CA2054807C - Wing modification method and apparatus - Google Patents

Abstract

A modification kit for the DeHavilland DH-2 Beaver and the DH-3 Otter aircraft. A replacement leading edge is provided for the wing together with replacement droop wing tips and a wing fence. A flap gap seal is provided to close the gap between the trailing edge of the wing and the leading edge of the flaps when the flaps are extended. The addition of these modifications modifies the performing characteristics of the airplane in an enhanced manner, particularly during take off and landing.

Description

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WING MODIFICATION METHOD AND APPARATUS
INTRODUCTION
This invention relates to a modification kit used for the DeHavilland DH-2 Beaver and the DH-3 Otter aircraft and, more particularly, to a modification which includes a gap seal for the open area between the leading edge of the flaps and the trailing edge of the wing, a replacement leading edge assembly for the wings, wing tip replacements and a stall fence for the wing.
BACKGROUND OF THE INVENTION
The DeHavilland DH-2 Beaver aircraft, manufactured by DeHavilland Aircraft of Canada Ltd and first flown in 1947, was an STOL, single engine, metal, cabin monoplane transport designed principally for Canadian bush flying on floats, skis or wheels although the United States Army was a major purchaser of the type.
The Beaver has been used for bush flying for many years.
Although currently out of production, many of the 1700 Beaver aircraft built continue to be carefully maintained and used daily throughout the world, particularly in bush operations. The aircraft is known for its reliability and strength in such operations.
The DeHavilland DH-3 Otter aircraft, first flown in 1951, was also principally flown in bush operations as a utility transport with larger seating capacity than the Beaver. It likewise has a reputation for reliability and strength and many of the 460 aircraft manufactured continue to fly and are carefully maintained.

While the flying characteristics of the aircraft are very satisfactory, the several modifications according to the present invention have been discovered which, taken both singly and in combination, enhance the flight characteristics of both aircraft. While it is not known conclusively why these modifications produce such improved flying characteristics, the explanations given herein are believed to be correct to the best of applicant's knowledge at the present date.
The first modification relates to changing the profile of the leading edge of the wing of the Beaver and otter aircraft. By adding a cuff of 2024 T3 aluminum having a thickness of .032 inches to the leading edge of the wing in a profile as described hereafter, the flight characteristics of the aircraft are enhanced. A plurality of blocks made from FR 3720 polyurethane foam having the desired contour are mounted to the leading edge of the original wing. The aluminum material is then fitted over the blocks and attached to the wing. Suitable provisions are made in the modification for the pitot tube, inboard fairings, air intake and landing lights, all as will be described.
A second modification relates to a droop wing tip modification used to cover the original wing tip tank and is also applicable to both aircraft. The wing tip modification is made from S Class fibreglass. It is intended to fit smoothly with the leading edge modification and has a notable change in configuration from the original which leads to the "droop" modifier.
Suitable provisions are made for the navigation light, the filler cap and the drain, all as will be described.
A third modification relates to a flap gap seal modification. This installation is used to cover the gap 05/01/01 TUE 21:98 FAX B04 922 2957 LIRENPAT-VYEST VANCOUVER f~ 004 between the flap and the trailing edge of the wing. The flap gap seal prevents they passage of a large portion of moving air through tha gap srheri the flap is moved to i-is axtanded position and is appZsa~le only to the Beaver airartft. The seal assists the stability of the aircraft is flap exter~dad flight and enhances the takeoff and general flight characteristics its conjunction vrith the other modifscationv made to the leading edge of the wing and to the droop wing t3.~ .
A fourth and final modification relates to a stall fence installed on the top of the wing just outside the flap area. This modifioativn is likev~rise applicable 4l~ly to the Beaver aircraft.
SW ~ TH 7TI(7 According to one aspect of the ~avention, there is provided a leading edge modificatioxi for the leading edge of wing flf a DeBaviJ.land Beaver or O#ter aircraft said leading edge modifioatioxi compxising of a cuff extending forWardly from said leading edg~ of an unmodified wing and being fitted 2Q over a plurality of blocks mounted interixlittently along said leadixig edge. said cuff extending smoothly from the top of $aid wing in a ganexally aorivex profile to a poirit approx~ately two in'vh°s forwardly and four iriohes below the forarardmo~t Point of said unmodified Ping'. laid Cuff then extenditrg is a giaeraliy straight lixi~ rearwardly to the bottoaa of said wing at a poir~t approxtely seven inches rearwardly of said fo~ardmost point of said wing.
According to a f~irther aspect of the iavQntiori, there is provided a combination of a v~iag tiP modification and ~) a leading edge modification for the wing of a DeHavilland Beaver or Otter aircraft, said wing tip modification having inboard, outboard, leading and trailing areas, said wing tip modification being generally concave at said trailing area between said inboard and outboard areas and said outboard and trailing areas of said wing tip modification being located below the outboard and leading edge of the original tip of an unmodified wing, said wingtip modification having outboard and rearward station lines which are substantially identical with the outboard and rearward station lines of the original tip of said wing, said leading edge modification comprising a cuff extending forwardly from the leading edge of said unmodified wing and being fitted over a plurality of blocks mounted along said leading edge of said unmodified wing, said cuff extending smoothly from the top of said wing in a generally convex profile to a point approximately two inches forwardly and four inches below the forwardmost point of said unmodified wing, said cuff then extending in a generally straight line rearwardly to the bottom of said wing at a point approximately seven inches behind said forwardmost point of said wing, said wing tip modification fitting smoothly with said leading edge modification.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with the use of drawings in which:

