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wstucklen1(at)cox.net
Guest

Posted: Sat Dec 03, 2011 4:13 am Post subject: Auto Aux Fuel Pump Circuit Idea

Hi All,

 

  After several hot day “Low Fuel Pressure” warnings while taxing out to the runway, I’ve been thinking about implementing a circuit that would allow the Aux fuel pump to be automatically turned ON for a short period of time, whenever the low fuel pressure warning existed.  We already have this ability in most modern fuel injected cars, why not our Aircraft? Having this might allow more use of Autogas as it is more susceptible to vapor lock conditions the result in the Low Fuel Pressure Warnings…..

 

    Implementation would probably have a fuel pressure sensor input (0-5VDC directly from the existing sensor), and a timer to keep the pump running for some duration. Some sort of small Processor IC with an A/D input would probably be the least expensive design approach.  The logic would be something like,

     IF Pressure low turn on pump, start timer; 

     If timer not timed out, keep pump ON; 

     If pressure low and timer not timed out, reset timer

     If timer timed out and pressure OK, shut off pump

 

  From a pilots perspective, the AUX Fuel Pump switch on the panel would be a three position switch: OFF, AUTO, ON. 

 

  I’ve had engine “Stumblings” several times while taxing, due to vapor lock and low the resultant “Low Fuel Pressure” warnings. Even had one on an approach  while using a 50/50 mix of autogas and 100LL. The Aux pump always took care of the issue (as the aux pump is located near the cooler fuel source). So why not automate the process and make it safer…

 

Any comments?

 

Fred Stucklen

RV-7A  N924RV

IO-360 Fixed Pitch

 

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 03, 2011 5:10 am Post subject: Auto Aux Fuel Pump Circuit Idea

  I’ve had engine “Stumblings” several times while taxing, due to vapor lock and low the resultant “Low Fuel Pressure” warnings. Even had one on an approach  while using a 50/50 mix of autogas and 100LL. The Aux pump always took care of the issue (as the aux pump is located near the cooler fuel source). So why not automate the process and make it safer…



   Doing what you suggest is not difficult technologically.

   The elegant solution will be the simplest, most robust

   and lowest cost of ownership solution. The "KISS Principal"

   has been defined by various individuals for centuries

   but one of my favorites was offered by Antoine de Saint

   Exupéry's who opined, "It seems that perfection is reached

   not when there is nothing left to add, but when there is

   nothing left to take away."



   You already have an Aux Fuel Pump and a switch

   for controlling it. Indeed, you've cited instances

   where operating this switch improved on system

   functionality during conditions most likely to

   produce poor fuel flow.



   Does the engine ever object to having the pump

   ON? In other words, if the pump is NOT needed

   to offset a poor flow condition, does having it

   ON during otherwise normal operations pose

   any potential for problems?



   I've flown several aircraft where the Aux Pump

   was switched ON for ground ops and approach to

   landing as a checklist item. If there is no

   downside to having the pump on, would it not be

   simpler to turn it on for all operations where

   vapor issues are anticipated?



   The idea of building an electro-whizzy to 

   automate that function will get the juices

   flowing in any ol' electron herder. At the same

   time, I am reminded too of the frustration

   displayed by some guys who worked for me when

   I asked,  "That works really slick. Now, what

   can you do to reduce parts count?"



   If in your estimation the automatic

   control feature goes to your elegant

   solution, we can certainly discuss the

   bits and pieces necessary to make it

   so.



 

   Bob . . .    [quote][b]

wstucklen1(at)cox.net
Guest

Posted: Sat Dec 03, 2011 12:51 pm Post subject: Auto Aux Fuel Pump Circuit Idea

From:

    

Robert L. Nuckolls, III (nuckolls.bob(at)aeroelectric.com ([email]nuckolls.bob(at)aeroelectric.com?subject=Re:%20Auto%20Aux%20Fuel%20Pump%20Circuit%20Idea&replyto=201112031307.pB3D70KR009307(at)matronics.com[/email]))

Date:

    

