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HET-RC - F-20 Tigershark EDF (Retract Mod)
By Carl Tulanko
June 15, 2006 - 10:05:50 AM
1 - The F-20 as it comes in the box.
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2 - Parts loosely assembled. This model will be retrofitted with Air Retracts.
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3 - Larger picture of the F-20 Tigershark.
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4 - We begin by measuring CG at 67mm from the leading edge. The leading edge root of the wing is placed perpendicular to the table along with a ruler used to find CG.
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5 - A mark is made at 67mm for CG.
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6 - With the ruler anchored to the CG mark at the bottom, a smaller ruler is used to keep the large ruler even with the Aileron root on the right. The Aileron root is perpendicular to the fuselage, so it makes a good measurement reference point.
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7 - The top and bottom of the ruler is made even using the Aileron edge.
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8 - The Ruler is taped in place and a line for CG is drawn.
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9 - Southeast Model Products small Air Retracts that will be used.
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10 - Top view dimension.
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11 - Height dimension.
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12 - The covering is trimmed from the bottom of the fuselage. It will be replaced with White covering once assembly is completed.
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13 - Covering being removed.
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14 - Covering removed from fuselage bottom.
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15 - Spar location is marked.
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16 - Second spar location marked.
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17 - A ruler is used to connect spar location marks on both sides.
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18 - Center strip, which was cut 1/8" forward of the spar to spar line. A second line was drawn 2 1/4" forward of the spar line (shown lifted on the left) and the 2 1/4" wide strip of balsa sheet is removed.
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19 - Inside of fuselage is exposed.
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20 - Paper towel is wadded up to prevent wheel from falling in while measuring.
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21 - Paper towel is wadded up to prevent wheel from falling in while measuring.
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22 - Wing is placed on fuselage and marked following normal instructions.
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23 - Wing area shown marked.
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24 - Covering is ironed, removing any wrinkles.
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25 - A razor is used to remove the covering where the wing will attach. Cut just inside the line.
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26 - Covering shown being removed from fuselage side.
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27 - Fresh cut edges are ironed down.
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28 - Marker was cleaned off with denatured alcohol and a paper towel.
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29 - Area for the retract is cut from the side of the fuselage.
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30 - Excess balsa removed from Aileron Servo wire hole in fuselage. It is a good time to enlarge this slot and make sure it aligns with the wing slot so the wires will feed through without binding.
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31 - Foam removed from Aileron Servo wire hole in wing.
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32 - Wing Initial measurements for Retract. Bare Balsa show the shape how the door will be cut.
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33 - Removing the area in the wing.
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34 - Initial cut shown and final forward cut must be made at the CG line.
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35 - Area cut and ready to remove.
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36 - Wing area removed. Note that more foam was removed later, all the way to the CG line shown on the left.
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37 - Forward balsa support for the wing spar was removed. This may take a little cutting to remove.
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38 - Note that some of the wing sheeting remains to the right of the ruler. This is so the wing spar has top and bottom sheeting to use when being glued in place.
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39 - Area cleaned and sanded. Note that the spar side area is 4" deep.
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40 - Note the lip / sheeting that still remains at the top...this is used to keep the main spar aligned when gluing the wing to the fuselage.
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41 - Aileron Servo Wire run cleaned out with a ruler.
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42 - The wheels we used are Hangar-9 Pro-Lite 1 3/4" for the mains and 1 1/2" for the nose wheel. They come with 1/8" shafts, so the next several steps show how to make a bushing to adapt the 3/32 rod to the 1/8" wheel.
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43 - Piece of 4-40 rod inserted into brass 1/8" OD tubing to keep it rigid.
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44 - Length of brass tubing cut at mark.
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45 - End ground flush.
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46 - Tubing was placed back on the rod and the rod was cut to the length of tube.
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47 - Edge of small piece is beveled for easier insertion.
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48 - End is placed into the wheel.
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49 - Hammer is used to drive the wheel over the brass tube.
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50 - Tube/Rod removed and short piece is now installed in wheel.
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51 - Retract and wheel is place in the wing to check for clearances
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52 - Forward ply wing spar being marked. Spar Templates will be available and many of these steps show the development process.
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53 - Wing being marked at 1mm above bottom per standard instructions.
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54 - Spar is epoxied in place and fuselage root area has epoxied applied. Tape shown at bottom is used to align wing during installation.