Figure 1 is a side view of the wing of a DeHavilland Beaver aircraft in its unmodified production configuration;
Figure 2A is an elevation view of the wing of the aircraft of Figure 1 illustrating the modified leading edge and wing tip installed on the wing;
Figure 2B is a sectional view of the wing of Figure 2A illustrating the profile of the modified leading edge in association with the blocks used to establish the profile;
Figure 2C is a view of the profile used for the blocks that set the configuration of the leading edge of the wing;
Figure 2D is an elevation view of the landing light cutout and a typical lap joint used in the leading edge modification;
Figure 2E is a view of the pitot tube access cutout used for the leading edge modification;
Figure 2F is a view of the skin doubler used about the periphery of the pitot tube access cutout of Figure 2E;
Figure 2G is a view of the pitot tube cutout used with the pitot tube access cutout of Figures 2E and 2F;
Figure 2H is a side profile view of the landing light modification with the new leading edge;

Figure 2I is a side view of the area of the wing illustrating the air dam fence and the outside air vent;
Figure 2J is a plan view of the inboard fairing leading cuff and the lap joint positioned at that station;
Figure 3A is a rear view of the droop wing tip modification looking forward from aft of the aircraft;
Figure 3B is a side view of the droop wing tip of Figure 3A;
Figure 4A is a bottom view of the wing illustrating the installed flap gap seal according to the invention;
Figure 4B is a side view of the wing of Figure 4A illustrating the flap in its retracted position and the stall fence according to an embodiment of the invention;
Figure 4C is a partial rear view of the wing of Figure 4A particularly illustrating the flap hangers and the flap recess brackets;
Figure 4D is a side view of the trailing edge of the wing of Figure 4A but without the attached flap;
Figure 4E is a side view of a foam flap cove mounting bracket; and Figure 5 is a plan view of the wing illustrating the stall fence of Figure 4B.

