Gliding and Soaring


What is Gliding?

I am often asked about gliding and soaring, so here is a brief introduction. Gliders are airplanes without any engines, that is, gravity pulls them down, but wings delay that action by creating lift (and drag) against it. For a given weight, a glider will lose altitude at a predictable rate that is only influenced by its airspeed, with the relationship between the two commonly called the "Polar".

../Russia_AC-4B/AC4A_Polars.gif Typical "polar" of sink rate function of airspeed

Essentially, the faster you fly, the faster you lose altitude, but you also sink faster when going too slow, as then the wings become less efficient. Between the two is a "sweet spot" of so-called "minimum sink". Let's say that you keep a constant airspeed, controlled by how much you point the nose up or down with the elevator on the tail, at a sink rate of 200 feet per minute (fpm). If you are at 3000 feet above the ground, it will take you a quarter of an hour to just glide down.

Cargo gliders were towed behind C-47s (DC-3s) during World War II to do just that, gliding silently from their release altitude to their designated Landing Zone after careful calculation of the winds aloft (often at night time).

What is Soaring?

Now, if you fly down at -200 fpm in air that itself happens to move up at 500 fpm, the net difference is that you climb at 300 feet per minute relative to the ground. If the air is instead going down at -500 fpm, you have less than 4 minutes to find a landing spot, or fly out of there. The whole art of soaring is to find the areas where air is moving up faster than your glider is going down, and circle to linger in those areas, to gain altitude, and conversely, to avoid the sink areas by fast flying straight out of them. That's all there is to it.

Air can move up for a variety of reasons. In the American Midwest, it is only in the form of inverted cones of hot air called thermals. The ground heated by the sun heats up in a mottled pattern like a sauce warmed up in a pan on a stove. Warmed air is less dense, and therfore rises, hopefully with your glider in it. At the top of the thermal, several thousands of feet higher, the air has cooled again and fountains down around the thermal. What makes soaring challenging is that you cannot directly see thermals, only indirect signs of them. Glider pilots learn to visualize them, and how they slant in the wind. How high can you climb in a thermal? Very high in the West, but for Illinois the record is 16,000 feet (and mine 10,500'). Realistic expectations can be gathered from the following plot:

ThermAlt2K0.jpg Samples of maximum altitude of thermal flights above Piatt County, 2000-2010

Air also rises on the side of a hill when wind blows against it, which is the basis for slope soaring or ridge soaring. Its ripples are sometimes felt several times higher, and that may very high (50,000 feet) when that hill is a mountain. There are also obscure means for air to rise, like a dense cold air wedge pushing under warmer air in a cold front, or humid air patches (humid air is lighter than dry air).

A typical number gathered from the polar is the "Best L/D" (Lift over Drag), here showing as the 31:1 tangent line. The best L/D is commonly used to estimate the distance covered for a given loss of altitude. For example, travelling 3100 feet (half a mile) consumes 100 feet of altitude, and heavier gliders would cover this distance faster. If you are one mile high, you can cover 31 miles. This Best L/D number is used to compare gliders, from 20:1 trainers to 50:1 high-performance ships.

The Magic of Soaring

Although the mechanisms of thermals are known, there is something eerie in being able to stay aloft a mile high, for hours on end, without any engine. To give you an small idea of what soaring is, here is the account of my first cross-country flight in a glider.

Unlike powered airplanes, which kind of fight it, gliders are part of the atmosphere. Bumps in the air are a nuisance for an airplane pilot, but they usually show the location of air boundaries to a glider pilot. Air masses take a surprinsing amount of time to mix, and this in turn creates small differences of density and temperature, but for huge volumes, that are taken advantage of by gliders.

In a glider you look around much more than in an airplane, and you notice things on the ground that you totally miss flying a typical airplane, or in an airliner. Gliders have often a large plastic canopy with very good visibility. Sometimes you are so high that you do not even see cars on roads, only semis. Even on a cloudless day the air below you gets hazy, and has sometimes like a milky opalescence, depending on the sun's elevation. It is like escaping from the Earth.

It can also be cold up there. Twice I had to abort a flight because my jaw muscles had become too stiff to talk fluidly in the radio, yet it was blistering hot on the ground. All glider pilots wear hat and sunglasses, but you recognize the pros at their somewhat overdressed garnments for the season.

