14-03-2013, 10:41 AM
I ordered some foam yesterday to make the cores, EPS foam comes in different grades. In the past I've mainly used M grade foam which has a density of 20 kg per cubic meter and it's reasonably tough stuff and feels harder than most EPS used for packaging. I thought that since this is an extra thin wing, It's thickness is only 7.3% of the chord length, I would like to try a denser, harder grade of EPS. After all with the wing being so thin it will be made of less foam and hence reasonably light. Because it's not going to be sheeted with balsa I want it to be a bit tougher and hopefully dent resistant.
So next week, enough foam to make several cores, with a density of 24, 28 and 32 Kg per cubic meter should arrive. EPS is not dear to buy. It cost $100 for enough foam to make 15 sets of these wings plus a foam box to transport my Big Yak (disassembled) and another foam box to transport my shoestring. All the pieces for the two boxes should arrive, already cut to size so all I have to do is glue them together. The other 3 pieces, enough to make 5 wings from each, of the 3 different grades are cut to length in one direction and will need to cut to the plan-form shape to make the individual cores.
The company is called Polyfoam their number is 02 9734 9555 and the man to speak with is Trevor.
But not wanting to wait 'till next week to start on the cores I managed to find a reasonably dense piece of EPS lying about the place and decided to make a set of cores for a bit of practice and to test out the jig. It's a bit of a daggy looking old piece of foam but I should be able to make something good out of it. This piece is quite hard tho’ about as hard as soft Balsa, quite a bit harder than the EPS a SkyFunjet is made from.
Here's a pic of the planform of the cores marked out on the piece of foam I found.
For cutting EPS foam there is nothing easier and cleaner than one of these. It’s simply a bow made from a piece of PVC pipe, strung with a piece of .7 mm mig welding wire. To heat the wire, simply connect it to your 12V power supply with an alligator clip and some cable. The wire is just normal mig wire used for welding steel. It has a very thin flashed copper coating on it, but this makes little or no difference to how it cuts foam.
And you want enough length between the clips so it draws about 1-3A at 12V and it should cut like a ripper.
So next week, enough foam to make several cores, with a density of 24, 28 and 32 Kg per cubic meter should arrive. EPS is not dear to buy. It cost $100 for enough foam to make 15 sets of these wings plus a foam box to transport my Big Yak (disassembled) and another foam box to transport my shoestring. All the pieces for the two boxes should arrive, already cut to size so all I have to do is glue them together. The other 3 pieces, enough to make 5 wings from each, of the 3 different grades are cut to length in one direction and will need to cut to the plan-form shape to make the individual cores.
The company is called Polyfoam their number is 02 9734 9555 and the man to speak with is Trevor.
But not wanting to wait 'till next week to start on the cores I managed to find a reasonably dense piece of EPS lying about the place and decided to make a set of cores for a bit of practice and to test out the jig. It's a bit of a daggy looking old piece of foam but I should be able to make something good out of it. This piece is quite hard tho’ about as hard as soft Balsa, quite a bit harder than the EPS a SkyFunjet is made from.
Here's a pic of the planform of the cores marked out on the piece of foam I found.
For cutting EPS foam there is nothing easier and cleaner than one of these. It’s simply a bow made from a piece of PVC pipe, strung with a piece of .7 mm mig welding wire. To heat the wire, simply connect it to your 12V power supply with an alligator clip and some cable. The wire is just normal mig wire used for welding steel. It has a very thin flashed copper coating on it, but this makes little or no difference to how it cuts foam.
And you want enough length between the clips so it draws about 1-3A at 12V and it should cut like a ripper.
“The knack of flying is learning how to throw your machine at the ground and miss.”
"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return." ~Leonardo Da Vinci