Dec 28, 2012, 08:23 PM
Registered User
Joined Sep 2003
333 Posts
Quote:
 Originally Posted by KJELL The way the Fan-effect is accelerating the air mass, is completely different to the way a propeller accelerate the air mass. The propeller rotate and the blades are using the same side of the blade to produce the pressure differences that accelerate the air mass. A Fan-Flapping wing is altering the side to produce the pressure differences in each stroke. The pressure differences in the Fan-Effect are very accentuates. The low pressure center (The Partial vacuum center) Works like a small “Black hole”, attracting the air mass in front of the wing. Once the “Black hole” if filled, the energy of accelerated air mass, is converted to kinetic energy and then leaving the wing as a Jet stream at high speed. The sum of the attracted air mass and the Jet stream air mass directed in the same direction produce the thrust force in the opposite direction. Attached Thumbnails
So, by your words we agree that propellers rotate and produce the pressure difference that accelerate the air mass, not some other effect.
Propellers produce lift and net thrust at constant speed,speeding up or slowing down.
When a membrane flapping wing is doing a downstroke it acts the same as a large slower propeller. It twists and forms camber and lift due to its relative wind and inertia. If you rotated your membrane wings 360 deg it would produce continuous lift and thrust.
Put that on your test stand. Then reverse the motor. If you didn't build the wing to favor one direction of rotation it will perform the same. One wing will be performing a continuous upstroke and the other wing a downstroke. the lift direction will vary with the rotation angle but the thrust will be forward.

There is no fan effect, only mind games.
Dec 29, 2012, 05:08 AM
Registered User
Zurich
Joined Apr 2006
3,590 Posts
Lift 101

Not to be pedantic, but it's easier to think creatively when one has a realistic view of a process, in this case LIFT, whether produced by a moving wing, a kite [tethered, usually simple wing], a rotating wing like a helicopter rotor, a rotating propeller blade or an ornithopter wing:

One finally learns in grad school that the high-pressure/ low-pressure concepts of lift usually taught in American HS & undergrad colleges is confusing cause with effect*. Lift is the result of changing the momentum of the airflow and turning it more downward [called the Delta Rho Vector, pointing with a scalar value in the direction of the momentum-change]. In the process the air on top has to move faster to catch up as best it can with the air it was with just before it encountered the wing. And the pressure is lower.

But in the end it's a simple action-reaction process, like a rocket motor. AND, if you measure the airflow pressure on the bottom of a vertically rising rocket you will find that it has more pressure at the exhaust end [bottom] than at the nose [top]. And it also LIFTS off ....

To review: the pressure diferential between upper & lower surfaces [front & back for a prop] is the RESULT of changing the direction of an airflow which has mass [delta mv, in this case, same mass, diff. directed velocity vector], a result necessarily produced in the PROCESS of changing the airflow's direction [in the case of a prop or rocket, also speeding it up].

This is likely difficult to accept if one has been taught incorrectly [hey, it's not the only incorrect info most of has have been fed! ] .... but it is very useful to learn.

Lastly, to give Kjell a bit of credit for somehow touching on the "reality" of the lift/propulsion process of a flapping wing, there is a kind of attraction involved:

Air, like other fluids we consider in fluid dynamics, is a viscous fluid! That means it tries to stick together and adhere to itself. Imagine a string of magnets. And note that we still don't know what's really behind magnetism, but we do know what it does and can mathematically describe its function.

In general I picture the fluid flow to be like a stream of molasses which might be freely falling downward & outward, like water from a garden hose, and which is then curved more downward by gravity. That is how the fluid flow bends, and reflects how the flow on the top of a lifting airflow leaves the T.E. before that on the underside, describes the fact > it's a geometric part of how the fluid bends and changes direction .... similar to a marching band turning a corner, or a centipede turning.

Note that the water stream, the marching band and the centipede try to stick together to themselves, for different reasons. And that is the attraction idea that Kjell grasped.

An easy way to describe what happens in an airflow is to picture or draw a curved section of a meandering river. If you've looked down from an airplane you can see that the river tends to move away from the shore on the inside of the curve [depositing sand & debris there], and "eat" into the shore on the outside of the curve. If the water was replaced by a lot of moving steel ball-bearings, you'd see something similar.

Now draw a curved line through the center of the curving river, cut the paper where you've drawn this curving river [or as a thought process] and REVERSE the outside with the inside parts of the curved river. THAT is what happens with an airfoil in a subsonic airflow.
[see Attached Thumbnails below]

If you either "don't like" or "don't understand" this ..., fine. No worries, no problem, as that does not change the observed realities of the two actually-similar situations.

And as to "why" the water- & airflows re-join, it's what we mean when we say that these are viscous fluids which try to "stick together" [like molasses]. Just like gravitational** and magnetic attraction, chemical or electrical attraction, like surface tension, is something we observe happening and we still don't exactly know "why" ....

Lee

*One time at Boeing some admins decided to make and distribute a large poster to schools, pictorially illustrating the air-pressure nonsense these non-aerodynamicists had learned in their schools. The real aerodynamicists flipped out, but it was too late. And so the silly myth continues, blythely ignoring Mr. Delta Rho. [insert Charlie Brown sigh here].

** For whatever yet unknown "reason" [we just know it happens] gravity actually is not a force, as noted in my above post, whereas magnetism IS a force which accelerates things differently according to their magnetic and/or electromagnetic attraction AND their actual mass [i.e., an only slightly magnetically attractible heavy body will be accelerated more slowly than a very magnetic, or EM-susceptible lightweight body]: in a gravitational field ALL masses will accelerate "downwards" [the masses radially towards each other] the same ... unless resisted by something.

