Bush Flying: Section II, Flying Techniques, Part II, Chapter 21: Ground Handling (Skiplanes)

Section II: Flying Techniques

Part II, Chapter 21: Ground Handling (Skiplanes)

Ski operations provide many fine opportunities for incidents of the "fender-bender" variety, and while these are naturally undesirable in themselves, they can also become quite serious -- even deadly -- if you happen to be in the remote bush when they occur and the skiplane is your only way home.

The techniques to prevent these problems are all quite straightforward, and in this chapter we will consider not only the normal techniques widely used by ski pilots, but also some specialized deep bush techniques that will permit you to handle strips so narrow that they are even considered marginal for wheelplanes during the summer.

The problem of sticking

Skis have an unpleasant tendency to stick to the surface of the snow or ice after the skiplane has been parked for a period of time. While this problem spans the spectrum from mild to impossible, it's useful to divide it into two classifications, based on operational considerations:

Mild. Here the skiplane is lightly stuck, and you will be able to free it by hand or power and depart without further difficulty. The degree of freeze-down will vary depending on:

Type of skis. Some models are very prone to this problem, while others are almost immune. This factor plays a large part in the pro's ski selection.

I have found that board skis, such as the skis Atlee Dodge manufactures for the Super Cub, cause less problems with stick-down than any other type I have tried. On the other hand, I have had difficulties with the molded fiberglass type that otherwise work so well on the C-180/185.
Type of surface. Sticky snow conditions and very cold temperatures aggravate the problem.

Mild freeze-down can occur almost instantaneously under adverse conditions but rarely progresses beyond the annoyance stage during short stop-overs of a few hours or so.

Serious. Here the skiplane is stuck so fast with compacted snow under the skis that you will be unable to depart until you jack it up and remove the accumulation. This degree of freeze-down usually takes several days to occur, and is generally the result of careless -- or lazy -- operating practices.

Releasing mild freeze-down

There are two techniques for this:

Once the skiplane is loaded, grab hold of one of the wing struts prior to getting in and rock the wings vigorously to break the skis loose from the snow. It works even better if you can get a bystander to do the job once you are in the skiplane and have the engine running, because then you avoid the risk of the skis refreezing during the starting procedure.
The second technique is somewhat inelegant. Get in the skiplane, start the engine, raise the tail with power, then sharply drop it. The idea is to jar the skis loose, and it often works.

Preventing serious freeze-down

There are also two methods for preventing freeze-down. These are SOP during the winter at the end of each day's flying, and ensure a trouble-free departure the following morning:

At home base I keep a few 2x4s -- pieces of cottonwood, birch, or willow can be used -- about four feet in length to block the skis off the ice and snow at my tiedown, and this resolves the problem nicely (see illustrations 15, 15.1, 15.2, and 31). Many pilots, in fact, carry a couple of short 2x4s in their C-180/185s, and one of these can also come in handy for turning the skiplane in restricted areas (to be covered next).
When flying above the tree line or over the pack ice, carry along a few 30-gallon plastic trash bags if weight or space restrictions prevent your having a couple of 2x4s along with your survival kit, for here you can not use the more southerly technique of just grabbing a branch off a spruce tree or cutting a piece of cottonwood or willow. When needed, these bags are split along the sides, opened up, and placed under the skis; sometimes easier said than done, admittedly, though necessity is the mother of invention.

If you are flying an airplane equipped with wheel-skis, and the tiedown area is ice or compacted snow, you will not need to bother with blocking the skis. All you have to do is raise the skis so the airplane is sitting on its wheels rather than its skis (see illustrations 18 and 27).

Turning the skiplane

The normal turning radius of a skiplane is quite a bit larger than a wheelplane's and depends to a great extent on snow and ice conditions. This turning radius will not pose any problems on reasonably-sized lakes or larger airstrips, but it separates the men from the boys on narrow strips. There is a whole spectrum of techniques, ranging from the common to the esoteric, and the most useful techniques will be described here.

Normal turns. During taxiing maneuvers you can use the following two turning techniques:

With the tail on the ground, using rudder and power, turn the skiplane as if it were a wheelplane. This type of turn is my first choice when I have the room for it.
In tighter areas, and on narrow runways, a modification of the above turn is used. Here, you will give the skiplane full nose-down trim, apply power, and, raising the tail fairly high, feed in rudder and blow it around on its fulcrum. Some skis allow a tighter turn than others, and the timing of power application in relation to raising the tail and applying rudder is important. Also important is keeping the tail clear of the snow when starting the turn, and not allowing it to contact the snow again until all sideways motion has ceased. The bent lower longerons on the tails of Super Cubs seen all over the place every winter are mute testimony to their pilot's lack of skill or care when performing this maneuver.