Sat Dec 03 - 5:10 AM 	  Quote: 	
		     I’ve had engine =93Stumblings=94 several times while taxing, due to vapor lock and low the resultant =93Low Fuel Pressure=94 warnings. Even had one on an approach  while using a 50/50 mix of autogas and 100LL. The Aux pump always took care of the issue (as the aux pump is located near the cooler fuel source). So why not automate the process and make it safer.    Doing what you suggest is not difficult technologically.   The elegant solution will be the simplest, most robustwhile taxing, due to vapor lock and low the 	
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		  resultant =93Low Fuel Pressure=94 warnings. Even had 	
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		  one on an approach  while using a 50/50 mix of 	
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		  of the issue (as the aux pump is located near the 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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		  cooler fuel source). So why not automate the process and make it safer. 	
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  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Dec 04, 2011 8:08 pm Post subject: Auto Aux Fuel Pump Circuit Idea

 	  Quote: 	
		   	  Quote: 	
		  The engine doesn’t care

that the Aux pump is ON, but there could be otherVapor lock issues if the pump is left ON with the fuel just

circulatingwithin the pump (causing the fuel to heat up and vaporize). The

pumpMotor doesn’t stop once normal pressure has been obtained. The fuel

isjust circulated.

	
	


   Yeah, sounds like a vane pump (constant volume) that

   cracks a bypass relief valve when the flow potential

   exceeds demand. That's one of the nice things about

   FACET put-put pumps. They're constant pressure and simply

   relax when the flow is restricted.



  	  Quote: 	
		   	  Quote: 	
		   The AUX pump is in

the cockpit, but, in excessively hotweather on the ramp while idling with the pump ON, can vapor lock,

causingthe engine to stall, and a VERY difficult restart.

	
	


   Some of the fuel injected fuel systems have a pressure

   relief valve that returns fuel to a tank as opposed

   to thrashing it in a tight loop. This has the effect

   of keeping a contiguous flow of cooling liquid in

   the delivery system.



  	  Quote: 	
		   	  Quote: 	
		  I have also seen situations

while using Autogas on hot days where theSame issue exist in the air. The pilot is usually “Notified” of

theVapor lock issues if the pump is left ON with the fuel just

circulating 	
0

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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
1

  	  Quote: 	
		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
2 	


    Sounds like an opportunity to design some deficiencies

    out of the fuel system. Autogas is a very successful

    aviation fuel but vapor-locking experiences beg to be

    solved with core design changes as opposed to work-arounds.



    Okay, it's a vane pump working into an incompressible

    space so full time operation cracks a pressure-relief

    valve causing a lot of Joules to be stirred into a small

    volume of fuel.  It would be difficult to come up with a

    set of fixed time intervals for cycling the pump triggered

    on some pressure value.



    How about a duty cycle controller that servos the pump

    to produce a selected pressure . . . some value below

    cracking pressure on the bypass. Here, leaving the pump

    on all the time means that under low flow demands, the

    pump runs slowly but ramps up to maintain pressure at

    higher demands.



    I proposed a system like that for a client some years

    back but we never made it to a prototype stage . . .

    the idea seems sound. A transducer like this might

    provide pressure data



  http://tinyurl.com/79ax3g3 



 

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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
4

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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
5 	


    If in the constant pressure mode, leaving it on

    wouldn't be a big deal . . . and again, it's

    not an unreasonable check-list item . . . backed

    up perhaps with a panel annunciator. If the low

    pressure event triggers a fixed time delay for

    full speed operation of the pump, then you've still

    got a situation that works the pump hard while

    stirring up the fuel.



 [quote] 	  Quote: 	
		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
6

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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
7

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		  Vapor lock issues if the pump is left ON with the fuel just

circulating 	
8

 [quote]controls). That’s what separates us from the “Certified” world…

wstucklen1(at)cox.net
Guest

Posted: Mon Dec 05, 2011 6:24 am Post subject: Auto Aux Fuel Pump Circuit Idea

>How about a duty cycle controller that servos the pump

    >to produce a selected pressure . . . some value below

    >cracking pressure on the bypass. Here, leaving the pump

    >on all the time means that under low flow demands, the

    >pump runs slowly but ramps up to maintain pressure at

    >higher demands.

 

Bob,

 

  Not a bad idea. This would emulate the faucet pump operation. That should be easy to implement….

