I’ve tested my IV-P (Continental TSIO 550 w/MT 4-blade)
with the following results:
I cannot stop the prop rotation by shutting down the engine in
flight—at least not down to my approach to stall speed. With the prop
control all the way out and the engine at idle power, the RPM stabilizes around
600-650 RPM. Turning off the ignition has little, if any effect on the
windmilling RPM. If you then push in the prop, the RPM increases. It might be
possible to push it in very quickly and stall the air flow over the prop,
causing it to actually stop, but I was not willing to abuse the equipment that
much…a possible (more likely?) outcome would be an engine overspeed when
the prop governor failed to compensate fast enough for the rapid
spin-up—or a stall/spin when you suddenly add a heap of drag up front?
I’ll leave that one for someone else to try…
My airplane descends at 450-600 FPM at 120 KIAS, depending
on the gross weight. 450 FPM at approx 2800#, and 600 FPM at approx 3600#. RPM
with the throttle idle and prop all the way out is approximately 700 RPM. I was
surprised (probably should not have been!) that the weight had such an effect
on descent rate. I used a 20:1 glide ratio to program my Chelton EFIS, and have
consistently been able to pull back the power and RPM to the stops, turn toward
an airfield from heading directly away, and successfully land without touching
the power (at intermediate gross weights; not max). Although I’ve not
used it in an emergency, it appears that the “glide range” display
on the Chelton would be very useful—so I’ve taken some time to
assure myself that it’s a good predictor of engine-out range. The
techniques in the messages below for controlling descent when you have the
airport made are all applicable.
Power-off glides for extended periods have some inherent risks,
so I’d caution that you ask some advice before jumping into the bird and
giving this a try. One thing you can do to test the glide setting/display on a
Chelton system is to start with a power off/RPM min/appropriate airspeed glide
from medium altitude toward the place of intended landing. If the glide ratio
set in the Chelton is too large (e.g. 30:1), the predicted glide range will
decrease—fall short of the airport—as you approach it. If
it’s too small (e.g. 10:1) the predicted range circle will move beyond
the airport as you head toward it. This glide ratio adjustment technique
doesn’t require that you descend all the way to the airport committed to
land if the engine doesn’t respond. Just a thought…
Bob
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of Sky2high@aol.com
Sent: Sunday, December 20, 2009 2:37 AM
To: lml@lancaironline.net
Subject: [LML] Re: Prop and Glide considerations
Thank God somebody actually tries this stuff (uh, somebody with
your piloting skills). Perhaps you are using Marvel Mystery Oil to reduce
engine friction..........
Is your MT prop electric? My understanding is that oil
pressure managed props (non-feathering) would go to a flatter pitch
as the pressure is diminished and the prop slows - perhaps the flatter
pitch keeps the prop from actually stopping?.
I think I only suggested that those with a fixed pitch prop try to
stop it (yes, a dangerous maneuver). Of course there is no choice if the
engine seized. I haven't flown a fixed pitch prop airplane since
1998. The fixed pitch prop Cozy MkIV flier I know said that there is a
range for his airplane - a two bladed prop can be stopped at around 90+ Kts and
will stay stopped until around 115+ Kts. Of course it comes to a stop
with the blades horizontal in the wing wash (ah, pushers). He
now has a three bladed prop and he doesn't know if it can be stopped.
Let's try this then - CS fliers have an option of pitch control
and should know the descent rate at best glide for the extremes.
I would say that a stoppage from seizure would be some in between.
Fixed pitch fliers (and others) should know the rotten descent rate they
get with the prop in cruise pitch and windmilling and use that for
rule of thumb range estimates. Uh, 1000 fpm at 5000 AGL = 5 minutes
and at 120 KIAS that's 2 NM per minute - ergo <10 NM depending on the wind
or about a 10 to 1 rate (distance to altitude). Here is where GPS ground
speed is useful. In other words, at least know the worst case descent
rate.
Your final paragraph is "spot on" and there
are many ways steepen the descent - wheels out, flaps down, prop to flat
pitch and/or entering a slip. Oh yeah, a 300 series slow-speed
flaps-out slip can lead to the nose bobbing up and down. As others
have mentioned, gear up landings on a hard smooth surface don't need much
"roll-out" - and note that it will turn away from the exhaust pipe
side since the metal slides easier than glass (believe me, I know).
Do what ya can to know your airplane...
In a message dated 12/18/2009 9:20:00 A.M. Central Standard Time,
n5zq@verizon.net writes:
Good info on glide ratios. You advocate stopping the prop. In most
cases, this would produce slightly less drag than a windmilling, but high angle
(prop control pulled back) prop. Problem is, I don't think that it can be done
in our planes. I know for sure that I can't do it in our 320...I've tried. With
the engine shut down and prop back I've slowed to just above a stall and the
prop just keeps going. I've got an MT prop which will go to a higher angle than
most others, maybe this is why. Has anybody been able to stop a prop (assuming
no engine damage and a non-feathering prop in any kind of Lancair?
My guess is that in an actual emergency, it would probably be best
not to attempt it. Speaking for myself, I've got just so much concentration and
the prop stopping maneuver would use up a bunch. When thinking about engine out
procedures we always think about maximizing the glide. This is, of course, the
proper thing to do to give you more time to think and plan. There are times,
however when it is advantagious to MINIMIZE the glide ratio. Pushing in the
still spinning prop will allow you to do this.
When I was an examiner I conducted hundreds of private and
commercial flight tests always including a simulated forced landing.
Getting too high was just as common as a too low and the
actual outcome would likely be worse. Having the ability to shove the prop
forward gives you one more tool to modify your descent. That option is
not available if the prop is stopped (the possible exception would be
a feathering prop with an accumulator).
I agree with Bill Kennedy. Learn how YOUR airplane glides and
practice simulated forced landings. In our 320 with the engine at idle and the
prop full aft I get a descent rate down of 500 fpm at 110 kts.
With the engine SHUT DOWN it's 900 fpm. My suggestion would be to
learn what your airplane does with the engine actually shut down, obviously at
high altitude, good weather, and over an airport with a long runway. Once you
have that number, you can do your engine out practice with the engine at idle
and the prop adjusted to the RPM that gives you the same rate of descent that
you discovered in your shut down test. Your practice then should give you very
realistic glide performance.
N6ZQ IV under construction