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Doubled Blades | 18 comments (18 topical)
Re: Doubled Blades (3.00 / 0) (#16)
by finnsawyer on Thu Nov 03, 2005 at 08:58:12 AM MST

The rudder of a ship must turn the ship in both directions.  Hence it must have the shape of a symmetrical airfoil.  It would appear that such a shape can not exhibit lift but it does.  Acrobatic air planes use such wing profiles to allow them to fly upside down.  As soon as the attack angle is greater than zero there is lift.  Hence the ship turns or the plane flies upside down.  The ship turns because the rudder exerts a force that acts around the ship's center of mass.  In a similar fashion the tail of a plane exerts a downward force that acts around the center of gravity of the plane to counteract the rotating effect of the wings.

If you think that the flow near the surface of the airfoil is all that matters, then I think you are missing the big picture.  Mathematical solutions exist for fluid flow around a sphere and a long cylinder.  I suggest you go study them.  Your kinetic approach requires you to determine the reaction of all of the air particles with all of the surfaces and then sum (integrate) them to get the results.  As it happens Bernouli's Equation has already done that, since all we want is a macroscopic solution anyway.  
GeoM
[ Parent ]



Re: Doubled Blades (3.00 / 0) (#17)
by rotornuts on Thu Nov 03, 2005 at 07:40:46 PM MST

GeoM, thanks for your input on this one. I agree with you entirely. Newton and bernoulli
go together like milk and cookies when it comes to lift forces.

You know, if we're wrong it will be the biggest fluke in the history of man that the study and application of aerodynamics has made it this far.

Mike

[ Parent ]



Re: Doubled Blades (3.00 / 0) (#18)
by finnsawyer on Fri Nov 04, 2005 at 08:05:05 AM MST

It is possible that the kinetic approach may allow one to more easily derive solutions to a sub class of aerodynamic problems, but I don't think it's something to become dogmatic about.  If he thinks he has a better approach, he should build it.  It's as simple as that.  But of course, "The devil is in the details".
GeoM
[ Parent ]


Doubled Blades | 18 comments (18 topical)

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