Van's Air Force
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Fuel Sending Units
- Thread starter dspender
- Start date
Well I got an answer to my question posted on this site June 30 from Terry Kohler which I will pass on to you.
Capacitance senders use the dielectric properties of the fuel to measure volume. Once installed, you need to calibrate them - typically by adding a few gallons at a time and "setting" the receiver at each point. You need a minimum of three points to fix a linear relationship. These are the more modern of the two systems. Still, not without some reliability problems and once installed, difficult to replace. The float units are just that - a sealed "barrel" is attached to an arm that moves up or down as fuel is added or drawn. The arm is attached to a potentiometer which measures electric resistance which is converted on the face of the gage. These are prevalent in most factory airplanes and in mine as well. If the barrel leaks, the gage becomes useless. Also, unlike the cap unit, these are installed at the inboard end of the tank and because of dihedral in the wing, don't show fuel consumption until at least 45 minutes have been burned off each tank (in my plane). With float senders, the only time you can be certain of complete accuracy is at the "zero fuel" measurement. I believe both Cessna and Piper point this out in their POHs as well. Too late for me, but I'd suggest you go with the "C" sending units. In many cases, the type of sender must be matched with the type of gage on the panel.
Thanks again to Terry for his interest and insights.
Capacitance senders use the dielectric properties of the fuel to measure volume. Once installed, you need to calibrate them - typically by adding a few gallons at a time and "setting" the receiver at each point. You need a minimum of three points to fix a linear relationship. These are the more modern of the two systems. Still, not without some reliability problems and once installed, difficult to replace. The float units are just that - a sealed "barrel" is attached to an arm that moves up or down as fuel is added or drawn. The arm is attached to a potentiometer which measures electric resistance which is converted on the face of the gage. These are prevalent in most factory airplanes and in mine as well. If the barrel leaks, the gage becomes useless. Also, unlike the cap unit, these are installed at the inboard end of the tank and because of dihedral in the wing, don't show fuel consumption until at least 45 minutes have been burned off each tank (in my plane). With float senders, the only time you can be certain of complete accuracy is at the "zero fuel" measurement. I believe both Cessna and Piper point this out in their POHs as well. Too late for me, but I'd suggest you go with the "C" sending units. In many cases, the type of sender must be matched with the type of gage on the panel.
Thanks again to Terry for his interest and insights.
You do a good job of summarizing information about both kinds of units. What is not mentioned is that in addition to L and R tank fuel measurements that you would get from either type of instrument, a typical EFIS/MFD will incorporate a fuel flow sensor and display total fuel remaining and an estimate of time remaining. This is an independent check of your remaining fuel, and if it is consistent with the information you have from the tank sensors, then you can be confident in the information.
After taking this into account along with the maintenance/ease of replacement/cost (?) factors, I chose the float sensors and am happy with that choice.
regards
erich
Pilottonny
Well Known Member
Fuel guradian.
I have the float-senders and a Dynon EMS with fuel flow. But additional to that I installed the Fuel-guardian, with sensors on the tank, telling me when I am down to 15 ltr.
In a real nasty situation, after getting both lights blinking (so in theory I am down to 30 ltrs, but actualy have a bit more) I could time how long it will fly on one tank, switch tanks and know exactly how much time is left before it will finally quit on the other (last) tank.
I do not intend to fly the plane that way on a regular basis though.
Regards,
Tonny
I have the float-senders and a Dynon EMS with fuel flow. But additional to that I installed the Fuel-guardian, with sensors on the tank, telling me when I am down to 15 ltr.
In a real nasty situation, after getting both lights blinking (so in theory I am down to 30 ltrs, but actualy have a bit more) I could time how long it will fly on one tank, switch tanks and know exactly how much time is left before it will finally quit on the other (last) tank.
I do not intend to fly the plane that way on a regular basis though.
Regards,
Tonny
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kentb
Well Known Member
I put in the CAP senders.
My reasoning at the time:
. Modern system
. No moving parts
. Nothing to repair or go wrong.
. They will be able to measure fuel level from full to empty.
The things that I didn't consider at the time:
. You need to buy converters to hook up to most engine monitors
. If the were to require repair, you would most likely need to open the tank
back up. Or you could just replace it with the float sender.
Issues I have seen using the CAP sender:
. My archer wing tip Comm antenna would interfere with the
converter/engine monitor when I broadcast. I replace the antenna with
a belly one.
