Gyroscopes and Flight Computers - Sperry Gyro Horizon Enables Instrument Flying
Copyright 2011 Franklyn E. Dailey Jr.
Triumph of Instrument Flight
Earlier chapters have introduced some of a Navy patrol aircraft's essential
systems. In this chapter, some of the less sophisticated instruments, the
breakthrough instruments for flight in clouds, along with advice that might
not be on an instructor's first list, will be recalled.
Pilot training involves an introduction to the cockpit and to the instrument panel. My initial introduction came in the Stearman. That aircraft had a simple instrument panel. There were no radios to contend with. Gas was gravity-fed to the Stearman engine. The all-important gas gauge was inherited from the automobile.
I remember looking out the car window in the 1920s when my Dad pulled into Coapman's Gas Station on Main Street, by the New York Central tracks in Brockport, New York. There was a line of five tall metal stands, each with a glass cylinder surrounded by a wire enclosure on top. There was a window in the mesh of that wire enclosure. The transparent sides of the glass cylinder revealed its contents, gasoline, in various shades of light yellow or light red, depending on the oil company whose pump our car was ready to receive gas from. The glass had numbered horizontal lines. Those lines marked the gallon level to which the cylinder had been filled. The attendant responded to Dad's wish and lowered the level in the glass by the called-for number of gallons as he let the gas flow into our car's gas tank. Early airplane gas gauges were like that, just smaller in scale. The Stearman gas tank gauge was not a remote electronic indicator on the instrument panel but was directly connected, liquid-wise, with the tank.
As the aircraft I flew increased in size, power and complexity, the instrument panel grew in number of indicators until space to put them became a designer's challenge. The first of two main messages that my instructors had delivered to me very early in flight training was that those were indicators, devices that communicated something about the basic performance of something else. The second message was, "Do not let your eyes be locked on any one indicator. Scan a selection of basic indicators on a regular routine." Here, the words indicator, gauge, and instrument are being used interchangeably, to mean a device that denoted the amount of something.
The aircraft we flew in after World War II were inherited from the war. Those were fine aircraft with state of the art systems. The U.S. was constantly upgrading all during the war. Changes were evaluated rapidly. The high volume of flight operations provided good statistical bases for change. Successful changes were confirmed quickly, while lemon changes were worked out of the pipeline rapidly. Aircraft accidents often revealed that more testing would have been in order. The accident was, in effect, part of the test. In military aviation in those war days, a new design aircraft could become operational too soon, and the early experience would tell if this were the case. This "correct while doing" was more acceptable than in passenger aviation. I believe that military aircraft acceptance today is more in line with commercial aviation.
Although manufacturing plants were converted to peacetime use as rapidly as possible after V-J Day, and the bulk of our fighting men came home to restart their lives, aircraft development programs already in progress had momentum. While many manufacturing lines were shut down immediately, some improvements coming along had already demonstrated their value and were put to immediate use in the peacetime world. This will lead into a brief discussion of those postwar advances after first noting some of the essential aids to flying already in use in aviation before the war.
WW II Navy officer Bill Rowan served aboard the attack transport, USS Doyen, in the Pacific war zone. He went to work for Sperry right after the war. His penchant for memorabilia gives us a glimpse of the Sanderson Flight Computer, SC-3.
Illustration 15-Sanderson Flight Computer
A subtitle on the computer is labeled, "For G.S. and T.H." Those initials stand for Ground Speed and True Heading. The receipt of the Sanderson sent me to my orange flight suit, hanging there untouched in a basement closet for over 30 years. I quickly emptied out the contents of its pockets. Sure enough, there was a Mark 8B computer, in aluminum just like the Sanderson, manufactured by Virginia Plak Company for BuAer (The Navy's Bureau of Aeronautics). My 8B is exactly the same as the circular center core of the Sanderson. Mine lacks the long near-rectangular base plate of the Sanderson. The Mark 8B is more of a pilot's aid and the Sanderson would be a navigator's assistant, with its oblong template for solving wind and wind drift.
