What does efficiency mean in relation to ducted fans?

I believe it means the same thing as any other time: Efficiency is the ratio of energy out to energy in.

sorry, but what do you mean by energy in. How does energy go back into the duct fan.

You need to specify a system (say electric, or glow fuel)and a fan. Then a test system could be designed, to measure the energy going into the fan system, and the energy produced and applied to the airframe.

What did you have in mind?

Dave Olson

Scar,

He wants to know the MEANING of efficiency, not the efficiency of a specific power system (yet).

There are a few levels to the efficiency of an electric power system. There's ESC efficiency. That's the electricity from the battery (energy in) compared to the electricity that's sent to the motor (energy out). There's motor efficiency. That's the electricity from the ESC (energy in) compared to how much power comes out of the motor (energy out). There's prop/impeller efficiency. That's the energy from the motor (energy in) compared to the power produced as thrust and speed (energy out).

Finally, there's overall efficiency. That's the electricity from the battery (energy in) compared to the output of the fan (energy out).

At each point through the system, there's some loss of energy, mostly as heat

Thanks a lot, that explained quite a bit. Now, could you guys tell me if this idea is going to work. I am planning on building a hovercraft like RC vehicle. I am goint to use four duct fans with 324 g of thrust. Two will go on the front on the x-axis. then there will be one further behind uin the center. Last of all, there will be one fan put vertically on the rear which will rotate on the z axis to control forward and directional motion. My theory is that the fans facing dow, will "throw air down, and at a certain height, the air going down will cancel out the gravitational energy of the earth on the vehicle, and the vehicle will hover at hopefull a few inches of the ground. Then I hope to use a three channel pistol controller to control the contraption. Is this a valid theory and will this idea work. Thanks for your input.

Aircraft companies experimented with similar ideas in the '50s and '60s. The end result was the modern hovercraft. They found that the setup was much more efficient with a simple rubber skirt to hold the air under pressure, and took far less power to maintain a hover. What happens is that unless you trap the air and force it to remain beneath the craft, it mostly "squirts out" in every direction shortly after it leaves the duct.

One of the first hurdles I see is getting an adequate thrust to weight ratio. It won't be so bad if you run it with an external power supply and umbilical cord, but if you want it self-contained, the batteries might make the craft too heavy to fly.

Another potential hurdle is maintaining balance. The three lift motors won't automatically produce the exact same thrust, and environmental conditions (e.g. uneven surfaces) will throw the craft off balance, so you won't always need the exact same thrust. You'll either need a more sophisticated radio, like a heli radio with CCPM mixing, or you'll need to design a gyro-driven system that automatically stabilizes the platform so you can control forward motion and steering with a simple pistol-grip transmitter.

Before you go spending money on fancy carbon fiber EDF units and hot brushless motors, you might want to build a prototype using inexpensive brushed can motors driving large props through gear reduction, with an external battery and "umbilical" for power. That way you can develop your control system and get a general idea of what the project requires without spending a bundle.

How exactly does a gyro work, and will the fans be able to lift the batteries as well if i used three 324 g thrust fans, and would it be easier if i have a skirt, but not bag like in modern day hovercrafts. Thanks again.

also, i have bought one duct fan and battery to see what kind of lifting power it has, and what is its possibility

lots of these topics were already covered in your previous thread(s)

http://www.rcuniverse.com/forum/m_26...tm.htm#2650927