Tuesday, 20 May 2014

Better airfoil wing build

Following on from the Bending Better Depron Airoils article, this is the complete wing build.


It's basically an Experimental Airlines Armin wing with a few tweaks for the 6mm paperless foamboard and a nicely shaped airfoil. I'll mainly cover the steps that differ from Ed's instructions so check out his superior videos for more in-depth coverage.
This wing will be 1500mm (59") wingspan made from two 750mm (29 1/2") halves, joined with a 7.6mm Skyshark P4X wrapped carbon fibre tube spar. 

Airfoil section design
% thickness
I wanted a speedy slope soarer so Max thickness will be a slim 10% of total chord.
Using the information from my previous tests:
No extra former on top of the spar = 19mm thick airfoil, so a total chord of 190mm gives a 10% section.
3mm former on top of the spar = 23mm thick airfoil, so a total chord of 230mm gives a 10% section.
6mm former on top of the spar = 26mm thick airfoil, so a total chord of 260mm gives a 10% section.
For this wing I decided on the narrowest option - 19mm thick x 190mm chord section.

Max thickness location
30% back from the leading edge is what I'm aiming for and ailerons are included in the total chord measurement. 30% of 190mm = 57mm, so the spar will be positioned 57mm back from the leading edge.

Aileron size
40mm ailerons give sufficient stiffness and some aerobatic performance so now we have the overall airfoil dimensions.
Total chord = 190mm with a 150mm main airfoil and 40mm ailerons. Thats roughly a 6" main wing section with 1.5" ailerons giving 7.5" total chord.

Wing build
For this 190mm chord airfoil we need 150mm for the bottom surface, 150mm for the top surface, 40mm for the ailerons PLUS 10mm extra for the leading edge bend. That gives 150 + 150 + 40 + 10 = 350mm



Cut out the wing panels - two 350mm x 750mm rectangles

Cover one side with packing tape and use a plastic gift card edge to smooth it down. Watch Ed's tape covering video for complete instructions.

 Mark the leading edge fold line 150mm in from one of the long edges.

Draw a line 25mm in from the same edge for the bottom layer bevel.

Draw a line along the edge 2mm up from the taped surface. The idea is to leave a bit of thickness here so that the sub-trailing edge ends up 8mm thick. This allows the ailerons to form part of the overall airfoil shape.

Slice and sand the bevel back to the marked lines.

The finished bevel with 2mm thickness left at the sub-trailing edge. 

Make a dent along the leading edge fold line. I'm using my specially designed tool, a rounded off piece of 10mm dowell. I want a reasonably sharp leading edge so I'm making a deepish dent here, maybe 3/4 of the way through. This is the only dent I make, the slimmer airfoil section means the depron doesn't have to curve too much over the top, so kinking is not a problem. 

Clamp down a stiff ruler at the fold line and, using another full length piece of something stiff, bend the depron up to 90 degrees.

Remove the ruler and bend the depron right over, squashing down hard on the leading edge.

Mark the spar position. 30% back from the leading edge is 57mm for this wing. 

Position the spar and formers and mark the positions. The formers are 20mm wide and only one layer with nothing on top of the spar for this wing.

Glue the formers to the bottom layer then apply glue along the top.

Fold the top layer over and hold down to set with a long stiff ruler.
Depending on how hard you push down, more or less bottom curve will be formed. For a flat bottomed wing push down hard on the leading and trailing edges. For a more symmetrical airfoil you can let the leading edge curve up a little. As there is no paper to stiffen the bottom layer, depron naturally tends to produce some bottom curve.

Squirt glue into the sub-trailing edge join and clamp down to set. Again you can decide how much bottom curve you want by holding it down flat or letting it lift up a bit.

To finish the ailerons score down the sub-trailing edge but dont go right through to the tape.

Crack the aileron hinge free over a straight edge then slice off a 45 degree bevel and sand smooth to allow the aileron to swing down. 

Slice off the aileron trailing edge bevel and sand smooth. I draw a line 20mm in and bevel back to that and all the way down to the tape on the trailing edge. 

Here's it is just about done. See how the aileron forms part of the overall airfoil shape, very nice.

Add more tape to form the aileron hinge and make a sharp trailing edge. Check out Ed's Kissing tape technique for more detail.

To finish the wing completely, tape over the open outer ends, fit servos and control horns then tape the two halves together. As this wing has a curved bottom it may not sit flat on the fuselage. Some packing under the leading and trailing edges may be needed to hold it level.

Tape on two icypole sticks where the rubber bands pass over the wing edges.

I'll make another fuselage to match this wing but this one will do for the moment.

1.5m depron wing build video

Maiden flight


Links for materials and information
Experimental Airlines for designs and techniques
Tradewarehouse for bulk depron
Kitesandfunthings for CF spars
My website for underwater photography, kite aerial photography and RC flight

20 comments:

  1. Awesome! Great job the build and the flight (love the catch, and then the "duck"!)

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  2. Thanks Andrew, The hit in the head actually dazed me for a second and left a ding on the wing.

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  3. Great work. Foamboard is pretty staticy after you peel the paper off. I modified your design a bit and added strands of dog hair throughout mine for uh re-enforcement.
    Thanks again

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    1. Ha yes, I use cat hair in the same way.

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    2. NICE!! I'll try that! Will Labrador fur do?

      Salute>

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    3. Oooh, the good stuff! That will work nicely.

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  4. Hi Andrew, I realized my first couple of wings following your method: they came out very nice, even if it was my first time using Depron (and building a plane, by the way).
    Now I have some questions on how to size the other parts: how big tail and elevator should be? And the distance between wing T.E. and elevator L.E ?

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    1. Hello supermic. Congratulations on building and flying, it's a buzz.
      There is no one answer to your question. I usually go by what looks OK usually works.
      Have a look at The Red and the 1.2m Acrobat posts in this blog for some examples with dimension.

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    2. Thanks, I like this approach :-) !

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  5. Thanks a lor for this! This technique helped me make my best depron wing to date. My wife got interested in flying, so I built a somewhat thicker wing, for a trainer plane.

    I also made a square tube per Ed's instructions, but with 2.5mm coroplast. Turned out really nice and durable.

    Buddyboxed with her today, and she loved it :D

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  6. Excellent Joni, that makes me happy.

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  7. Good job and thanks for sharing! I would like to know how much this wing weights.

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    Replies
    1. 250g was the final weight, including servos and spar

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  8. This comment has been removed by a blog administrator.

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  9. Nice Plane, What is the overall weight of this plane?

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    1. Cant recall sorry, the wing was 250g so all up it might have been 500g

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  10. Mucha Gracias por tu videos .Omar from Chile

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