Yes! that's the one, thanks for reposting.
Thanks, Dan for the reminder about the counterweighted prop.
So I guess there are actually 3 options? 1) full feathering: always goes to feather with loss of oil pressure 2) counterweighted: ?goes to almost feather with power loss (or is it pressure loss) 3) normal constant speed: always goes to fine with oil pressure loss.
So are the scenarios like this? I show in red any situation that is undesirable. I think the most likely situation is power loss only followed by power and pressure loss only.
situation Full feathering counterweighted constant speed
pressure loss only feathered ? fine
power loss only pilot control pilot control pilot control
power and pressure loss feathered feathered fine
Colyn,
Maybe you are referring to the included chart from "Aerodynamics
for Naval Aviators". The Hartzell prop for the 320 engine has a pitch
range of 12 to 40 degrees. If the engine has not seized (stationary prop),
pulling back to coarse pitch results in almost the same drag reduction as a
feathered prop. Slick Lancairs are affected greatly by such drag as there
are no struts, rivets or fat wings to moderate the effect.
In my 320, zero thrust, cruise pitch resulted in a 1500 fpm descent at
best glide (about 107 KIAS via AOA) and pulling back to coarse pitch the descent
rate decreased to about 400-500 fpm. It was an eye opener.
<Prop%20Drag.jpg>
Grayhawk
Those
are very interesting numbers.
I think Scotty's got a chart that shows that the advantage of a full
feathering prop over constant speed is pretty marginal.
After I wrote my last post I realized that the 120 knots/600 fpm number I
had in my head was from a IV-PT which has less drag in the
nose than a IVP. Keeping that in mind, Bob's numbers are quite
impressive.
Bob points out that the prop is a nice adjustable speed brake when
windmilling.
I have not tried it but I suppose a fully featherable prop could do the
same thing IF you don't just yank it all the way back all at once.
Once you lose oil pressure you can't do anything with the fully
featherable prop unless you get one with an unfeathering accumulator (I don't
know of an approved one for the IVP - maybe someone else does).
Keeping the prop windmilling will keep you in oil pressure if you don't
have an oil leak.
Colyn
On Jun 18, 2011, at 5:32 PM, Robert R Pastusek wrote:
For
what I have gathered so far the lancair 4p has a glide ratio similar like a
piano LOL In other words if the engine quits then open the door, throw out
your keys because there is where you land LOL
Well,
this might not be true, or is it?
So
how about the full feathering prop ? Does anyone have experience with the
before and after installation? How much they cost and
data?
And
I needed to respond to this…
My
IV-P has a glide ratio (at 120 KIAS) of between 5:1 and 20:1, depending on
configuration. The difference is truly amazing/impressive/sobering…
depending on your situation and mind set. With the gear and flaps down and
the RPM at max (prop all the way in), the glide ratio approximates that of a
brick…not really, but you’re coming down so fast relative to forward
progress that it’s difficult to plan and execute a planned touchdown (at
least for me). With the gear and flaps up, AND THE PROP CONTROL ALL THE WAY
OUT, my glide ratio at gross weight is approximately 18:1, increasing to a
bit better than 20:1 at 800# under gross. At this glide ratio, the
performance and “sight picture” approximates that of some gliders. It’s easy
to plan and execute an approach and landing to a pre-planned spot…ideally a
runway. I have practiced this many times from various altitudes/distances
from the airport to a full stop on the runway, using the gear to increase my
descent rate, and then the flaps and/or the prop control to adjust the
touchdown point. Using the prop control is ideal because the drag
effect/descent rate increase almost immediately reversible by pushing it
back in. Not so with the flaps. One feature of my Chelton
EFIS is a wind-adjusted glide range predictor. I have tested this many times
starting at altitudes up to 17,500’ and (set at 18:1)
gives me a very accurate and immediate sight picture of airfields within
glide range. If it’s within the green circle, I can turn toward an airfield
and execute a safe landing there. My MT 4-blade is not full feathering, but
allows the engine to run at approximately 700 RPM when at idle and the RPM
set to min. I believe this is pretty close to 0 thrust, as the engine idles
at approximately 600 RPM on the ground.
So,
in summary, the throw out the keys and follow them down scenario can be
executed if you really want to go down, but a planned glide at 120 KIAS
(very close to best glide for my airplane) in clean configuration yields
approximately the performance of a 2-place sail plane—and you have the
ability to transition easily between these limits as needed. Try it; you’ll
be impressed.
Bob
PS:
I considered and rejected a full feathering prop for what I have.
Wouldn’t trade for any amount of
money… =
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