_ 7 _ DESCRIPTION OF SPECIFIC EMBODIMENT
Referring now to the drawings, a DeHavilland DH-2 Beaver aircraft in its factory or production configuration is illustrated generally at 100 in Figure 1. The aircraft 100 comprises the fuselage 101, the tail section generally illustrated at 102 which comprises the rudder 103 and the horizontal stabilizer 104, the engine area 110 which includes a 450 H.P. Pratt & Whitney R-985 powerplant and the wings generally illustrated at 111, the left hand wing of which is illustrated at 124 in Figure 2A.
Referring to Figure 2A, the wing 124 includes an aileron 112 and a flap 113 inboard of the aileron 111.
A navigation light 114 is located on the wing tip 120 of each of the wings 124 and a pitot tube 121 is mounted on the leading edge of the wing 124 outboard of the flaps 113. The wing 124 illustrated in Figure 2A includes the leading edge modification generally illustrated at 131 and the droop wing tip modification generally illustrated at 132.
With particular reference to the leading edge modification shown in Figure 2A, the wings 111 (Figure 1) are removed from the aircraft 100 to incorporate the leading edge modification 131. Only the left hand wing 124 will be described in respect of the leading edge modification, it being understood that the operation will be identical for the right wing.
Following the removal of the wing 124, the original wing tip 120, the landing light 115 (Figure 2H) and the pitot tube 121 are removed from the wing 124. A
plurality of nose blocks 134 conveniently made from FR
3720 rigid polyurethane foam are cut to the shape 2~J~~~7 _$_ illustrated in Figures 2B and 2C. Eleven (11) such blocks are cut for each of the wings 124 and their positions, when placed in correct configuration on the wing 124, are illustrated in Figure 2A. The leading edge 122 of the original wing 124 is thoroughly cleaned to remove any wax and other buildup such as dirt or oil. In each of the stations where the nose blocks 134 are to be mounted, it is convenient to lightly scuff the surface of the wing 124 to remove any dead paint still adhering to the surface.
The back 135 of each of the nose blocks 134 is covered with an appropriate adhesive, conveniently SILASTIC 732 (Trademark), and the respective nose blocks 134 are placed in the positions illustrated in Figure 2A.
Specifically, the nose blocks 134 are placed with their inboard edges at stations 1.25, 29.75, 57, 84, 111, 123.5, 138, 165, 192 and 219. The nose block 134 positioned at station 246 has its outboard edge placed at this station.
The nose blocks 134 are then held in place with clamps, masking tape or otherwise for a period of approximately twelve (12) hours for curing purposes. Each block 134 must be in its proper position within ten (10) minutes following the application of the SILASTIC adhesive.
There are three leading edge cuff sections for each wing 124 and after the nose blocks 134 have been cured in their respective positions, the outboard leading edge cuff 160 is temporarily installed in position, conveniently with tension straps. The outboard leading edge cuff 160 will previously have been drilled with holes within which the rivets will eventually be mounted, the holes 161 (Figure 2B) on the top of the leading edge cuff 160 and the holes 162 on the bottom of the leading edge cuff 160 being spaced 1.5" apart with a 5/16" distance both from the lateral edges 163 (Figure 2A) and from the rearward edges 164.

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_ g _ The rivet holes 161, 162 are drilled through into the leading edge 122 of the unmodified wing 124.
CLECO fasteners are then inserted into the holes 161, 162 and used to hold the leading edge cuff 160 to the wing 124 in correct position.
The inboard leading edge cuff 170 (Figure 2A) is then similarly installed. A lap joint 171 (Figure 2D) is created between the outboard and inboard leading edge cuffs 160, 170 in which the outboard leading edge cuff 160 is overlapped by 1 1/4". The previously drilled rivet holes 172 are aligned and CLECO fasteners are used to maintain the inboard and outboard edge cuffs 160, 170 in proper position. The rivet holes 161 in inboard leading edge cuff 170 are drilled into the original leading edge 122 and CLECO fasteners are inserted into the holes to maintain the proper position as drilling continues in a method identical to that used with the outboard leading edge cuff 160.
The left hand inboard fairing 173 (Figure 2J) is then similarly installed. A lap joint 174 is created in which the fairing 173 overlaps the inboard leading edge cuff 170 by 1 1/4". The previously drilled holes 180 in the inboard leading edge cuff 170 are aligned with the corresponding holes 180 in the inboard fairing 173. MS
832 anchor nuts are conveniently installed in the aligned holes 180 at 3" intervals as indicated. The previously drilled rivet holes 161 in the inboard fairing 173 are drilled into the leading edge of the original fairing 181 and CLECO fasteners are inserted into the holes to maintain the proper positioning of the fairing 173 as drilling continues.

