Intro: Hover Sled 1.0
Some time ago, I saw someone, somewhere floating about on a homemade hovercraft, slapped together with little more than a shower curtain, a piece of plywood and an old vacuum cleaner. This of course set me to thinking about how I could join the ranks of such bold aeronauts of the DIY persuasion. So, I naturally started reading up on the subject and scoured webpage after webpage. Finally I found one that spoke to me in both ease of construction, and in simple enough terms that would allow my mind to easily digest the concepts while allowing for my own improvising of design. The author, WilliamJ. Beaty appears to be a research engineer and as far as I can tell his design for the ULTRA-SIMPLEHOVERCREFT was created for a child’s science fair project. I won’t go into detail or rip off any of the pictures from his website out of respect and more importantly because I am lazy when it comes to displaying all my research.
One day while at Lowes I spotted some 7/16th roofing OSB that was on sale for nine dollars. I just couldn’t resist and ended up buying a piece. For deep within the recesses of my mind the dreams of sliding about on a personal hovercraft started to bubble forth into my consciousness. A small voice whispered to me, “It is time”, and before I knew what was going on, I was strapping a 4x8 piece of OSB to the top of my vehicle.
Step 1: Setting the Stage for Success, Let's Draw a Circle!
I am roughly following the plans for the ULTRA-SIMPLE HOVERCREFT. For manageability I cut the 4x8 piece of OSB in half so I would not be tripping over it in my garage. Here you see the piece up on saw horses. If you look closely you will see my failed attempt at drawing a circular pattern on the board so I could cut it down into a disk shape. On further inspection of this photo, particularly in the background you will notice that it is also trash night, and I still have left over flags from Memorial Day on the floor of my garage.
Because, and I must stress again that, I am lazy. I was all ready to engage my saber saw into cutting out this crudely drawn pattern on the OSB, when I started to feel a little pang of shame growing inside of me. Sure this is a crappy ghetto version of a hovercraft but I should at least have an ounce of self respect in making it appear as if some symmetry was involved with its construction. It then became clear to me that I needed a better way to draw a circle on to the OSB.
Step 2: Drawing a Circle Part Deux
I started by carefully measuring where the center of the OSB was and then drilled a ½ inch hole there.
Next I drilled two ½ inch holes in a scrap piece of wood. The distance apart being the radius of the circle, this was around 2 feet. I then secured one side of the scrap wood to the center hole of the OSB and dropped a purple crayon into the other hole.
I have to say that I was pleased with the results. I was left with a big fat purple line that my saber saw could easily follow. Unfortunately, by the time I had figured all of this out it was starting to get late so I decided to save the cutting for another day.
Step 3: Time to Start Cutting
The next day I went to work with my saber saw. Here you can see my semi-nicely cut disc which will be used to propel me ever skyward. I took the liberty of sanding the edges to make them somewhat smooth as not to tear any experimental skirt that I will be wrapping around it.
Additionally, I notched out the vent hole, where the air will enter the skirt. According to Beaty’s Ultra-Simple Hovercraft design, the vent hole is placed halfway between the center and the edge of the disc. I obliged him on this. While I was cutting this hole I started to think about the center hole. Beaty uses a bolt to hold the center of the skirt up close to the disc to create a doughnut shape. I wondered if, instead of using a bolt and nut, I instead used a small pipe and then screw a pressure gauge onto the pipe. This way I could get a pressure reading of the air under the skirt.
Step 4: Mounts
Moving on, I used a miter saw to cut out the mounts for the leaf blower power plant. I had toyed with the idea of boxing it up, but I wanted to make sure that all the air that it required would be delivered to it, so two mounts would do the trick and keep the weight down. I think I will add a small third one under the junction between the blower and the 90 degree elbow.
Step 5: Finshing the Mounts
One of the things that held my concern was how far the vent pipe would protrude from the bottom of the disc.
If I wanted the vent pipe to be secure against the disc I would need it to protrude at least a little from the bottom. To minimize this distance I used a PVC coupling that I cut down with the miter saw.
Once the vent pipe was installed I used a sort of woodworkers putty/glue to secure it into the hole.
Step 6: Considering the Skirt
I then started to consider the flimsy nature of the blue tarp skirt I would be using and decided I needed to protect it from ripping. To facilitate this I stapled some weatherstripping to the edge of the disc to protect the skirt from ripping along the jagged edge.
Next I drilled a hole though an old lid from a drywall Spackle bucket to act as the center support for the skirt. for measuring purposed a bolt was screwed into it and the center hole of the disc. Later, I plan to fasten it to the disc with a small pipe that will allow me to take pressure readings. Some may be puzzled as to what the lid is used for. This will act like a big washer holding the center of the skirt against the disc and allowing the air filled skirt to maintain a doughnut shape. The skirt will have strategically placed holes in it to allow air out to form a cushion of air. For now I am using this dirty lid to measure how far away from the center I will place the standoffs.
