Wednesday, 7 October 2015

Construction - Basic Electric Trainer Airplane with Coroplast and Balsa wood - Part 2

Construction- Part 2
Make an Electric Trainer Airplane in 01 day.

  • All the measurements are in inches.
  • In this construction we are replacing the PVC former used in original SPAD design by Balsa Wood.
  • For Fusalage - Cut a 4mm coroplast sheet in to 12x3/4" x 44"  with the flute running in the 44" direction.

  • For Upper Wing Panel - 02 pieces of 2mm coroplast sheet ( if avialiable or else use the same 4mm sheet) that measure 13" x 32" - with the flute running in the 13" direction.

  • For Lower Wing Panel - 02 pieces of 04mm coroplast sheet, that measure 10" x 32 1/2" - with the flute running in the 10" direction.

  • Marking the Fuselage sheet - Mark the following dimensions for the fuselage sheet. All the measurements are from the front of the fuselage (except where noted).

  • Score on lines (one flute only) adjacent to the 21/2" mark to allow the fuselage to fold up. Here ins-ted of PVC formers in the original construction, you can use balsa wood strips for reinforcement. The curve on the front can be made by scissors. 

  • For Horizontal Stabilizer - Cut a piece of 4mm coroplast sheet that measures 9"x18" - with the flute running in the 18" direction. You can insert 3/4mm carbon fiber tube through the flute to reinforce the stabilizer. 

  • Vertical Stab/Rudder- Cut a 4mm coroplast sheet that measures 9"x15" - with the flute running in the 9" direction. The coroplast sheet is cut in an angle so that the hinge line is at a 15 degree sweep - that is accomplished by cutting an angle across the front that is 2" off of a right angle.

  • This is what the vert stab/rudder looks like when it is cut out.
  • Now take out 5mm balsa sheet and cut out 02 pieces of 30"x1 3/8" and 02 pieces of 6"x1 3/8". The 6" piece will be used as doublers.

  • Using the dimensions shown earlier - cut out the fuselage with a straight edge. Also - crease the flutes down the two lines for the balsa reinforcement. 

  • This picture shows the PVC formers, but in our construction we will use balsa strips. Use CA glue and make sure that the balsa formers are square and centered.

(Caution - CA glue dries very quickly, so be careful about the alignments before applying the glue) 

  • After gluing the balsa formers to the bottom of the fuselage, glue the sides to the formers.Apply the glue to both sides, fold up the sides immediately (CA dries very fast) and lay the fusalge on its side and put some weight on it till the glue dries.

  • After the glue has cured, put some tape on the aft part of the fuselage to help hold the sides square. After applying the tapes to hold the shape - run the CA down the inside corners to help the aft part of the fuselage to hold shape. Here you can glue the balsa strips along the corners and edges to give extra strength to the fuselage. After the glue cures remove the tapes.

  • Cut out the bottom of the fuselage for the taper. The back end sides (2 places) should be cut so that there is gap for the rudder to fit in - cut out the aft part leaving 2mm gap on both sides (after closing you should get 4mm gap). The front of the taper needs a small angle slot cut so that when the back is drawn together- there is room for the sides to draw in.

  • Flip the fuse over and tack glue the tapered sides together - ensuring that the aft part of the fuselage stays square and straight.(building the fuselage straight and square is very much important). Cut a piece of balsa wood 20" long. Using the inner part of the fuselage as a guide- mark and cut the balsa strip doubler so that it matches the taper close enough so that the balsa strip fit excatly inside the rear of the fuse all the way back. Glue it in place.

  • Here you can see the doubler glued in place. Notice the 4mm gap for the vertical stab/rudder, which will fit into later.

  • See the bottom pictures to understand, how to use the balsa wood strips as doublers.

  • Take the vertical stab/rudder piece that was made earlier and temporarily fit in to place, lining up the rudder hinge line with the aft part of fuselage. The vertical stab/rudder assy sits on top of the balsa doubler that was previously installed. After verifying that the assy will fit correctly- use Araldite (epoxy glue) on all of the areas that make contact and after ensuring that the entire fuse/vertical stab/rudder assy is square - hold in place until it dry by suing clamps or weights or any other support.(Here do not use CA as it will dry very quickly and you will not be able to do any corrections).

  • Use balsa strips as stringers on the fuselage to help hold the upper aft cover in place. Run the stingers all the way to the back as far as they can fit between the vertical stab assy and inner side of fuse. Space the stringers 4mm below the top of fuse sides so the top cover will fit flush.

  • Cut out a scrap piece of 4mm sheet with the flute running the 2 1/2" direction - measuring 2 1/2"x18 1/2". Draw a line on both sides from the front corners to the back leaving 4mm gap for the vert stab assy to fit in to.

  • Here use 5mm balsa wood sheet in place  of yardstick.

  • Again use 5mm balsa wood sheet.

  • The doublers will sit on the balsa wood formers.

  • Use 5mm balsa wood in place of yardstick doublers wherever it is mentioned.

  • Here use Araldite (epoxy glue)

  • For the reinforcement of vertical and horizontal stabs you can use two methods, Insert carbon fiber tube through the flutes near to the hinge line or attach 2mm cycle spokes to the vertical and horizontal stabilizers, make 04 brackets from 1or2mm aluminium strips and use wheel stop collers to attach the spokes, this will reduce the risk of fluttering of tail plain.

  • Use Araldite (epoxy glue) for fixing the LG attachments.

  • Here we have the completed fuselage. All we have left to do is to mount the motor wall, landing gear, control surface connectors and the receiver connections.

  • Here use metal bolts in place of nylon bolts.

  • Here you can use balsa wood strips/carbon fiber tube pieces/ cycle spokes/ bamboo sticks.

  • Here, cut out a piece from plywood and 5mm balsa wood which will fit exactly inside the forward fuselage and glue it together, this will form the motor mount for electrical conversion.Make this part as per your motor and nose gear selection. I used 2mm aluminium sheet along with the ply and balsa mount to give extra strength.

  • See the bottom pictures for Motor mount and Nose wheel attachment.

  • Do this step if you want to use a steerable nose wheel.

  • You can make the push rods using carbon fiber tube or if you want to save money you can use cycle spokes for the same.

  • The control horns can be made out of 1 or 2mm aluminium strips also. (No problems in using ready made ones)

  • If you are going to attach the wings using rubber bands use the following method. Since we are using electric motor, fuel proofing is not required (wherever it is mentioned).

  • You can modify the wing attachment, if you do not want to use rubber bands. See the bottom picture for attachment of wing with wing bolts.

  • The fuselage is basically done at this stage.
  • The only thing left is the installation of receiver and battery.
  • We will wait for it until the wing is built, so that we can temporarily rubber band it into position to figure out where the battery and receiver will need to be placed to obtain correct CG position. 
  • The correct CG position for this Airplane is on the wing spar. 
  • Now you can decorate and give details to your finished fuselage. 
  • Next we will construct the wing.

Next :- Wing Construction.

No comments:

Post a Comment