Richard Kline & Floyd Fogleman: Airfoil (US Patents
3,706,430 & 4,046,338)

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**Richard KLINE & Floyd FOGLEMAN**

**Airfoil**

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[***Omni***
(1984)](#omni)   
[***The
Ultimate Paper Airplane*** (Excerpt)](#ultim)   
**[US Patent
# 3,706,430](#3706)**   
**[US Patent
# 4,046,338](#4046)**

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***Omni***
(1984) 

**"Fancy
Flights"**

**by Scot Morris**

The sleek and silvery
airplane shown here, flying in formation with its creators,
Richard Kline and Floyd Fogleman, isnt just any paper
airplane. It is a paper airplane so remarkable and original
that it is protected by two separate US patents.

It is a paper airplane so
revolutionary that mockups of its wing have been put through
wind-tunnel tests by NASA, the Navy, the Air Force, and the
Army.

It is a paper airplane so
unconventional that it drives aerodynamics experts crazy. It
seems to violate one of the major laws of flight: the
Bernoulli principle, which explains, theoretically, what keeps
all ordinary planes aloft. And it is a paper airplane whose
plans are made public, for the first time, in this issue.

Most wings are round on top,
flat on the bottom, so air plows over the top. This means the
air is less dense on top and more dense on the bottom. As a
result there is greater pressure on the bottom, which provides
lift.

This wing, however, is flat
on top and notched --- partially hollowed out --- on the
bottom. Because it has more area on its underside, its "lift"
should propel it toward the ground; it should sink like a
rock.

It soars. So much for
Bernoulli.

Richard Kline, a New York
advertising-firm art director, had no idea he was about to
start such a stir when, in 1968, he sat in his kitchen table
in Mount Vernon, NY to make a paper airplane for his 6-year
old son, Gary. He folded back the leading edge of a delta-wing
design in such a way that he left an open slot on the
underside of each wing. The plane flew straighter and farther
than any paper airplane he had ever seen before. Even a living
room was too small for a fair flight test.

More significant, when
balanced and launched properly, the plane wouldnt stall.
Stalling is on of the principle causes of airplane accidents:
the plane turns at too great an angle to the wind, loses its
lift, and crashes into the ground. Some crashes can be traced
to engine failure or an onboard fire or explosion, but most
are tied to stalling. The plane suddenly loses its lift, and
all the pilots controls become worthless.

Klines little paper plane
simply refused to stall. "I was just trying different things",
Kline said later. "I had this idea that I wanted to make a
glider that would reach its apogee and automatically level
off."

 "One day I cut this
thing out of paper, and it did exactly that, and I said,
Thats what Im looking for."

Kline noticed that the plane
was more stable when he opened the slots under the wings, but
it was really his friend and advertising colleague, Floyd
Fogleman, a weekend pilot and model builder, then realized
that the notch under the wing represented "a whole new concept
in aerodynamics". A partnership was born, and the men kept the
discovery to themselves until their first patent was granted
in December 1972. Soon after that, the articles began
appearing in magazines and newspapers. There were stories in *Time*,
*The London Daily Telegraph*, and *The Paris Express*.
A 1973 feature on CBSs *60 Minutes* proved so popular
that it was repeated three years later.

Kline and Fogleman remained
cautious about revealing the instructions for folding their
marvelous plane. Hobbyists studied pictures of the plane and
footage of the few seconds of the *60 Minutes* segment
during which Kline shows TV interviewer Morley Safer the first
few folds. Viewers tried to reconstruct the design, but most
failed miserably.

The fold, in fact, isnt
simple; youll probably make a few mistakes before you get it
right. You can make two planes from our master designs --- one
to practice on one to get exactly right. Even so, you might
want to practice first on an ordinary sheet of heavy typing
paper. Cut the paper down to the dimensions in our diagrams,
and use the fold lines on the master designs to get all the
proportions correct.

A few flying hints: Before
each launch, view the plane head-on and make sure the tops of
each wing are horizontal and that both wings are of equal
thickness. Check to see that the vertical stabilizer is
pointing straight up and that the tape on the nose has no
loose ends. You can wedge a paper clip into the fuselage just
behind the nose to balance the plane and extend its flights.
Experiment with clips of different sizes. And when you find
one that works, use a small piece of tape to reinforce the
fuselage just in front of the tail. Fogleman reports some
exceptionally long glides after tossing the plane up into the
wind. If properly launched, the craft gains altitude rapidly
and then flies with the breeze.

Aerodynamics experts who
looked at the plane said it would never fly --- not with that
notch, or "step", on the underside of the wing. "They would
tell me, Forget it. It wont work, Kline says. "But me, I
never heard of Bernoulli, so what do I know? It works, thats
all."

How does it work? The
inventors didnt know. So with patent papers safely in hand,
they set out to find someone who could tell them. They took it
to one of Americas leading aerodynamics experts, John
Nicolaides, a former NASA official and onetime head of the
aerospace-engineering departments at both Notre Dame and
California Polytechnic State University at San Luis Obispo.

Nicolaides, whose "flying
flivver" was the subject of a story in one of *Omni*s
first issues ["A Flyer for the Masses", Dec. 1978], was
skeptical at first. He became a believer, however, when the
men visited him at Notre Dame and tested a paper model in the
campuss athletic center. "One of my throws went into the
lights of the arena, struck the roof, and then glided clear
across the building and into the seats", says Kline.
"Nicolaides couldnt believe it."

This one flight, more than
anything else, convinced the aerodynamics expert that the toy
deserved some serious wind-tunnel tests. "The data were
strange", Nicolaides said, "not like any wind-tunnel data I
had ever seen". Nicolaides confirmed that the wing was a true
breakthrough in design and that it greatly resists stalling.

But why? "I dont know",
Nicolaides told Safer on *60 Minutes*. "A conventional
wing, with increasing angle of attack, increases its lift. But
eventually, at a steep critical angle the wing can suddenly
lose its lift, causing the plane to crash. The Kline-Fogleman
wing doesnt do that. It has good lift for small angles of
attack, but a t larger angles, the lift declines and the plane
just levels off. This happens even at very large angles of
attack, which allows it to avoid the tragic stall phenomenon."

Wind tunnel tests showed
that the Kline-Fogleman wing was stable at angles well over 16
to 18 degrees. Thats the inclination at which ordinary wings
lose their lift and begin to stall. In fact, the
Kline-Fogleman wing stubbornly resists stalling all the way up
to a 45 degree angle of attack.

Fogleman says that the tests
complement observations he made using a homebuilt
radio-controlled model plane with a 6-foot wingspan. "I tested
our design with different curvatures on the top and the bottom
of the wing", he says, "and the most impressive thing about
them all is that they dont want to spin. There is a spinning
maneuver in competitions. You take the normal radio-controlled
plane and fly it up to a stall angle, and it will suddenly
snap over and go into a spin. Our plane wont do that. You
have to cut the throttle and control the ailerons and rudder
all at once to force it to spin. And you can spin it in either
direction, which is unusual. Most planes will spin only in the
direction of their torque, opposite the way the propeller is
turning. Our plane seems to resist that torque, so you can
spin it either way. When you take your hands off the controls,
the plane comes out of the spin in less than half a turn and
returns to straight and level flight."