"Computer" is stretching it a bit if one is fussy about words. These devices fit more realistically into the "slide rule" category. The 8B is a circular slide rule. The Sanderson does not physically fit in any pocket of a flight suit so that reinforces my recollection that it was more often brought aboard by a navigator using a carry-on case.
While I was thus drawn back to gadgets in use at war's end, I also re-discovered other paraphernalia in that flight suit, which carries the label, "COVERALLS, FLYING INDIAN, ORANGE, TYPE II, SIZE 42R," specifically, its two emergency packets.
Both packets bear the manufacturing label of the Van Brode Milling Co., Inc. of Clinton, Massachusetts. Their plastic outer envelopes are still sealed and are now a bit milky. I can see the "contents" page well enough through one plastic envelope to discover that it contains Sweet Chocolate, D-Amphetamine Sulphate tablets, APC tablets, Tetracaine Opthalmic Ointment, Chloroquinone Phospate tablets, bandages, pure aluminum foil (marked for making a container to heat fluids), soaped tissues and a Sewing Kit. I wonder if it is "legal" for me to have that D-Amphetamine Sulphate today. The aluminum foil probably was used as a sun reflector more often than as a cooking pan. The other packet contains some of the same items, plus Water Purification tablets, Benzalkonium Chloride Tincture, a tube of Petrolatum jelly, a Hacksaw Blade, a single edge Razor Blade and a tube of Sunburn Preventative Lipstick. There are also matches, adhesive plaster, a Gauze Compress and a package of Bouillon Cubes. Of the lot, I can see no deterioration except a little stain outside of those bouillon cubes. Heat probably caused them to ooze through their wrappers. I do recall that I traded in my original issue brown flight suit for the orange suit at some airbase along the way. The original one was not worn out. Most likely some guys in a ready room came over to me and asked me to get rid of that old suit. Possibly, they had some nasal hypersensitivity.
The Sanderson computer comes with a warning, "Do not leave plastic computers and plotters exposed to excessive heat or direct rays of the sun." This reminded me that the early models were plastic but all the later issue came in aluminum. The Sanderson package also contains a checklist for Sanderson models SC-1 through SC-4 inclusive, plus a "Student Pilot Guide" dated 1946 and issued by the Department of Commerce, Henry A. Wallace Secretary, and the Civil Aeronautics Administration, T. P. Wright, Administrator.
In a Prefatory Note in the Student Pilot Guide, F.M. Lanter, Assistant Administrator, informs student pilots that the guide contains a summary of rules on which the student will be examined on Civil Air Regulations before a cross country solo flight is permitted. It covers Part 43 of the Civil Air Regulations (those existing then, of course) dealing with General Operation Rules and Part 60 on the subject of "contact flight rules." It was noted that 25 questions would be found on the examination and a passing grade of 80 percent was the minimum requirement.
Examples of regulations: "You are not permitted to pilot an aircraft carrying a person except a private, commercial or airline transport pilot."..... "The minimum proximity of aircraft in flight is 500 feet (except by pre-arrangement of the pilots)...." "Experienced pilots consider it unsafe to indulge in aerobatics at altitudes less than 1500 feet." (My Navy teaching stressed 3,000 feet as the minimum.) These Civil Air Regulations are part of history and are different today. In the four Roosevelt Presidential terms, Henry Wallace served at different times as Secretary of Commerce, Secretary of Agriculture and Vice President.
In an earlier chapter, I described Boston & Maine Airways' pilot Hazen Bean and his Stinson Trimotor's flight out of Boston into thick fog, and how he used his turn needle to keep the wings level while he climbed slowly and finally got on top of the fog bank. I used the expression, "needle-ball and airspeed" to characterize the era of instrument flying feasible at that time in our aviation history. Using needle-ball and airspeed for instrument flight was strictly defensive, used only when one got caught in instrument conditions that had not been anticipated. If anticipated, instrument-flight, totally blind and without a visual horizon, was to be avoided.
One of the Navy instrument flight manuals of the era in which I was a student pilot (specifically, NAVAER 00-80W-1; my copy is dated 1944) contrasted the earlier method, needle-ball and airspeed, known also as the "1-2-3 system," with the later method known as the "attitude system."
