How to design a propeller for UAV? I need some advice on designing a propeller for a UAV and choosing the right motor for it. I am doing a project which requires the fix-wing UAV to travel at cruise speed of 20 m/s and weighs a total of 12kg, the propeller will have to be a pusher and the aircraft has a L/D of 35 at cruise. I am told by the lecturer to ignore take off velocities as it takes off on a seperate VTOL system before the propeller is activated at 300m for horizontal flight.

As a mechanical engineering student I don't have much experience in aerodynamics. So far I've looked into blade element theory and airfoil designs but there are many different variables to consider such as airfoil profile, pitch, angle of attack, diameter and I'm at a bit of a lost on how to determine these values to match the UAV requirements. So I would like to ask what is the best way I can go about doing this? The ultimate goal is to maximise flight time by designing a propeller and reducing power requirements.
It's been a long time since I did this but here's then general idea. 


Work out your requirements. 
Thrust, speed (usually cruise speed) and diameter (usually determined by the available space) being the key ones.
Use a piece of software such as this one to optimise other design parameters for your requirements.
You may also consider off-design (non-cruise) performance. 


The link above also contains more details about the design process and considerations.