snips...

Paul and Jerry,
   I would love to see the variable PP design installed and
tested.  Jerry, would you
be interested in installing the variable PP intake valves that
Paul built?  I would be
happy to send them to you if you are interested.
   It is thought by some that a PP motor with large amounts of
overlap has
somewhat poor idle characteristics due to exhaust gas dilution of
the intake charge.
In order to minimize this intake charge dilution we decided to use
the same
technique that are used on 2-stroke racing motorcycles, i.e., vary
the port timing on
the intake port.  A secondary benefit is that at small throttle
settings the velocity of
the intake charge is accelerated while in the intake port, further
promoting fuel
atomization.  Also note that the BSFC should improve at cruise due
to the more
conservative port settings.
   A slower idle is important because even at 700 - 800 prop rpm a
highly pitched
prop will generate lots of thrust.  Since the Fast Glass and the
RV's are difficult to
slow down a slower prop speed is beneficial.  Note that a 1200 rpm
idle (engine)
when used with a 2.85 redrive will result in a prop rpm of only
421 rpm, a
substancial reduction over a 1800 rpm idle and a 2.17 redrive wich
results in a prop
rpm of 830 rpm.

Ken Powell

If you are good you can get a high sink rate by putting the
airplane on the
back side of the power curve. Pull the nose up short of stall and
watch
the vertical sink rate increase. Its called "dragging it in".
Also a slip will increase the sink rate.

Paul Lamar

This has come up before. Paul, don't you think you should be
careful about what you might be saying to low-time pilots
out there?

Before you guys make that a regular practice, it would be a
good idea to find an old gray haired instructor who's spent
his career doing primary instruction in simple a/c. Ask him
what he thinks about the idea.

Charlie England

You have a very good point there Charlie. I forgot to say; "practice
at altitude!".

Paul Lamar

And, practice at altitude with an instructor who will, at
some point in the simulated 'behind the curve' approach,
pull the mixture to simulate an engine failure. Enjoy the
ride...

Charlie E

Another good point Charlie. I wonder what the altitude window is
to survive? :-) I am sure it depends on how far behind the power curve
you
are. If you are making a conventional approach you can still die
if the engine quits on final. I see no real difference.
The only safe approach if the engine is going to die is the slip.

Paul Lamar

I used to love to slip my Luscombe.  It had a big rudder and you could
do a lot with the slip.  I was shocked by the anaemic response the first
time I slipped a  152.  The slip was relatively useless.    So it all
depends.  To get back to what started this thread,  we have to get the
idle down to the point the prop is no longer pulling the aircraft or we
are playing Russian Roulette.  Sooner or later you won't be able to get
down in the alloted space.   The peripheral ported engine needs to
provide a safe idle of around 500 prop rpm.   Using 2.17 reduction, that
means we have to idle the engine at 1085 rpm or less.       Jerry

P.S.  you can slip a Tailwind with full flaps but it still does not fall
out of the sky like my Luscombe did.

In the old days we used to be able to ask Everett or Alan his pilot 
what his PP idle RPM was. Are you still on here Alan Tolle?

You are just going to have to build one Jerry and find out.
I can't guarantee it will idle that low.

Paul Lamar
 
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