DA62 fuel tanks

[Boatguy]

How many gallons are in the inner, middle, and outer chamber of the main wing tanks? Not the total, their individual capacities.

[Boatguy]

Really? Nobody knows?

[CFIDave]

See next post...

[CFIDave]

I went back and found an old DA40-180 (Lycoming) factory training class file, and here's what it says for the DA40 fuel tanks (I would assume the 3-chamber DA62 tanks are the same as the long-range DA40-180 tanks, since Diamond likes to re-use parts):

Fuel System Storage
• Fuel tanks in each wing, and each tank is made up of 2 (short range) or 3 (long range) chambers.
• Inboard chamber 52.6 lts (13.9 US gal)
• Outboard chamber 26.1 lts (6.9 US gals)
- Total 78.7 lts (20.8 US gals)
• Aux chamber (optional long range)
- 15.9 lts (4.2 US gals)
- Total 94.8 lts (25 US gals) per wing.

[MackAttack]

Closest I’ve come is 25.4 gal per side in the mains, and 18.5 per side in the aux tanks. 86.4 useable with the aux tanks. I haven’t seen it broken down by the main tank chambers. The AFM isn’t that specific. You might have to contact Diamond or a dealer directly.

[Boatguy]

I went back and found an old DA40-180 (Lycoming) factory training class file, and here's what it says for the DA40 fuel tanks (I would assume the 3-chamber DA62 tanks are the same as the long-range DA40-180 tanks, since Diamond likes to re-use parts):

That’s what I think Rich suggested a few weeks ago. After flying one all these years, isn’t it clear from the tank gauges and totalizer?

[CFIDave]

I went back and found an old DA40-180 (Lycoming) factory training class file, and here's what it says for the DA40 fuel tanks (I would assume the 3-chamber DA62 tanks are the same as the long-range DA40-180 tanks, since Diamond likes to re-use parts):

That’s what I think Rich suggested a few weeks ago. After flying one all these years, isn’t it clear from the tank gauges and totalizer?

As has been discussed here on DAN before, Diamond fuel gauges are unusual in that the *middle* chamber (in a DA62, DA42, or DA40-180 with extended range tanks) lacks the capacitive rod fuel sensors found inside of the inner and outer chambers. As fuel is drawn down from each wing, the G1000's fuel gauges that initially show 25 gallons (with full tanks) are programmed to decrease to 17 gallon indication for quite awhile (i.e., the "dead spot"), to approximate the middle chamber (that can't be measured) being partially full.

For a DA40NG, things are much simpler: capacitive rods only measure fuel in the inner chamber, i.e., only the last 14 gallons per wing.

[Boatguy]

Diamond fuel gauges are unusual in that the "middle" chamber (in a DA62, DA42, or DA40-180 with extended range tanks) lacks the capacitive rod fuel sensors found inside of the inner and outer chambers. As fuel is drawn down from each wing, the G1000's fuel gauges that initially show 25 gallons (with full tanks) are programmed to decrease to 17 gallon indication for quite awhile (i.e., the "dead spot"), to approximate the middle chamber (that can't be measured) being partially full.

I was aware of the fuel sensor issue. Based on that I would have expected that with 4gal in the outer tank, the gauges would drop from 25 to 21, stick on 21 until 7gal more were consumed, then show 14.

But the G1000 is programmed to "fake it" part way through the middle chamber? Or it uses the totalizer to calculate the fuel level rather than the sensor?

[Rich]

And now I will presume to correct myself. I noticed that the total gallons for the 62 are 26, not 25, gallons. I also noted that the part numbers in the IPC between the 40 and the 62 do not exactly match.

I made the inference that the drawings in the respective AMM's for the DA40L/42NG/62 are isometric and to scale. Specifically fig.2 for the 40 and fig.1 for the others. It should be noted that fig.1 for the DA40 is specifically depicted to NOT be to scale.

I also make the assumption that the cross sections of all three chambers are the same for any given model. Therefore the ratios of the volumes of each chamber to the total volume would be the same as the ratio of the length of each to the total of the length of all three.

I tested these hypotheses by comparing the stated individual volumes of each of the three DA40 to calculated volumes as a fraction of their total. Within the ability to measure the drawing, the calculated volumes matched up pretty well.

Armed with this approach I measured and calculated the numbers for the DA62 and find them to be 13.0, 7.5, and 5.5 gallons, respectively, from inner to outer chambers. Just for grins, I checked the 42 and found them to be the same as the 62. So pretty close to the distribution of the DA40, but not quite identical.

Make of this what you will.

[CFIDave]

Based on that I would have expected that with 4gal in the outer tank, the gauges would drop from 25 to 21, stick on 21 until 7gal more were consumed, then show 14.

But the G1000 is programmed to "fake it" part way through the middle chamber? Or it uses the totalizer to calculate the fuel level rather than the sensor?

I think it would be pretty disconcerting for pilots to see a sudden drop in fuel from 21 to 14 gal, so yeah, the G1000 is programmed to "fake it" as the middle chamber is emptied. Even with the wing's dihedral, we can't assume that all of the fuel is used in the outer chamber before some fuel is drawn from the middle chamber; similarly, there's some fuel drawn from the inner chamber before the middle chamber is completely emptied. I'm sure some clever Diamond/Garmin engineers figured out how to program the G1000's fuel gauges to try and minimize the 17 gal dead spot.