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55 - Epoxy is applied to the Spar area.
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56 - Wing installed against the rear tape, then pinned and tape is removed leaving the rear of the wing 1mm from the bottom. There is a slight dihedral in the wing.
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57 - Wing shown with clamp holding spar in place while epoxy sets. Clean up excess epoxy with denatured alcohol and paper towels.
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58 - Wing glued and you can see the Spar on the left side where it's identified.
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59 - The lip that was left in place to assist with Spar alignment is now removed.
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60 - Initial cut is shown for the Forward Spar.
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61 - Forward Spar fit checked to the fuselage.
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62 - Piece cut to extend the Main Spar.
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63 - Ply Main Spar extension shown in place.
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64 - Ply end cap is cut and initially fit.
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65 - Additional rear spar support added.
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66 - Pic showing retract area boxed in.
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67 - Area to the right will be lowered/shortened so a retract mounting tray can be fit in the location.
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68 - Final cuts on spars, shortening them on the right where the retract tray will be installed.
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69 - 3/16" x 1/2" piece of balsa was glued underneath the forward sheeting flush to the edge of the forward fuselage sheeting. The Forward Spar will attach to this area.
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70 - Ply Retract Tray initially cut.
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71 - Final fit of all spars shows recessed area that was lowered for the tray.
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72 - 1/4" wide by 3/8" tall spruce supports added to bottom of tray for retract screws to bite into when installed. 3/8" Balsa pieces were fitted forward for support.
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73 - Tray is ready to install.
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74 - 1/8" balsa plug was installed just under the lip of the forward wing sheeting so the Forward Spar has something of substance to adhere other than foam. Scrap pieces of balsa were used to wedge the piece in place until the epoxy set.
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75 - Plug shown installed.
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76 - Forward Spar shown with epoxy applied.
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77 - Spar is held in place with scrap balsa used to "wedge" it in place. Note the 1/4" balsa square added top right to support the corner and give the retract plate more surface to adhere.
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78 - Spars glued in place and ready for the retract tray. Two 1/4" balsa supports added flush to the top of the spars for support.
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79 - Dry fit the tray before gluing.
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80 - Epoxy is applied to tray and wing area.
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81 - Tray installed into wing.
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82 - Full view of tray area.
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83 - Retract installed and holes marked for screws.
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84 - Holes drilled with 1/16" bit. Tape was used on the bit to mark depth so you don't go through the top of the wing.
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85 - Screws were run in holes to make threads, then the holes were reinforced with thin CA.
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86 - Retract installed with Great Planes #2 x 1/2" Button Head Screws.
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87 - Retract is shown installed.
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88 - Photo showing gear installed in "Gear Down" position.
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89 - Photo showing gear installed in "Gear Up" position, with about 1/8" clearance in the front and back for the tire.
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90 - A Retract Cover is made from a 1/32" ply base on the right and covered by a piece of 3/16" balsa shown in the middle. The ply piece is cut to fit around the retract, while the balsa is cut to only expose the moving part.
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91 - Ply base for the retract cover put in place this base will allow reset screws to be used for mounting.
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92 - Balsa Retract Cover top piece set in place over the ply lower cover.
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93 - Balsa and ply plate trial fitted and drilled through retract plate.
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94 - 3/16" holes for the entire screw head to sit recessed are drilled in balsa plate only! The ply and balsa are glued together with medium CA, then screws are inserted through the holes into the lower ply plate and the assembly is tightened.
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95 - Covering was removed and 100 grit sandpaper was used to properly shape the Retract Cover so it sits flush with the wing.
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96 - Retract Cover completed.
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97 - Retract Door was made from initial template from 1/32" plywood. Note the grain orientation in this photo and all that follow.
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98 - The Retract Door was temporarily set in place, evenly spacing it between the two plywood spars and its location was marked.
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99 - Pencil Marks show Door location.
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100 - Pieces of 3/16" balsa were cut and fitted to each side of the bay, then glued in place. The top of the balsa is flush with the spar and there is a 3/16" overhang for the door to rest on when closed.
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101 - 3/32" balsa was glued along the door line on both sides, then sanded flush to the wing.
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102 - Balsa shown fitting flush to the door with a small gap on each side to allow for the covering.
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103 - Door shown in place with sanding completed.
