Most experienced ski pilots will tell you that any aircraft ski design that includes the word “wheel” in its title is going to offer lots of opportunities to get stuck, especially if operated in deep or challenging snow conditions. This was certainly my experience prior to working that Husky on the Rosti Fernandez skis. Retractable wheel skis are invariably heavy, and typically have much less bottom area than comparable straight skis. Wheel penetration skis are also heavy and add substantial drag due to the wheels protruding through the ski bottoms. But, if you need the flexibility to land on either snow or runways during the same flight, wheel skis are your only option.

In the mid 90’s a glacier pilot in Germany named Thomas Dietrich searched for a better ski design to use on glaciers in the Alps. His hope was to develop a ski that would offer both better performance and lighter weight than the skis available at the time. To be practical for use in the Alps, the skis needed to be capable of landing on either snow or runways.
After looking at a number of ski designs, Dietrich developed a belief that curved bottoms, such as those found on an out of production ski produced in Alaska thirty years before, might offer the best performance. He developed a clean sheet ski design around the curved bottoms, and the result is the Rosti (for Dietrich’s glacier flight instructor) Fernandez (for the out of production Fernandez skis) 8001 ski.

The curved bottoms of these skis are made from a material similar to that which downhill ski bottoms are made from. The remainder of the ski structure is made from various composite materials. The rigger yokes, which connect the skis to the aircraft landing gear, are made from a high strength yet very light carbon fiber material, to withstand the stresses these parts will be subjected to. The skis have very large bottom surface area, even compared to most straight skis. The combination of very large curved bottoms, high tech materials, and light weight contribute to the great performance of these skis.

Total weight of the skis, including hydraulics and rigging, is 71 pounds. For those of you familiar with retractable wheel skis--that is not a typo. The skis I flew weighed 76 pounds, but improvements have since been made to the skis to remove a few more pounds. Compare this to other wheel skis appropriate to this size aircraft, which weigh approximately 120 pounds, not including the required hydraulics.

The skis are a twin beam design, with the wheels and tires riding between the beams in the skis-up position. The skis are approved with 8.50 X 6.00 tires, which afford a generous 4 to 4.5 inch ground clearance at tails of the skis, which are the the portion of the skis closest to the ground. I routinely operated from gravel strips with these skis, and never dragged a heel, even crossing irregularities often found at Alaska’s rural airports. As the skis are lowered, they rotate downward and aft, such that in the skis down position the tires rest on the skis. This provides a bit of additional cushioning to the airframe, an important feature in that snow conditions can subject an airframe to substantial loads.

The hydraulic system provided with these skis is a simple yet effective system. The heart of the system is a hydraulic pump which actuates the skis. This pump is reversible, as is the electric motor which drives it. The pump also has internal pressure relief valves, precluding the need for shuttle valves, stop switches or pressure switches. An electrical switch on the instrument panel selects skis up or skis down, by switching the direction of the current flow through the electric motor. The pilot then actuates a “Do” switch, which energizes the electric motor, driving the pump and moving hydraulic fluid in the desired direction. As the skis reach their limits, pressure builds in the system, the relief valve opens in the pump, and the Do switch is automatically reset for the next cycle. The system is elegant in its simplicity, as well as its light weight. The hydraulics in the airplane I flew weighed approximately 7 pounds total.

Simple hydraulic rams are used to move the skis. The system isn’t designed to move the skis on the surface, but by lifting up on one wing at a time at the struts, it is possible to cycle the skis while on the ground. I’ve never found many situations where cycling skis while on the surface was really necessary in any case.

The hydraulic lines from the airplane to the ski actuator cylinders are terminated at the airplane’s skin with quick disconnect fittings. After initial installation and rigging, the skis can be installed or removed easily in 15 to 20 minutes with just a couple of wrenches to remove/attach the limit cables. No other skis I’ve seen, including straight skis, are so simple to install or remove.

The workmanship on the skis is simply superb, as one would expect from a German manufacturer who also happens to be a perfectionist. The skis can be ordered in colors to match the aircraft as well. But, the true beauty of these skis isn’t apparent until you take them out into their natural environment—deep powder snow, or similarly challenging operating conditions. Deep snow is where these skis really shine.

