Building the prop has been the most fun, and nearly the most satisfying part of building the entire craft. I got my plans from Universal Hovercraft. The plans cost about $25 and cover about every type of lift fan and thrust prop that Universal designs into their plans. I then bought the hovercraft general construction video ($20). This video (poor optical quality) has a good section on Prop construction and is well worth the money. There are only 3 measurements you need to lay out a good prop. #1 The leading edge #2 the Top Flat area, #3 the trailing edge. These are all in the plans from U.H. Once you get comfortable building these props, you are ready to make a great prop.  The cost for each prop runs about $20 for materials and glass.  If you don't want to build one you can buy one directly from Universal.

My experiences with building props...

Prop #1 When I first completed the craft. June 2000

• 80 lbs thrust with my 1st wood prop.
• The craft went about 38 to 42 mph.
• I would fall behind other crafts quickly when I encountered waves or swells of any size.

Prop #2 After asking more questions. August 2000

• 115 lbs thrust 2^nd wood prop
• The craft will easily run 50 mph.
• The craft would maintain a high rate of speed when I encountered waves or swells. I could hardly believe how big the difference was!

Time to play a little…

Prop #3 Prototype of ideas…Same plans just different materials. I believe I can get a better throttle response with a lighter prop.

• Part wood part styrofoam.
• 10/2/00 #95 thrust…making changes….read below.

Not started…

Prop #4  Built similar to #3 but used less wood.  The leading edge is maple.  The rest is foam.  I also made it 6" deep.  Where the trailing edge usually goes flat, I continued it.  I have not finished this prop.  It is fiber glassed and I will finish it this winter when the hovering slows down.

Prop #5 Will be all wood.  Not started.

My first mistake...The first prop I made I used 3 - 3/4 " boards to make the prop. After extensive investigation and only 80 lbs.  of thrust, I found out that the 42-36 prop is supposed to be made out of 4 - 3/4" boards. I still could not find out where I went wrong in the plans. The second prop I made, (all wood) made an unbelievable difference in the performance of the craft.

Laying out a prop with the UH Prop plans.

I will continue to work on this. I hope these instructions will help you.  Please let me know if you do not understand them.  I would print them out and place them next to the UH plans while you layout the prop. The description below is for a standard rotation lawn mower engines used in the UH plans. 

Prop Plans: I took the plans and taped them to a well-lit window and then taped several sheets of printer paper together, enough to cover the plan. I then traced the prop onto the printer paper. I cut out the shape, labeled it and put the fold on the fold line. I am assuming that you have already glued the boards together, found the center, scribed to the prop tips and cut them to length.

There are 3 major measurements you must make to lay out the prop.

Orienting the Prop. Lay the prop down so the leading face or front of prop is up (top flat area). Lay the prop so the center is in front of your left arm. You will be working on the right side. You can label the top of the prop (front or top flat area). The side facing you (leading edge) and the side away from you (trailing edge). These labels are for the right side of center. You then rotate the prop clockwise and label the other blade if you like.

#1 Trailing edge: Take the template you made and lay it on the blade front of your right arm. There will be about a 3/4" piece of that template that lies on the top of the wood (fold line). The rest of it will be folded over the back side ie. the side that is away from you (trailing edge) The template will be out to the tip of the prop as shown on the template you just copied. (tip) Trace the shape that the template makes from the tip down to where you hit the table you are working on. Spin the prop clockwise and do the other blade.

#2 Top Flat Area: The leading edge will be closest to you on the right side and opposite of the side you drew the trailing edge, the top flat area is facing up. Still working on the right half of the prop... working on top of prop and the closest edge to you on the top of the prop, lay out the measurements shown in the prop plans for the top flat area, root etc. Scribe a line between the tip and root measurements.

#3 Leading edge: The leading edge will be facing toward you on the right side of center. Again the trailing edge you scribed earlier should be away from you on the right side of center. Mark the leading edge as directed in the prop plans from tip to root. Scribe a line between the two.

Shaping the prop

Shaping: Grind from the top flat area line, to the trailing edge until you have a perfectly straight line between the two. I run a straight edge to ensure uniformity between the two lines and two blades of the prop. Grind from the leading edge line to the trailing edge until you have a perfectly straight line between the two. Again run a straight edge between the two scribe lines to ensure accuracy. Round over the square leading edge from tip to root to create an airfoil shape. See the UH general construction manual and the instructions that came with your plans for the exact shape. Hint: I ground down to just above the lines then hand sanded down to the lines.

These are the pictures of a 42-36 composite prop (Foam).   The shaping you see is the same with a wood prop.  The 42-36 is the prop called for in the UH-13P plans.   I find it fascinating to see the thrust difference that just a little change can make.  

This shows the final sanding from the bottom of the leading edge

Top of prop from rear of top flat area to the trailing edge.

Again this  shows  sanding from the rear of the top flat area to the trailing edge.

Once the initial shape is where it needs to be...then you can shape the leading edge and the airfoil by rounding off the edges.

10/2/2000

Today I balanced the prop and ran it at full throttle. I got #95 lbs. thrust @ 2800 rpm. I would like the rpm to be at 3100 or 3200 while static. This means I have to much pitch and am not using all 20 horses. I took the prop off and ground 1/2" off the trailing edge*. I then reground the top side of the prop to taper it down to the trailing edge. I then fiberglassed this area with 2 layers of 6 oz fiberglass.

*When I was tweaking my wood prop I would gain about 150 rpm for every 1/4" that is removed this way. It also gave me more thrust.

*Another way would be to grind the 1/2" off the trailing edge and then regrind the bottom of the prop to the trailing edge. This (I think) would be a more accurate way of "changing the pitch". I will do more of this type of adjusting in the future.

2/5/2001

I ran the prop above and got 95# of thrust. It did run very smooth, it's lighter weight was easier to turn but I need to adjust pitch. I will do more this spring 2001.  

7/7/01 Sorry, having to much fun hovering I have not had time to do more.

As soon as I run the prop with this change I will update this information.