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Automatic header tank filling

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air.peter(at)googlemail.c
Guest

Posted: Tue May 30, 2017 2:43 am Post subject: Automatic header tank filling

Hi,

I am flying a Lancair 360 with wing tanks and the standard header tank. Rather thinking every 20 to 30 minutes to fill up the header tank again I would like to have an automatism filling the tank.

I have a capacitive fuel gauge (output 0 to 5 V) and an independent emergency reminder looking up at the annunciator panel (at) about 5 gallons. 

Rather re-inventing the wheel – is there a circuit diagram out there I can use for such a fuel filling mimic ?

 

Thanks in advance,

 

Peter

LNC 360 MKII

D-EPSO

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 30, 2017 10:05 am Post subject: Automatic header tank filling

Hi,



 I am flying a Lancair 360 with wing tanks and the standard header tank. Rather thinking every 20 to 30 minutes to fill up the header tank again I would like to have an automatism filling the tank.



   I've done a couple of similar systems. Last

   one was for the Piaggio P-180.



 I have a capacitive fuel gauge (output 0 to 5 V) and an independent emergency reminder looking up at the annunciator panel (at) about 5 gallons. 



   The analog output makes the 'control' easy to do.

   The dragon to slay is failure mitigation.

   Any time you add a automatic feature to the

   airplane, it's wise to assume that it will

   fail at some point.



   What are the ways it can fail? How will you

   become aware of the failure? Is the failure

   pre-flight detectable? What are plans A, B, etc.

   for dealing with the failure(s)?

   

   You have a low level warning light . . . this should

   be totally independent of any other function.

   Suppose the transfer sticks ON and overfills the

   tank. What happens if the tank is over filled; 

   what happens to excess fuel? Is there a practical

   way to add a high level warning?



 Rather re-inventing the wheel – is there a circuit diagram out there I can use for such a fuel filling mimic ?

  

   You can watch the dc voltage from the

   fuel gage with a comparator that will,

   for example, turn the transfer ON at 

   3 volts or below and OFF at 4 volts or

   above . . . or what ever hysteresis values

   seem most practical.



   The existing low level warning backs up

   a failure to transfer, some kind of high

   level warning should back of a failure to

   stop transferring.



 

 

   Bob . . .

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ceengland7(at)gmail.com
Guest

Posted: Wed May 31, 2017 4:45 am Post subject: Automatic header tank filling

On Tue, May 30, 2017 at 1:03 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    Hi,



 I am flying a Lancair 360 with wing tanks and the standard header tank. Rather thinking every 20 to 30 minutes to fill up the header tank again I would like to have an automatism filling the tank.



 Â  I've done a couple of similar systems. Last

 Â  one was for the Piaggio P-180.



 I have a capacitive fuel gauge (output 0 to 5 V) and an independent emergency reminder looking up at the annunciator panel (at) about 5 gallons. 



 Â  The analog output makes the 'control' easy to do.

 Â  The dragon to slay is failure mitigation.

 Â  Any time you add a automatic feature to the

 Â  airplane, it's wise to assume that it will

 Â  fail at some point.



 Â  What are the ways it can fail? How will you

 Â  become aware of the failure? Is the failure

 Â  pre-flight detectable? What are plans A, B, etc.

 Â  for dealing with the failure(s)?

 Â  

 Â  You have a low level warning light . . . this should

 Â  be totally independent of any other function.

 Â  Suppose the transfer sticks ON and overfills the

 Â  tank. What happens if the tank is over filled; 

 Â  what happens to excess fuel? Is there a practical

 Â  way to add a high level warning?



 Rather re-inventing the wheel â€“ is there a circuit diagram out there I can use for such a fuel filling mimic ?

 Â 

 Â  You can watch the dc voltage from the

 Â  fuel gage with a comparator that will,

 Â  for example, turn the transfer ON at 

 Â  3 volts or below and OFF at 4 volts or

 Â  above . . . or what ever hysteresis values

 Â  seem most practical.



 Â  The existing low level warning backs up

 Â  a failure to transfer, some kind of high

 Â  level warning should back of a failure to

 Â  stop transferring.



 

 

 Â  Bob . . .  

	


"Suppose the transfer sticks ON and overfills the

Â  tank. What happens if the tank is over filled;Â Â  what happens to excess fuel? Is there a practicalÂ  way to add a high level warning?"



The additional issue I never considered (but a research scientist friend who tests *everything*, did), was what happens to the *tank*. If you have a typical vent system using -4 (1/4" OD) tubing, when fuel hits the vent, the transfer pump can cause pressures in the tank to reach 10 psi. In case you don't know, more than about 2 psi will damage most a/c fuel tanks in planes like most of us fly.

Dilemma: positive protection from overfilling that can't fail and prevent transfer.

Secondary dilemma, when using auto-transfer: Especially if there's more than one aux tank, preventing the transfer pump from running (and destroying itself) when pumping from an empty tank.Â

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