It is not uncommon to circle with hawks in thermals, and regardless what biologists say about their piercingly sharp vision, they are often way too high to be hunting anything; they are then just flying for fun. They also always beat you up in the same thermal, which makes you think that technology has still a way to go. African vultures are said to travel miles to come circle with a glider, which is the opposite of what pilots do in Illinois, flying towards any bird of prey, or anything, like corn stalks, dust clouds, floating in the sky. That's where a thermal is, or was.

One day I had a passenger for his first-ever glider flight, not that high. Suddenly his cell phone rang, and he received a beautiful sunset picture from a friend vacationing in Austria. That did not phase him. He asked me to circle around the town below, videotaped it on his cell phone, and sent the clip back as a reply. I hope they are still friends.

Passengers are always in the front seat, because it provides a much better view for them. What they often do not realize is that when flying from the back seat, there are no flight instruments, just a second microphone jack for the radio. You do not need instruments, you can get all your information from looking outside, the noise, and the feel of the controls. It gives a great sense of freedom from "things"; you only have wings.

There are also unexplained phenomena. Once I encountered a very brutal bump, so sharp I was glad to be tied to the glider by a four-point harness, in air that was otherwise quiet. Also, towards the end of one day, in ultra-smooth air above a marshy park, I was drifting down lazily at minimum sink rate towards the airport, except that the altitude would just not wind down. I thought the altimeter had jammed, but no, for half an hour I remained at the same altitude, not in a thermal, but possibly in humid air released from between the trees.

Some benefits of Soaring

Soaring is one of the few human activities where the older you get the better you are at it; where else can an 80-year old repeatedly beat a 20-year old? I always viewed this activity as ideal for retirement (but living in the USA, I don't know if I'll ever be able to afford to retire...). It also puts a welcome pressure on the pilot not to gain too much weight over the years, as there is a payload limit for all gliders.

DerekPiggott_Me7.jpg Derek Piggott, aged 81, after a 505 km task in England aboard a Me7 (AC-4) where he beat many younger pilots with superior machines (Wikipedia).

Soaring is also a perfect school for judgement, because it is essentially a constant stream of decision-making. Beyond decision-making, it is also learning to partition what is important from what is not, especially for details. I consider a Glider Pilot license to be a requirement for the good education of children. In the US it is FAA-legal to solo when you turn 14.

Flying gliders is actually much more fun than flying airplanes (with the exception of flying seaplanes, but that's another story). If I had to do it all again, I would never have learned to fly powered airplanes (and also saved significant monies). In Europe, flying gliders is much more common than flying airplanes, mostly because of cost. In the USA, it is the opposite; it is the glider pilots who are the happy few.

If you also fly powered planes, flying gliders will definitely make you a better pilot. Even the infamous "engine failure" becomes trivial. When extending the dive brakes on a Schweizer 2-33 trainer, you happen to glide down at the same vertical speed and airspeed as a Cessna without power. It is a good exercise to reach the runway after having promised yourself not to retract the dive brakes until a few feet above the runway. Engine failures become second nature in no time.

Some dangers of Soaring

I am often asked if flying gliders is dangerous. I used to reply with the classic "driving to the airport is more risky", but now I say that "you can make it as dangerous as you want". When in competition or trying to break some record, one is naturally prone to stretch limits and gamble with marginal odds, although in Illinois the whole countryside is a runway. On the other hand, training and judgment can also make soaring very safe.

What most car drivers do not realize is that cruising along a road lined with trees, turning the steering wheel a couple degrees, and hitting one, survival is very unlikely. This is the same in gliders, if you do not control your pitch within a couple of degrees when about to land, you are not likely to survive either. As a glider pilot driving a car, now I instinctively see trees, bridges, utility poles, and parked cars along the road as deadly reinforced concrete pillars. Also, you have no control on the many drunk and other rogue drivers, even if you drive perfectly yourself. A glider crash (or even a plain off-airport landing) will make the front page of the local newspaper, yet in the USA car accidents kill 40,000 people a year without a second thought.

