price is more than I'd like to spend.

  

 Just to add some data points.... In my case, I know the fuel level in the tank but I wish to know when fuel stops being delivered to that tank so alternate plans can be made. So, a "fuel is not flowing" indicator would add a level of comfort (would be "nice" but certainly not mandatory since I am currently flying without this).

  

 More specifically, I have a large main tank from which fuel is pumped into the header.  The header is about 5 gallons (one hour of flight time).  I typically leave my transfer pump on all the time.  If it were to stop and I didn't notice (which is likely), I have a warning light that will come on at about 2.5-3 gallons.  That leaves me with about 30 minutes to figure out what to do.  If I had known immediately, I would have had 60 minutes.  Of course, I have a backup fuel pump which I would immediately switch on.  However; it can take some time before seeing the fuel level start to rise. When dealing with a 30 minute window, knowing now versus knowing in 5-10 minutes is a big deal (at least in terms of my stress level - FYI, I live out west were airports are frequently more than 30 minutes apart).

 

Jon Finley

 N314JF - Q2 - Subaru EJ22

 http://www.finleyweb.net/Q2Subaru.aspx

  

  

 

--

BobsV35B(at)aol.com
Guest

Posted: Tue Apr 20, 2010 6:58 am Post subject: Facet pumps: Energy vs. Flow

Good Morning Ira,

  

 I have what I consider to be relatively good fuel gauges in the tanks, but  find that there is at least a ten to fifteen minute window between where the  gauge says empty and it actually will be dry. I do not wish to turn the pump off  too soon and have fuel in the tank that has not been used and I do not like to  run the pump when it is not actually pumping fuel. 

  

 It would be very nice to be able to verify the accuracy of the fuel gauge  by noting when the pump stops pumping fuel rather than running the pump while  dry for possibly an extra ten to fifteen minutes every time I utilize the  auxiliary fuel tank. 

  

 I do have excellent fuel use measuring capability and what I do now is note  the fuel burned number when I turn on the pump and shut it off when the  amount of fuel known to be in the tank has been burned.  

  

 Nevertheless, it would be nice to know within seconds when the tank has run  dry so that the pump could be turned off.

  

 I really would rather not be running the pump when it is not pumping  fuel.

  

 Happy Skies,

  

 Old Bob

  

  In a message dated 4/20/2010 7:43:50 A.M. Central Daylight Time,  ira.rampil(at)gmail.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "rampil"    <ira.rampil(at)gmail.com>



Good engineering principles favor    measuring the actual parameter

you want, rather than a surrogate,    especially when there is no

reliable one-to-one mapping of one to the    other.



In the case of current draw, for example, overheating the coil    or dirt

in the mechanism will probably change the current draw

Pressure    downstream would depend on where the fill hose enters the 

downstream tank,    if at the bottom, or at a positive hydrostatic head, the 

pressure    downstream of the pump will stay positive while there is fuel

in the    tank.



What about measuring fuel level in the feeding tank, is not that    what you

really want to make a decision with? When it reads zero, stop    pumping?



--------

Ira  N224XS



	


  [quote][b]

mdnanwelch7(at)hotmail.co
Guest

Posted: Tue Apr 20, 2010 9:35 am Post subject: Facet pumps: Energy vs. Flow

Bob,

  

   Pardon me for butting in, but from my experience with certificated airplanes, it is virtually impossible to get a field approval like you're after.

  

   I used to have a 1961 Cessna 172, with an O-300 Continental.  On those hot mid-summer California days (100+), my oil temps got well into the red on climbout!!  I checked the accuracy of the gauge, and it was correct!  

  

   Therefore, I wanted to add an oil cooler to my Cessna 172.  It didn't come with one, but I could get a later model 172 oil cooler to fit.  I sent off my Form 337 to the local FSDO, and their first reaction was "NO!"  Their attitude was "if it didn't come with one, it doesn't need one!!"

  

   I was irritated (to say the least), and requested an appeal.  They finally relented and said it would be okay.  For crying out loud , it was just an oil cooler!! (all certified parts, too)

  

   My opinion is; there ain't no way you can legally add any kind of permanent parts to modify to your fuel pump, fuel lines, or anything else, on a certificated airplane, without that approved 337. 