For the 1-2-3 system, the manual tells the reader (on its page 4), "The rudder governs the turn needle, the ailerons govern the ball bank indicator and the elevators govern the air-speed indicator needle." That was how the NAVAER manual expressed the 1-2-3 system, otherwise known to those who did not read manuals as "needle-ball and airspeed." It is a good thing that Hazen Bean had not read that manual. He kept his plane on a steady course using his ailerons to keep the wings level. Had he had the ball, it would have helped him keep from skidding his aircraft by keeping the ball centered. Without a visual horizon and with no gyro (artificial) horizon, a skid would put G-forces on the plane and its pilot and lead to disorientation for a pilot not sure of himself on instruments. Page 7 of a 1945 Navy publication, NAVAER 00-80W-7 is more helpful. "The (turn) instrument is activated by a gyroscope which is rotated by air entering the case through a jet. Although a suction of 4 in. Hg. (Hg is the abbreviation for the element, Mercury) is supplied by a mechanical pump, the pressure differential between the inside of the case and the surrounding atmosphere is kept constant at 2 in. Hg. by means of a restrictor valve. The gyro rotor is so mounted that it precesses whenever the airplane turns, causing the indicator needle to move off-center." And so we learn that Hazen Bean's turn needle involved our friend, the gyro.
An interesting piece of collateral information is that the turn indicator was the only flight indicator that continued to provide valid information if the aircraft went into a spin. The 1944 Navy manual also added:
"In the attitude system, he (the pilot) thinks and acts in exactly the same manner as he would in contact flight."
That 1944 manual reads to me now, more than 50-years after it was provided to me, as quite likely the transcription of a classroom instructor's spoken words. It appears to be an effort to persuade pilots who had done some instrument flying by needle-ball and airspeed to convert to the new attitude system as a better system. Since student pilots in our World War II military classes had not been flying by the 1-2-3 system, and most in fact had not been flying at all, the ground instructor's effort to convert us was at best, academic, and at worst confusing.
The emphasis that seems to have been almost totally overlooked in language intended to persuade one to leave one system for another, is the huge change brought about by the introduction of the gyro horizon to the instrument panel in the cockpit. That gave a pilot a horizon. It was a sea change in instrument flight. The earlier instruments had many powerful virtues and would help one be a better pilot and would remain relevant, but the real message was that cockpits could now have a horizon at all times. It was the gyro horizon. There was no "Attitude System" without it. It changed flying.
Author Mudge in "Adventures of a Yellowbird" exhibited a keen intelligence to choose to relate to his readers the experience of pilot Hazen Bean's conversion to the use of the turn needle. It was vital for Bean, with the instrumentation he had then, not to turn the airplane. The later addition of the ball in the bottom of the turn indicator helped a pilot who could not always "feel" his aircraft, to make a coordinated turn, avoiding slipping and skidding. Later training exercises emphasized patterns one could fly to "calibrate" the turn needle, and deduce how many degrees per second one would be turning in a specific airplane with a "one needle-width turn." Still, with the needle and the ball, the rudder and the aileron, in reasonable control, one also needed to know what was happening due to the action of the plane's elevator. The altimeter would indicate if the plane was going up or down, but only yielded a result, a new altitude, as the plane arrived at that new altitude. The rate of climb indicator would tell the pilot whether his plane's nose was up or down, but it is a "jumpy" instrument-it does not integrate at all. Oversimplifying a bit, the altimeter needle is too slow for "blind flying" and the rate of climb indicator is too fast. This set of instruments was never going to be adequate for planned instrument flying and could only buy limited time for the best pilots who ran into unpredicted weather conditions.
The Stearman pilot had the very basic instruments, airpseed, altimeter, needle-ball and rate of climb or descent indicator. Provided that he was sticking to contact flight rules, the pilot had a visual horizon. With that combination, a Stearman pilot could learn smooth, coordinated flight under visual flight rules sufficient to satisfy the fussiest check pilot. For instrument flying, the gyro horizon would need to be added to that earlier basic flight instrument set. This proved to be the instrument that the trained pilot needed to achieve smooth, coordinated flight in the thickest of placid or turbulent clouds. It was a substitute for the visual horizon and provided an indication of nose up or down or level and wings level or dipped left or dipped right. I give testimony here and now that in the case of smog over a city, the gyro horizon is much friendlier than a hazy, visual horizon.
