How to calculate the power required during transition from VTOL to fixed wing? In a VTOL, I have calculated the power required for take off and cruise which was not difficult at all. Between take off and cruise, there is a phase where the VTOL has to transition by tilting the rotors from 0 to 90 deg. I am finding it hard to calculate the power required for this transition. I feel this is very important because it consumes more power than take off since it is creating lift (hasn't reached the minimum velocity for the lift requirement) for balancing weight and also needs to provide thrust for forward motion.
Given to me are:


Rotor parameters


number of rotors
Rotor diameter
rpm
number of blades

Fixed wing parameters


span and chord (rectangular wing)
lift and drag coefficients  



What are the factors considered to calculate the power required for transition? 
Please note: Make as many assumptions/approximation as you like. I just want a simple formula for a basic understanding.


The VTOL is a tilt rotor type with ducted fans
Like Hobbes said. For instance, after take-off, tilt the thrust 10° forward. The cosine is 0.98 so you only lose 2% of propulsion lift. The sine is 0.17, so forward thrust is 0.17 * total thrust.

The craft will speed up until aerodynamic drag = forward thrust:

$$ T = D = C_D \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$
$$ V^2 = \frac{2 \cdot T}{C_D \cdot \rho \cdot S}$$

Then tilt to 20° where you have sin(20) = 34% of the propulsive thrust pointing FWD and 94% pointing UP, etc.

Note that it is usual to express the drag equation relative to wing area S.

A simple real-time approximation in a spreadsheet would look like underneath. 9810 N thrust pointed back 10 deg results in sin10*9810 = 1703 N forward thrust, which takes about 300 seconds to speed up the craft to 97 m/s. Of course, because of the aerodynamic lift the craft climbs, changing AoA and creating induced drag etc. The simulation should be extended with reduction in rotor thrust proportional to aerodynamic lift. But I hope the gist of things is clear enough.


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