Friday, December 26, 2014

Legend of the Lame Loon

This is the Loon, a first experiment in developing what, at the time, was called a hydroaeroplane. It failed miserably, never becoming airborne and eventually sinking. But sometimes, failure spurs further development and research, and ultimately leads to success. And of course, it also leads to a really good story (and several digressions).
The Aerodrome #3, aka June Bug, reborn as the Loon sometime in late 1908 or early January 1909 on Keuka Lake, NY.

When most people think of Alexander Graham Bell, they naturally think of the telephone, with which he is credited as inventor. However, Bell was responsible for so much more, and aeronautics was one of his biggest passions. To a certain degree, he can be credited with ensuring that the world of American aeronautics was not dominated by two monopolizing brothers from Dayton, Ohio.

Bell's personal secretary had a son, J. A. Douglas McCurdy, who had just recently graduated with an engineering degree. Being close to the Bell family, Douglas one day invited his close friend and classmate Frederick "Casey" Baldwin over to the Bell's for dinner and a discussion on aeronautics. Alexander Bell's wife, Mabel, suggested that the three men establish a research society in order to collaborate and experiment in aeronautics. Since Mabel was independently wealthy through real estate investments, she offered to finance the endeavor with a fund of $35,000 (almost a million, in today's dollars). They called the collective the Aerial Experiment Association, and it was officially established on September 30, 1907; Bell later described it as a "co-operative scientific association, not for gain but for the love of the art and doing what we can to help one another."

The airplanes they hoped to build would need engines, so the group approached Glenn H. Curtiss, who had made a name for himself by developing gasoline engines, and had became famous as "the fastest man on earth" when he had ridden his V-8 engine-powered motorcycle to an unofficial world speed record of 136 mph in 1907. Curtiss had also realized that aviation was the future, and had offered one of his engines to the Wright Brothers, only to be rebuffed; they had their own engine design, thank you very much. Curtiss thus readily accepted membership with the AEA.

The AEA Five, (L-R) Curtiss, McCurdy, Bell, Baldwin and
Selfridge. (Photo from Wikimedia)
Understanding that the government would likely be very interested in the new developments in aeronautics, Bell became aware of Army Lt. Thomas Selfridge's interest in the technology, and wrote a personal letter to President Teddy Roosevelt asking if Selfridge could be assigned to participate in the AEA. Teddy was more than happy to accommodate the request, and the AEA was then five.

Since the AEA was intended as a non-commercial scientific endeavor, they also solicited input from other inventors, and the Wright Brothers as well as Octave Chanute willingly shared some of their experimental design data. The AEA's first project was an unpowered hang-glider based on some of Chanute's design knowledge. Subsequently, the AEA group built five aircraft, each having a different one of the five principal AEA members as its chief designer.

The first was a plane designated Aerodrome #1, and named the Red Wing, designed by Selfridge (the name came from the red silk used for the wings, and oddly, the color red was chosen because it would look the best in a black and white photograph). On March 12, 1908, with Baldwin at the controls, the Red Wing took off from the ice of frozen Keuka Lake, new Hammondsport, NY, flew 319 feet, reached an altitude of 200 feet. The flight was heralded as the first public flight in the US (all of the Wright Brothers' US flights had been done in secret), and the first flight piloted by a Canadian citizen. Then, during a second flight on March 17th, it crashed, damaged beyond repair.

The AEA's second project, Aerodrome #2, built on the lessons learned. It was designed by Baldwin and called the White Wing. The design incorporated a number of innovations, including using wheels for its landing gear, and ailerons championed by Bell for roll and directional control (more on this a bit later in the story). First flight, with Baldwin at the controls, took place on May 18, 1908; unlike the Red Wing, this one flew quite well. The following day, Selfridge flew it (becoming the first US military pilot), and on the 20th, Curtiss took it into the air with a flight of 1,017 feet. Two days later, on the 23rd, McCurdy flew it but crashed on landing. It, too, was beyond repair.