Just as when you have to
force the plane to spin, you also have to force it to stall.
"You cant get it to stall like an ordinary plane", Fogleman
says. "It just keeps on porpoising on ahead. When you cut
power on landing, it doesnt stall either, as other planes do,
but just keeps going flat ahead. Also, other planes will tip
stall --- one wingtip goes down, and the plane spins out of
control and crashes --- if they are brought in for a landing
at too slow a speed or too high an angle. Our plane just
refuses to tip stall."

One would think that the Air
Force and NASA would be eager to perform exhaustive tests on
the Kline-Fogleman wing and its variations. Apparently that
hasnt happened. "We know NASA tested it", Fogleman says, "but
we couldnt get any results from them, and neither could
Nicolaides."

In 1979, P.K. Pierpont, then
manager of the airfoil-research program at NASAs Langley
Research Center in Virginia, told Omni about three studies,
one of them partially funded by NASA. All had come up with the
same results: The Kline-Fogleman wing was found to have a poor
lift-to-drag (L/D) ratio --- a standard measure of wing
efficiency. These results indicated that the airfoil had no
practical application, Pierpont said, so no further tests were
made.

And according to Bud
Bobbitt, chief of NASAs transonic-aerodynamics division, test
showed that the Kline-Fogleman wing was inefficient. The L/D
numbers werent encouraging, so studying the wings resistance
to stalling became a low priority.

Max Davis, of the Air Force
Flight Dynamics Lab at Wright-Patterson Air Force Base in
Dayton, OH, told a similar story. A few tests were performed
after all the publicity in 1973, he said, but preliminary
studies indicated that the wing was not suitable for a
full-size aircraft because it has too much drag and not enough
lift.

"All that is true",
Nicolaides says, "but it misses the point. This airfoil
doesnt have great lift at low angles, I grant that. But at
high angles, where most planes spin out of control and crash,
this one keeps flying."

Furthermore, Nmicolaides
found that at subsonic speeds, the wing worked even better
when it was turned upside down, with the notch on the top
instead of on the bottom. In the notch-up mode, the wings
lift improved by 44% and its L/D ratio improved by about 30%.
And it still refused to stall.

That was enough to convince
Nicolaides that the Kline-Fogleman wing deserved serious study
by the US government.

In April 1973 Nicolaides
wrote letters to NASA, the Air Force, and the Navy, urging
them to test the Kline-Fogleman wing in all conceivable
configurations: notch down, notch up, rounded leading edge,
curved wing surfaces, varied curvature and placement of the
notch, and so on. Nicolaides enclosed copies of his
encouraging wind-tunnel data.

Apparently, the government
experts with the big testing facilities generally ignored most
of Nicolaides recommendations. Even when they put the
Kline-Fogleman wing through its paces, they concentrated on
the lift and drag data, not the resistance to stalling, or
they studied only the razor edge version, not the rounded,
more winglike variation. In explaining the space agencys lack
of interest, Pierpont said in 1979 that the flight
characteristics of the Kline-Fogleman wing were no better than
those of a flat plate. But this assertion was disputed by the
wind-tunnel data in Nicolaidess 1973 letter to NASA.

All of this would seem to
indicate a marked lack of interest in exploring an idea that
could save lives and airplanes. At worst, it suggests that the
government did test wings that qualify as Kline-Fogleman
variations but wont reveal the test results.

It boils down to this: If
the suggested tests werent done, why not? And if they were
done, why werent the results made known to Nicolaides, Kline,
Fogleman, or an inquiring reporter from *Omni*?

One line of speculation is
that the government is withholding the data for national
security reasons. Another is that officials perceive a
possible overlap between the Kline-Fogleman idea and the
do-called Whitcomb supercritical wing. This wing, invented by
Richard Whitcomb and patented by NASA in 1976, permits planes
to fly close to the sound barrier without being buffeted by
turbulence on top of the airfoil. This feat is made possible
by the wings unusual shape. Its relatively flat on the top,
with a concavity on the undersurface, The hollowed section
isnt the abrupt notch of the Kline-Fogleman patent drawings,
but it is well within the range of variations that Nicolaides
suggested for testing (When I asked Nicolaides to describe the
Whitcomb wing, he called it "a regular wing with a
smoothed-out Kline-Fogleman notch on the bottom.")

Its possible that Kline and
Fogleman were awarded a patent on an idea that includes
features of the Whitcomb wing. If so, government officials,
firmly wedded to Whitcombs design, may be trying to sharpen
the distinction between the two ideas by downplaying the
airworthiness of the Kline-Fogleman prototype.

"I dont know whether the
whole story will ever come out", Nicolaides says. "But the
important thing to remember is that the Kline-Fogleman wing
doesnt stall. If the government tsters say that it is not
quite as good as other wings in terms of lift-to-drag ratios,
they are neglecting to say that it is infinitely better in
terms of not killing people. Thats what the Kline-Fogleman
wing is all about."

 "What I keep coming
back to", says Kline, "is the whole question of what makes our
airfoil so stable. We believe that the notches cause pockets
of air tubulence to be trapped on the underside of the wings
and that these pockets somehow support the aircraft at steep
angles of attack. No one, as far as I know, has studied whats
going on in these pockets."

Until proper tests are
conducted, it is hard to tell what promise the Kline-Fogleman
wing holds. So far the most encouraging findings have come
from model plane hobbyists, backyard testers and small
aircraft companies.

Amerijet, Inc., an Ohio firm
producing single-engine planes, is testing a Kline-Fogleman
wing to be used on a two-seater aircraft. If the
stress-analysis and wind-tunnel tests go as expected, the
company will build the first full-scale Kline-Fogleman
aircraft in about two years.

J.B. Mitroo, president of
Amerijet, told Omni that preliminary tests indicate that the
wing will actually improve the efficiency of flight, bringing
about a 25 to 35% saving s in fuel.

On the model-airplane front,
findings continue to be impressive. Pete Reed, of Avon, CT,
tried a Kline-Fogleman wing on a radio-controlled model plane
that had a habit of stalling. "It solved the problem", he
says. "The plane doesnt stall anymore, and the difference is
spectacular. It flies better than any other plane I have used.
With my old plane, if you slowed it down it would stop flying
and it would tip stall to one side or the other. I can haul
the Kline-Fogleman model up to a very high angle of attack or
slow it way down, and the plane still wont tip stall. The
only problem is that the wing adds a lot of drag and the plane
flies slower than before."

Reed thinks the drag problem
might be corrected if the Kline-Fogleman shape were used only
on the outer quarter or third of each wing, rather than along
its full length. "If a stall starts at the base of the wing,
next to the fuselage, you have time to correct it. But if it
starts at the wingtip, it spreads to the rest of the wing
before you know it, and there is nothing you can do but watch
the thing crash."