  

   Just my opinion.................

  

 Mike Welch

 

  From: BobsV35B(at)aol.com

Date: Tue, 20 Apr 2010 09:34:57 -0400

Subject: Re: Re: Facet pumps: Energy vs. Flow

To: aeroelectric-list(at)matronics.com



 Good Morning Ira,

  

 I have what I consider to be relatively good fuel gauges in the tanks, but find that there is at least a ten to fifteen minute window between where the gauge says empty and it actually will be dry. I do not wish to turn the pump off too soon and have fuel in the tank that has not been used and I do not like to run the pump when it is not actually pumping fuel. 

  

 It would be very nice to be able to verify the accuracy of the fuel gauge by noting when the pump stops pumping fuel rather than running the pump while dry for possibly an extra ten to fifteen minutes every time I utilize the auxiliary fuel tank. 

  

 I do have excellent fuel use measuring capability and what I do now is note the fuel burned number when I turn on the pump and shut it off when the amount of fuel known to be in the tank has been burned.  

  

 Nevertheless, it would be nice to know within seconds when the tank has run dry so that the pump could be turned off.

  

 I really would rather not be running the pump when it is not pumping fuel.

  

 Happy Skies,

  

 Old Bob

  

  In a message dated 4/20/2010 7:43:50 A.M. Central Daylight Time, ira.rampil(at)gmail.com writes:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rampil" <ira.rampil(at)gmail.com>



Good engineering principles favor measuring the actual parameter

you want, rather than a surrogate, especially when there is no

reliable one-to-one mapping of one to the other.



In the case of current draw, for example, overheating the coil or dirt

in the mechanism will probably change the current draw

Pressure downstream would depend on where the fill hose enters the 

downstream tank, if at the bottom, or at a positive hydrostatic head, the 

pressure downstream of the pump will stay positive while there is fuel

in the tank.



What about measuring fuel level in the feeding tank, is not that what you

really want to make a decision with? When it reads zero, stop pumping?



--------

Ira N224XS



	


 	  Quote: 	
		  



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ww.matronics.com/contribution



	
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BobsV35B(at)aol.com
Guest

Posted: Tue Apr 20, 2010 10:05 am Post subject: Facet pumps: Energy vs. Flow

Good Afternoon Mike,

  

 Believe it or not I do understand your frustration and the problems that  are faced when dealing with the FAA.

 It is my opinion that the vast majority of the folks at FAA want to do a  good job, but are so hamstrung with regulations and paper work that it is easier  to just say no.

  

 However, I have had fairly good luck getting local approvals from my  supervising FSDO. 

  

 As I think we can all agree, each FSDO is a kingdom unto itself and what is  easy to get approved at one office may be impossible at another. Nevertheless, I  have gotten several local approvals here locally. I do hold an A&P with  Inspection Authorization. It does help me know who I should present the data to  and how the presentation should be made. 

  

 In general, if we can think of a way to add something that has no chance of  interfering with required equipment, the local approval has a better chance of  being approved. 

  

 Once again, the FAA has no obligation to ever issue a local approval. In  fact, if an individual inspector does issue the approval, he is doing it on his  own knowledge and is personally responsible for what happens. In many ways it is  surprising that any FAA inspector ever issues a local approval. He/she has no  obligation to do so.  It is just a privilege he has been accorded.  Failure to do so does not hurt his career at all, but making a dumb approval  could end his career.

  

 Happy Skies,

  

 Old Bob

  

  In a message dated 4/20/2010 12:37:05 P.M. Central Daylight Time,  mdnanwelch7(at)hotmail.com writes:

  	  Quote: 	
		  Bob,

 

  Pardon me for butting in, but from my    experience with certificated airplanes, it is virtually impossible to get a    field approval like you're after.

 

  I used to have a 1961    Cessna 172, with an O-300 Continental.  On those hot mid-summer    California days (100+), my oil temps got well into the red on climbout!!     I checked the accuracy of the gauge, and it was correct!     