My 100th glider flight had an exciting moment. Dragged down to a pattern altitude, I hit a strong and narrow updraft and decided to go for it. Banking at 60 degrees to remain in the narrow core, the glider suddenly got spat out of the thermal. No more wind noise, no pressure on the controls, full stall. I remember clearly looking straight down at corn stalks, with more curiosity than disbelief. Training pays off in those rare occasions. I was focusing on keeping the yaw string straight to avoid entering a spin, and resisting the urge to pull the nose up before I had regained sufficient airspeed to fly again. It is only after landing that I realized that had I pulled the stick instead of pushing, it could have been the end. This is what training is all about, to transform mishaps into non-events.

Mid-air collisions
To my sense, the only risk that is a little open-ended is a mid-air collision. All the other risks (maintenance, weather, flying itself) are entirely and squarely under the pilot's control. I like to wear a parachute, for any mishaps above 1000 feet above ground level, like a collision most probably with another glider in the same thermal. This risk increases significantly in "gaggles" of thermaling gliders, and this is why parachutes are required in competitions.

One day I heard a twin-engine airplane as I was lazily circling on a clear VFR afternoon, noise distant, closer, than distant again, but I never ever saw it! That plane probably happened to remain geometrically behind me in my turn, or hidden in the glare of the sun. As a result of this event, I also monitor nearby transponder-equipped aircraft with a portable Traffic Proximity Alert System, which looks like a minipack of cigarettes rubber-banded on the glareshield.

SurecheckTrafficscopeMicro.jpg Trafficscope(R) only provides relative distance in "bars" to nearest transponder-equipped aircraft swooped by ground radar.

Zaon_MRXA_Diag.jpg Second-generation MRX(R), with audible alerts (2 beeps) and warnings (4 beeps), great for gliders, where you look out all the time.

Zaon_MRXA_Display.jpg The MRX showing target 1.9 nautical miles away, 500 ft above, and descending (towards you!).

In Europe most gliders are equipped with the successful GPS-position broadcasting FLARM system, but it is unfortunately FCC-illegal, probably because there are not enough gliders in the US to warrant a dedicated frequency. There was a collision between an errant Airbus and a glider in France some years ago (glider totaled, no fatalities). After a well-publicized collision of a glider and a private jet above the Rockies (both totaled, but no fatalities), the FAA is starting to move, and ADS-B looks like a promising way to go.

Cost-wise, the MRX from Zaon can be bought for less than $500 (gulp) including shipping, but is absolutely worth every penny (and compare with a real $30,000 TCAS-II). When it detects a target, I like to follow it both visually and on the MRX, to get a good feel of the MRX behavior. The relative altitude is extremely useful, because it is always harder to see aircraft below you. Airliners have more powerful transponders, so they are detected earlier, which is perfect since they fly faster.

The sky always looks empty, but it is not. For example, from the "other side", in a small jet after taking off, the TCAS showed the following blur

Universal_TCAS.jpg (turbulence is realistic)

yet I did not see any of the 12 targets, not even the two closest ones. And this does not show the non-transponder aircraft, like most gliders. But with the MRX, I have a good chance of detecting the jet if it heads for my glider, even if it does not see me.

The Illini Glider Club

Champaign-Urbana is in the Midwest, mid-distance (2 hours) from Chicago, Indianapolis, and Saint-Louis, so yes, it is in the middle of nowhere. No beach, no nice parks, not even hills, no lake, and if the University of Illinois and its 30,000 students was not there, it would just be a coal stop for the Chicago - New Orleans railway line. There is not much else to do than work (hence the good reputation of UIUC), or watch corn grow. As the coasties say, it is "fly-over" country. But that's exactly that; there is a big sky overhead.

One of the best-kept secrets of Urbana-Champaign are the activities of the Illini Glider Club, founded in 1948, based at Monticello airport (2K0), 13 miles West. It is a 60-member all-volunteers non-profit corporation operating 4 gliders, plus one on loan from the Collegiate Soaring Association. The club operates mostly from March to October, but over the winter as well with a reduced fleet. For more general information on soaring in general, check out the Soaring Society of America (SSA).

If you have 200 hours airplane time, of which 25 taildragger, you can also tow gliders for the Club.

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