I spotted what I think was NASA's Supper Guppy following I-10 west (eastbound) over west Houston the other day. I was driving, else I would have gotten a picture. It would have been easy to get a clear pic too, since the thing was just crawling along - must have a stall speed in the single digits.
Pardon the intrusion, gents, as I’m not a pilot but have a question for pilots.
I’m fortunate to own a watch purchased by this gent back in the late 60’s (he’s wearing it in this pic):
Here is the watch:
This watch was purpose built for pilots, and for just one example the original owner gave me this bit about his own utilization:
“I bought this Universal Geneve Aero Compax chronometer in Grande Prairie Alberta on the third of May 1968. It cost about three times what I expected to spend, but the watchmaker had no others, and I needed it for the job I was doing. I normally kept track of my helicopter’s fuel consumption in my head, but this job entailed very shortflights and numerous periods of idling on the ground with unequal burn rates, so the stop watch and elapsed timeregister made the chronometer the only tool for the job.
Flying charter, cargo and passenger airliners over severaltime zones later in my thirty year aviation career, the outer bezel set to local time allowed for keeping GMT on the twenty four hour face. That face was so rare it was enough of a conversation piece to somewhat offset the condescending“ big watch and sunglasses” remarks that came withoversized watches on pilots at the time.”
For more pictures of him (or the watch) and a bit more of his tales, you can check the thread here.
My question for the pilots is this: you’ll notice that this watch’s chronograph has a 15 minute totalizer, which is I think somewhat unusual (typically there’s a 30 minute totalizer).
At some point I’d read that certain pilot’s watches in the late 60’s used a 15 instead of 30 minute totalizer for a specific reason related to flight or their crafts. But I have yet to find a clear or coherent reason for the importance of the 15 minute time interval as relates to pilots.
One post I read suggested that at one point it was coming for certain planes to have as part of their pre-flight check some exactly 15 minute long test or tests (perhaps a 15 minute long idle test, or I don’t know?).
Here taking a long shot that anyone might know (or know someone) with any insight as to why some pilot’s watches may have specifically chosen a 15 instead of 30 minute totalizer.
Note that a few other manufactures at this time (late 60’s) we’re also using the same Venus 178 movement in their pilot’s watches, and so also suggest some importance of either the 15 minute timeframe and/or increments of 3minutes being clearly discernible in the sun-dial, e.g.:
I point out that these above Venus 178 make a point of the 3 minute increments, because I’ve seen one or two other pilot’s watches from the late 60’s that while utilizing the more standard 30 minute totalizer none-the-less draw some attention to 3 minute increments, e.g.:
Accordingly, the relevance of the 15 minute totalizer to a pilot’s watch (if intentional at all), might have instead been about 3 minute increments - with a 15 minute dial simply making it easier to discern those 3 minute increments compared to a 30 minute totalizer.
Notably, even as far back as the 1930’s these three minute intervals seemed of some import to pilot’s watches:
In fact, the 15 minute totalizer with 3 minute increments was so indicative of the Breitling AVI’s that for the 765 AVI 1953 Re-Edition in 2019 Breitling modified the base B01 movement to replicate the 15 minute totalizer
Some of the press pieces around the 2019 re-edition go so far as to say that 15 minute totalizers were unique to 50s/60s pilot’s watches, but never say boo as to why.
And that’s the sort of thing that I’d like to understand!
Awesome thread to read, and appreciate the intrusion!
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Some of the press pieces around the 2019 re-edition go so far as to say that 15 minute totalizers were unique to 50s/60s pilot’s watches, but never say boo as to why.
And that’s the sort of thing that I’d like to understand!
Awesome thread to read, and appreciate the intrusion!
It's much easier to see the 3/5 minute makers on a 30 minute dial than a 60 minute one.
And so, too, is it easier to see the 3/5 minute markers on a 15 minute dial than a 30 minute one.
All that said, the Hour Angle’s 15 degrees theme does at least point to some further possibility that the 15 minute totalizer, highlighting a few 3 minute intervals, may well be exactly related to some fundamental principle of navigation.
