Ralph E. Taggart

Rotorcraft Magazine Dec./Jan. 1993/94

At first glance, it did not look like a day to inspire any gyro flying. The runway was blanketed with unplowed snow in both directions and the aircraft tied down outside had a positively melancholy look as they sat amidst their individual snowdrifts. In short, Bergeon Field had an all-too familiar Michigan winter look about it, nicely complimented by a gray sky and a cold wind quartering across the obviously inactive runway.

I'm standing out in the snow with John Bergeon, the owner of this aviation Mecca, and we're both staring off to the east like a bunch of bird-watchers looking for a snowy owl. It's a bird of quite a different sort, however, that swings around the woodlot a half-mile off the end of the runway, boring toward us with the steady drone of a Rotax engine.

The bird in question is our Gyrobee autogyro, piloted by Don Chubb, my intrepid flying partner, bundled up like the Pillsbury Dough Boy in a snowmobile suit, ski mask and goggles. As Don crosses the end of the active, he pivots 45 degrees into the wind and hovers in place, providing a perfect display of the skis which have replaced the wheels on our darling little flying machine. With those skis, our Gyrobee has become perfectly adapted to the snow-covered runway, not to mention the, surface of every one of those farm fields out there!

Just a few minutes later, Don touches down, having completed a 20-minute flight that marks our first try at the ultimate adaptation of our autogyro to winter in Michigan.

Now, flying gyros in the middle of snowbelt winters is not common. The Indiana club gets together for an annual New Year's day flying session, but most of them don't make a habit of it. Winter is, in fact, one of the reasons why Bensen Days is such a popular fly-in! Those of us up in the north-country love it here and, in the past, our license plates have proclaimed Michigan as a "Winter Wonderland".

If you live up here and don't plan to hibernate with your VCR for the duration, you have to find things to do each winter. Up here you'll find the natives hunting, ice fishing, snowmobiling, cross-country skiing, or snow shoeing. In short, the locals expect you do be doing something energetic and snow-related.

Since the social system demands that you spend your time freezing parts of your anatomy, Don and I figure we might as well keep flying and have some real fun! I have written about our winter flying in the past, but the Great Ski Experiment represents still another attempt to open up our options. Most specifically, to free us from the constraints of having to fly from plowed runways.

The skis, in this case, are far from new. In fact, they are over 12 years old. We got them back in the late fall of 1981 as we were winding up our first "season" flying our old weight-shift Quicksilver. Having discovered the sheer delight of ultralight flying, we weren't willing to give it all up just because winter was coming.

Off went a check to Eipper Aircraft for a set of skis for the Quicksilver. We had a ball with them (as did almost all the local ultralight crowd who seemed to appear as if by magic every time we had a nice winter flying day). In the end, I wrote up an article on ski flying for the now defunct Ultralight Aircraft magazine and ended up doing a chapter on ski flying in Markowski's book on Ultralight Techniques.

We sold our old Quicksilver back in 1988 to help finance big ticket items like blades and engine for our Gyrobee, but we didn't include the skis with the package. We've been flying the Gyrobee since 1990, but between marginal snow cover the past few years and john's runway plowing, we never quite got up the incentive to dust them off and try them on the gyro.

This year (1993) we got quite a bit of snow after Christmas and John had not gotten the plow out to bother clearing the runway. With really deep snow for a change, if we were going to fly, it would have to be from skis, unless we wanted to haul our baby over to the county airport for each flying session.

While I have no trouble generating enough enthusiasm to fly in the cold, freezing to death by loading and unloading the trailer and setting up and tearing down the machine had no such appeal. If there was ever going to be a time to haul down the skis and give them a try, this was it!

Our skis are of bonded wood construction, but metal or fiberglass, if scaled and engineered for equivalent strength, would do just as well. Our skis have a completely smooth lower surface, resulting in some interesting handling characteristics which I will get into later. Metal or fiberglass skis can be fabricated such that they have longitudinal ridges and grooves on the lower surface which can improve handling if not taken to extremes.

Most skis have a lower surface that will allow the application of wax to cut down on frictional drag. Even if you don't plan to use wax, bonding a material like formica or some other smooth surface material will cut down on frictional drag.

