Text updated on July 12, 2007

...In the drawing below, we see the anti-stall, anti-pitch device that exists on all wings nowadays. At the ends there are “deflectors” or “floaters,” attached to the leading-edge tube. The ends of the struts are also connected to the top of the mast via guy wires.

In this way, the entire grayed-out portion of the wing helps to straighten out the aircraft in case of an accidental dive.

...Between this current design and early models: a path littered with many deaths. In the drawings below, we see the structure of a modern delta wing:

The “framework” of the wing: tubes and cables.

...The harness has changed a lot. Twenty-six years ago, pilots flew standing up, suspended in a parachute-type harness. Then came flying while lying down. At takeoff, the pilot would run while holding part of his cocoon-like harness between his teeth; he then had to twist himself to get his legs inside it. Later, someone had the crazy idea of adding a kind of wasp-abdomen to these harnesses, as seen in the drawing above. Right after takeoff, the pilot “retracts the legs,” meaning he slides both legs into that bag, which he then closes by manually operating a zipper. The most amazing thing is that all this happens without any problems.

...This is what I look like under my Tecma “Cloud” after taking off (my own machine). On my belly, there’s a reserve parachute. It’s a wing you can really have fun with—covering distances, handling turbulence. A solid wing, both structurally and in terms of flight qualities. Of course, one shouldn’t be foolish and fly under cumulus clouds turning into cumulonimbus clouds, or near rolling hills. ...At landing, you pull another zipper and “extend the legs.” This maneuver never ceases to delight me. Who would have thought, twenty-five years ago, that such devices would ever appear (back then I landed using skis modified with stroller wheels. Thankfully, that didn’t last long).

The free wing, today.

...Can we say all problems have been solved in the ultralight sector? Let’s say the machines have progressed quite a bit. But sadly, this progress happened because many people died. Why? Because ultralight aviation grew like a wild plant. My mind is heavy with tragic memories. One day, a manufacturer introduced a double-surface wing. Performance immediately improved. Nowadays, heavily strutted on both upper and lower surfaces, these Dacron wings end up looking almost like airplane wings. With high aspect ratios, they bear little resemblance to the Manta models from the seventies. Switching to “double surface” increased fineness, reduced drag, and lowered the sink rate. But with that wing, when turning, if it went into a slide, the aircraft would nose-dive.

...More deaths. Pressure had to be exerted on the manufacturer for the scandal to stop.

...Was it necessary for people to die so that this sport could once again progress “freely”? No, they could have tested those materials in a wind tunnel. At ONERA, engineer Claudius Laburthe had access to the large Chalais-Meudon wind tunnel where wings could be tested at full scale. Is that wind tunnel still available? Was it still operational back then? Couldn’t tests have been done on scale models, possibly remotely controlled?

All this costs a lot, one might object? But how much is a human life worth?

...Ten years ago, my friend Michel Katzman, with whom I’d flown for 15 years, died stupidly. He was one of the pioneers of this sport and had lots of experience. A component broke mid-flight. He was flying a two-seater, with a passenger, no reserve parachute. Here’s that component, at full size:

...The attachment method shown here is only schematic, but it’s a simple stainless steel “hole lug” allowing a lower guy wire to be fixed to the aircraft’s tubular structure. That lug broke mid-flight. Michel and his passenger found themselves trapped in a coffin of fabric, cables, and broken tubes. During the fall, he shouted; he was clearly heard from the ground: “Close your eyes, we’re doomed!” Throughout that endless descent, Michel must have thought, “I never believed in parachutes. But now, maybe they’d actually help us...”

...No hole lug had ever broken on any delta wing since their inception. So why?

Material fatigue.

...All aeronautical engineers will tell you: what matters most in sizing parts in aviation isn’t so much static strength as fatigue resistance. You’ve all bent and unbent a wire or sheet metal many times until it finally snapped. That’s metal “fatigue.” In this case, we’re forcing things. But any metal part subjected to alternating fatigue loads gradually loses its strength. It could be a rotor blade working under bending stress, or the wall of a liner cabin experiencing pressurization and depressurization each flight. It could be... anything. A hole lug, for example.

...I’ll tell you a story written in blood in the history of international aviation. After the war, the British launched an incredibly advanced aircraft: the four-engine Comet. It was the first of its kind. We know the British were leaders in jet propulsion right at the end of the war, with their “Gloster Meteor.” The Comet was sleek, attractive, fast. But a few months after dozens of units entered service, there was a series of baffling accidents. Each time, a hundred passengers lost their lives. The planes were grounded and the Hawilland company saw all its orders cancelled. Many teams were left unemployed.