Precision turns. When the turning area is too restricted for the safe use of either of the above techniques, you can turn the skiplane on the spot where it is sitting. Part of the success of the following techniques depends upon the initial placement of the skiplane prior to the turn, for each technique requires a different amount of room and this also varies with snow and ice conditions.

Turning it by hand. This is the easiest, and works well if the skiplane is sitting on smooth hard-packed snow or ice. Here, you push the tail around until the skiplane is facing in the direction you want to go, straighten out the tailwheel, and you are on your way.

The situation changes when the snow is deep, or badly rutted, for under these conditions if you try to turn the skiplane by hand you risk snapping the landing gear. Many pilots fail to realize that the length of the tail provides quite a powerful lever to the axles, and, were a ski to catch in a rut or be blocked by deep snow, the forces could exceed the relevant design loads.
Hanging on the wing strut. While hardly precise, this is better than the foregoing when conditions start to get rough, for the skiplane will have forward motion and therefore the skis and landing gear will receive some protection against the turning forces. It works best with the Super Cub, though it can be used to advantage with the C-180/185.

What you do is get in the skiplane, start the engine, and then apply power as one or more of your customers holds back on one wing strut. This pivots the skiplane about its axis, and, while effective, it is hardly as precise as the following techniques, which are rarely seen outside the deep bush.
The rope. This technique, like the one above, is fairly easy on the skis and landing gear because the skiplane is moving forward during the maneuver. It will work best with dense or compacted snow, and is suitable for all skiplanes:
1. Take one of the tiedown ropes from your emergency kit and tie a bowline knot in one end.
2. Wrap this rope around the ski on the side you wish to turn towards. The number of loops will determine the turning radius, and it is placed in front of the pedestal but behind the bungee-cord and safety-cable assembly at the front of the ski. The rope should be tight enough so that under the pressure of the skiplane's forward movement it will slide back to a point just aft of the axle before the pedestal stops it. The free end of the rope is tied to the loop of the bowline knot with a slipknot so it can be removed easily after the turn. (See illustrations 36 and 37 for the general idea.)
3. Get in the skiplane, start the engine, apply nose-down trim, and give it a bit of power. Allow the skiplane to move forward until the rope slips back and catches on the pedestal. At this point, apply more power, raise the tail, and feed in full rudder. The skiplane will start its turn.
4. Continue the turn carefully, and, on reaching the point where you wish the plane to stop turning, come back on the power just enough to stop the turn while keeping the tail in the air. Once all sideways motion has ceased, let the tail down.
5. Shut down the engine, get out, and remove the rope. Your turn is now complete.
The 2x4. This technique, a modification of the above, is used when the snow is too deep and powdery for the rope technique to work, or when it is important to make a very tight 180 degree ground turn, e.g., when using tree-lined creek bottoms barely wider than the wing-span. However, the following should be kept in mind:
1. This technique can put a strain on the ski/landing gear assembly, and is probably too severe for the Super Cub except with a very short 2x4 in exceptional circumstances.
2. While it is the best way to precisely position a C-180/185 under difficult conditions, it should be restricted to skiplanes with the proper ski axles. These are the special eight-bolt Cessna axles designed for serious ski operations (see illustration 37), not the cut-down stock axles. Failure to heed this caveat could easily result in the stripping of the axle bolts (at best) and the incapacitation of your skiplane until new bolts are installed.
  
  Using this technique, the 2x4, which can be about a foot to a foot-and-a-half longer than the ski is wide, is placed crosswise on the snow under the front of the ski. A rope is then tied to one end of the 2x4 with a bowline or slipknot, passed over the ski between the pedestal and forward bungee-cord/safety-cable attachment fitting, and tied with a slipknot to the other end (see illustration 36). Then, the engine is started and the turn performed exactly as with "the rope" (see illustration 37).

A technique for wheel-skis in deep snow. While skiplanes equipped with wheel-skis have a noticeably smaller turning radius -- due to ski length and weight-distribution patterns -- than those equipped with board-skis, you will occasionally need to turn them even more sharply than possible using normal techniques. This you can easily do by taking advantage of the mechanical action of the skis when they are being retracted.

