A low power ducted fan

[quorneng]

Commercial ducted fan units produce a lot of thrust for their size but they need quite a lot of power to do which tends to result in fast and relatively heavy planes.
So I wondered if it was possible to tone things down a bit and produce a lightweight slow flying ducted fan park flyer.
A bit of experimentation. To save weight the 3" fan is fixed directly to the bell of a 1650kV outrunner
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A short shroud to reduce the tit losses from the broad chord blades.
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On a 3s LiPo it produced 6oz thrust and draws 13A.
This is the sort of plane I had in mind.
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With an estimated all up of 12oz the fan should provide reasonable performance.
We shall see.

[David]

All looks good and 13amp is not bad (dependant on the original motor rating).

If you do future tests try a fan with less blades or one that you cut some off evenly. From the photo's its a little hard to tell, but the tip gap at the bottom looks huge yet at the top looks quite snug.

You can always tighten the gap with various materials used as a liner. Another point is you could do with some flow straighteners. Spiralling air at the duct exit looses loads of energy up to a 1/3 of its useful thrust.

Nerveless this may work to your expectations "as is" in which case dont change anything.

[quorneng]

The test shroud is rather heavy so the first task was to build something much lighter. I ended up with a paper/depron//paper sandwich built over a paint tin former.
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Amazingly rigid yet it weighs just 4g.
So on with the build.
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The span has been reduced to 36". The top wing skin will go on when the aileron servos, radio and motor have been installed.

Still on course for an all up weight of 12oz.

[quorneng]

The radio and ailerons servos added.
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The "bath tube" fuselage with the ESC and battery will be mounted on the underside of the fuselage to protect the fan and so allow belly landings.
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Should still come out at 12oz all up which will give a power loading of 150W/lb.

[YOUNG GUN]

Its looking promising - Watching with interest!

[quorneng]

Moving towards the final stages.
The first test of the fan and duct in the airframe.
[video=youtube]Pk3wRv37eOo[/video]
The elevator servo mounted in the port fin.
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Not particularly elegent but admirably simple.
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The nose (and the final battery position) will be completed once the tail assembly is complete.

[David]

Is that fan clipping in the vid? Or is it just bedding in

[quorneng]

The clicking noise is something to do with the camera (overloading the mic?).
Like you when I first heard it I thought something must be rubbing but it is not audible for real and it not coincident with fan speed.

The shroud actually has rather too much clearance so I am making another with 3mm smaller diam.

[YOUNG GUN]

Looking good - Have you got a close up photo of the shroud and how it is fixed in place?

[quorneng]

The shroud is simply glued in place supported by the booms each side and at the bottom by the end of the fuselage.
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Now complete it is in the process of being painted in my "house" colours of yellow and black.
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It weighs just under the target of 12oz.