...One thing was known: the accidents always occurred after a certain number of flights. There were no black boxes back then. When accidents happened, pilots didn’t even have time to send a distress call; it was as if the planes literally exploded mid-air. Well, that’s exactly what happened. To reach this conclusion, they simulated pressurization-depressurization by enclosing a Comet fuselage in a chamber. Tests began. After a certain number of cycles, the fuselage gave way at a window area. That number matched closely the cycles endured by the plane during its initial commercial operation.

...It’s practically impossible to predict fatigue phenomena. The problem is too complex. The only solution is to test materials and whole structures. On special test rigs, aircraft landing gears endure countless impacts simulating runway landings; wings undergo alternating flexing, commanded by simple cranks mimicking gust forces. This can go up to a hundred million cycles.

Actually, material strength declines from its static value. This decline curve is called the Wöhler curve, if I recall correctly. Some structures, under given stresses, see their strength drop then stabilize at a constant level. If this value exceeds the load expected in normal use, we conclude the structure is “fit for service.”

...The aerospace industry has set standards and adopted safety factors. Today, when you sit down in a commercial airliner, you can be sure all components have been tested against shock, cold, heat. Safety comes at this price.

...Same goes for “small planes,” two-seaters, four-seaters: they aren’t built haphazardly but calculated and tested for fatigue. Same for what’s called “light aviation.” Amateur construction thrives, but is regulated. Take the example of a rather famous single-seater, the “Cri-Cri,” originally powered by two lawnmower engines. At first, one man designed, drew, and built it. But he filed calculations reviewed by competent experts. He tested his craft under stress and fatigue, respecting existing standards. The mechanical strength of a wing depends primarily on a “longeron.” The Cri-Cri inventor tested his own, using an eccentric mounted on an electric motor. One hundred million cycles. The test was validated. The inventor got the green light to market his product. No Cri-Cri wing has ever broken mid-flight.

...And in ultralight aviation? Sadly, nothing similar (&&& written in 2001. But it’s safe to bet that six years later nothing has changed). In this field, we’re still in the Wright brothers era; as we know, they started out as bicycle makers. Nobody calculated or tested the hole lug whose break caused my friend’s death. “It seemed thick enough to hold,” that’s all. You can’t blame the manufacturer: no regulation required him to do such testing, and I believe he simply had no idea what “material fatigue” meant.

...Under static load, the part could withstand several times the harshest forces. But nobody tested its fatigue resistance, nor even thought about it. Yet it would’ve been easy. A frame, an eccentric, traction, flexing, thousands, millions of times, simulating ten or a hundred times the stresses experienced in the toughest conditions, well beyond the aircraft’s lifespan.

...The broken hole lug was cut from fifteen-tenths thick stainless steel sheet. With two millimeters thickness it never would have broken. All hole lug thicknesses were later checked, some increased. But for that, two more deaths were needed.

...I don’t blame the manufacturer, Mallinjoud. The poor man spent plenty of sleepless nights over this tragedy that cost the life of a man who was also his friend. It’s the system that’s totally flawed. No standards, no periodic checks, no helmet requirement, no need for a reserve parachute. Just glorious freedom.

...Regarding construction, in ULM there’s total chaos (&&& written in 2001. If things have changed, let me know). We’ll dedicate a full article to this. In this area, it’s the main issue. I’ll merely cite a recent, very revealing fact. A few months ago, a friend drew my attention to an idea seemingly appealing due to its simplicity. Someone decided to build ULM using ordinary recycled duralumin ladders. He bought a whole batch cheaply at a big-box store. Light, relatively strong. The man opted for the “sky flea” formula.

The “structural” part of this revolutionary ULM: Three lightweight alloy ladders.

The same, “clothed.”

...Of course, it flies. With fifty horsepower you can make a ULM fly, built from anything. But let’s take a closer look at these famous ladders.

...Any beginner engineer would explain that these square holes, where ladder rungs are inserted, are ideal spots for “cracks” to appear under bending and torsional stress, eventually causing mid-air failure. But who oversees the brilliant experiments of this “job creator”? (I’ve even heard of “subsidies”). Which technical authority is authorized, mandated to poke its nose into this affair? None. In ULM, anyone can make anything, however they wish, and sell it to anyone, whether they have a pilot license or not. Did you know that?