Trivia Testers : The First Controllable Rotorcraft

The first controllable rotorcraft

In 1907, in France, the European cradle of aviation, the world’s first rotorcraft lifted itself straight up. But the first vertical flights of Breguet and Richet’s gyroplane (steadied by four men) and then Paul Cornu’s machine a few months later (which was more stable, and which rose only a very short distance), were not truly controllable. Aside from the fact that the first truly flyable rotorcraft was not a true helicopter but an autogyro, who designed and flew the first rotorcraft with the ability to fly forwards, backwards, and sideways by means of a “cyclic” control?

  1. Louis (and Jacques) Breguet
  2. Igor Ivanovich Sikorsky
  3. Raul de Pescara
  4. Heinrich Focke
  5. Thomas Edison

Answer: a regular United Nations to choose from here, ain’t it? The answer is C. In case you are unaware, a cyclic control varies the pitch of individual rotor blades over specific sectors along their circle of rotation, as opposed to a simple collective pitch control of all blades at once (like, um, in an airplane). Juan de la Cierva is often credited with creating the first succesful helicopter, which was actually an autogyro, where forward thrust was provided by a conventional airplane propeller and lift was provided through rotor blades which would have otherwise simply been in a constant state of autorotation. (The Russian inventor Boris Yuriev, also written as Yur’ev, proposed the idea of using an anti-torque rotor, as early as 1912.) Cierva’s C.8 Mk IV made the first crossing of the English Channel by a rotary-wing aircraft in September, 1928. Heinrich Focke’s Fa-61, flown by the well-known Hanna Reitsch in June, 1936 was an early rotorcraft, which looked like an autogyro, with twin rotors on outriggers on either side of what looked like an airplane fuselage (however the engine actually drove the rotors as well as a front-mounted tractor propeller). Igor Sikorsky’s VS-300 was the first successful US-built helicopter, in September 1939 (and it really looked like a helicopter). But it was an Argentinian engineer, the Marquis Raul Pateras de Pescara (who at the time was living in Barcelona) who first figured how to build a vertical flight machine that allowed the pilot to vary the pitch of the main rotor blades. Why is that so important? Due to the dissymmetry in aerodynamic loads between the sides where the rotors are advancing into the direction of motion, and retreating away from it on the other side, a means of changing the pitch on the blades during their rotation is needed. Also, by selectively varying their pitch even in the absence of forward motion, any desired lateral motion can be induced. (To be fair, there were others who realized the necessity of having a means of effecting a cyclic variance in blade pitch, such as Yur’ev, as well as an Italian named Gaetano Crocco, in 1906, and also a Danish aviation pioneer named Jen Ellehammer.) After moving to France in 1922, de Pescara’s third design the following year incorporated the first credible use of cyclic and collective pitch controls (although it was based on wing warping). Incidentally, he also proved that a helicopter could still autorotate and land safely in the event of an engine failure. The world’s first “true” helicopter is credited to Louis Breguet. His coaxial rotor Laboratoire was the first to use articulated blades to effect inputs from a cyclic control. It first flew in June 1935. Edison really did experiment with helicopter models too, by the way (in the 1880s).

Which of the following situations is most difficult for a pump-driven attitude gyro to overcome?

  1. a sustained turn at a shallow bank angle
  2. two or more 360-degree steep turns
  3. due to the loads placed on the gimbals, just one single snap roll
  4. in a gyro without a caging mechanism, a single loop, because it can can damage the bearings
  5. a long descent at idle speed

Answer: A. As has been mentioned in a previous Trivia Tester, currently the attitude and heading indicators in most general aviation airplanes are most often vacuum powered. Although we need to periodically readjust our heading indicators against our magnetic compass to correct for precession, we rarely need to make in-flight adjustments to our “artificial horizon” because our usual vertically oriented axis of rotation allows a means of automatic correction with the aid of a pendulum which senses the local gravity vector, allowing this instrument to erect the spin axis back to the vertical. This is somewhat akin to the phenomenon of low accelerations going unnoticed within the semi-circular canals of our own inner ears. Although from a mechanical standpoint, abrupt changes in g-loads are hard on the gimbals, it is also almost impossible for an attitude gyro not to be fooled by sustained shallow turns, resulting in erroneous readings. Remember that the next time you perform any series of successive practice course reversals under the hood! Typical approaches usually are not flown long enough, or at a low enough power setting to be a problem. (However, high altitude flight or excessively low temperatures can create some trouble.)

Black Arts
When was the first practical “black box” required aboard airliners?

  1. 1903
  2. 1925
  3. 1934
  4. 1958

Answer: D. There was a huge increase in commercial air travel after WWII, but in the early 1950s, many tragic airplane crashes occurred, and with no surviving crewmembers (or even passengers) to explain what went wrong, investigators could only speculate. The solution was the FDR, or the flight data recorder. In the 1930s, an Imperial Airways’ Handley-Page HP-42 airliner had a crude form of FDR, recording engine rpm, as did the Airspeed Ambassador in the 1950’s. (Actually, if you want to get academic about it, the Wight Brothers pioneered the use of a device to record propeller rotations, so if you want to look at it that way, then that would push it back a ways.) The first requirement to have recorders on board certain aircraft was published by the Civil Aeronautics Administration (forerunner of the FAA ) on August 1st, 1958. A similar rule was issued in the United Kingdom in 1960 (although there were some uses of them several years earlier). It said that all civilian passenger carrying aircraft over 20,000 pounds should carry a crash protected flight recorder.