A number of fixed-wing ultralight manufacturers have skis available for their aircraft and, since these generally fall into the same gross weight range as our gyros, they could all be used with mounting modifications.

Our Quicksilver skis were designed to slip over the standard axles, but the KB2 axles on our Gyrobee had a significantly greater diameter. Rather than re-weld the trusses, we simply had new axle tubes welded to the existing ones, raising the height of the main gear axles by about one inch. Modifications for the nose ski will typically be more extensive, as you want a solid mount, typically using the existing nose wheel fork. Ibis should be done after the modifications have been made to the main gear skis, since you want the gyro to sit on the skis with the same attitude that it normally has on its wheels. If you end up with the nose down a bit, compared to the wheels, you reduce the rear angle of the blades on the ground (not in the air), and that will make it much harder to spin them up.

The biggest practical problem we encountered concerned the length of the nose ski strut assembly. Given the height of the main gear struts, the nose strut ended up significantly longer than the radius of the normal nose wheel. That, in turn, puts a lot of extra stress on the nose wheel fork because of the longer lever-arm. The nose fittings take a lot of abuse on snow and it is best if you can keep the lever arm as short as possible.

Over the long haul, we plan to completely re-design the truss fittings for all the skis so that the axle-to-ski distance is equal to the radius of the standard wheels, thus minimizing both nose gear stress and the proper ground trim.

Some means has to be provided to keep the ski tips at a high attitude in flight. If you don't do this, you may catch a tip on landing and that would definitely spoil the day. On our old Quicksilver, the attitude of the skis was assured by using small bungee chords to put a positive load at the front of the ski with a short cable restraint at the back to limit the nose-up angle. This tip-high attitude is clearly evident in the picture of Don landing, where you can see that the skis are definitely nose-high, relative to the keel.

Some skis used on DC3/C47's in the 50's used an airfoil on a pylon at the back of the ski to maintain a positive attitude. We elected not to use this approach since a gyro lands MUCH more slowly than a DC-3 and we weren't sure we could get the angles right fast enough to survive the first few test flights. Passive loading with bungees and cables is a more conservative approach.

Let me start with the observation that handling a gyro on the ground with skis can be just plain work! Let me let you in on why, since you are not likely to think of all the problems in advance-at least we didn't!

First comes the hangar. Nice concrete floor, but how do you move the machine around? Not easy, let me assure you! There it was, sitting solid and immovable on the skis. Dragging it was out of the question, since that was both hard work and sure to tear up the bottom of the skis. At that point, memories of picking up and horsing around the Quicksilver came flooding back, but that aircraft had lots of tubes where you lift and haul.

The Gyrobee was far more compact (one of the things we love about it), but carrying it with just two people was pretty marginal, since there is remarkably little structure to grab on to. The first few times we put it on a tarp and dragged it, but that is not a long-term solution. In many ways, it is easier to put the wheels on for moving around the hangar, switching to the skis when we hit the snow.

Most of the year, the Gyrobee goes into the hangar nose-first and we back it out when it's time to fly again. Trouble is (trust me here), backing up a gyro on skis in the snow is not a productive way to spend your time. Bungee loaded or not, the rear of each ski digs in and burrows under and you're going nowhere! That means you have to lift and carry until you have the clearance to turn it around.

You think we're brain-damaged, right? Why not put it in the hangar backwards and bring it out forward? That's fine, except it won't back up any easier going into the hangar than it will coming out. It's lift-and-carry time either way! Of course, we could turn it around IN the hangar, if the hangar were not packed to capacity with aircraft and machinery.

It is possible to leave the wheels on a bit longer for maneuvering, if the snow isn't very deep. Unfortunately, if the snow is thin enough to make that practical, it is far from ideal for the skis! Once you have it generally pointed in the right direction outside, it will tow on the skis, but it's still hard work!

The point is, you can't expect to sail out on the snow and flit around like a deranged ballet dancer. The routine moving around that you take for granted on wheels is just plain hard work on skis and is often accompanied by crude expletives drifting on the frosty air!

