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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.

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  • $\begingroup$ Have you got to actually build this propeller? If so, what manufacturing methods do you have available? $\endgroup$ – Notts90 Sep 5 '16 at 14:36
  • $\begingroup$ We will not be building an actual prototype just designing as a university project. $\endgroup$ – user16799 Sep 5 '16 at 15:04
  • $\begingroup$ That helps, it will give you more options. I would recommend using fixed pitch propeller as it keeps it simple (less moving parts) and it also sounds like you are mainly designing for cruise condition. When at uni I used a piece of software that did a lot of the hard work for you. I'll try and find it and let you know if I do. $\endgroup$ – Notts90 Sep 5 '16 at 15:11
  • $\begingroup$ I think it was this software. It has some design method info. You essentially need to work out your requirements (available diameter, required power/thrust) then adjust parameters to find an efficient prop that gives you what you need. propdesigner.co.uk/html/prop_designer.html $\endgroup$ – Notts90 Sep 5 '16 at 15:23
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    $\begingroup$ good to hear! How about making my answer the accepted answer? $\endgroup$ – Notts90 Oct 4 '16 at 12:25
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It's been a long time since I did this but here's then general idea.

  1. Work out your requirements. Thrust, speed (usually cruise speed) and diameter (usually determined by the available space) being the key ones.

  2. Use a piece of software such as this one to optimise other design parameters for your requirements.

  3. You may also consider off-design (non-cruise) performance.

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

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Try to get Xrotor to run. It has been written for designing minimum induced loss propellers, and you can input speed, power or thrust and diameter and the program will output the ideal propeller geometry, including twist over radius. Its first application were the propellers of the MLE and the Dedalus HPA.

Yes, it is written in Fortran. This makes it almost self-documenting.

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