There are three areas that require particular attention during the installation of the leading edge cuffs 160, 170.
A first area for attention is the pitot tube area 182 (Figure 2A). A cutout 183 (Figure 2E) is provided in the outboard leading edge cuff 160. A skin doubler 184 (Figure 2F) is installed over the cutout 183 with rivets installed in holes 185 as indicated. A pitot tube cover 190 (Figure 2~) is installed over the skin doubler 184 with rivets installed in holes 185 and anchor nuts installed in holes 186 (Figure 2F) as indicated.
A second area for attention is the air vent area shown generally at 191 (Figures 2A and 2I). A scat hose 192 is used to extend from the original outside air receptacle 193 to the outside air receptacle 194 at the position indicated in the inboard fairing 173.
The third area of attention is the landing light area generally denoted 200 (Figures 2A and 2H). A 3/32"
plexi glass lens 201 is installed as illustrated in Figure 2H with the use of a lens retainer 202 connected to the top and bottom of the inboard cuff leading edge cuff 170 and the lens 201 with rivets 203. The original landing light 115 remains in its production position.
Following the fit and location steps involved with each of the outboard leading edge cuff 160, the inboard leading edge cuff 170 and the inboard fairing 173, they are then removed. All holes for rivets and anchor nuts are burred slightly.
The final installation of the outboard and inboard leading edge cuffs 160, 170 and the inboard fairing 173 then occurs. The inside of each of the members 160, 170, 173 is cleaned and an adhesive, conveniently SILASTIC adhesive, is applied to the forward face 204 (Figure 2B) of the nose blocks 134 and along the top row of rivet holes 161. The outboard leading edge cuff 160 is installed initially. CLECO fasteners are used on the top and bottom holes 161, 162 and the rivets are then installed, completing the riveting operation in the top of the leading edge cuff 160 first. Following the completion of the riveting operation on the outboard leading edge cuff 160, the inboard leading edge cuff 170 is installed using the same procedure. The scat hose 192 (Figure 2I) and the outside air receptacle 194 should also be installed at this time.
The landing light lens 201 (Figure 2H), the pitot tube 121 (Figure 1) and the pitot tube cover (Figures 2E, 2F and 2G) are also installed at this time.
Referring now to the droop wing tip modification 132 as illustrated in Figures 2A, 3A and 3B, the droop wing tip 132 is positioned over the tip tank 210 (Figure 3B) and is then fastened into place using the original fastener locations and using the original filler cap 211 (Figure 3A) and drain 212. The original navigation light 114 is reinstalled in the droop wing tip 132.
The leading edge cuff modification and the droop wing tip modification are applicable to both the Beaver and Otter aircraft.
Reference is now made to the flap gap seal modification 140 illustrated in Figures 4A, 4B, 4C and 4D. The flap gap seal 234 is operatively positioned across the entire length of the flaps 113 and is connected to the lower edge 133 of the wing 123.

