NOTE: the computer printout of airframe parts should be cut out with a sharp knife and the pieces taped to appropriate balsa blanks to facilitate the easy formation of pieces needed. Note that all parts are laid out on these printouts with the wood grain running horizontally.
The Fuselage sides are cut from 1/16th balsa. Note there are 1/16th by 3/16th balsa strip doublers that run the almost full length of the sides at the top. The doublers along the wing saddle are cut from the pattern on the plans. All other doublers are stripped from 1/16th balsa sheet using a balsa stripper. These doublers start 1/8th of an inch back from the nose to allow room for the plywood firewall and also stop about a half inch from the fuselage rear to allow easier pulling of the sides together. There is a 1/6th by 3/16th strip doubler along the wing saddle and 3/16th by 1/16th doublers along the front nose section as well as the rear underside of the fuselage. Note that adding the doubler strips creates a left and right fuselage side.
Note the vertical doublers at the leading and trailing edge of the wing (3/16th by 1/16th balsa strips) which allow easier placement of formers F2 and F3. Both these formers have their bottom areas sheeted on both sides with 1/64th ply for added strength.
Note that formers F2 and F3 in the pictures here were modified later in construction to facilitate movement of the aileron control horns and to allow more battery movement for airframe balancing. Their shape has been changed considerablty. Note: These changes have been updated on the plans. Don't forget to drill the 1/8th inch holes in F2 for the wing hold down dowells.
Glue formers F1 (firewall) F2, and F3 to one fuselage side while it is still on the building board. Use a square to align these formers 90 degrees to the fuse sides and 90 degrees to the fuse top. Note that the fuselage from former F1 through F3 is straight sided and is basically a box. Turn this fuselage side so that it is sitting with the top down over the plans. Align the second fuse side and glue it to the three formers already in place.
I used a 3/16th square balsa stick pinned vertically to the plans at the fuselage rear which serves as a tail post and a guide to pull the sides together and to give the proper thickness at the fuse rear end. NOTE: Glue the sides together only at the bottom portion below the stabilizer cutout. The top portion, above the stabilizer cutout, is NOT glued to allow the easy insertion later of the fin and stab. The third and fourth pictures above show this installation. Note where the fuselage edge doublers end in these pictures. This is to allow proper spacing when the sides are glued together.
The above pictures show the fuselage with formers F4, and F5 glued into position. F5 is located just in front of the stabliizer. Formers F3A, F4A and F4B are the rounded tops of F3, F4 and F5 which are cut out as separate formers and glued into postition to form the basis for the turtle deck. Note: There is a fourth curved former F3B which is identical to F3A except for the top notch that is used when building the removable fuselage top.
Before adding turtledeck formers install the servos in the fuselage and run the pushrods. Both photographs above were made later in the construction and after the servos were installed. Note the area cut away from former F3 to allow aileron movement. (This is reflected on the plans) This picture also shows the spruce block used as a rear wing hold down. A single 4:40 bolt with blind nut on the underside of the block holds the wing in place. Note the servos are mounted upside down, and in the left picture you can just see the two 3/16th balsa rails glued along the fuselage sides which will support the battery plate. You can also see a piece of 1/8th scrap balsa supporting the pushrod tubes.
Above is the fuselage with the fin and stab temporarily in place to check alignment. This pictures also shows the fuselage top which is constructed from crossgrain 1/16th balsa glued to 3/16th square sticks at the edges. Four 3/16th square sticks add support at front, center, and rear and can be seen in the right photograph. Former F3B (identical to former F3A except for the notch) forms a cockpit backrest and gluing area for the canopy. The top is held on by a 1/8th dowell through the backrest and a 4:40 bolt and blind nut located aft of the firewall above the motor. A piece of scrap 3/16th sheet (not shown above) supports the blind nut.
The canopy was made by cutting a standard Sig 12 inch bubble canopy down to size. The 12 inch canopy is a bit extravagant, but is necessary as the smaller ones have adequate depth, but not enough width.