Aerodrome #3 was designed by Curtiss, and again took advantage of lessons learned. The team had their eyes set on the $2,500 Scientific American Cup, a prize offered for the first aircraft to make a public flight of one kilometer (3,280 feet, or about three times farther than the White Wing flew). Named June Bug by Bell for the ochre color of its coated silk wings, the resemblance to the insect and the month of its completion, it first flew on June 21st, and between then and the 25th made five flights with Curtiss at the controls, each progressively longer, the last being 3,420 feet. Buoyed by these successes,  the team contacted the Aero Club of America and requested the opportunity to fly for the prize. In an attempt at fairness, the Aero Club asked the Wright Brothers if they wanted to attempt the record first, but they declined saying that they were too busy preparing for a government demonstration flight. So, Curtiss was given the opportunity to fly on July 4th, and a huge crowd gathered to watch the spectacle. After one false start, Curtiss easily exceeded the measured course, covering 5,360 feet in one minute, forty seconds, clinching the prize.

Then, on September 17th, the 26-year-old Selfridge was riding as a passenger with Orville Wright as the Wright Flyer was demonstrated for the Army Signal Corps, when the right propeller broke and the subsequent damage led to the crash of the plane. Neither man wore any kind of safety restraint, and both were violently thrown forward in the impact. Wright was badly injured, and Selfridge suffered a skull fracture, passing away several hours later after an unsuccessful surgery; he thus became the first person in history to be killed in an airplane crash. He had not been wearing any head protection, and as a result, the Army specified that their pilots would henceforth wear helmets.

While the faces of most of the men are obscured making identifying them problematic,
it is likely that the man working on the engine is Curtiss, with Baldwin at the controls.
The AEA team mourned his loss, but continued their development. Bell and Curtiss had both been intrigued by the idea of flying a plane from water rather than land, so decided to modify the June Bug with twin pontoons. The modified plane was re-christened the Loon and testing began on November 28th on the 20-mile-long Keuka Lake, one of New York's Finger Lakes. Try as they might, though, the team could not get the Loon to exceed 29 mph, and at that speed it couldn't break free from the water and become airborne. The AEA team continued to try until on January 2, 1909, one of the pontoons was damaged and the plane sunk. Though it was recovered, no more attempts were made, and the Loon eventually rotted away while stored in a nearby boathouse.

The failure of the Loon to get airborne was the result of one rapidly-progressing technological discipline, aeronautics, running head-on into the limitations of another, hydrodynamics. As soon as the AEA team bolted on the floats, they entered a different world, and had two areas of engineering to deal with. To understand the challenges, we need to digress for a moment and talk about boats (this will be a general overview...if you want a bit more technical of an explanation, jump down to the engineering notes at the bottom of this article). As a boat, say your average rowboat, sits in the water, it is held afloat by buoyancy, one of two forms of water-related "lift" that a boat can experience. As the rounded hull (known as a displacement hull) moves through the water, it has to shove a whole bunch of water aside and ahead of it, and that creates a whole bunch of drag, called wave-making drag. In addition, the boat also experiences friction drag from the hull interacting with the water over what's known as the "wetted" area. As the boat moves faster, the drag increases significantly, meaning that ever-increasing amounts of power are required for even small increments of additional speed. In addition, such displacement hulls have a tendency to tuck under if too much power applied.

The second type of lift is what's known as "planing" or "hydroplaning", in which the boat is supported by the dynamic lift provided by the water rather than its buoyancy. It's not unlike part of the lift experienced by an airplane's wing. If a boat is properly designed and can reach the point (and speed) where it is planing, it will no longer tend to tuck under, but instead the nose will pitch higher and higher as the center of lift (aka dynamic pressure) moves aft with increased speed.

What doomed the Loon to failure was the fact that it used two very thin, knife-like pontoons, and so all of its water-derived lift was displacement, and as the pilot tried to accelerate to the speed where the wings would produce enough lift to fly away, the water drag would increase dramatically, and tuck-under would start to happen. In the parlance of the day, the AEA team described it as not being able to become "unstuck" from the grip of the water.

