|Sep 02, 2010, 03:53 PM|
Build Thread - Pixie 20" Symmetrical Electric Flying EPP Wing
This build thread is intended to be an all inclusive how to for building the Pixie 20" Symmetrical flying electric wing. As my intention is to present this as if this were a person's first scratch or kit build, some of the information may be too basic for some in the beginning. I will attempt to present as many techniques and approaches as necessary to build the plane well, but invite other ideas also. Enjoy!
The Pixie flying wing has been designed to be a fun aircraft that is inexpensive, exceptionally durable, great flying and easy to transport. The use of inexpensive components embedded within the 20 symmetrical EPP wing makes the Pixie the perfect choice for recreational flying, small course pylon racing, or full on combat. The comprehensive, photograph rich, construction thread covers all aspects of the assembly and setup process so that even inexperienced builders can successfully construct the Pixie with good results. Particular attention was given to durable, low drag construction that places the servos completely inside the wing and shields the push rods and control horns from wind drag and damage. The high lift, low drag airfoil provides predictable flight characteristics over a wide range of speeds and wind conditions, while accepting large control deflection for maximum aerobatics with minimum drag.
Wing : 20 1.3# EPP
Airfoil : Symmetrical CG3S
Typical AUW : 5.5-6.0oz
Wing Area : 110 sq.in
Wing Loading : 7.2-7.9oz/sq.ft
|Sep 02, 2010, 03:56 PM|
Kit Contents :
EPP wing cores
beveled balsa elevons ( 2 )
carbon fiber flat spar stock ( 24 stick )
carbon fiber push rods ( 2 )
Z-bent wire push rod ends ( 2 of .020 size, 2 of .032 size )
micro control horns ( 2 )
corrugated plastic for winglets
push rod sleeve material ( 1 straw )
Mylar sheet component cover ( 1 )
scrap EPP cleaning block ( 1 )
foam blank for CG and lateral balancer. ( 1 )
Template sheet for winglets and deflection reference marks ( 1 page )
Additional Tools & Materials Required/Suggested for building the Pixie per manual :
Glues, Tapes & Adhesives :
3M Super77 Spray Glue
Goop ( Household variety is fine )
Low temperature hot melt glue stick and low temperature glue gun
3M Scotch Extreme Bi-Directional fiberglass packing tape ( about 36 worth needed )
2-3 Rolls of light wight colored packing tape for covering ( this will cover a LOT of Pixies )
5-6 Minute epoxy
30 Minute epoxy
Blenderm hinge or bandaging tape ( Bi-Di can be substituted, but it will make plane heavier in the end )Nail polish
Medium or thin CA glue
Low tack masking tape
Double Sided tape ( or hot melt glue ) for testing the CG
Tools and Equipment :
Steel ruler ( various sizes )
Fine tip markers and pencil
#11 razor knife and extra blades
Needle nose pliers
Channel lock pliers
Wire lead crimping tool and ends ( if resizing the servo leads )
Various small metal files
Drill and 1/16 drill bit
Electric rotary tool with flat stone bit and router base ( if available )
Small Phillips head screwdriver ( for servo arm )
Solder iron and electrical solder
Butane torch ( or flame ) and lighter
Ψ7/16 O D Brass tube ( for cutting motor mount )
Ψ9/32 O D Brass tube ( local hardware store )
Small plastic card ( such as credit card ) for applying the tape
Dial or digital calipers ( nice but not necessary )
Electronic scale ( if available )
Square blocks and book ends ( during gluing )
Various weights ( soft preferred )
Consumable Supplies :
Scrap balsa ( 3/32 flat, 1/2 triangle )
Lead shot or BBs ( for CG correction )
Micro-balloons ( preferred ) or talcum powder
A few coins ( to determine balance weight )
Small stack of paper
Sandwich bag ( 1 )
Small nuts ( 2 ) ( slightly smaller than the side of servos )
Small board or book
Index card ( 1 )
120 Grit sandpaper
Mixing cups and stir/application sticks
Light weight spackle ( as desired )
Paper towels or rags
|Sep 02, 2010, 03:59 PM|
Prepping the Wings :
Materials Required : Wing block, scrap foam ( if desired )
Gently separate the wing cores by starting at the leading edge and running your fingers between the wings and husks. Proceed slowly across the span toward the trailing edge with each pass to release any adhesion between the foam pieces. In order to prevent tearing, be particularity careful as you approach the trailing edges of the wings as they become thinner and more fragile. Remove any foam whiskers that remain from the cutting process from the wings and the inner surface of the outer husks by using your fingers and/or a scrap piece of foam. The outer husks need to be clean as they will be used in the building process repeatedly.
