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[bogstandard]

I wrote a very long treatise on aerofoil shapes, flaps, slats and slots, but eventually decided to stop preaching to people who have their own views on how things work, and duly deleted it all.

So I thought I would show you MY way of explaining lift on aerofoils, yacht sails, lower pressures in venturis etc.

It is a very expensive exercise, but it does show that lift can be easily generated without the higher pressure underneath.

Take the sheet of paper holding the ends of the narrow side and pull it tight. Take a sharp intake of breath, and blow onto the top of the curve that the drooping paper produces. You should find that the paper at the back lifts up. This is caused by your blow travelling over the top curved surface and producing an area of lift, without any help from high pressure underneath. So in my mind, the area of high pressure isn't required to produce the forwards motion of a yachts sails, it only assists.

John

[Arrow5]

Very wise John , succinct and proof in laymans terms  now can we get back to fans  and the autogyro boat.

[Arrow5]

No more fan power then here is one for tobyker and the druid to debate. Cant put a date on the pics but from the activity on the dockside looks like Canary Wharf tower isnt quite finished.  The "triplane wing-sailed" PLANESAIL seems to have camber adjustable wings.  What ever happened to this experiment ?

[Welsh_Druid]

I.



It is a very expensive exercise, but it does show that lift can be easily generated without the higher pressure underneath.

Take the sheet of paper holding the ends of the narrow side and pull it tight. Take a sharp intake of breath, and blow onto the top of the curve that the drooping paper produces. You should find that the paper at the back lifts up. This is caused by your blow travelling over the top curved surface and producing an area of lift, without any help from high pressure underneath. So in my mind, the area of high pressure isn't required to produce the forwards motion of a yachts sails, it only assists.

John

John,
   
Thats an interesting way of looking at, and interpreting it.  But another interpretation is that the air blown over the top curved surface is then deflected downwards at the trailing edge (remember my suggested experiment of the spoon in the tap water flow ?) and the applicationof Newtons  law to this downward flow causes the back to lift up !!    Obviously we can both adopt the interpretation that suits us !!


BTW - what happened to your explanation of what causes the downdraft from the helicopter blades which I suggested you gave us ?
+++++++++++++++++++++++++++++++++++

Arrow5 -

Is there anymore to  be said about the fan power - other than , as has been pointed out, it won't work ??

I must say though that this thread has led me to look at a lot of the research and development  which has been carried out on wing sails - fascinating stuff isn't it ?

Don

[Arrow5]

Just pulling your leg Druid...hmmm , that was covered in the boot-strap explanation.    OK ,what about the autogyro blades at negative angle of attack creating "lift" enough to power a boat, Brabazon`s "Redwing" and others ? That is for John I think.    Yes I agree it is a fascinating subject. Lots of research for the better mouse-trap , all sorts of acedemic theories and learned technical testing in wind tunnels etc etc and yet the sailor still opts for the "tried and tested" cloth and rope devices that havent changed much in a thousand years. Apart from modern materials such as Kevlar, Mylar, carbon fibre and metal alloys etc the only change I can see is the squaring-off the top of the triangular shapes of sails (tip-stalling?). Many millions of quid spent on America`s Cup development and they still are not much removed from Thomas Lipton`s era. My son lives in Germany and crews for some very sophisticated international racing teams and yet his own boat is a vintage Dragon class woodie !   Is it nostalga that make them hang on to old ways ?  I dunno thank goodness I`m not a sailor. Too many days hanging onto a wet rope, sorry LINE, getting very cold wet,  near lighning strikes, getting bruised and abused....and and  well I suppose a good party after the event sort of made up for that

[Jonty]

  Just found this whilst hunting for something else (as usual):

                 http://www.rexresearch.com/boats/1boat.htm#ford

  Some other daft ideas, too.

[tobyker]

Indeed but the jib is a big heavy thing that needs a stay to set it. I was thinking of really narrow chord flaps hung off the fwd edge of the mast with a fixed amount of float to make them self-tacking. of course to make them work properly you'd need an aerofoil mast with a luff groove.