Practicing SFLs with a constant speed prop - how?

On Mon, 12 Apr 2004 05:06:12 GMT, Ed wrote:

snip

In idle, with the prop at flat pitch, it feels too draggy and comes
down like a rock. With it at high pitch, it seems to have too
optimistic a glide ratio. What's the happy medium?

I'm a little confused by this portion of your question, and a couple
of the replies.

I have never actually messed around a bunch with airspeed/descent
rate/idle engine/prop rpm, but am pretty familiar with how a typical
pressure-to-increase pitch constant-speed prop/governor works.

Somewhere around 1600-1800 rpm, the prop governor ceases to output
enuff pressure to change/maintain the propeller pitch, and the
propeller goes to flat pitch. I've seen it on a gov bench, and on
approach-to-land.

Whether or not the engine is "running" if the rpm is below this range,
moving the prop control has no effect on the pitch of the prop.

TC

snip

In article ,
wrote:



Whether or not the engine is "running" if the rpm is below this range,
moving the prop control has no effect on the pitch of the prop.


That's what I thought until I tried it on my 182. Idle power, trimmed
stable 80 mph glide with the prop control all the way forward. Pulled
the blue knob back and watched the airspeed increase about 5MPH...pushed
the blue knob in and I slowed again.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

With our Mooney F model at best glide speed when I pull the prop control all
the way back (max pitch), it saves me about 300 fpm while maintaining best
glide. With a minimum pitch, the blades are one big braking force.

"Dale" wrote in message
...
In article ,
wrote:



Whether or not the engine is "running" if the rpm is below this range,
moving the prop control has no effect on the pitch of the prop.


That's what I thought until I tried it on my 182. Idle power, trimmed
stable 80 mph glide with the prop control all the way forward. Pulled
the blue knob back and watched the airspeed increase about 5MPH...pushed
the blue knob in and I slowed again.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

On Tue, 13 Apr 2004 05:49:10 GMT, "Roy Epperson"
wrote:

With our Mooney F model at best glide speed when I pull the prop control all
the way back (max pitch), it saves me about 300 fpm while maintaining best
glide. With a minimum pitch, the blades are one big braking force.

I'll gladly take your collective word for it from in-flight
observations.

Mine were limited to shoving the prop ahead turning final (in every
complex aircraft I've ever flown in) at approx 1200-1400 rpm (prop
control previously set to 2300 in cruise) with no change in engine
rpm/prop noise noted.

Have pulled mis-rigged PT6A props to "flat" on short final a couple of
times, have the stained shorts to prove it.

Before I posted, I called my gov shop buddy to make sure his views
coincided with what I remembered from hanging around in his shop. He
related same, that the gov bench doesn't indicate useable gov pressure
until around 1500-1600 rpm. As I recall, on most engines, the gov
drive turns at about 90% of the indicated rpm.

I stuff I work on now has a fixed-pitch first stage "prop", and I
ain't allowed to drive it, so I can't add anything further.

Regards;

TC

wrote in message
...
Mine were limited to shoving the prop ahead turning final (in every
complex aircraft I've ever flown in) at approx 1200-1400 rpm (prop
control previously set to 2300 in cruise) with no change in engine
rpm/prop noise noted.

That's a completely different situation. At that power setting, the engine
didn't have enough power to drive the prop at the selected RPM (2300), and
so the blades were already at flat pitch. Selecting high RPM would have had
no effect, since the governor was already trying to increase RPM, to its
limits (maximum flat pitch).

Next time, pull the prop to *minimum* RPM and see your glide angle decrease.

Have pulled mis-rigged PT6A props to "flat" on short final a couple of
times, have the stained shorts to prove it.

Not sure how that statement fits in to the discussion, but the PT6 governors
work differently from those found on most piston-engine singles.

Before I posted, I called my gov shop buddy to make sure his views
coincided with what I remembered from hanging around in his shop. He
related same, that the gov bench doesn't indicate useable gov pressure
until around 1500-1600 rpm.

You mentioned "gov pressure" in an earlier post, and I still don't
understand what you mean. The force to change the prop blade angle comes
from springs and oil pressure, not the governor itself. All the governor
does is adjust oil valves to control how the oil moves through the pitch
change mechanism.