|Sep 02, 2010, 04:00 PM|
Joining the Wings :
Materials Required : Wing panels, 3M Super 77 Spray Glue, 120 grit sand paper, marker, timer
Confirm that the spar locations are marked and visible on the bottom of each wing root and tip to serve as a reference for locating the spar in later steps. Spray a moderate coat of 3M Supper 77 spray glue onto each wing root, allow to dry for 6 minutes, then carefully tack the wing halves together. Once satisfied with the alignment of the wings relative to each other, press the two panels together firmly to finalize the joining. Sand any alignment imperfections along the seam with 120 grit sandpaper after the glue has fully dried and lost its tack.
|Sep 02, 2010, 04:03 PM|
Components Required :
( 2 ) 5g micro servos
( 1 ) “end pin” park flyer receiver
( 1 ) 6-10A ESC
( 1+ ) 1000mAh 2S ( 7.4V ) Lipo battery ( approx. 61g )
( 1 ) 12mm inrunner brushless motor
( 1+ ) GWS 3X2 propeller
Note : The Pixie was designed, built, and tested with the following gear : Keep in mind, this particular approach was to keep the cost to a minimum, not build the ultimate performer. Most likely, there are better components that can produce an even more responsive and exciting plane. Going "cheap" on equipment is not recommended and high performance alternatives will be researched. Any suggestions in this area are welcome.
HXT500 5g / .8kg / .10sec Micro Servo ( decent and inexpensive , but some midpoint “drift”.
Spektrum AR6110e RX (small, light, inexpensive, 2.4GHz )
TURNIGY Plush 10amp 9gram Speed Controller ( With the Pixie pulling less than 5A, this ESC may be overkill, but has been a solid performer. In some cases, the amp draw of the system is too low for the low voltage shut-off function to work correctly. For this reason, it is suggested to calculate the flight time for each setup. Soft start/stop settings suggested. Long term durability of this item is currently in question.)
Turnigy 1000mAh 2S 20C Lipo Pack ( Performs great, but consider a faster charging equivalent for convenience. )
Turnigy 1230 12mm Brushless Inrunner Motor 4500kv ( Great performance value. Only compatible with the 2S Lipo and the 3X2 prop due to overheating potential. Alternative motors should be close in weight for CG and total weight considerations. )
Substitution of alternative components may improve performance, or not, but is entirely the responsibility of the Builder. The above components were chosen on the basis of costs and availability. Keep in mind that weight and CG can change very quickly on a plane as small as the Pixie. A heavier motor and/or battery combination may quickly increase the wing loading to an unacceptable level when balanced. Efforts should be taken to keep the All-Up-Weight as low as possible for best performance.
|Sep 02, 2010, 04:04 PM|
Component Layout :
Place each component upon one surface of the wing, which will be referred as the top of the wing from this point on. As the wing airfoil is symmetrical, it makes no difference which side you start with. Trace around each component with a fine tip marker while making any necessary allowances for wiring and connectors. Start with the largest battery you may consider for the plane so as to leave adequate space for later modification. Place the elevon servos so that the center of the servo arm will be 3 inches from the center of the wing with the corner of the servo case 1/2 from the leading edge. The servo arm and lead should be positioned aft ( toward the tail of the plane ). Mark the location of the motor last, placing it in the center of the wing root behind the other components while allowing enough space for the wiring and connectors.