  The Auto industry is essentially doing the same thing with their ‘in-the-tank’ fuel pumps where they are cooled by the surrounding fuel, and where they always have a liquid to pump. This results in the whole fuel delivery system being kept at a higher pressure, making it less susceptible to a vapor lock condition.

  Our problem with our current fuel delivery system design in aircraft is that some portions of that system are at low pressure, and in a heated environment. When the engine mounted pump starts sucking fuel (creating even lower pressure) from these heated lines, we get a vapor lock situation. We’ve done a ‘patch job’ by placing the Aux pump ‘near’ the cool fuel source, and use it when a vapor problem occurs (or to prevent one from occurring). Having a constant pressure Aux fuel pump might solve this, but is still a “Patch” as it doesn’t have redundancy.

  Moving the fuel pump operation into each tank, with a constant pressure controller, could open up the usage of Autogas to more planes. Two tanks, each with a pump, gives redundancy too…

  Something to think about…..

 

  And to those whom have made (or thought about making) comments about the use of Autogas in our planes, I’ll ask you a few questions: If Autogas is a problem, why do you use it in your car? Is it the gas that’s the issue, or the system that utilizes the gas? If it’s the system, what can we do to change it to be an acceptable, safe replacement for the current  100LL aviation systems in our aircraft?

  Most of the issues of Autogas usage have been solved in the auto industry already. If we keep open minds and study these solutions, apply them to the aviation industry with the required redundancy for safety, we can overcome ….

 

  We have the ability to make changes in this industry IF we choose too……. 

 

Fred Stucklen

RV-7A  N924RV  650 Hrs

  [quote][b]

ronburnett(at)charter.net
Guest

Posted: Mon Dec 05, 2011 12:37 pm Post subject: Auto Aux Fuel Pump Circuit Idea

Gentlemen and Ladies,



I have an H-4 Subaru modified from the original Eggenfellner package.  I purchased an electrical manager from Protek.com called the Protek Bus Manager that auto restores a backup fuel pump for auto operations.  My twin pumps are located on the floor of my RV-6A.  We do have a bypass purge line that Jan Eggenfellner developed because some builders ignored his advice and mounted the pumps over the muffler firewall forward without cooling air or protective cover.  I have 77 hours of satisfactory service with this arrangement.



My project can be found on kitlog.com under builders and Ron Burnett.



Ron Burnett N524RB

H-4 Subaru

On Mon, Dec 5, 2011 at 12:58 PM, Richard Girard wrote:



 Excuse me for jumping in here, but I think you guys are working the wrong end of this problem. Vapor lock has all but disappeared in automobiles, even though ethanol has been added and the vapor pressure of the fuel has gone down. Why? Because, for the most part, engine driven fuel pumps located in hot engine compartments have gone the way of the dinosaur. Modern cars don't draw the fuel, they push it with in-tank fuel pumps. Pushing fuel pressurizes it all the way from the tank, instead of drawing it from the engine which reduces the pressure and brings vapor pressure into play. 

Fix the problem permanently by putting a block off plate where that engine driven pump is mounted and either put the fuel pump(s) in the tank(s) or so close that head pressure drives the fuel to the pump(s). 

Now all you need to do is fashion an essential buss / emergency power source architecture to make sure that the pump is never in danger of losing power. 

Just a thought. 



-=   --> [u]http://www.matronics.com/contrib==================== 

 [quote][b]

ceengland(at)bellsouth.ne
Guest

Posted: Mon Dec 05, 2011 2:53 pm Post subject: Auto Aux Fuel Pump Circuit Idea

On 12/05/2011 08:20 AM, Fred Stucklen wrote:      	  Quote: 	
		                         <![endif]-->   <![endif]-->                

    >How about a duty cycle           controller that servos the pump         

    >to produce a selected pressure .           . . some value below         

    >cracking pressure on the bypass.           Here, leaving the pump         

    >on all the time means that under           low flow demands, the         

    >pump runs slowly but ramps up to           maintain pressure at         

    >higher demands.         

Bob,         

  Not a bad idea. This would emulate the           faucet pump operation. That should be easy to implement….         

  The Auto industry is essentially doing           the same thing with their ‘in-the-tank’ fuel pumps where they           are cooled by the surrounding fuel, and where they always have           a liquid to pump. This results in the whole fuel delivery           system being kept at a higher pressure, making it less           susceptible to a vapor lock condition.         

