Question about SR20 (from workbook)

spiderweb

spiderweb

Final Approach
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Ben
The question is: "In an engine failure situation with the prop windmilling, how can you gain addtional glide distance?"

I can't find the answer in the POH. I know what I would do if I had a prop control, but the SR20 has an automatic linkage.

What would you do?
 
I seem to recall that a stopped propeller is less draggy than a windmilling prop. So, if you pulled back and slowed down sufficient to stop the propeller (without stalling or losing excess altitude), you might get a little cleaner and thus extend the glide.
 
From SR20 POH 11934-003 Rev A7:

Section 3-11 Engine Failure
"• Note •
With a seized or failed engine, the distance that the airplane will glide will be more than the distance it would glide with the engine at idle, such as during training.
If the propeller is windmilling, some additional glide range may be achieved by moving the Power Lever to idle and increasing airspeed by 5 to 10 knots."
 
Mike I said:
From SR20 POH 11934-003 Rev A7:

Section 3-11 Engine Failure
"• Note •
With a seized or failed engine, the distance that the airplane will glide will be more than the distance it would glide with the engine at idle, such as during training.
If the propeller is windmilling, some additional glide range may be achieved by moving the Power Lever to idle and increasing airspeed by 5 to 10 knots."
Click to expand...

Good eye!
 
Mike I said:
With a seized or failed engine, the distance that the airplane will glide will be more than the distance it would glide with the engine at idle, such as during training.
Click to expand...

Is this true for all planes? I would not have guessed this.
 
Auburn2002 said:
Is this true for all planes? I would not have guessed this.
Click to expand...

A stopped prop builds a stagnation layer in front of the flat surface that acts as a fairing. If the prop is spinning, this stagnation layer cannot form.

In the case of a constant speed prop, some POH's recommend setting the prop to full coarse (minimum rpm) to increase the pitch, to reduce the drag on a windmilling prop. Assuming you have oil in the engine and sufficient oil pressure, I would probably prefer to do this than stop the prop entirely, as a restart would be more easily accomplished with a spinning prop.
 
Sac Arrow said:
A stopped prop builds a stagnation layer in front of the flat surface that acts as a fairing. If the prop is spinning, this stagnation layer cannot form.
Click to expand...

I guess I just assumed an idling engine is producing at least some thrust, versus one that is shut off with the prop windmilling. So in other words I know glide performance is better with a stopped prop than windmilling, but expected it would be better than either of the above with an idling engine.

The more you know....
 
Sac Arrow said:
A stopped prop builds a stagnation layer in front of the flat surface that acts as a fairing. If the prop is spinning, this stagnation layer cannot form.

In the case of a constant speed prop, some POH's recommend setting the prop to full coarse (minimum rpm) to increase the pitch, to reduce the drag on a windmilling prop. Assuming you have oil in the engine and sufficient oil pressure, I would probably prefer to do this than stop the prop entirely, as a restart would be more easily accomplished with a spinning prop.
Click to expand...

Indeed, also cannot count on stopping the prop. I shut down the engine once in a falling leaf, prop never stopped.
 
Auburn2002 said:
I guess I just assumed an idling engine is producing at least some thrust, versus one that is shut off with the prop windmilling. So in other words I know glide performance is better with a stopped prop than windmilling, but expected it would be better than either of the above with an idling engine.

The more you know....
Click to expand...

Actually what I said was in reference to a stopped engine vs. a windmilling one. I would agree that an idling engine would be better as well. Might be some exceptions depending on the type and pitch of the prop.
 
Sac Arrow said:
A stopped prop builds a stagnation layer in front of the flat surface that acts as a fairing. If the prop is spinning, this stagnation layer cannot form.

In the case of a constant speed prop, some POH's recommend setting the prop to full coarse (minimum rpm) to increase the pitch, to reduce the drag on a windmilling prop. Assuming you have oil in the engine and sufficient oil pressure, I would probably prefer to do this than stop the prop entirely, as a restart would be more easily accomplished with a spinning prop.
Click to expand...

I did some testing of this in a Trinidad, pulling the prop control back on the three-blade prop made a significant difference (the difference between landing short of the runway and on it) to an engine failure on base leg.
 
TMetzinger said:
I did some testing of this in a Trinidad, pulling the prop control back on the three-blade prop made a significant difference (the difference between landing short of the runway and on it) to an engine failure on base leg.
Click to expand...

I did the same test. The Trinnie sinks like a rock, so pulling back the prop made a big difference.
 
Another question frustrating me:

"When does the BOOST pump need to be in operation."

I know the answer to this, but I can't find it in the section of the POH the workbook implies it will be in--Limitations.
 
I don't think it'll be in limitations, but should be in normal procedures, and probably the emergency procedures too for engine failure in flight.
 
TMetzinger said:
I don't think it'll be in limitations, but should be in normal procedures, and probably the emergency procedures too for engine failure in flight.
Click to expand...

It is there, but this workbook is supposed to be sequential; IOW, all of the questions in one section are supposed to be found in the corresponding section of the POH. I'm far beyond this section now--just going back to try to get those unanswered questions.
 
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