Variable camber leading edge assembly for an airfoil

A variable camber leading edge device having a movable nose section and an upper flexible panel extending rearwardly from the nose section. To move the nose section between its upper cruise position and a high lift downwardly deflected position, there is attached to the nose section a generally arcuate cam track, having its forward and rear portions curving upwardly. The cam track is constrained to move in a generally arcuate path by means of two spaced pair of rollers, and it is driven by a pinion gear engaging an upwardly facing middle portion of the track.

TECHNICAL FIELD 
The present invention relates to airfoils, and more particularly to a 
variable camber leading edge assembly for an airfoil. 
BACKGROUND ART 
A common way of modifying the lift characteristics of an airfoil for low 
speed operation is to use leading edge devices which either pivot or slide 
outwardly from the leading edge of the airfoil to a deployed position. 
With many such devices, there is a problem that during deployment there is 
an interruption of smooth airflow over the upper surface of the airfoil. 
Also, many such devices are not able to be deployed to intermediate 
positions while maintaining the proper flow of air over the airfoil. 
Accordingly, there have appeared in the prior art various devices to vary 
the shape of the airfoil itself in a manner to vary the camber of the 
leading edge. Variable camber leading edges are particularly desirable in 
solving the airfoil stall problem for small, thin, swept-back wings which 
have good cruise performance, but require high lift devices to make their 
low speed performance acceptable. However, there is a problem of 
installing such variable camber leading edge devices on such wings since 
these thin wings have the least space available in which to house such 
devices. 
Accordingly, it is an object of the present invention to provide a device 
to vary the camber of an airfoil, and particularly such a device used as a 
variable camber leading edge assembly. It is a more particular object to 
provide such an assembly with a flexible upper skin panel which is moved 
from a cruise position to a more curved high lift position, with the 
flexible panel having a desired aerodynamic contour throughout its path of 
travel between the upper cruise position and the downwardly deflected 
position, with the assembly being relatively compact, and with the major 
part of the aerodynamic load on the assembly being transmitted into the 
support structure so as to relieve loading on the drive mechanism of the 
assembly. 
SUMMARY OF THE INVENTION 
The present invention relates to apparatus to vary the camber of an 
airfoil, and more particularly to such apparatus which can advantageously 
be used as a leading edge assembly. This assembly comprises a main support 
structure for the airfoil and a moveable nose section at the leading edge 
of the airfoil. There is an upper skin panel having a rear part connected 
to said main structure, a forward part connected to the nose section, and 
an intermediate flexible panel portion extending between the rear part and 
the forward part. 
There is actuating means operatively connected between the nose section and 
the support structure to move the nose section about a general center of 
rotation between a first upper position where the flexible panel portion 
has a lesser degree of curvature and the nose is more horizontally 
aligned, to a second lower position where the flexible panel portion has a 
greater degree of curvature and the nose section is aligned in a more 
downward slant. This is done in a manner so that the curvature of the 
flexible panel portion increases with movement of the nose section toward 
its second position. 
The actuating mean comprises a cam track connected to one of the support 
structure and the nose section, and also a cam track contact member 
connected to the other of the support structure and the nose section. The 
cam track has a lengthwise axis curved in a generally arcuate path about 
said general center of rotation. The cam track contact member and the cam 
track are operatively interconnected to be constrained to move relative to 
one another along a path generally aligned with the lengthwise axis of the 
cam track. There is drive means to move the cam track and the cam track 
contact member relative to one another to move the nose section between 
its first and second positions. 
In the preferred form, the cam track has a forward end connected to the 
nose section, and the cam track engaging member is connected to the 
support structure. The cam track contact member engages the cam track at 
two space locations along the lengthwise axis to restrain angular movement 
of the cam track relative to the cam track contact member. Desirably, the 
cam track contact member comprises two roller means engaging the cam track 
at the spaced locations. 
In the preferred form, the drive means comprises a rotatably mounted drive 
pinion gear engaging a cam track gear rack segment at a drive location 
spaced from the two support locations. Preferably the drive gear is 
located with its drive location positioned intermediate said two support 
locations. The cam track has a forward cam section contacting a forward 
one of the roller means in a manner to move along a path having a forward 
and upward slant. The cam track also comprises a rear cam section 
contacting a rear one of the roller means for travel along a path having 
an upward and rearward slant. The track has an intermediate drive section 
adapted to engage the drive means. 
