MP Turn Dia (at 45d) as displayed in Flight Planner Incorrect ?

#### Issue details
It looks like the calculation for the Turn Diameter at a 45deg Bank may be incorrect. This number is very useful for determining whether alternating lanes etc need to be used for a survey mission. It is only useful if it correct.

Standard equations for this are given at the bottom of this web page.
https://en.wikipedia.org/wiki/Standard_rate_turn

A couple of examples are also given here, where a speed of 50m/s gives a turn radius at 45deg bank of 255m (diam = 510m) yet MP gives a Turn Dia (at45d) of 728m ?
https://aviation.stackexchange.com/questions/2871/how-to-calculate-angular-velocity-and-radius-of-a-turn

Thank you

#### Version
1.3.74

#### Platform
n/a

#### Airframe type
n/a

#### Hardware type
n/a

#### Logs
n/a

Start by locating the Flight Planner calculation that displays “Turn Dia (at45d)” and compare it with the standard-rate-turn equations and examples linked in the issue. Done means the displayed diameter uses the correct 45° bank calculation, including the cited 50 m/s example of approximately 510 m.

Written by the indexing model from the issue text.