|Sep 02, 2010, 04:06 PM|
Creating the Component Pockets/Recesses :
With the gear locations marked on the top of the wing, lay the plane in the two husks so as to support the wings firmly on a flat surface. Using a rotary tool in a router attachment with a flat stone bit , if available, route a cavity for each component just barely deeper than the item being fit so it will fit below the contour of the airfoil. This is particularly important for the servos as they will be “potted” in a future step, which will consume a minor, but present, amount of height. Begin with the smallest components first so as not to route away the router base support which would make the process more challenging. ( Note : If you do not have access to a rotary tool router, you can mark the item depth on the stone bit with a piece of tape and lay a piece of paper over the wing to serve as a depth guide for freehand routing. If using a razor knife, mark depth on the blade and cut the perimeter first, then carefully remove the foam in the pocket with pliers. For a smoother floor, it can be melted smooth with a hot knife by hand. ) Repeat this pocket routing process for each component except the motor and confirm proper fit making each component just below flush with the upper surface of the airfoil. The placement of the motor should allow approximately 1/4” air gap forward of the motor and the aft end of the motor canister should extend beyond the trailing edge of the foam about 1/4” as well for cooling and clearance purposes. It will be necessary to cut full thickness through the wing in the location of each servo arm, as the servo arm is directed down into the wing and the push rod connections will be made from the bottom side of the wing later.
|Sep 02, 2010, 04:08 PM|
Creating the Prop Clearance Cutout :
Materials Required : Ruler, marker, wing, wing bed, elevons
Draw a line along each wing to mark the trailing edge of the foam in the motor region. ( Remember, the motor needs to stick out 1/4 beyond the trailing edge of the foam for cooling purposes. ) Using the elevons along each trailing edge, place the wide end of each elevon 1/8 in from the the tip of the airfoil and mark the location and angle for cutting the foam to the prop clearance trailing edge. Cut the prop clearance pocket from the wing and wing bed at this time. ( The bed needs to be notched as well to assist in cutting the motor mount pocket later. ) Check for proper clearances.
|Sep 02, 2010, 04:09 PM|
Making the Motor Mount Cutter :
The motor will be mounted into a cylindrical recess centered in the trailing edge of the wing. This pocket is easiest cut by using a thin walled tube. The outside diameter ( OD ) of this tube should be slightly smaller than the OD of the motor so as to provide a friction fit of the motor into the EPP foam. Cut small notches to serrate the edge of the tube to help with the cutting process and bevel the inside of the tube as needed to sharpen the edge as you would a chisel.
|Sep 02, 2010, 04:12 PM|
Cutting the Motor Mount Pocket :
Materials Required : Ruler, marker, squared blocks, masking tape, weights, motor mount cutting tube from previous step, stack of paper, motor ( for test fit )
Place the wing firmly in the beds on a flat surface with the center line of the wing along a straight line marked on the table or paper underneath. Mark the center of the wing and motor location, height-wise, and measure the distance down to the table. Take a tube approximately 1mm smaller in OD than the OD of the motor case, which will be used as a hole cutter for the motor mount, and subtract its radius from the same value of the wing center. This value represents how high the cutting tube needs to be shimmed up off of the table to center the motor pocket into the center of the wing straight and level. ( In practice, the motor doesn't need to be perfectly centered, just straight and level relative to the center line of the wing halves and cord line. )
Lay the cutting tube along the center line behind the plane and shim up the entire length of the tube with a stack of paper equal to the calculated height performed earlier to bring the center of the cutting tube to the same level as the center of the wing at the trailing edge. Secure the tube into position between a couple pair of squares, blocks, or brackets to keep things in place and apply some weight onto the cutting tube as well to keep it down against the paper shim. A couple of weighted bags will keep the tube down yet allow it to turn during the cutting procedure. Slowly rotate the cutting tube while feeding it into the trailing edge of the foam at the center of the wing. The tube will slowly cut a cylinder out of the foam wing as you progress and push a plug into the tube. You should be able to perform the entire cut in one plunge. Cut the tube to the mark of the most forward portion of the motor canister, not up into the air space. We will cut this in later so as to keep the motor from being able to ride up into the extra space. With the #11 razor knife, cut the leading edge of the foam plug core to free it from the wing without ripping. Remove the plug from the cutting tube and discard. Test fit the motor into the mount pocket. It should have a mildly snug friction fit yet be adjustable for centering.