To precisely control the movement of the nose section from the first to the 
second position, the lengthwise axis of the cam track deviates at least 
partially from a true circular arc, in a manner that the center of 
rotation of the nose section shifts during movement of the nose section 
between the first and second positions. Thus, a proper aerodynamic contour 
of the upper skin panel can be obtained throughout the movement of the 
assembly. Preferably, the center of rotation shifts rearwardly during 
movement of the nose section from the first to the second position. Other 
features of the invention will become apparent from the following detailed 
description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIGS. 1 and 2, there is shown a leading edge assembly 10 
which forms the forward portion of a wing 12. For convenience of 
illustration, only the forward portion of the wing 12 is shown. The wing 
12 has an upper surface 14, a lower surface 16, a leading edge 18, and a 
trailing edge (not shown for ease of illustration). The wing 12 has a main 
support structure, comprising a front spar 20 to which the leading edge 
assembly 10 is mounted. 
At the leading edge 18, there is a nose section 22 in the form of a 
substantially rigid beam extending in a spanwise direction along the wing 
leading edge 18. The nose section 22 has an upper surface 24 and a lower 
surface 26. There is a flexible upper skin panel 28 which has (a) a 
forward part 30 which is attached to the upper rear portion of the nose 
section 22 and blends into the upper surface 24 of the nose section 22; 
(b) a rear part 32 which butts against and is aligned with the main upper 
skin 34 at the location of the front spar 20, and a flexible intermediate 
portion 36 which reaches between the front part 30 and the rear part 32. 
The lower surface of the leading edge assembly 10 comprises a forward 
portion 38 connected to and extending rearwardly from the lower edge of 
the nose section 22, and a rear portion 40 which is a forward extension of 
the main lower skin section 41 at the lower part of the front spar 20. At 
the front edge of the rear portion 40, there is a seal 42 to close the 
small gap at the juncture of the lower skin portions 38 and 40. 
Of particular significance in the present invention is an actuating 
assembly, generally designated 44, which functions to move the nose 
section 22 from an upper cruise position shown in FIG. 1 through an 
intermediate position of FIG. 2, to a fully deflected high lift position, 
shown in FIG. 3. This is accomplished in a manner that as the assembly 10 
moves from the position of FIG. 1 to that of FIG. 3, the curvature of the 
upper skin panel 28 progressively increases so as to assume a proper 
aerodynamic contour throughout the movement of the assembly 10 from its 
cruise configuration to its fully downwardly deflected position. During 
such downward movement, the forward lower skin portion 38 simply moves 
downwardly with the nose section 22 to separate from the rear portion 40, 
with the rear edge of the forward lower skin portion 38 moving rearwardly 
beneath the rear lower skin portion 40. 
The actuating assembly 44 comprises a generally arcuately shaped cam track 
46 and cam track contact means comprising forward and rear sets of 
rollers, the forward set being made up of upper and lower rollers 48 and 
50, and the rear set being made up of upper and lower rear rollers 52 and 
54. Also, there is a drive means which, in the preferred embodiment, 
comprises a drive gear 55 which meshes with upwardly facing gear teeth 56 
at the middle portion of the cam track 46. The gear teeth are formed on a 
gear segment between halves of the cam track 46. 
The forward end of the cam track 46 is formed with a clevis 58 which is 
rigidly connected to the nose section 22 through two connecting locations 
60. The four rollers 48-54 are rotatably mounted to a support rib 62 which 
is fixedly connected to and extends forwardly from the front spar 20. 
The cam track 46 can be considered as having a forward cam track section 
64, a rear cam track section 66 and an intermediate drive section 68. The 
upper and lower surfaces of the forward cam section 64 contact the upper 
and lower front rollers 48 and 50, respectively. The rear cam section 66 
has upper and lower surfaces which contact the upper and lower rear 
rollers 52 and 54, respectively. The intermediate drive section 68 is the 
portion of the cam track 46 having the teeth 56 that engage the drive gear 
55. 
The cam track 46 has a generally arcuate configuration, and has a 
lengthwise axis which, for purposes of illustration, has been drawn as a 
circular arc, indicated at 70, and having a center of curvature at 72. 