The liquid-cooled V-8 engine on the Loon was a direct
descendant of Curtiss' air-cooled V-8 motorcycle engine.
The tall component is the engine's radiator.
The AEA went on to build two more land-based aircraft, the successful McCurdy-designed Silver Dart which first flew on February 23, 1909, and the highly unorthodox and unsuccessful Bell-designed Cygnet II, which was not able to get airborne. By this point, Curtiss saw the commercial potential for aeroplanes, and partnered with August Herring to form the Herring-Curtiss Company in late March. This led, ultimately, to the dissolution of the AEA. Curtiss purchased the design rights to Aerodrome #3, and modified it to become the Curtiss No. 1 (aka Curtiss Gold Bug, aka Curtiss Golden Flyer), with which he again won the Scientific American Cup in 1909.

Despite the failure of the Loon, Curtiss and Bell hadn't given up on the idea of water-borne flight. The lakes, rivers and oceans presented, as Curtiss saw it, a lot more places to fly from than land, with a lot few obstacles. An article in the March 1906 issue of Scientific American by William Meacham on the principles of hydroplaning had intrigued Bell, and he and Baldwin did some experiments in 1908 to test out some of the principles the article advocated. It is unclear whether Bell continued to work with Curtiss on the concept of hydroplaning after the break-up of the AEA, or whether they studied the same concepts parallel to each other; Bell's efforts drifted towards developing the hydrofoil, culminating in his HD-4, which set a world marine speed record of 70.86 mph on September 19, 1919.

Curtiss also continued studying the concept, and achieved some success by employing single pontoon with a wide, flat bottom. This became his Model E Triad (which we featured in this December 31, 2011 blog post). The flat, curved nose of the pontoon promoted planing as the flying speed was approached, but at the same time also caused excessive nose pitching. In addition, flat-bottom hulls have their own sets of problems - they're harder to turn at speeds greater than 30 knots, and they tend to ride very rough moving from wave to wave. So the Triad was progress, but not the end.

Through the efforts of Curtiss, as well as powerboat pioneers Gar Wood and Christopher Smith (who went on to found Chris-Craft), hydrodynamics came of age and the key turned out to be the "stepped" hull. By cutting a notch or "step" across the hull roughly amidships, the area of the hull supporting the weight of the vessel was split in two. This accomplished two primary things: first, it reduced the "wetted area", the amount of the hull directly in contact with the water, thus dramatically cutting the drag of the water, and allowing the vessel to go faster on less power. Second, it supported the weight by two pressure points spread over the length of the hull, which meant that the nose didn't pitch up nearly as much. For the boating world, the innovation of the stepped hull was huge, resulting in dramatically increased power boat racing speeds. For the aviation world, it now opened up all kinds of technological development possibilities, which Curtiss and other designers exploited, moving from traditional airplanes mounted on pontoons to true flying boats, stepped-hull boats with wings attached. Curtiss finally found success with his Model F Flying Fish (which we covered with this post from March 8, 2013). For this development, Curtiss was awarded the 1912 Robert Collier trophy, aviation's highest award for innovation. In 1918, Curtiss received a patent for his stepped hull design.

The triangular ailerons on the Loon, nearly identical to those first used on the
White Wing. And one has to wonder about the hat of the person in the back of
the rowboat in the distance....
But there's another digression to the June Bug/Loon story which we'll take for a few minutes, the bit about the ailerons that I mentioned early on with the White Wing. The Wright Brothers controlled lateral stability (meaning roll) through the use of wing warping. The AEA crew were leery of this methodology, because of the stresses it placed on the wing's structure and wires. Over-stress things, and you break your wing and fall out of the sky. Instead, Bell came up with the idea of moving triangular surfaces mounted to the ends of both wings. Ailerons (French for "little wings") had been used experimentally by Robert Esnault-Pelterie in France since as early as 1904, and it is unclear whether Bell had "borrowed" the concept from the French, or whether he came up with it independently.

The ailerons were connected by cables to a harness (on the White Wing) worn by the pilot...lean to the left and the surfaces (which initially were known as "horizontal rudders") moved to turn left. For the June Bug, the harness was replaced by a yoke which the pilot sat against with his shoulders, but again, it was lean left, bank left.

All was fine during the flights of the White Wing, because it was a purely scientific research project. The June Bug was a different story altogether. As soon as the AEA cadre had clinched the $2,500 Scientific American Cup prize, they received a nasty-gram from the Wright Brothers, chastising the AEA team as the Wrights had not give permission for the use of what they considered their proprietary aircraft control technology for public exhibitions or other commercial use - this despite the glaring fact that the AEA used ailerons whereas the Wrights used wing warping. The letter was a first-shot in an epic legal battle that would span the next several of years and dominate the politics of American aircraft development.

