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Hi all:

I'd like to practice some engine out approaches in my DA40NG. I know with the throttle all the way back to idle the prop really acts as a speed brake. Would it be better to practice with just a little power left in, say 5%?

In my training in the DA42 I was taught 10% was the setting to simulate a secured engine.

You don't want to add any power for engine out practice. If you lose your engine in a single, the prop is likely to windmill, which creates as much drag as a solid disc with the same diameter as your prop (i.e., a LOT of drag). With the throttle of an operating engine brought back to idle to simulate a failed engine, your prop with residual idle thrust will not generate as much drag as with a failed engine windmilling prop, but it's as close as you can get for practice.

In a twin, windmilling prop drag because of a failed engine can be deadly, because the asymmetrical force out on one wing can cause loss of control, and the additional drag will make it virtually impossible for the plane to hold altitude even with the good engine at full power. Therefore virtually all twin engine prop planes require feathering props to stop windmilling and reduce drag. To simulate a "feathered" prop in a twin (without shutting down the engine), it *IS* necessary to add a slight amount of power. For a DA42/DA62 with Austro engines, I experimentally determined that 11% power can simulate a feathered prop.

But this doesn't apply to a DA40NG because it doesn't have a feathering prop.

So with the Low Power Correction on the Austro Engine it turns out you can't practice engine out maneuvers to a high altitude airport. My home field, Driggs, Idaho is at 6200 ft elevation and typically start maneuvers at 8500 ft. Pulling the power back to idle gets you about 20% power.

ScottOHare wrote: ↑Wed Aug 05, 2020 4:25 pm So with the Low Power Correction on the Austro Engine it turns out you can't practice engine out maneuvers to a high altitude airport. My home field, Driggs, Idaho is at 6200 ft elevation and typically start maneuvers at 8500 ft. Pulling the power back to idle gets you about 20% power.

I never really considered that, but I believe you are correct.

This gets to the question about what thrust is produced with the power lever pulled back to zero but the EECU is calling for 10-20% power output (because of ambient pressure altitude). Normally, the 20% position of the power lever would call for 1800 RPM (propeller) and 20% power output from the engine. In situations involving "idle power correction" (e.g. 20% minimum power at PA=700 mbar≈9900 MSL), the power lever at 0% would call for 2150 RPM. Assuming that 20% power output and 1800 RPM provide optimum thrust (efficiency), what is the thrust generated when 20% is driving the propeller at 2150 RPM with a smaller propeller pitch? The RPM is controlled by the power lever position, not by the actual power being produced by the engine.

Scott, if you're practicing 180 no-power approaches from the pattern, 6200 MSL is below the 800 mbar point that idle power correction begins to take effect. At 7200 MSL, it looks like you'd be right at about the 10% Dave recommended for emulating an engine-out situation in the DA40NG. So you could be reasonably OK for having meaningful practice power-out approaches from pattern altitude.

I don't know about the NG model, but, in general, with a constant speed prop you pull back to lowest rpm setting this dramatically improves glide but nothing like full feathering which is not possible. When I do power-off 180s in my DA40-180, I pull power to idle and leave prop at cruise RPM of 2400-2500 (note: I have the Hartzell composite prop which is STCed to 2700 rpm). if I look like I'm having trouble making the runway, I would pull back on RPM lever to reduce braking effect of windmilling prop.

If I was in a real engine-out condition, I would remain as high as possible and then forward slip to get down for landing.

Thanks, Paul. I think my problem was I was practicing an off field landing scenario north of Driggs where the wheat fields are closer to 7000 feet MSL so I was starting at 8500 feet MSL. Next time I think I'll just fly west where the ground elevation is closer to 4500 feet and I won't run into the low power correction.