However, for reasons which will be explained more fully hereinafter, the 
lengthwise axis 70 of the track 46 deviates slightly from a true circular 
arc so as to program the movement of the nose section 22 more precisely so 
as to obtain the proper degree of curvature of the upper skin panel 28 
throughout its movement from the cruise position of FIG. 1, through the 
intermediate position of FIG. 2 to the full down position of FIG. 3, while 
maintaining proper engagement of the pinion gear 55 with the gear segment 
teeth 56. 
The rollers 48 and 50 are positioned substantially opposite one another 
relative to the lengthwise axis 70, as are the two rollers 52 and 54. The 
center axes of the rollers 48 and 50 are arranged along a line 76 that 
slants upwardly and rearwardly toward the center of curvature 72. The 
center axes of the rear rollers 52 and 54 are aligned on a line 78 that 
extends upwardly and forwardly toward the center of curvature 72. 
In the cruise position of FIG. 1, the track 46 is at its forwardmost 
position, so that the forward rollers 48 and 50 engage the lower rear 
portion of the forward cam track section 64, and the rear rollers 52 and 
54 engage the upper rear portion of the rear cam section 66. In that same 
position, the pinion gear 55 engages the rearwardly located teeth 56. 
Although not illustrated herein, it is to be understood that the two 
rollers 48 and 50 are arranged in a suitable support structure which has 
side load pads that engage lateral surfaces of the cam track 46 to keep 
the track 46 properly located on rollers 48 and 50. The rear rollers 52 
and 54 have a similar support structure and side load pads. Further, the 
rear end of the track 46 has a stop member 80 which limits the forward 
rotation of the track 46 by engaging the side load support pads for the 
rear rollers 52 and 54. Likewise, the clevis 58 serves as a stop member by 
coming into engagement with the forward support rollers 48 and 50 when the 
assembly 10 is in its full down position of FIG. 3. 
Also, it is to be understood that the leading edge assembly 10 is shown at 
only one cord length location of the wing 10. It is to be understood that 
there are similar assemblies 10 at other spanwise locations along the 
length of the wing 12. The drive gears 55 at these various locations can 
be interconnected by a drive shaft so as to be driven from a common power 
source. 
In operation, to move the assembly 10 from the upper cruise position of 
FIG. 1, the drive gear 55 is rotated counterclockwise, as seen in FIG. 1. 
This causes the cam track 46 to travel in a path closely following the arc 
approximated by the axis 70 so that the center of rotation is relatively 
close to the center of curvature 72 of the arc. When the assembly 10 
reaches the intermediate position of FIG. 2, the nose section 22 has moved 
downwardly and moderately rearwardly, and also has rotated so that it is 
at more of a downward and forward slant. Further, at this location the 
movement of the nose section 22 has been such so that the forward part 30 
and rear part 32 of the skin panel 28 have moved moderately closer to one 
another so as to place the flexible intermediate portion 36 of the panel 
28 in a rather moderate curve, as shown in FIG. 2. This curvature is such 
that it forms a proper aerodynamic contour of the upper skin section 
extending from the nose section 22 to the location of the forward spar 20. 
Further counterclockwise rotation of the gear 55 causes the cam track 46 
to move further rearwardly in the rollers 48-54 so as to deflect the nose 
section 22 yet further downwardly to the position of FIG. 3. 
With regard to the precise alignment of the lengthwise center axis 70 of 
the cam track 46, for purposes of description, let it be assumed for the 
moment that the lengthwise axis 70 is formed exactly in a true circular 
arc having a location and degree of curvature which would move the nose 
section 22 from the position of FIG. 1 to the fully downwardly deflected 
position of FIG. 3. For purposes of the following analysis, that 
particular circular arc shall be termed the "reference arc line". If the 
entire alignment of the axis 70 did correspond exactly to this reference 
arc line, the movement of the nose section 22 would follow generally a 
path which would give an unacceptably flat aerodynamic contour to the 
flexible skin panel 36 throughout its path of travel from the full up 
position to the fully downwardly deflected position, because the center of 
rotation would coincide exactly with the center of curvature 72. 
However, to fine tune the movement of the nose section 22 to obtain the 
desired aerodynamic contour of the panel 36 more precisely throughout the 
path of travel of the nose section 22, it is desirable to position the 
middle portion of the forward cam track section 64 moderately outwardly 
from the arc reference line. Thus, during movement of the nose section 22 
from the position of FIG. 1 toward the intermediate position of FIG. 2, 
the center of rotation of the nose section 22 shifts a moderate distance 
rearwardly in a manner to increase the amount of curvature of the flexible 
panel section 36 to a moderate degree more than it would be otherwise for 
that particular location on its path of travel. 
