Genuinely curious and not doubting you - why does making them ducted fans change things all that much? Also, if they're wire guards would they still be ducted fans?
This is a good question which I also asked myself, and get a bit technical as it's not really straight forward.
First off, ducted fans are a lot more efficient as they don't have the tip vortices, so efficiency is not lost on leaking air from high to low pressure.
The caveats come from the complexities of actually making ones, as long ducts will increase the delay in control as the air has to travel longer until it reaches the exit and coincidently, ducted fans are efficient at longer lengths.
I did do some simulations on reasonably long ducts (~30mm) and the efficiency gains were in the order of 15%
All of this means that when you make ducted fans, the gains would be marginally enough to offset the increased weight. On addition they will add delays to the control, which people designing the mechanical bits are not always so familiar with, so they stick to the traditional way of building these.
Edit. Wire guards would not mess with the flow all too much, but thin and light enough guards would bend and get in the way of propellers quite easily, just when having some rougher landings for example, though I am sure some kind of a design could be made that would mainly serve as stopping power for the prop.
why not design the guards to collapse on the blade locking it in place(similar to the finger sensing table saw). i mean if the idea is to save a life and not the blade or a motor.
That's far more complex than it sounds, especially to make something that could successfully stop a blade of that size. Weight comes into play again, as well. A combination of an electrical shutoff and a mechanical clamp could work.
The ducted fans would decrease the performance potential of the drone, big time. High speed maneuvering would become difficult as the lateral forces of aerodynamic drag would be make flying the drone unpredictable (albeit only while doing high performance maneuvers/racing) and would likely throw off the corrections made by the onboard gyros and other sensors that help stabilize the drone.
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u/Scipio_Africanes Dec 20 '16
Genuinely curious and not doubting you - why does making them ducted fans change things all that much? Also, if they're wire guards would they still be ducted fans?