Lift

I will be using a Tecumseh 10 or 13 HP vertical shaft motor with a Multi-fan lift fan. The fan will be 26" in diameter which is standard for a 12T4. I decided to use the Multi-fan as the blades are replaceable and I have enough to build without adding a wooden lift prop to the list.
The duct is generally cut to shape but I will have to cut it to fit into the hull and shape the inlet. This is likely the next big step in the build process.
Peter Tew made the lift motor mount for me. He has made quite a few for other hovercrafters and they are professional looking. Talk to him if you need one as he does EXCELLENT work. Thanks Peter!!!
June 8, 2002. I made a hole cutting hotwire bow and cut out the lift duct hole. Chris Keirs, being a PhD, was in charge of the math issues. Based on his calculations, we made a foam block with a 15 deg slope to use to drill the center hole with a very long drill bit. Then we forced the 3/4 tube of the hotwire bow through the hole (hole was 5/8") and attached the cross wood of the bow to the bottom to make the cuts. We used a saw to make a slot for the hotwire. Then did the cut with the hotwire. We also needed the saw to cut through the epoxy between the hull quarters (Chris shown with the fine detail saw...). It came out ok.
The hotwire was not without excitement. The hole bow was much shorter than the 7' bow I used for the foam blocks. I did not take this into account and used the same voltage. Well...we were rather surprised to see a "thermal event with visual indications" which is to say we set the foam on fire. Poor form. I put it out with my hand (leather gloves on). Experience is what you get when you don't get what you want. We are now more experienced.... Does not look too bad and will get filled in with the two part foam so no big deal. But it was a surprise.
Duct tacked into place with foam-in-the-can. I will use the two part foam to finish filling in the space as the two part foam sands and the can foam does not. The 2nd picture shows how I am holding up the duct with pieces of foam until the spray foam cures. I will eventually use a hotwire to shape the bottom of the duct to match the bottom of the hull.
June 12, 2002. HC flipped over and the lift duct starting to be shaped on the bottom. Used a saw and hotwire cutter to shape to this point. Will use two part foam to fill in gaps then it will be sanded to final shape. I made two small filler pieces to use at the sides of the duct to save on the two-part foam.
June 13, 2002. Did the ramp today. This allows air from the duct to move into the plenum freely and helps prevent splashing the fan/engine when going slow. I used the 7' hotwire and stood inside the duct to make the two cuts. I could not cut through the epoxy with the hotwire so a saw was pressed into service. I still need to fill around the duct with foam.
March 28, 2003. Cut the lift duct to size. Made two hot wire guides with 1/4 MDF. They were 4' long and cut to a 15 degree angle. The height of the guide at 4' was 12 7/8". 2x4s were used to stabilize the guides and each side had a screw that went into the duct to keep the alignment correct during the cut. The 7' hot wire bow was used to do the cut.
March 30, 2003. Shaped the lift duct. I tried just sanding it with a shaped tool but that just made a mess. Then I made a hotwire fixture which worked once adjusted correctly. After the basic shape was achieved I used dry wall sandpaper to smooth it out. The gaps are where the hotwire was not adjusted correctly. I will fill it with thickened epoxy. I also need to cut in the wood mounts for the lift engine mount.
Picture is the wood fixture used to check the curve. It is a 3.5" quarter circle. The minimum curve should be about 12% of the duct size which works out to be about 3.2". The 2nd picture is me with the hotwire fixture.
April 13, 2003. Went to Rob Tilton's house and balanced the prop and picked up the lift fan. Rob made the lift fan - thanks Rob!
April 20, 2003. Cut the slots in the lift duct to mount the engine mount boards. I will embed boards into the surface of the deck and the front of the engine mount boards will be bolted to them to transfer the weight and torque of the motor to the deck.