There is some very useful analysis of data and the laws of physics here:
http://www.nar-associates.com/techni...ide_screen.pdf
The ‘rough approximation’ is to add a quarter of the headwind velocity, to maintain the maximum distance speed.
Hence the answers to my questions above are:
- Nil wind: 80
- 5 knots head wind: 81
- 10 knots head wind: 82
- 15 knots head wind: 84
- 20 knots head wind: 85
- 25 knots head wind: 86
See Trent: It’s not that hard!
I stand corrected.