## onsdag 7 december 2011

### Missing Physics of Sailing

In The Secret of Sailing a new explanation of the physics of sailing is presented based on the new analysis of the generation of lift and drag of a wing in The Mathematical Secret of Flight and The Secret of Flight summarized in a talk.

Let us compare with current state-of-the-art:
The most ambitious treatment is given in Physics of Sailing by J. Kimball, where both Bernoulli and Kutta-Zhukovsky's circulation theory are presented, but with a disappointing sum-up on p 163:
• The sail experiences lift because the sail deflects the wind. Equal and opposite forces mean that is the sail pushes the wind in one direction, the wind pushes the sail the other way. This explanation, which relies only on the rule of equal and opposite forces, is surely correct.
Yes, it is surely correct, as any empty theory which explains nothing, as illustrated in the above picture.

We see that there is surely a great need for a correct theory which explains the physics of sailing and that there is no such theory as state-of-the-art.

Our work fills this gap in physics theory and in particular shows that the state-of-the-art explanations represented by Newton, Bernoulli or Kutta-Zhukovsky are all incorrect.

Of course, the physics of flying and sailing is not of any interest to physicists of today paralyzed by string theory, but it is an interesting problem of physics of importance to many.

#### 6 kommentarer:

1. Interesting! I see forward to a software where you put in the sail and wind data to get the lift and drag values. I´ve been using the following simple formula but don´t know how exact it is.

L=alfa*(pi/180)*2*pi*(1/2)*ro*S*(Vr)exp2*corr

where alfa=angle of attack in deg, ro= air density, S=sail area, Vr=relative wind speed and corr= a correction factor = 1/[(1/zeta) + 2*S/(b)exp2] where zeta is a formfactor~0.9, and b=sail length(height)
It would be very interesting to know how well this formula predicts the lift force.

2. Claes, In my view physicists know little about Fluid dynamics which is an engineering discipline. It is engineers who design aeroplanes, ship, rockets etc.
I am surprised you have not mentioned Peter Joubert, Professor of Mechanical Engineering Melbourne University see here http://www.unimelb.edu.au/unisec/calendar/honcausa/citation/joubert.html & look at some of his publications listed here http://www.findanexpert.unimelb.edu.au/researcher/person15107.html. He designed and sailed many boats including a winner of the Sydney_Hobart yacht race.
I am fairly sure he designed a catamaran with a solid sail which achieved remarkable speeds.
Melbourne University has possibly the most sophisicated wind tunnel in the world.
I suggest it worthwhile for you to contact the Professor here http://www.mech.eng.unimelb.edu.au/people/staff/ivan_marusic.html

3. Claes, did you ever meet Hans-Uno Bengtsson (now passed away). He was obsessed with flying and wrote popular books about it. Have you read them, any comment?

4. Not sure whether Claes needs to contact the people in Melbourne, as the Mechanics department at the Royal institute of technology (KTH Stockholm) is also quite renowned for their research in turbulent wall flows, both in the wind tunnel and simulations. However, there seems to be no interaction...? Something to change?

5. I am open to interaction, but the establishment at KtH is closed to new discovery.

6. I think that the working way of sails is simply due to their ability to modify the linear momentum of the wind. They act as the turbine blades. With following wind there is enough only one sail which behaves as the blade of an impulse turbine using the change of the direction of the velocity relative to it, whereas, close to the wind, there are needed almost two sails which do modify both the module and the direction of the velocity, that’s they behave as the blades of a reaction turbine.
Bernuolli doesn’t matter. The wind pushes the sail, the wind doesn’t pull the sail.

Michele