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It has always been a mystery why Harriet flew so far off her planned course. Contemporary reports state that she had never used a compass before, and there is nothing quoted about the weather conditions in the Straits of Dover during her flight.
The prevailing wind in the Straits is normally from the SW. If it had been, it would have helped Harriet to reach landfall in the Calais area as planned. But if the wind that morning was blowing from a northerly direction, could it have been a contributing factor to her being so far off course?
An enquiry to the UK Meteorological Office (MET) Archives has provided validating evidence as shown in the attached files.
The April 1912 File gives the daily weather conditions for the whole of April. Page 5 of 10 shows that on the 16th April, the weather conditions as recorded at the Folkestone Weather Station at 07:00hrs indicate that the wind was blowing from the ENE at Force 3. Air temperature was recorded at 52° Fahrenheit (12° C).
(Please ignore page 10, as this data is for the 12th April on the French coast.)
The 16 April File is day specific. The French Bulletin International weather data for the Cap Gris-Nez/Boulogne area (page 1 0f 3) indicates that the wind was blowing from the NE at Force 3 with light cloud (leger nuage). From the Folkestone Synoptic Chart (page 2 of 3) it indicates that the wind was from the ENE at Force 3 with cloud.
With these factors in mind, the following three points have to be considered:
The Bleriot XI was powered by a 50hp rotary engine, but modern performance data reveals that this type of engine normally operates at approx 35hp. A Force 3 (Beaufort Scale) wind strength is equal to a speed of 8 to 12 mph (12 – 19km/h)Harriet had kept the aircraft pointing in a NE direction as instructed by Gustav Hamel
It can therefore be deduced that Harriet was flying into a 'headwind' of a strength sufficient to blow her down-wind of Calais by approximately 20 miles to make landfall at Cap Gris-Nez. Realising that she was off course, and low on fuel, Harriet must have made the decision not to head for Calais, and to save fuel, fly with the wind down the coast to land near to Hardelot where she knew Bleriot lived.
This deduction has been ratified by a commercial airline pilot associated with the 2465 Squadron (Luton Icknield) Air Training Corps who has said that from his experience flying light aircraft, Harriet's plane would have been side slipping west due to be being underpowered to hold a true course against a moderate ENE head wind speed of 10mph. even though the plane was being kept pointing on a NE compass bearing.Martin Young. Chairman. HQCP.