Every measurement needs a STANDARD and a BASELINE. For temperature, for example, there are four standards and each of those has a baseline: 0°C on the Celsius scale , 0K (-273°C)on the Kelvin scale, and so on.
Water in the sea (not an inland sea) finds its own level, more or less, so surveyors have agreed on a “mean sea level” to base their altitude measurements.
And now something for my aeronautical friends.
You may note with surprise that airplane pilots do not use this height measurement at all.
Pilots are given sensitive altimeters which have an adjustment knob known as a baro setting knob. The baro setting is displayed in a baro-setting window in the altimeter, also known as the Kollsman window to older pilots, because Paul Kollsman first patented the extremely sensitive altimeter, contributing immensely to safe, collision-free air traffic management by assigning separated altitudes to flights in a given airspace at the same time.
Regional or airfield pressure setting (QNH) is set when flying by reference to altitude above mean sea level below the transition level; Altimeter pressure setting indicating height above airfield or touchdown (QFE) is set when approaching to land at airfield where this procedure is in use.
A wrong altimeter setting could mean you will not see your family again:
The Low-Down on Altimeter Settings
Above the transition altitude (18,000 feet in several countries following the US lead), all aircraft altimeters are set to a baro setting of 29.92 inches of mercury or its equivalent in millibars or whatever. This is the standard baro setting and is used by every piloted aircraft on this planet.
▲Kollsman sensitive altimeter with Kollsman window and baro-setting knob, 1940. The tradition continues today, although the shape and form of the instrument have changed.
You might as well learn the story of Paul Kollsman and the sensitive altimeter.
Paul Kollsman: The Father of Sensitive Altimetry
It was in 1923 that Paul Kollsman, educated at the German universities of Munich and Stuttgart, sat down with himself to consider his future. Germany was in the midst of an attempt at post-war economic rehabilitation which wasn't helped much by what the bankers know as cheap money.
Engineering ideas were going begging.
A brother, Otto, already had gone to America.
Well, why not? It was pretty tough sledding over here.
He not only drove a truck. He also worked as a garage mechanic.
Presently he took a job with an instrument company, the Pioneer Instrument Company in Queens.
Paul Kollsman was a willing toiler but some of his superiors thought he was a crackpot. Good altimeters were being made, weren't they? And as for making one as sensitive as Kollsman proposed, well, he must be "hitting the pipe."
He left Pioneer in 1928, when the company failed to accept his recommendations for an altimeter, and formed the Kollsman Instrument Company in Brooklyn as a one-man firm. His laboratory was in an attic. His tools were a second-hand lathe, a small drill press and a vacuum pump. As president, general manager, treasurer, workman and night watchman, Kollsman had to double in brass, but he did produce his sensitive altimeter.
Paul Kollsman designed the first reliable altimeter in the late 1920s.
That altimeter's accuracy was amazing.
The Navy Department of the US began placing orders.
The fact was that the first Kollsman altimeter actually was not the "sensitive" altimeter to come. Inside of another year he had developed a second one—used by Jimmy Doolittle in the instrument landing experiments underwritten by the Guggenheim Fund.
[Of the many pilots who enthralled the public with the romance of aviation, Jimmy Doolittle was perhaps the most active. By 1927 Doolittle had been an Army pilot for 10 years. A rare combination of daredevil and scientist, he held several speed records and a doctorate in aeronautical engineering from the Massachusetts Institute of Technology.
Doolittle made the first blind landing in the US, at Mitchel Field, Long Island, on Sept 24, 1929. For the precise navigation needed for the landing, the Bureau of Standards of the US designed a homing beacon and a marker beacon, which were installed on the field. The signals they sent out were picked up in the cockpit by a radio set, designed by the Aircraft Radio Corporation, which had an indicator consisting of reeds that vibrated according to the airplane's position to the left or right of the radio beacon. As the airplane approached the ground station the vibration increased. Also developed for the flight: the Kollsman barometric altimeter, the Sperry artificial horizon and the Sperry directional gyroscope—the direct ancestors of the instruments we use today.
▲Lieutenant James H. Doolittle, U.S. Army Air Corps, in rear cockpit of the Consolidated NY-2 Husky, NX7918, a trainer equipped with experimental flight instruments.
All told, Doolittle used 11 instruments in the test, aside from the normal engine gauges. He gave careful consideration to the arrangement of the instrument panel, in an attempt to reduce pilot fatigue.
Funding for the Full Flight Laboratory at Mitchel Field was provided by the Daniel Guggenheim Fund for the Promotion of Aeronautics. (Development cannot depend solely on government funding, the US has shown.)
