I don't see the cube rule on the chart.

It's in the power required due to parasite drag curve. In the Perkins & Hage example, 147 mph requires 340 units of power, and 180 mph requires 810 units of power. The graph in your book is scaled with major units on 1/2" intervals, so you can easily measure and see.

\( {P_2} = P_1 ( \frac{V_2}{V_1} )^3 = 340 ( \frac{187}{140})^3 = 340 \times 2.38 = 810 \)

Or, to look at doubling the speed, as

@cheapracer suggested:

\( {P_2} = P_1 ( \frac{V_2}{V_1} )^3 = 360 ( \frac{300}{150})^3 = 360 \times 8 = 2880 \)

The yellow curve is the same for any given aircraft. Remember that \(D=\frac {1}{2} \rho V^2 S C_d \), so changing Cd for a different airplane simply results in a different "scale" of power units and the cube relationship remains the same.

As I mentioned earlier, this "cube rule" does not take into account the diminishing effect of induced drag as speed increases (the other dashed curve). No one here knows what \( V_{L/Dmax} \) is for Raptor (and therefore where its induced curve is located, and further, how much it "offsets" the cube rule). But, the further we are to the right of this point, the more the power required curve matches the parasite curve, and the more it approximates the cube rule.

Again from Perkins & Hage, \(D_i = \frac{L^2}{\pi q b^2} \), so the power required for induced drag curve for an individual plane (at a given altitude) is dependent on weight and span ( \(D_i \propto ( \frac{L}{b} )^2 \) ). Because Raptor is relatively heavy, the induced curve would be relatively higher, meaning that the power increase from 147 to 180 would be something less than 240% (although its power requirement just to get 147kt is quite high due to its weight^2/span^2). But if it were closer to advertised weight, it would be closer to a 240% power increase.

One could reasonably expect that a flight test regimen for a new airframe design (especially where the power output of a new engine is unknown) would include some exploration of these curves.