The Foam I use is the heaviest I could get. It's polystyrene with a weight of 35 kg / M³. You do the converting yourself. I think it's ± 2.18 lbs/Ft³. It is a 100% closed structure and will never absorb moist. The size per block is 157" X 48" X 10". Some gluing and the hull was almost ready !
If you walk careful over it, it will not leave a mark or dent. This foam is used in road construction as the base to build a road on top. I saw big fully loaded sand trucks drive over it to dump the sand on it.
Here they are I had five of them.
In the back you'll see the big blocks of foam, I had 5 of them. Down here is my first glue action. Those straps give a lot of pressure, I could play guitar on them when on full tension.
I kept the whole thing together with straps again to let cure the spray polyurethane foam, otherwise it would push the four parts apart.
To make the duct I First had to glue two pieces together to get the right thickness about 20" (50 cm). The lower two parts (left pic.) are the duct to be, the rest is to get pressure with 2X4 between the ceiling and the floor (right pic.).
I made a stand to hotwire the block of foam, clamped the hotwire to it and started turning the block, you can see for yourself. IT WORKED !
↑ Left some material to
make a flat underside
Rough cut parts stacked to give the first outline. The "duct" you see is a leftover from the real one, just gave me an idea how it looks. It's BIG on my attic.
After some gluing and cutting it looks like this.
How I made the lift duct.
Left: The guide. I had to make a guide to make the center hole for the hotwire. It was just a piece of pipe glued in a piece of wood, but exactly under the right angle (10° forward and 90° sideways) in the right spot. Fixed the wood to the foam with screws
Right above and under: Heated a thinner pipe with a soldering torch and melted the hole trough the guide, sorry no pic. from above.
Left above: After the heated pipe fell trough, the guide was smoking.
Right above: I was happy to see that it came out at the right spot, look at the center line!
Left above: Squeezed a pipe in the hole and made some arms on it for the wire. Made the arms longer to get a better hold turning it.
Bottom: Turned the hotwire around till the "plug" fell trough.
It relieved the hull ± 25 lbs. It's upside down here.
Cutting the inside of the duct was just like the outside. Set the whole thing up. Drill a hole through the duct on roughly the edge of the inside. Somehow get your hotwire through and tension the hotwire bow. Heat-up the wire and start turning the block of foam.
Ok, after I did all of this, I glued it back in and made a smaller hole.
Same trick just smaller, about 4". This is after I decided (and ordered) a smaller lift fan.
Next was the task of making a nice rounded edge. After some trying and
finding out that a lot of sanding was inevitable, I made a rough shape from thick copper wire
and stuck it in my electric soldering gun. Hey presto, it worked!!
The left picture is after a few minutes sanding. Odd shaped cutters I used for all sorts of jobs.
Here are two of my Foam-monkeys working there butt of to get a beer!
They are the BBB-group (beer-burgers and building) one evening a week. Mostly it's a nice glass of wine and a lot of fun. Both are quite handy and are over twenty year old friends.
Rudder Time
I stole a shape from the internet and printed
it. Glued it on to some wood and cut that out.
Glued the airfoil shapes on to the foam and a hotwire cutter did the rest.
I put some strengthening in the flimsy thin foam. The groove is made with soldering gun, look above, it has the "U" cutter still in it.
↓ Here you see how it worked out with the elevator
Ok, fill the slots where the metal work sits with "foam in the can". Than some sanding and cutting of the glass weave, epoxy, vacuum bag. Ready !!
This is the first try-out: DON'T TOUCH IT !! It hangs just on spit and a prayer.
How it all connects, pivots, hangs and moves is on the "Steel-page" next week!
Now the bottom
Cutting the plow plane was straight forward, I just had to draw the lines where to cut and fix the aluminum strips. I use these strips as rulers to make a nice straight cut. I screw them on with long thin screws.
Cutting the hollow part in the bottom was a thing on it's own.
First I tried to make a big hotwire to cut out all of the foam in once. That did not work, due to the fact that the wire would bend and just was not stiff enough. Than I made a smaller wire that would cut 1/3 of what was needed. This means I had to cut 3 times, two sloping sides and the middle leftover. The result was again some sanding and a nice "plenum" as some call it.
Tack strips
With my soldering gun we made two grooves in the foam. One for the upper/outer attachment and one for the under/inner attachment. Easy, but took some time.
The bottom two left metal colored cutters where used (see above soldering gun picture). Some sanding and I used epoxy to glue the wooden pieces in place. Next time I would use PU glue. I have the feeling that it fills the voids better and if it squeezes out I know there is enough glue. I'm not going to use the strips to attach my skirt directly. In the future I'll attach the Poly-fastener strip on the wood. More about that on the skirt page.
The left shows the gluing and you can see that all the stuff is in place to apply tension when ready with that. The right one is drying/hardening of the epoxy.
Done !! for now.
Inside the duct I need some extra stiffening. Not only that but I like the sight of flow straightners and I'm convinced that they work. (all the racers use them not for the show). There is some calculating and figuring out to do before you can start making these. The wrong shape will cause you to loose thrust and create more noise.
Like the rudders I made drawings of the shapes for the inside/cone and the outside/duct of the straigtners. Glued them on wood, jig sawed, sand them and glued them on foam. Cut the rough shapes and more sanding made it perfect.
Now I needed a cone in the center, actually I needed two. One in front of the fan and one behind. The one behind would serve as a center point to hold the straightners. I made one big round bomb shaped piece of foam and glassed/vacuumed it.
This I cut in two and now I have two perfect aligned cones to sandwich the fan in !! (forgot to take a pict)
The pointed cone is fitted with the straightners and the front round one will be worked on later.
A few pics back you all saw the underside of the hull allmost ready, well it was time to get the whole thing glassed this was a major undertaking. The size of the thing was worth some extra planning and an extra saturday morning.
After preparing the glass and the pots and pans with rollers, brushes etc. etc. we pre-made the vacuum bag with all the breathers and peelply and seams.
THIS WAS THE RESULT:
NOW I KNOW I'M MAKING A MESS of the chronological order of it all and I should have put some of the pics from the Epopxy page here but, I'm an amateur and a hovercraft builder not a websitebuilder.
OK !!
The solid hull was all glassed and the loose parts, to create the cockpit, where all made and fitted more or less. Under here you will see the "before and after" pics of the making of the cockpit.
Finaly it's looking like a Hovercraft
There are more pics on the epoxy-page
Making the lift fan duct diameter smaller.
Along the way I found out that the diameter was just a hair too big. What to do ?? I had the whole inside done and at the circle where the fan was rotating, I overlapped the glass for extra safety and strength. More glass or thick filler is not what I wanted. I decided that a thin layer of foam would do the job so I cut a 0.12" slab of foam and glued that in. I will just "paint" it with a real thin layer of epoxy-filler and let it be. No glass, so in case of a strike I hope I will not have major damage to my duct. Of coarse the foam needed some persuasion to get in to shape.
more to come