Questions from the Cockpit: Sailplane vs. glider

Kenny, a flight instructor in Florida, asks: What’s the difference between a sailplane and a glider?

It depends on who you ask, but I think the best way of thinking about the differences — and similarities — between these two closely-related terms is laid out in the FAA’s Glider Flying Handbook, H-8083-13A.

This manual sets the stage by telling us that the FAA defines a “glider” as a “heavier-than-air aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces.”

Which, you might say, would also nicely serve as the definition of a sailplane. And, in fact, you would be right, as the manual goes on to say, “another widely accepted term used in the industry is sailplane.”

Then the book really gets to the heart of the matter, in my mind, by parsing the terms further — by differentiating flight dynamics between the two — saying that sailplanes are designed to gain altitude by leveraging natural forces, whereas traditional gliders are always, well, falling out of the sky, albeit slowly.

The feds even go so far as to point out that, while “gliding” is easy to learn, the sailplane art of “soaring” — actually going places and remaining aloft for extended periods of time — is more difficult to master.

But then, sadly, after that quite intelligent analysis, the feds go on to say that “both terms are acceptable and are synonymous.”

Further complicating the linguistic inbreeding between the terms, it’s worth noting that to be pilot in command of a sailplane, one must have a glider category pilot’s certificate, while there is no sailplane certificate whatsoever.

Anyway, there you have it. While an intelligent distinction between the two can be made, as far as the FAA is concerned, there is no difference between a glider and a sailplane at all — although I’m not sure the soaring community would agree. Chime in, engineless aviators.

But to really understand why we have two synonymous (or not) terms for fundamentally the same category of flying machine, it’s helpful to take a quick look at the timeline of engineless aircraft.

I think most aviators know that the Wrights tinkered with gliders before mastering powered flight. And a lot of folks in the aviation community have heard of Otto Lilienthal, who came before the Wrights.

But the father of gliders is Sir George Caley, who did stunning work on fixed-wing flight in the late 1700s, just a few short years after the Montgolfier brothers historic first hot air balloon flight.

Caley started with models of increasing size, working out the dynamics of fixed-wing flight. In fact, he was the first person to identify what we now know as the four forces of flight: Weight, lift, drag, and thrust.

But he did more than tinker and experiment. Sometime between 1843 and 1849 he designed a biplane glider which a “small” 10-year-old boy flew a short distance, becoming both the first Young Eagle and first human being to fly a fixed-wing aircraft. His name, sadly, was not recorded for posterity. A pity. It would be interesting to know whatever became of the first aviator.

The first adult fixed-wing pilot was likely John Appleby, a coachman (think chauffeur) in Caley’s employ. Or maybe Appleby was his butler. Or his footman (assistant butler). Or maybe it wasn’t even Appleby, but some other employee of Caley’s. It seems Sir Caley was better at recording scientific facts than details on his assistants.

Anyway, I got off course there. This was in 1853, and at the time Caley was in his 80s and judged himself too old — and perhaps too important — to be a test pilot, hence the hapless coachman-butler-footman was tapped for the historic job.

The glider was launched and “soared” 200 yards — five times further than the first powered flight of the Wright Flyer, which would follow 50 years later. But the coachman’s flight also ended in the world’s first fixed-wing airplane crash.

Some sources say that, although having the honor of being the first fixed-wing pilot in history, the coachman quit his job the very next day. He, like the boy pilot, then disappears from history.

Nearly four decades later, between 1891 and 1896, Otto Lilienthal — not at all lost to history — made nearly 2,000 flights in gliders that might be viewed as the forebears of modern hang gliders.

And, as mentioned, the Wright brothers themselves used gliders, actually making thousands of test flights over two years, using three different gliders, before their successful first powered flight — and they didn’t stop there.

In 1911, Orville Wright returned to the glider platform to experiment with a new control design featuring a “conventional” tail, rather than the front-mounted canard-style elevators of previous Wright machines.

Of course, between World War I and World War II, the Germans used gliders to train pilots as a way around the Treaty of Versailles, which officially hobbled German powered aviation. During the war Allied Forces used various large gliders as initial assault vehicles, carrying troops and vehicles into combat.

I was always impressed with the British Hamilcar glider that could — no kidding — carry an honest-to-Pete military tank into battle. Granted, only a “light” tank, but still…

The Brits built 344 Hamilcars, each capable of gliding to its target with a payload of nearly 9 tons. It was a big beast, with a wingspan of 110 feet. For comparison the wingspan of the Boeing 737 is 117 feet, 10 inches.

Then, after World War II, sometime in the 1950s or 1960s, the humble glider began to change. To evolve.

The postwar period in aviation witnessed leaps and bounds in both military and civilian aviation, and the birth of composites for airplane structures in the 1960s really turbo-charged design changes in gliders, resulting in the development of high-performance machines.

For perspective, consider that sport gliders in the 1930 had glide ratios of 17:1. By the 1960s fiberglass sailplanes were boasting glide ratios nearly double that at 36:1. Today’s machines commonly boast 50:1, with some competition machines reaching 70:1.

Anyway, by the time we get into the 1970s, we have engineless airplanes that could climb, stay aloft for hours, and go places — not just simply mimic a “flying” squirrel. And during this same time frame, we start to see the word “sailplane” really takeoff… pardon the pun.

Now, in fairness to history, the word “sailplane” had been around, if not used much, for decades. According to the Oxford English Dictionary, the first recorded use of “sailplane” was all the way back in 1922, in the journal Flight International.

Back to our timeline: The evolution of the sailplane is hardly over, even today. The ultimate modern sailplane is probably the Perlan 2, which has taken soaring, literally, to new levels, rising to 76,124 feet with no engine.

And let’s not forget the now-retired Space Shuttle. It’s perhaps the ultimate engineless (at least when landing) flying machine. Of course, it’s solidly a glider, not a sailplane. The shuttle’s glide ratio is a meager 4.5:1. Still, from carrying hapless coachman to astronaut transport, in under 128 years? Amazing.

So back to our question. I think that gliders evolved so much over their century and a quarter of existence that it really became necessary — especially in the engineless airplane community — to differentiate between the modern designs and the traditional designs. Basically, many gliders had become so different from their forebears that, by the end of the 1970s, they really needed to be called something else, hence the rise of the sailplane — as a word.

Of course, it would take an Act of Congress (literally) to change the FAA pilot certificate terminology, so regardless of the tech and performance they command, sailplane captains remain glider pilots — at least on paper and on their plastic pilot certificates.