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Unwanted vibrations are identified and designed out of the system. However, nothing comes for free. Think of scale too--as propellers get larger, the duct has to grow with them.
Imagine the difficulties in putting a 20' duct on a B propeller! Second, the manufacturing tolerances on the duct are critical--the tighter it is, the more efficient you are to a limit, naturally And, speaking of flexing blades and the necessary support structure you'd need, this could make pitch control on a propeller, variable pitch, and on a rotor, cyclic and collective difficult to implement, depending on which of those schemes you're looking to do.
Then again, for a small implementation using RPM control Similarly, while a crosswind on an open rotor leads to a sudden decrease in power, a crosswind on a ducted fan leads to a sudden pitching moment due to the lip of the duct and the asymmetric inflow to the fan which, since you're now producing more thrust to begin with, asymmetric inflow effects become even more pronounced.
Now, if you stick this on the front of a typical Cessna , say, and throw a crosswind at it which, if you think of takeoffs and landings, which since they must be in a certain direction, having a crosswind is actually quite likely imagine the yawing moments that would be induced by the propeller proportional to the static thrust -- even before the aircraft got off the ground and before you have a lot of control authority to counteract it!
A similar scenario in the air could be as dramatic. And, yeah, you could throw some guide vanes at it to help, but nothing comes for free. Or, by contrast, you could just bolt a fixed pitch prop on a shaft at the front of said Cessna and call it a day. In the long run, and this is some speculation, I think it just leads to a more complex system, particularly in full-size implementations, which is a maintenance, cost, and manufacturing headache that isn't worth having if you can get plenty of performance from a regular open propeller.
If you venture into the world of diffuser augmented wind turbines, there have been similar debates going on for decades Similarly, while ducted fan aircraft have flown Ryan XV-5A Vertifan, circa The ducted fans are underneath the circular domes on the wings and another under the shuttered area on the nose for pitch control. Another thing to keep in mind is that ducted fans have much more than 2 blades. The main advantage of increasing number of blades is to get higher thrust density, i.
So, what ducted fans really do is: the multi-bladed fan provide a lot of thrust density and the duct try to compensate the efficiency lost. Hopefully, the ducted fan can achieve the same efficiency of the 2-bladed propeller It's nonsense that ducted fans are more efficient. It always gets bandied around the internet as if it were the truth, but it simply isn't so. Ducted fans look cool and they make props look and sound like jets, so people WANT it to be true, but it doesn't make it so. But that's in a static setting.
In the air, where you have drag created by the duct and duct inlet, that gets even worse. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?
Learn more. Are ducted fans more efficient? Ask Question. Asked 5 years, 6 months ago. Active 1 year ago. Viewed 33k times. Source Of course I can see how an improperly implemented duct could really kill efficiency creating more interference and turbulence , but what about a well designed one?
Improve this question. Daniel Caoili Daniel Caoili 1 1 gold badge 5 5 silver badges 10 10 bronze badges. That is what happens when the air at the tips of the propeller goes in circles through the blades repeatedly.
The shroud stops that. Add a comment. Active Oldest Votes.
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