While the Wrights didn't use ailerons in their design, they had written their patent application so broadly that the concept behind ailerons was included as part of their exclusive intellectual property, or so they alleged. And, after firing off several warning shots, they alleged it with success in court. In response, Alexander Graham Bell filed and was granted a patent that specifically applied to ailerons in December 1911. Unfortunately, his claims were later overturned by a court in 1913, which ruled Bell's attempt as a violation of the Wright's 1906 patent. The fight went beyond the AEA, and the Wrights specifically went after Curtiss. Undeterred, he and his lawyers put up one legal roadblock after another, and he all the while continued to utilize ailerons, and refined how they were implemented, in his designs.

The legal wranglings between the two parties so chilled American aircraft development that when WWI started, the US had no practical aircraft with which to fight, and initially had to use French-designed planes. Fed up with the impasse, the US government forced all the parties into a patent pool, and innovation once again started flowing, at least for the duration of the war. Ironically, in 1929, the Curtiss and Wright companies merged, creating the Curtiss-Wright Corporation, which continues in business to this day.

The irony is that no one, at the time, remembered an early but very important bit of aviation history: that ailerons as a method of lateral control had been actually developed and patented way back in 1868 by Englishman Matthew Piers Watt Boulton. But because no one as yet had successfully built a powered aeroplane on which ailerons could be used, the Boulton patent sat all-but-forgotten. Had this little bit of information been remembered and brought up in court, it is very likely that the Wright's claims over the designs would have been thrown out, and the course of American aeronautical development might have taken a very different, and much faster route.

Some hydro engineering notes for my aero friends (those prone to boredom beware: the fun story is over and it's essentially a technical snoozefest from here on out): As mentioned briefly above, the primary limiting factor for a rounded-bottom displacement hull which constantly is pushing its bow wave out in front of itself, is its "limiting speed" or "hull speed", the speed at which no amount of additional power can result in any additional speed (as long as the boat remains in displacement mode); in other words, the drag curve exceeds the power curve. Essentially, it is the speed at which the wavelength of the bow wave is equal to the length of the boat, and the boat is thus trapped in its own wave and cannot accelerate further. This is usually measured by its Froude number, the speed-length ratio of the boat (to be clear, the ratio is actually speed in knots divided by the square root of the length of the loaded waterline); the Froude number is analogous to a Mach number in an the Mach limit is approach, resistance rises exponentially. Hull speed is typically reached at a speed-length ratio of 1.3 to 1.5. This "limiting speed" is affected by two factors: weight of the vessel (and longitudinal weight distribution as a subset), and length of the hull.  If you want to go faster, you either reduce weight or lengthen the hull (or both).

However, if the hull shape is altered, the boat is light enough and enough power is used, a boat can move beyond displacement speeds. What happens then is that the bow wave is pushed aside so forcefully that it doesn't fully close behind the boat, and the stern drops down into the resulting trough, raising the nose. Now, suddenly, the waterline of the boat is shorter than its hull length, and the boat begins to interact dynamically with the water, creating a hydrodynamic pressure point (ie, creating hydrodynamic lift) which then moves aft as the speed continues to increase. In practical terms, then, as the speed increases, the boat breaks out of displacement mode and literally climbs on top of and begins planing on the bow wave. In the speedboat world, this was first achieved in 1908 (there's that year again!) by Henry Crane with his Dixie II, which then dominated the Gold Cup and Harmsworth Trophy competitions for the next few years.

The next step in the technological development of boat hulls (and hydroaeroplane hulls) was to refine the shape of the bottom to promote planing, essentially making it easier for the boat to climb up on top of its bow wave. By creating a sharp "chine", or edge where the bottom of the boat meet the side, the planing hull tends to force the bow wave down, rather than pushing it to the side as the displacement hull does. This does two things. First, it starts to lift the nose out of the water, allowing the boat to climb on top of the bow wave. Second, it keeps the water away from the vertical, flat side of the boat, reducing wetted area, and thus reducing drag. Meanwhile, it was also discovered that a flat-bottomed hull also reduces drag (remember Curtiss and his Triad?), so a typical planing hull with be vee'd in front with sharp chines, but flat abaft.