LIFT is one of those nice things.

.... and, oh yeah. ρ /rho is the symbol used to represent momentum, mv

# Images

Last edited by xlcrlee; Dec 29, 2012 at 09:12 AM.
 Dec 29, 2012, 03:47 PM Kjell Dahlberg Mallorca Spain Joined Nov 2005 1,119 Posts I am glad that you are talking about what happening in water. The Fan-Effect used by the fishes is, thanks to the differences in the density is 800 times stronger.
Dec 29, 2012, 04:36 PM
Registered User
Zurich
Joined Apr 2006
3,590 Posts
fish story

are these guys flapping or fanning?

 Life - Flying Fish (1 min 5 sec)
 Dec 29, 2012, 05:52 PM Kjell Dahlberg Mallorca Spain Joined Nov 2005 1,119 Posts [QUOTE=xlcrlee;23653655]are these guys flapping or fanning? They are FAN-FLAPPING.
 Dec 29, 2012, 06:04 PM Registered User Zurich Joined Apr 2006 3,590 Posts Very FINny [are you FIN'ished? ]
Dec 30, 2012, 01:27 AM
Kjell Dahlberg
Mallorca Spain
Joined Nov 2005
1,119 Posts
If you don’t know the differences between Flapping, Fanning and Fan-Flapping. Here is how it works.

# Images

Dec 30, 2012, 04:07 AM
Registered User
Joined Sep 2003
333 Posts
Quote:
 Originally Posted by KJELL If you don’t know the differences between Flapping, Fanning and Fan-Flapping. Here is how it works.
How amusingly Quixotic, the accepted names are flapping with passive or active twist. You are on a mission, but there is not a fan effect to tilt with.
Last edited by Plantoflap; Dec 30, 2012 at 04:22 AM.
 Dec 30, 2012, 04:59 AM Kjell Dahlberg Mallorca Spain Joined Nov 2005 1,119 Posts I think it is time to accept new names like FANNING, FAN-FLAPPING and FAN-EFFECT. Flapping with active or passive twist is FAN-FLAPPING. In the name FAN-FLAPPING is included the wing rotation at the end of each stroke. In the moment of wing rotation is where the FAN-EFFECT is really actuating. Thanks to the FAN-EFFECT it is possible to make the Stall-delay and the Wake capture.
Dec 30, 2012, 02:26 PM
Registered User
Joined Sep 2003
333 Posts
Quote:
 Originally Posted by KJELL I think it is time to accept new names like FANNING, FAN-FLAPPING and FAN-EFFECT. Flapping with active or passive twist is FAN-FLAPPING. In the name FAN-FLAPPING is included the wing rotation at the end of each stroke. In the moment of wing rotation is where the FAN-EFFECT is really actuating. Thanks to the FAN-EFFECT it is possible to make the Stall-delay and the Wake capture.
You think,we accept. Reads like a history lesson or things to come.
Dec 30, 2012, 03:18 PM
Registered User
Zurich
Joined Apr 2006
3,590 Posts
curious Lee

Quote:
 Originally Posted by KJELL I think it is time to accept new names like FANNING, FAN-FLAPPING and FAN-EFFECT. Flapping with active or passive twist is FAN-FLAPPING. In the name FAN-FLAPPING is included the wing rotation at the end of each stroke. In the moment of wing rotation is where the FAN-EFFECT is really actuating. Thanks to the FAN-EFFECT it is possible to make the Stall-delay and the Wake capture.
Kjell, how many fans do you surmise have directly come out of your efforts?

Is there now a Fan Club? Can anybody join? Where/how?

Dec 31, 2012, 01:45 AM
Kjell Dahlberg
Mallorca Spain
Joined Nov 2005
1,119 Posts
Quote:
 Originally Posted by xlcrlee Kjell, how many fans do you surmise have directly come out of your efforts? Is there now a Fan Club? Can anybody join? Where/how? just curiously askin'
I understand your problem to know what “Fan or Fanning” I am talking about.
According to English dictionaries definitions.
fan
n.
1. A device for creating a current of air or a breeze, especially:
a. A machine using an electric motor to rotate thin, rigid vanes in order to move air, as for cooling.
b. A collapsible, usually wedge-shaped device made of a light material such as silk, paper, or plastic.
2. A machine for winnowing.
3. Something resembling an open fan in shape: a peacock's fan.

v. fanned, fan•ning, fans
v.tr.
1. To move or cause a current of (air) with or as if with a fan.
2. To direct a current of air or a breeze upon, especially in order to cool: fan one's face.
3. To stir (something) up by or as if by fanning: fanned the flames in the fireplace; a troublemaker who fanned resentment among the staff.
4. To open (something) out into the shape of a fan: The bird fanned its colorful tail.

In other languages The Word “FAN” has a unique name. In Spanish. Fan = Abanico. In Swedish. Fan = Solfjäder .
 Dec 31, 2012, 05:29 AM Registered User Zurich Joined Apr 2006 3,590 Posts fantástico you forgot this one > "A fan, sometimes also called aficionado or supporter, is a person who is enthusiastically devoted to something, such as a band, a sports team or entertainer. Collectively, fans of a particular thing or person constitute its fanbase or fandom. They may show their enthusiasm by being members of a fan club, holding fan conventions, creating fanzines, writing fan mail, or by promoting the object of their interest and attention." L
Jan 26, 2013, 12:24 PM
Kjell Dahlberg
Mallorca Spain
Joined Nov 2005
1,119 Posts
Bat Wing Test.
 BatWingTest 0001 (3 min 34 sec)