# TIGHAR

## Amelia Earhart Search Forum => Celestial choir => Topic started by: Bill Roe on July 09, 2012, 05:31:08 PM

Post by: Bill Roe on July 09, 2012, 05:31:08 PM
And could it be important to understanding how she could have ended up 300 miles off track?

My involvement with this site and you guys has brought back all kinds of memories.  Been pulling out old military remembrances - one of those is my rubberized E&E charts.  Not maps - charts.

These charts and, I'm recalling, my nav charts were all scaled in nautical miles.

The possibility exists that the Electra instrumentation was scaled in Miles or MPH?  Noonan's charts in nautical miles?

Even so, Noonan was experienced enough and good enough to work the conversions.  But did he do it?  Or was he mentally/physically able?

Or is this absolutely nothing?  Bull?

Title: Re: Has this Been Addressed..........?
Post by: Anthony Allen Roach on July 10, 2012, 12:42:06 AM
Fred Noonan's charts would be mercator's projections, scaled in nautical miles.  A nautical mile is about 2000 yards, or a little over 6000 feet.  Incidentally, and not coincidentally, a nautical mile is one minute of arc of latitude.  (There are 60 minutes in a degree.)
The sides of the charts are scaled for degrees and minutes.  A navigator learns very early not to use longitude for scale.

The only instrumentation on the Electra that I know of that would be of any relevance would be the airspeed indicator.  This would be calibrated in knots, which is shorthand or nautical miles per hour.  (The word knots actually derives from an older practice of counting knots in what was known as a pit log, but that is not important for this discussion.)  The air speed would be measured from a pitot tube mounted on the outside of the aircraft.  Noonan would only be using the airspeed to prepare his DR, or dead reckoning.

A navigator actually determines the actual speed of a vessel or aircraft from speed over ground.  To calculate speed over ground, the distance between known fixes is compared with the time between the fixes.  The formula is simple:  Distance = Rate multiplied by Time.  You can actually do this yourself.  If you pass mile marker 336 in your car, and pass mile marker 337 exactly a minute later, you are going 60 miles per hour.  That's because you are travelling a mile a minute.  If you pass the next mile marker in half a minute, you are doing 120 miles an hour (and you are probably going to be getting a ticket.)

The navigator's calculation of speed over ground helps him or her determine headwind, or tailwind, and it's direction.  Surface navigators call this "set and drift."
Title: Re: Has this Been Addressed..........?
Post by: Gary LaPook on July 10, 2012, 03:23:12 AM
Fred Noonan's charts would be mercator's projections, scaled in nautical miles.  A nautical mile is about 2000 yards, or a little over 6000 feet. Incidentally, and not coincidentally, a nautical mile is one minute of arc of latitude.  (There are 60 minutes in a degree.)
The sides of the charts are scaled for degrees and minutes.  A navigator learns very early not to use longitude for scale.

The only instrumentation on the Electra that I know of that would be of any relevance would be the airspeed indicator. This would be calibrated in knots, which is shorthand or nautical miles per hour.  (The word knots actually derives from an older practice of counting knots in what was known as a pit log, but that is not important for this discussion.)  The air speed would be measured from a pitot tube mounted on the outside of the aircraft.  Noonan would only be using the airspeed to prepare his DR, or dead reckoning.

A navigator actually determines the actual speed of a vessel or aircraft from speed over ground.  To calculate speed over ground, the distance between known fixes is compared with the time between the fixes.  The formula is simple:  Distance = Rate multiplied by Time.  You can actually do this yourself.  If you pass mile marker 336 in your car, and pass mile marker 337 exactly a minute later, you are going 60 miles per hour.  That's because you are travelling a mile a minute.  If you pass the next mile marker in half a minute, you are doing 120 miles an hour (and you are probably going to be getting a ticket.)

The navigator's calculation of speed over ground helps him or her determine headwind, or tailwind, and it's direction.  Surface navigators call this "set and drift."
It's actually exactly 1852 meters, 6076 feet now, it was 6080 feet in 1937.

I doubt that the airspeed indicator was marked in knots, that did not become the standard in the U.S. until 1973, prior to that they were marked in mph. The Navy did use knots which caused a number of crashes for Naval aviators trained in flying SNJs who were then given some Army T-6s (almost identical aircraft) that had the airspeed marked in mph. The navy guys knew that the plane would not stall at 60 knots but found that with the airspeed needle pointing at "60" on the T-6 ASI that they were in a stall.
Anyway, for any navigator, the conversion is trivial and Noonan had a Dalton wiz-wheel to make it for him. Of course, his celestial navigation was done in knots and nautical miles.

gl

gl
Title: Re: Has this Been Addressed..........?
Post by: Anthony Allen Roach on July 10, 2012, 10:59:45 AM
Mr. LaPook makes some good points.

I used the words "about" 2000 yards, because I always rounded down when standing bridge watches.  It made station keeping and maneuvering board solutions easier to just round down and use a whole number.  As he points out, what is important is that a nautical mile is measured as a minute of arc of latitude.  The actual physical measurement and changes in the amount of yards/ meters/ feet is based on more precise measurements of the earth's surface.

I was probably wrong to assume that the Electra's air speed indicator was calibrated in knots.  My statement was based on my experience of sitting in naval aircraft, which are calibrated in knots, or both knots and miles per hour.  It would be interesting to locate any primary source material on what instruments the Electra actually had.

Regardless of the calibration, Noonan would have only used the airspeed to lay out his DR lines.  He would be more concerned with finding his speed over ground, which he would get from his navigation work and the time elapsed.
Title: Re: Has this Been Addressed..........?
Post by: Gary LaPook on July 10, 2012, 10:09:28 PM
Mr. LaPook makes some good points.

I used the words "about" 2000 yards, because I always rounded down when standing bridge watches.  It made station keeping and maneuvering board solutions easier to just round down and use a whole number.  As he points out, what is important is that a nautical mile is measured as a minute of arc of latitude.  The actual physical measurement and changes in the amount of yards/ meters/ feet is based on more precise measurements of the earth's surface.

I was probably wrong to assume that the Electra's air speed indicator was calibrated in knots.  My statement was based on my experience of sitting in naval aircraft, which are calibrated in knots, or both knots and miles per hour.  It would be interesting to locate any primary source material on what instruments the Electra actually had.

Regardless of the calibration, Noonan would have only used the airspeed to lay out his DR lines.  He would be more concerned with finding his speed over ground, which he would get from his navigation work and the time elapsed.
Noonan had an airspeed indicator at his station and he had a Dalton wiz-wheel to find TAS which he needed to use in conjunction with his drift meter to find the true wind. But we know that Noonan, like all other navigators, actually worked in nautical miles, not statute miles. Is this clear from his notations on his chart to Dakar available here.