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I am 10 days away from taking my private pilot check ride and was wondering if there was any small/weird thing on the DA-40 that I should know about or be prepared to answer

For me the gotcha question that I could not answer during the ground part of my practical exam (check ride) was "Where is the ELT antenna". You can see the post here:

• viewtopic.php?f=8&t=6748&p=73275#p73275

If the examiner fails the PFD or turns down the brightness all the way (assuming you have a G1000 bird), be sure you know to hit the red reversionary button to get the PFD on the right side. Know the electrical system backups (essential bus and emergency switch) and what functionality remains. Always use checklist throughout the flight.

I don't know that in the US not knowing where all your antennae are would be cause for failure. But the examiner may ask you off-the-wall questions like that to probe the limits of your knowledge of the aircraft. Location of the VOR antenna also comes to mind, as it's hidden (along with LOC/GS) in the horizontal stabilizer. Some planes are also equipped with additional hidden antennae, such as GPS/XM combos.

I was also surprised to learn it's not uncommon among us not to recognize the OAT probe. I have been asked in Flight Reviews about each thing poking out of the airplane, most of which are antennae for one device or another (transponder, marker beacons, etc.)

Be sure you're up on fuel management. I note that managing the fuel gauges on the 50 gal tank versions is a bit out of the ordinary. Using the fuel totalizer might be a better method. (In my 40-gal variant, I'm too lazy, as the gauges are simpler and work fine.)

Rich,
Because the silly 'tank dipping' method is abandoned by most after the first week of ownership, largely because they break or loose the clumsy tool, the totalizator is an essential verification of the fuel gauges. That gap in the 50 gal gauges is a non-issue because it comes at a point where you know there are still a few hours of fuel on board. Also, if you have the G1000 the range-ring is magic. Love that tool.

BRS wrote: ↑Mon Jun 17, 2019 2:07 pm Rich,
Because the silly 'tank dipping' method is abandoned by most after the first week of ownership, largely because they break or loose the clumsy tool, the totalizator is an essential verification of the fuel gauges. That gap in the 50 gal gauges is a non-issue because it comes at a point where you know there are still a few hours of fuel on board. Also, if you have the G1000 the range-ring is magic. Love that tool.

As I understand it from reading the POH, there really isn't a gap in the 50-gallon display, but beyond 16 gallons per side you have to manually/mentally deal with the additional amount. From the POH:

Long Range Tank:
At an indication of 16 US gal the quantity of auxiliary fuel can
be determined by switching the AUX FUEL QTY switch to the
respective position (LH or RH). The auxiliary fuel quantity is
added to the 16 US gal.

Though the totalizer is more practical in this scenario, I can see a DPE wanting to see you know how to deal with this quirk in the gauges. In short, you should be able to demonstrate you know how to operate everything in the plane.

In my case I have confidence in the gauges, and being I'm the only one flying my plane I know how much it's been flown since last fillup (I log each fillup in the hour log I keep in the plane). And I should be using the totalizer function, but haven't been in the habit.

The 'gap' is in the G1000 display. There is no switching.
Sorry, I don't have a better pic at the moment.

For the G1000 Lycoming DA40's, which I assume is what the OP is taking his check ride in, there are 2 options - standard 40-gal tanks, and 'long-range' 50-gal tanks. Both options have 'gaps' in the fuel gauge display. The 40-gallon DA40's have 2 tanks in each wing - the outer-most tank is something like 6 gallons, and the inner one around 14 gallons (so 25 gal per wing). Only the inner tank has a fuel sensor in it, so there is a 'gap' at the top end of the fuel gauge (full tanks only show 17 gallons on each gauge instead of the 20+ that are in the tanks). The gauge doesn't start showing anything used until the level in the inner tank starts to drop, after burning about 3 gallons out of the outer tank.

With the 50 gallon option, there are 3 tanks in each wing - an extra 5 gallon tank is added outboard of the 6 gallon tank. This extra tank also has a fuel sensor, but the middle tank still has no sensor, so the fuel gauges have a 'gap' in the middle. The gauges shows 25 gallons (per side) when full, but after burning about 5 gallons from a side, the gauge suddenly drops from 20 to 15 gallons, and stays there until the middle tank is low.

In both cases, the fuel totalizer shows the true amount of fuel in the tanks, assuming it was reset when the tanks were filled. I have found the totalizer to be quite accurate in all the DA40's I have flown over the years. The gauges are also very accurate, as long as you understand where fuel is (and is NOT) being measured!

Interesting. It appears that the POH is incorrect with respect to fuel indication. It looks like it describes operation of auxiliary tanks if you have a VM1000. (I suspect that no such DA40's exist.) It describes aux fuel indication not at all for the G1000. Presumably the supplement for the G1000 needs to be used.

The POH is certainly wrong on one point with resoect to the VM1000 setup. I've found the gauges will register fuel below 3 gallons. The gauge alternates between "low fuel" and display of an actual gallon reading from the gauge. I've taken one tank down well into the point where it displays 1 gallon, trying to run a tank to empty. (I chickened out and wound up draining the remainder through the sump drain while parked on the ground.)

Also on the topic of fuel: Remember the silly fuel quantity measuring device is Required Equipment, so make sure you have that in the plane somewhere and know how to use it. Unless the examiner really knows the DA40 likely this will not be an issue... but some do.