Illustration 4, the Lockheed Electra cockpit, told this story. Complete "dual" instrumentation was not yet achieved in this aircraft but the "makings" were there. The vital flight attitude control indicators were placed in the center of the panel where both pilots could see them. The altimeter location favored the pilot and is just behind the right rim of his control wheel. The gyro horizon is top left center. Airspeed is just below. Just to its right is the turn needle with its ball in the same enclosure below. To the right of the needle and ball is the rate of climb or glide. Its needle is at nine o'clock or "zero," appropriate for a plane on the ground.
The foregoing discussion covers some of the instruments that came into aviation use, one at a time. Together, these would now comprise a "system" but in aviation parlance they were not conceived as such and are not generally thought of as such.
It took the military and its big contractors, sometimes now referred to as the military-industrial complex, to bring systems into aviation. The APS-15 radar on our PB4Y-2 or the APS-20 in the later P2V aircraft were conceived and installed as systems, with antennae, receivers and transmitters including magnetrons or klystrons, and visual displays, all defined as subsystems which when put together functioned as systems. The same was true for the Electronic Countermeasures (ECM) system. The navigation system, LORAN, came to aviation as a system. Its transmitter stations and transmitters had to be geographically located and provisioned, and receivers in aircraft had to be designed, the whole with compatibility in frequency, pulse shapes and pulse durations all built in.
An example for our new century would include Ground Positioning Systems (GPS) with their indicators (readouts) in cars or ships or aircraft containing one essential part of such systems, and satellites contributing the other essential element. One utility of the concept of systems is the idea of subsystems and these in turn can have subsystems.
The magnetic compass has been important to mariners and to aviation. It needs constant attention for a correct reading. There is "variation" in the earth's magnetic field, a correction for which needs be introduced to determine true heading. Each magnetic compass has its own "deviation" signature, another correction that needs to be entered.
The gyro horizon may turn out to be the instrument that had the greatest impact on aviation. With it, instrument flying became practical, and the teaching of instrument flying could be extended to most persons healthy enough to pass flight physicals.
An important system that came to aircraft directly as the result of World War was the IFF system. IFF stands for Identification, Friend or Foe. With the system turned "on" in an aircraft, a transponder reacts automatically to an interrogation signal from a Distant Early Warning (DEW) line ground station or aircraft, keeping watch along the 70th parallel. The object is to make sure that all aircraft entering an airspace are identified as "friendly." In the war, friendly was the opposite of foe, or unfriendly. In peacetime, friendly means that "you, and we now know who you are, are definitely there" in an air traffic control situation. Pilots who have failed to energize the IFF in their aircraft have risked their lives by not being deleted from the potential "foe" status, or have risked the lives of other friendlies by being an unknown target in an ever more crowded air traffic control airspace.
The extremely rapid progress in aviation between 1928 and 1948 reached a crescendo in 1952 with jet-powered commercial flight. The jet airliners took over from the Douglas DC-7s and Lockheed Constellations and have now provided for a half-century a golden age of airline passenger safety and comfort.
This progress has now slowed. The objective to lower the ennui and fatigue and tension of pilots and ground air controllers has moved forward but high subsonic speeds and crowded skies means that the margins are tighter today. Air Traffic Control meets this crowded sky and is barely able to hold its own. The same is true on the ground where the oversight function is identified as Ground Control. It is crowded there too.
No longer can the Corps of Engineers or the Navy Seabees go in and hack out an aircraft runway in almost no time at all. The ten years it takes to construct new runways and approaches in a metropolitan area involves many, many systems. Right here in my home state of Massachusetts, the aviation authorities are fighting to add one new runway at Logan Airport. Next door to Logan Airport, the Commonwealth of Massachusetts is living with the example of the Big Dig. Forget time. Forget money. Just do it and we'll add up the cost later. It could be a long time before a new runway is approved for Logan Airport in Boston.