Are ducted fans thrust output dictated by the shape of the duct in the aircraft or does the fan and engine combo alone have only a certain amount of thrust. Any explanations are much appreciated.

Alex.

I would say that the shape of the duct including intake lip shape are important factors in order to get most thrust out of a given fan engine combo.

ducting plays a big part in both thrust AND velocity. 20 pounds of thrust means nothing unless you move that air fast enough. look at all the work BVM used to put into their fan ducting and compare that to what Byron used to do....VERY different performance from the same basic amount of horsepower.


dave

I would say that both thrust and forward speed are important factors for how the plane behaves in flight.
Without enough thrust you never reach the pitch speed or you can't take off from the ground.
Also with a too little thrust the plane lose ability to climb.

The fan's output power is = thrust * forward speed.
The fan's efficiency is = thrust * forward speed / input power

By optimising the ducting one gets better efficiency, which means higher output power for a given power input and fan engine combination.

INLET DESIGN IS MORE IMPORTANT, THAN TAIL PIPE.. GOOD CLEAN ,SMOOTH AIR IS WHAT YOU WANT.. INLET LIP IS CRITICAL !! INLET SHOULD GET SMALLER IN CROSS SECTION AS IT GETS TO FAN SHROUD. PIPE OUTLET DETERMINS AIR SPEED. MOST ARE 3" TO 4" 3.5 GOOD FAN, AIR SPEED ON THE GROUND ,,165,MPH.. DONE ALOT OF TESTING IN THIS AREA!!!RD

is the shape of the intake ducked affect any of the efficiency? is one shape better than another? say is the rectangle shape used by US fighters beter than a roung or oval opening??

Corners will produce a bit of turbulence. Remember that the flow in the ducts of the latest fighters is often supersonic at the opening but reduces down as it travels into the duct. So the shape of those is not always suitable for us.