skis

Ok, I hate to be sitting here during summer vacation and thinking about snow but........... its Maine and its coming sooner than we'd like to admit. At the last club meeting there seemed to be some interest in building up some ski type landing gear and having an early spring fly. Well, it got me going, I have got a completed set of skis and have them mounted up on my Airmadillo all set for their test flight tomorrow (8/19) at Hogan field off the grass. The project is really very simple and with some cutting, wood bending and assembling you can have a very pretty set of skis for your plane. I am including a bill of materials for those of you that are ready to start accumulating materials. I will have 4 or 5 jigs ready quickly and they will be available to pass around for the bending of the skis. The ski blanks are cut out of 1/8 birch plywood, boiled for 3 minutes then placed in the bending jig. The drying time depends on conditions - I dried mine for 2 hours over a wood stove but if they are air drying I would give them a couple of days. This process is used for all three skis. I found that the Bend in the skis would settle out after about a week and during this time all 3 skis are settling at different rates so don't be alarmed if you compare and find 3 complete different bends. I will start to get jigs ready and have them available quickly If you are ready for patterns and a jig just get let me know. I would also be happy to cut out parts for any that need them cut - just get the birch plywood to me. Here is the materials you will need (don't cut your plywood to these sizes - they're just given for an idea of the quantities you will need):

Birch Plywood
1/16" thickness	1/8" thickness	Other
1 1/4 X 2-1/2	2 2-1/2 X 12	3 feet of 1/8" square balsa
2 1/4 X 6	1 1-1/2 X 7	3 Wheels collars
	2 1-1/4 X 6-1/4	3 pieces of 1/16 X 1/2 X 1-1/2 brass
	2 1/2 X 3/4 4 3/4 X 2 1 3/4 X 3-1/8	5/32 ID brass tubing (this is for the axle bushings - don't buy any! I have a ton of this stuff left over from an Amateur radio club antenna project)
		3 Springs
		some fine wire

The Bending Jig The bending jig is made from a 2X4, 18" long. Draw lines 3/4 from each edge parallel o the edges. Draw a 4 in. radius 3" from one end connecting the lower line to the upper line (see photo). Cut along the line on to separate the 2 halves of the jig. With 1/8 spacers inserted between the 2 halves reassemble the block (I used double faced tape to hold everything together). Drill 3/8" holes through the jig 1" forward of the ski tip and 2 more exactly the length of your ski blanks to the rear (both for the long and short ski. Use 4-1/2" long X 5/16" bolts to hold the mold together.

The Bending Jig

Procedure for making the Skis 1. Cut the ski blanks from 1/8" Birch
2. Place a ski blank nose down in boiling water for 3 min.
3. Put the blank in the bending jig and tighten the bolts (make sure rear of ski is against rear bolt in jig).
4. Allow the ski to dry for at least 2 hours near a wood stove or air dry for a couple days
5. Repeat for other main ski and for nose ski (make sure to move the bolt forward in the jig for the nose ski).
6. Cut the remainder of the parts (you will need 2 main splines, 1 nose spline, 4 main doublers, 2 nose doublers, 2 main keels and 1 nose keel).
7. After sanding, glue the splines to each ski with the spline on the centerline of the ski and the "point" (or center) of the spline 5" from the rear of the ski (for main ski) and the spline for the nose ski should be centered between the rear of the ski and the point where the bend of the ski starts. Use slow setting epoxy!
8. Epoxy 1/8" square hard balsa gussets on each side of the spline. Sand the gussets to 1/4 round before gluing.
9. Epoxy the spline doublers to each side of the splines.
10. Round the front and rear of the keels and epoxy them on the centerline of the bottom of the skis centered on the flat area.
11. Drill a 7/32" hole through the spline and doublers for the axle bushing (centered in the doubler). This should be done in a drill press if possible to keep the hole straight.
12. Drill a 1/16" hole center in the radius on the front and rear of each spline.
13. Sand the skis but keep the edges of the ski square (to aid tracking).
14. Apply your choice of finish. I choose to apply clear polyurethane. After applying the poly, I used fine steel wool dipped in paste wax and buffed it out with a cloth. Made for a beautiful finish.

Attaching the Skis to Plane 1. Make up the brass strap as shown in the illustration below. It can be as simple as a rectangle 1/2 X 1-1/2 or rounded up as shown in the picture. For better alignment, locate and solder the wheel collar on the strap and then drill through the wheel collar and brass strap with a 5/32 bit.
2. Mount the skis to your plane between a wheel collar and the brass strap assembly.
3. Attach a spring between the hole in the front of the ski and the hole in the top of the brass strap. The spring should be strong enough to pull the nose of the ski up but not too strong (remember the ski has to be able to move on take off and landing).
4. Some experimentation will be in order on this step. Take some fine wire or steel fishing leader and make up a piece to go from the hole in the rear of the spline to the hole in the top of the brass strap. The length of this wire will keep the ski in the proper position during flight. Keep in mind that this wire also needs to flex on take off and landing. The ski wants to be "nose" up by about 5 degrees. Attach the wire by looping it through and soldering together. I found that the springs I used held fine on the skis with just a loop bent in them but you can also solder them or slip them through a small piece of tubing and crimp it.