So this is the best layout for VTOL fixed wing drone now? There are like a dozen drones from different manufacturer all using this design with no exception (or did I missed it?).
Chinese UAV/UCAV development
- Thread starter AssassinsMace
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Are the VTOL propellers useless after takeoff? I feel that they may add drag if allowed to spin freely.
Not dolphin, blowfish.
I am also interested in this!
They look like they might be. I wonder why no one still made this configuration:
AssassinsMace
Lieutenant General
With eight props (just for vertical capability) it doesn't look terribly efficient. Until they can half that number, and still retain the overall weight, battery powered operation, and overall capability, I'm not sure the design has an immediate mass produced future. Having a twin body design (instead of a three body one now) and with one tractor and one pusher tilt rotor on ends of each body would make the whole design more effective. Of course, tilt rotors are not trivial to solve, and the bigger they are, the harder it is to pull them off with pure battery powertrain. Plus, with just 4 props it'd be crucial for the whole thing to be either extremely reliable or to be cheap and expendable - as just a single prop failure might very well lead to airframe loss.
plawolf
Lieutenant General
There are all sorts of reasons why this dedicated VTOL prop design is winning through, some of the more obvious ones are listed below:
- Economic efficiencies
Due to China’s booming commercial drone sector, there are huge economies of scale savings on popular motor sizes. Why spend 10 time’s the money to get a motor with twice the power when you can just use two or even three popular off-the-shelf motors instead?
- structural weight for tilt rotors
For conventional fixed rotors, you only need to design the structural bracing for them to deal with forces in one directional plain. With a tilt rotor design, the structural design needs to be strong enough to deal with forces acting in a 90 degree arch, so you need significantly more weight for structural support that will eat up a lot of the weight savings you are expecting to enjoy form having fewer motors
- sensor and software burden
You need a lot of additional sensors and exponentially more complex software to allow a tilt rotor design to safely and consistently balance the shifting forces as the plane transitions between rotor configurations. That’s more cost and weight and a much longer development cycle
To sum up, I think the key reasons for why this design is winning through is down to a combination of costs and ease of design.
So even though theoretically it might not be the most aerodynamic or fuel efficient design, it is tye cheapest and quickest one to develop and manufacture, and probably the most mechanically reliable due to the redundancy of engines.
And also we might find that there isn’t a huge amount of efficiency gains in the real world compared to a tilt rotor design once you factor in all the additional ‘hidden’ weight a tilt rotor design would need in the form of additional structural supports and sensor packages.
The aerodynamic penalises from having the extra props may also not be that significant due to the lowish speed of these designs. In addition, if they lock the VTOL rotors during level cruise flight, I don’t think you will get that much extra drag to start with.
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