Reed suggests another
promising variation: carving the blades of a propeller into a
Kline-Fogleman profile. "I tried it once. I didnt take any
hard measurements, but the plane seemed to fly faster", he
says.

In another test on the idea
of a Kline-Fogleman propeller, George Leu, of South Orange,
NJ, cut a Kline-Fogleman notch into the two blades of an
11-inch diameter model airplane propeller.

When he attached a fish
scale to a plane equipped with an ordinary propeller and
revved the engine, he got a maximum pull of about 10 pounds.
"When I put the Kline-Fogleman prop on the same plane, I got
11 pounds of pull. It was amazing. The people I was flying
with could hardly believe it. Fish scales arent the most
accurate devices, but the one I used did measure a positive
difference, and that sure makes me think this design has
possibilities. When I flew the plane with its Kline-Fogleman
prop, it seemed to have a lot more vertical power than before,
and I needed to give it less correction than usual to get it
to do such standard maneuvers as rolling and looping."

The romantic in us would
like to think that a significant breakthrough in aerodynamics
had its beginning on a kitchen table in New York. That a
father making a toy for his son hit upon just the right
combination of paper glue, scotch tape and luck. Whether this
is a tale of genuine discovery or just a fantasy of what might
have been has not yet been answered. Were rooting for the
kitchen table.

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**Paper Plane Instructions:**[Page 1](1instrx.gif) ~ [Page
2](2instrx.gif)

**Paper Plane Plans:** [Page 1](1plan.gif) ~ [Page 2](2plan.gif)

---

  
  
Excerpt: ***The Ultimate
Paper Airplane*** by **R. Kline & F. Fogleman
(1985, Simon & Schuster; ISBN 0-671-55551-0) ~**

A friend of Floyd's George
Leu of South Orange, NJ, was one of the recipients of an
experimental set of propeller blades. Leu had many years'
experience flying radio-controled aircraft with Floy, and he
agreed to conduct the propeller-blade test. The experimental
blades were 11 inches long and had a 7 degree angle of pitch;
the engine used was a Webra Speed 0.60 cubic inch.

Leu conducted a simple
static test with a radio-controlled plane anchored to the
ground. A spring-loaded fish scale was used to determine the
mount of pull or thrust prodcued by both a conventional blade
adn the Kline-Fogleman prop. The results were striking. The
conventional blade pulled a maximum of 10 pounds. But when Leu
put the Kline-Fogleman prop on, he got 11 pounds of thrust, or
a 10% increase in thrust with slightly fewer RPMs (a 200 RPM
drop in a 13,500 RPM run). The test was repeated a second
time, adn teh results remained the same.

Then Leu put the
Kline-Fogleman prop on his radio-controlled plane and flew it.
he noticed that it climbed vertically with much more power
than with the conventional prop that he had flown before...

![](1upa.gif)

*Above*: A close-up of the
tip of a model airplane propeller blade with a Kline-Fogleman
step carved into the tip. From leading edge to trailing edge at
the tip is 3/4". The length of the step measures 2".

*Below:* The
conventional airofoil (top) shows the four major forces that
act upon a wing during flight: lift, thrust, drag adn gravity.
The Kline-Fogleman airfoil (bottom) traps seom of the
displaced air molecules, reverses their direction, adn
produces a forward "push". this action will support the
airfoil up to a 45 degree angle of attack, whether it is used
with the step on teh bottom or on the top.

![](2upa.gif)

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**US
Patent # 3,706,430**

**Airfoil
for Aircraft**

**Richard
L. Kline & Floyd F. Fogleman**   
(Dec. 19, 1972)

**Background of the
Invention**

The invention relates to
airfoils, especially airfoils having lift and drag
characteristics suitable for aircraft wing sections and the
like. In the comparatively low or subsonic speed range, the
conventional airfoil has cambered surfaces that define a
profile of gradually decreasing thickness from the leading
edge to the trailing edge. For high or supersonic speeds, the
airfoil camber is comparatively small and the wing thin so
that the upper and under surfaces tend to be substantially
planar.

It follows therefore, that
the drag characteristics of the subsonic airfoil are not
suitable for supersonic speed, whereas the lift
characteristics of the supersonic airfoil are not well suited
for low airspeeds. The present invention is concerned with
providing a new and basic airfoil design that can be readily
varied to meet the requirements of a wide range of airspeeds.

**Summary of the Invention**

In accordance with the
invention, an air foil having a basic design that lends itself
to use in aircraft throughout a wide range of airspeeds,
comprises a continuous upper surface, and a stepped under
surface. The leading edge of the airfoil is defined by the
apex of a wedge-shaped section that is formed by angular
convergence of the upper surface and a generally planar
portion of the under surface. Starting at the leading edge,
the diverging under surface terminates abruptly in advance of
the leading edge to form on the airfoil under surface a
step-like discontinuity that extends spanwise of the airfoil.
Rearward of the discontinuity, i.e., the base of the
wedge-shape section, the airfoil has a comparatively thin
cross-section that terminates as the trailing edge of the
airfoil proper.

For varying drag and lift
characteristics according to airspeed, the apex angle of the
wedge-shape section can be varied, and the diverging under
side can be shortened or lengthened to vary the location of
the defined step with respect to the trailing edge.

A principal object of the
invention therefore, is a new and improved airfoil for
aircraft having a minimum of design parameters for adapting
the airfoil to a wide variety of airspeeds.

A further object of the
invention is an airfoil of the character above having a
continuous upper surface and a lower surface having a stepped
discontinuity, the surfaces being angularly and spacially
related to define a chord section that increases in thickness
from the leading edge of the airfoil to the discontinuity.

A related object is an
improved airfoil as defined above, having advantageously
combined lift, drag and stability characteristics.

These and other objects,
features and advantages will become apparent from the
following description with reference to the accompanying
drawings.

**Brief Description of the
Drawings**

Figure 1 is a side view, in
partial perspective, of high speed fixed wing aircraft having
airfoils embodying the invention;

![](3fig1.gif)

Figure 2 is a
cross-sectional view of one of the airfoils taken at the
indicated junction of the airfoil and aircraft fuselage as
shown in Figure 1;

![](3fig2.gif)

Figure 3 is a front
half-section view of aircraft showing a wing airfoil typical
of the invention;

![](3fig3.gif)

Figure 3A to 3D inclusive,
are sectional views of the airfoil taken respectively, at the
correspondingly lettered section location of Figure 3;

![](3fig3ad.gif)

Figure 4 is a front
half-section view of aircraft showing the airfoil in modified
form;

![](3fig4.gif)

Figure 4A to 4D inclusive,
are sectional views taken respectively at the correspondingly
lettered section locations of Figure 5;

![](3fig4ad.gif)

Figure 5 is a plan view of
the airfoil shown in Figure 3;

![](3fig5.gif)

Figure 5A to 5D inclusive,
are sectional views of the airfoil taken respectively, at the
correspondingly lettered section locations of Figure 5;

![](3fig5ad.gif)

Figure 6 is a leading edge
view of the airfoil of Figure 5 taken from the right as shown;

![](3fig6.gif)

Figure 7 is a perspective
view of a cross-section taken along the line 7-7 of Figure 6;

![](3fig7.gif)

Figure 8 is a perspective
view of a rotary wing type aircraft embodying the invention,
and

![](3fig8.gif)

Figure 9 is an enlarged view
of the peripheral edge section of a rotary airfoil as shown in
Figure 8.