Bevel the trailing edge of the motor cutout pocket to the center line from top and bottom.
|Sep 02, 2010, 04:15 PM|
Fitting the Spars :
Materials Required : Wing, wing bed, weights, ruler, spar stock ( Carbon Fiber Strip .019 x .118 x 24 / .5mm x 3mm x 610mm ), fine tip marker, straight pins, razor knife with old #11 blade, flame ( heat source )
Place the wing, bottom side up, into the beds and weight it down to force the wing straight. Since the Pixie is symmetrical, the beds will properly support and align the wing. Close to the tips, insert two ( 2 ) pins into the foam at the spar mark on either side of the carbon fiber ribbon spar with the narrow edge of the spar facing up to hold the spar in place. Repeat on the other wing. Bend the spar forward along the center until the spar is tangent to a line 1 behind the leading edge and pin in place along the length of the spar. ( Note : If using different radio gear, the bend of the spar may need to be altered to place the center in a location of sufficient foam depth.) Mark along one edge of the spar with a pen onto the wings to record position in case the spar is removed before the spar channel is cut. The spar shouldn't run to the very tip and should stop 3/4 shy at each tip, thus the spar channel will also be a little less than the full wingspan. The remaining flat carbon is to be used as the secondary spar, which is placed centered 1/4 forward o f the motor.
Rather than just cutting a slot to push the carbon fiber ribbon spar into the wing, which would deform the airfoil slightly, foam will be removed to allow space to accept the spar material using an old #11 razor blade. By heating the blade momentarily, the application of the blade into the EPP foam will melt a small portion of foam away which will create the spar channel needed. The channel needs to be only deep enough to allow the spar to be fully recessed below the airfoil surface, but no more. With the spar pinned in place upon the wing, momentarily heat the #11 blade in a flame and guide it along the bent carbon fiber spar along either the forward or aft side. Only cut a few inches at a time and turn the blade slightly to widen the path a little. Do not get the blade excessively hot during the cutting and practice on a piece of scrap to get a feel for how fast the foam will melt. Continue along the path of the spar, bypassing the location of the pins, then reposition the pins and complete the path. Press the carbon ribbon into the slot to test the fit, then cut to length.
The remaining piece of the carbon fiber ribbon spar material will serve as a secondary spar which is positioned just forward of the cooling vent of the motor ( i.e. 1/4 forward of the motor ), also along the bottom of the wing. The length is relatively arbitrary, so just use what you have left over from the spar stock and center it from side to side. Cut the spar slot the same way as with the main spar to allow full burial.
Gluing the Spars in Place :
Materials Required : Wing, wing beds, weights, spar material, Goop and applicator ( toothpick ), low temp hot melt glue and gun, light weight spackle and sand paper ( as desired )
With the wings pressed firmly into the wing beds on a flat table, confirm the fit of the spars then press a thin layer of Goop into the spar slot along the entire length. Firmly insert the spars into the slots and secure the spar in place and fill in any gaps with low temp hot melt glue. Wipe away any excess hot melt glue while still warm. This will hold things still so you can keep working while the Goop dries over the next 24 hours, but overnight drying under the pressure of weights is preferred. Repeat this procedure for the shorter aft section spar/doubler as well. Light weight spackle can be applied to fill in any voids in the foam along the spar to smooth things over, sanding as needed.
