How to I replace a fiber glass cowl? Or do I even bother?

[Paul Taylor]

I acquired this Akrobat plane from a flying buddy that got it from a local estate. It seems to be a project that was started years ago and then never finished. It needs a little work and some TLC but should be flyable. I want to use this as a learning opportunity as there are some areas that could be improved. There is a tire weight being used as a wing tip weight with gobs of Ambroid glue holding it in place. A tip weight box will replace it. Also there are no flaps or dorsal fin for the rudder. And I am sill in need of a canopy. I was going to make one from a soda bottle but think I will just buy one and use my limited building time on something else. Like maybe how in the heck do I replace the fiber glass cowl. The current fiber glass cowl weighs in at 2.2 ounces. I know I need to replace it with a balsa one but I do not know where to start. Do I build one just like the fiber glass one to slip over the nose? Or do I just build out the current fuse?


As it sits right now without flaps and dorsal fin and including the fiber glass cowl it weighs in at 29.3 ounces. I have a LA .46 ready and waiting.

[Randy Powell]

Paul,

Were it me, I would build the nose out and put a conventional cowl on. The cowl that comes with the kit is pretty heavy injection molded plastic and quite heavy as you note.

[Bob Reeves]

I agree with Randy, some time ago I posted pictures of how I did it on a Nobler ARF...

Look about half way down in this thread...

http://stunthanger.com/smf/index.php?topic=3162.0

Then take a look at the more or less finished product here.. The landing gear didn't stay, went with aluminum.

http://stunthanger.com/smf/index.php?topic=3515.msg25333#msg25333

[Joe Gilbert]

Paul only user it if you need the noise weight and you wont with a LA 46. You could make a three sided one and leave the bottom open ,just to keep it simple.

[Andrew Borgogna]

I guess I am not sure if you have a fiberglass cowl that you want to replace or if you have an injection molded plastic cowl.  Anyway to answer you original question " how do I make a cowl" there are a couple of ways I have used.  The complicated way is to take the cowl you currently have build a wooden box to fit around it the coat it with mold release and use plaster of paris to make a negative mold of it.  Make sure you make the mold with partitions so it can be split in half. After the mold is set up split it in half remove the cowl and use the mold to make a new cowl.  This is a time consuming process and is really recommended for making several molds.  

The simple way is to get some dense foam and use contact cement to attach it to the plane where the cowl will go.  I also install a plywood nose ring for the nose of the cowl, it will be on the inside of the glass.    Then carefully shape and sand (use very fine sandpaper to  finish it) the cowl to shape including the nose ring.  When you have the shape you want use epoxy and 2oz glass and cover the foam cowl.  Take your time at this point and use slow setting epoxy, this will be the outer layer of the cowl.   Let it set up for at least a day.  Remove the cowl from the plane and use Acetone to dissolve the foam from the inside of the cowl.  Again let it set until it has some stiffness then apply a second layer of glass and epoxy on the inside of the cowl.  I recommend using strips of glass for this process.  When the epoxy has set up sand and finish the outside of the cowl.  You may have some pits in the surface these are easily filled with puddy.  I have made several cowls with the lost foam method with good results.

Andy