![](3fig9.gif)

**Description of Preferred
Embodiment**

The airfoil of the invention
is illustrated in Figures 1 and 2 as applied by way of
example, to fixed-wing aircraft of the high speed type. It
will be understood, however, from the following description
that the invention is not limited to high speed or even fixed
wing types, and that it can be used advantageously in rotary
wing aircraft, and also in comparatively small, low-speed
aircraft of the propeller-driven type, as well as in
intermediate speed types.

Referring first to Figure 1,
the aircraft 10 comprises a conventional streamlined fuselage
12 with empennage 14 and swept-back wings 16 and 18 that
constitute the improved airfoils of the invention. The lateral
edges of the wings converge toward the rear of the fuselage so
that as viewed from above, the composite area of the wings is
of generally diamond configuration. Since descriptions of
remaining equipment, such as thrust engines, landing gear,
etc., are unnecessary for understanding the invention, these
items are not shown in the drawings; it is sufficient to
mention that conventional jet engines can be carried by the
wing structure in suitable manner (suspension, cantilever,
etc.) according to aircraft CG and other factors.

The airfoils constituting
the wings 16 and 18 in Figure 1, are mounted on the fuselage
so as to have a small angle-of-attack according to usual
practice when the aircraft is on the runway. Each wing, taking
for example wing 16 and referring now to Figure 2, comprises
an extensive main section 24 that extends from along the wing
leading edge 26 toward the wing trailing edge. The section 24
terminates to form a step 28 that defines a discontinuity in
the under surface of the wing between the leading and trailing
edges. As indicated in figure 1, the step 28 extends outwardly
from the fuselage, its root section at, or spanwise of the
wing in the general direction of the wing Y-axis, in contrast
with the angular direction of the swept-back leading edge 26
of the wing. As in the general case of airfoils that
constitute aircraft wings, the relative air flow with respect
to the airfoil is from the leading edge in direction generally
parallel to the root section and rearwardly to the free
trailing edge, and thence downstream in substantially the same
general direction.

As best shown in Figure 2,
the underside of the wing is basically formed by the main
section 20 and the undersection 24 that is of wedge-shape with
its apex coinciding with the leading edge of the wing. The
wedge-like section 24 is joined to the main section 20 beneath
the forward part thereof, with the wedge apex as indicated
above merging with the front edge of the main section to form
the leading edge 26 of the wing, and the wedge base forming
the "riseR" of the step at 28.

The design angle made
between the sections 20 and 24, i.e., the apex angle, can be
varied in accordance with aerodynamic considerations, lift,
drag, etc., as also can the location of the step with respect
to the trailing edge that determines the ratio between the
wing top and surface area (section 20) and the under surface
area of section 24. The "riser" portion at 28 of the step
(indicated by dotted line in Figure 1) can be either sealed or
left open, depending on preferred construction of section 24,
aerodynamic stresses, etc. For low airspeeds, the riser
portion may remain comparatively open, as desired.

Reference will now be made
to Figures 3 to 7 for a more detailed description of the new
airfoil embodying the invention. As the aircraft is
symmetrical with respect to its main axes, the half-sections
shown in Figures 3 and 4 are sufficient for illustrating
possible variations in the airfoil configuration. Figure 3
indicates a conventional fuselage 30 with one wing 32
constituting an airfoil of the basic character illustrated by
Figures 1 and 2. The view, looking toward the swept-back
leading edge at 34, shows the continuous upper surface 36 of
the airfoil as slightly convex between the fuselage and outer
wing tip 38, as is also the lower surface 40 of the wedge-like
under section 42.

For illustrating the
structural form of the airfoil 32, Figures 3A to 3D are
cross-sectional views taken at the section lines A-A, B-B,
etc., respectively, of Figure 3. The section nearest the
fuselage (Figure 3A) shows the wedge-like under portion 42 as
shaving a small apex angle and extending to the step 44 at
somewhat less than half the distance to the trailing edge 46.
The apex angle increases somewhat at the mid-section of the
airfoil, Figures 3B and 3C, to about 10 degrees with the step
distance from the leading edge decreasing as shown by Figure
1. Neat the wing tip, Figure 3D, the wedge apex angle
decreases for gradual tapering-off at the wing tip. The upper
wing section shortens, generally according to distance from
wing tip so as to conform with the wing shape of Figure 1.

Figure 4 illustrates the
invention as embodied in a modified airfoil 50 especially
adapted for high speeds, such as in the supersonic range.
Here, the apex angle of the wedge under portion 52 remains
substantially constant at a small angle, such as 5-6 degrees,
throughout the leading edge 54 from the fuselage 30 to the
wing tip 56. The under-surface discontinuity or step, is
located with reference to the trailing edge as illustrated in
Figure 1. Accordingly, the thickness of the airfoil 50 is
materially reduced as compared with Figure 3 and the upper
wing surface, as well as the lower surface of the wedge are
substantially planar. The airfoil cross-sections at the
transversely spaced sections A, B, C, and D, are shown by
Figures 4A to 4D respectively, and further description thereof
is unnecessary in view of Figures 3A to 3D for an
understanding of this aspect of the invention.

Figure 5 is a plan view of
the airfoil shown in Figure 3;

![](3fig5.gif)

Figure 5A to 5D inclusive,
are sectional views of the airfoil taken respectively, at the
correspondingly lettered section locations of Figure 5;

![](3fig4ad.gif)

Figure 6 is a leading edge
view of the airfoil of Figure 5 taken from the right as shown;

![](3fig6.gif)

Figure 7 is a perspective
view of a cross-section taken along the line 7-7 of Figure 6;

![](3fig7.gif)

Figure 8 is a perspective
view of a rotary wing type aircraft embodying the invention,
and

![](3fig8.gif)

Figure 9 is an enlarged view
of the peripheral edge section of a rotary airfoil as shown in
Figure 8.

![](3fig9.gif)

**Description of Preferred
Embodiment**

The airfoil of the invention
is illustrated in Figures 1 and 2 as applied by way of
example, to fixed-wing aircraft of the high speed type. It
will be understood, however, from the following description
that the invention is not limited to high speed or even fixed
wing types, and that it can be used advantageously in rotary
wing aircraft, and also in comparatively small, low-speed
aircraft of the propeller-driven type, as well as in
intermediate speed types.

Referring first to Figure 1,
the aircraft 10 comprises a conventional streamlined fuselage
12 with empennage 14 and swept-back wings 16 and 18 that
constitute the improved airfoils of the invention. The lateral
edges of the wings converge toward the rear of the fuselage so
that as viewed from above, the composite area of the wings is
of generally diamond configuration. Since descriptions of
remaining equipment, such as thrust engines, landing gear,
etc., are unnecessary for understanding the invention, these
items are not shown in the drawings; it is sufficient to
mention that conventional jet engines can be carried by the
wing structure in suitable manner (suspension, cantilever,
etc.) according to aircraft CG and other factors.