A planing monohull has its limits, though. Once on top of the bow wave, and as the pressure point continues to move aft, the angle of attack will start to drop, meaning that the wetted area - and drag - will increase. Again, a limit is reached where no amount of additional power will result in additional speed. That, then is one of the primary factors in limiting the top speeds of a racing boat, and why even slight variations and refinements in hull design can result in victory or defeat. For a seaplane, this limit speed becomes important relative to the flying speed of the wings. With a big, slow biplane such as the Triad, the wings will simply lift the hull off the top of its bow wave before the limit speed is reached. But larger, heavier planes (ie, planes big enough and with enough of a payload to be genuinely useful) typically have higher flying speeds, which can easily exceed the limit speeds of a planing monohull. This is the situation that Curtiss then found himself in. The Triad was nice, the Navy was intrigued, but it really wasn't terribly useful for anything really practical. And that's why he continued to seek better hydrodynamic answers.

In a planing monohull, the majority of the lift is generated at the front of the water contact area, with the area behind it creating mostly drag. By using a step (or multiple steps) to split up the areas of dynamic pressure, a single long, narrow (ie, low aspect ratio) area is replaced by several short, wide high-aspect areas. By shortening the length of the wetted areas, the portions primarily producing drag are significantly reduced, meaning that now the boat (or seaplane, in Curtiss' case) can go significantly faster on less it can reach flying speeds. In addition, use of distributed pressure points allow the surfaces to contact the water at the optimal angle of attack over a much wider range of speeds and thus it is very efficient hydrodynamically.

The development of a stepped hull can be traced as far back as 1872 in England when the concept was theorized, but at the time, there were no powerplants yet invented that could drive a boat to the speeds necessary for a stepped hull to be effective. Development in the US in the early 20th Century took place on multiple fronts. William Henry Fauber received a patent in (you guessed it) 1908 for a stepped hull, but found little commercial or racing interest in the US, so went to Europe to try to find interest. Gar Wood won the Harmsworth Trophy in 1920 with the first Miss America, a boat with a single step, and his subsequent designs so dominated the competition that few other boats even chose to compete. The stepped hull developed by Curtiss is used universally on seaplanes to this day. At slow taxiing speeds, a sea plane will be in displacement mode, which can easily be seen by the large bow wave it pushes out in front of itself. But as the pilot accelerates, in aviation terms, he "gets up on the step", meaning that the hull begins to plane and rise up out of the water, riding on top of its bow wave. Fast taxiing is referred to as "step taxiing".

The shape of the step is critical, and different shapes can be "tuned" to be most efficient at different speeds. Because the basic purpose of the step is to raise a portion of the hull out of contact with the water, it is essential that an air path be included. This is why the steps are cut all the way to the edge, or chine, of the hull. As the boat is lifted when reaching planing speeds, a low pressure region is created immediately behind the step, and this pulls in air from the sides. An unobstructed air path is critical. If, for instance, the air path on one side of a boat is momentarily blocked, the planing is interrupted on that side immediately. One marine writer describes it as if the boat was suddenly grabbed on that side by a giant hand. The result is usually a sharp, uncommanded turn - as much as 180 degrees! - and potentially even capsizement. Because of this, some boat designs use air inlets far above the waterline, and/or vent engine exhaust into the step region. This can be a factor for seaplanes, as well, as was demonstrated in a well-publicized crash of a Grumman Goose on an Alaskan river (video clip here). Loss of planing on the step on one side leads to a wing float strike and then all control is lost.

Not bored enough? A detailed paper on the math of hull design factors can be found here.

Note on the print: The Archive's print appears to be one of a series (photo #6 in the set) that was commercially offered as souvenirs. This is not necessarily a unique image, as there are several other low-resolution examples out on the internet (I have yet to see any, though, that have the degree of detail that this print features). There appear to have been at least two different commercial offerings of the image, as the numeral "6" appears in different places. However, all seem to demonstrate the same zebra striping over the ridge in the background, indicating that the master negative, probably a wet-plate type, was damaged early on.

No comments:

Post a Comment