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The flap 113 (Figure 4B) is removed from the wing 123 and the rivets 213 (Figure 4D) on the bottom of the trailing edge of the wing spar 123 are removed. A
plurality, conveniently six (6), flap seal mounting brackets 214 (Figures 4A and 4C) are mounted on the flap cove skin 220 (Figure 4D) with rivets 231 with the bottom leg 221 of the flap cove mounting bracket 214 extending between the rear spar 222 and the bottom skin 233 of the wing 123 (Figure 4D). The flap seal mounting brackets 214 are conveniently made from .032 2024T3 aluminum material.
An alternative and preferred installation is to use FR 3720 rigid polyurethane foam, the same material as is used for the nose blocks 134, in place of the 2024T3 aluminum material for the flap seal mounting brackets 214 as seen in Figure 4E. In such event, rivets 231 will not be utilized. Rather, the foam blocks 214 will simply be held in position by the adhesive, again and conveniently, SILASTIC 732 adhesive.
There are three flap hangers 224 mounted on wing 123 (Figures 4A and 4B). At the location of each flap hanger 224, two flap seal brackets 230 (Figure 4C and 4D) are mounted on opposite sides of the flap hanger 224 with rivets 232 as illustrated in Figure 4D.
The flap cove skin 220 is slipped under the bottom of skin 233 of wing 123 and the gap seal 234 is positioned between the flap cove skin 220 and the bottom skin 233 of the wing 123.
The gap seal 234 extends the length of the flap 113 between the trailing lower edge of wing 123 and the leading edge of flap 113 as seen in Figure 4A. The position of the gap seal 234 must be carefully adjusted prior to final location. To that end, a clearance distance between the gap seal 234 and the leading edge of the flap 113 is 1/8" when flap 113 is in its extended position and such gap should be uniform from the inboard to the outboard ends over the distance of the flap 113.
The adjustment is facilitated by use of the flap seal mounting brackets 214.
Rivet holes are drilled through the gap seal 234 and the gap seal 234 is securely but temporarily held in place with the flap seal mounting brackets 214. The gap seal 234 should be substantially flush with the bottom skin of the wing 233 and the bottom surface of flap 113.
After alignment, two holes 240 are then drilled through the gap seal 234. The gap seal 234 is riveted to the flap seal brackets 230 at each of the nine locations of the flap hangers 224.
The gap seal 234 is manufactured from .040 2024 T3 aluminum material. It is painted as desired.
The flap 113 is then reinstalled.
The wing stall fence is generally illustrated at 150 in Figures 4B and 5. A single fence 150 is mounted on each of the wings 111, right hand wing 123 being shown in each of Figures 4A and 4B. Each fence 150 is mounted on the top of the respective one of the wings 111, just outside the area of the flaps 113 as seen in Figure 5.
The wing stall fence 150 extends along the top of each wing generally parallel to the top wing surface 152 (Figure 4B). It tapers smoothly from a position generally flush with the leading edge of wing 123 to a distance approximately 2 inches from the surface 152 of the wing 123 until a position close to the trailing edge of the top of wing 123 is reached. The stall fence 150 is connected to the wing 123 by the use of seven (7) stall fence brackets 153 located as indicated in Figure 5.
Rivets are used to attach the stall fence 150 to the stall fence brackets 153 and the stall fence brackets 153 to the top of wing 123.
The wing stall fence 150 installation is applicable only to the Beaver aircraft.
OPERATION
In operation, the leading edge modification 131, the wing stall fence 150 and the droop wing tip 132 are passive and not controlled by the pilot. The degree of their influence does, however, depend on the flight altitude of the aircraft. The effect of the added flap gap seal 140, however, is determined by the operator in association with the operation of the flaps 113 that is, when the flaps 113 are extended by the operator the flap gap seal 140 has been found to give the airplane enhanced performance characteristics. Although it is not intended to bind the patentee, the flight characteristics which have resulted during two initial test flights will be described. First, the takeoff characteristics have been improved by allowing the plane, in its float configuration, to get on the step more quickly. Indeed, takeoff can occur without the use of flaps. Once lift off has occurred, it has been found the climb rate is much improved without the need for flaps since wing lift is enhanced. The kit further offers improved stability on the ailerons and a high nose climb configuration.
Secondly, the stall and cruise characteristics have also been improved. Stall recovery has been enhanced; recovery seems to be almost automatic when the controls are released and without pilot input. Likewise, when on approach for landing, the aircraft appears to have substantially increased stability. As well, the flying attitude at cruise speed appears to be improved.
It is generally agreed that the improved flight characteristics, set out above, are obtained in the Beaver and Otter aircraft with the combination of the leading edge modification, the droop wing tip and the flap gap seal. Nevertheless, it is also noted that flight characteristics are improved with each modification taken individually. For example, it is believed that the use of the leading edge modification specifically allows the plane to fly in a nose high attitude both during climb and acceleration. The wing tips allow the plane to be flown with greater maneuverability at slow speeds since it is believed they keep and hold the air over the aileron surface which is particularly desired when there is turbulence at low altitudes and the aircraft may be losing air because of the turbulence or because of the attitude of the aircraft.
While a detailed description of the modification kit for the Dehavilland Beaver and Otter aircraft has been given, it is to be understood that the invention is not limited therefor and various other changes and combinations may readily occur to those skilled in the art to which the invention relates. The invention, therefore, should be construed by reference of the accompanying claims.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMS ARE DEFINED AS FOLLOWS:

