Sender: <marv@lancaironline.net> (Marvin Kaye)
To: flyrotary
Date: Sun, 13 Apr 2003 09:00:07 -0400
Message-ID: <redirect-2120872@logan.com>
From: "Ed Anderson" <eanderson@carolina.rr.com>
Subject: Heavy Load +Stalled Prop+Wet Grass = Long Roll & damaged seat cushion
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Thought I would share an experience I had on take off out of Shady Bend
this AM. After spending a great week with Tracy and Laura due to weather
over the
Carolinas,  I loaded up the aircraft before dawn and after cleaning off the
heavy dew from
the canopy, started the engine.

I then taxied throught the damp grass on down to the south end of the runway
for runup and takeoff..  The enginereally like the cold morning and the sea
level atmosphere pressure!  The engine ran up to 5900rpm - possibly even
6000 rpm at static (nominal is between 5200-5400).  I thought WOW! I am
going to really roll. (I had gotten this type of static rpm on other cold
mornings, but once
I started take off, the prop would unstall and load up dropping the rpm down
to a more nominal 5300)

Well, I rolled, but not quite as I had anticipated.  With the engine still
revving around 5900, I started my take off roll.  I did notice acceleration
seemed a bit on the slow side, but decided that with my heavy weight, wet
grass, etc that it would pick up once the prop unstalled and loaded up.
Well, the prop never unstalled and I rolled and rolled - almost decided to
abort,
but elected to continue the roll knowing that stopping on dew wet grass in
time to avoid the (damp) overrun was problematic.

I went past (not over) Tracy's house just above the roof level and kept the
aircraft between the
trees (centered in the overrun cleared strip) as I finally reached 80 mph
and started to climb at a decent rate. Prop finally loaded at around 500 ft
and 90 mph and rest of trip was
uneventful. I don't think I was ever in any real danger and was above the
tree
line even as I kept it over the cleared part of the overrun, but it was seat
cushion replacement type of excitement.

The essence of the lesson is that while a stalled prop will spin a lot
faster, it clearly is producing significantly less thrust than when loaded.
I knew that intellectually, but now my seat cushion knows it as well.

As pointed out by Tracy Crook when I related my tale, reducing the throttle
sufficiently for the prop to unstall and load up might have been an action I
could have taken.  However, unless that thought would have occured to me way
early in the take-off roll, I don't think I could have acted on the thought.
Retarding the throttle would certainly have been counter intuitive even if
it would have been the correct action.

I had experience a similar situation one cold January morning taking off
outside Atlanta.  However, in that case it was on a hard surface runway and
no damp grass to imped acceleration, so there was not the pucker factor as
in this case.  A varable pitch prop is clearly something that would
eliminate the "stalled" prop situation where the angle of attack of a highly
pitched prop stalls (thereby producing less thrust and less load on the
engine).  The Formular 1 aircraft racers frequently fly with a prop that is
stalled on take off roll but unstalls and loads up once airspeed has
increased, but I don't recommend the practice {:>) for general flying (at
least not on damp grass strips).

In any case, boys and girls, as is my normal practice, I will continue to
provide you with the tales of some of my "learning" experiences.  Live and
Learn.

So after a wonderful week at Shady Bend with Tracy and Laura, I am now back
in North Carolina


Best Regards

Ed

Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com