  Our problem with our current fuel           delivery system design in aircraft is that some portions of           that system are at low pressure, and in a heated environment.           When the engine mounted pump starts sucking fuel (creating           even lower pressure) from these heated lines, we get a vapor           lock situation. We’ve done a ‘patch job’ by placing the Aux           pump ‘near’ the cool fuel source, and use it when a vapor           problem occurs (or to prevent one from occurring). Having a           constant pressure Aux fuel pump might solve this, but is still           a “Patch” as it doesn’t have redundancy.         

  Moving the fuel pump operation into each           tank, with a constant pressure controller, could open up the           usage of Autogas to more planes. Two tanks, each with a pump,           gives redundancy too…         

  Something to think about…..         

  And to those whom have made (or thought           about making) comments about the use of Autogas in our planes,           I’ll ask you a few questions: If Autogas is a problem, why do           you use it in your car? Is it the gas that’s the issue, or the           system that utilizes the gas? If it’s the system, what can we           do to change it to be an acceptable, safe replacement for the           current  100LL aviation systems in our aircraft?         

  Most of the issues of Autogas usage have           been solved in the auto industry already. If we keep open           minds and study these solutions, apply them to the aviation           industry with the required redundancy for safety, we can           overcome ….         

  We have the ability to make changes in           this industry IF we choose too…….          

Fred Stucklen         

RV-7A  N924RV  650 Hrs

     Congrats on being a lot more diplomatic in your response to that     autofuelkills rant than I would have been. You & Rick Girard are     right; a decent late-20th century fuel system would almost certainly     solve the problem.

     There's a guy on the VAF forum that's run 2 pairs of in-series Facet     pumps for years with no problem. (Series operation is to get     pressure high enough to work with the otherwise stock Bendix style     injection.)

     Charlie

      [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 05, 2011 3:06 pm Post subject: Auto Aux Fuel Pump Circuit Idea

At 12:58 PM 12/5/2011, Gill wrote:

Excuse me for jumping in here, but I think you 

guys are working the wrong end of this problem. 

Modern cars don't draw the fuel, they push it with in-tank fuel pumps.



    Which goes to a suggestion I posited earlier that

    it's more attractive to design vapor-lock bottle-necks

    out of the system as opposed to pasting a 'fix' on

    top of a demonstrably deficient design.



Fred: The Auto industry is essentially doing the 

same thing with their ‘in-the-tank’ fuel pumps 

where they are cooled by the surrounding fuel, 

and where they always have a liquid to pump. This 

results in the whole fuel delivery system being 

kept at a higher pressure, making it less 

susceptible to a vapor lock condition.



Our problem with our current fuel delivery system 

design in aircraft is that some portions of that 

system are at low pressure, and in a heated 

environment. When the engine mounted pump starts 

sucking fuel (creating even lower pressure) from 

these heated lines, we get a vapor lock 

situation. We’ve done a ‘patch job’ by placing 

the Aux pump ‘near’ the cool fuel source, and use 

it when a vapor problem occurs (or to prevent one 

from occurring). Having a constant pressure Aux 

fuel pump might solve this, but is still a 

“Patch” as it doesn’t have redundancy.



Moving the fuel pump operation into each tank, 

with a constant pressure controller, could open 

up the usage of Autogas to more planes. Two 

tanks, each with a pump, gives redundancy too…



Something to think about…..



    Bob :The Facet pumps are really compact . . . could

    they not be located so close to the fuel outlet

    that vapor lock in that short span is unlikely

    to impossible?



Fred: And to those whom have made (or thought 

about making) comments about the use of Autogas 

in our planes, <snip> If we keep open minds and 

study these solutions, apply them to the aviation 

industry with the required redundancy for safety, we can overcome ….



    Sure, the issue isn't about the fuel, it's about the system

    in which the fuel is to be used. I had a neighbor about 15

    years ago that had already been burning autogas in his 170

    for years.



    He did extensive testing and found that the gravity flow

    system installed on his airplane needed only a short run of

    plumbing to be insulated to eliminate the hazard on his

    particular machine.



