Aerosquare - A pair of skis for winter

A pair of skis for winter

This winter the snow fell in abundance. Not always easy to keep flying when the track disappeared under a beautiful white coat.
As I am not a fan of indoor flying, I decided to equip my Wilga (estar models) with a pair of skis in order to fly in any weather.
The achievement has nothing very complicated. A few hours are enough to make a pair and equip an aircraft. But if you want to fly with your skis on weekends will require Plan the production during the week. The shaping of parts requires time to press to respect; as well as the time required for drying varnish or paint, which is essential to protect the skis to bad weather.

The realization of the skis

As mentioned above, making these skis do not pose any particular problem.

The dimensions shown on the drawing (click for larger image) are well suited to my little Wilga.
Wingspan 1.30m and mass flight order: approximately 1.2 kg

Drawing skis PDF 26.06 Kb

These skis gain elsewhere to be a little bigger for a better grip in deep snow. But on "Runway" rammed the deportment and takeoff are impeccable.
It would obviously fit the dimensions depending on the model to be equipped.
Several more or less empirical methods circulating on the net to determine the ideal dimensions. It must still avoid equip your skis with disproportionate model that will create a trail especially detrimental to flight quality.
We start by cutting the needed parts from the ctp of 1.5 mm. The most delicate phase, will be the bending of the tip before. For a beautiful shape without breaking the fibers of the veneer cons, I dipped the piece in boiling water and gradually curved ski for getting in shape. Then, each ski remained under strain overnight to let the wood dry.
The next day, once the dry room will well up the spatula. Just then paste the different elements to the epoxy glue or wood glue OUTSIDE. remember that these skis will be subjected to severe operating constraints (cold and humidity).

The picture for understanding the assembly of different elements. The small "keel" in skiing is not necessary, but ensures better tracking during takeoff and landing.
For the protective layer, as I work at the same time on the masking of another model glass fabric epoxy resin over, I took the opportunity to varnish the skis with the rest of resin. This process ensures a finish and especially long-lasting protection against the snow. Otherwise a varnish or exterior paint suit as well.

Installation and adjustment of the skis

Now that the skis are completed, yet to install them on the plane!
Skis should be resolved in a slightly nose up, about 15 degrees to the flight line. This will prevent the tip from crashing into the snow upon landing. Skiers know how it ends up, if by mistake you plant the front of his ski in the snow. By plane is the same: The aircraft will finish on the back!
The biggest hole for attaching the ski on the wheel axle. This allows a fast and without modifying the original train. That's great stuff, but how to maintain the ski in place?

Again, each model will adopt the method that suits him best.
The solution must meet two requirements:
- Maintain the ski tip slightly raised (about 15 °)
- Be flexible enough so that each ski can pivot during takeoff and landing and absorb uneven terrain

In effect during the rotation, with a rigid tow skiing remain in position (or rather he will follow the rotation of the plane) and spatula will crash into the snow. This will put an end to the attempted takeoff with the added risk of damaging or tearing the train. Assuming the plane took off anyway, the problem will be landing. In conclusion, rigid fasteners are prohibited.

A common method is to attach the front of the ski to the fuselage with a rubber band. What sets the ski a little nose while remaining flexible. Although this method works very well, I can not find the result very aesthetic. I adopted a slightly more complicated solution but more discreet and highly effective.
The photos are more understandable than a long explanation.

Necessary parts (for skiing):
- A piece of piano wire (Ø 1.5 to 2mm
- A ball cap with a 2mm screw
- A flexible spring working in compression
- A domino to pushrod

The piano wire slides freely in the domino set on the landing gear, which allows the ski to pivot on the axle. The spring, acts as a shock absorber and keeps the ski in the desired position during flight. Simply find where to drill to attach the domino on the gear leg to obtain the proper setting.
This system provides excellent shock absorption. Each ski may follow the uneven terrain. By the time the plane leaves the ground, you can clearly see the skis back in position by the springs of the shock. A light spray of WD40 protects all the corrosion and ensures a very smooth operation.

In flight ...

This is pure happiness! First there is the unique pleasure of seeing the plane sliding on snow, gently, against a liftoff with wheels. Then it's fun to evolve over a winter landscape of great beauty.
In flight, I did not notice any change from the conventional train. The extra drag generated by the ski does not seem excessive. It must be said that the Wilga is not a aerobatic aircraft. By cons with its shutters he has very good skills in slow flight at large angles.
This Wilga remains sensitive enough to the landing and nosed likes. Whether equipped with wheels or skis, the behavior does not change. We must therefore make the aircraft pitch well and leave quietly slipping on the snow. once we realized the thing is a real treat.

To improve things, a third small ski instead of the tail provide better glide especially in deep snow (as in the photo). But this is not essential in a model of this size.
Finally, when the snow fell in abundance, any pre transforms into a beautiful runway. This allows to fly in many places usually inaccessible because we do not have a driving surface for the small wheels of our models.
Take advantage quickly, before spring comes and the snow has melted.