 

  Therefore, I wanted to add an oil cooler to my    Cessna 172.  It didn't come with one, but I could get a later model 172    oil cooler to fit.  I sent off my Form 337 to the local FSDO, and their    first reaction was "NO!"  Their attitude was "if it didn't come with    one, it doesn't need one!!"

 

  I was irritated (to say    the least), and requested an appeal.  They finally relented and    said it would be okay.  For crying out loud , it was just an    oil cooler!! (all certified parts, too)

 

  My opinion    is; there ain't no way you can legally add any kind of    permanent parts to modify to your fuel pump, fuel lines, or    anything else, on a certificated airplane, without that approved    337. 

 

  Just my    opinion.................

 

Mike  Welch

 

	


  [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Wed Apr 21, 2010 4:01 am Post subject: Re: Facet pumps: Energy vs. Flow

A "tank empty switch" can be made with a magnet attached to a float inside of the tank.  A magnetic reed switch on the outside of the tank will close when the magnet gets close to it.  Of course this is only legal for home-built aircraft.  The only thing visible on the outside of the tank will be a pair of wires with heat-shrink on the end that the covers the switch.  Perhaps there are similar tank empty switches commercially available.

Joe

_________________
Joe Gores

BobsV35B(at)aol.com
Guest

Posted: Wed Apr 21, 2010 5:25 am Post subject: Facet pumps: Energy vs. Flow

Good Morning Joe,

  

 Another great idea! This list is resourceful.

  

 For my purposes, the fuel gauge I have does a good job as far as telling me  when my usable fuel is out of the tank.  Admittedly, there are times when  four or five minutes of fuel will make a difference and if the flight is planned  to land with the FAA suggested thirty minute minimum planned fuel reserve, five  more minutes will make a difference to me.

  

 However, I rarely cut fuel that close so my effort is oriented more toward  reducing the time the pump will be operating dry. That is why I am more  interested in finding out when the pump is pumping nothing but air. So far, the  best answer appears to be the optical monitoring of fuel flow.  I  originally thought pressure would do the trick, but as many have pointed out,  there may not be enough head pressure to allow consistent measurable  differences. 

  

 When the idea of measuring current required by the pump surfaced, that  seemed to have merit, but 'Lectric Bob seems to feel that may not be a useful  measurement. I think the pressure and electron measurement solutions are worthy  of some breadboard testing, but that optical monitoring of the fuel looks like a  winner. Unfortunately, I now have to figure out a way of getting my local FED to  agree that it is a good solution.

  

 As an aside, It appears that an earlier offering by the Pillar  Point  folks used a stock AN Tee for a base unit with the detector potted into the  standing leg of the tee. They have now decided to manufacture their own  Tee. It is my off the wall guess that I might have had better luck using the  modified AN unit than I will one that is newly manufactured. Such are the  vagaries of getting FAA approval for anything. I just hope that sometime in the  future I will be able to afford a homebuilt instead of my present factory built  steed.

  

 This is WAY off topic, but my investigation of the market shows that I can  still buy an ancient factory built flying machine for less money than it would  cost to get a home built machine of equivalent performance.

  

 This would be a no brainer if I could afford a homebuilt.

  

  Difficulties such as I am now encountering may get me to change my mind!  <G>



  

 Happy Skies,

  

 Old Bob

  

  In a message dated 4/21/2010 7:04:31 A.M. Central Daylight Time,  fran4sew(at)banyanol.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "user9253"    <fran4sew(at)banyanol.com>



A "tank empty switch" can be made with a    magnet attached to a float inside of the tank.  A magnetic reed switch on    the outside of the tank will close when the magnet gets close to it.  Of    course this is only legal for home-built aircraft.  The only thing    visible on the outside of the tank will be a pair of wires with heat-shrink on    the end that the covers the switch.  Perhaps there are similar switches    commercially available.

Joe



--------

Joe    Gores





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  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 21, 2010 6:27 am Post subject: Facet pumps: Energy vs. Flow

At 08:08 AM 4/21/2010, you wrote:

  	  Quote: 	
		   Good Morning Joe,

  

 Another great idea! This list is resourceful.

