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post #1 of 7 Old 08-05-2011 Thread Starter
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Question IB Extended Essay on physics in sailing... help!!!

Hey guys, i'm new over here. i am really interested in dinghy sailing and just completed my RYA level 2. this has inspired me to base my 4000 word extended essay on the physics behind sailing.
The question that i'll be researching on is:
‘How does the angle of the sail on a sailboat from the direction of wind affect the total drag force on the sail?’
i'm trying to conduct an experiment on the the above with a model of a sail using a table-fan as a constant wind source.

Any ideas or suggestions?.....
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post #2 of 7 Old 08-05-2011
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Quote:
Originally Posted by yashgore View Post
Hey guys, i'm new over here. i am really interested in dinghy sailing and just completed my RYA level 2. this has inspired me to base my 4000 word extended essay on the physics behind sailing.
The question that i'll be researching on is:
‘How does the angle of the sail on a sailboat from the direction of wind affect the total drag force on the sail?’
i'm trying to conduct an experiment on the the above with a model of a sail using a table-fan as a constant wind source.

Any ideas or suggestions?.....
First off, a table fan will produce far too turbulent a flow pattern to get you any meaningful data. You will be better off using a homemade wind tunnel. They're cheap and easy to make using thin plexiglass. Put a box-fan at the downwind end of the tunnel, and have some sort of funnel arrangement at the upwind end to minimize the turbulent flow as the air enters the tunnel. Also, to minimize boundary layer effects, make sure the cross-section of the tunnel is at least twice the longest dimension of the test object.

Second, and undoubtedly more difficult, you'll need some way of simultaneously measuring both drag AND lift on your test foil (as well as some other variables, like flow speed, and projected frontal surface area). The best way to do that is with a three-dimensional force platform instrumented with strain gages and the proper amplifiers (poke around the InterNet a bit and I'm sure you'll find some schematics).

I realize all that probably sounds way more complicated than you were prepared to bite off. But, as someone who has done just this sort of thing (only with marine invertebrates in water), I can tell you that that is that is what you need to do. On the other hand, there is a ton a literature on just this sort of question. How lift and drag vary with angle of attack is a problem dating back to before the Wright brothers. A good place to start is a Dover Science Classics book, by Robert Granger, called "Fluid Dynamics". It's a fairly cheap book (I think it's less than $30, new), but it probably has more than enough info for what you want to do.

Good luck.

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post #3 of 7 Old 08-05-2011
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If you are interested in the physics of sailing, be sure to check out C.A.Marchaj books:
"Sailing Theory and Practice" (196?), "Aero-Hydrodynamics of Sailing" (1979), "Seaworthiness, The Forgotten Factor" (1986), and "Sail performance" (1990). I haven't seen any more recent books by him...
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post #4 of 7 Old 08-06-2011
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I found a lot of intriguing stuff just by googling "physics of sailing"


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Quote:
Originally Posted by SlowButSteady View Post
First off, a table fan will produce far too turbulent a flow pattern to get you any meaningful data. You will be better off using a homemade wind tunnel. They're cheap and easy to make using thin plexiglass. Put a box-fan at the downwind end of the tunnel, and have some sort of funnel arrangement at the upwind end to minimize the turbulent flow as the air enters the tunnel. Also, to minimize boundary layer effects, make sure the cross-section of the tunnel is at least twice the longest dimension of the test object.

Second, and undoubtedly more difficult, you'll need some way of simultaneously measuring both drag AND lift on your test foil (as well as some other variables, like flow speed, and projected frontal surface area). The best way to do that is with a three-dimensional force platform instrumented with strain gages and the proper amplifiers (poke around the InterNet a bit and I'm sure you'll find some schematics).

I realize all that probably sounds way more complicated than you were prepared to bite off. But, as someone who has done just this sort of thing (only with marine invertebrates in water), I can tell you that that is that is what you need to do. On the other hand, there is a ton a literature on just this sort of question. How lift and drag vary with angle of attack is a problem dating back to before the Wright brothers. A good place to start is a Dover Science Classics book, by Robert Granger, called "Fluid Dynamics". It's a fairly cheap book (I think it's less than $30, new), but it probably has more than enough info for what you want to do.

Good luck.
thnx a lot for the advice. i only wish i could carry it out like that but the problem is that i study at a fully residential school. so i dont actually have much to work with and have to make do with whatever is available. i'm trying to place some card or something like that around the fan so that the airflow will be focused on one direction. i'm gonna use a spring balance to measure the force on the sail at different angles, keeping the boom's movement restricted by 2 poles + or - 2 degrees from the angle being investigated. any improvements that you can offer?
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hey guys, could you please fill out this tiny questionnaire for my primary research... only a few simple questions...

Questionnaire
1. What is your name?
 ________________________________________________

2. How often do you sail in a week?
 During the vacations ___________________________
 For the rest of the year _________________________

3. Do you own a boat?
 ¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬( Yes / No )

4. How many years/months of experience do you have in sailing?
 _____________________________

5. What is the wind speed (in knots) that you prefer to sail with?
 ___________________

6. What type of boat do you prefer to sail in? Choose the appropriate. [More than one response per category is acceptable
Occupancy
o Single
o Double
o Four people
o Six or more people
Sail shape
o Triangular
o Rectangular
Number of sails
o Only mainsheet
o Mainsheet and foresail
o More than two sails
Onboard motor
o Yes
o No
 Name of make and model:____________________________________________ ___

7. What angle do you prefer to keep your sail at in accordance with the direction of the wind? Choose any one.
o 20-30
o 30-40
o 40-50
o 60-70
o 80-90

8. Do you reef your sail? If yes, at approximately what wind speed?
o Yes
________knots
o No

Thank You!
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hey guys, could you please fill out this tiny questionnaire for my primary research... only a few simple questions...

Questionnaire
1. What is your name?
 ________________________________________________

2. How often do you sail in a week?
 During the vacations ___________________________
 For the rest of the year _________________________

3. Do you own a boat?
 ¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬( Yes / No )

4. How many years/months of experience do you have in sailing?
 _____________________________

5. What is the wind speed (in knots) that you prefer to sail with?
 ___________________

6. What type of boat do you prefer to sail in? Choose the appropriate. [More than one response per category is acceptable
Occupancy
o Single
o Double
o Four people
o Six or more people
Sail shape
o Triangular
o Rectangular
Number of sails
o Only mainsheet
o Mainsheet and foresail
o More than two sails
Onboard motor
o Yes
o No
 Name of make and model:____________________________________________ ___
 Weight:______________________
 Length:______________________

7. What angle do you prefer to keep your sail at in accordance with the direction of the wind? Choose any one.
o 20-30
o 30-40
o 40-50
o 60-70
o 80-90

8. Do you reef your sail? If yes, at approximately what wind speed?
o Yes
________knots
o No

Thank You!

Last edited by yashgore; 08-06-2011 at 09:37 AM. Reason: additional questions
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