VM1000 fuel totalizer

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Rich
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Re: VM1000 fuel totalizer

Post by Rich »

The limit on the fuel gauge maximum is a consequence of the segmented tanks. The probe on each side can only read to the point where the inboard compartment is filled, at which point there is still room (for about ~3 gal.) in the outer compartment. There is a calibration process that needs to be performed on each side, and it's tedious. In addition I believe it's possible to subsequently remove/install the probes incorrectly such that the calibration is no longer accurate. In my case, the gauges are far more accurate in indicating how much fuel the tanks take to be filled than using the fuel computer REM number. I have a suspicion why, but need to gather more data, as my theory has a discrepancy I need to resolve.

I once ran a tank dry, Well, almost, as I chickened out after running it for about 10 minutes indicating 0 gallons on the gauge. Using the tank drain afterward I got about 1/2 gallon out of the tank.
2002 DA40: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: VM1000 fuel totalizer

Post by Robodog »

Rich wrote:
Tue Sep 24, 2019 3:41 pm

I once ran a tank dry, Well, almost, as I chickened out
That's not being a chicken.
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Re: VM1000 fuel totalizer

Post by Colin »

There was a guy I used to follow who built an RB-6 and blogged about the process and his flights afterward. On a return from Mexico with his wife onboard he ran the left tank dry over Big Bear on their way home to Fullerton. His wife burst into tears when the engine stopped and he said it wasn't really possible to console her during the restart, descent and navigation of the complex Los Angeles airspace. But he said that they have a rule now that he'll only do that if he's alone in the plane.
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Lance Murray
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Re: VM1000 fuel totalizer

Post by Lance Murray »

My VMS-1000 fuel gages are accurate within 1 gallons. My gages also only show 15 gallons max. That wasn't the case when I first got the airplane.
Steve wrote:
Tue Sep 24, 2019 3:05 pm
Roger:

Your aircraft seems to be the rare exception with respect to VM1000 fuel gauge accuracy. After more than 16 years on the various Diamond Forums, almost everyone reports a high degree of accuracy and repeatability with the VM1000 capacitive gauges. They do have the weird characteristic of not reading the outboard tank quantity (in the 40 gallon DA40s), but you will get used to that. My aircraft reads a maximum of 15 gallons per side (which is the actual capacity of the inboard tank). In my case, the gauges have never been off as much as one gallon per side in almost 18 years of ownership. Typically, they are off less than 0.5 gallons per side. I never fully trust the gauges (thanks to my primary flight instructor in the Navy), and crosscheck visually when possible, calculate fuel burn using the fuel flow numbers and book burn values, and in general, probably fly around with more fuel than I really need.

It is possible that your probes need to be recalibrated...

Steve
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Re: VM1000 fuel totalizer

Post by Rich »

Lance Murray wrote:
Fri Oct 18, 2019 5:34 am
My VMS-1000 fuel gauges are accurate within 1 gallons. My gauges also only show 15 gallons max. That wasn't the case when I first got the airplane.
Mine are like that, also. The left gauge tops out at 15 gallons, the right at 16. (Note that this is an almost 18-year old plane.) But once they start reading below these numbers, they're also accurate within the 1 gallon resolution. I could go through the calibration procedure again, but it's a really tedious process to correct a minor area of inaccuracy and is itself subject to error.
2002 DA40: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: VM1000 fuel totalizer

Post by Rick »

Rich wrote:
Fri Oct 18, 2019 2:39 pm
Lance Murray wrote:
Fri Oct 18, 2019 5:34 am
My VMS-1000 fuel gauges are accurate within 1 gallons. My gauges also only show 15 gallons max. That wasn't the case when I first got the airplane.
Mine are like that, also. The left gauge tops out at 15 gallons, the right at 16. (Note that this is an almost 18-year old plane.) But once they start reading below these numbers, they're also accurate within the 1 gallon resolution. I could go through the calibration procedure again, but it's a really tedious process to correct a minor area of inaccuracy and is itself subject to error.
I don't think you can "correct" this error via calibration. The failure to show the first 5 gallons on each side is due to the lack of fuel sensor in the outer tank. Remember, with the 40-gallon DA40's, each wing has a 15-gallon inboard tank (with a sensor) and a separate 5-gallon outboard tank (the one with the filler cap) with no sensor. So, there is no way to measure the first 5 gallons in that outer tank!
2007 DA40 XL - Roanoke, VA (KROA)
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Re: VM1000 fuel totalizer