|Sep 02, 2010, 04:18 PM|
Cutting the Wiring Paths :
Materials Required : Wing, servos, receiver, battery, ESC, razor knife with old blade, flame
Due to the the fact that the Pixie's size makes it a thin wing, most of the wire routing will need to be run just below the surface level. Decision Time : To decrease the final weight of the plane and minimize the difficulty of fitting a lot of gear in a very small space, it can be advantageous to re-size the servo leads, ESC leads, and even solder the motor to the ESC directly. The extra wire and connectors, if left in place, can become challenging to run otherwise, but not impossible. Creating wire paths and pockets may be done by several methods such as routing with a rotary tool or burning with a hot knife. Remove just enough foam to allow each component to reside below the foam surface while providing access to critical areas such as the receiver plugs, battery, and power connection. Once satisfied with the component placement and access, each item ( except battery, which should remain removable ) can be tacked in place with a small drop of low temp hot melt glue.
Potting the Servos :
Materials Required : Servos, scissors, plastic sandwich bag, 30 minute epoxy, micro balloons, stir stick and applicator, mixing cup, 2 small blocks or nuts slightly smaller than the size of the servo case, a board, weights
Potting the servos into the EPP foam allows a more rigid attachment that will stay tight over time and help prevent development of slop in the controls. Place the servos, with servo arms removed, into the pockets routed in the earlier steps to confirm proper fit. Cut two ( 2 ) small, single layered squares out of the sandwich bag about twice the size of the servos and set aside. These bag pieces will serve as a release film in the next step which will allow the removal of the servos after potting. Mix a relatively small quantity of 30 minute epoxy in your mixing cup and add the micro-balloons ( talcum powder can also be used, with varying results ) until it forms a moderately thick paste about the consistency of peanut butter . The epoxy needs to be pretty thick for potting to work well. ( Note : The addition of the micro-balloons to reach this consistency drastically shortens the pot life of the epoxy, making it necessary to work faster. For this reason, 5 minute epoxy is not suggested when potting servos in this manner. ) Apply a generous layer of splooge ( epoxy and micro-balloons ) into main area of each servo pocket where the case of the servo will rest into the foam. Do not place too close to the spline region as it will just need to be removed later. Make sure to apply a good layer of splooge at the servo tabs, but leave a little space dry at the area where the servo lead exits the case for give on the wiring. With each servo pocket layered with the splooge mixture, lay the small squares of sandwich bag over the servo pocket and firmly press the servos down into the pocket, trapping the bag between the foam and the servo. This will keep the servo from being epoxied in place. Position the small wooden blocks or nuts onto the case of each servo and then place the board across both blocks. This will force the weight onto the servos and ensure they seat firmly into the foam without deforming the foam around it. Apply a little weight onto the top of the board to press the servos in to the foam pockets and allow to cure at least an hour. ( Note : While the micro-balloons tend to speed up the exothermic reaction and pot life of the splooge mixture, it also seems to lengthen the final cure rate a bit, so be patient here. Let the epoxy fully cure before proceeding. ) After fully cured, remover the weights, board, nuts and gently remove the servos from the wing. Remove the plastic bag to reveal a form fit hardened pocket in which your servos will pop into place and not shift around. Clean up any excess dried splooge with a razor knife and/or rotary tool with the flat stone bit used for routing the pockets.
|Sep 02, 2010, 04:20 PM|
Path of the Push Rods :
The servos are positioned with the arms pointing down into the wing to minimize air drag as well as add a degree of durability to the plane. Without excessive push rod material and servo arms hanging out in the air, there is less stuff to get snagged in contact situations. The push rod jig is designed to line up the two ends of the push rods at the servo arm and the control, while letting the bulk of the distance to be traveled within the wing, where it is protected. The measurements are based on the servo arm being 3 off center and 1 1/8 aft of leading edge, as discussed when locating the servos earlier. Slight deviations from the 3 mark will be relatively insignificant in the final outcome of the push rod path, as it is a little over sized to allow some leeway. The control horns will be placed upon the top of the elevons and the servo arms will be concealed while facing down into the wing upon final installation.