"The demonstration was more than an exhibition of blind flying and instrument perfection," said the page-one story in The New York Times. "It indicated that aviation had perhaps taken its greatest single step in safety." ]
Kollsman was tireless in traveling back and forth between his shop in Brooklyn. N. Y., and Mitchel Field, the Army post in the wide open spaces of Long Island. He would install his instrument in Doolittle's ship, wait for a report on its performance, then tote it back to his tiny laboratory to tear it down and study it anew.
The sensitive altimeter was the backbone of the company's production for a long time. The secret of its construction is a superlative aneroid unit, an evacuated box which expands and contracts with changes in atmospheric pressure, and an almost frictionless gear transmission which actuates the needle telling a pilot his height above sea level.
Properly calibrated, it reads true within five feet.
"Take any instrument in the shop," a Kollsman official used to say, "and carry it from the second floor here downstairs to the first floor. You will be able to read the difference in the Kollsman altimeter."
He wasn't fibbing.
Like a good many other Kollsman instruments, altimeter pinions are set in sapphires. Gears are precision-cut. Compared with Kollsman gears, those in a high-priced pocket watch are the work of an amateur.
In fact, a whole row of jeweler's lathes, designed for super-sensitive work, could be found in one corner of the factory.
Sales to the Army and Navy, supplemented by some to other interests, grew.
Kollsman expanded. By 1932, he had 19 names on his payroll. He had opened a new shop but it was subject to expansion overnight. By 1938 the girth of Kollsman, Inc., was busting the buttons on its attire so often that the head of the firm had to move, bag and baggage, to a plant across Long Island in Elmhurst.
Its 70,000 square feet of floor space held his project for awhile.
▲When WW2 came, Kollsman altimeters were ready to be put on board airplanes of the US Army Air Corps.
The Kollsman concern was a one-man organization in that its founder owned it, lock, stock and barrel. In New York's marts of trade, Kollsman stock was conspicuous by its absence. The head of the company played them close to his chest. What the establishment, with its old-maidishly prim facade on a quiet street in New York's Borough of Queens, was worth was Paul Kollsman's own business.
Kollsman re-capitalized his business in 1937 at $800,000. That is not a fancy figure in big business, but eleven short years do not constitute an age, either.
▲Kollsman ad, 1945
▲One of the most important and unheralded jobs performed by the Kollsman Sensitive Altimeter in the WWII was to give the bombardier the precise altitude indication he requires for setting his bombsight.
Kollsman's outstanding contribution to the science of flying, apart from his precision instruments, is ripping a lot of the "plumbing" out of the engines, wings and fuselages of transport planes.
Gone are many of the pipes leading to the instrument panel. Manifold pressures, for instance, are transmitted electrically to dials on the panel.
"Why the plumbing?" asked Kollsman in effect. "Why not pick up the reading at the manifold and telegraph it to the pilot?"
He did it with a tiny mechanism which, attached to the hand on the face of a gauge at the manifold, accurately registers and transmits by wire to a small, compact dial the power output of those motors many feet away from the man at the control wheel. Kollsman ingenuity produced the electric tachometer. It consists of a generator on the engine and a synchronous motor which drives a magnetic tachometer. Voltage errors due to temperature can be ignored.
The company was only the lengthened shadow of the man who founded it. Faced with a problem, he explored every approach. In any factory where he was not lord and master, he would drive a production engineer to drink. He refused to let production start if he thinks an instrument can be improved beforehand. Athletic, a bachelor and a man with tremendous powers of concentration, he not infrequently rode to work from his Manhattan apartment in a subway train. Quiet and contemplative, he never made statements. Once, when he had to put an opinion in writing for general consumption, he relented enough to drop a few remarks which a subordinate had to whip into shape. It was the closest he ever came to breaking his silence.
▲Kollsman ad, 1970
▲Kollsman General Aviation encoding altimeter, 1975. Encoding altimeters display pilot’s altitude information on the ATC radar screen automatically without the pilot’s intervention.
“Not Guilty”
When you are a successful instrument manufacturer, you also get embroiled in lawsuits.
An American Airlines Electra with 72 aboard, American Airlines Flight 320, crashed and exploded in the East River a mile east of Rikers Island shortly before midnight as it came in for a landing at LaGuardia Field after a non-stop flight from Chicago, killing more than 20 on February 3 , 1959.