Post by Rich »

Rick wrote:
Fri Oct 18, 2019 3:39 pm
Rich wrote:
Fri Oct 18, 2019 2:39 pm
Lance Murray wrote:
Fri Oct 18, 2019 5:34 am
My VMS-1000 fuel gauges are accurate within 1 gallons. My gauges also only show 15 gallons max. That wasn't the case when I first got the airplane.
Mine are like that, also. The left gauge tops out at 15 gallons, the right at 16. (Note that this is an almost 18-year old plane.) But once they start reading below these numbers, they're also accurate within the 1 gallon resolution. I could go through the calibration procedure again, but it's a really tedious process to correct a minor area of inaccuracy and is itself subject to error.
I don't think you can "correct" this error via calibration. The failure to show the first 5 gallons on each side is due to the lack of fuel sensor in the outer tank. Remember, with the 40-gallon DA40's, each wing has a 15-gallon inboard tank (with a sensor) and a separate 5-gallon outboard tank (the one with the filler cap) with no sensor. So, there is no way to measure the first 5 gallons in that outer tank!
When new, they topped at 17 gallons each. That's the documented behavior. There is fuel in the outer chambers before the inner chambers are completely full. And the chambers are not 15 and 5 gallons. From the AMM:

Each inboard chamber has a capacity of 52.6 liter (13.9 US gal) and each outboard chamber has
a capacity of 26.1 liter (6.9 US gal). The total fuel tank capacity of each wing is 78.7 liter
(20.8 US gal).


As a side note, I once drained one side as completely as I could and upon refilling, it took 20.9 gallons per the fuel delivery meter. The addition tenth is likely a consequence of the volume of the interconnecting hose.

Here is an exercise I did that approximates the volumes of different areas of the tanks, be it air or fuel. It's useful to illustrate the fueling of the outer chamber before the inner chamber is totally full.
DA40 Fuel Tanks - 40 Gallon.jpg
2002 DA40: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: VM1000 fuel totalizer

Post by Lance Murray »

Can anyone explain why when the airplane was new it would show 17 gallons max indication but now it only shows 15 gallons max indication? Could this have had anything to do with the battery chip replacement?

Both numbers are still accurate after burning below that number. My current procedure is to burn a tank to 14 gallons, then switch tanks and burn that one down to 14 gallons. From that point I have an accurate 28 gallons on the gages.
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Re: VM1000 fuel totalizer

Post by Thomas »

I do the same thing to have the correct indication with 28 gallons. I did replace the VM1000 Batt chip 3 yrs ago - but it had no effect. (2003 plane)
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Re: VM1000 fuel totalizer

Post by Steve »

Lance Murray wrote:
Fri Oct 18, 2019 4:35 pm
Can anyone explain why when the airplane was new it would show 17 gallons max indication but now it only shows 15 gallons max indication? Could this have had anything to do with the battery chip replacement?
No. The fuel indicator calibration data is stored in non-volatile memory in another IC. I have replaced the memory battery twice with no loss of calibration. The only "non-linear" behavior I've noted on my airplane is occasionally, after filling the tanks they read 14 gallons instead of the usual 15 on the ground. After a few minutes in the air, they will come up to 15 and stay there until I burn off just over 5 gallons a side.

I assumed that when I fill the tanks, some air bubbles may get trapped on the sensor, enough to slightly alter the capacitance of the probe. After flying a few minutes, the vibration of flight shakes them off the probe, and gives the accurate full reading.

Steve
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