If so, I suspect a complete and satisfactory explanation may be in the minds of very few extant pilots today - though perhaps some military schools have professors with this sort of topic as a day’s worth of a historical curriculum.
I may be off to search for professors of navigation theory at the Us Naval War College!
I've seen a few suggestions that the three minute and five minute markers on the 15 and 30 minute dials were for navigation purposes.
By factoring in your speed you could divide your track into 3 or five minute intervals and then check at those intervals to see if you were on track. It's much easier to see the 3/5 minute makers on a 30 minute dial than a 60 minute one.
(2) take running timing of approximately how far one has traveled over longer periods (ie accordingly to all my totalizers I’ve been flying 1hr and 48 minutes at an average of 10 knots, so I’ve travelled about 24.5 miles)
Needing to stew on it all a bit more, and eager for other’s thoughts
I think may have sorted it out, though I’d call it still a hypothesis and not yet a theory.
We’ve all collectively recognized that one practical reason for a 15 minute rather than 30 minute totalizer is merely the resulting incremental legibility to the watch-wearer: it is easier to glance down at a 15 minute totalizer and note elapsed single minutes than if glancing instead at a 30 minute much less an hour totalizer.
I think this legibility has to in part explain why simultaneously there are (1) 15 minute totalizer, remarking 3 minute intervals, but also (2) even in other watches with 30 minute totalizer, still marks better displaying 3 minute intervals.
Once we’ve agreed that a 15 minute totalizer has this practical effect of making shorter minute increments more legible, including specific 3 minute intervals - what remains is the still lingering question regarding any technical relevance of a 3 or 15 minute increments?
And for that, I propose as a contender the “3 minute rule” (or 6 minute rule)!
Try this video on for size:
While the video speaks in terms of nautical navigation, I am too ignorant to know why it would not also apply to aeronautical navigation. Assuming it applies equally to aeronautics:
In short, the 3/6 minute rules are techniques for quickly estimating how far an aircraft will travel in a given amount of time - but necessitating divisibility by increments of 3
Specifically, the “3 minute rule” states that the distance a craft will travel in 3 minutes in yards is equal to speed in knots [multiplied by] 100. So in 3 minutes at 5 knots, you’ll travel 500 yards.
Meanwhile, the “6 minute rule” states that the distance a craft will travel in 6 minutes in miles is equal to the speed in knots [divided by] 10. So in 6 minutes, at 5 knots, you’ll travel 1/2 mile.
And, “because math,” one can instead use the 3 and 6 minute rules to create also other variations of the rules holding 3 minute increments as constant: in other words, one can formulate 9 minute, 12 minute, 15 minute, and 30 minute rules using the same approach.
Let’s look back at this watch:
the totalizer in question would allow for a pilot (using any preferred version of a rule in 3 minute increments) to either:
(1) use the chronograph to calculate a set distance before turning (ie., I want to turn in about 1 mile, which at my current speed of 10 knots will occur in roughly 12 minutes) or
(2) take running timing of approximately how far one has traveled over longer periods (ie accordingly to all my totalizers I’ve been flying 1hr and 48 minutes at an average of 10 knots, so I’ve travelled about 24.5 miles)
Notice then that because the hour totalizer has tic marks for 30 minute increments, the 15 minute totalizer with further 3 minute breakdowns allows for easily digesting longer periods of time down into 3 and 6 minute increments (or larger “15 minute rule” increments, etc., as desired).
I’m feeling pretty good about this hypothesis, and frankly pretty stoked to realize: this essentially behaves as a type of reverse tachometer for navigation
Needing to stew on it all a bit more, and eager for other’s thoughts
D dervI’d guess it’s just for legibility while dead reckoning, where you’d check your planned vs. actual time from checkpoint to checkpoint. These are often 20-50 miles apart, coinciding pretty well with a ten minute timer when in an airplane.
Here’s my ride, though she ain’t that fast…
Great pic. May I ask which aircraft type this is?
It looks like it's only got the bare minimum of instrumentation in the front cockpit!
It looks like it's only got the bare minimum of instrumentation in the front cockpit!
