Hull

This is the hovercraft web site for Howard Boyle

July 1, 2003. The truck delivered the foam. You can see how UH packages it. One sheet got somewhat beat up but I ordered an extra sheet so I should be ok. The plywood is quite nice looking stuff.
Here is the foam in the garage. I really don't know how I am going to build it in here.
June 24, 2003. Mark and Chris helping to shave the 2x4x20' lumber into attach strips. The plans only call for one 2x4x20 but I made two of everything just in case one brakes during the build process. We created an amazing amount of saw dust. The 2nd picture does not do it justice.
June 27, 2003. Made a bender for the bottom skirt attach strips. They are treated wood and are too stiff to bend all at once. Got the idea from the pictures of Zach Bell and his 18SP. 2nd picture taken July 1. It is getter closer to the proper shape.
July 8, 2003. Wood bent pretty much to the final shape now. Thanks for the idea Zach! Now to get to the point that I need the attach strips....
July 10 - 11, 2003. Lane and I put the joist hangers on the 2x12s and Chris and I assembled the work table for the hull. I needed a flat and level surface to glue together the hull foam. Zach Bell used a fire house floor but I was fresh out of fire house floors so ... the table was built. We used 12" x 18' engineered I beams with 2" x 12" wood end headers. The feet are 4x4s and the whole table was leveled for my garage floor which is anything but level. It is a BIG strong table. That is Chris Keirs sitting on the end of the table. I had my doubts about the table so Chris did a jig on top to prove it was strong. It was worth seeing....
Here is the hull foam on the table. The foam was 1.5" wider and 2" longer than it said. This is great as I do not need to glue on a small piece of foam for the nose now. Kind of odd that it is not the proper size however.
July 12 - 13, 2003. Here we are laying out the hull shape using a piece of wood. I marked a few of the hull points on the foam and used the wood to give it a smooth shape. We decided to epoxy the foam together and then cut the hull out as it seemed easier.
Chris and I started to epoxy the foam sheets together. Since there was only the two of us we turned to technology. No that is not my wife's mixer! We purchased the mixer for the project. It worked great. Chris would mix a large batch and I would spread it with a paint roller. We went through 2.5 gal of epoxy. The plans said we should use 1 gal? Well what can I say? Now I have to order more epoxy for the plywood. We then taped up the vacuum bag and connected the vacuum pump. We were getting about 350 lbs on the bathroom scale inside the bag. Not too bad.
Lane came over Sunday and helped cut the hull to shape. We used a Sawzall blade cut down to fit the jig saw (thanks for the idea Zach). It was a challenge to cut it with the space I had but we got it done. Now I have to sand the sides flat.
Alas poor jigsaw, I knew it well.... The saw finally gave up the jig, so to speak, from cutting the hull foam. It was a 25 yr + old saw. That is smoke coming out of the top of it. Use the full resolution to see it. 2nd picture is me sanding the edges flat for the skirt attach strips. Made the sander from two pieces of 1x6 with stick-on sand paper.
July 14-15, 2003. Used epoxy to glue the side and back skirt attach strips onto the hull. The plans call for this to be done after the top is contoured but it would be harder to clamp the wood to the hull so we glued it on first. Pictures show the straps and clamps. We used 26 clamps.
This picture shows the bow of the hull. The right side was done last night and the left side was glued tonight. The side strips were also held in position by long screws. We coated the screws with soap to keep them from getting glued into the hull permanently. Thanks Lane for the help!
July 16, 2003. Added the top side wood strips (they were a pain to do) and rough shaped the top. The plans were not real clear on how to cut the foam to shape the top so I hope I got it right. Chris Keirs came up with a timely geometric solution. Thanks Chris! All the side attach strips are treated wood.
July 17, 2003. Lane, Mark and Chris came over to help vacuum bag the plywood onto the hull. The vacuum bag was not very good and we only got about 270 lbs of pressure on the scale this time. We clearly had some big leaks. However we were committed at that point so what do you do? It will be ok but I may have some minor fill work to do at the curve to flat portion of the hull. If I ever do this again, I will not taper the sides of the hull.
July 18, 2003. Chris and I scribed the ellipse to cut the hole for the lift duct. We used a sawzall and a 30 degree fixture to make the actual cut. I left the plug in so I can still vacuum bag the bottom this weekend.
July 19-23, 2003. Cut the foam plow plane foam and the plywood reinforcement that fits on top of the foam. It was quite a pain to do. I epoxy coated the wood to help with waterproofing. Chris and I then vacuum bagged the hull.
Here I am patching up the small leaks in the seams. We were getting over 370 lbs on the bathroom scale so I turned it down to 340. Not bad!!! I did not take a picture as I was way too busy but I also inserted the rear skirt attach strip into a slot in the bottom of the hull.
July 26-27, 2003. I did not take a picture of just the foam plow planes but I am now putting on the bottom skirt attach strips. This task was made much easier by pre-bending them as shown above. Even then it required some pushing and shoving to get the tapered end to bend into shape. I drilled 1/4" holes through the attach strips and 1/8" plywood top and used 1/4" dowels coated in epoxy to hold the strips into position. You can see the rear attach strip imbedded in the hull. You can also see that I used carbon fiber cloth to reinforce the engine mount backing plywood. Terrence Tousignant indicated his engine mount supports flex during operation so I am beefing that portion of the design up some.
