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A new attempt to start right.

#1
About a year ago I started flying. The only plane I have flown is my Cessna 182 scratchbuilt, apart from a cardboadr FT Simple Scout that only flew for one day. :p.
The point is that i started flying an airplane that was not really a trainer for a beginner. Even so, I managed to master it quite well. But after many repairs, it became unstable and fragile. As a result, I crashed it last week, in a short flight that only lasted a few seconds.
So I decided to start again, but this time in the right way.

Said that, I've decided to build a real trainer model, specifically the Biloute, a model from this French page.
3_axes_1.jpg sol_3.jpg

As part of continuous learning, I have decided to test new construction techniques by taking ideas from FT and others from the method I use regularly. I will try to describe in this post the process of construction, as well as any doubt that may be coming up. ;)
 
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#2
Sorry for not having photos of the process, I will try to be more careful from now on.
The tail group is ready.
Tail group.jpg

I have used thin sheets of 3mm / 4mm EPP obtained with the hot wire cutter. I have also added some light wood reinforcements to improve the strength.
IMG_20190711_205403.jpg IMG_20190711_205419.jpg IMG_20190711_205412.jpg

Better visibility of backlit reinforcements
IMG_20190711_235012.jpg IMG_20190711_235021.jpg IMG_20190711_235037.jpg

So far the structure looks very strong and light. And the weight of the whole (although I don't have a scale) looks lighter than the EPP solid piece.

That's all for now, I'll publish more Monday morning.
 
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#3
I forgot to mention that the real size of the original plane was 101cm wingspan. Although the model accepts up to 3100 mAh, I think my 2200mAh batteries would be heavy for a model of only 1m wingspan, so I've scaled it up to 120%.
 
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Seahunter

Active member
#4
About a year ago I started flying. The only plane I have flown is my Cessna 182 scratchbuilt, apart from a cardboadr FT Simple Scout that only flew for one day. :p.
The point is that i started flying an airplane that was not really a trainer for a beginner. Even so, I managed to master it quite well. But after many repairs, it became unstable and fragile. As a result, I crashed it last week, in a short flight that only lasted a few seconds.
So I decided to start again, but this time in the right way.

Said that, I've decided to build a real trainer model, specifically the Biloute, a model from this French page.
View attachment 135925 View attachment 135926

As part of continuous learning, I have decided to test new construction techniques by taking ideas from FT and others from the method I use regularly. I will try to describe in this post the process of construction, as well as any doubt that may be coming up. ;)
Beautiful aircraft, will follow this thread closely. Your use of the materials available there is great. Neat construction and reinforcing. I never tried cutting foam with a hot wire. Great job, looking forward to the maiden flight.
Fred
 
#5
Beautiful aircraft, will follow this thread closely. Your use of the materials available there is great. Neat construction and reinforcing. I never tried cutting foam with a hot wire. Great job, looking forward to the maiden flight.
Fred
Thanks Fred, and wellcome to the thread :D
This new building way has given me the chance to work with scraps, literally. Now i can obtain valuable and usefull parts from the remaining EPP pieces in the workshop. :geek:
I am specially fucused in the reinforcements, i want to have an strong plane which allow me to fly without fear of losing a wing :ROFLMAO:.

Cutting foan with hot wire is super easy, it take some time to get the trick but once u get there, it'll be worth it. Allways is a good time for learn new things.
 
#6
I want to share with you some pictures of my hot wire cutter.
It is a simple piece of wood from an old table. The hot wire is fixed at one end and at the other end it has a bottle with water to tighten the cable. The thickness of the cut is regulated using shims at both ends.
For the 3mm cut I am using two identical metal rods.
1.jpg 2.jpg 3.jpg
 
#8
The wings are almost ready. All that's left is to cover one wing and join them together.
The first thing I discovered was that to work with such thin sheets of foam, the surface must be completely straight and smooth. Otherwise unwanted twists will appear.
1.jpg

I glued the bottom reinforcement, and then used it as a guide to mark the position of the ribs.
2.jpg 3.jpg 4.jpg 5.jpg

Then glue a 5mm thick front piece and then glue the leading edge.
6.jpg 7.jpg

I also added another piece for the trailing edge. and then glued the top reinforcement.
8.jpg 9.jpg

In the middle of the wing I decided to add a solid block of foam to improve strength.
1111.jpg 10.jpg 222.jpg 11.jpg
 
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#10
That's all for now. I hope you like it.
This is my first construction using this technique and I wouldn't want to make any mistakes. So if u have any advice, let me know ;)

In general, the wings look light and extremely strong. I think adding packing tape to decorate will add a little more strength.
 
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Seahunter

Active member
#11
That's all for now. I hope you like it.
This is my first construction using this technique and I wouldn't want to make any mistakes. So if u have any advice, let me know ;)

In general, the wings look light and extremely strong. I think adding packing tape to decorate will add a little more strength.
Nice work, going to be a strong lightweight airframe :)
 

quorneng

Well-known member
#12
cdfigueredo
That is very neat work and a construction sequence I have used many times on my Depron wings.
My only comment is really structural.
Your wing will have virtually the same bending strength all the way along whereas the actual bending load on a wing in flight is a maximum at the root and gradually reduces to zero at the tip.
It could thus be argued that your wing is thus heavier than it need be for no structural benefit.:eek:
The answer is of course to taper the spars. Tedious to do but you will save nearly 50% of their weight and even balsa is a great deal heavier than Depron. ;)
 
#13
cdfigueredo
That is very neat work and a construction sequence I have used many times on my Depron wings.
My only comment is really structural.
Your wing will have virtually the same bending strength all the way along whereas the actual bending load on a wing in flight is a maximum at the root and gradually reduces to zero at the tip.
It could thus be argued that your wing is thus heavier than it need be for no structural benefit.:eek:
The answer is of course to taper the spars. Tedious to do but you will save nearly 50% of their weight and even balsa is a great deal heavier than Depron. ;)
Hey, welcome to the thread. Your comment is welcome. I understand what you're telling me perfectly. In future constructions I will use itn no doubt. In this I can no longer, I have covered one half wing and the other is about to do so.
I have seen your constructions, you are a master with the technique :eek:. We can;t find Depron here, that's why I use EPP, which is less flexible.
I also believe that before hard landings, the wing would resist better with extra reinforcements. :ROFLMAO:
 
#14
I took this from one of your posts. ;)
Is this what u mean about taper the spars? :unsure: It could be done using balsa, little harder using other woods as i am doing. I am using cedar.
46729_a1f9d066aa410ade74fa6dd5443b0bbf.jpg
 
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quorneng

Well-known member
#17
cdfigueredo
Yes that is a tapered spar.
Note the spar in that case is above the rib and is the same thickness as the foam skin which is added as two separate pieces.

This solves another issue resulting from using a 3 mm thick skin as the spar ends up in total 6 mm 'shallower' compared to the thickness of the wing.
In simple terms the stiffness' of a spar is proportional to the square of its depth so the loss of 3 mm top and bottom can be quite significant, as much as a 50% reduction in strength!