1. A leading edge modification for the leading edge of a wing of a DeHavilland Beaver or Otter aircraft, said leading edge modification comprising of a cuff extending forwardly from said leading edge of an unmodified wing and being fitted over a plurality of blocks mounted intermittently along said leading edge, said cuff extending smoothly from the top of said wing in a generally convex profile to a point approximately two inches forwardly and four inches below the forwardmost point of said unmodified wing, said cuff then extending in a generally straight line rearwardly to the bottom of said wing at a point approximately seven inches rearwardly of said forwardmost point of said wing.

2. A leading edge modification as in claim 1 and further comprising a droop tip for the outboard end of said unmodified wing having a wingtip, said droop tip fitting smoothly with said leading edge modification, said droop tip having inboard, outboard, leading and trailing areas, said tip being generally concave at said trailing area between said inboard and outboard areas, said outboard and trailing areas being located below said outboard and leading areas of said tip, said droop tip having outboard and rearward station lines which station lines are located at positions substantially identical with said wingtip of said unmodified wing.

3. A leading edge modification as in claim 2 and further comprising a seal positioned within a gap between a respective flap and the trailing edge of said wing, said seal extending substantially the length of the flap of said wing and being attached to the bottom skin of said wing so as to be stationary relative thereto, said seal extending rearwardly from the leading edge of said flap over a distance such that the bottom of said flap is overlapped by said seal when said flap is in its retracted position and said seal closes a substantial portion of said gap between said flap and said wing when said flap is in its extended position.

4. A combination of a wing tip modification and a leading edge modification for the wing of a DeHavilland Beaver or Otter aircraft, said wing tip modification having inboard, outboard, leading and trailing areas, said wing tip modification being generally concave at said trailing area between said inboard and outboard areas and said outboard and trailing areas of said wing tip modification being located below the outboard and leading edge of the original tip of an unmodified wing, said wingtip modification having outboard and rearward station lines which are substantially identical with the outboard and rearward station lines of the original tip of said wing, said leading edge modification comprising a cuff extending forwardly from the leading edge of said unmodified wing and being fitted over a plurality of blocks mounted along said leading edge of said unmodified wing, said cuff extending smoothly from the top of said wing in a generally convex profile to a point approximately two inches forwardly and four inches below the forwardmost point of said unmodified wing, said cuff then extending in a generally straight line rearwardly to the bottom of said wing at a point approximately seven inches behind said forwardmost point of said wing, said wing tip modification fitting smoothly with said leading edge modification.

5. A combination of a wing tip modification and a leading edge modification for the wing tip as in claim 4 and further comprising a seal positioned within the gap between the respective flap and the trailing edge of the wing on a DeHavilland Beaver or Otter aircraft, said seal extending substantially the length of the flap of said wing and being attached to the bottom skin of said wing so as to be stationary relative thereto, said seal extending rearwardly from the leading edge of said flap over a distance such that the bottom of said flap is overlapped by said seal when said flap is in the retracted position and said seal closes a substantial portion of the gap between said flap and said wing when said flap is in the extended position.