    The vapor lock phenomenon is well understood as well as

    design techniques for eliminating it. I REALLY like

    the system that recirculates part of the pump's flow

    back to one tank. Keeping the system flushed with cool

    fuel seems a pretty solid technique. It's hard for an

    air/radiation conducted heat source to compete with a

    liquid cooling source.



We have the ability to make changes in this industry IF we choose too……



    Absolutely! Whether things discussed in this thread

    have any influence on Fred's endeavors isn't the

    point. The fact that we've laid a lot of simple-

    ideas on the table as proposed recipes for success

    using those ideas is being archived for future

    readers.



    Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 05, 2011 3:07 pm Post subject: Auto Aux Fuel Pump Circuit Idea

At 02:33 PM 12/5/2011, you wrote:

  	  Quote: 	
		   Gentlemen and Ladies,

 

 I have an H-4 Subaru modified from the original Eggenfellner package.  I purchased an electrical manager from Protek.com called the Protek Bus Manager that auto restores a backup fuel pump for auto operations.  My twin pumps are located on the floor of my RV-6A.  We do have a bypass purge line that Jan Eggenfellner developed because some builders ignored his advice and mounted the pumps over the muffler firewall forward without cooling air or protective cover.  I have 77 hours of satisfactory service with this arrangement.

 

 My project can be found on kitlog.com under builders and Ron Burnett. 	


   Thanks for the data points Ron.



 

   Bob . . .    [quote][b]

ronburnett(at)charter.net
Guest

Posted: Mon Dec 05, 2011 4:59 pm Post subject: Auto Aux Fuel Pump Circuit Idea

Bob,



Thanks for all you do.  Took your course twice and learned and enjoyed it both times.  It gave me the confidence to actually start wiring.  You are a most noble soul and asset to all us builders.



Ron Burnett N524RB



M71 Greensfield, MO

On Mon, Dec 5, 2011 at 5:05 PM, Robert L. Nuckolls, III wrote:



 At 02:33 PM 12/5/2011, you wrote: 

Gentlemen and Ladies, 



I have an H-4 Subaru modified from the original Eggenfellner package.  I purchased an electrical manager from Protek.com called the Protek Bus Manager that auto restores a backup fuel pump for auto operations.  My twin pumps are located on the floor of my RV-6A.  We do have a bypass purge line that Jan Eggenfellner developed because some builders ignored his advice and mounted the pumps over the muffler firewall forward without cooling air or protective cover.  I have 77 hours of satisfactory service with this arrangement. 



My project can be found on kitlog.com under builders and Ron Burnett. 

  Thanks for the data points Ron. 



  Bob . . . 



 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 05, 2011 8:38 pm Post subject: Auto Aux Fuel Pump Circuit Idea

At 06:55 PM 12/5/2011, you wrote:

  	  Quote: 	
		  Bob,

 

 Thanks for all you do.  Took your course twice and learned and enjoyed it both times.  It gave me the confidence to actually start wiring.  You are a most noble soul and asset to all us builders. 	


   Thank you for the kind endorsement sir.

   I will endeavor to remain worthy.



 

   Bob . . .    [quote][b]

aerobubba(at)earthlink.ne
Guest

Posted: Wed Dec 07, 2011 5:49 am Post subject: Auto Aux Fuel Pump Circuit Idea

Hi All-



I may have missed something in the exchanges here, but I think a couple data points might have been overlooked.  First, one of the differences in the aircraft and automotive fuel systems is that the automotive system works at ground level.  The aircraft system needs to work at lower ambient atmoshpheric pressures, and is therefore inherently more vapor lock prone than an automotive system with the same fuel at the same temperature.



Another data point is that when the automotive, tank mounted pump fails, you coast over to the side of the road.  It's a little more complicated when the pump in a pump dependent aircraft fuel system quits.



A a reminder, the common philosophy behind aircraft boost pumps is to provide fuel pressure when the engine driven pump can't, I.E. for priming or when the EDP has failed.  If an aircraft fuel system has turned out to need the boost pump in order to operate safely under nominal circumstances, I would suggest that there is another problem that needs to be addressed and that using the boost pump is a band aid, not a solution.



The last thing is that the plans for my fuel injected RV called for quite a bit of seemingly unnecessary tubing in the return line back to the selector valve.  Turns out that the whole point there is to provide a radiator.  If one were to get creative and shorten that line, the system would end up more vapor lock prone.



