FLC for best glide in DA40NG?

[Boatguy]

Best glide in the DA40NG is 88kts. Assuming I lost the engine, I'm guessing I'd be a busy pilot trying to aviate, navigate and communicate. Could the AP help?

Today I was flying at about 5,000' with the AP in HDG/ALT modes. I selected 2,500', an FLC of 88kts, and then pulled the power to 0%. The plane nosed over and settled at a 950fpm rate of descent. There was a bit of pitching up and down (winds aloft were 25-30 and gusty), but -950 was pretty much the stable rate of descent. The good news is that in an engine out scenario the AP will fly the plane at max glide, reducing workload so that I could figure out the best way to use the remaining time aloft.

In a real loss of engine scenario the prop would not be spinning which I believe means less drag. In a perfect world I think setting the power lever at 20% would pseudo-feather the prop and perhaps improve the results. But I don't understand enough about the prop governor to believe that with the engine shut down the prop pitch would change when I move the power lever.

[smoss]

Russ,
Good idea on using FLC / HDG for best glide, but it would probably be hard to implement in real time. Assuming you are flying along happily in cruise, and lose your engine, first you'd have to quickly dial Altitude select down to 0, then change ALT mode to ALTS, then change to FLC from pitch, then dial to best glide FLC speed. And don't forget, with initial engine loss, you'd probably immediately disconnect AP, or it would quickly pitch up to stall to maintain your current altitude.

[Boatguy]

Russ,
Good idea on using FLC / HDG for best glide, but it would probably be hard to implement in real time. Assuming you are flying along happily in cruise, and lose your engine, first you'd have to quickly dial Altitude select down to 0, then change ALT mode to ALTS, then change to FLC from pitch, then dial to best glide FLC speed. And don't forget, with initial engine loss, you'd probably immediately disconnect AP, or it would quickly pitch up to stall to maintain your current altitude.

Not quite that bad. In an EFATO scenario I agree you'd never do this, there just isn't time.

Does engine failure disconnect the AP? I don't know for sure, but I doubt it. The documentation makes no mention of disconnect on engine failure. I know that the AP will engage in the hangar when the engine is not running. On shutdown the only failure indications are for the engine sensors. It's easy enough to test this question the next time I shut down after a flight. Good suggestion to check on that.

This was basically the scenario of the "miracle on the Hudson" (read Fly By Wire). The Airbus envelope control actively controlled the pitch to avoid a stall through the ditching.

I agree the AP would start to pitch up, but from cruise at say 145-150KTAS there is a lot of energy to bleed off and it will take awhile. I separately posted about "35% power" in the Austro forum. I did my test of best glide starting at 70KIAS coming out of my turbo failure test. From 40% to 35% power it took awhile for the energy to bleed off from 90KIAS to 70KIAS as a result of the AP pitching up.

If we are in level flight and the AP is in NAV/ALT, the button sequence would be:

- FLC (which will capture the current speed of say 120KIAS depending on altitude)
- Nose Up as required to adjust target speed to 88
- Twist the Altitude button to 1,000'

Again, this is a scenario that can be more thoroughly tested.

[smoss]

Definitely worth giving it a practice try...

[Chris]

I've practiced using FLC for this scenario and the sequence I use is to first give the ALT SEL knob a quick twist before changing to FLC mode. Otherwise I think the AP might switch back to ALT mode if you happen to already be near the selected altitude. it's easy to do once you practice it since the knob and buttons are all right together.

[Rick]

Assuming you were on already AP when the engine failed, I think the fastest way to get to FLC at Best Glide is to just hold the CWS button while you bleed off speed and then push the nose over and establish best glide speed. Then, just release the CWS button and press FLC. That's it. FLC will capture the current speed when you press it. You can tweak it a couple of knots with Nose Up or Down if needed. You can set the altitude later - in fact, if you set the altitude to the elevation of the field you are (hopefully) headed toward, the glide arc will tell you if you are going to make it or not at your current GS and descent rate.

[tahoemark]

I learned this on another plane. The technique is to put the auto pilot in heading mode and alt hold. While the speed is bleeding off set the heading bug to your desired course. Then turn the altitude knob down to zero. By this time you will be getting close to your best glide speed and when you reach it hit FLC. Once you are in FLC mode, you can fine tune your speed with the nose up and down buttons if you didn’t get the exact speed you wanted when you hit FLC. With a little practice this is easy to do. Once the Auto pilot is flying at your Best glide speed you can take the time to troubleshoot the situation.