program to find velocity of a UAV -

This is a fun problem (aircraft design). I guess it's OK to give an answer on this, since it was homework 8 years ago!

A quick method to get the velocity of a small, electric UAV is using work/energy methods as follows:

Start with the estimated power draw from the electric motor.

Now assume that the motor is 70% efficient in converting electric power to shaft power.

A typical hobby size propeller is 70% efficient in converting shaft power to thrust. So the available power for thrust is ~50% of the electric power consumed.

This thrust is working against the aerodynamic drag. There are two primary sources of drag: Induced drag, and skin friction. The induced drag is an artifact of creating lift. It will be determined based on the wing loading (Weight/Area) and the Wing Geometry (for rectangular wing, this is mainly the aspect ratio (Area/Chord length). Using aerodynamic design tables, you can obtain an estimate for the induded drag and the skin friction drag (in terms of drag coefficient). The Drag force is = 1/2 (air density) (Drag ciefficient) (Wing Area) (Velocity)^2

Energy dissipated by drag = Drag Force x Velocity = (1/2 rho Cd A) V^3

Set the dissipated energy (Drag x V) equal to the thrust power available and solve for V. This is the horizontal speed of the aircraft at the specified electrical power consumption.

An aircraft design table will give reasonable estimates for drag values. Similarly, you can get the actual power consumption of your motor from the manufacturer or from a test bench. Some propeller manufacturers will likewise publish performance data for their products.