However, it must be kept in mind that the movement of the intermediate 
drive section 68 must be such that the gear teeth 56 remain in proper 
meshing engagement with the teeth of the drive gear 55. This requires that 
the positioning of that portion of the axis 70 that passes through the 
rear portion 66 of the cam track 46 be shifted from the reference arc line 
in a manner to compensate for the shifting of the forward cam track 
section 64 from the reference arc line. Thus, where the forward cam 
section would have a portion thereof positioned moderately radially 
outwardly relative to the center of curvature 72, the corresponding 
portion of the rear section 66 (i.e. the portion which would be engaged by 
the rear rollers 52 and 54 at the same time that the portion of the 
forward section 64 was engaged by the forward rollers 48 and 50) would be 
positioned radially inwardly to a moderate extent. This would give the 
entire cam track 46 what might be described as a slight rocking motion as 
it moves in a generally arcuate path from the full forward position in 
FIG. 1 to the full rear position of FIG. 3. This slight rocking motion 
would be about a pivot axis which is at the tangent point 56a of the two 
gear pitch circles, indicated at 56b and 56c. 
The axis 70 is contoured in a manner that the center of rotation about 
which the nose section 22 moves shifts generally rearwardly during 
movement of the nose section 22 from the position of FIG. 1 to the 
position of FIG. 3. 
The kinematic program provided by the cam track 46 is one in which the arc 
height of the upper skin panel 28 is increased in a linear manner, with 
the gear teeth 56 held in proper mesh on the pitch circles of the gear 55 
and the gear rack 57 as the nose section 22 is deflected from the cruise 
position of FIG. 1 to the fully downwardly deflected position of FIG. 3. 
This program is tailored to insure that no curvature reversal occurs in 
the panel 28 throughout its full bending excursion, since such curvature 
reversal would compromise its fatigue life. 
To explain yet another facet of the present invention, reference is made to 
FIG. 4 which shows an arrow 86 that represents the net lift component 
exerted on the leading edge assembly 10 as the result of aerodynamic loads 
imposed on the wing 10 when cruising at design speed. It can be seen that 
the net force component is generally upward and moderately forward so as 
to tend to pull the nose section 22 upwardly. In the particular 
configuration shown herein, these loads are reacted in a manner that 
approximately 60% of the loads are transmitted from the track 46 directly 
into the rollers. More precisely, the forward upper roller 48 exerts a 
downward and forward force component 88 normal to the plane of surface 
contact of the roller 48 with the upper surface of the cam track 46. The 
lower rear roller 54 exerts a forward and upward force component 90, which 
component 90 is normal to the plane of surface contact of the roller 54 
with the lower surface of the track 46. The two force components 88 and 90 
provide resistance to the upward movement of the nose section 22, but 
create a resultant force component 92 in a forward direction so as to tend 
to move the track 46 forwardly. This forward force component 92 is 
resisted by the gear 55 engaging the teeth 56. However, since the force 
component 92 is only about 40% of the aerodynamic force 86, the drive 
components for the gear 55 and the gear itself can be made smaller and 
lighter, than it would be if it were required to react against a greater 
proportion of the aerodynamic load. 
As the assembly 10 is moved downwardly, the aerodynamic loads tending to 
pull the nose section 22 upwardly become somewhat less. Thus, the force 
component illustrated in FIG. 4 represents the maximum load condition on 
the assembly 10. 
While the present invention is particularly adapted to be used in, and to 
uniquely resolve the problems of, a variable camber leading edge assembly 
of an airfoil, within the broader aspects of the present invention, it 
could be utilized in other arrangements relative to an airfoil or similar 
device. Specifically, in the following claims, it is to be understood that 
while this assembly is recited as a leading edge assembly, the term 
"leading edge assembly" is to be interpreted broadly enough to refer to an 
assembly positioned at the trailing edge of an airfoil, in which case the 
terms "forward" and "rear" would simply be reversed within the meaning of 
the claims. Also, it is to be understood that various modifications could 
be made without departing from the basic teachings of the present 
invention.