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104 - A piece of 1/16" Ply with grain shown running top to bottom was cut 3/4" wide and half of it was glued to the door, then shaped to contour.
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105 - Back side showing 3/8" overhang on ply plate. CA was added for drilling to prevent splintering.
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106 - The piece was laid over its position and the hole was marked , then drilled. The bolt for the landing gear wire is used to hold the door in place.
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107 - Hole drilled and CA added.
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108 - Retract Door shown installed using the bolt for the wire gear. Note the area to the left on the Retract Cover that was cut out for the door so the retract could lock in place.
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109 - Retract extended and locked in place, showing why the area under the door needed to be removed.
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110 - A piece of 1/8" ply 1/4" wide was cut, the ends were beveled, then it was set in place as shown. Make sure it is 1/8" above the wheel so it doesn't rub. A pencil marks the gear location.
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111 - a second piece of 1/8" ply 1/2" long was beveled and glued to the center.
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112 - The ply brace was cut out to clear the landing gear wire.
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113 - Brace was then pushed over the wire.
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114 - Brace test fit. The ends are beveled to help with alignment, making sure the door closes straight.
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115 - A rule is used across the back spar in the fuselage to make sure the wheel is parallel to the fuselage centerline.
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116 - CA is added to the brace, then the door is swung in place. IMPORTANT! Note the 1/8" clearance between the brace and the top of the wheel; make sure you space it like this so there is no rubbing.
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117 - Retract Door with Brace installed.
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118 - Fuselage door cut from 1/32" ply and 3/32" balsa, then laminated. Note that the ply grain is cross while the balsa grain is vertical. Crossing grains like this is important for strength.
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119 - A piece of balsa 1/8" thick by 3/8" wide by 1" long is installed with the top recessed and even with the rear ply spar plate.
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120 - The Fuselage Door is tack glued in place, then sanded until it is flush with the fuselage.
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121 - Door is "popped" out from its tack spot.
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122 - Edges of the door are sealed and strengthened with thin CA.
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123 - Door is set in place and checked for clearance. Marks are made where the top of the wheel is located.
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124 - A piece of 1/16" ply 1/2" wide is glued to the inside ply of the door. The center of the ply is 1/8" to the right of the wheel edge previously measured.
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125 - A piece of micro pushrod wire is installed in the fuselage at the second mark (left) which is 1/8" beyond the first marker (top of wheel). Wire holes were drilled 1/16" below the top of the ply spars.
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126 - 1/16" thick by 1/4" wide strips of ply were cut and glued in place with the wire running down the center. Note the door has been notched on the right to clear the ply spar when opening.
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127 - A 1/32" ply cap was glued to retain the wire on the left.
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128 - A hole was drilled and a piece of 2-56 rod was glued in place, protruding about 3/8". Pliers are used to fine tune the wire by bending it until the door closes without binding.
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129 - Retract Door Assembly shown fully opened.
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130 - Retract Door Assembly closing.
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131 - Retract Door Assembly wheel contacts 2-56 rod.
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132 - Retract Door Assembly wheel pushes rod downward closing the door.
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133 - Retract Door Assembly Fuselage Door and Retract Door closed.
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134 - Top view showing clearances and fit with doors closed.
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135 - Fuselage Door Stop cut from 1/8" ply.
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136 - Wing Door semi closed and Fuselage door is checked for clearance. The inner door (left) was adjusted for around 1/4" clearance to the wheel.
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137 - While the inner Fuselage Door is held at the angle, the door stop is installed.
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138 - The Wing was covered, as were the doors and retract cover, then the insides were painted with aluminum paint.
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139 - Retract Assembly area covered, painted and installed.
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140 - Finished Retract area with doors closed.
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141 - Upright View of the retract Assembly.
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142 - Retract Outside View.
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143 - Starting the second wing. Covering is ironed down to remove wrinkles.
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144 - Masking tape is stacked to make a block, then positioned so the wing rear top butts against it and the wing rear bottom is positioned 1mm from the bottom of the fuselage.
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145 - Fuselage is marked once the wing is in place.
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146 - Wing pattern marked on fuselage.
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147 - A razor is used to cut inside the drawn line.
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148 - Covering is removed so there is a good glue surface.
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149 - Once cut, the covering is ironed to seal the edges.
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150 - Area shown ready for epoxy. Marker can be cleaned with alcohol .
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