# Is a chambered fan more efficient than a ducted fan?

A chambered fan is not exposed to the oncoming airflow in forward flight. I am working on a VTOL design that uses a chambered fan.

There will be a wing attached to top of the thrust arms.

Could it produce 12,000 pounds of lift force using a GE T901 with 3,000shp with 8' dia. contra rotating fan?

• How does air flow through this apparatus? Which way through the disc-shaped grill? Through the four pipes, if that's what they are? If so, why four and not twenty? Commented Oct 27, 2019 at 19:29
• The grill around perimeter of craft is the intake. Contra rotating push prop fans are located in the center fan chamber. The fan forces air into the four thrust arms, splitting the air flow and spreading the air flow out for 4 points of balance. Commented Oct 27, 2019 at 19:39
• There are only four thrust arms instead of twenty thrust arms, because it only takes four to have great balance like a quadcopter. The steering is controlled by swivel nozzles at the 4 thrust arms exit ports. Commented Oct 28, 2019 at 17:33
• Differential thrust, e.g. from vanes at each arm's intake, would be more efficient than vectoring the thrust at each arm's exit. Commented Oct 28, 2019 at 20:16

The design is not very efficient:

• It does not use forward airspeed to pre-compress the airflow entering the engine.
• It blows exhaust air into the air inlet.
• It bends the exhaust flow 180 deg, creating friction and loss of thrust.

Short, straight, unimpeded airflow works best.

• Here is a link that shows a straight pipe compared to U shaped bent.facebook.com/… Commented Oct 28, 2019 at 14:28
• Do those screenshots claim some advantage for a U-bent pipe? If so, what? Commented Oct 28, 2019 at 15:59
• Yes the straight pipe put out 2,457lbs of force and the U shapped pipe put out 4,736lbs of force. Maybe someone else could do a calculation? Commented Oct 28, 2019 at 17:23
• If adding a U to a pipe doubles its thrust, why don't we see them on many aircraft? The bolder the claim, the stronger the evidence needed to support it. Step away from the computer and measure something physical. Commented Oct 28, 2019 at 20:20
• It's a Facebook page. It shows two long pipes, which is never the best due to boundary layer effects. It only states Pressure, while maximum thrust is created at maximum exhaust stream velocity - when the exhaust stream expands to ambient pressure (maximum exhaust gas velocity). A collection of half truths and funky special effects that draw attention. A piece of engineering in the manner of Twitter. Commented Oct 29, 2019 at 2:34

In aviation there is no generally accepted meaning for the term "chambered fan," so there is no way to claim in general that a chambered fan is or is not more efficient than the corresponding ducted fan.

In fluid dynamics, straight pipes are more efficient than bent ones, so the 180 degree bends in the four exhaust pipes (and between the intake grill and the fan) are less efficient than the corresponding ducted fan design, whose intake is at the top and exhaust is at the bottom.

If this chambered fan is shielded from the airflow induced by horizontal flight, then it cannot exploit translational lift, so it would be less efficient below about 50 knots. But for horizontal flight the aircraft must tilt in that direction, pushing that airflow into the circular grill intake.

Some of the thrust leaving the four pipes would be entrained into the grill intake just below, causing at best some inefficiency, and at worst a partial vortex ring state.

The simplest way to compare the thrust and efficiency of this design to the corresponding ducted fan design blowing directly downwards would be to build a small model and measure it. Radio-control model suppliers sell cheap "EDF" electric ducted fans, and the ductwork could be 3D printed.