FWIW, YMMV, ETC



Glen Matejcek

klehman(at)albedo.net
Guest

Posted: Wed Dec 07, 2011 8:02 am Post subject: Auto Aux Fuel Pump Circuit Idea

 	  Quote: 	
		   The last thing is that the plans for my fuel injected RV called for

 quite a bit of seemingly unnecessary tubing in the return line back

 to the selector valve.  Turns out that the whole point there is to

 provide a radiator.  If one were to get creative and shorten that

 line, the system would end up more vapor lock prone.




	


Actually after watching attempts to cool and reintroduce bypassed fuel 

into the pump end in bent airplanes, most folks agree that the issue is 

venting the vapour bubbles back to a tank or header. Merely cooling 

doesn 't cut it for automotive EFI installations. Maybe it works better 

with 100LL. When the pressure drops at the regulator there is excellent 

conditions to create vapour bubbles, some of which are air and not all 

of which will readily re-condense.



Ken

kjohnsondds(at)yahoo.com
Guest

Posted: Wed Dec 07, 2011 2:15 pm Post subject: Auto Aux Fuel Pump Circuit Idea

Hi All,

I seldom write because I am far from an expert in this area.  In addition I have not finished building my plane.  However, I will offer this suggestion as it has been recommended for my engine.  I am using a Mazda rotary engine.  This automotive engine has a fuel rail with a return fuel line to my main fuel tank.  With the engine, a MSD Ignition high pressure electric fuel pump (Part # 2225) was included.  Because this is a very important part for engine function, a second pump has been plumbed in parallel with check valves for each.  There are separate switches for each, which allows one to use either one.  I am uncertain about using them both together, as I am not that far, or if would even be necessary.  These fuel pumps have been placed on  the pilots side of the firewall and the fuel is pumped about 2 feet to the fuel rail.   I have looked up information regarding this fuel pump and it appears to be reliable and that is why I have written.  If others have experience with this fuel pump, it would be open for discussion.  



Ken Johnson

       From: Glen Matejcek <aerobubba(at)earthlink.net>

 To: aeroelectric-list(at)matronics.com 

 Sent: Wednesday, December 7, 2011 7:45 AM

 Subject: Re: Re: Auto Aux Fuel  Pump Circuit Idea

  

 --> AeroElectric-List message posted by: Glen Matejcek <aerobubba(at)earthlink.net (aerobubba(at)earthlink.net)>



Hi All-



I may have missed something in the exchanges here, but I think a couple data points might have been overlooked.  First, one of the differences in the aircraft and automotive fuel systems is that the automotive system works at ground level.  The aircraft system needs to work at lower ambient atmoshpheric pressures, and is therefore inherently more vapor lock prone than an automotive system with the same fuel at the same temperature.



Another data point is that when the automotive, tank mounted pump fails, you coast over to the side of the road.  It's a little more complicated when the pump in a pump dependent aircraft fuel system quits.



A a reminder, the common philosophy behind aircraft boost pumps is to provide fuel pressure when  the engine driven pump can't, I.E. for priming or when the EDP has failed.  If an aircraft fuel system has turned out to need the boost pump in order to operate safely under nominal circumstances, I would suggest that there is another problem that needs to be addressed and that using the boost pump is a band aid, not a solution.



The last thing is that the plans for my fuel injected RV called for quite a bit of seemingly unnecessary tubing in the return line back to the selector valve.  Turns out that the whole point there is to provide a radiator.  If one were to get creative and shorten that line, the system would end up more vapor lock prone.he Builder's Bookstore www.homebuilthelp.cnbsp;                         -Matt Dralle, List ectric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectution Web Site ;                     &nb="http://www.matronics.com/contribution" target="_blank">http://www.mat=====================



 

 

  

 [quote][b]

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Thu Dec 08, 2011 8:06 am Post subject: Re: Auto Aux Fuel Pump Circuit Idea

FWIW, I am running a Simple Digital Systems EFI on my Franklin powered Glasair. I modified the Glasair fuel system to provide gravity pressure to two electric fuel pumps (with integral check valves) under all positive G conditions. 



