DA40 Best Angle Speed, Vx

[Britton]

Hi everyone, apologies if this has been covered already I couldn’t find this particular subject by searching. If it has, please point me to it.

The manual talks a lot about Vy, but I only find Vx in the front for abbreviations nomenclature.

As I’m going for my check ride in a few weeks I just know the examiner is going to raise an eyebrow to any comment that “Vx isn’t listed in the book, but it’s less than Vy by 5-10kts or so”.

I know this is pedantic given the awesome climb performance we have. I just have a feeling I’ll be called on it when explaining situations for takeoffs over obstacles.

I’ve emailed Diamond a while ago and never got a response. I’ve also downloaded a few DA40 checklists from the net and the numbers for Vx are all over the place on the homegrown lists.

So looking for pointers, advice, the numbers would be nice, or a kick to a different thread if someone’s has the time.

Thanks, I appreciate it.
Britton

[Rich]

The correct answer is that Vx for the DA40 is not published. The real answer is that you will get a better climb angle at somewhat slower than Vy, though I believe some have received advice from Diamond to use Vy for Vx.

[Keith M]

When I bought my DA40 TDI from Diamond UK, I was informed that Vx wasn't published because it was too close to the stall speed for safety. I've also heard that it's not different enough from Vy to be worth bothering with, but in that case, there would be no reason not to state it in the AFM.

[Lance Murray]

The differences are small enough to just be academic. Use Vy for normal ops. Trapped in a box canyon? A speed just above stall will get you what you need. At least you will hit the ground at a slower speed.

[Rich]

To get back to the original context of the question, which is a potential question from the examiner. For a PPL exam, you can't go wrong referencing the AFM, including what's missing. In the absence of specific information, though, it's good to be prepared to describe what you would do in, say, an obstacle-clearance challenge.

Here's another one that's not explicitly covered: Soft-field takeoff. Not a procedure covered in the DA40 AFM, but the short-field procedure that is listed is the one you should use.

[Britton]

Understood, thanks everyone.
Britton

[Mikael W]

Regarding soft-field take-off, please see DA40 AFM chapter "Abnormal Operating Procedures" (page 4B-7):

4B.4 TAKE-OFF FROM A SHORT GRASS STRIP
1. Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . apply
2. Flaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T/O
3. Throttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . MAX PWR
4. Elevator (control stick) . . . . . . . . . . . . . . . . . fully aft
5. Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . release
6. Hold direction . . . . . . . . . . . . . . . . . . . . . . . using rudder
NOTE
In strong crosswinds steering can be augmented by use of
the toe brakes. It should be noted, however, that this method
increases the take-off roll, and should not generally be used.
7. Elevator (control stick) . . . . . . . . release slowly, when nose wheel has lifted
Allow airplane to lift off as soon as possible and increase speed at low level.
8. Airspeed . . . . . . . . . . . . . . . . . . . . . . . 66 KIAS (1150 kg, 2535 lb)
60 KIAS (1000 kg, 2205 lb)
54 KIAS (850 kg, 1874 lb)
9. RPM lever . . . . . . . . . . . . . . . . . . . . . . . . . . 2400 RPM, above safe altitude
10. Flaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UP, above safe altitude
11. Electrical fuel pump . . . . . . . . . . . . . . . . . . . OFF, above safe altitude
12. Landing light . . . . . . . . . . . . . . . . . . . . . . . . as required

Cheers /Mikael

[Rich]

I hadn't noticed the "grass" in the short field. I'm going to add one real-world caveat to this though: Not all "grass" strips are particularly pristine. Running up to full power while at a standstill risks picking up debris from the surface and dinging your prop. You'd be amazed at the size of the stuff you may wind up hitting for a home run while doing this. I was when I wrecked a McCauley prop years ago.

[LuckyDube07]

Britton et al:

I just purchased a 2008 DA40 XLS (N873MA), this is my first post on the forums. I will soon use 3MA to complete my Commercial/CFI ratings, and plan to use the plane for follow on CFI work. I'll apologize in advance for the length of this note.

I put 3MA in leaseback with my local flight school, so I'm in the process of writing up a pre-solo exam for those who want to use my DA40 for their own training. In the course of making the exam I came across the Vx issue as well. I started digging into the FAA Handbook of Aeronautical Knowledge to see if there was any general guidance that would help. The closest thing I was able to find was on pg 11-7, where it described maximum angle of climb (AOC) as a function of excess thrust available (given the best combo of AOA and airspeed). According to the handbook, max excess thrust in a prop aircraft "normally occurs at an airspeed below L/Dmax and frequently just above stall speed." Not sure if this helps, but at least you can provide some sort of "book" answer to your examiner (although I would not be comfortable trying to climb at just above stall speed at takeoff). Another potential option would be to infer the climb airspeed noted in the short grass strip procedure above as your Vx; for mine (serial 40.833) its 67 KIAS @ 2646 lbs (got the long-range tanks). Either way, I would be interested in how your DFE handled the Vx issue, if it ever came up. For now, I plan to put VX as "not defined" in my pre-solo test.

I'm also vexed by the lack of a short field procedure in the AFM that's comparable to what I used the C172 when I got my PPL, especially with regard to an expected Vr speed. The ProPilot DA40 checklist that came with the plane uses the same procedures for short and soft field, but does not mention a defined Vr speed either. I also reviewed Qref's version, they use a maximum performance climb checklist but don't break it down between short or soft field takeoffs. I assume then that we should use the short grass strip procedures for both short field and soft field applications?

One last aside re: the ProPilot checklist - I emailed the company this week about getting a revised set of checklist since the ones I have were last updated in 2010. Turns out they are closing shop very soon, so no updates coming.