sheik480

After doing some aerodynamics research and reflecting upon previous responses to similar questions, I have come to the conclusion that if you can reduce the absolute velocity of the thrust jet from a ducted fan, it may increase low speed efficiency. This may be used to increase flight times for a edf jet flown at park flyer speeds. Can anyone input on why this may or may not be a valid idea?

RAPPTOR

My Feedback: (41)

static or dynamic??

sheik480

Mostly dynamic. As airspeed approaches the speed of the jet of air accelerated by the prop (small diameter ducted or open), efficiency approaches it's possible maximum. I figure if you lower the speed of the air accelerated by the prop (or fan), then a system will be more efficient at a specific speed below its most efficient speed. Every prop is 0% efficient at 0 airspeed, but ducted fans are usually less efficient because the planes they are put into fly at speeds that are far below the speed where a ducted fan would be most efficient. This is compared to an open, large diameter propeller that is much closer to its optimum efficiency zone at the speeds an rc is usually flown at. Of course, a ducted fan will more efficient at speeds above a propeller's maximum speed (its rpm times its pitch in inches, converted to miles per hour or kilometers per hour) because it's jet of accelerated air is at a far higher velocity than an open propeller. Using this logic, I figure a ducted fan will be more efficient at the speeds an edf is usually flown at if the velocity of it's jet of accelerated air is reduced; this brings the system closer to it's maximum efficiency.

BeanerECMO

My Feedback: (1)

To increase the efficiency more and easier; i.e., smoother; inlet airflow is required. And, to increase eflux for higher speed and efficiency, reduce the exhaust opening to no less than 85-90% FSA with a smooth exhaust 'tube'.

sheik480

So you're saying my logic is entirely backwards?

RAPPTOR

My Feedback: (41)

[X(] yep ,backwards. i have had very good results by speeding up the air, to the fan. the fan can only accerate incoming air. so, if the air starts out faster to the fan ,it will speed up the faster air...inlet and outlet are everything. if inlet area is smaller than swept fan area,then you need to have a, pluum affect in front of the fan. if not make the inlet a little smaller at thr fan.. also about 3 to4 inches in front of fan should be fan shroud diam. and straight.oulet size is according to thrust, needed and effulx. effifency times power,divided by diamiter..tail pipe out let size.

sheik480

So, the higher the absolute velocity of the inlet stream, the higher the efficiency?

RAPPTOR

My Feedback: (41)

im not sure about effency,but helps performance. higher inlet air speed,,,,lets say ,,,helps turn the rotor..like a, prop plane in a dive. so it is possible you could have less engine load,less amp draw,ect.. rotor blade pitch /angle is also in the mix ,for dynamic end results. that,{blade angle} will have a ,good deal to do with effeceny..rpm,fuel useage,amp draw,watts,ect,...

sheik480

How does increasing the inlet velocity affect your flight times for a specific battery?

RAPPTOR

My Feedback: (41)

less rotor drag,, run it up to speed. then use an air hose ,blow in the ducts.. fan will turn faster......[X(]

sheik480

Pray tell, good sir, where does the energy from that fast moving air come from?

RAPPTOR

My Feedback: (41)

air hose or fan.. [X(]

sheik480

You do realize that static thrust usually means sh*t, right? I'm talking about increasing efficiency in the air, you know, where you actually fly the plane.

RAPPTOR

My Feedback: (41)

VARIABLE INLETS AND TAIL CONE