A sump tank (1 qt) was squeezed between the belly pan and the wing bottom. The header tank and  wing tanks feed  the sump tank. Check valves are installed between the wing tanks and sump. The pumps are at the aft end of the sump tank and push fuel through a FW mounted filter then to the fuel rail, to the pressure regulator and back to the header tank.



Within the header is a dam to within 3/4" of ceiling of the header, creating a 1 gal. capacity dry space.On the dry side of the dam, outside vent air (2) is supplied and wing tank vents and sump tank purge vent are near the top of the dam. At the bottom of the dry side, drain lines back to the mains are installed so that any fuel over the dam from recirculated fuel and a topped off header returns to the wing tanks.



 Normal ops is to leave the header open to feed the sump tank, then select a wing tank R, L, or both. With header open and wing tanks on both, the system accesses total tankage.   As angle of attack is increased, the header tank rises relative to the sump tank increasing gravity pressure at the pump intake. If desired for CG reasons, the header only or wing only may be selected.



The system pressure is 40 psi. The pumps draw 3.5-4 amps each and deliver 20 gph each. Both on delivers 28 gph. One pump is on the main bus, one on the battery bus.



The system has not been flown, but operates as expected in all conceivable +/- AOA.

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Thu Dec 08, 2011 8:33 am Post subject: Re: Auto Aux Fuel Pump Circuit Idea

 	  aerobubba(at)earthlink.ne wrote: 	
		  Hi All-



Another data point is that when the automotive, tank mounted pump fails, you coast over to the side of the road.  It's a little more complicated when the pump in a pump dependent aircraft fuel system quits.

Glen Matejcek 	




My queries and investigations into automotive hi pressure fuel pump failures revealed that a fuel pump rarely has an abrupt total failure. The gearotor and vane type premature failure of the pump mechanism itself is from dirty fuel. Motor failure is age/time related the same as any certified, mechanical/electric AC fuel pump. The symptoms of impending failure  of automotive fuel pumps are the same...falling pressure/increase amperage draw. But people being the fallible monitoring system that they are, is the reason for redundant essential systems.



Anecdotally, I have never experienced an automotive fuel pump failure inspite of two Toyota trucks, a Ford Taurus, a Ford truck and a MBZ sedan being driven over 1,000,000 miles. 



John

Bill & Sue

Joined: 10 Jan 2006
Posts: 48
Location: Malvern, Worcs. UK (Defford, Croft Farm)

Posted: Thu Dec 08, 2011 11:45 am Post subject: Re: Auto Aux Fuel Pump Circuit Idea

Here in the UK Nigel Charles published what I thought was an elegant (and LAA approved) modification for the Europa with its main and reserve feeds to a Rotax engine running on Mogas.

The essence of the mod was to remove the mechanical fuel pump and use two electrical pumps, one fed from the main tank and one from the reserve.

By sensing the fuel pressure, when the fuel pressure dropped (i.e. when the tank ran empty or was blocked) the reserve pump was switched on automatically and illuminating a light on the panel.

I've seen it, it works, and by all accounts seamlessly, changing over without so much as a cough.

Using this system, and insulating the fuel lines in the engine bay, Nigel was also able to avoid vapor lock with sufficient confidence to eliminate the need for a return fuel line to the tank.



Bill

aerobubba(at)earthlink.ne
Guest

Posted: Fri Dec 09, 2011 6:29 am Post subject: Auto Aux Fuel Pump Circuit Idea

HI John-



I once had a Rabbit that developed a rather annoying habit of sputtering and quitting at random and inconvenient times and locations on hot days, and it seemed like vapor lock was the culprit.  The dealer could find nothing wrong with the car and insisted I was buying crap gas.  So, I took it to a sharp independant mechanic (a pilot, as it happens) who determined that when my tank mounted fuel pump got hot, it failed.  When cooled sufficiently, it would function and test normally.



However good and predictable modern pumps may be, my fundamental premise remains that if normal operations can require the use of both pumps to keep the engine running, there is in fact no redundancy.  Finding myself at the side of the road amongst the cornfields in the Rabbit was a nuisance, in the RV it would be a bit more problematic.



