Introduction: DIY Human Powered Wooden Hydrofoil - the "Hydrothopter"
Behold! The HYDROTHOPTER!
The human powered hydrofoil you can build yourself.
It's made from mother nature's favorite material, WOOD!
As seen in Fly a Human Powered Hydrofoil, this amazing thing will be bigger than the Segway and the Internet put together!
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Click on this picture to see a movie of the hydrothopter's maiden voyage.
Step 1: Anatomy of the Hydrothopter
There's a big purple MAIN WING in back that does most of the work.
Two UPRIGHTS connect it to the CROSSBEAM.
Four FRAME STICKS connect that to the FORK with two HINGE LASHINGS at the EYEBOLT and HANDLEBAR.
At the very front of the machine is the SURFACE FEELER, a wooden disk that skips a long the surface of the water. It's bolted to the FRONT STRUT and sets the angle of attack of the FRONT WING, also called the CANARD WING.
Step 2: Parts
I painted these wooden parts with epoxy then put them out here in the sun to heat up and cure.
In the lower left are the two UPRIGHTS.
To the right is the HANDLEBAR.
In back is the CROSSBEAM, with the nails still sticking out of it from gluing it together.
Resting on the nails are the STRUT, FRONT WING, and SURFACE FEELER.
Step 3: Crossbeam
The crossbeam is 41.5" long, not counting the tenons. A regular 2x4 would have been stiff enough.
I'd planned to have two small ash crossbeams, but they turned out to be too wiggly.
So I boxed them together with thin birch plywood and epoxy.
I thickened the epoxy with beltsander dust from the dustcatcher. I used a few copper nails to hold the ash parts together. When I epoxied the plywood on I used lots of little nails that I pulled out after the glue set.
I'd planned to dowel them together with bamboo skewers.
The bamboo split when I pounded them, so I switched to nails.
Step 4: Main Wing
This MAIN WING is 87.25" long, 5.5" wide, 0.717" thick, which is approx 13% of chord.
The bolt holes to attach it to the UPRIGHTS are 48" apart.
The foil section is a very crude approximation of the NACA 63013 section. I left the trailing edge square, truncating the section, just to make the trailing edge stronger. The bottom of this foil is mostly flat, also due to laziness. There are lots of foil sections that would work. Try them all.
Scroll down to see the data for Trampofoil and Aquaskipper wings.
I made this wing from a fir board. It was a shelf I had on hand.
It was about the right size, straight grained and knotless.
I drew foil shapes on the ends of the board and shaped it with full-length passes with an electric planer. I made some mistakes so the shape wasn't quite what I had in mind, but because of the full-length passes the section is pretty uniform from end to end. Having made tapered foils such as rudders and centerboards before I was amazed how fast it is to make an un-tapered foil. Joy.
After the planer I smoothed it with a disk sander then hand sanded it.
Then I sprayed it with quick-drying auto-body primer, let it dry, wet-sanded, and repeated a couple of times til it seemed smooth enough and sufficiently sealed. Then I sprayed it with purple spraypaint, also from an autoparts store.
The primer is a lot more important than the paint that goes over it. The topcoat paint dries a lot slower than the primer. Don't use any primer that doesn't say "fast drying".
Having made various wood, epoxy, and fiberglass boat parts, I was thrilled with not having to wait for epoxy to cure. That fast-drying autobody stuff is a revelation for boatwork. Definitely good. Finishing the wing took less than an hour, including waiting. Joy.
After having subjected the wing to much exposure to water and mechanical trauma, I'm pleased that the surface is still good. Although the paint has worn off at the edges and is scratched a fair bit, The grain hasn't risen any and there are no visible cracks appearing. I'll definitely use autobody methods to finish wings in the future.
Malin Dixon writes:
"The Trampofoil wing is about 12 cm chord, and about 1.5 cm thickness. The section is
asymmetrical, and it is slightly concave on the underside, from about halfway to near the
trailing edge. The span is about 280 cm. It is extruded, with little end bits that only add
about 3cm to the span each. The wing is hollow, but there isn't much hole in the middle as
the wall thickness of the extrusion is about 0.5cm. The front wing is a solid extrusion."