The airfoils constituting
the wings 16 and 18 in Figure 1, are mounted on the fuselage
so as to have a small angle-of-attack according to usual
practice when the aircraft is on the runway. Each wing, taking
for example wing 16 and referring now to Figure 2, comprises
an extensive main section 24 that extends from along the wing
leading edge 26 toward the wing trailing edge. The section 24
terminates to form a step 28 that defines a discontinuity in
the under surface of the wing between the leading and trailing
edges. As indicated in figure 1, the step 28 extends outwardly
from the fuselage, its root section at, or spanwise of the
wing in the general direction of the wing Y-axis, in contrast
with the angular direction of the swept-back leading edge 26
of the wing. As in the general case of airfoils that
constitute aircraft wings, the relative air flow with respect
to the airfoil is from the leading edge in direction generally
parallel to the root section and rearwardly to the free
trailing edge, and thence downstream in substantially the same
general direction.

As best shown in Figure 2,
the underside of the wing is basically formed by the main
section 20 and the undersection 24 that is of wedge-shape with
its apex coinciding with the leading edge of the wing. The
wedge-like section 24 is joined to the main section 20 beneath
the forward part thereof, with the wedge apex as indicated
above merging with the front edge of the main section to form
the leading edge 26 of the wing, and the wedge base forming
the "riser" of the step at 28.

The design angle made
between the sections 20 and 24, i.e., the apex angle, can be
varied in accordance with aerodynamic considerations, lift,
drag, etc., as also can the location of the step with respect
to the trailing edge that determines the ratio between the
wing top and surface area (section 20) and the under surface
area of section 24. The "riser" portion at 28 of the step
(indicated by dotted line in Figure 1) can be either sealed or
left open, depending on preferred construction of section 24,
aerodynamic stresses, etc. For low airspeeds, the riser
portion may remain comparatively open, as desired.

Reference will now be made
to Figures 3 to 7 for a more detailed description of the new
airfoil embodying the invention. As the aircraft is
symmetrical with respect to its main axes, the half-sections
shown in Figures 3 and 4 are sufficient for illustrating
possible variations in the airfoil configuration. Figure 3
indicates a conventional fuselage 30 with one wing 32
constituting an airfoil of the basic character illustrated by
Figures 1 and 2. The view, looking toward the swept-back
leading edge at 34, shows the continuous upper surface 36 of
the airfoil as slightly convex between the fuselage and outer
wing tip 38, as is also the lower surface 40 of the wedge-like
under section 42.

For illustrating the
structural form of the airfoil 32, Figures 3A to 3D are
cross-sectional views taken at the section lines A-A, B-B,
etc., respectively, of Figure 3. The section nearest the
fuselage (Figure 3A) shows the wedge-like under portion 42 as
shaving a small apex angle and extending to the step 44 at
somewhat less than half the distance to the trailing edge 46.
The apex angle increases somewhat at the mid-section of the
airfoil, Figures 3B and 3C, to about 10 degrees with the step
distance from the leading edge decreasing as shown by Figure
1. Near the wing tip, Figure 3D, the wedge apex angle
decreases for gradual tapering-off at the wing tip. The upper
wing section shortens, generally according to distance from
wing tip so as to conform with the wing shape of Figure 1.

Figure 4 illustrates the
invention as embodied in a modified airfoil 50 especially
adapted for high speeds, such as in the supersonic range.
Here, the apex angle of the wedge under portion 52 remains
substantially constant at a small angle, such as 5-6 degrees,
throughout the leading edge 54 from the fuselage 30 to the
wing tip 56. The under-surface discontinuity or step, is
located with reference to the trailing edge as illustrated in
Figure 1. Accordingly, the thickness of the airfoil 50 is
materially reduced as compared with Figure 3 and the upper
wing surface, as well as the lower surface of the wedge are
substantially planar. The airfoil cross-sections at the
transversely spaced sections A, B, C, and D, are shown by
Figures 4A to 4D respectively, and further description thereof
is unnecessary in view of Figures 3A to 3D for an
understanding of this aspect of the invention.

Figure 5 which is a plan
view, referring to Figure 3, shows more explicitly the spacial
relation between the under-surface discontinuity and the
leading and trailing edges. Here, the airfoil 60 is in top
plan view, with the sectional views Gigs. 5A to 5D taken as
before at spaced points between the fuselage junction edge 62
and the wing tip 64. The step 66, as generally shown in Fig. 1
(and in Fogs. 5A to 5D) extends from the fuselage edge to the
wing tip at a swept-back angle materially smaller than that of
the leading edge 68. The apex angle in this instance can be
comparatively small, i.e., ranging between 4 and 6 degrees, so
that the wing is sufficiently thin for high air speeds.
Although the upper wing surface and the under surface of the
wedge portion are preferably slightly convex with respect to
the generally linear leading edge, these surfaces for
practical purposes may be considered planar.

Figs. 6 and 7 are different
views of sections of the airfoil, Fig. 5, wherein the upper
and lower wing surfaces are slightly convex with respect to
the horizontal center line, Fig. 6, rather than linear as in
Fig. 4. In Fig. 6 the airfoil 70 has an upper surface 72 that
increases in convexity from the root or fuselage end, to the
wing tip, Fig. 7. The apex angle of the under-surface wedge
portion 78 varies in the manner described above for defining
convex wedge surfaces as shown in Figs. 6 and 7. The resulting
airfoil is of moderate thickness suitable for lower airspeeds
than those for Fig. 4; also the convex surface provides for
increased stability. Fig. 7 which shows a perspective view of
the airfoil at the section line 7-7 of Fig. 6 illustrates the
relationship between the varying apex angle and height of step
79 to the convexity of the upper and lower wing surfaces.

The comparatively thin
trailing portion resulting from the abrupt undersurface
discontinuity as described above, is intended to be
aerodynamically functional throughout full utilization of the
airfoil; that is, the space beneath the thin portion
downstream of the step is not intended to be occupied, as for
housing auxiliary equipment, flaps, etc., that would in
effect, tend to eliminate or markedly reduce the aerodynamic
effect of the discontinuity.

Figs. 8 and 9 show the
invention as embodied in the airfoils of rotating wing type
aircraft. In Fig. 8 a helicopter 80 is provided with rotating
airfoils or blades 82 wherein at least the outer portion of
each blade is constructed according to the basic configuration
described above. Fig. 9 is an enlarged view of the outer (or
peripheral speed) end of the rotor blade wherein the
continuous upper surface 84 is substantially planar and the
under surface is characterized by a wedge-like portion 86
defining a step-like discontinuity 88 intermediate the leading
edge 90 and the trailing edge 92. The apex or leading edge
angle is a function of rotor rpm and required lift
characteristics, and as shown is approximately 10 degrees.

