35% ??

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Boatguy
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35% ??

Post by Boatguy »

This is really only relevant to the DA40NG since the twins have lots of data in the AFM about one engine operation.

I'd heard that loss of the turbocharger in an Austro engine cuts the power back to about 35%. Since a DA40NG popped its boosted intake hose off last year leading to an off field landing (all safe), and there are many ways for a turbocharger to fail, I wanted to understand what 35% meant. I had previously established that 40% gave me 90KIAS in a holding pattern so I was pretty optimistic about 35%.

Today I flew at 7,500' with the AP in HDG/ALT modes and pulled the power to 40%. I waited for the plane to slow down and it eventually settled to 90KIAS as expected. Then I pulled the power to 35%.

The plane again began to slow, and then pitch up. It slowed, pitched up, and slowed and pitched up as it attempted to hold altitude. At 70KIAS and continuing to pitch up I decided this was going to just lead to a stall so I changed the vertical mode to VS -100fpm. The plane pitched down slightly and settled at 86KIAS. It continued smoothly at 86KIAS and a 100fpm rate of descent for a few minutes.

Conclusion: At 35% power I could not hold altitude, but I could hold a -100FPM descent rate at 86KIAS (very close to the 88KIAS glide speed). If in fact the loss of the turbocharger yields about 35% power, then even at 1,000' AGL, I should have some time to find a place to put down.

I hope neither you or I ever have to use this information!
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pietromarx
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Re: 35% ??

Post by pietromarx »

That's very interesting indeed.
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Davestation
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Re: 35% ??

Post by Davestation »

It would eventually find an altitude that it can hold indefinitely, no? So say that it loses 100pfm to maintain 86 at 7500 is not to say the same at 1000 methinks. Unless you’re just figuring on a field elevation of 6500 as the scenario.
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Re: 35% ??

Post by Boatguy »

Davestation wrote:
Sat Jan 16, 2021 6:22 am
It would eventually find an altitude that it can hold indefinitely, no? So say that it loses 100pfm to maintain 86 at 7500 is not to say the same at 1000 methinks. Unless you’re just figuring on a field elevation of 6500 as the scenario.
With no turbocharger the power will change with altitude so it’s entirely possible it can hold some altitude.
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Re: 35% ??

Post by mbitran »

Super helpful, thank you.
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neema
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Re: 35% ??

Post by neema »

The question is really at what altitude the engine will make 35%.

If it's 35% at sea level, even your experiment was optimistic.

35% of 168 hp is 59 hp. If that's sea level power, then 7500' should yield roughly 75% of sea level power, so roughly 44 hp or 26% power.


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Re: 35% ??

Post by CFIDave »

At 35% power (e.g., due to loss of the turbocharger) a DA40NG should have no problem holding altitude near sea level.

But at higher altitudes 1) an un-boosted engine with loss of turbo will make less than 35% power, and 2) the prop and wings aren't as efficient in the thinner air, requiring a higher angle of attack and getting you closer to a stall. So at higher altitudes if you lose the turbo you're going to descend.

A Beech Baron with a pair of (un-boosted) 300 hp engines will "drift down" to 6000 feet if it loses one engine (roughly half of 75% power, or around 35% power). Loss of the turbo in a DA40NG will cause something similar to happen.
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mbitran
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Re: 35% ??

Post by mbitran »

This is very helpful.

Is there an optimal power setting to set if you lose a turbocharger in the NG? I'm wondering if this is the mechanical failure that is addressed by the AFM Checklist under: [ECU A & B failure checklist - Indicated LOAD unchanged, perceived thrust is reduced, engine noise level changes or engine running rough]?

If so, the AFM suggests that you decrease thrust to idle and then set to maximum perceived power, not to exceed 1975 RPM?

Although this checklist item suggests the engine can produce 65% under this scenario?
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Re: 35% ??

Post by ultraturtle »

mbitran wrote:
Sat Feb 27, 2021 9:26 pm
... the AFM suggests that you decrease thrust to idle and then set to maximum perceived power, not to exceed 1975 RPM?

Although this checklist item suggests the engine can produce 65% under this scenario?
At 1975 RPM, you may be lucky enough to reach 65% power at sea level. From the AE300 operating manual:
Screen Shot 2021-02-27 at 6.31.42 PM.png
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