Sir pnr2 updating
To check our math we can subtract this from the endurance of giving us hoursto return to New Britain.Seven hours multiplied by the actual return ground speed of 153 knotsmeans the plane will travel 1071 NM back towards Lae.We know that on the planned flight from Hawaii to Howland they considered the possibility of turning around and, after Noonan had computed a PNR for that leg, had taken on additional fuel to allow for a return to Hawaii against the existing wind which makes it logical that they would have done the same if they had encountered a problem on the last flight.The entire "around the world flight" was planned around the need for celestial navigation on the leg to Howland and just two days before takeoff Earhart had sent a radiogram from Lae saying "FN MUST HAVE STAR SIGHTS." return to New Britain from the vicinity of Howland thus making that theory very unlikely.We do this by using a “fictitious aircraftcarrier.” The east end of New Britain is 344 NM east of Lae on the course line to Howland.If afictitious carrier departed Lae at the same time as Earhart, steaming towards Howland, it wouldhave arrived at the east end of New Britain at the end of (the proven endurance of theplane) by steaming at 17 knots.
Sincewe know the plane went past this PNR and proceeded for at least further, to the vicinity of Howland, it would not have been possible for the plane to make it back to New Britain even witha 24 hour endurance. We know that they did not turn around prior to the PNR because they continued on to the vicinity of Howland which is well past the PNR.Boy, that term "Point Of No Return" makes shivers run down my spine and has been used in many movies to heighten tension."We can't turn back, we must go forward, no matter what! The "point of no return" is just another example of the more general "radius of action" calculation.The inputs are the endurance (based on the fuel on board divided by fuel flow) the head (or tail) wind component for the approximate first half of the flight and the true airspeed of the plane.The true airspeed and the wind component are combined to determine the ground speed out (on course towards the destination) and the ground speed for the return leg.