Step 7: The Standoffs
The vent pipe sticking out still had me concerned. Sure I could place the skirt over it and for the most part the whole thing would probably work, but I did not like the fact that something would be sticking out of the bottom and could possibly tear the skirt if I hit something. I needed something that would lift the disc off of the ground and still allow some flexibility for the skirt to be freely inflated. Something soft yet ridged. Something I can easily affix to the bottom of the disc. My solution was a pool noodle.
These things are cheap and have all the properties to fit my needs. I think I spent $1.99 on one at Target. What else can you buy for $1.99? I just needed to run some tests on how I could secure pieces of this to the bottom of the disc. I figured I can slice it down like a meatloaf into 2 inch thick pieces and then line the outer perimeter of the disc with them. I took a small slice and used epoxy to affix it to a scrap piece of OSB. I then placed a weight on top of it and let it sit overnight. The result was perfect. No matter how hard I tried I could not pull the noodle off of the OSB. I just need to slice the noodle down and get to gluing.
Step 8: Drawing More Circles
To start we needed to find the placement of the standoffs that we will be used. To accomplish this I pulled my trusty circle drawing stick from the trash that I had originally used to trace out a circle on the OSB sheet in the beginning of the project. I measured out a twenty inch radius and drilled a hole in the stick. This time around I used a yellow crayon for tracing. Ooooo pretty circle.
Next I roughly placed the standoffs along the yellow line.
Step 9: Glue and Wait
I then mixed up a generous portion of epoxy glue and started in on the gluing. Because this was quick setting stuff, five minutes I believe, I only squirted out enough to provide epoxy for two or three standoffs at a time. I would smear and glue, smear and glue, then mix more up. I did this about eight times until everything was glued on. The problem now was that I needed a way to apply pressure to all the standoffs to insure that they would not move at all and take hold. Luckily I still had the other half of the OSB sheet on hand. I placed this on top gently with the aid of my scoffing wife and then topped it off with a paving stone for added weight.
Twenty four hours later and everything appeared to be glued nicely. I was not able to remove any of the standoffs no matter how hard I twisted and turned them. I must admit that the picture made me think that I was assembling a gigantic escarpment wheel. Hmm, a neat idea for a future project?
Step 10: The Skirt
I have never played with cutting and shaping a plastic tarp, so this was a first for me. My apprehension stemmed mainly from me getting confounded easily over how to make a two dimensional cut on something that will be inflated into three dimensions. Rather than thinking about it too much, I just decided to dive in. So far I’ve had decent luck with that.
The main issue I had to tackle was how to get a hole in the plastic that would be strong enough that it would not rip the plastic when tugged around by the forces of movement and inflation. I tried two things. I cut the plastic with a razor and I also melted a hole with a soldering iron. The melting seemed to produce a better more durable hole in the plastic so I settled with that. I further reinforced the hole with a piece of Gorilla Tape on each side of the hole. Below is a picture of my test piece. I pulled and tugged and attempted to rip the hole and was not able to. So I think I have my method.
Finally, I laid out my 6x8 tarp and placed the disc on top of it. I then marked where my cuts and holes would go.
Step 11: More on the Skirt
Attaching the skirt went a lot smoother then I had imagined. I used both a soldering iron and a razor blade to cut/melt the holes that I needed. I then reinforced those holes with plenty of Gorilla Tape to insure that the tarp would not rip along any of my cuts. As stated before, I took my time and made sure everything went as smoothly as possible. In the end I was rewarded with a speedy process and holes cut exactly where I wanted them.
Next I needed to secure the skirt to the center of the disc to insure a doughnut like shape. I used the top of an old Spackling container as a sort of giant washer to take some of the wear off of the skirt when inflated. Also, I was able to find a small ½ inch threaded pipe to secure it all together while allowing for pressure measurements top side.
Step 12: Up on the Top Side
Up on the top side I threaded the ½ inch pipe onto a stainless steel T, with one end plugged up and the other going into a gauge that reads PSI.
Next I had to tape and staple the skirt around the edges of the disc. I first pulled the skirt taunt and then placed a small piece of Gorilla Tape on the tarp to hold it to the wood. I then stapled through this to hold things permanently. I made sure that every staple went through both tape and tarp. There had to be a layer of Gorilla Tape on top first to insure nothing would rip. The end result was like a billion staples and about a quarter of a big roll of Gorilla Tape. Yeah I know it looks trashy, but what the hell, it was holding :P
Step 13: Mounting Everything
No thought went into what would hold the power plant onto the craft so I ended up using pull ties attached to an L bracket secured to one of the mounts. I also used a scrap piece of foam on one of the mounts to cut down on the vibrations caused by the running engine and then used Gorilla Tape to tape the 90 degree vent to the output of the blower. This was all sort of slapped together since I was getting anxious to try things it out.
Step 14: The Test Flight
Complete details of construction at Zero Sum Hacking
The attached video pretty much shows the life cycle of the construction, a brief test flight and some analysis at the end. Enjoy!