What are the differences between controlling a standard aircraft propeller (sometimes called an airscrew) and a ducted fan? I believe one difference is that the pitch of the propeller can be controlled. Is this the only difference when it comes to controlling each type?
Hello Mike, I remember propeller equipped aircrafts having a controllable propeller pitch without shrouds or ducts already many years ago. So I think that is not unique to ducted fans. Of course a standard is often simple / basic, meaning usually the propeller pitch is fixed rather than being changable. I have the Impression it is more about having a controllable pitch or not (thrust control, to taxi on ground, thrust free start / stopp, ...). The ducted fan is attractive because of its higher efficiency due to air guidance and lower losses at the outer propeller Ends.
"The ducted fan is attractive because of its higher efficiency due to air guidance and lower losses at the outer propeller Ends." I take it this is because of the shoud that surronds the ducted fan propeller. What are the benifits standard propellers have over ducted fans as there seems to be many more standard propellers used in aircraft than ducted fans. Where would ducted fans have the advantage?
Thanks...
If you think about a Jet Engines, it begins with a series of ducted fans to
compress and direct the incoming air.
Thanks Michael. I was thinking more along the lines of comparing standard prop to ducted fan craft. Take for example this rc plane:
http://www.horizonhobby.com/products/a-10-warthog-arf-with-ducted-fans-GWS1055?cm_mmc=Adwords-_-ProductSearch-_-Productlist-_-GWS1055&gclid=CPL2wp-cr7gCFeU7OgodlC8AWg
I understand the ducted fan gives the visual apperance wanted here, but if the visual effect is not needed, do the ducted fans offer any improvement over having standard props mounted on the wings instead?
They move more air at a slightly higher velocity. The curved shape of the
duct ( in cross section ) is an important aspect in creating a smooth flow
of air into and out of the fan.
The duct separates the air into an essentially non moving area outside the duct,
and a moving area inside the duct.
Without the duct, as in the tip of a propeller, eddies form such that the air is
moving in a circle at the tip of the propeller.
Wing tips do the same thing, so they now have little vertical wing tips to
break up the vorticies that spiral off wing tips.
Thanks Michael. Could the ducted fans be used in vertical lift applications? The Osprey uses standard props:
https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey
do the eddies at the prop tips cause it to have problems (I understand they have a lot of stability problems)? Could using ducted fans in such an applications improve the crafts stability?
In this case, the props (or ducted fans) have to supply lift, rotate and then supply thrust. I imagine there are a greaet many problems for a craft like this to go from lifting to forward motion. I wonder if ducted fans might improve this and if that was looked at?
Would the equations that model the dynamcis of an aircraft utilizing tilt-rotor techniques for vertical take-off, but level flight be different if ducted fans were used instead of standard props? The dynamics I'm thinking of are the lift phase (vertical take off), then through the rotation (where the rotors go from vertical to horizontal), into the forward thrust phase (where it flys like a plane).
If the duct was stationary, it is possible, but a rotating duct would tear itself apart.
They used the idea in some craft that looked like a flying saucer, six fans, but I
guess it did not sell well and I do not see it advertised anymore.
The first Ospreys had stability problems. It makes sense if you think that the force
applied is not centered on the mass of the vehicle, so if the force of the two
rotors is not equal, it tips over.
You could try rotor tips that deflect excess air inward toward the center,
so the next rotor sees denser air.
Maybe the tips could be vertical bladelets that force air inward.
There was a classical booklet: 'Ducted fans for light aircraft', R W Hovey, perhaps the one I attach may be of interest, too.
Regards, + salut
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