DIY 3D printed Skis for FT Planes (& More)

Winter has hit us here in West Michigan. We have a few inches of snow on the ground and more on the way. Normally I would call it quits for the year and head inside to work on build projects or fly mini quads. However, this year I joined a club and we have at least one winter fly in January. I'm not too bothered by the cold so I thought why let the snow stop all the flying fun? I know some like to fly off the snow with floats. I do have a set of floats for my apprentice and they seem to move fine across the snow. The FT floats are also a great design but I don't know how well they would work on the snow and as with all floats, they add weight to the plane.  I decided to model up a set of light winter skis in cad that would meet a few criteria making them easy to build.

1. I want them to work for most all landing gear (FT planes as well as others)

2. utilize items that may just be laying around

3. minimal parts so they are easy to assemble.

Below is an image of the cad model I made that I feel fits all the criteria above. 

Each ski uses minimal parts (two printed pieces) and the rest of the items are pieces that most of us FT fliers will have laying around. The skis are set to lock in at 15 degrees above horizontal so as the plane comes in for a landing, it should come down on the back of the skis then pull them flat to follow the grade. Rubber bands are used to hold them in this position while flying so the skis don't flow around in the air. With that said, lets get building!

First you will need to print the skis. Here is a link to the files on Thingiverse:

https://www.thingiverse.com/thing:2709373

 I have a few different parts in there so you can choose exactly what you want. There are two types of skis, one with grooves and one without. The thought with the ones with out grooves is that packing tape could be applied to the bottom to make then extra slick and prevent ice build one. Also there are two "axle blocks" as I am calling them. One is deeper than the other. Due to the way the axle blocks locate on the gear wire, the longer blocks may be needed if the bend at the gear is less than 45 degrees. If all else, the long blocks will work for everything, they may just add a tiny bit more weight because they are a bit larger. I use simplify 3D for slicing my models and it has the option to mirror the files so I only have one side of all the parts loaded. If it becomes an issues where you can't get the parts to mirror, let me know in the comments and I can probably do a bit more work to mirror the files in solidworks. One ski, and one axle block per side. If you are flying a tail dragger, that's 4 parts total, if you are using a tricycle gear setup with a front wheel, that's 6 pieces total. I printed the parts at .2mm layer height and ran 4 perimeters with 20% infill. The 4 perimeters helped make the triangular upright on the skis stronger where they attach to the landing gear.

Now that the parts are printed, its time to assemble. The holes on the skis might be too small for your landing gear so you may have to drill them out to size. I did this on purpose as its easier to drill them bigger than to have them loose. Check the fit to the gear your plane has and drill both the skis out and the axle blocks to fit your landing gear. It would also be a good time to grab some small rubber bands (.5" diameter or so) as well as two servo mounting screws for each ski (If you have built a few FT planes, you should have these laying all over since most planes require the servos to be glued in). 

With the skis and axle blocks drilled out, its time to assemble them on the landing gear. Remove the existing shaft collar (if equipped) and the existing wheel. If there is another shaft collar behind the wheel, remove that also. Essentially we are looking for a bare wire at this point. Now grab the axle block. There is a small hole on it that a servo mounting screw will go in. It may need to be drilled out with a 1.5mm bit so the screw goes in easier. Do that, and put the screw in leaving a few millimeters of space below the screw head. Now to test fit the block. Quick note here, the landing gear for the FT cub and others is directional by design, make sure you have it the right way. 

The slot on the axle block needs to face in and the wedge point facing forward. Slide that on all the way and make sure the flat surface the ski will rest against is square to the shaft. Now slide it off a bit and grab your glue gun. Put some glue on the shaft as well as in the notch and slide the block back on while making sure its still square the the shaft. This needs to be done rather quickly as the metal wire cools the glue quicker than normal. Do this for the other side as well.

We can now grab the Skis. The skis have a little knob on them that is used as an end stop against the axle block. Make sure this is facing in and under the wedge of the axle block. There is a small screw hole on the skis near the bottom as well. This is for another servo screw. As with the axle block, this small hole may also need to be drilled out. Put the servo screw in from the inside so the head is facing the planes fuselage. Leave a little room on this one as well.

We are almost done. All that's left now is to put the shaft collar back on (if equipped) or just make a dab of hot glue that goes around the shaft just like Josh does in the build videos when installing wheels on the FT planes. Finally grab the small rubber band and attach it between the two screws. If it feels to loose, hook the rubber band on one screw, loop it around the next and bring it back to the first screw to double it up. 

Install your landing gear back in the plane and you are ready to fly off the snow!

As for tail draggers, I didn't seem to have an issue with the tail dragging in the snow. I tried these on my FT cub as shown in the video below and even in deeper snow, it wasn't an issue. That said, if it is an issue, a simple small piece of waterproof foam cut in a rectangle and attached to the rear tail drag would likely be enough to prevent any drag or friction in the snow. 

Also, if you are flying a larger plane, just scale them up in your slicer software! I will also likely be adding more skis of varying sizes as winter progresses so keep an eye on the thingiverse page for updates!