  

 For my purposes, the fuel gauge I have does a good job as far as telling me when my usable fuel is out of the tank.  Admittedly, there are times when four or five minutes of fuel will make a difference and if the flight is planned to land with the FAA suggested thirty minute minimum planned fuel reserve, five more minutes will make a difference to me.

  

 However, I rarely cut fuel that close so my effort is oriented more toward reducing the time the pump will be operating dry. That is why I am more interested in finding out when the pump is pumping nothing but air. So far, the best answer appears to be the optical monitoring of fuel flow.  I originally thought pressure would do the trick, but as many have pointed out, there may not be enough head pressure to allow consistent measurable differences. 

  

 When the idea of measuring current required by the pump surfaced, that seemed to have merit, but 'Lectric Bob seems to feel that may not be a useful measurement. 	


    I've researched the evolution of the thump-thump pumps

    and found quite a cache of history in the patent files.

    A selection of examples have been posted at:



  http://aeroelectric.com/Mfgr_Data/Pumps/



    It seems our old friend the "Bendix electric

    pump" is well represented and appears to have been

    taken over by Facet. An example of the Facet cube

    pump is including. All of these are "solid state"

    versions of the original design that simply used a

    set of contacts to control the solenoid coil current

    to re-stroke the pump. I was surprised to find

    that "solid state" went back so far. The 1968

    Bendix patent still has the mechanical switch

    contacts but uses transistors to buffer the coil

    current so that the contacts don't erode electrically.



    Later versions use hall effect devices to sense

    plunger position. The surprise was to find a

    couple of designs that used a free-running

    oscillator (555 timer) to simple pulse the

    solenoid periodically. No plunger position

    sensing at all.



    It's possible that some versions will present

    a unique current signature that could be used

    to detect when the pump was running unloaded

    but you'd have to do some all-conditions,

    all-variables studies to make sure that your

    sensing scheme did not risk false indications.



 

  	  Quote: 	
		   I think the pressure and electron measurement solutions are worthy of some breadboard testing, but that optical monitoring of the fuel looks like a winner. 	


    Back in the summer of 08 we had some discussion here

    on the list about optical liquid level sensors. These

    have a rich history of practical application in automotive

    applications dating back to the 1950's.



    Modern incarnations include a series of devices

    I was responsible for at Electro-Mech in the 80's

    that have been built by the thousands and incorporated

    into dozens of applications on Beech/RAC/Hawker-Beech

    products. Here's a collection of pictures that

    show features and products in the optical liquid

    level sensors technology:



  http://aeroelectric.com/Pictures/Fuel_Level/



    Gem Sensors is a good place to start for

    commercial off-the-shelf devices. They're

    quite rugged and entirely suited to the

    task.



  http://www.gemssensors.com/content.aspx?id=282



 

  	  Quote: 	
		    Unfortunately, I now have to figure out a way of getting my local FED to agree that it is a good solution. 	


    You're not proposing to do anything new,

    daring and fraught with risk. Successful

    integration of these devices into a tank

    have only to do with mundane issues of

    craftsmanship that go to keeping the fuel

    inside the pipes . . . i.e. leaks.



    The neat thing about sensing absolute

    level in the tank is the "dipstick" accuracy

    of the value. There are no variables of

    calibration associated with setting trip

    points to light indicators from fuel

    level transmitters, etc.



    I could see a 337 mod to add the sensor

    to the side of a tank. It's an ADDITION

    that is an operating convenience and

    has no effect on the basis for certification

    for the original TC. Risks are limited to

    issues of good shop practice and craftsmanship.



    Bob . . .

     [quote][b]

BobsV35B(at)aol.com
Guest

Posted: Wed Apr 21, 2010 7:40 am Post subject: Facet pumps: Energy vs. Flow

Good Morning 'Lectric Bob,

  

 Thanks for the update.

  

 Your answer coordinates well with my thoughts. If I could find a  certificated optical flow monitoring device, I would install it using part 43 as  data. No sweat at all!

  

 While I do not have any desire to install more sensors in my fuel tanks, I  agree that Part 43 substantiation should work there.

  

 Thanks again to all who have responded. It really helps flesh out the  answer.

