Wonwings diary-Building from plans-Part 9-Blue Foam construction.
We can now deal with thinning out the fuselage shell, to save even more precious weight and preparing it for finishing and fitting out.The Blue foam laminations would have been lightly glued together at the centre datum point,in between this would be a coloured piece of paper that constantly confirms the centreline no matter how much sanding or cutting is done,the next job is to take a blade and split open the two halves,ease a wide pastry knife between the blocks and gently rock the two foam cores apart,the paper will have done its job and is no longer required but even now it will aid separation of the cores.Once this has been done you can clean up the flat surfaces with a large Permagrit block,next take a marker pen and draw a line right along the edge of the fuselage sides,within this area is where we will be scooping out any surplus foam,start by taking a knife blade and running this around the marker pen line,this will enable a clean line as the inner debris is parred away that butts up to this cut,the best tool to use is your trusty clean wire brush,gently pull and stroke the foam from nose to tail,soon you will get the idea as the beads come away,we are not aiming for precision because you will not get it with any foam,the aim is to remove dead weight that has no purpose,the more you remove the better the model will fly,gently finish off with coarse glasspaper glued around an half round piece of wood,once again a simple dragging action will prove the best.
Once you are satisfied that the two halves are as good as you can get them now is the time to make up some inner formers,you will almost certainly need one for the nose of the aircraft,one just aft of the wing trailing edge,and one forward of this,to arrive at the shape obtain a carpet fitters shape tool,this looks like dozens of wire pieces that when pressed into the concave produce an exact pattern of the shape.Simply draw around the patterns straight onto some wood,cut out the formers and check fit into position,once you are happy then fix them into place with a glue gun,this is adequate for everything except the front former which should be fixed with epoxy,we use the glue gun for two reasons,one it is convenient and sticks well and quickly,two it is lighter than epoxy adhesive which is heavy and should be used with care and for consideration of the weight penalty it carries.
Regarding the formers you can use either laminated balsa sheet,or liteply both are ideal.
Control runs can be positioned into the formers using snakes,these can be locked into place with the glue gun,make sure that they exit cleanly with the minimum of bends,best to install things such as this now while you have good acces,even doing the job whilst the halves are unglued together.
Other considerations are the positions of the tailplane and fin,mark and cut the slots now at this stage checking the angles very carefully,the nose bulkhead needs careful treatment,make balsa fillets at the back of this crucial former and glue well,if necessary add any blind mounting nuts for the engine bearers,PSS soarers simply need an hard balsa block cut to shape and sanded to blend into the shape of the fuselge.
If the model has a cockpit,cut away at that point and fair in the sides with medium sheet balsa,for this job use PVA or Aliphaetic adhesive holding in place and tacking with the glue gun,servo rails can also be made up from quarter square hard balsa with basswood cross pieces to take the servo mounting screws.Once everything is installed do a dry run on the two sides,then apply PVA or Aliphaetic and bind firmly together with masking tape,leave for at least 48 hours to throughly dry out.
We can now deal with thinning out the fuselage shell, to save even more precious weight and preparing it for finishing and fitting out.The Blue foam laminations would have been lightly glued together at the centre datum point,in between this would be a coloured piece of paper that constantly confirms the centreline no matter how much sanding or cutting is done,the next job is to take a blade and split open the two halves,ease a wide pastry knife between the blocks and gently rock the two foam cores apart,the paper will have done its job and is no longer required but even now it will aid separation of the cores.Once this has been done you can clean up the flat surfaces with a large Permagrit block,next take a marker pen and draw a line right along the edge of the fuselage sides,within this area is where we will be scooping out any surplus foam,start by taking a knife blade and running this around the marker pen line,this will enable a clean line as the inner debris is parred away that butts up to this cut,the best tool to use is your trusty clean wire brush,gently pull and stroke the foam from nose to tail,soon you will get the idea as the beads come away,we are not aiming for precision because you will not get it with any foam,the aim is to remove dead weight that has no purpose,the more you remove the better the model will fly,gently finish off with coarse glasspaper glued around an half round piece of wood,once again a simple dragging action will prove the best.
Once you are satisfied that the two halves are as good as you can get them now is the time to make up some inner formers,you will almost certainly need one for the nose of the aircraft,one just aft of the wing trailing edge,and one forward of this,to arrive at the shape obtain a carpet fitters shape tool,this looks like dozens of wire pieces that when pressed into the concave produce an exact pattern of the shape.Simply draw around the patterns straight onto some wood,cut out the formers and check fit into position,once you are happy then fix them into place with a glue gun,this is adequate for everything except the front former which should be fixed with epoxy,we use the glue gun for two reasons,one it is convenient and sticks well and quickly,two it is lighter than epoxy adhesive which is heavy and should be used with care and for consideration of the weight penalty it carries.
Regarding the formers you can use either laminated balsa sheet,or liteply both are ideal.
Control runs can be positioned into the formers using snakes,these can be locked into place with the glue gun,make sure that they exit cleanly with the minimum of bends,best to install things such as this now while you have good acces,even doing the job whilst the halves are unglued together.
Other considerations are the positions of the tailplane and fin,mark and cut the slots now at this stage checking the angles very carefully,the nose bulkhead needs careful treatment,make balsa fillets at the back of this crucial former and glue well,if necessary add any blind mounting nuts for the engine bearers,PSS soarers simply need an hard balsa block cut to shape and sanded to blend into the shape of the fuselge.
If the model has a cockpit,cut away at that point and fair in the sides with medium sheet balsa,for this job use PVA or Aliphaetic adhesive holding in place and tacking with the glue gun,servo rails can also be made up from quarter square hard balsa with basswood cross pieces to take the servo mounting screws.Once everything is installed do a dry run on the two sides,then apply PVA or Aliphaetic and bind firmly together with masking tape,leave for at least 48 hours to throughly dry out.
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