Since the major part of the
lift produced by helicopter blades is at the outer third of
the blade length by reason of the greater swept area and
higher blade velocity thereat, the under-surface step can be
terminated as desired by gradual merging with the blade at an
intermediate point as indicated by dotted lines 88 in Fig. 8.
An important consideration in the use of the present airfoil
for helicopter blades is that the blades can be efficiently
rotated at speeds for bringing the tip speeds into the
supersonic range by reason of the improved lift and drag
characteristics of the thinner high speed airfoil. It will
also be apparent that where desired, the invention can readily
be incorporated in airfoil control sections such as elevators
and rudders, as well as in the main lifting or wing sections.

Referring further to the
airfoil configuration of Fig. 9, it will become apparent that
the basic geometry of the airfoil can be varied to
considerable extent while retaining the essential novel
concept of the invention. For example, the apex or wedge angle
can be varied from several degrees as described above, to as
much as 30 degrees for obtaining lift and stability
characteristics under lower airspeed conditions. Also, the
ration of the upper or camber surface area at 84 to the
under-surface area at 94 of the wedge portion (always greater
than unity) can be varied by location of the discontinuity
(step) with reference to the trailing edge, according to
aerodynamic characteristics desired.

The upper and lower camber
surfaces of the airfoil can be substantially planar, as in
Fig. 4, or slightly convex as in Figs. 3 and 6. Preferable,
the convexity of these surfaces is limited at the point of
maximum bow with respect to a horizontal reference to about 2
percent of the fore-aft length of the surfaces at 84 and 94
respectively. The so-called riser portion of the step at 88 is
not limited to an approximately right angle as shown for
convenience in Figs. 3A, etc., and 5A, etc., but may be
inclined to a greater or lesser extent than that shown in Fig.
9 for example.

As regards aerodynamic
theory, the technical reasons for the improved performance of
the present airfoil are unknown to the inventors. Small-scale
airplanes constructed according to the configurations of Figs.
1 and 3 were tested in flight and demonstrated unusually good
lift, stability, and pitching moment characteristics; further,
the airfoil parameters thereof were found by modern computer
technique, to be suitable for both high speed and low speed
conditions, and to have lift, drag and moment characteristics
within the limits of modern aerodynamic design criteria.

Although the invnetion in
its preferred form is shown applied to the airfoils of
aircraft, application as well to guided-entry type spacecraft,
missiles, etc., in instances where airfoils are used, is
implicit.

Having set forth the
invention in what is considered to be the best embodiment
thereof, it will be understood that changes may be made in the
apparatus as above set forth without departing from the spirit
of the invention or exceeding the scope thereof as defined in
the following claims: [Claims not included here].

---

**US Patent # 4,046,338**

**Airfoil for Aircraft having Improved Lift
Generating Device**

**Richard L. Kline & Floyd F. Fogleman**

**Abstract --** An airfoil for an aircraft having a first
surface extending between the leading edge and the trailing
edge, and a second surface joined to the first along the leading
edge and projecting rearwardly in the direction of said trailing
edge. The second surface of the airfoil terminates materially in
advance of the trailing edge to define a step-like discontinuity
of the airfoil. One or more lift generating members are
pivotally mounted on the second surface of the airfoil adjacent
the step-like discontinuity. The lift generating members are
selectively movable to various positions relative to the
airstream to alter the aerodynamic forces on the airfoil during
conditions of flight.

**References Cited**

**U.S. Patent Documents:** 1841804 -- 2271226 -- 2346464 --
3706430 -- 846,311 -- 688,452 -- 715,266 -- 272,455

***Description***

BACKGROUND OF THE INVENTION

**1. Field of the Invention**

This invention relates generally to an airfoil for aircraft,
and more particularly, to an airfoil that has improved stability
and performance characteristics through a wide range of
airspeeds.

**2. Description of the Prior Art**

The present invention constitutes an improvement over
applicants' previously patented unique airfoil disclosed in U.S.
Pat. No. 3,706,430, dated Dec. 19, 1972, entitled AIRFOIL FOR
AIRCRAFT. The airfoil of that patent included a wedge-like
section formed by a continuous first surface which extended
between the leading and trailing edges, and a second surface
that was joined to the first surface along the leading edge. The
second surface projected rearwardly in the direction of the
trailing edge and terminated materially in advance thereof to
define a step-like discontinuity of the airfoil. The thickness
of the airfoil gradually increased from the leading edge to
approximately 50% of the chord to form the wedge-like section,
at which point, the second surface was sharply projected in the
direction of the first surface to form the step-like
discontinuity.

It was found from flight tests of small airplane models
constructed having the above described airfoil, that the tested
airfoil demonstrated unusually good lift, stability and pitching
moment characteristics. For example, the airfoil greatly
resisted stalling in that it was necessary to induce an angle of
attack between 30.degree. - 40.degree. before the stall
occurred, as distinguished from angle of attack values between
18.degree. - 22.degree. common to conventional airfoils. The
technical explanation for such improved performance is unknown
to the inventors and appears to be contrary to accepted
aerodynamic theory. However, since the effect of stalling plays
a significant role in accident reports, it is apparent that by
resisting stalling, the above airfoil can materially increase
the safety of flight.

Continued tests have shown that the patented airfoil has a poor
glide ratio in the range between 3:1 - 4:1. While various lift
generating devices, such as flaps, are known to be employed on
conventional airfoils to increase the glide ratio such flaps are
commonly mounted at the trailing edge of the airfoil. However,
the use of such flaps on applicants' airfoil is not practical
due to the relative thinness of said airfoil at its trailing
edge. Furthermore, the portion of the airfoil downstream of the
step is not intended to be used for housing auxiliary equipment,
such as flaps, that would tend to eliminate or markedly reduce
the aerodynamic effect of the step-like discontinuity.

During the course of further tests, applicants decided to place
a lift generating member, such as a flap, adjacent the step-like
discontinuity of the airfoil. As a general matter, the placement
of a flap on either the top or lower surface of an airfoil is
well-known wherein such flaps serve as spoilers to decrease the
lift and increase the drag. However, contrary to applicants'
expectation, the placement of a flap adjacent the step-like
discontinuity of the airfoil produced increased lift when the
flap was moved to an extended or deflected position in the
airstream. Thus, applicants have improved their previously
patented airfoil by incorporating therein lift generating means
to increase the glide ratio thereof.

As used herein, the term airfoil is defined as a body, such as
an airplane wing, designed to provide a desired reaction force
when in motion relative to the surrounding air.

Applicants' improved airfoil is to be distinguished from a
class of airfoils designated as being "supercritical." In this
regard, all airfoils have a characteristic known as critical
Mach number (Mcr) which is the air speed ratioed to the speed of
sound (Mach 1) at which the flow over some portion of the
airfoil just reaches Mach 1. Airfoils usually are designed to
fly below their critical Mach number because of the high drag
rise caused by the formation of shock waves and, possibly, flow
separation associated with super-critical speeds. However, the
supercritical airfoil is capable of flying close to the speed of
sound (Mach 1) without experiencing the high drag rise
associated with more conventional shapes.

