My UH12R : Lift System

Construction of the Lift System

First off, I'd like y'all to know that I dropped the ball in documenting the construction of the skirt and for that, I'm sorry. I thought I had taken more pictures but got caught up in the construction process and simply forgot and so this section won't be as complete as I'd like it. This is the only picture I took of the actual construction process.

The skirt was constructed from about 8 running yards of 18 oz/sq yd vinyl coated nylon 60" wide. The material was cut into two 30" wide strips. One 30" wide strip made up the right side and rear skirts and the other made up the left side and front skirts. The plans provided a template for the shape of the seam on the front corners and the rear corners. I copied each template onto a piece of card stock and used it to draw the seam location on the skirt material with a yellow marker which can't be seen in this picture. This picture was taken after the rear corner of the right side skirt had been marked and cut. The white template is in the position of a yellow line that shows where the actual seam will be. The excess 1.5" to the left is where the seam will be glued with the back skirt. The material on the far left is scrap that was removed. When two seams are mated (like the side skirt seam and rear skirt seam) and then turned inside-out (outside-in actually), the result is a curved corner. Since there are 4 corners on the craft, 8 of these seams had to be cut and joined with their counterparts. Each of the 4 skirt panels have seams on each end. The side panels have a rear seam on one end (the rear) and a front seam on the other (the front). The rear panel has a rear seam on each end (mating with the rear of seams of the side skirts) and the front panel has a front seam on each end (mating with the front seams of the side skirts).

The rest of the construction process involved adding lengths of material to the top or bottom of the skirt panels to allow the skirt to reach areas of the hull not normally in direct contact with the skirt. Examples would be a 3" extension of the bottom of the front skirt to reach the air splitter in the lift duct and a 3" extension of the bottom of the rear skirt to accommodate the step. One other extension that wasn't documented in the plans but is a good idea is an 8" extension to the top of the front skirt to accommodate the rise in the hull at the nose.
After constructing the skirt, I laid it out beneath the craft (which you can't really see in this shot but it's hanging above.
I then used thumbtacks to temporarily attach the skirt in its position on the skirt attach strips first on the outside...
...and then on the inside. You can see in this shot where the extra 3" of material are made useful to accomodate the step in the bottom-rear.
After I felt comfortable with the position of the skirt on the attach strips, I wrapped 1" of skirt material around a 3/8" diameter nylon cord and drove a 5/8" #6 screw (and washer) through the material and cord and into the attach strip every 4" starting at the outside rear...
...along the outside sides...
...and then around the front Notice in this shot that the skirt has been extended several inches at the top to accommodate the rise of the nose. I did this to ensure that the contact line of the skirt to the ground was even and level all around.
I then did the same thing on the bottom (inside) attach strips starting from the rear and working forward. Since the hull curves in toward the center of the craft at the front, there was too much material on the inside which had to be overlapped upon itself to take up the slack.
After I screwed the skirt to the rear and sides, I attached it to the front and air splitter as shown in this picture. Notice again how an extra 3" of skirt material comes in handy to reach the air splitter.
This is what the 12R looks like with the skirt attached and hanging from the ceiling over my car. Reminds me a little of a nesting hen or something.

To better assist me in removing wrinkles from the skirt, I placed a small blower fan in front of the lift fan splitter, sealed around the edges of it, and inflated the skirt. These 4 photos show how the skirt looked before adjusting for wrinkles.

After the skirt was fitted, it came time to finish the lift fan which came from UH rather rough. Finishing involved sanding the fan smoothe, glassing it, and balancing it which is what each of the photos represents. Balancing was accomplished by leveling 2 rails and inserting a spindle through the fan and placing it on the rails. The spindle consisted of 2 1/2" ID/1" OD locking collars locked to a 1/2 bolt. The fan is considered balanced when it can be placed at rotation on the spindle and not start spinning on its own. In the case of this fan, balancing required a heavy 2" washer to be bolted and epoxied to the hub at the root of one of the blades (not shown).
After the fan was complete, it was time to install the lift engine. This was accomplished by reinserting one of the plywood disks that was originally used to form the duct. The fan hub with bushing were bolted to the center of the disk. The 1/8" steel mounting brackets were then positioned temporarily against the wood mount approximately where the engine bolt holes would line up. The engine in this photo is suspended from the pulley system I used to hoist the craft to the ceiling.
The lift engine was then lowered down and the shaft was mated with the hub (temporarily) to find the center position of the engine. The engine to 1/8" steel mount holes were marked as were the 1/8 steel to wood mount holes (8 holes total). The whole works was removed and the mounts were drilled.
The 1/8" steel mounts were then bolted to the hull and the engine was bolted to the mounts. Finally, the fan was fitted to the shaft of the engine and locked on. If this were a perfect world, that would have been the end of it, but Murphy's Law required the alignment to be off slightly and so I had to auger out the holes on the steel mounts to allow fine adjustment of the engine. Also, as long as I'm complaining, the fan bolts were practically inaccessible. The photo to the right shows the angle at which the lift engine is mounted. Pretty steep.

Finally I got to test the lift system! It started up easily enough and I made sure that the fan didn't contact the edge of the duct. I slowly brought the throttle up and the skirt started making the most gawd-awful flapping noise you've ever heard and was vibrating wildly. I expected 'skirt flutter' to happen but wasn't expecting it to be quite so violent. I shut the engine down to idle and was able to push it around the garage with very little effort. After I was happy with everything and ensured the spectators that the flapping was normal for hard surfaces, I loaded the ma-in-law up and pushed her around the driveway and spun her around in circles... well, SHE had fun. :-)

Next it was the pa-in-law's turn and then my turn with the pa-in-law while my wife, Kelly pushed us (thanks hon!). Now that's a payload!
Ahead lies the task of adjusting the skirt when on cushion to ensure the most efficient fit when traveling at speed on water. No skirt drag is the goal... as little drag as possible will be the reality.