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fed up with the hobbyist RC plane scene's apparent disregard for fundamental principles of aerodynamics and rotating machinery, I decided to design an electric ducted fan of my own
note that this is purely a preliminary aerodynamic design, thus many of the parts needed to make these files into a practicable propulsion unit are not modelled, such as mechanical interfaces and *cable management*
it's built around a turnigy sk3 inrunning brushless motor designed for 90mm EDFs, with an operating point of 29.6V and 22,000 RPM chosen to produce a mechanical power output of roughly 3.5 horse. Additionally, preliminary numbers were derived from a flight speed of 734 ft/s
at high speeds, incoming flow must be restricted and decelerated in order to prevent choking, as the displacement of the rotor hub would accelerate the flow to mach, making the fluid very hard to work with given the fixed operating point (22KRPM is Very Slow for turbo this size)
additionally, inlet stators were added to induce a negative prewhirl in the opposite direction of rotor rotation so that the rotor would be able to impart more dVswirl, as the low speed of the motor limits the work that the rotor is able to do with purely axial inflow
you'll notice that labyrinth seal intended to reduce losses as air sneaks around the tips of the blades, this isn't commonly seen in actual compressors due to centrifugal stresses and manufacturing constraints, but hell this is child's play compared to those so i did it anyways
these blades were designed using the free-vortex Vswirl distribution, meaning the imparted swirl velocity is an inverse function of radius: this makes the math easier but in extreme design cases can produce stress from "twist" that may just cause your blades to explode
my primary gripe with commercial EDFs is the lack of properly-developed outlet stators, meaning most of the kinetic energy imparted into the flow is lost as swirl velocity, therefore it's important to "straighten" the flow back out
...and now we come to the nozzle. As the dinky little turnigy is incapable of raising the pressure high enough to choke the flow and produce mach exhaust, this nozzle is purely convergent
this nozzle was designed to accelerate the flow to ambient pressure, thus producing an outlet mach of 0.69. However, this only produces 1.2 lbf of thrust at speed, as the incoming air is already moving at mach 0.66, and the like pressure reduces the thrust equation to F=mDot*dV
rough calcs suggest that more aggressive inlet diffusion may produce a higher thrust, as a slow rotor can do better work on a slower, denser flow, but all these calcs are very conservative preliminary estimates
I'd like to flesh this out into a proper powerplant, but at the moment i'm split between something like three other propulsion projects so that may not happen quite yet lmao i think thats about it for this thing
