As a young boy or girl you may have experimented with water rockets. They are fast, they go high, they are awesome. But I asked myself, what if I put wings on a water rocket? Then the wings should be foldable or else they would compromise the launch. With this in mind I created a winged water rocket which launches with its wings folded to eventually spring open mid-flight. Impressed? Want to build one yourself? Be sure to keep reading!

Requirements:

- Balsa sheets: 3x10mm, about 2 metres

- Balsa stick: 3mm, about 20cm

- 2 PET bottles (keep in mind the shape has to be aerodynamic) 1 - 2 litres

- 2 cork

- an old bicycle valve

- lots of rubber bands

- a light fabric (an old tent, kite, cloth etc.), about 1m²

- a metal hook (or a peg)

- light foam, about 15cm²

- a pen

- wood glue

- superglue

- duct tape

- a bicycle pump

Step 1: Making the Wingparts

Folow for each wing the above instructions and cut these shapes out of the balsa slats. Remember: you have to do this 2 times!

First we have a 350mm slat which is the base of the wing. Next is a 300mm slat for the end of the wing. There are also 2 small pieces which keep the two parts in the correct position and function as stability.

Step 2: Assembling the Wings

Glue the small triangle-shaped part on the 350mm slat, about 50mm from the edge (at the side where the second hole is 30mm from the edge), this is the side we are going to attach to the second part of the wing. Be sure to use wood glue.

Now we can attach the second part of the wing with a piece of balsa stick (about 10mm) through both slats secondary holes.

Finnaly glue the second small piece on the triangle piece throught the stich as show on the picture. Now the end part of the wing is sandwiched between the base part and de small piece. The triangle piece keeps the wing at a fixed angle.

Step 3: Making the Top

Cut one of the PET bottles in half and cut small pieces as show on the picture. Be sure to do this symmetrical on the other side as well. The right rectangle is where the wings will be attached. Put a hole above and below the rectangle. The left rectangle is where we will be able to fold the wings into. Check with the angle of your wings where exactly this should be.

Step 4: Attaching the Wings

Put the base of each wing through the front rectangles and attach them with a small piece of balsa stick (about 20mm) both through the hole in the bottle as through the secondary holes of the wings.

Step 5: Adding the Fabric

Cut a shape similar to the shape in the picture out of your fabric (do this for the other wing as well). Be sure to leave some room for the hinge. Now glue the fabric with superglue to the wings. Add some duct tape for extra firmness.

When you're finished put a balsa stick (about the lenght as the diameter of your PET bottle) through the back of the half bottle and attach it with a rubber band to the primary holes of the wings. This will help opening the wings in the future.

Step 6: Making the Opening Mechanism

If we want our plane to be able to open its wings mid-flight we have to build a mechanism which is able to take care of that. First cut a cork in half and put a metal hook through it. Be sure the hook has a circular end. Add a small top piece of a pen between the cork and the end of the hook.

*Optional: You can add a small piece of plastic to make it spin more smooth.*

Now put the cork in the bottle and attach a rubber band between the hook and the stick at the end of the bottle.

Attach a small string to the ends of the wings (through the only hole wich hasn't been used yet) and put it through the end of the hook. This will wind up during flight and open the wings.

Step 7: Adding Fins

Offcourse every water rocket has fins to stay on course during flight. Cut out of your foam three fins, the shape doesn't really matter just make it about the size of the fins on the picture. Attach them on a 120° angle from eachother to the back of the second bottle.

Step 8: Launch Valve

Just as every other water rocket cut a cork in halve and put an old bicycle valve through it. Now put it in the second bottle.

Step 9: Launch!

Now put the top bottle on the back of the second one and your plane/rocket is finished! To launch fill the second bottle for 1/3th with water put the cork on it and attach the valve to a bicycle pump. Fold the wings in the bottle, fill the second bottle with air untill it launches and watch it fly away. Be sure to put your wet pants on!