Kline-Fogleman Airfoil Comparison Study 2-1, plany modelarskie, plany depron 1
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[
KF AIRFOIL EVALUATION BY RICH THOMPSON
BY RICH THOMPSON (KAOS2)
]
February 1
5, 2008
February 15, 2008
KLINE-FOG
COMPARISON STUDY FOR
BUILT FOAM
FOGLEMAN AIRFOIL
COMPARISON STUDY FOR SCRATCH
BUILT FOAM AIRPLANES
AIRFOIL
SCRATCH-
There have been many claims about the performance traits of the various KF
airfoil renditions. To help confirm the
two traditional airfoils along
Flight characteristic scores were recorded for each wing. The majority of
airfoils had sufficient positive attributes to indicate that they may be the best
selection for a specific application
here have been many claims about the performance traits of the various KF
To help confirm the facts and possibly separate the
airfoils along with several KF airfoils were flown and evaluated
Flight characteristic scores were recorded for each wing. The majority of
airfoils had sufficient positive attributes to indicate that they may be the best
selection for a specific application or set of objectives.
here have been many claims about the performance traits of the various KF
separate the fiction,
nd evaluated.
Flight characteristic scores were recorded for each wing. The majority of
airfoils had sufficient positive attributes to indicate that they may be the best
Introduction
Methods and Evaluation
This past year, there have been many
claims about the performance traits of the
various KF airfoil renditions. Since most
wings are built once for a given aircraft,
it’s not always clear which flight traits
the direct result from an airfoil,
product of other aircraft design elements
or a combination of the two. This
occur most often when someone designs a
new aircraft, using a new experimental
airfoil. It is natural to want to attribute
the positive flight characteristics
exhibited by this new aircraft to the new
airfoil design. Consequently, it is difficult
to know which information is myth,
which information is actually fact. The
intent of this study was to evaluate
flight performance of several versions of
the KF airfoil.
This past year, there have been many
claims about the performance traits of the
various KF airfoil renditions. Since most
wings are built once for a given aircraft,
it’s not always clear which flight traits are
an airfoil, the
of other aircraft design elements,
. This tends to
someone designs a
experimental
airfoil. It is natural to want to attribute
Choosing a Method
The method I chose for this airfoil test
was to design an Experimental
(XTB) airplane that would permit the
installation
The method I chose for this airfoil test
was to design an Experimental Test Bed
B) airplane that would permit the
installation of
different wings.
This XTB was
created in such a
way that other
design elements
airplane flight
characteristics were minimized. It was a
simple box type shoulder wing fuselage,
n Ugly Stick. The wing was
held in place with rubber bands for easy
he wings were
ed with a 40” wingspan, a 10” wing
2” wide ailerons, and had no
wing saddle had zero
as did the elevator
Two traditional airfoils were
along with a variety
were test flown
on the exact same fuselage.
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different
This XTB was
created in such a
way that other
design elements
that
can
affect
airplane
characteristics
craft to the new
it is difficult
which information is myth, and
which information is actually fact. The
o evaluate the
several versions of
characteristics were minimized. It was a
simple box type shoulder wing fuselage,
similar to an Ugly Stick. The wing was
held in place with rubber bands for easy
exchange. Each of the wings
designed with a 40” wingspan, a 10” wing
chord, 2” wide ailerons,
dihedral. The wing saddle had z
degrees incidence as did t
stabilizer. Two traditional
included in the study along with a
of KF airfoils. All wings were test
for evaluation on the exact same
Control Airfoils and Test Airfoils Defined
Traditional Flat-plate Airfoil
KF m3 Airfoil
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KF Bottom-Step 40% Airfoil
Traditional Symmetrical Airfoil
KF Bottom-Step 50% Airfoil
KF Top-Step 50% Airfoil
KF Top & Bottom Step 40%
Traditional Clark-Y
Method of Evaluation
Evaluation Criteria & Scoring Defined
Since all aspects of the aircraft remained
the same throughout this test except for
the airfoil being used, the resulting flight
performance differences are attributed
directly to the airfoil in use.
Each airfoil was evaluated against ten
flight characteristic categories.
Top Speed – A score indicating how fast
the plane was able to travel in level flight
at wide open throttle.
Each airfoil was installed on the XTB and
flown by two pilots, myself and my son
(Kaos2 & 30V2). We each formed our
own opinions and compared them after
the flights were complete. The results
were
Slow Speed - A score indicating how slow
the plane was able to continue to fly on its
wing, as opposed to prop hanging or
harrier style flight.
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documented
against
several
Pitchiness - A score indicating how
abruptly the plane responded to elevator
inputs.
subjective categories.
1
Roll Rate - A score indicating how quickly
the plane responded to aileron inputs.
1
There may be some who criticize the use of
subjective data simply because itÓs subjective.
My response to that criticism is that in my 30+
years of flying RC, IÓve observed one thing that
remains true of all RC pilots. If you hand the
controls of a great flying plane to any RC pilot,
they immediately know they have a great flying
plane on their hands. If you hand the controls of
a poor flying plane to any RC pilot, they
immediately know that they have a poor flying
plane on their hands. This knowledge is
completely independent from what one might
observe in a video or by watching nearby,
because this information is based on their feel,
and is totally subjective. I claim that it is the
subjective information about how a plane
handles that is most significant to RC pilots.
Inverted Flight - A score indicating how
the plane handled inverted.
Stall - A score indicating how the plane
stalled and stall recovery.
Glide - A score indicating how far the
plane was able to glide from a given
altitude.