Just one guy's perspective-

 	  Quote: 	
		  My queries and investigations into automotive hi pressure fuel pump failures revealed

that a fuel pump rarely has an abrupt total failure. The gearotor and vane

type premature failure of the pump mechanism itself is from dirty fuel. Motor

failure is age/time related the same as any certified, mechanical/electric

AC fuel pump. The symptoms of impending failure  of automotive fuel pumps are

the same...falling pressure/increase amperage draw. But people being the fallible

monitoring system that they are, is the reason for redundant essential systems.



Anecdotally, I have never experienced an automotive fuel pump failure inspite of

two Toyota trucks, a Ford Taurus, a Ford truck and a MBZ sedan being driven

over 1,000,000 miles. 



John




	




Glen Matejcek

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Dec 09, 2011 11:06 am Post subject: Auto Aux Fuel Pump Circuit Idea

At 08:25 AM 12/9/2011, you wrote:

 	  Quote: 	
		  

<aerobubba(at)earthlink.net>


	


 	  Quote: 	
		    So, I took it to a sharp independant mechanic (a pilot, as it 

 happens) who determined that when my tank mounted fuel pump got 

 hot, it failed.  When cooled sufficiently, it would function and test normally.



However good and predictable modern pumps may be, my fundamental 

premise remains that if normal operations can require the use of 

both pumps to keep the engine running, there is in fact no redundancy.


	


 	  Quote: 	
		   >Anecdotally, I have never experienced an automotive fuel pump 

 failure inspite of

 >two Toyota trucks, a Ford Taurus, a Ford truck and a MBZ sedan being driven

 >over 1,000,000 miles.


	


     I've experienced two pump failures . . . on the same

     vehicle. It was a generic design common to millions of other

     vehicles. "Reliability studies" that speak to 1 failure

     per bazillion flight hours are statistically correct

     but often interpreted poorly. The explanation is pretty

     lengthy and easily accesses elsewhere.



     This is why your's truly has always encouraged builders

     to assume that EVERY component is going to fail at some

     point in your lifetime experience with the airplane. Then

     run the failure mode effects analysis to determine how

     that failure can be accommodated . . . as opposed to

     anointing it with the holy-oil of prevention.



     See chapter 17 of "the Connection".



     With respect to fuel pumps, any time you can integrate

     a modern FACET pump into your design, you've got a big

     step up in service life. One moving part, two simple

     valves, totally sold state management of the energy

     used to compress the pumping spring.



     We discussed these pumps at length some years ago here

     on the lists. I researched the patents that spoke to the

     evolution of this technology dating back to the 20's.



     You can tiptoe through the patents on this style of

     pump at:



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



     The neat thing about modern incarnations of this

     style is elimination of the breaker contacts found

     in the earliest versions. Another nice feature is

     their ability to simply shut down when fluid flow

     is restricted of stopped of hard. Fuel pressure

     is a function of a compressed spring force and not

     stalled rotor current.



     One would be hard pressed to find a pump more

     friendly to the failure modes effects analysis

     for moving fuel around the airplane.



   Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Dec 09, 2011 12:22 pm Post subject: Re: Auto Aux Fuel Pump Circuit Idea

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 08:25 AM 12/9/2011, you wrote:

 	  Quote: 	
		  

<aerobubba>



	


 	  Quote: 	
		    So, I took it to a sharp independant mechanic (a pilot, as it 

 happens) who determined that when my tank mounted fuel pump got 

 hot, it failed.  When cooled sufficiently, it would function and test normally.



However good and predictable modern pumps may be, my fundamental 

premise remains that if normal operations can require the use of 

both pumps to keep the engine running, there is in fact no redundancy.



	


     



     One would be hard pressed to find a pump more

     friendly to the failure modes effects analysis

     for moving fuel around the airplane.



   Bob . . . 	




Glen and Bob,



No argument with either of you. I appreciate both of your observations.



The Facet solid state pumps are hard to beat and I have one as a transfer pump. But they don't make the high pressure required by EFI.



And Glen,  of course, if you need two pumps for a system, there is no redundancy if only two are installed. My system needs one operable pump. Two are installed in the hopes that I will be able to choose a runway over a freeway as a place to land if the primary pump dies.



I was glad when this subject came up as it gave me the opportunity to put my fuel system on the table for the analytical minds that hang out here. 



John

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