Fuel header warning light / test switch

[Marty_d]

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

[IBob]

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.

[Marty_d]

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.  

[IBob]

That's the one. Works fine for me.

[AndyDrain]

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.

[Blueadventures]

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.

 

Edited August 6, 2021 by Blueadventures
add image

[Marty_d]

Love that carbon panel!!

[ivark]

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..

[IBob]

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.

[facthunter]

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

[IBob]

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.

[facthunter]

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

[AndyDrain]

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.

 

[nomadpete]

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 November 30, 2021 by nomadpete

[eightyknots]

On 06/08/2021 at 4:36 PM, AndyDrain said:

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.

Hi Andy,

 

What kind of extra sensor systems have you added to your tanks?

[AndyDrain]

These.. Currently integrating them into a combined display of Carb Icing prediction and flap display.  (I have electric flaps).

I use an Ardunio NANO. The sensors  are a little sensitive to set up as you need to adjust a small screw to allow for the thickness of the tank. They are capacitance based  so your hand can get in the way of things.

More info here

[AndyDrain]

These might be better as they incorporate a relay so you could simply add lights next to the existing warning light using the relay contacts. They were not around when I started.

[lyle janke]

On 06/08/2021 at 2:06 PM, AndyDrain said:

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.

i have bought these to use some time they are low level warning light & sensor (new version is ultra sonic prev. ver was sensor)  https://radiantinstruments.com/bingo-4-liquid-detector/ they have a whole range of instruments as well  see on the website 

this my be of interest to you 

[Blueadventures]

On 01/12/2021 at 6:29 AM, nomadpete said:

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!

Also, a way I check the sensor and whole circuit is at engine service time start engine with the fuel tanks turn off, after a while the low fuel light needs to luminate.  I added the savannah collector / surge tank to my build and it give  reassurance when low on fuel as if the collector tank is not filling from the two wing tanks then need to land within 15 to 20 minutes or a bit longer.  Will get you in preparation mode with some added flying time.

[AndyDrain]

@lyle janke

Looks like the same sensor- there is probably only one company producing these. They come in  range of different versions.  I have to say it looks a bit expensive at US$129.95.

 

The actual sensor is of the order of US$5-10. 

Edited June 15, 2022 by AndyDrain
typo

[AndyDrain]

I see the image I pasted earlier on the sensor didn't appear so I will try again.  

[RFguy]

suggest using multiple sensors , Just like ships have three clocks....

 

three of them wired in a majority vote configuration, although this is usually only used for devices that have some implicit reliability issues . 

 

Or just three sensors and three LEDs and let the human do the majority vote.

 

of course yep the system still needs to be tested. if u have majority vote, then one sensor gets unplugged, but for system  test, tank needs to be drained (run down) to trigger sensors.

Edited June 15, 2022 by RFguy

[Markdun]

I’m new to this idea of a low fuel warning as there is such a device on the J200 I’m restoring, and I am inclined to heave it overboard. My current and past aeroplanes didn’t/don’t have one. You know how much fuel you put into the tanks; you then checked this by dipping the tanks; you have an indicator of fuel level from either a window or a fuel level sensor; you have calculated fuel remaining from fuel consumption multiplied by time (either estimated or via a fuel flow sensor).  It seems to me the only scenario is that fuel has leaked out... which would have been picked up in your walk around or from your EMS fuel flow high alarm setting.

 Don’t get me wrong. I’m a total Nervous Nellie when it comes to fuel starvation. In an unfamiliar aircraft I flew from Kal to Forres, I calculated estimated fuel remaining every 20 minutes and compared that to my flight plan and adjusting fit the headwind. This was from fuel burn estimates using 3 sources of data: from estimated fuel burn; from the unknown calibration fuel flow computer; from the wing tank fuel level gauges (one of which I had to do a ‘Taranaki’ repair on because the LAME found it too difficult...& of-course that doofer repair remains 5 years on).  Yeh, yeh, more work, a bit autistic, but it gave me something to do, other than tick off each railway airstrip we flew over while the owner held the stick. We landed with 35l actually remaining compared to my estimate of 28l, from 100l at Kal.

[IBob]

Markdun, I would suggest it is a matter of horses for courses, as they say: depends on the configuration of the fuel system and the pilot's understanding of that.

So I have no opinion as to whether it is a good idea in your aircraft.

In my own, it is a nice feature, allowing outboard tanks (which have no sight glasses) to be flown to exhaustion: they are less used than the inboard tanks, and would otherwise have stale fuel sloshing round in them.

I n addition, I and others have written here about the benefits of having a 6L receiver tank between the main tanks and the engine: having a low level (its actually a not-high-level) indicator in that tank is the icing on the cake, giving assurance that we have the full benefit of the time that 6L buys.

[facthunter]

Fuel indications are often not  very accurate and Jabiru's have long thin tanks. . Jet liners have had fuel leaks in flight and had to glide. Nev