The Polar Flap
Lieutenant Commander Richard E. Byrd’s flight on May 9, 1926 was man’s first successful aerial assault of the North Pole. It catapulted Byrd to international fame and made him a national hero. He overtook Amundsen who was poised at Spitzbergen waiting for better weather to launch his dirigible, the Norge, to transit the pole. Byrd accomplished his mission in his recorded 15 hours and 57 minutes flight in a trimotor Fokker named the Josephine Ford in honor of the daughter of Edsel Ford who was a staunch supporter of the expedition. The flight stirred controversy almost from the beginning. The perceived early return (believed to be 15 hours and 30 min-utes), European and American press releases and the friendly rivalry of the two contenders helped fuel the controversy over the claim of this historical flight over the past 72 years. The accusations were not long in coming. An alleged confession from Byrd’s pilot Floyd Bennet was circulated that Byrd, fearful that an oil leak would endanger completion of the flight, ordered him to simulate the flight by orbiting just north of Kings Bay, Spizbergen. In 1960 G.H. Liljequist, a meteo-rologist, in a Interavia article claimed that the Fokker did not have the speed to reach the North Pole and return in 15 hours 30 minutes. His contention was that there was a high pressure ridge that remained stationary in the region that could not lead to an early return of the Josephine Ford. The absence of the original records, such as flight charts and in-flight records, were further used by critics to discredit Byrd’s achievement. But in 1994, Dr. Raimund Goerler, an archivist at Ohio State University, found relevant entries in Byrd’s 1925 diary that were used for the 1926 flight to the North Pole and a notebook. Critics were still not satisfied as they suspiciously viewed erasures of two Sun observations in the diary. Byrd’s records showed tail winds both ways. How was this possible? We call upon you to use your analytical skills to help explain the early return of the Josephine Ford (see Figure 6 ). The given information is in Table 2 .
Figure 6. The Flight of the Josephine Ford
Table 2. Byrd’s Itinerary
|From/To||Time GMT||Distance Nautical Miles (Approx.)||Average Groundspeed Knots (nmi/hr) (Approx.)||True Airspeed Knots (nmi/hr) (Approx.)||Wind Component Knots (nmi/hr) (Approx.)|
|Kings Bay/ North Pole||0037||665 to pole||75|
|Amsterdam Island||0122||52 from Kings Bay||69.3||75||+5.7|
|North Pole/ Kings Bay||1634 per Byrd’s records||670||91.6||75||+16.6|
How do we account for the earlier than expected return of Byrd’s flight (based on Byrd’s recently found records):
Byrd experienced tail wind components on both legs of his flight since:
a. A high pressure cell traversed the navigation legs from west to east
b. A low pressure cell traversed the navigation legs from east to west
c. A high pressure cell traversed the navigation legs from east to west
d. The stagnant high pressure ridge began moving
The answer is:
Byrd found the winds strengthening from the south enroute to the North Pole. Liljequist alludes to a high pressure ridge in the region (that remained stationary). Byrd also detected winds from the north on his inbound leg. The explanation for his flight exper-iencing tail wind components on both the outbound and inbound legs was that the high pressure cell traversed his flight path from east to west. A high pressure cell has winds circulating clock-wise about its center. Thus, the leading edge of the cell gave him a tailwind component outbound and as the center of the
cell crossed his inbound leg he received the benefit of a tail
wind component from the trailing edge of the cell as shown in Figure 7 . This would account for the average round trip groundspeed of 85 knots. A wind triangle is illustrated in
Figure 8 .
The critics focused their attention on: 1) an alleged confession by Chief Warrant Officer Floyd Bennet (Byrd’s pilot) that the flight was simulated by orbiting north of Amsterdam Island, 2) the absence of a flight log and maps, 3) the belief that the flight took place in a "no-wind" condition since it returned to its origin in a perceived static weather condition (a stationary high pressure ridge in the region), and 4) perceived navigational computational errors and erased sextant observations in the recently found diary.
The National Geographic Society appointed a committee to examine the records of Commander Byrd’s flight in 1926. The committee re-calculated all computations and replotted the mission. Their conclusion was Byrd’s time of arrival at the North Pole was within one minute of the committee’s calculation. Byrd made ten sextant observations of the Sun (four of which were in the region of the North Pole). On the return leg, the sextant slid off the chart table and the horizon glass was broken.
