Help! Foamboard weight - scaling UP

[10tpeg]

Hi there!
Im in South Africa, and plunged right in and bought 5 large sheets of 5mm foamboard. Then I built a Simple Scout as my first build, to become acquainted with the FT build tecniques. All went well, but the CG was WAY out, so after reading the forums, I designed an extension to the nose, and got it to balance perfectly. It flew like a brick! With full power, it flew ok but fast; but glided straight into the ground! When i weighed it it was about 80% heavier than the FT design.

Now I am left with 4.5 sheets of this board, and am trying to figure out what to do with it! I have weighed it and have found the following:

FT board 5mm = 290gsm
FoamX 5mm = 611gsm

I have peeled off the thick paper and weighed the foam - it is really light, but only can be used for formers, as it is flimsy. Rather than toss the board out, I want to use it. It occured to me to scale up the designs to decrease the wing loading.

Given the weight of the construction material, is there a formula that determines how much I should scale UP a design by?

 

[Hai-Lee]

Hi there!
Im in South Africa, and plunged right in and bought 5 large sheets of 5mm foamboard. Then I built a Simple Scout as my first build, to become acquainted with the FT build tecniques. All went well, but the CG was WAY out, so after reading the forums, I designed an extension to the nose, and got it to balance perfectly. It flew like a brick! With full power, it flew ok but fast; but glided straight into the ground! When i weighed it it was about 80% heavier than the FT design.

Now I am left with 4.5 sheets of this board, and am trying to figure out what to do with it! I have weighed it and have found the following:

FT board 5mm = 290gsm
FoamX 5mm = 611gsm

I have peeled off the thick paper and weighed the foam - it is really light, but only can be used for formers, as it is flimsy. Rather than toss the board out, I want to use it. It occured to me to scale up the designs to decrease the wing loading.

Given the weight of the construction material, is there a formula that determines how much I should scale UP a design by?

Sadly not everyone has access to the correct FB as used for the FT designs. I am not sure if your country has any trade or other restrictions but you could buy kits from the FT store, Sadly plus freight). Having said that there are other things you can do to make you FB planes lighter and to fly better.

If you can remove the heavy paper then do so and glue on your own substitute lighter weight paper. You can also use the Foam alone as a laminate, (2 layers glued together), and the glue in between the layers will provide a marked increase in stiffness.

You can also build the planes out of the foam alone and coat the outer surfaces in tape or even just PVA glue which when dry will increase the rigidity of the structure.

You can also build your plane with all of the internal layer of paper removed to save weight.

When you have finished your build and if it is significantly heavier than the original design you should also consider that you may need to increase the wing lift which is easiest to do by increasing the wing incidence angle.

Yes you can scale up the designs but eventually you may find that the structure is actually quite weak and easily damaged due to the actual mass of the entire structure. Once beyond a certain size the plane will require more internal support structure especially within the wings to avoid mid air collapse.

I am sure others will have advice on what works for them so do not give up as you can and will get it all sorted out. Here the FT Fb is rare and expensive and I build in the local FB. So far I have been able to build and fly every FT design I have built though some do require drastic weight reduction procedures to be used.

Have fun!