As seen above the whole fuselage top is designed to come off for easy battery placement, as well as easy access to all components within the fuselage. Structural strength is not compromised. At this stage in the construction, the fuse sides will feel a bit flexible above the wing saddle, but the addiition of two 3/16th balsa rails and the 1/16th crossgrain battery tray provide considerable stiffening.
There is adequate room in the fuselage cavity above the wing with the careful placement of mini servos. The aileron servo as shown on the plans is set deep into the wing and the EZ connectors we use have the usual screw replaced with 4:40 setscrews taken from wheel collars. This allows the battery tray to be placed deep enough so there is no interference with the removable top.
The rear turtledeck is sheeted with two pieces of 1/16th sheet balsa cut from the pattern shown on the plans. Slight variations in building might make this pattern slightly off, but it should be accurate in most cases.
WING CONSTRUCTION
Note: the wing is built in one piece over the plans. It is built upside down, but since the airfoil is fully symmetrical, this really isn't noticeable. When finished and removed from the plan, the wing top has no dihedral, but the bottom has some natural dihedral due to the wing taper and different thickness of the ribs. Cut Balsa blanks of appropriate size, two for each rib and tape the rib outlines to them. The slot at the rib trailing edge makes for a rather thin area and is easiest cut out before cutting the whole rib outline. Carefully cut the 3/16th square spar slots in each rib and sand the ribs lightly to remove saw irregularities.
Strip wing spars (3/16th square) from 3/16th medium to firm balsa, ensuring the grain is pretty straight and there are no imperfections, which could compromise spar strength. DO NOT use soft balsa for the spars. Pin the bottom spars to the plan. Place all ribs in position over the plan. Note both center ribs are just glued together and rib 2 is there to provide some support for the fuselage sides once the wing is covered. The trailing edge is simply a half inch strip of 1/8th firm balsa sheet which is carefully located in the slots at the rear of each rib. Note that there are three small spacers (make two each) labelled R1A, R4A and R7A. These are pinned to the building board at locations of rib 1, rib 4 and rib 7 to support the trailing edge during building and in effect align the whole structure. Pin these securly to the plan about 1/8th inch from the appropriate ribs. Do not pin directly alongside the rib itself and be careful NOT to glue these supports to the wing.
When all ribs, top and bottom spars, and the trailing edge is in place and aligned glue permanently with CA. The leading edge is a strip of 3/16th balsa sheet glued to the front of the ribs and carved to the airfoil shape when the finished wing assembly is removed from the building board.
Install 1/16th balsa vertical grain sheer webs in across the whole length of the wing. This sheer webbing is necessary and adds tremendoue strength with little weight to the structure. The strength is such that there is no need for a dihedral brace.
Landing gear mounts are pieces of 1/32nd aircraft ply applied to the underside of both R2 ribs. The front piece is 1/2 inch wide and the piece at the rear of the spar is one inch wide. Small pieces of scrap triangle reinforce the glue joints. In the right picture, the plywood mounts can be seen from the wing top, the aft one under the aileron servo.
The left photo above shows two 1/8th shishkebob skewers used for the front wing hold down. Align the wing in the wing saddle making careful measurements from the wing tips to the tail. Push a skewer through each of the mounting holes on former F2 and twist while pushing carefully to make holes in the wing leading edge. Small sections of the skewers are then glued permanently into the leading edge.
The right picture shows the wing trailing edge with aileron horns glued into place. Note the small section of 1/32nd ply used to reinforce the area where the wing hold down bolt will go.
The ailerons are built up over the plans using strips cut from 1/8th balsa sheet stock. Note that the leading edge aileron strip is wider than the trailing edge, allowing room for bevelling. Note the small pieces of 1/64th ply added over the area where the horns actually go into the ailerons for added strength. These ply doublers, 1/4 inch by 3/4 inch are added to both sides of the ailerons.
