For the record, I am not a pilot although I do have a quantitative background. However, I am researching my father F/Lt Cave, 419 Squadron WWII. I have thousands of pages of wartime documents, that relate directly to his service, his service files, log books photos. I have essays on all of his 31 operations during the period 27-September-1944 to 25-March-1945. One particularly interesting operation was to Chemnitz, 5/6-March-1945. I have the navigator's log (Form 441) and chart completed for this operation by dad's navigator, F/O Seale, as well as 3 others. It would be an understatement to say these are fascinating documents which detail, minute by minute the flight of the aircraft that night.
The first page of the Form 441, includes the meteorological forecast, the flight plan with turning points and speeds. The flight plan includes a row for each turning point, Latitude, Longitude RAS, Ground Speed, Wind Speed, Wind direction, Height and outside air temperature. The navigator has calculated "Required Track True", which he adjusts using wind speed and direction and TAS, to calculate "Course True" which is then adjusted for "VARN" or Magnetic Declination. He then calculates Distance to Run between Turning Points from the Latitudes and Longitudes. Next, he calculates ground speed from TAS, Required Track True, Course True, and wind speed and direction.
Note: I have verified all of these calculations, including headings and great circle distances, from simple trigonometry. Differences between my calculations and those by my father's navigator are very small and likely due to rounding or very small mechanical error as a result of the Mark III D Navigation Computer, in use at that time.
However...I am struggling with the calculation of TAS. I cannot come up with a historical formula (from 80 years ago) on calculating this parameter. Virtually everything I can find on the web is difficult to interpret in this situation. F/O Seale uses RAS (what I understand to be "Rectified Air Speed". This parameter is provided to aircrew from the "Operational Orders" (AKA Form "Bs") which they term "Indicated Air Speed" i.e. visible to the pilot on his Air Speed Indicator
calibrated in MPH (yes, MPH--I know this to be true). So Seale must have used Indicated Airspeed, recorded as RAS (Rectified Air Speed) together with height and forecast air temperature to calculate TAS.
From a post
(1) entitled “TAS from IAS, PA and OAT” from this forum (I am not allowed to post the URL) came up on a search and post #8 is compelling as he comments "
Was given to me long time ago by an old retired navigator and it's surprisingly accurate." However, I cannot get this formula to match the results, which I will post in the next post.
Jim
(1) this one ? TAS from IAS, PA and OAT - PPRuNe Forums
JT