Figure 7. High Pressure Cell Traverses Byrd’s
Flight Path from East to West
Figure 8. Wind Triangle
The inbound leg navigation relied solely on dead reckoning. Byrd’s navigational equipment is listed in Table 3 .
Table 3. Instruments Used for Navigation
|Bubble sextant||Artificial horizon||Arcminutes (although resolution is to arcseconds)||Marine sextant with bubble level used for instantaneous shots-affected by aircraft motion.|
|Drift indicator||Pioneer Instrument Co.||1°||Used to determine drift angle (difference between true heading of aircraft and track).|
|Sun compass (2)||Bumstead||1°||Worked like a sundial in reverse. Provided true heading of aircraft.|
|Compass (pilot) (navigator)||Periodic and earth induction magnetic||1°||Provided compass heading of aircraft.|
|Chronometer (2)||Torpedo boat||Rated to a fractional second||Maintained Greenwich Civil Time essential for sextant observations.|
|Aneroid barometer||Provides altitude information to obtain groundspeed by timing.|
To maintain his track, Byrd had to steer, make drift readings, and determine true heading accurately to maintain course:
True course = true heading ± drift + operational error (pilot’s error to respond to corrections and maintain course)
course error = 1.5°
Groundspeed (GS) error = 5% at 2,000 feet altitude
Computing ground speed uses this formula:
where K is a constant of the device and angle subtended by the target timed, AA is absolute altitude and T is the elapsed time of observation. Absolute altitude in Figure 9 is obtained by sub-tracting both the pressure altitude variation (PAV) and the terrain elevation from barometric pressure. Pressure altitude variation is the difference between the standard datum plane in feet and the datum plane above which indicated true altitude is measured. Byrd had no way of knowing with certainty the value of PAV for the duration of the flight. One tenth inch of mercury error is equal to 100 feet of altitude error. Nor was he absolutely certain that his knowledge of the terrain elevation was correct. The baro altimeter had an intrinsic error as well as did the timing obser-vation of a target. Groundspeed by timing is sensitive to altitude and timing errors. The results are less accurate at lower altit-udes than at higher altitude. A 100 foot error in altitude at 3,000 feet flight altitude results in a 3.3 percent error whereas at 30,000 feet it is a 0.33 percent error in ground speed. Timing also affects accuracy as well but is better controlled. The combined error of these components could be as high as 10 – 20 percent. The error analysis used 5 percent realizing that at the North Pole the Fokker’s position error would be contained within the boundaries of the sunline and courseline uncertainties. Byrd’s flight was at altitudes of 2,000 to 4,000 feet.
Figure 9. Computing Absolute Altitude
Within two years of his aerial triumph at the North Pole, Byrd wrote the book, “Skyward” which chronicled his polar achieve-ments, transatlantic flight and included future plans. He devoted a chapter on his historical transit of the North Pole. The chapter contained numerous details and a plot of his flight path, anno-tated DR positions, sunlines, and times. He earlier provided the special committee appointed by the National Geographic Society with his flight records and his own report on the flight to the Navy Department. Both were scrupulously reviewed by experts and found to be a validation of the event. But the critics persisted in their view that the flight was simulated or fell far short of its goal. Byrd’s diary and notebook of the flight were given to Ohio State University with many of his personal papers. Some records reside at the National Archives and National Geographic Society. It was not until 1996 that the diary and notebook were located by Ohio State University archivist Raimund Goerler who discovered them as he was cataloging Byrd’s papers. The original flight charts, graphical plots of the sextant derived lines of position (using the pole as an assumed position) and computations on eight of the ten sextant altitudes were not reported in Goerler’s find. During this period, a TV documentary devoted to Byrd was being prepared for PBS by Nancy Porter Productions, Inc. (aired in February 1999 on the American Experience Series). Sup-porters and critics of Byrd’s triumph were interviewed for their views by the documentary team.
Let us examine this flight in the light of the data furnished and the intrinsic accuracy of the instruments and techniques employed for navigation to establish the uncertainty of Byrd’s position at the North Pole. We will analyze the cases where the Fokker falls short of the pole as portrayed in Figure 10 .
Our error analysis (assumes):
1926 Committee (assumed)
1) GS error ±5% (0.05 x 600 nmi = ±30 nmi
along track error @pole)
2) Course error ±1.5° (1.5° x 600 nmi/60 nmi x 1 nmi/°) = ±15 nmi cross track error @ pole.