. Even after calibrating I sometime see incorrect readings. It usually reads
lower while in flight then on the ground. It seem to read lowest when
I am watching it more.
I have recently replaced my engine monitor with an EFIS. The fuel used is very accurate and is set to 5% high. I recalibrated both tanks. On a resent flight I was reading 4 gal in left tank and 6 in right tank. The fuel used was showing 21 used out the the 36 that I carry. When I refueled I added 20.3 gal.
Why didn't it know about the other 6?
Kent
My reasoning at the time:
. Modern system
. No moving parts
. Nothing to repair or go wrong.
. They will be able to measure fuel level from full to empty.
The things that I didn't consider at the time:
. You need to buy converters to hook up to most engine monitors
. If the were to require repair, you would most likely need to open the tank
back up. Or you could just replace it with the float sender.
Issues I have seen using the CAP sender:
. My archer wing tip Comm antenna would interfere with the
converter/engine monitor when I broadcast. I replace the antenna with
a belly one.
. Even after calibrating I sometime see incorrect readings. It usually reads
lower while in flight then on the ground. It seem to read lowest when
I am watching it more.
I have recently replaced my engine monitor with an EFIS. The fuel used is very accurate and is set to 5% high. I recalibrated both tanks. On a resent flight I was reading 4 gal in left tank and 6 in right tank. The fuel used was showing 21 used out the the 36 that I carry. When I refueled I added 20.3 gal.
Why didn't it know about the other 6?
Kent
Actually when connected and calibrated with a modern electronic gauge such as the Electronics International, float gauges can be quite accurate.
Just to add my $.02.
The flow sensor does NOT replace a fuel level indicator. The current EMS units can use the flow info to compute remaining fuel and remaining flight time based on current flow. The level indicators actually measure remaining fuel. I have been flying my 9A with the floats connected to a Dynon unit and have found this combo to be very accurate when within the measurement range (<14 gal ). I use this limitation (of not reading >14gal) to announce when to switch tanks. A 4 gal burn left tank then switch. When using the flow calculations I have seen a significant error. The flow unit often shows higher flow than I am actually burning.
If you plan on using LL100 and auto fuel you will have to recalibrate for each fuel type. In addition, if you plan on using auto fuel there will be a measurable difference between the winter blend and summer blend (at least in Sunny California).
Just MHO and YMMV
Bill
The flow sensor does NOT replace a fuel level indicator. The current EMS units can use the flow info to compute remaining fuel and remaining flight time based on current flow. The level indicators actually measure remaining fuel. I have been flying my 9A with the floats connected to a Dynon unit and have found this combo to be very accurate when within the measurement range (<14 gal ). I use this limitation (of not reading >14gal) to announce when to switch tanks. A 4 gal burn left tank then switch. When using the flow calculations I have seen a significant error. The flow unit often shows higher flow than I am actually burning.
If you plan on using LL100 and auto fuel you will have to recalibrate for each fuel type. In addition, if you plan on using auto fuel there will be a measurable difference between the winter blend and summer blend (at least in Sunny California).
Just MHO and YMMV
Bill
Rick_A
Well Known Member
I have a 7A with float senders and use an MVP-50 for the gauges and fuel flow (fuel remaining). Due to the design of the sending units, the gauges max out at 15 gallons. The float is at the top of tank at this point. Once I get below 15 gallons, the gauges are quite accurate. My brother has cap senders and an MVP-50, this combo provides accurate readings above 15 gallons.
The MVP-50 has to be calibrated for both types of senders which is the norm for most electronic gauges.
One other point. The fuel flow/totalizer also needs to be calibrated and errors are cumulative between fill-ups. In other words, you must periodically reset the totalizer by filling the tanks to the top.
The MVP-50 has to be calibrated for both types of senders which is the norm for most electronic gauges.
One other point. The fuel flow/totalizer also needs to be calibrated and errors are cumulative between fill-ups. In other words, you must periodically reset the totalizer by filling the tanks to the top.
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I'm not sure you are understanding all of the advice provided. Go with BOTH fuel level sensors and a fuel flow sensor. The choice of what type of fuel level sensor is less important.
Erich
RetiredRacer
Well Known Member
I've got a question, I take it the float type senders "ground" through their mounting?
Yes, they do!
