LONGINES CAL. 19.71N | AIRCRAFT CLOCK
As seen from the two presentations of the watches that equipped the aircrafts manufactured at IAR Brasov and SET Bucuresti the movement/caliber most frequently meet is - Longines cal. 19.71N in the variant with central secondary.
Next, a technical presentation for it [according to: Patrick Linder | “At the Heart of an Industrial Vocation – Longines watch movement (1832-2007)", Editions des Longines, 2007]:
• produced since | 1910
• movement | manually wound mechanical
• ebauche | “open-face” type, base board and 6 bridges
• functions | hours, minutes, seconds / indirect central second
• frequency | 18.000 vph
• diameter | 19’’’, 41.90 mm
• height | 7.25 mm with central second
• rubies | 15 rubies
• gear | traditional, 7 wheels
• discharge | right crank
• balance | bimetallic cut and compensated
• balance-spring | Breguet spiral
Considering that for all the aircraft clocks identified (1933-1943) so far, the 19.71N movement was found (in the variant with central seconds) becomes obviously that it was used in all the Longines variants specified: type 6550, type 6036, and type 4331.
The cases in which these movements were mounted are made from aluminum with 4 (four) for 6550 type, respectively 5 (five) for 6036 type and 4331, mounting holes.
There is also a variant with 5 mounting holes (here called - type X) that, considering the year of sending to Romania, it cannot be associated with any of the 3 specified above.
It is Longines aircraft clock - serial 5114380 | delivered to Romania on 1.June.1933 (the “oldest" serial known to us for this kind of clocks) that has different fonts for the "hours", "lance" type indicators and also the crown at 12:00 hours.
Among all these variants there existed differences at the dial design (the "minutes” fonts) and at the seconds hand but also at the crown presence, either at 12:00 hours for type X, either at 6:00 hours for type 6550, 6036 and 4331 (see images):
aircraft Longines crowns (left-right): type X, 6036, 4331
Also, among the four variants there exist differences, beside the dial design and the geometry of the hands (for entire type X set and only between second’s hands for type 6036 and 4331) – see images:
Longines aircraft dials and indicators (left-right): type X, 6036, 4331
For the above images one can notice, besides the fonts difference (type X --> type 6036, 4331) also the change of orientation for the minutes marking - 20, 25, 30, 35, 40 for the variant 4331.
For a correct identification of an assembly case-movement-lid at an aircraft clock - Longines – one has to consider (beside the dial elements already specified) that each clock was individually marked on the aluminum case either with the movement serial (for type X, 6550 and 6036) or with the number of the case type [21125] + an item number made from 3 figures, beside the “classic” movement serial for type 4331 (see images):
• Longines type X:
• Longines type 6036:
• Longines type 4331:
The way in which all the markings on the component parts are presented for a Longines type 4331 is detailed illustrated in the images from the right column.
In the Romanian archives were identified so far the Longines original technical documents only for the variant type 4331. These accompanied the initial offers of the Longines representative in the epoch – Max Weissblűeth.
documents source: National Military Archives - Pitesti
Thanks for the support in this research to my colleagues Jan Bejan and Ciprian Ganea that had the amiability to provide images of the watches from their collections or technical explicative information.
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