Practicing SFLs with a constant speed prop - how?

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

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

"Ed" wrote in message
...
I'm fairly new to GA after a 19 year break flying jets. I routinely
fly a single engine experimental with a constant speed prop mounted on
a Lycoming IO-360.

2 QUESTIONS:

1. What's the proper setup to simulate the way the plane would glide
in case of an engine failure? I'm looking for pitch and possibly a
manifold pressure number here.

Unfortunately, it will be with the engine at idle at flat pitch. I will
explain why below.


2. It that motor quits, will it still rotate through the flying
airspeed envelope or can I expect it to stop rotation (assuming it's
not frozen due to a mechanical failure)?

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?


The prop pitch is maintained by oil pressure. Most single engine piston
installations set up the constant speed prop so that it will go to flat
pitch if oil pressure is lost (the exact opposite of turboprops and piston
twins). This is supposed to maximize your chances of restarting the engine,
but you pay for it with glide range. The propeller will continue to windmill
and create a lot of drag, but with the engine out you have little choice --
your oil pressure will be zero. It makes sense when you consider that most
'engine failures' are caused by fuel mismanagement. All you have to do is
switch tanks and with the windmilling prop your engine will start right up
again. You can make the propeller quit rotating by flying very slowly, but
that will not improve your glide.

Turboprops and piston twins set the prop to feather if oil pressure is lost.
These propellers will stop rotating almost immediately.

I don't live near a dry lake bed or I'd just shut it down and find
out. I have the proper airspeeds for max range and min sink out of
the POH but it does not quote any type of glide ratio.

You could just stay in the pattern and shut it down. It should start right
up again just by giving it some fuel.

On Mon, 12 Apr 2004 16:21:39 -0700, "C J Campbell"
wrote:

snip

but you pay for it with glide range. The propeller will continue to windmill
and create a lot of drag, but with the engine out you have little choice --
your oil pressure will be zero. It makes sense when you consider that most

As long as there is oil in the engine, the oil system isn't
compromised, and the engine is windmilling oil pressure will remain
consistent with the rpm the engine is turning. The oil pump doesn't
care if it's being rotated by infernal combustion or by the wind
blowing through the prop.

Looked at a T-Arrow awhile back that fractured the turbo oil feed
fitting. Oil fire ignited, and was fed by the oil being pumped out of
the engine by the windmilling propeller until it ran out of oil.
Wasn't pretty, but the pilot walked away from it.

IMHO the rest of your info was right on the money.

Regards;

TC

snip

I just want to clear this up. My home field (O17) - and just about
all those around it for 50nm are heavily wooded and surrounded by
pines reaching up about 50'.

Some of you guys are men to faith, obviously. I however, am not and
prefer to try to perfect the simulation rather than log glider time.
My goal is simply to set it up so the configuration for best glide or
min sink (depending on distance to the runway) so as to get a feel for
expected glide performance.

Thanks for all the various suggestions. It convinces me there is not
any one procedure past what the POH says about getting the motor
started again and then technique becomes the rule.

Ed (N119NC)

On Mon, 12 Apr 2004 16:21:39 -0700, "C J Campbell"
wrote:


"Ed" wrote in message
.. .
I'm fairly new to GA after a 19 year break flying jets. I routinely
fly a single engine experimental with a constant speed prop mounted on
a Lycoming IO-360.

2 QUESTIONS:

1. What's the proper setup to simulate the way the plane would glide
in case of an engine failure? I'm looking for pitch and possibly a
manifold pressure number here.

Unfortunately, it will be with the engine at idle at flat pitch. I will
explain why below.


2. It that motor quits, will it still rotate through the flying
airspeed envelope or can I expect it to stop rotation (assuming it's
not frozen due to a mechanical failure)?

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?


The prop pitch is maintained by oil pressure. Most single engine piston
installations set up the constant speed prop so that it will go to flat
pitch if oil pressure is lost (the exact opposite of turboprops and piston
twins). This is supposed to maximize your chances of restarting the engine,
but you pay for it with glide range. The propeller will continue to windmill
and create a lot of drag, but with the engine out you have little choice --
your oil pressure will be zero. It makes sense when you consider that most
'engine failures' are caused by fuel mismanagement. All you have to do is
switch tanks and with the windmilling prop your engine will start right up
again. You can make the propeller quit rotating by flying very slowly, but
that will not improve your glide.

Turboprops and piston twins set the prop to feather if oil pressure is lost.
These propellers will stop rotating almost immediately.

I don't live near a dry lake bed or I'd just shut it down and find
out. I have the proper airspeeds for max range and min sink out of
the POH but it does not quote any type of glide ratio.

You could just stay in the pattern and shut it down. It should start right
up again just by giving it some fuel.

I don't have a lot of propeller driven time (4250 hrs maybe) however
most AFM's give you a setting to simulate 'zero thrust'. Since the
throttle is retarted and your'e out of the prop governor range, the
propeller lever is full foraward, and the manifold 15" or so on the
Lycoming. Of course I may be off a bit and any input is welcome here.

Have a great one!

Bush

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

I'm fairly new to GA after a 19 year break flying jets. I routinely
fly a single engine experimental with a constant speed prop mounted on
a Lycoming IO-360.

2 QUESTIONS:

1. What's the proper setup to simulate the way the plane would glide
in case of an engine failure? I'm looking for pitch and possibly a
manifold pressure number here.

2. It that motor quits, will it still rotate through the flying
airspeed envelope or can I expect it to stop rotation (assuming it's
not frozen due to a mechanical failure)?

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 don't live near a dry lake bed or I'd just shut it down and find
out. I have the proper airspeeds for max range and min sink out of
the POH but it does not quote any type of glide ratio.

Ed