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

Well guys, I just finished my flight training (the formal part leading

to the PPL) in 1999 and the

standard approach taught in the 172 is full flaps on final and 65 kts.

Roundout at 60kts and hold her

off to touch down.  Works like a charm.  My instructor showed me the

difference in approach speeds and

their effect on sink rate early in my training.  When my pre solo check

out pilot bitched about my

approaches, I showed him the difference.  He now trains the way I was

taught.

Rick Girard
13B + LEZ

Did they teach you slips Rick? Just curious.

Paul Lamar

John Gibbons wrote:

 Rick,

    What would you do after a 4 1/2 hour flight to the tiny strip in the
middle of nowhere, when you find out your electric flaps won't work ? Been
there, done that. Twice.
Cheers,
John

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