40% Extra 260: Own-design build thread

[dmichael]

Pg 5

[as722]

That's awesome dave. I had a Godfrey laser back around 1989 that had a foam ribbed wing and was very light unfortunately it met with the ground and we all know who won !

Albert

[dmichael]

Last Page

[dmichael]

And so, armed with this knowledge and the experience of having done this on a 98" wing once before, I set out to build a foam ribbed wing.

First, I took my wing plans and built a jig over it.

[dmichael]

With the jig done, I inserted the rib blanks. The foam was a sheet of 4ft X 8ft 1/2" thick blue foam insulation from Home Depot or Lowes cut up into smaller blanks and instered into the jig. The jig spacing was tight enough that it would easily hold the blanks in place while we cut them.

[dmichael]

With the blanks installed, I tacked on the root and tip templates, making sure they were level. Top was cut using a very crude bow and power source. Even so, the top came out fine.

After the top was cut I used a Zona saw to cut out the notches for the 3/8" hardwood main spars and 1/4" hardwood and balsa spars at the aileron leading edge. This went fine too.

Before I did any sheeting, I decided to do some experimenting with the cutting of the bottom of the wing.

In case you didn't read through Wayne Ulery's instructions above <VBG> the way this works is that you cut the top of the wing, build the top of the wing including spars, phenolic hole and installation of phenolic, sheeting and anything else you would need to build before sheeting the top of the wing. All this happens in the jig. Once the top is done, you cut the bottom of the wing foil including and build the bottom- including stringers, sheer webbing, bottom sheeting and such- again, all in the jig- when applying the sheeting you apply glue where the ribs and sheeting will contact, put the skins on and apply weight until dried. Same for bottom sheeting- you put the skins in the jig with glue applied, lay the wing back in place and apply weight until dried.

Once the glue is dry you can take it back out of the jig, glue on leading/trailing edges as well as root and tip ribs (making sure the spars reach to the root rib- it needs to do carry the load). Then you cut out the ailerons and face/bevel/hinge.

A very sound way to build a wing.

Now, as I said, I decided to see if I could cut the bottom of the wing before getting to far on the top. I found that, with my crude foam cutting equipment I was not getting a straight cut. After a few attempts I bailed and went with a traditional foam core wing instead. I sent templates and a wing planform to www.flyingfoam.com and they cut a beautiful set of foam cores for me that worked great.

[dmichael]

The wings came from FlyingFoam with the phenolic tubes cut. I started by gluing in the phenolic tube. The hole in the wing just barely reached the end of the tube so I cut it back an inch or so. Then I constructed and installed a 1/8" aircraft ply plate. After that I glued an end-cap onto the end of the wing to prevent the wing tube from sliding around. Finally, I glued back in the piece of foam that I removed from hole but on the other side.

The two pieces of balsa in the last pic are there just to hold things in place while the glue dries. They were removed after the glue dried.

[dmichael]

After laying out the ailerons and servo placement, I used the dremel to cut servo mounts and pockets as well as the servo lead channels.

[sweetpea]

	Quote: Originally Posted by dmichael
	Thanks, sweetpea- got a website for GS racing?

http://www.gsracing.com

or

www.horizonhobby.com

[dmichael]

More- including the laying in of the servo wires- this is done before the sheeting and becomes a permanent part of the wing.

[dmichael]

Wing skins prepared- first I had to add on to the end of multiple sheets of 48" 3/32" sheeting. I cut the joints at an angle to provide greater gluing surface. Then I glued the sheets together with Pica wood glue. Then sand, sand, sand.

[dmichael]

Wing skins applied in the traditional method using Pro-Bond and weights in the shucks overnight.

[paffy]

So why exactly did you give up on the foam rib technique ?

Also - you should slow down the posting frequency. You make me look real slow with my build

P.

[dmichael]

Ha! I had a four year head start on the build! It takes me longer to reduce the picture size than anything else!

I bailed on the foam ribbed wing because I encountered difficulty cutting the bottom of the wing with my very crappy homemade foam cutting apparatus. I am sure that it would be easy to do with a decent bow that would cut 50-60". The sheer length of the cut makes it difficult for the neophyte foam cutter like myself.

I think it would be great to do a 40% wing that way someday.

Dave

[xed]

What happens if one of the servo extensions gets damaged? Won't you have to undo the balsa covering?