The control horns are made up from 1/16th music wire and 3/4 inch pieces of 1/8th brass tubing. The tubing is pounded flat over the formed horns and soldered securely in place. (for more information on this control horn setup see PfCruiser construction notes). Inner nyrod (the smaller size) was used as a bearing and glued to the trailing edge of the wing. When covering, a strip of covering material was also added here to for additional support as shown in the last picture above.
Note the servo placement deep in the wing behind the wing spar. Note also the small pieces of balsa added after servo installation to provide a surface to seal the covering to.
TAIL FEATHERS
Build both the stabilizer and fin over the plans using the computer printout to cut out the sheet pieces. Do the same for the rudder and both elevator halves. Note that the elevator leading edge is actually one continuous piece of 3/16th balsa and is the easiest and lightest way to allow both elevator halves to work with one pushrod. Sand all assembled elevator and fin parts before assembly. On the prototype I sanded to a thickness slightly over 1/8th inch. Align the fin on the stabilizer to that it is 90 degrees to the vertical as well as 90 degrees to the stabilizer trailing edge. The whole assembly can now be trial fitted and glued in place on the fuselage. You may opt to cover these assemblies before gluing into place. In this case mark the fuselage outline on the stab bottom and cover just to this line, leaving bare balsa areas for gluing on final assembly.
Bevel both elevator halves on the bottom to allow a hinge movement. I didn't bevel both sides of the rudder; just one and this has worked perfectly. Clear cellophane tape over the entire rudder and elevator hinge lines after final assembly and covering makes for a simple and foolproof hinging system. Any of the CA type of easy hinges could be used as well.
Make two control horns from 1/6th ply as shown on the plan and cut 1/16th slots in the rudder and elevator at the appropriate spots (in alignment with the pushrod exit holes).
FINAL ASSEMBLY
Glue a 3/16th square balsa "spar" along each fuse side on the inside as shown on the plans. These pieces make up the base for a 1/8th balsa plate, which will hold the receiver and battery pack. (NOTE: Former F2 was modified after the airframe was completed and the 1/8th balsa plate extended further forward as the battery pack could not be moved far enough forward to balance the airframe. The final shape is shown on the plans.) I use either thick ca (wrap your finger in wax paper) or epoxy (sparingly) smeared over the balsa plate, which seals the wood and allows Velcro to stick strongly. Moving the flight battery fore and aft can easily change the center of gravity. The servos are installed on two 3/16th square balsa rails as shown. Wick a drop of ca into the holes drilled to accept the servo screws. Location of the radio gear shown on the plan has worked well. Larger heavier servos might want to be installed in a more forward position. Simply placing the gear on the balsa plate can give a pretty good idea of where things should go.
The motor installation is pretty simple. The gearbox is held to the ply firewall with two small screws. The gear ratio used is 3:1 and the prop a 9x4.7 APC slow flyer prop. The prototype is using monocote covering. Flying weight is 18 ounces.
After covering the complete airframe, run the two pushrods inside the previously installed outer tubes. . I use a z-bend at the control surface and an easy connector on the servo. Because of space limitations we opted to remove the normal screws from te EZ connectors and used 4:40 set screws from wheel collars instead. This allows the battery tray to be placed lower in the fuselage. Trial fit without hinging the elevator and rudder and determine the location of the plywood control horns. Cut a 1/6th slit in the leading edge of both surfaces and glue the control horns in place. (NOTE: Small control horns and easy connectors are now available for park flyers and you may opt to use these.) Now you can actually install the rudder and elevators using clear cellophane tape. I was surprised the first time I saw this used, but it is ideal for these small models. Some brands of tape have finishes, which makes it virtually impossible to see on your nice covering job.
Now is the time to install the landing gear. Bend .090 music wire as shown and install using small plastic straps cut from a margarine container or similar. Use very small lightweight screws. Use lightweight foam wheels designed for park flyers.
Any questions may be directed to me at astroflyer@rushcomm.ca
