Over the past couple weeks we have begun flight testing on our newest aerial sensor platform. It is a standard quad rotor configuration with one major improvement.
Below is a short video of our first test flight.
By fabricating a carbon fiber duct to surround the prop you can realize several benefits. Most obvious is the safety factor offered by enclosing the propellers. with a carbon fiber duct, a substantial impact could be survived without serious damage being suffered by the aircraft or persons or property..
There is also the increased efficiency due to the reduction of propeller blade tip losses. The ducted fan is more efficient in producing thrust than a conventional propeller, especially at low speed and high static thrust level . This "high static thrust" describes the way that a multi rotor operates. This can only be realized by getting very tight tolerance between the propeller tips and the body of the duct.
Clearance between the propeller tip and duct body are > 1 mm. This reduces the induced drag and associated noise level creating a quieter more efficient propulsion system.
Reducing the induced drag on the propeller tip has an added benefit of also reducing the associated noise. By shielding the noise and reducing the propeller tip drag the resulting noise level of the aircraft can be lowered substantially.
Our first tests actually were a bit louder than a similar sized prop/motor combo used on the current MK09 (IVAN). This is likely due to a couple of factors including the result of an even number of props causing resonate vibrations in the duct as well as the inherent quality of a material like carbon fiber to act more as a speaker than to diffuse vibration(sound). Our upcoming iterations on this design will incorporate 3 or 5 blade configurations to counter this effect.