The new US STC also includes installation of Dietrich’s “Soft Gear Stops” or SGS, which considerably soften gear rebound on the Husky, which has been known to bend cabane struts on the landing gear.

Shortly after we initially installed these skis on the Husky, some of my co-workers decided to try three different airplane types on different models of skis to compare takeoff performance. The test was done in untracked, fresh waist deep snow. The Husky with the Rosti Fernandez skis outperformed every other airplane in the test except another Husky mounted on straight skis. The Husky that won that contest had a much longer propeller than the Husky on the Rosti Fernandez skis did at the time, though.

For a wheel-ski equipped airplane to outperform several straight ski equipped airplanes is remarkable in itself, but even more remarkable is the minimal increase in weight of the Husky on these skis. In the world of ski performance, weight is incredibly important. Dietrich has landed his Husky at over 15,000 feet in the Alps, and at that height, weight and power are critical factors in performance. Even at lower elevations, very deep snow or overflow conditions (slush to lower 48 ski pilots) demand the lightest weight and the most power possible. More than once, I’ve left a passenger somewhere to snowshoe to a longer operating surface to allow us to depart safely with two aboard. Once, this occurred during a recurrent company checkride….the check airman asked me when my next recurrent checkride would be. I responded that it would be in July on floats, and he asked if I’d remind him to bring his swim suit.

As a natural resource pilot working an area north of Fairbanks, Alaska, I had the opportunity to explore a wide variety of ski conditions with these skis. Since I was working the airplane, as opposed to recreating with it (though some would say that my job was as good as recreational) there was at least some pressure to land in some challenging places with the airplane. When you are working a ski plane, the likelihood of getting stuck is very high, at least on occasion. Good survival skills, adequate survival equipment and a satellite phone to let the folks back home know what’s going on should all be part of the working ski pilot’s tools, so that the result of getting stuck somewhere is an inconvenience rather than life threatening.

The Rosti Fernandez skis served me very well in conducting wildlife research work that required me to land as close as possible to animals we were studying, and they performed well during law enforcement duties, which included visiting trappers and their traplines on the Yukon Flats. Which brings me back to the beginning of this story.

I was on a trapline patrol in the eastern Yukon Flats, on the Black River, a tributary of the Yukon. There was a fellow here who I had been trying to contact for some time now--a trapper with a somewhat casual approach to the game and land use regulations.

Well--I’d been stuck before, there was a cabin just across the river, and I was prepared to both spend a night or two out here and to dig the Husky out of a mess if necessary. This is what I was being paid to do. A satellite phone to communicate my situation to my spouse and my boss cinched the deal.

A short straight stretch of the river provided a landing site, but the overflow on the river ice meant that stopping on the river ice would just about guarantee the airplane would be stuck, and retrieval might not be a one man deal. At the upstream end of the straight stretch of river lay a gravel bar, just before the river made a hairpin turn to the left. My plan was to land on the river ice, slide up onto the gravel bar to keep the plane out of the overflow, and then figure out how to turn the plane around for a downstream takeoff. The deep snow on that gravel bar would make turning the plane around a challenge, but at least I wouldn’t be in ankle deep icewater.

The landing went as planned, and as I slid up onto the gravel bar, the skis floated nicely up onto the snow there. As the airplane slowed, I decided to take a shot at turning the airplane around with power and rudder. Forward stick to lift the tailski and a blast of power, combined with full left rudder allowed the tail to slide downhill on the gravel bar. The Husky slid around beautifully and plopped its tail down smartly as I once again faced the landing site, but now in position to use it for takeoff.

Somewhat surprised and quite delighted not to be stuck, I shut down, climbed out of the plane, applied the insulated engine cover and donned snow shoes for the short trip to discuss various transgressions with the alleged perpetrator.

An hour later, I was back in the Husky, warming the engine for takeoff. Pushing up full power, the Husky and its Rosti Fernandez skis displayed their thoroughbred lineage, sliding up on top of the snow, out onto the river ice, accelerating and performing an easy climb out over the bluffs downstream.

This was the only time in my ski flying experience where I fully expected to get stuck, and suffice it to say that I was not disappointed to be headed home without even breaking a sweat. The Rosti Fernandez skis are simply the best skis of any kind that I’ve had the opportunity to work on an airplane. In combination with the Husky, it would be pretty difficult to find a higher performance ski-equipped airplane.