Navigation rule of thumb: 1°course error
subtends 1 nmi cross track error for every
60 nmi of travel (approximation of 1 radian
= 57.3° = 57.3 nmi)
3) Sextant altitude error ±5 arcmin used
instantaneous shots from a platform not free
of dynamic errors. Aircraft sextants were later
developed to observe the body over time and
thus average out dynamic errors of the aircraft
Case 1. Ignoring all sextant observations except at the pole applying 1.5 course error for a distance of 600 nmi.
Case 2. Giving credence to the 0456:27 sunline which showed close adherence to the desired course as a start point for applying 1.5° course error for the distance 330 nmi between latitude 84°30'N to the North Pole 90°00'N
In this analysis we show the semi-diagonal uncertainty in the lower left section of the parallelogram for the sunline limits and the lower left quarter of the rectangle for the DR limits. The Fokker can reside in any of the quarter sections. Based on this error analysis, the Fokker can be anywhere within the par-allelogram or rectangle depending upon the premise used sunlines aided by DR or DR excluding sunlines. Byrd’s
Figure 10. Position Uncertainty at the North Pole Based on Instrument Uncertainty
frequent use of the Sun compass for obtaining true heading and the taking of drift readings leading to corrections to the steering of the aircraft and ground speed by timing led him to believe that he was adhering to a precise north track along longitude 11°04'E. He even obtained a sunline @ 0456:27 that plotted very close to this longitude (as shown in his book Skyward). He was certain that he had maintained his intended course on the return leg as he sighted the Sun’s shadow on the Sun compass hour hand at the moment it was to cross the 15°E longitude which was his course and later when he sighted Gray Point just west of the end of course. His DR navigation on the return leg was unaided by sunlines as the sextant slid off the chart table and could not be used.
Nevertheless, Figure 10 Case 1 shows that the flight would fall short of its goal by up to 21 nmi, (based on sunline and cross track errors) which reduce by 42 nmi the total distance traveled and at no-wind speed of 75 knots would account for an earlier return of 34 minutes. It would also result in the Fokker being off the perceived course that Byrd believed he held. In Case 2, the sunline cross track errors (giving credence to the 0456:27 sunline showing close adherence to his course along 11°04'W longitude) yield an along track error of up to 15 nmi, one sigma which would reduce by 30 nmi the total distance flown by the Fokker and at no wind speed of 75 knots. would account for an earlier return of 24 minutes. Remember this is a statistical analysis; Byrd could be where his navigation plot indicated. Lindbergh in August of the following year (1927) crossed the Atlantic and hit the southern coast of Ireland solely on dead reckoning before altering course for Paris. Lindbergh without use of a drift meter, ground speed by timing and sextant relied upon precomputed magnetic headings (based on weather forecasts and flight plan charts) and drift estimations based on waves maintained his course to within tenths of a degree. He was indeed lucky as compensating errors were responsible for such close adherence.
In conclusion, one must examine the inherent errors introduced in the navigation process and analyze the effects in the use of the instrumentation and the uncertainties in the driftmeter, altimeter, magnetic compass, Sun compass and their inter-actions to establish how close the North Pole could be attained. We have shown two possible scenarios. The criticism was that Byrd returned too early to have flown the total round trip. If we give credence to his recorded time and his detection of tailwind components on both legs, Byrd accomplished his goal despite the uncertainty of his instrument errors. The committee could not find any computational or plotting errors. Giving credence to erased data and extrapolating Byrd’s navigation on this basis will clearly yield a shortfall in Byrd’s accomplishment as some critics claim. I believe the erased data should not be used. (It was discarded because it did not reconcile with Byrd’s DR position.) It is clear that not all of the records and data pertaining to this historic flight were retrieved. The remaining records may never be retrieved, therefore, there will be lingering concern in certain quarters that Byrd fell short of his goal. I believe that Byrd attained his goal within the instrument error uncertainty of his era and may very well have obtained the North Pole as his plot indicated especially in view of his 0456:27 sunline verifying close adherence to his outbound leg, his sighting of the Sun on his meridian at the expected moment on the inbound leg and later the sighting of Gray Hook near the end of his return leg directly south and slightly west of his course.