The most demanding thing about flying a gyro is actually getting the thing in the air. Aircraft and rotor attitude, airspeed, thrust and rotor rpm all have to come together smoothly or you simply aren't going to fly. All of this can be a lot more difficult on skis, so you shouldn't be trying it if you're not completely comfortable flying your machine. Most of the problems arise from ground handling (or lack of it!) when you trade your wheels for a set of skis.

I don't know anyone who raves about the ground handling of most sport gyroplanes. It's adequate, with experience, but nothing to revel in. At low speed, on the ground, directional control is provided by the nose wheel, shifting to the rudder and then the blades as speed increases toward the point where you lift off.

With skis, things are much messier at the low-speed end. Under the best o conditions (hard-frozen crust that will support the loaded gyro or an inch or so o soft snow on smooth, frozen ground), things aren't too bad. In this case, not too bad means that the nose ski is not particularly effective in directional control, but at least it doesn't make things worse!

In the case of the worst possible conditions (deep, soft snow), the nose ski may dig in unexpectedly, in which case you have your work cut out for you. The ski may well initiate a heading change and then be virtually ineffective in straightening the machine out when required!

In our experience, slow speed ground handling is almost impossible if you don't have the blades up to speed. With good speed on the rotor, you are "flying" the ship on the skis and you can manage. If the blades are turning slowly, the shifting weight distribution can actually degrade handling. If you have a prerotator, use it to put the best spin on the blades you can- the faster the better! With the blades moving fast enough to take up their weight and get a "bite," you will be able to steer the aircraft around with a bit of practice.

Our Gyrobee doesn't have a prerotator and that turns out to provide some very real limitations on when we can fly. If there is no wind, we are more or less out of luck. You cannot hand spin the blades fast enough to be any help and you would need to taxi slowly to get them going faster. Unfortunately, to taxi slowly you need the blades really spinning! Catch 22!

If the wind is blowing, particularly down the runway, we are in business. The blades can be hand started and then kited up in the wind to get enough control power to taxi a bit and really get them going. If the wind is light with a significant cross-wind component, things can be very marginal.

This business of directional control is very critical on a winter runway, for if the runway was plowed earlier in the season, it may well be lined by banks of snow. Get too close to the edge and you can catch a blade tip. The point is, despite the fact that directional control is degraded, you have no room to "wander". As the gyro picks up speed, you must track right down the center. Fortunately, the faster you are going, the more effective both rudder and blades will be in helping you out. You will, however, be flying the gyro while it is still on the ground, which is why I don't recommend this if you don't have a reasonable level of flight experience.

All of this presupposes a runway, where your directional options are limited. If you have a big, open field where you can move in any direction, everything can be done into the wind and even a light wind will do the job. Once they are spinning, via any combination of wind and/or prerotator, you can maneuver the aircraft. Fortunately, takeoff distances are very short with the added density provided by the cold air.

Once those skis clear the snow, you have it made! Cold air will keep your engine happy and give you a level of flight performance you can only dream of in the heat of summer. As long as you dress to stay warm (See my earlier article on winter flying in Rotorcraft, Feb/March, 1993), you'll have a ball. The added bonus is that any one of the snow-covered fields below you is a no hassle landing spot if your engine should act up. I don't know about Macs, VWs and Subaru's, but Rotax engines love that cold weather!

Landings are very much routine if you just remember to hug the runway centerline if you have snow banks on either side. judging your height when landing on smooth snow takes some practice. If you are uncertain, round out a bit high, since the cold air will provide plenty of margin in modulating or correcting the flair. Most of the time you will be hard-pressed to know when the flying stops and the sliding begins! Touching down near your turn-off point is a help, since it minimizes the distance you have to taxi. In any case, work to maintain your blade speed after landing and you will have the control you need.

Flying the Gyrobee on skis definitely involves extra work, but the effort is often well worth it. Prime winter flying weather is rare enough in the Great Lakes area and the skis definitely expand our options. If we arrive at the field and the runway has been plowed and scraped, we use the wheels. Without the skis, we would be out of luck with an unplowed or lightly-plowed runway. Barring dead-calm weather (very rare in the case of our winter scene), the skis give us aflying option. Besides, there's nothing to touch it on TV, so why not fly?!