> IF I put a cone shape (with two open ends),. .> with big openning after a propeller which . .> direct the flow and speed up the flow to the . .> smaller openning. Will that increase any thrust. .> at all?
The answer is yes or no depending on the shape. .of the duct you are adding and the airspeed that. .the aircraft is operating at (and a load of other. .factors).
Here is one way to look at it...
Motors have a limited maximum power output. If the power being produced by the motor is the same with or without the duct then... The only thing you are changing by adding a duct is the EFFICIENCY with which that power is being applied to moving the craft through the air.
Adding a straight duct typically reduces the vortex drag caused by the tip of the blades but adds drag due to the friction of the air flowing through it.
A tapered duct will increase the velocity of the air coming out but will add drag so the volume of air per second will be reduced.
It's also interesting to think about the air flowing over the outside of the duct when the aircraft is moving. That 'sees' a taper going the other way so it's slowed down (= more drag).. . . .For more info raise the subject in the Jets section of the discussion forum at:
<a href="http://www.ezone.com" target="_blank">www.ezone.com</a>
..which is a forum for modellers building electric powered ducted fan aircraft.
Colin