Results of glue lam test

Checkout below to see the results of the glue lamination test.  

An example of filling in a patched corner.  It seems to work fine.

There's still some gaps between the foam, though it's still pretty sold.  More even weighting would also help this.

Keeping the edges aligned will be a problem.

Epoxy definitely doesn't fill in the gaps well.  It will need some filler. 

Carefully cut edges match up much better.

Another place where filler would help a lot. 

A good contrast between well cut edges and poorly cut edges.

More hovercraft news out of Russia

In Russia there's lots more excitement with respect to hovercrafts.  The largest hovercrafts in the world just show up on the beach in the summer!

There are lots of news sources covering this one little video
http://www.businessinsider.com/russian-hovercraft-on-beach-2013-8
http://www.telegraph.co.uk/news/newstopics/howaboutthat/10257870/Navy-hovercraft-surprises-sunbathers-as-it-lands-on-Russian-beach.html
http://gizmodo.com/giant-military-hovercraft-lands-on-crowded-beach-becaus-1178684399

To cite a few.

It appears to be a Zubr.  More info on wikipedia. 

First test of the epoxy

When Wim was here last night we also tried out gluing sheets of foam together with the epoxy from the Univeral Hovercraft Kit.

 


The epoxy provided is System Three two part epoxy.  We started out by getting the pumps setup.  Which is mostly inserting the right length tube at the end to get to the bottom of the bottle.  For the smaller one we had to cut one off by a few inches.

 

And few added some secondary containment shortly after deploying them. Since epoxy often can lead to a mess.

With the epoxy mixed we were ready to glue things together.  

We started with wax paper on the ground and layed down the 3 sheets of freshly cut foam with the new knife.  (The pattern I showed previously.  We cut a 3rd copy with the new knife in addition to the two previous ones I had cut. ) 

The very precise cuts were able to be glued on the sides well, but the cuts from previous iterations ended up with a noteable gap which the straight epoxy could not fill.  

 We built up three full layers all at once.  Just wetting the surface with epoxy seems to have done well.  We wetted the sides as well but I don't think it is holding much.

We left it to cure last night with a few weights on top.

 

This morning I took a quick peek before heading to work. It is amazingly solid but still super light.  

The first gluelam foam test

I'll look more closely as the result tomorrow, especially at the joints that I don't think are glued at all, but with the lamination it doesn't seem to matter much.

New knife blades from Bullet Tools

So in my previous posts I showed what I was able to do with the box cutters and that seemed to be reasonable.  However I felt there might be better solutions.  With a little bit of research I found that Bullet Tools has a line of products for cutting insulation.  Their Magnum Rigid Foam cutter looks like it would be very useful for large scale installers. But it's way too big for me to find useful.  However the 7" blades for utility knives looked like they might hit my requirements exactly.  They're designed for foam, and require no other infrastructure.  Though they do also mount in a reciprocating saw if I need to do some more bulk cutting.

Here some pictures of the blades.

The new razor blades as delivered.  

It's quite impressive when mounted in my utility knife handle.  It doesn't quite fold up for safety anymore. 

We  were able to successfully cut the foam very cleanly with the new knife.  See below for the example.

A successful cut.

The key we found to making a good cut was to take advantage of the length of the knife to keep it running straight and iterate in the same slot.  With the long blade you can hit the same line relatively well so as to not get parallel cuts.  This was even good enough to shave off 1/4" from the sides of the foam.

Cutting the foam with a good low angle of approach.

Our first attempt we scored the surface a little and then sawed through it with the blade almost perpendicular.  In the picture below you can see the issue was that the sawing motion drifted side to side leaving rough edges where the knife cut parallel to the original scoring.

What you get if you saw instead of slice.

PS Thanks to Wim for helping me with this.  Several of the fingers in the pictures are his.  And luckily despite the large and sharp knife all of his and mine are still attached.

BBC Covers 50th Anniversary of Trans Bristol Channel Hovercraft Trial

The route was Weston to Penarth 10 miles in 10 minutes. And landing on the beach.  It was the SRN2 sponsored by Castrol.

Unfortunately I can't embed the video, but you can watch it on the BBC's website.

