Wing construction

total rethought

Main goals of the wing construction

  • Easy to make
  • Quick to produce (Less man-hours, less expensive for client)
  • Possible to inspect

Hollow wing

I know that the Horten wing has a lot of many different ribs. Much time would have been lost if i would have wanted to make those all. So ...i came up with the idea to use reinforcements on the skin.

I was inspired by a piece of composite i found in the workshop of Kees Radius. It had a foam skin and some trapezium section strips on it. All together it was rock solid! And amazingly light for such a solid structure.

How we did it. The outer skin.

Mainly the answer to all our goals was ...foam. Remarkably ...one answer came from the car-industry. Wrapping!

Let's start by the main skin. The skin was a combination of carbon, glassfibre and foam. The strongest part of the spar (a "thick" layer of carbon) is laid into this skin. The bottom reinforcements of the "ribs" are also placed at the same time. Looks all very time consuming work, but ...a few simple jigs made out or cardboard is all you need to make it a speedy process. Vacuum it all. Done. Oh yeah ...tip: do this step with a WARM mould. It makes the resin flow better. Remember: you have to do a laaaaarge surface and a lot of placing work. Don't let the resin become less fluid during that work. We could have saved some weight during this step. The first wingtip was made without that knowledge and became heavier. 

As you might see, the leading edge is mainly carbon around a foam plate. All behind the spar is made in a thinner foam and covered with glassfibre. This was out first step of wing production.

You might now think: "Hey, where is the gel-coat?" Well, ...there is none! No, i found something that might beat gel-coat. I saw it in a car-show. Wrapping! That skin can endure higher speeds that i plan to fly with the hangglider. It is UV-resistant and ...VERY LIGHT! Also, it can follow complex curves. And ...last but not least ...you can have it in all kinds of coooool colours. No joking, i planned to use CHROME! Really. A silver looking flying wing. How much StarWars feeling would that give??

How we did it. The spar.

The next step was the spar. Making the spar is not that hard. Most important part is in the outer skin.

The wing bending forces would be taking by those carbon strips. I guess to remember that the biggest layer int he spar would be 6mm. Mostly ...it was 3mm. Making the mould to create the spar was more difficult. Here is how we did it.


We let the 3D drawing program draw us how the sides of the U shape, which we intended to place over the carbon spar layer in the upper outer skin. We make those sides in hardboard, but did not use the full height. We made it 1 cm less high. The final adjustment we wanted to create when we would place both moulds onto each other.

Here you see the sides placed on top of the first outer skin. It needs to be ultra vertical to the expected forces. We used a jig (touching the outsides of the mould and having a T-square slide over that jig, which actually only served to place the T-square higher) to get it at that angle.

Near came the moment to close both moulds on top of each other. But ... how would we be sure about the right height! Easy! Place a glossy plastic on the outerskin which lays in the other mould. Place some expanding foam composite on top of the hardboard structure. Close the moulds  and bring a extra weight on the top mould so it will not be pushed up. Make sure not to use toooo much weight. You don't want to mould to sink down due to the weight.


What do you get? The nearly perfect shape to use as positive mould for your spar U part. Make the hardboard structure and the expanded foam into a solid, shiny block and make a negative mould of it. Done! Watch out! This all sounds very easy, but mould making takes a lot of time due to the endless sanding.

How we did it. The ribs.

Making exact ribs is very exact work and normally time consuming. We degraded that to a small job you can do between other jobs. Kind of a time filler while waiting when things dry and harden out.

Sadly i lost most of my pictures of those days. Once i found them back, i will place them here. But the following pictures might give enough hints.

No ribs were placed in front of the spar. Behind the spar most ribs were just small strips glued on top of the outer skin. At the elevons we needed to use a more classic approach. 

Closing the wing.

We used a mix of resin and microbubbles to create a kind of putty. This putty was placed on all parts that would touch the other side. I guess for our first wingtip assembly we probably used too much. So the weight would have been higher than needed. But ...it worked perfectly.

Testing the wing.

A special structure was made to hold the wingtip of 5m length. We prepared weights in shape of boxes filled with metal and water. Each box had a specific weight according to the calculations of the lift distribution. We tested to 6g. Not even a single sound was heard during that test. It is a secure construction.

The result of a single wing tip.

The wingtip you see here already had the hinges installed. The elevon is hanging freely downwards. You can see the ribs a bit through the top outerskin. The hole at the root is the location of the coupling insert. Just slide it over the insert and prevent it from sliding of it with a single Jezus-pin.