Air Ministry stop watch query
Thread Starter
Join Date: Aug 2019
Location: Hants
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Air Ministry stop watch query
Newby here, so forgive if stupid query. I have an Air Ministry issue stop watch dated 1941. It has the usual stop watch functions, a sweep hand registering seconds and a small dial registering minutes. What I don't understand the function of is a scale round the periphery of the dial above the seconds graduated 0 to 360. Anyone know what it would be used for?
Yes, on some watches (not stop watches to my limited knowledge) that outer scale is a tachymeter which allows the determination of a groundspeed by timing how long it takes to cover a mile.
The 360 on that stop watch is a bit beyond me unless it's a tachymeter using some other set of distance measurements. Someone will undoubtedly have an answer here. I can't noodle out how it could be related to 360 degrees of a compass rose.
https://www.govbergwatches.com/blog/...-a-tachymeter/
The 360 on that stop watch is a bit beyond me unless it's a tachymeter using some other set of distance measurements. Someone will undoubtedly have an answer here. I can't noodle out how it could be related to 360 degrees of a compass rose.
https://www.govbergwatches.com/blog/...-a-tachymeter/
Agree is appears to be a 'rate' indicator as posted by spekesoftly. Standard 'rate 1' turn as used in procedural instrument flying is three degrees per second, or 2 minutes for 360 degrees.
I can't find out when turn & bank indicators came into use. Was the watch in question in use before T & B indicators came around ? Can't think of a reason to time a turn unless it there's some unique military application.
I was intrigued by the 0-360 scale but couldn't imagine how this scale would be of use to a navigator.
After some searching, I found another entry on Worthpoint:
https://www.worthpoint.com/worthoped...iths-308582907
Even as a pilot's watch, I still have difficulty understanding how the 0-360 scale would help the pilot, or act as a backup for failed instruments. If it was to be used to make timed heading changes, a 0-180 scale would make more sense, assuming Rate 1 turns.
Anyone got Wesolowski's book? I looked it up and it's out of my price range!
After some searching, I found another entry on Worthpoint:
ww2 raf bundle - stopwatch,photo and service book - all found in the same sack so the assumption these are all linked. The stopwatch is an air ministry bomber cockpit watch by smiths - rear is engraved - A.M. 6B/221 faded date below is 1943 - designed to be '' fixed in an aperture of the instrument panel of the cockpit - allowing the pilot to monitor his flight without constant reference to the navigator.The timer also acted as a back up to a number of instruments in the event of them being put out of action - assisted by the 360 degree graduations around the dial; or a fuel management system. (from "A Concise Guide to Military Timepieces 1880-1990" by Z. M. Wesolowski)
Even as a pilot's watch, I still have difficulty understanding how the 0-360 scale would help the pilot, or act as a backup for failed instruments. If it was to be used to make timed heading changes, a 0-180 scale would make more sense, assuming Rate 1 turns.
Anyone got Wesolowski's book? I looked it up and it's out of my price range!
Quote from India Four Two:
"If it was to be used to make timed heading changes, a 0-180 scale would make more sense, assuming Rate 1 turns."
Yes, quite. As I think you have in mind, on "limited-panel " (instrument flying) exercises for our commercial licences (a long time ago!), we used to time a Rate 1 turn to achieve a heading change of a certain amount. A magnetic compass, of course, goes haywire during the turn, but settles down once the wings are level again. (The gyro compass and artificial horizon had been deliberately "caged" for the exercise.)
Is it possible, as I think you are suggesting, that the instrument in question was used to time Rate 2 turns? Seems a bit unlikely, as even a Rate 1 needs (say) nearly 20 deg of bank at 120 kt. I imagine a Rate 2 would need about double that, which would be a bit tricky if accuracy were needed. And gyro compasses were pretty good by 1941...
"If it was to be used to make timed heading changes, a 0-180 scale would make more sense, assuming Rate 1 turns."
Yes, quite. As I think you have in mind, on "limited-panel " (instrument flying) exercises for our commercial licences (a long time ago!), we used to time a Rate 1 turn to achieve a heading change of a certain amount. A magnetic compass, of course, goes haywire during the turn, but settles down once the wings are level again. (The gyro compass and artificial horizon had been deliberately "caged" for the exercise.)
Is it possible, as I think you are suggesting, that the instrument in question was used to time Rate 2 turns? Seems a bit unlikely, as even a Rate 1 needs (say) nearly 20 deg of bank at 120 kt. I imagine a Rate 2 would need about double that, which would be a bit tricky if accuracy were needed. And gyro compasses were pretty good by 1941...