Making the Elevon Push Rod Tunnel Jig :
Materials Required : 9/32 brass tube, scrap 3/32 balsa, 1/2 triangular balsa stock, thin or medium cyanoacrylate glue, stick pin
Prepare the 9/32 brass tube to cut through the foam in the same manner as with the motor mount cutting tube in previous steps. This diameter tube has been chosen to accommodate the push rod shields installed later.
The elevon tunnel cutting jig is constructed from scrap 3/32 balsa sheeting and 1/2 triangle stock. Cut three ( 3 ) small wedges, two ( 2 ) larger wedges, two ( 2 ) 1 long pieces of triangle stock, and one ( 1 ) rectangular top piece to the dimensions shown in the pictures. Make note of the orientation of each piece, as they can start to look the same. Place the 3 smaller wedges together side by side and attach the larger triangle pieces on either side while all pieces are flat on the workbench and flush along the rear edge. It is useful to insert a pin through all five ( 5 ) wedges to keep them in alignment while gluing with thin cyanoacrylate glue. After these pieces are dry, remove the pin and glue the two ( 2 ) triangular blocks to either side of the assembly. Attach the rectangular stock upon the top in order to create a tunnel in which the 9/32 brass cutting tube will pass through during the cutting process. Some of the wood may swell during the gluing process, so use the cutting tube to adjust the final fit inside the jig as needed. Mark the center of the leading and trailing edges of the jig for alignment purposes when in use.
|Sep 02, 2010, 04:21 PM|
Cutting the Elevon Push Rod Tunnels :
Materials Required : Marker, ruler, 9/32 brass cutting tube, tunnel cutting jig, wing, wing bed, weights
Mark a line upon the top of the wing 3 1/16 from the center that is parallel to the center line of the plane. This line should be 1/16 further out from the previous line you drew that represented the center of the servo arm. ( Note : The center of the push rod path should be offset a little due to the lateral shift of the push rod that will occur with the use of the Z-Bend that will attach the push rod to the servo arm. Position the offset further out the wing to place the control horn further into the aileron where it will be a little stronger. ) With the wing firmly weighted in the wing bed, place the tunnel jig upon the top of the wing with the front and rear center marks aligned with the line 3 1/16 from the center of the plane and flush with the trailing edge of the wing. Using the 9/32 brass cutting tube, slowly cut the push rod tunnels until the cutter just enters the aft edge of the servo arm pocket. Do not proceed any further forward into the wing. Back the tube out of the wing and jig then remove the foam plug to reveal the elevon tunnel. Repeat with the other wing.
|Sep 02, 2010, 04:23 PM|
Reinforcing the Leading Edge :
Materials Required : Wing, Elevons, Bi-Directional fiberglass packing tape, razor knife, plastic card or scrap piece of plastic, 3M Super 77 spray adhesive, timer
Lightly mist the top and bottom leading edges of both wings, as well as top trailing edges ( for the upcoming elevon attachment ), with 3M Super 77 spray adhesive and set aside to dry for 10 minutes. Go ahead and mist the top surface of the elevons as well for the next step to save on glue and time. Meanwhile, cut a piece of 2 wide bi-direction fiberglass packing tape ( Bi-Di ) 13 long and then split it so you end up with two 1 X 13 pieces. Center one of the pieces of tape at the tip of one of the leading edges and tack it along the leading edge toward the nose and around toward the other tip. Cut the Bi-Di at a slight angle near the nose along the top and bottom, then carefully fold the edges of the tape onto the top and bottom of the wing using a credit card or similar flat stock to help prevent wrinkles. Repeat along the other wing. The tip sections will overlap slightly at the nose adding strength where needed.
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