In any case, as with the others, I've had no trouble at all reducing the
blade pitch even in low-RPM, idle-power situations. I have no reason to
expect I'd have any trouble in an actual engine failure, assuming the engine
continued to windmill and run the oil pump.

Pete

On Tue, 13 Apr 2004 16:15:11 -0700, "Peter Duniho"
wrote:

snip

Next time, pull the prop to *minimum* RPM and see your glide angle decrease.

It'll likely be years, I don't do GA anymore.

Have pulled mis-rigged PT6A props to "flat" on short final a couple of
times, have the stained shorts to prove it.

Not sure how that statement fits in to the discussion, but the PT6 governors
work differently from those found on most piston-engine singles.

Doesn't have anything to do with it, this is Usenet. You really owe to
yourself to try it once, though. It's similiar to tromping on a
non-ABS brake pedal at 40 mph. Gets your attention at 75 feet AGL with
the nose down coming-over-the-fence.

Before I posted, I called my gov shop buddy to make sure his views
coincided with what I remembered from hanging around in his shop. He
related same, that the gov bench doesn't indicate useable gov pressure
until around 1500-1600 rpm.

You mentioned "gov pressure" in an earlier post, and I still don't
understand what you mean. The force to change the prop blade angle comes
from springs and oil pressure, not the governor itself. All the governor
does is adjust oil valves to control how the oil moves through the pitch
change mechanism.

The base of a governor is another oil pump, stepping up engine oil
pressure to over 175 psi. Maximum pressure is limited by a
spring-loaded pop-off valve, just like the engine oil pump.

http://www.mccauley.textron.com/prop...g03govern.html

was the best picture I could find of it in a 30 second Google.

In any case, as with the others, I've had no trouble at all reducing the
blade pitch even in low-RPM, idle-power situations. I have no reason to
expect I'd have any trouble in an actual engine failure, assuming the engine
continued to windmill and run the oil pump.

Agreed, like I indicated in another post, the oil pump/governor
doesn't care what's turning it.

TC

wrote in message
...
Not sure how that statement fits in to the discussion, but the PT6
governors
work differently from those found on most piston-engine singles.

Doesn't have anything to do with it, this is Usenet.

Okay...just thought I'd ask.

The base of a governor is another oil pump, stepping up engine oil
pressure to over 175 psi. Maximum pressure is limited by a
spring-loaded pop-off valve, just like the engine oil pump.

Yes, but as far as I know, that pump will work just as well as the engine
pump. Also, even if for some reason that pump failed, my understanding is
that it would simply reduce the responsiveness of the governor. It wouldn't
cause it to stop working altogether. The engine-supplied oil pressure would
be sufficient.

Agreed, like I indicated in another post, the oil pump/governor
doesn't care what's turning it.

Well, color me confused then. I thought we started this thread with you
suggesting that if the engine has failed, resulting in low RPM, you wouldn't
be able to get the prop to the coarse pitch setting.

But, if you agree with what I said, so much the better.

Pete

I don't buy that. I can play with the prop at IDLE and zero knots and
get it to change RPM. My run-up is done at 1700 and the prop oil wash
exercise has a big effect.

Ed

On Mon, 12 Apr 2004 18:06:09 -0400, wrote:

On Mon, 12 Apr 2004 05:06:12 GMT, Ed wrote:

snip

In idle, with the prop at flat pitch, it feels too draggy and comes
down like a rock. With it at high pitch, it seems to have too
optimistic a glide ratio. What's the happy medium?

I'm a little confused by this portion of your question, and a couple
of the replies.

I have never actually messed around a bunch with airspeed/descent
rate/idle engine/prop rpm, but am pretty familiar with how a typical
pressure-to-increase pitch constant-speed prop/governor works.

Somewhere around 1600-1800 rpm, the prop governor ceases to output
enuff pressure to change/maintain the propeller pitch, and the
propeller goes to flat pitch. I've seen it on a gov bench, and on
approach-to-land.

Whether or not the engine is "running" if the rpm is below this range,
moving the prop control has no effect on the pitch of the prop.

TC

snip