Consider this reroute on a VFR nav trip from Great Malvern to Chipping Norton.
Maintaining 120 TAS.
Track 110 °M Heading 103 °M (taking 3/4 of Max Drift - MD)
In still air this 30nm section would take 15 minutes. However, with a 5-10 headwind the groundspeed would be lower than TAS, around 110-115 kts
Is there a good rule-of-thumb, or quick method in the air to estimate the timings and ETA when considering the effect of headwind or tailwind on the timing of a reroute leg?