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Fuel header warning light / test switch


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Hi Sav owners,

 

I'm installing the Sav wiring harness and instruments on my 701.

 

Noticed that the wiring plans show the fuel header warning light and test switch installed on the far right side of the panel.

 

Seems to me that if I have a warning light telling me I have 18 minutes of fuel left, I want that bugger right in front of me.

 

Have any of you changed the position of this?  Or is it noticeable enough where they position it?

 

Thanks, Marty

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Hi Marty. Couldn't agree more.

First. I changed the regular bulb supplied for a large flashing LED.
Then I put another in parallel to that on the LH side of the panel.

The RS part number for the flashing LED I used is 209-119. It comes with it's own bezel.

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6 minutes ago, IBob said:

Hi Marty. Couldn't agree more.

First. I changed the regular bulb supplied for a large flashing LED.
Then I put another in parallel to that on the LH side of the panel.

The RS part number for the flashing LED I used is 209-119. It comes with it's own bezel.

This one?

https://au.rs-online.com/web/p/indicators/0209119/

 

Thanks Bob.  

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Remember the test switch only checks the bulb is good - not the sensor.  In 600 hours I have only had the warning light come on twice, when unplanned.  On both occasions I picked up the warning while it was in the flashing state - prior to becoming steady. The light is in the default location. ( I would move it if I built another).

 

I'm currently mounting sensors on the outside tanks to give a 5 litre warning.  They will not be very accurate but will at least tell me when those tanks are empty. I can set those up so that a light goes off when the level is low, so it is reasonably fail safe.

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On 04/08/2021 at 12:19 PM, Marty_d said:

Hi Sav owners,

 

I'm installing the Sav wiring harness and instruments on my 701.

 

Noticed that the wiring plans show the fuel header warning light and test switch installed on the far right side of the panel.

 

Seems to me that if I have a warning light telling me I have 18 minutes of fuel left, I want that bugger right in front of me.

 

Have any of you changed the position of this?  Or is it noticeable enough where they position it?

 

Thanks, Marty

In front is good, that is where I mounted mine.  I also installed another amber to alert if every the starter stays on / engaged due to faulty solenoid.  (That saves cooking starter and draining battery both which can result in expense to rectify, replacement cost ad inconvenience that flight etc.  My low fuel has the push to function built in.  Cheers.

 

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Edited by Blueadventures
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  • 3 months later...

has anyone had unplanned indication from the warning light? I  have had it now twice with tanks at  least half full.. the light started flickering, turned on, and went off after 10-15min..

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Hi Ivark,

the newer Savannahs have a vent pipe, from the top of the receiver tank up to the top of the LH wing tank. This allows any air in the receiver tank to vent.

The older Savannahs do not have this vent pipe, so if you get some air in the receiver tank (perhaps from momentary unporting of the wing tanks), it can become trapped there, and you may get false low fuel indications.

Typically this happens as you gain altitude, because the trapped air bubble increases in size as the air pressure is reduced. I have flown in a VG that did this.

 

This may be the reason for your warning light coming on. If there is an air bubble in your receiver tank, you may be able to see it with a bright light.

 

...................................................................................................................................................................................

 

The low level switch is a simple reed switch, operated by a floating magnet in the tank: when the level falls, the magnet closes the switch. It is possible for this switch to fail. I do not know if this would cause the intermittent fault that you describe.

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19 minutes ago, facthunter said:

 A warning you can't trust creates it's own risks.  Nev

True enough. But very few warnings systems are entirely foolproof.

So I believe the emphasis needs to be on understanding the system. And the number of forced landings due to poor pilot fuel management would seem to bear that out.

 
I think most here would agree that tanks should always be physically dipped before flight.

After that, in the case of the Savannah, there are sight glasses for the inboard wing tanks, which inevitably slosh around some, but still provide the pilot with a reasonable indication of tank contents.
I would go so far as to say that I think the Savannah has a very well thought out fuel system.

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An alarm clock set to a time were fuel starts to be a problem may be just as good as many set ups. Yes the  Savannah would seem to be better than most. A poor fuel system is always with you as a risk. Try to get it as good as you possibly can. Nev

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Ibob - I do agree but have a worry that relying on a non fail safe warning on a small header tank is a little worrying.  Hence I'm in the process of adding an additional fail safe sensor to this tank.

 

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In my past employment we used many magnetic reed switches. The only failures I recall were caused by the rare stuck 'closed' switches. This usually coincided with years of being constantly in the 'closed'state . Never had an intermittent one.

If you are worried by the low probability of a stuck switch, add a test into your 100hr/yearly maintenance. Slip the reed switch out of its holder and verify that the alarm works. Better still, you WILL be doing a gravity fuel flow rate check, won't you? When you drain the last of the fuel, the alarm is verified, and the switch gets an annual workout which should prevent long term sticking.

 

Oh, I assume you didn't buy the cheapest little reed switch you could find on the net!

Edited by nomadpete
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