Maxx Fan Teardown

Part of the "kit" I bought is a small reference to building ducting out of foam.  However, I know that good ducting can promote efficiency, but poor ducting will be detrimental.  And secondly, building a cowling out of foam seems like a risk for impact and safety.  In particular the propellers attached to the engines are a good approximation of a wooden baseball bat and if anything falls into the fans the pebble or other object will eject radially very fast.  And for that I'd like to have some good metal in the way.  As such I felt that finding a cowling on an existing fan would provide me with an easy way to get one shaped correctly as well as already having facing material for protecting fingers from the fan.  

After some online research I choose two models of Maxx Fan which were the right size for each of the fans on the hovercraft. One 24" model and one 36" model. 

36" Maxx Fan

24" Maxx Fan

They will fit the hovercraft propellers well: 

Large Fan with hovercraft propeller

Small fan with lift propeller

But to use them I need to tear them down so here's some interesting things I found. 

5/16" sheet metal screws holding the screen

With a few quick removals of screws around the perimeter I got the fan out.

The motor removed from the fan.

Here's the full assembly after removing the screws around the perimeter.

Attachment point to the back.

A few spade connectors got the power wiring disconnected from the switch and motor.  And a few screws on the back of the motor released the motor from the back screen.

Additional bracing internal to the fan.

There was also two struts attached to the front face of the motor and required one bolt to remove. 

The power cord snapped out of the housing with squeezing the appropriate tabs.

Removing the power cord

After which I found this neat removable clamp on the cable.  It first clamps onto the cable, then inserts into the housing.  To get it out of the housing press the 3 tabs on on the sides.  And then it can be released from the cable

A neat collar for passing through sheet metal 

Lastly I removed the main cowling from the stand.  It was just a single bolt with a hand nut.  And a large composite rubber lock washer.

Mounting free to rotate until tightened. 

Internal view of external mounting. 

Actual progress, using real tools

This weekend marked a great occasion; I started real work on the hovercraft!

I picked up some foam to use for practice cutting and to verify that I can cut with the precision I want to be able to make the hovercraft.  The main foam I have is 2" thick "rigid insulation" according to Home Depot.  I was able to pick up some small squares of 1" foam which fit in my car more easily.

I turned one of them into a scale model of what I'm thinking of building for the hovercraft. You can see the two model layers at 1/6th scale.

Scaled layouts for the glue-lam foam layers

The main vehicle will be 3 layers like this.  And I'm planning to stick to the very easy to build size of 6'x12' which means that I just need to split a few sheets of foam in one cut.

Upcoming will be to determine a good way to cut the through hole for the lift fan.  Also I will need to experiment with gluing the foam and plywood.  I also picked up some small pieces of plywood for testing, as well as aluminum angle iron.

In doing the above I started exploring cutting techniques.  I've got lots of pictures below with descriptions.


Here's some of the cutting techniques I explored.  

I read online that sharpening a putty knife works well.  I ran into this Flush Cut Pull Saw which has the same properties of being a flat piece of metal and not tapered which is better for cutting deep into the foam.  However you can see below that the blade made a mess of cutting.  The teeth all dug in and created lots of

Messy cutting with a pull blade saw. 

Lots of detritous

Next I broke out the box cutter.

Cutting with a dull box cutter

As can be seen in the photo the dull box cutter did even worse.  But as anyone who's worked with box cutters/exactos on foam core knows being sharp is critical, and does not last.  So I changed the blade.

Cutting with a sharp razor.

Cutting with the sharp razor was much more effective. I was able to get good clean cuts and with a little practice I was able to get quite clean edges.

Early attempts at cutting with the razor.  

A good clean cut with using a razor. 

So it looks like I'll plan to use the razor/box cutter approach.  These pieces are 1" thick not 2" thick.  I think if I am good about cutting from both sides vertically it will work pretty well.  And I'll look at getting some slightly longer blades too.

I chose to avoid the hot wire/hot knives as they tend to produce a lot of fumes etc, and I expect they actually take longer than a good blade.

Of course if I was going to be doing a lot of this.  There's a really good product from Bullet Tool the Magnum Rigid Foam Cutter