The conventional airfoil, particularly one designed to operate
in the subsonic speed range, has cambered surfaces that define a
profile of gradually decreasing thickness from the leading edge
to the trailing edge. The supercritical airfoil has a much
flatter shape of the upper surface thereof which reduces both
the extent and strength of the shock wave, as well as the
adverse pressure rise behind the shock wave, with corresponding
reductions in drag. To compensate for the reduced lift of the
upper surface of the supercritical airfoil resulting from the
reduced curvature, the airfoil has increased camber near the
trailing edge. This is to be distinguished from applicants'
unique airfoil which has substantially no camber at the trailing
edge. Furthermore, the supercritical airfoil does not provide
for any step-like discontinuity as incorporated in applicants'
airfoil.

Applicants unique airfoil is also to be distinguished from
those incorporating leading edge extensions and fences, such as
shown and disclosed in U.S. Pat. No. 2,802,630, dated Aug. 13,
1957 entitled WING LEADING EDGE DEVICE. The use of such
extensions apparently has value in the design of sweptback wings
in obtaining a more perfect airflow over the outboard portion of
the wing. Applicants' improved airfoil, as will become more
apparent hereinafter, is directed toward the use of lift
generating members located in the region of the step-like
discontinuity to improve the aerodynamic characteristics
thereof.

**SUMMARY OF THE INVENTION**

The improved airfoil of the present invention provides for a
first surface extending between the leading and trailing edges
and a second surface joined to the first surface along the
leading edge and projecting rearwardly in the direction of the
trailing edge. The second surface of the airfoil terminates
materially in advance of the trailing edge to define a step-like
discontinuity of the airfoil similar to that embodied in
applicants' previously patented airfoil disclosed in U.S. Pat.
No. 3,706,430 and referred to above.

One or more lift generating members, such as flaps, are
pivotally mounted on the second surface of the airfoil adjacent
the step-like discontinuity. The lift generating members are
selectively movable to various positions relative to the
airstream to alter the aerodynamic forces on the airfoil during
conditions of flight.

In another embodiment of the invention, a movable cover member
is pivotally mounted to the airfoil, and has an outer surface
extending from the step-like discontinuity to the trailing edge
of said airfoil. The cover member is selectively movable to
various positions relative to the second surface to further
alter the aerodynamic forces acting on the airfoil during
conditions of flight.

Accordingly, an object of the present invention is to provide
an improved airfoil for aircraft having movable lift generating
members mounted thereon to improve performance characteristics
though a wide range of airspeeds.

Another object and feature of the present invention is to
provide an improved airfoil for aircraft having lift generating
members mounted thereon and selectively movable to increase the
glide ratio.

The above and other objects, features and advantages of the
present invention will become more apparent from a full
consideration of the following detailed description when taken
in conjunction with the accompanying drawings.

**BRIEF DESCRIPTION OF THE DRAWINGS**

FIG. 1 is a side view, partly in perspective, of an aircraft
having airfoils constructed in accordance with the present
invention;

![](4fig1.gif)

FIG. 2 is a bottom plan view of the aircraft illustrated in
FIG. 1, showing the location of the lift generating devices on
the airfoils;

![](4fig2.gif)

FIG. 3 is a front elevational view of the aircraft illustrated
in FIG. 1, showing the lift generating devices in their extended
positions;

![](4fig3.gif)

FIG. 4 is a cross-sectional view of one of the airfoils taken
along line 4--4 of FIG. 3;

![](4fig4.gif)

FIG. 5 is a view similar to FIG. 4 showing the lift generating
devices disposed for movement between various positions;

![](4fig5.gif)

FIG. 6 is a perspective view of one of the airfoils, removed
from the aircraft, showing the location of the lift generating
devices;

![](4fig6.gif)

FIG. 7 is a view similar to FIG. 6 illustrating another
embodiment of the invention;

![](4fig7.gif)

FIG. 8 is a view similar to FIG. 3 illustrating the airfoil
embodiment of FIG. 7 mounted on the aircraft; and

![](4fig8.gif)

FIG. 9 is a view similar to FIG. 4 illustrating another
embodiment of the invention.

![](4fig9.gif)

**DESCRIPTION OF THE PREFERRED EMBODIMENTS**

Referring to the drawings, particularly FIGS. 1,2,3 and 8,
numeral 10 represents an aircraft having airfoils constructed in
accordance with the present invention. Aircraft 10 comprises a
conventional streamlined fuselage 12 with empennage designated
generally by numeral 14, and sweptback wings 16 and 18 that
constitute the improved airfoils of the invention. The lateral
edges of the wings converge toward the rear of the fuselage so
that as viewed from the bottom, the composite area of the wings
is of generally diamond configuration as illustrated in FIG. 2.
However, it will be appreciated that the illustrated
configuration may be altered and is not to be deemed a
limitation on the invention. Other conventional portions or
components of the aircraft, such as the location and type of
engines, landing gear, etc., are omitted from the drawings for
the purpose of clarity in that they do not form part of the
invention.

The structure and overall general configuration of wings or
airfoils 16, 18 is essentially similar to that of applicants'
previously patented airfoil disclosed in U.S. Pat. No.
3,706,430, and the subject matter thereof is incorporated herein
by reference. More specifically, and with reference to FIGS. 3 -
9 herein, the airfoils for any disclosed embodiment of the
invention extend outwardly from fuselage 12 and are of identical
construction when viewed in cross section from the leading edge
to the trailing edge. In other words, the airfoils 16, 18
associated with the aircraft of FIGS. 1 - 6 are identical in
construction and the corresponding airfoils associated with the
aircraft of FIGS. 7 and 8 are also identical in construction.
However, the respective airfoils of the aircraft in said FIGURES
represent different embodiments of the invention.

FIGS. 1 - 6 illustrate one airfoil embodiment 16, 18 of the
invention. In this regard, since airfoils 16, 18 are identical,
it will be appreciated that the description and illustration
relative to one of said airfoils is applicable equally as well
to the other one of said airfoils. Referring to the FIGURES,
airfoil 18 is constructed having a first surface 20 extending
between the leading edge 22 and the trailing edge 24 of the
airfoil. A second surface 26 is joined to the first surface 20
along the leading edge 22, and projects rearwardly in the
direction of trailing edge 24. The arrangement is such that
surfaces 20 and 26 are in diverging relation to define a
wedgeshape represented by numeral 28. Second surface 26
terminates materially in advance of the trailing edge 24 to
define a steplike discontinuity of the airfoil represented
generally by numeral 30. The riser portion 32 of step 30 serves
to connect the second surface 26 of the airfoil to a third
surface 34 which extends from the step to the trailing edge 24.
Airfoil 18 has a span-wise dimension defined by the distance
between its root end 36 and its tip end 38. The step-like
discontinuity 30 extends span-wise of airfoil 18 and has an end
edge 40 terminating in advance of the root end 36 of said
airfoil. This construction permits the wing to have sufficient
depth or thickness over much of its chord-wise dimension
adjacent its root end to accomodate the landing gear assembly or
other auxiliary equipment.

