NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Earhart's Plane - Search For?
From: Gary LaPook
Date: 2011 Apr 25, 18:39 -0700
From: Gary LaPook
Date: 2011 Apr 25, 18:39 -0700
| My further comments on the Waitt report: ---------------------------------------------------------------- My further review of the Waitt report. This is not complete, just pointing out the glaring problems. Page 8 mixes and matches statute miles and nautical miles. Page 9 for support for its statements about celestial navigation (n1 and n2) it cites the TIGHAR report written by the guy I already mentioned who invented the term "look angle." Page 11 the report states it used as a source "the celestial Almanac Pub 249 used for celestial navigation." There is no document named "celestial Almanac." There are two American published almanacs used for celestial navigation, the Nautical Almanac and the Air Almanac, each published by the U.S. Naval Observatory. These contain the positions of celestial bodies for each second of the year which is needed for calculating celestial fixes. There is a completely separate three volume document entitled Sight Reduction Tables for Air Navigation, U.S. Navy Hydrographic Office Publication H.O. 249 which is used for the actual computation starting with the data already retrieved from one of the almanacs. H.O. 249 and the Air Almanac were not published until years after AE's flight so were not used by Noonan. Noonan used the Nautical Almanac and H.O. 208 which is a set of trig tables used for similar computations as H.O 249. Page 14 states "Indicated airspeed is roughly equivalent to ground speed at low altitudes" which is wrong. Indicated airspeed is roughly equivalent to "True Airspeed" at low altitudes. You must correct your indicated airspeed to obtain true airspeed and then allow for the wind to find ground speed. So if you indicated airspeed is 130 knots at one thousand feet your true airspeed will be about 133 knots but if you have a 25 knot headwind the ground speed will only be 108 knots, nowhere near the indicated airspeed. Page 20 states the "EON" point A is an overshoot, meaning the plane went past Howland but the use of his octant by Noonan with the sun almost directly in front of them would keep this form happening. Page 21 states that with reduced winds the EON C ended up short of Howland. Reduced winds, since they were headwinds, would result in an overshoot, not an undershoot. Page 21 It also states that Noonan improperly applying the refraction correction and the dip correction to his octant observation of the "sunrise celestial calculation" could have caused up to a 70 nm error. First, Noonan couldn't take a"sunrise" observation because the correction table he had in his Nautical Almanac and in H.O 208 only has corrections for angles above the horizontal that are greater that six degrees. Refraction becomes much greater vary fast below this altitude. The refraction correction for 6 degrees is 8 minutes of arc but at zero altitude it is 34 minutes of arc. A sunrise observed from 10,000 feet is actually at 1 degree and 37 minutes below horizontal. The refraction correction for such a negative observation is 50 minutes of arc but Noonan would not have known this because a refraction correction table covering negative altitudes was not available until 1952. Noonan would have to wait about 25 minutes after the sun rose to allow it to climb above 6 degrees covered by his refraction correction table. Noonan knew this so would not have relied on observing sunrise. see: http://groups.yahoo.com/group/earhart/files/Refraction see my prior post at: http://groups.yahoo.com/group/earhart/message/8021 When using a marine sextant you must allow for "dip." When using this type of sextant you use the visible horizon as your horizontal reference but unless you eye was exactly at sea level you are actually looking down towards the visible horizon so that the angle measured by the sextant will be too big. This is the reason for dip correction and is based on your height above the sea. This is applied by sailors. For example from a ship's bridge 25 feet above the sea the correction is 5 minutes of arc but the correction for an altitude of 10,000 feet would be 1 degree and 37 minutes. But this is only used with a marine sextant, not with the type of octant that Noonan was using. His octant utilizes a bubble for its horizontal reference, not the visible horizon, so there is no dip error and so no dip correction is applied. The myth of the "sunrise observation" was created by people who know "a little bit" about celestial navigation. The 337°-157° sunline line of position (LOP) was derived by an observation of the sun when the sun's azimuth (not "look angle") was 67° true since the LOP is at right angles to the azimuth to the celestial body. When the sun rose in the vicinity of Howland on July 2, 1937 its azimuth was 67° true. Those with "a little bit" of knowledge fastened on this fact to claim that Noonan took a sunrise observation and used only it in planning the approach to Howland. (They apparently believe that Noonan then opened the door and dropped his octant into the sea.) But what these people didn't understand is that the sun's azimuth stayed at 67° until 1847 Z, an hour after sunrise! This means that Noonan would have computed the same 337°-157° LOP from any sight taken during this one hour period and we have already seen that he would have had to wait until the sun was above 6° before taking the sight leaving about a half hour period for taking sights. He would have taken several sights as he approached the LOP then more after the interception to ensure staying on it. See attached Air Force navigator's document about this procedure. Page 23 I already pointed out the ridiculous level of precision to which they state the coordinates of the "EON" points. Page 25-26 states that the route was chosen to facilitate "an afternoon setting-sun celestial fix." A number of problems with this. First, you can't get a fix from observing one celestial body, it takes at least two and preferably three. Noonan would have waited till it got dark and then taken two or three stars for a proper fix. The only reason they were using a sun line LOP for finding Howland was that no stars were available during the day. Second you can't take a sunset observation for the same reasons that you can't take a sunrise observation as discussed above. Third we know that Noonan was able to take observations of bodies almost directly behind the plane on the flight to Hawaii so no advantage to this route. ....To be continued........ gl --- On Mon, 4/25/11, Gary LaPook <glapook@pacbell.net> wrote:
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