Flight data recorders that were introduced in the 1940’s weren’t much more than etching pens on steel foil (basically a strip chart) and could not meet the requirements for survival of the forces involved in an aircraft crash (nor the possible fire exposure) until 1958. While he did not actually originate the idea, the inventor of the first practical FDR was Dr. David Warren of the Aeronautical Research Laboratories in Melbourne, Australia. His crash and fireproof device was able to record the flight crew’s conversation along with a few instrument readings. It became known as the “black box” due to its concealment, both in terms of location and functionality. Invented in 1953 and in production by 1957, the first ones were painted bright red or orange to make them easier to find after a crash. The first such recorder was called the “ARL Flight Memory Unit”, but they were not made compulsory in Australian planes until years later (although Australia claims they were the first country to mandate their use). In 1958, world aviation authorities approved minimum operating requirements for FDRs. Cockpit voice recorders were mandated for all commercial operators in 1965.

David Warren was born in 1925 in northern Australia. A very bright boy, he attended boarding schools in Sydney for 12 years, but in 1934 when he was nine, his father was killed in one of Australia’s earliest airline crashes. Later, he began building radios as a hobby but when the wartime ban on amateur radio squelched that, he turned to chemistry as a hobby and ultimately, as a career. He taught science for two years and then lectured in chemistry at Sydney University. At the start of the space age, he joined the newly-formed Woomera Rocket Range and was sent to England to perform research on rocket fuels at the University of London, where he earned his doctorate. Somewhat ironically (or rightfully), he was involved in investigating the crash of the world’s first jet-powered aircraft, the Comet, in 1953. He argued that a cockpit voice recorder would be a useful means of solving otherwise unexplainable aircraft accidents. The idea initially received little interest, so he designed and build a prototype, to demonstrate the concept. The modern-day equivalent of this device is installed in passenger airlines, worldwide. They are made by several companies.

To say that flight data recorders must be sturdy is an understatement. They must withstand a 3400-g deceleration in 6.5 milliseconds, penetration by a one-quarter inch hardened steel spike dropped from 10 feet with 500 pounds of force, a 5000-pound pressure against all six axis points for five minutes, 1100 deg C for 60 minutes (such as in a fuel fire), or 260 deg C for 10 hours (a baggage fire), immersion in sea water for 30 days at an equivalent depth of 20,000 feet, and a 48-hour immersion in aviation fuel, lubricating oil, hydraulic fluid, toilet flushing fluid, or fire extinguishing agents. Their batteries have a shelf life of six years. Their underwater locator beacon is designed to continue “pinging” at 37.5 kHz for 30 days at depths of up to 14,000 feet. CVRs and FDRs cost roughly between 10 and 15 thousand dollars each.

In the United States, a minimum of between 11 and 29 parameters are required to be stored and in 1996 the proposal was made to increase this range to 17-88, depending on aircraft type. Many of the available recorders exceed these requirements, their solid-state components storing over 700 parameters, which are typicaly storable for 25 hours before any crash, and help investigators to pinpoint the development of faults, as well as to help picture the aircraft’s final moments. Modern CVR’s are required to store the last 30 minutes of speech immediately preceding a crash (two hours, for solid state units). Both types of recorders are kept in the tail of an aircraft, because following any impact (which usually involves significant forward motion), the rear of the aircraft is both cushioned somewhat by the fuselage preceding it, as well as being decelerated to a slower speed, and thus recorders have a much greater chance at survival. Examples of some collected FDR data are time, altitude, airspeed, vertical and longitudinal accelerations, heading, times of each radio transmission, pitch and roll attitude, engine thrust, control and control surface positions. CVRs record ambient cockpit sounds (including the sounds of engines, flaps or landing gear deployment, and conversations between pilots and ATC). Any of these might provide vital clues about what caused of a crash or incident.

Incidentally, CVRs have a “bulk erase” button that pilots press after a safe landing. This was added at the request of the pilots union to protect their privacy. Typically, it is interlocked with the “squat switch” that detects weight on the landing gear, preventing accidental (or intentional) erasures in flight. There is also a “soft-crash” feature, where if a very hard landing is detected, it stops recording after 10 minutes. This is to prevent meaningful data from being overwritten, since the electrical system is still functional after such an “arrival”.

There is also an interconnect between the FDR and the CVR. The FDR produces a chirp once every four seconds with an encoded time stamp. The audio of that chirp is superimposed on one of the CVR channels. When that channel is played back in the lab, the FDR timestamp can be recovered from the chirp. Of course, the FDR also records its timestamp in its own data. In this way, investigators can synchronize FDR and CVR events. More recent models and dual FDR/CVR recorders make this link digitally (and military fighter aircraft or helicopters use combined “one box” CVFDRs).