Grooving or Smoothness - A score
indicating how well the plane maintained
its course, particularly in turns, without
additional control inputs.
High Alpha Flight - A score indicating
how well the plane maintained high alpha
flight (harrier style flight).
Adverse Yaw - A score indicating how
much the airfoil caused the plane’s nose
to yaw, or pivot, in the opposite direction
of an aileron induced bank.
Results
Airfoils Tested
Bottom-
Step
KF 40%
Bottom-
Step
KF 50%
Flat
Plate
Top-Step
KF 50%
Top-Step
KF3
T & B -Step
KF 40%
Criteria
Symmetrical
Clark-Y
Top Speed
5
4
3
3
3
1
2
4
Inverted flight
3
4
5
4
3
1
3
3
Stall
1
3
5
4
5
4
3
2
Pitchiness
1
5
5
5
5
5
5
5
Slow Speed
2
1
4
3
4
3
2
5
Roll Rate
4
5
3
3
2
1
2
4
Groove
1
5
4
4
3
1
3
3
High Alpha
1
2
5
4
5
3
3
2
Glide
2
4
2
3
2
1
1
5
Adverse Yaw
3
4
4
5
4
1
3
4
Score Total
23
37
40
38
36
21
27
37
The scoring system is a five point system where a score of 5 indicates the best performing
airfoil in that category and a score of 1 indicates the poorest performing airfoil in that
category. Please note that a score of one does not mean that a given airfoil is a bad
performer; it just means that of the various airfoils tested, it was the poorest performing
airfoil in that category. Numbers assigned between 1 and 5 depict performance between
the strongest and poorest performers, and are relative.
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Discussion
Airfoil Scoring
Initial Impressions
The table displaying the airfoil scores
requires some further discussion. Airfoil
scores that are only one number apart are
very close in performance, and the
differences may only be observed when
an airfoil can be exchanged on the same
aircraft. Airfoils that were given the same
score were so close in performance that
no discernable difference could be noted.
One of the first things that immediately
became clear during this study was that
airfoil selection for an airplane has a
dramatic effect on the aircraft’s handling
and performance. Nearly every time we
changed wings, the XTB felt like a
completely different plane. The wing not
only produced the lift necessary for flight,
but it had an impact on each of the other
controls as well.
The scores in pichiness were all the same
except for the Flat-Plate airfoil. My
hypothesis for this result is that
pitchiness is more directly related to the
thickness of the leading edge than the rest
of the airfoil shape.
Since the Symmetrical airfoil is not
traditionally known for its glide
performance, it was surprising to find
that the Symmetrical airfoil outperformed
the others in the glide tests, with the only
exception being the Clark-Y airfoil. The
Clark-Y and Symmetrical airfoils were the
most aerodynamically clean wing designs.
A possible explanation for this observed
gliding result is that due to the low inertia
that small foam airplanes possess, the
reduction of drag may be of greater
importance to extending glide than the lift
generated by Bernoulli’s Principal.
2
Since
the Clark-Y airfoil produced significantly
more lift than the symmetrical airfoil, it is
also clear that additional lift produced in
addition to an aerodynamically clean
design will further extend glide.
airfoils would display similar stall
characteristics. This idea was supported
by the fact that even the worst
performing airfoil in the stall category
exhibited a stall with very manageable
characteristics for all average pilots.
Airfoil Performance Summary
Of the eight airfoils evaluated, there were
four airfoils that were considered to be
the top contenders. Listed in the order
they appear on the chart, they are:
Symmetrical, Top-Step KF 50%, KFm3,
and Clark-Y.
The Symmetrical airfoil created an
airplane that had very good all around
flight characteristics. The plane was very
well mannered as it grooved through our
test flight. It’s only real weaknesses were
that it wouldn’t fly as slowly as the others
tested, and it didn’t like flying in a high
alpha attitude. The symmetrical foam
wing is best suited for aerobatic aircraft
not required to fly well slowly.
Additional evidence was observed to
support the idea that Newton’s 1
st
. and 3
rd
Laws of Motion
3
play a greater role in
flight performance of small foam
airplanes than Bernoulli’s Principal. The
stall test did not display the abrupt type
of stall that would normally be expected
from a Symmetrical airfoil. Newton’s 3
rd
Law of Motion indicates that the force
exerted on the bottom of the wings as
they fall through space is equal, so most
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The Top-Step KF 50% airfoil was
another all around great performer. The
strength of this airfoil seemed to be its
slow flight performance without
sacrificing good handling in the other
categories. This airfoil received the top
scores in the three categories that
pertained to slow flying. It also tied for a
top score in pitchiness, and was the best
performing airfoil flying inverted. There
were no glaring weaknesses for this
airfoil, but its weakest points were top
speed, roll rate, and glide. The Top-Step
KF 50% foam wing is best suited for
aircraft requiring good performance over
a broad flight envelope.
2
The Bernoulli principle states that the internal
pressure of a fluid decreases as its velocity
increases. This principle is used in many
everyday objects, including spray paint cans and
airplane wings.
http://www.seed.slb.com/qa2/FAQView.cfm?ID=
976
3
Newton's first law states that every object will
remain at rest or in uniform motion in a straight
line unless compelled to change its state by the
action of an external force.
The third law states that for every action (force)
in nature there is an equal and opposite
reaction.
http://www.grc.nasa.gov/WWW/K-
12/airplane/newton.html
The KFm3 airfoil was a great all around
performer as well. The KFm3 produced
the best score in the adverse yaw
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