The American airliner was one of the new Lockheed turbo-props that went into service 12 days ago. It is the first craft of its type designed and built in the U.S. Although it is 104 feet 6 inches long, with a 99-foot wing span, and has a cruising speed of 400 miles an hour, it was acclaimed for its ability to operate with only 4,700-foot runways as well as for its smoother, quieter operation as compared with the conventional piston-engine plane.
It was the first crash for the Electra.
Flight 320 apparently encountered no trouble until the last moment. It had been cleared for a landing on Runway 22, bringing it in over the East Bronx and Rikers Island.
The crew of Flight AA320 were carrying out an ILS backcourse approach to New York-La Guardia (LGA) runway 22 with autopilot engaged. The Lockheed Electra aircraft descended until it struck the water some 5000 feet short of the runway and 600 feet to the right of the extended centreline. Ground speed on impact was 150 mph and undercarriage and flaps were extended. The wreckage sank in 10 m deep East River.
It was raining at the time of the crash, with visibility of two miles and fog with a 6 knots SSW wind but a ceiling of only 400 feet.
The spot where the plane hit was a mile east of the island and a mile north of the field.
As the investigation to discover the possible cause of the accident began the instrument group, headed by Rudolph Duncan, began its investigation with the assumption that the altimeters had failed. While he was waiting for the cockpit to be found, he had begun to search for reports of mechanical difficulties with drum altimeters. The instruments were made by the Kollsman Instrument Corporation, of Elmhurst, L.I., which had spent years on their design & development & had only recently begun to sell them.
At the Kollsman plant, Duncan and his group called on Walter Angst, the designer of the drum altimeter. Nothing of significance was turned up. Dissecting of Flight 320's altimeters was performed by Angst. To the disappointment of some of the watchers, but the great relief of Angst, there was not the least flaw -certainly no indication of faulty manufacture.
The second altimeter gave a like result.
The following day, the committee went out to the Lockheed Air Terminal, where an Electra was waiting for them.
A member of the ground crew squirted a powerful stream water on an inlet port of the plane's static-air system, but all the water drained out quickly without getting new the altimeter.
Finally, the whole group climbed into the plane, & took off for a rendezvous with a converted B-29 borrowed from the Air Force. At about 15,000 feet, the B-29 put forth a spray of water that froze in the outside air. For hours the test continued with various tests, but the altimeters did not vary from their proper readings.
Final findings of the Civil Aeronautics Board on causes contributing to the crash of the Electra in New York's East River, Feb. 3, 1959, disclosed no evidence of failure in the much discussed new type Kollsman altimeters aboard the aircraft.
Ascribing the crash "primarily to failure to properly monitor the flight instruments," CAB, in effect, completely absolved the Kollsman product from any mechanical failure.
"The Board determines the probable cause of this accident was premature descent below landing minimums which was the result of preoccupation of the crew on particular aspects of the aircraft and its environment to the neglect of essential flight instrument references for attitude and height above the approach surface.”
And among the contributing factors: “Possible misinterpretation of altimeter and rate of descent indicator.”
CAB_Aircraft_Accident_Report_American_Airlines_Flight_320.pdf
Paul Kollsman, the one-time truck-driver, never mentioned those hard, early struggles in the United States.
▲In front of a Kollsman window: Paul Kollsman, inventor of the sensitive altimeter and rate-of-climb indicator, living comfortably on a hilltop in Beverly Hills in 1977. A great many of important aviation events and developments took place in 1927 or so.
Paul Kollsman died in late September 1982 in Los Angeles after a brief illness. He was 82. Although he had hundreds of patents to his credit, Kollsman is best remembered for his altimeter, which was first shown publicly on September 24, 1929, at Mitchell Field, Long Island, New York, USA. The altimeter, which measures and registers the altitude of an aircraft and enables a pilot to fly ''blind,'' was considered his outstanding contribution to aviation science. In the view of some authorities, it was one of the milestones in the advance of piloted aircraft after the Wright Brothers' flight in 1903.
A re-enactment of the flight, with both General Doolittle and Mr. Kollsman at the scene, was carried out on Sept. 24, 1979, at a small grassy airstrip near Boonton, N.J. By that time, ''blind'' flying was routine. General Doolittle recalled later that he had full confidence in the Kollsman altimeter because shortly before the Mitchel Field flight in 1929 he had made a trial run with Mr. Kollsman holding his altimeter on his lap and had been impressed by the instrument's performance. The general described Mr. Kollsman as ''a mild-mannered genius'' and ''a perfectionist.''
His is a fascinating story: he developed many more aircraft instruments. Read it sometime. And understand why free enterprise succeeds, and socialism breeds nothing but poverty and sloth.
America! Only in America!