VFR Navigation, rerouting timing corrections due to wind - rule of thumb? 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?
If you know or have a reference to Ground Speed, estimating reasonably accurate flight timings is straightforward. Whatever your GS, you will cover 1/10th of the distance in 6 minutes. So at 90kts, 9 miles in 6 mins. At 70kts, 7 miles in 6mins and at 120kts, 12 miles in 6 mins etc. If you mark your pen/pencil with 5 &amp; 10nm distance marks measured in the same scale as your map, it’s easy to interpolate say, 7nm (for say 70kts GS) and mark your map with 6minute marks. If needed dissect these markings in half, for 3 minute markers.