Get out of the skiplane and go to the side opposite the direction you wish to turn.
Take hold of the wing strut and pull down as hard as possible. This will shift the weight of the skiplane more onto the non-turning side than the turning side.
Go back to the cockpit, reach inside, and start pumping the skis up. The ski with the least pressure on it will retract first. When the ski on the side you wish to turn towards is in the full-up position, and the ski on the opposite side is still in the full-down position, place the wheel/ski selector in neutral. This will lock both skis hydraulically in their current position.
Get in the skiplane, start the engine, and make the turn as you would if using the rope or 2x4 technique. The skiplane will come around as sweet as can be, and then all you have to do is lower the raised ski and you are ready to go.

Taxiing on glare ice

Glare ice can present some interesting operational hazards for the bush pilot, and during ground operations will easily account for its share of the fender-bender accidents suffered by the unwary or careless during this time of year. The main problem here is that the surface is so slick and hard that neither the tailwheel nor the ice runners on the bottoms of the skis can get a satisfactory grip on the surface. This slickness and hardness leads to the following problems:

Starting to taxi. Admittedly, this is a somewhat unusual occurrence, and the idea that there might be a problem in getting a skiplane to start moving on glare ice may be greeted with raised eyebrows.

To occur, this problem requires a fairly rare combination of events. It is the by-product of the placement of ice runners on the highly esteemed Atlee Dodge board-skis used on Super Cubs. These skis have a single six-inch long ice runner in the center of each ski directly below the pedestal, and on warm spring days the black "no-slip" upper surface of these wood skis can get hot enough to cause the runners to melt into the ice. This in turn blocks one or both skis quite nicely, and, unless the skiplane is parked on a fair-sized lake and aimed in the proper direction, the standard method of laying the whip to it and bouncing the tail or wagging the rudder is not going to produce positive results. This situation is best resolved by simply moving the skiplane by hand a few feet prior to loading and departure. It takes just a slight rocking of the wings to raise each ski high enough for the ice runner to clear the hole it made, while pushing forward, to accomplish the job.

Stopping. Once the skiplane has started to move on glare ice it will demonstrate a shocking reluctance to stop, and the pilot who has not taken this into consideration might suddenly find himself in the unenviable position of being a passenger, along only for the ride, as his skiplane slides towards a row of parked airplanes.

Turning. Due to the inability of the skis or tailwheel to get a grip on the ice, turns are very difficult -- and sometimes impossible -- unless you blow the tail around with power. This power-turn can be tricky in confined areas unless a strong wind is present to weathercock the skiplane in the direction you wish to turn and hold it on a steady heading.

As a result, in confined areas the best technique is to plan a stop at the point where the turn is to be made, then shut the engine off (usually during the deceleration slide), get out, and turn the airplane by hand.

Taxiing crosswind. Glare ice, in strong crosswinds, makes a pilot wish it were summer and the skiplane on floats, for above a certain velocity taxiing becomes impossible, and sailing and tacking, no matter how tiresome, is better than closing up shop for the day and taking an unscheduled holiday.

Taxiing downwind. When taxiing downwind, remember that when the tailwind is stronger than the forward speed plus propwash it will cause the rudder to work in reverse, and due to the slick ice the tailwheel will not have enough purchase to prevent the tail from swinging. On a narrow runway or in confined areas you could end up in trouble.

I discovered this one sunny spring day many years ago when going into Chitina with my wife on a gas and supply run in the C-180. The runway was glare ice, with a nice little layer of flowing surface water provided by the warm 41 degrees F/5 degrees C temperature, and a 20 knot wind down runway 13.

I landed carefully, slid, came to a stop, and got the skiplane turned around by hand with help from my wife. Then I started to (idle) taxi back to the passenger loading area where my fuel dump was.

Everything went fine until a drift to the right developed. I applied a touch of left rudder; then, as the drift increased, I applied a bit more. Suddenly we found ourselves heading sharply to the right, towards a nasty drop off the side of the runway into the trees below, so instantaneously -- by reflex, not forethought -- I opened the throttle, blasting the skiplane 210 degrees to the left and into the wind. The C-180, on that slick ice, spun like a top within its own wingspan, demonstrating extreme agility, along with a mind of its own, and came to a stop facing down the runway directly on the center line. "Interesting maneuver," my wife remarked dryly.

I decided to leave the skiplane where it sat in the middle of the little-used runway -- better to quit while ahead -- and haul the cans of fuel by hand from the storage tank a thousand feet away. This was probably a good idea, for the area where we were parked turned out to be so slick with its slightly downhill run that part of our job had to be accomplished on hands and knees.

[Please Note: The next two Chapters, Chapter 22: Takeoffs, and Chapter 23: Landings, are unavailable on the web. The online edition continues with the Images Section, perhaps my favorite section in this book.]