Vintage WWII Minerva Stop Watch JEAN VIAL Bomber Plane Bomb Timer INDICATEUR

Description

EXTREMELY
Rare Air Force Military Bomber Clock (Stop Watch),
Vial-Paris Cockpit Instrument
JEAN VIAL - Paris Bomber Stop Watch with Minerva movement.
Very good used condition. works perfect. Some scratches on glass and case. Bezel rotates. Button works, movement works. Check photos.
-
nickeled brass case (not sure)
- Diameter 52mm (case)
- Case No. 1415
-
Original enameled black dial
- Turning bezel with a red arrow
- signed 'INDICATEUR B.C.V. Breveté S.G.D.G., J.Vial-Paris."
- scale 5 - 60 hm und 0 - 30 seconds
- central 30-secound-stop hand
- 15 min-counter
-
Minerva
9 jewels
movement (unmarked)
gold plated
By Konrad Knirim of Düsseldorf Germany (prepared for the NAWCC Bulletin)
"Introduction These special time pieces were used in multiseated aircrafts in combination with a 'visier' -Feature. The different types were mostly manufactured in Switzerland and implemented in the air forces of several countries. I saw items with markings of the Italian, French and British Air Forces. Suppliers were some well known Swiss manufacturers, so I heard about an IWC Bomb Timer' which was send from Austria to an auction house in Geneva, but instead of coming to the auction, it disapeared in a private collection. The French items especially of Jean Vial used movements of Minerva of Villeret. ... "
The very special feature of this watches is, that the stop hand turns backward after the second push of the button ('count up' or 'ritorno' or 'a retour').
Manufacturer: These Cockpit clocks were manufactured by Minerva and Longines. Jean Vial / Paris has obtained watches from both manufacturers and delivered under his own name to the French Air Force.
General principle:
The bomber squadron used an optical system to visier the target. This instrument had three marks e.g. A, B and C (see figure 3). Normally the distance between AB and AC are equal. The target should be G. The problem is shown at the folowing scheme: By the time meter the crew knows the time between A' = G and B' = G. For the bomb reaching the target at C' = G, one has to know the duration of the fall of the bomb, we call it t. The bomb is thrown at (T' -t) measured from that moment, when B' = G. is. With a normal time keeper the bomb is to get away at the time point T + (T' - t). This calculation is possible but too complicated and unexact, when the bomber is under stress maybe in combat. With the 'count down' of the 'ritorno'-system no calculations is needed, the time is to be seen on the dial.The duration of fall of the bomb was investigated by practical testing. In vacuum the point C' = G would be vertical to the plane, but the air causes that the real point of touch is behind the plane and the theoretical point. The duration of fall depends on the type of the bomb.
Calculation of the free fall:
We can calculate the duration of the fall of the bomb in vacuum: The speed of falling is: V = g * t, with the geoid acceleration g = 9,81 m/s² is this case v = g * t = V 2 g * h. It follows T = V 2 g h / g² = V 2 h / g. E.g. is at a height of 2000 m the free falling time in vacuum t = 20,2 s. The real time maybe t = 22 s. The crew can take this time at the height of 2000 m from a table work. When the bomber personal reads the 22s during the 'count down' of the 'ritorno time piece', he gets off the bomb. We don't know, how the absolute speed, the wind and the real height-difference is influencing, but the basic problem is not changed.
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