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THE PILOT'S CHRONOGRAPH
Almost every watch company today has an offering of a "pilot's chronograph watch".
Some watches are more "pilot chronograph worthy" than others and are a pillar of strength reminiscent of the originals that served the brave men of the skies in WWII. If you were extremely punctilious, a certain Big Pilot's watch is actually a navigator watch and therefore is a misnomer with it's modern day name.
In this short article, I won't bore you will all the usual advertising speak on "pilot's chrono watches" and their key marketing words of being 'antimagnectic' and 'resistant to loss of cabin pressure' et cetera.
The aim is to take you too the roots of a chronograph watch that was worn by the WWII German Pilots.
First we must ask ourselves, what is the fundamental essence of a pilot's chronograph watch and how was it used by the pilot? Why did the pilot wear a chronrograph? How did the pilot use one?
The answer is simply because the pilot's needed a quick and reliable timepiece to aid him in navigation of the aircraft. The number one tool of any pilot was the compass and these watches were the tools used in conjunction with and flight charts and slide rules, adjustments were necessary for time error as small deviations in time accuracy would lead to a huge error in flight calculations (fuel consumption, longitude/latitude position and time to destination calculations et cetera).
In aviation times of past (present we use GPS!), with the aid of the compass and known speed; dead reckoning allows a pilot to determine his present position by projecting his past courses steered and speeds over ground from a known past position. He can also determine his future position by projecting an ordered course and speed of advance from a known present position.
It would be near impossible for a German Stuka pilot to use a sextant combined large chonometre clock and then do the required calculations to figure out his location. The pilot was simply too busy trying to fly the plane (no autopilot unlike the aircraft of today). Speed, distance and time are intertwined by a fixed formula Distance=Speed x Time. The pilot knows the speed of the aircraft and he now needs an accurate, fast and reliable watch to measure the time - This is where the pilot's chronograph comes into the picture.
Traditionally in air navigation, displacement or position caused by wind were taken into account, using a tool called a wind triangle. [The wind triangle is a graphical representation of the relationship between aircraft motion and wind in a vector diagram.] Dead reckoning (DR) positions were calculated at least once every 300 miles or when making combined turns totaling more than 30 degrees from the initial heading out of the last DR position. The watches also had rotating bezel (the ring surrounding the watch dial) that can be turned in order to allow the pilot to perform different timekeeping functions by tuning the marker on the rotating bezel.
The other method of navigation was by using radio "lighthouses" or on the ground. In WWII these beacons would send out a signal followed by radio silence at fixed intervals. A chronograph was used to time the interval of this signal to identify the beacon - e.g. becon had signal beep once every 20 seconds. Sometimes the (later and more modern) aircraft also may have an automated display which shows the direction of the beacon from the aircraft. The pilot may use this bearing to draw a line on the map to show the bearing from the beacon. By using a second known beacon, two lines may be drawn to locate the aircraft at the intersection of the lines. This is called a cross-cut method to determine own location based on two known beacon positions.
Later on in the the beacon got more advanced and this was called a "compass transmitter". This kind of beacon transmitted a focused radio beam that rotated clockwise thru 360 degrees. It would pass thru north at exactly the start of each new minute. So if the pilot head the signal in his headset 30 seconds after each new minute, his present position was due south of the compass transmitter. The pilot would obviously start his chronograph on hearing the start signal and stop it when he heard the direction signal in his headset to get this bearing information. One could also extrapolate that if the pilot had a split second chronograph on the wrist, he could simultaneously time two such beacons in succession and once again use a cross-cut method to determine own location.
Interestingly in WWII when the British flew into German territory at night, there were obviously no beacons on German soil to guide the bombers/aircrast into Germany for their run. The Swiss actually extended broadcast on some of their radio stations well past the closing times to serve as 'beacons' and the British pilots used the signals of these radio stations to reach their targets. It took a while for the Germans to figure out why the Swiss radio stations were sometimes broadcasting past their closing times into the night to give the British an important navigational aid (Radio back then was different, it was not 24hrs - the radio station would close at night).
Rotating Bezel with Red-Marker on the Watch, The Bezel is knurled for grip when operating with gloved hands
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