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

I agree with Paul.  You can get a nice high sink rate without building up
airspeed, similar to using a slip with the nose straight down the runway.
However, you must remember to allow enough altitude to pick up some
airspeed/energy for the flair or else you will get current on one approach
{:>). I have a 72 inch pitch prop and while the RV does not like to slow
down its really no problem once you get use to and anticipate the need.  I
generally throttle back to 3000 engine rpm for base and final.

Ed Anderson

Tracy demonstrated to me how an RV4 would maintain altitude with a ridiculous
low RPM. I forgot the exact number.

Paul Lamar

Interesting Ed, 3000 is the RPM I use on base and final also, 500 fpm
descent at 80 knots.

--
Perry Mick
Duckt N7XR
http://www.ductedfan.com

For the new guys Perry is direct drive so it is difficult to make
direct comparisons.

Paul Lamar
 
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