  

 Happy Skies,

  

 Old Bob

 AKA

 Bob Siegfried

 Bob's Aircraft Service

 Downers Grove, IL 

 Stearman N3977A (and others)

  

  In a message dated 4/21/2010 9:29:14 A.M. Central Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  At 08:08    AM 4/21/2010, you wrote:

    	  Quote: 	
		  Good Morning Joe,

 

Another great idea!      This list is resourceful.

 

For my purposes, the fuel gauge I      have does a good job as far as telling me when my usable fuel is out of the      tank.  Admittedly, there are times when four or five minutes of fuel      will make a difference and if the flight is planned to land with the FAA      suggested thirty minute minimum planned fuel reserve, five more minutes will      make a difference to me.

 

However, I rarely cut fuel that close      so my effort is oriented more toward reducing the time the pump will be      operating dry. That is why I am more interested in finding out when the pump      is pumping nothing but air. So far, the best answer appears to be the      optical monitoring of fuel flow.  I originally thought pressure would      do the trick, but as many have pointed out, there may not be enough head      pressure to allow consistent measurable differences. 

 

When the      idea of measuring current required by the pump surfaced, that seemed to have      merit, but 'Lectric Bob seems to feel that may not be a useful measurement.      	


   I've researched the evolution of the    thump-thump pumps

   and found quite a cache of history in the    patent files.

   A selection of examples have been posted    at:



http://aeroelectric.com/Mfgr_Data/Pumps/



      It seems our old friend the "Bendix electric

   pump" is well    represented and appears to have been

   taken over by Facet. An    example of the Facet cube

   pump is including. All of these are    "solid state"

   versions of the original design that simply used    a

   set of contacts to control the solenoid coil    current

   to re-stroke the pump. I was surprised to    find

   that "solid state" went back so far. The    1968

   Bendix patent still has the mechanical    switch

   contacts but uses transistors to buffer the    coil

   current so that the contacts don't erode    electrically.



   Later versions use hall effect devices to    sense

   plunger position. The surprise was to find    a

   couple of designs that used a free-running

      oscillator (555 timer) to simple pulse the

   solenoid    periodically. No plunger position

   sensing at    all.



   It's possible that some versions will    present

   a unique current signature that could be    used

   to detect when the pump was running    unloaded

   but you'd have to do some    all-conditions,

   all-variables studies to make sure that    your

   sensing scheme did not risk false  indications.

    	  Quote: 	
		  I think the pressure and electron measurement      solutions are worthy of some breadboard testing, but that optical monitoring      of the fuel looks like a winner. 	


   Back in    the summer of 08 we had some discussion here

   on the list about    optical liquid level sensors. These

   have a rich history of    practical application in automotive

   applications dating back    to the 1950's.



   Modern incarnations include a series of    devices

   I was responsible for at Electro-Mech in the    80's

   that have been built by the thousands and    incorporated

   into dozens of applications on    Beech/RAC/Hawker-Beech

   products. Here's a collection of    pictures that

   show features and products in the optical    liquid

   level sensors technology:



http://aeroelectric.com/Pictures/Fuel_Level/



      Gem Sensors is a good place to start for

   commercial    off-the-shelf devices. They're

   quite rugged and entirely    suited to the

   task.



http://www.gemssensors.com/content.aspx?id=282

    	  Quote: 	
		   Unfortunately, I now have to figure out a way      of getting my local FED to agree that it is a good    solution. 	


   You're not proposing to do    anything new,

   daring and fraught with risk.    Successful

   integration of these devices into a    tank

   have only to do with mundane issues of

      craftsmanship that go to keeping the fuel

   inside the pipes . .    . i.e. leaks.



   The neat thing about sensing    absolute

   level in the tank is the "dipstick"    accuracy

   of the value. There are no variables    of

   calibration associated with setting trip

      points to light indicators from fuel

   level transmitters,    etc.



   I could see a 337 mod to add the    sensor

   to the side of a tank. It's an ADDITION

      that is an operating convenience and

   has no effect on the    basis for certification

   for the original TC. Risks are limited    to

   issues of good shop practice and    craftsmanship.



   Bob . . .

 	  Quote: 	
		  



	
	


  [quote][b]

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