Is it completely clear that is true? While the author doesn't actually present the supporting calculation for the assertion that the RTH speed is set to maximize distance, the calculations are relatively trivial. I posted a similar calculation on the Mavic forum a while back that suggested a pitch of around 30° was optimal, but I didn't use model specific data and that does change things.

The motor thrust (force) vector

*F*, which aligns approximately with the aircraft z-axis, decomposed into vertical and horizontal components at a pitch

*θ*, solves for equilibrium in constant-velocity flight. Ignoring body aerodynamic lift, which is not large for a quadcopter:

*F* cos*θ = Mg *[1]

*F *sin*θ* = -*D* = -*k*₁*u*² [2]

where

*M* is the mass of the aircraft and

*D* is the horizontal drag, which goes roughly with the square of the airspeed,

*u*.

Eliminating

*θ* ( since cos²

*θ* + sin²

*θ* = 1):

*F* = √(*M²g²* + *k*₁*²u*⁴) [3]

Power,

*P*, is related to thrust by

*P² =* *F³*/

*k*₂

*, *which allows us to express power as a function of airspeed:

*P* = (*M²g²* + *k*₁*²u*⁴)^(3/4)/*k*₂ [4]

and the ratio of airspeed / power, which is equal to energy per unit distance, as

*u*/*P* = *k*₂u/(*M²g²* + *k*₁*²u*⁴)^(3/4) [5]

We don't need to know

*k*₂ to calculate a normalized

*u*/

*P*, but we do need

*k*₁. That can be obtained from the published specifications on pitch angle vs. speed and combining equations [1] and [3].

*Mg*/cosθ = √(*M²g²* + *k*₁*²u*⁴) [6]

Giving

*k*₁ = 0.033 for the

P4P and 0.016 for the MP.

That gives the following relationship between the airspeed/power ratio and airspeed:

View attachment 99664
That suggests maximum range for the

P4P at 16.4 mph and for the MP at 14.4 mph. The author calculates a slightly higher optimal airspeed, but has a couple of errors in his estimates.

There are a few uncertainties and simplifications in those calculations, but I find it difficult, given the shapes of those curves, to see how the real peak u/P values could be at much higher airspeeds. Are there actual solid data to support much greater speeds for maximum distance, or is it mostly anecdotal?