In the preferred embodiment, the first surface 20 defines the
upper contour of airfoil 18 whereas the second and third
surfaces 26, 34 define the lower contour thereof. The view in
FIG. 3 shows the upper wing surface, as well as the lower
surface of the wedge, as being substantially planar.
Furthermore, as shown in FIG. 2, the lower surfaces of airfoil
18 merge with the corresponding lower surfaces of airfoil 16
which project outwardly from the opposite side of fuselage 12.

In accordance with the teachings of the invention, lift
generating means, represented generally by numeral 42, are
provided on the second surface 26 of airfoil 18 adjacent the
step-like discontinuity 30. Lift generating means 42 is
preferably a flap-like member 44 pivotally mounted on airfoil 18
in conventional manner to project rearwardly of the step. Flap
44 is disposed for movement between a first position in which
the outer surface 46 forms a smooth continuation of airfoil
surface 26, a second position in which said outer surface 46
projects outwardly of said airfoil in the direction away from
airfoil surface 34, and a third position in which said outer
surface 46 projects inwardly of said airfoil in the direction
toward said airfoil surface 34.

FIG. 4 illustrates flap 44 in its second position corresponding
to when the flap is moved to an extended position in the
airstream. FIG. 5 shows the flap 44 disposed for movement
between its first, second or third positions, which movement is
represented by the arrow indicia. Although movement of flap 44
to its third position may serve to reduce any turbulent airflow
downstream of the wedge by permitting smoother flow over the
step-like discontinuity 30, the primary importance of flap
movement is toward its second position which produces increased
lift thereby improving the glide ratio of applicants' previously
patented airfoil. Accordingly, the invention herein provides for
the range of movement of flap 44 from its first position to its
second position to be greater than the range of movement of said
flap from its first position to its third position. For example,
whereas the range of movement of flap 44 from its first position
to its second position may be in the order of 30.degree., the
range of movement of said flap from its first position to its
third position will be in the order of only 10.degree. .

As is apparent from the drawings, flap 44 is spaced from
airfoil surface 34 to define an open zone of said airfoil which
is bounded on three sides by the inner surface of flap 44, the
riser portion 32 of step 30 and a portion of the airfoil surface
34. The arrangement is such that the zone is always open
regardless of whether the flap 44 is in its first position,
second position or third position.

The embodiment of FIGS. 1 - 6 provides for the lift generating
means 42 to comprise a plurality of flap members 44 disposed in
laterally spaced relation on each of said airfoils 16, 18
whereby each of said flaps 44 may be selectively disposed for
movement between their respective positions. In other words, the
flaps 44 on each airfoil may be operatively connected to move
separately or in unison, as desired. Thus, for example, as
viewed in FIG. 3, the inboard flaps 44 may be operatively
connected to move in unison to their respective second positions
to improve the glide ratio of the airfoils, whereas the outboard
flaps 44 may be operatively connected to move separately to a
selective position relative to the airstream to further alter
the aerodynamic forces on the airfoils during conditions of
flight. Accordingly, one or more of the lift generating membes
may be selectively moved and used in a manner similar to that of
ailerons to increase the lift on only one of the airfoils, such
as in executing a bank or turn maneuver of the aircraft.

FIGS. 7 and 8 disclose another embodiment of the invention
wherein the improved airfoils are designated by numerals 48 and
50, each having lift generating means 52 located adjacent the
step-like discontinuity. In this regard, those portions of
airfoils 48, 50 which are common to corresponding portions of
airfoils 16, 18 are designated by the same reference numerals,
and further description of such correspondingly similar portions
is not deemed necessary. Lift generating means 52 comprises a
single flap-like member 54 pivotally mounted in conventional
manner on the second surface 26 of airfoils 48, 50, and disposed
to project rearwardly of the step-like discontinuity. The flap
54 is disposed for movement between positions corresponding to
those positions previously referred to in connection with the
lift generating flaps 44 of airfoils 16, 18. Furthermore, as
shown in FIG. 7, the step-like discontinuity extends span-wise
of airfoil 48 and has end edges 40, 56 terminating in advance of
the root end 36 and tip end 38, respectively, of the airfoil. It
will be appreciated that flaps 54 may be operatively connected
to move separately or in unison, as desired, in the manner
similar to that of the corresponding flaps 44 of the embodiment
of FIGS. 1 - 6.

FIG. 9 discloses another embodiment of the invention wherein
the improved airfoil is designated by numeral 58, and is
constructed having lift generating means 60 in the form of a
flap-like member 62 pivotally mounted on the second surface 26
of the airfoil adjacent the step-like discontinuity. Here again,
those portions of airfoil 58 which are common to corresponding
portions of airfoils 16, 18 are designated by the same reference
numerals. However, in this embodiment of the invention, the
second surface 26 of the airfoil terminates short of the
steplike discontinuity, and the outer surface 64 of flap 62
constitutes an extension of said second surface 26 to form the
terminal end portion thereof. In other words, flap 62 is
disposed for movement between first and second positions
corresponding to those positions previously referred to in
connection with the lift generating flap 44. Thus, when flap 62
is in its first position, as illustrated by the phantom line
drawing in FIG. 9, the outer surface 64 forms a smooth
continuation of the second surface 26 of the airfoil, which
outer surface 64 extends chord-wise to the step-like
discontinuity.

The airfoil embodiment of FIG. 9 further comprises a movable
cover member 66 pivotally mounted on airfoil 58 adjacent the
trailing edge 24. Cover 66 has an outer surface 68 that extends
chord-wise from the step-like discontinuity to the trailing edge
of the airfoil. Cover member 66 also has a spanwise dimension
substantially co-extensive with the corresponding span-wise
dimension of the step-like discontinuity. The cover is disposed
for movement between a first position, as illustrated by the
cross-line drawing, in which the outer surface 68 is off-set
relative to the second surface 26 of the airfoil, and a second
position, as illustrated by the phantom-line drawing, in which
the outer surface 68 forms a substantially smooth continuation
of said airfoil second surface 26 to eliminate the effect of the
step-like discontinuity. In this regard, there may be instances
where it is preferable to move the cover member 66 to its second
position to reduce any turbulent airflow downstream of the wedge
by permitting smoother flow over the step-like discontinuity.

The pivotal mounting arrangement for cover 66, as well as for
the lift generating means 42, 52 and 60, have not been shown in
detail since such mounting techniques are conventional and
well-known in the prior art. Furthermore, although the invention
is shown applied to airfoils of aircraft, it will be appreciated
that the invention has application as well to other types of
vehicles having airfoil-like components. Accordingly, there is
now provided an improved airfoil having lift generating members
selectively movable to various positions relative to the
airstream to alter the aerodynamic forces on the airfoil during
conditions of flight. Furthermore, in another embodiment of the
invention, a cover member is pivotally mounted on the airfoil
and is selectively movable to various positions to reduce the
effect of the step-like discontinuity to further alter the
aerodynamic forces acting on the airfoil.

While preferred embodiments of the invention have been shown
and described in detail, it will be readily understood and
appreciated that numerous omissions, changes and additions may
be made without departing from the spirit and scope of the
present invention.

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