As there were some small gaps between the bottom of the attach strips and the plywood, I used an epoxy mix with cut fiber to fill any gaps that might have been present. I then vacuum bagged the hull so the attach strips were forced against the plywood. It worked well and that should be the last time I need to vacuum bag the hull. There is a small gap between the front ends of the attach strips that I will fill with a shaped piece of wood like on Ken Robert's craft.
July 28, 2003. Rough cut the plow planes using a hand saw and 1/2" wood guide. Worked ok and was faster than using a hot wire. I was concerned the hot wire would bog down with the epoxy joints. Now to sand them smooth.
Aug. 5-6, 2003. The bottom is sanded and I am taping the seams with 3" 5.5 oz carbon fiber tape and a layer of 3" 3.8 oz tight weave fiberglass. I doubt the carbon fiber is needed but it is 3x stronger than the same weight fiberglass. The wax paper over the fiberglass is used to give a smooth finish when the epoxy is cured.
Aug. 7-10, 2003. Finished taping the bottom wood seams (kind of a pain to do) and flipped it over to work on the lift duct. This is a pretty heavy hull! The foam is 2.5 lbs/cu ft. vs. 1lb/cu ft. foam that I used for the 15T4. Lane and Rhonda Crampton, Joe Arrambide, Ken Jansen, my neighbor Rick and my wife all helped take it out of the garage, flip it over, and put it back on the table. Thanks!!!!
The instructions said to put fiberglass under each of the seams on the decking. I used carbon fiber tape between the foam and deck and on top of the deck. Should add quite a bit of stiffness. Also, I cut the lift hole before I put the plow planes on the bottom. I covered the areas of the foam that would be cut out with wax paper so the plow plane foam would not get glued on. This should make it easier to do the final cuts through the plow plane foam and wood as I can see what I am doing.
Aug. 18, 2003. To help prevent the rear skirt attach strip form coming loose if it gets hit, I added 5 5/16" dowel rods 5" long into the foam along the back and 1/4" dowel rods through the corners to attach the rear and side skirt attach strips. This should make it far more tolerant of a sheer force. I used a mixture of epoxy/fumed silica & cut fibers to glue them in.
Rob Tilton is making the 60" thrust duct. Looks like it is almost finished. Very nice - Thanks Rob!!! The blue rectangle is a UH-6F that Rob is also building. The 6F is 3' by 6' to give a size comparison. Last picture is the duct and lift fan.
OCT 1, 2003. Based on Terry's comments, I have added reinforcements to the bottom section of the hull between the engine mount and the cockpit. The trick is to add stiffness without too much weight.
Terry indicated he is getting some deflection in that area during operations. The wood I used is 1"x2" oak. It is glued on to the foam with epoxy mixed with cut fibers. It was weighted down to eliminate gaps to the extent I could.
I then glassed the wood to the foam using one layer of 10oz carbon fiber and a 6 oz layer of fiberglass tape on top of the carbon. I used wax paper to help smooth out the joints.
The first picture is taken from the rear of the craft and you can see the four engine mount reinforcements. They are 6" x 6" solid wood instead of plywood as called out in the plans. The second picture shows the front landing skids.
These pictures show the bow of the hull with the wood reinforcement I added to the front. I figured the bow would take a bit of abuse getting out of the water and the like during operation. The wood would protect the foam somewhat. It is glued on with epoxy and cut fibers and then fiberglassed to the foam. I stole the basic idea from Ken Roberts.
This shows the fiberglass over the foam joints. Bob Zang said to fiberglass ALL seams. Don't ask him for advice as he will make you do more work!!! The bottom is finished except for sanding & painting. I am going to use a primer that locks out water (so it says) and then use an exterior latex paint.
OCT 7, 2003. Well, I thought I was done. It turns out I needed to make slots for the wing spar strap to go through the skirt attach strip. And, the landing skid is also located where the strap needs to go. So, I had to cut a 2" wide slot through both the skirt attach strip and landing skids on both sides of the hull. I ended up drilling holes with a real long bit, then some small wood chisels and lastly a sawzall to make the slot. Kind of a pain to do. It pays to plan ahead.....
OCT 8. 2003. Made the other slot and tested the web strap. Got the strap at Harbor Freight for $8.00. It is supposed to be good for 8500 lbs!
OCT 12, 2003. Added a section of 1/8" plywood to the bottom under where the wing strap will go to help keep the holes for the strap clamps from making bigger holes in the foam due to movement/vibration. I also added a small piece of Kevlar to the sides where the web strap will pass over the foam sides. I don't know if the Kevlar was necessary but I really do not want to have to fix the bottom later if the strap digs into the foam during use.
OCT 22-24, 2003. The bottom is now painted with two coats of water block primer and I added the aluminum skid plates. The skid plates are made from 2" wide aluminum strips.
OCT 29, 2003. Lane, Chris, Ken, Joe and my oldest son Mike came over to help me flip the hull so I can work on the top. This is a pretty heavy hull now. We flipped it and put it on furniture dollies I purchased at Harbor Freight. Now I can roll it in and out of the garage by my self. Thanks everyone! Chris, Mike and my youngest son Billy helped cut up the table that I used to support the craft while I worked on the hull. It was a very nice table made from engineered beams and plywood. Oh well.