December 08, 2004
Kitfox II installation
The HKS 700 E installation phase is complete on the Kitfox II.
We're running a 70 inch 3 bld Ivo HP prop. At current setting of
14 degrees at 8 1/2 " from the tip, static rpm is 5400, yielding 700 fpm
climb. We will be activating the in-flight adjustable capabilities of this
shortly. It is believed that may make for some very good all around performance.
During debugging and continued testing, we'll try to keep a chronology
of those events here.
December 13, We dropped back another degree on pitch. The weather
was a little cooler here this morning, around 50 degrees during the flight.
Over the last few days, on numerous flights, sustained climb has been indicating
between 700 and 800 fpm. Today's flight with about 5600 on climb had increased
about 100 fpm.
December 14, A 68 GSC Tech II was tested at 15 degrees
pitch. RPM was low 5K range. On a faster aircraft, this combination would
probably be pretty good, but not for the KF II. The next day,
we dropped pitch back to 13 degrees. RPM was up to 5600 on take off, and
performance was about the same as the original Ivo test.
December 18, A 71 x 37 Perry prop was installed. RPM
was about 5700 on take off and would hold 5800 in climb with a sustained
rate of about 800 fpm through 3k feet. General performance was slightly
better than the second Ivo test.
December 18, The 68 Tech II was reinstalled, pitched
to 12 degrees. Take off rpm was now 5800 and climb 6000. Climb rate
increased to almost 900 fpm.
January 12, The 71 x 37 Perry was once again installed to check
speeds. At 2500 feet msl and 5800 rpm our Kitfox is running 78 mph. At
5000 rpm, 68. Leveling the nose to accelerate just after liftoff allows
the rpm to come up to 6000 fairly quickly, and climb rate at that power
is about identical to high angle low speed climb. ...just a bit under 800
fpm OAT was in the mid seventies.
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What have we learned?
Exactly what one might expect. The Kitfox is not fast. This one is
a seventies something airplane. With encouragement, it will go faster,
but it seems pretty happy stuck in the seventies. With steep pitched props
loading the engine heavily, our plane goes a little faster for any given
rpm. So theoretically, we could use a prop that limits rpm to 5800
(maximum allowable continuous) in level flight, and fly around at wide
open throttle. That would be a condition that would provide the most encouragement
to make the plane go fast. You could call it a cruise prop. Every
prop tested so far, flys our plane around nicely in the seventies. Take
off and climb performance have increased with every increase in rpm. The
68 Tech II at 12 degrees was the first we've flown during this test series
that allows rpm in excess of max allowable continuous in climb attitude.
So while climbing out at 6000 rpm, we will have to reduce power to 5800
or less after 5 minutes. This has been the best climbing configuration
tested to this point. Also, it is probably the slowest.
How much slower?
December 20, 2004. We ran a gps speed check with the Tech II
68 set at 12 degrees. 5800 rpm at 1500 feet yielded 76 mph. Remember, in
this configuration the engine is really unloaded. A short run of wide open
throttle in level flight would run past the 6200 engine rpm limit.
On the slow side, it takes about 5000 rpm to maintain flight. This
testing is solo, with 8 gallons of fuel or less.
Climb rate at altitude
December 22, 2004. Since our field elevation is only 158 ft. msl, our
take off and climb performance is optimal. To explore climb capability
that may exist on a hot summer day somewhere other than Florida, the following
climb test was performed.
"I went for some altitude climb numbers today
on the GSC Tech II 68 at 12
degrees. Initial climb is pretty close to
900fpm. We could call it that if
fudge factor is considered. VSI is better
than 8 most of the time and
occasionally 10. RPM can be 6000, but
I elected to run wide open throttle
with a little higher angle, which pulled rpm
to 5800. With flaperon, climb
gradually diminished to about 500 + fpm at
5,000 feet.
At that point, I leveled off for a few minutes
(Oil temp was still only up to
maybe 170, CHT a little over 300, but this
is the highest I've seen it, and
I'm still testing heat proximity to gascolator
and cowling.)
On application of full power at 5k feet, 6000
rpm was max observed, but I
didn't let speed build, so it may have gone
higher. I ran a climb angle that
held rpm around 5600 to 5800, initially searching
for the best climb rate.
That was about 500 or a little over.
Now, I do have our HACman mixture control
installed on this, but at this point
had only leaned very modestly because results
to 5000 feet were not dramatic.
In this climb test after 5000 feet, I was
shooting for 7500 to establish an
average rate. It held pretty close to 500,
but gradually dropped off, as did
rpm.
Around 8000 feet, it would only hold about
5500 rpm at a high angle, maybe 300
rpm more at higher airspeed, but climb rate
had diminished below 400 fpm.
While in climb, at high angle, holding 5500
rpm wide open throttle, I turned
out the HACman controller towards lean and
observed an rpm increase of 300,
and climb increase of about 150 fpm. I repeated
this from full rich to lean
several times, and the results were the same.
This is not like "war emergency"
power, but it is very dramatic." |