The Aquaskipper rear wing has 91" span plus some little plastic winglet caps
that add 4" or so at each end. the caps fall off and it doesn't seem to make any difference.
Chord is 4.75" and the section is 12.8 % of chord thick(.608"). The section is similar
to a 63010 scaled up to that thickness, but it has a bit of hollow in the tail.
I haven't found that section in the foil library yet. The wing is a hollow aluminum extrusion with a web down the middle. The front factory wing is solid aluminum. It is 2' span, 2.42" chord, 12% thick.
Here's a flatbed scan of end views of the Aquaskipper Main and Canard wings.
Following that are some airfoil plots of other sections my designer pals like to use.
Step 5: Uprights
The UPRIGHTS are ash wood, same as a hockey stick.
They are .95" thick and 5" chord. The foil is thus 19% thick.
How long are they?
It is 22.5" from the underside of the CROSSBEAM to the top surface of the MAIN WING.
The bottom end is left thick and is shaped to match the curved top surface of the wing. The top is ornamentally long like an antique saw or a Kenyan outrigger canoe.
Cut two mortises to mate with your crossbeam. At the bottom drill a vertical hole for the bolt through the wing. Drill a horizontal hole into that for the nut the bolt screws into. Just like an Ikea futon couch.
Don't worry about foil section. Make them blunt in front and taper to a thin square edge in back.
If you can't help yourself, here's a NACA 0018 section to look at.
Step 6: Front Fork and Handlebars
The front FORK is ash wood, 0.9" thick. It is 3.95" wide at the top where it tenons into the handlebars.
It is 66" long and tapers down to 2.25" wide at the bottom, where there is a slot and a bolt hole for the STRUT. 19" below the top of the handlebars is a hole for the EYEBOLT.
The FORK is springy about like a giant slalom ski, if that means anything to you.
Any downhill ski would work fine. I'll use one of those next time.
Step 7: Canard Assembly
The CANARD WING is maple, 25" long, 2.4" chord, .28" thick. See step 4 for foil section. Any 12% or 13% thick section that's strong enough would be fine.
It's bolted up into the STRUT with the same bolt-to-nut-in-cross-hole method as the main wing uses.
The STRUT is .72" thick plywood, 27.5" in the longest dimension. The vertical part has 3.9" chord and is shaped into a foil similar to the UPRIGHTS. It is 11" tall and is shaped to mate with the top of the CANARD WING.
The SURFACE FEELER is a 6" disk of plywood. When the canard wing is flat on the ground, it is 3" off the ground, inclined upward at a 5 degree angle.
Step 8: FRAME STICKS and Setup.
Using a plumb bob and level I set up my frame so the handle bars are 22.5" horizontally from the back edge of the CROSSBEAM and 32" vertically. I would prefer to have them a few inches higher. Next time maybe 35". I attached the FRAME STICKS to the CROSSBEAM with epoxy mixed with wood dust and some small bits of fiberglass cloth over that.
I attached them at the front to the EYEBOLT with a HINGE LASHING.
I did mine with some string covered with bicycle innertube.
Step 9: Top HINGE LASHING
Then I lashed on two more sticks with bicycle innertubes to complete the fame. I thought it was temporary but after some tests and more lashing it was good enough. Here it is after the rides you saw in the video.
As you can see, the lashing at the top is a bit strange. It sort of slipped into that configuration and works really well. There's cord around the thin part of the HANDLEBAR, and a big ball of innertube lashing around that between it and the top FRAME STICKS. This lets you steer and also move the HANDLEBARS up and down relative to the top FRAME STICKS.
Don't think too much about how you make this lashing, just do it. It'll naturally get itself into this condition.
Enjoy! Let me know how things go with your Hydrothopter project!
Step 10: Gabriel's Hydrothopter
Gabriel Benito Sobrino built one in Spain. It looks great! Soon he'll be soaring like an angel!!