Hydrofoil winglets?

[Stefan H]

Can anyone explain what the purpose is of "angled hydrofoils tips" on boats such as eg Hydroptere and Groupama? And how come they are facing down instead of up like winglets on aeroplanes?

I understand how winglets work on aeroplanes but not why they are facing down on trimaran hydrofoils.

[Doug Lord]

They do the same thing on hydrofoils as on airplanes with one addition: they also provide a degree of lateral resistance at high speed on a surface piercing foil.
They go down because to go up would present a high drag acute angle as well as probably causing a degree of interference with the last portion of the foil span at high speed.

[Stefan H]

Originally Posted by Doug Lord

They do the same thing on hydrofoils as on airplanes with one addition: they also provide a degree of lateral resistance at high speed on a surface piercing foil.

Ok, I can buy this since the angle of the hydrofoil is at 45 degrees it works a little different. But since the force is vertical + horisontal you could say that it is a 45 degree lift?? Or is the two lift forces working independantly?

Originally Posted by Doug Lord

They go down because to go up would present a high drag acute angle as well as probably causing a degree of interference with the last portion of the foil span at high speed.

Yea, but I meant 90 degrees angle, not straight up. Like a curved "C foil" but only at the last section. Some aircrafts have so called fenced winglets facing both up and down but after some research they found out that a curved extension of the tip upwards saves a few % more fuel.

[Doug Lord]

Originally Posted by Stefan H

Ok, I can buy this since the angle of the hydrofoil is at 45 degrees it works a little different. But since the force is vertical + horisontal you could say that it is a 45 degree lift?? Or is the two lift forces working independantly?



Yea, but I meant 90 degrees angle, not straight up. Like a curved "C foil" but only at the last section. Some aircrafts have so called fenced winglets facing both up and down but after some research they found out that a curved extension of the tip upwards saves a few % more fuel.

===========================
Lets put it this way: for all practical purposes, a surface piercing foil has a vertical lift vector and a horizontal lift vector. Going upwind the whole boat operates at a leeway angle that increases the lift vector(s) on the leeward foil.
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If you look at a 45 degree foil with a tip going "up" at 90 degrees to the surface of the foil you'll see that the value of that tip for a given area is less, in terms of lateral resistance, because it is angled to the flow-its effective area(for lateral resistance) would be less going "up" than it would be going vertically down.

[DaveJ]

There is alot of money to be made in winglet design, to the fact there are companies out there that make winlet kits for all sorts of aircraft. You thought wing deigns where a closely guraded securit, winglets even more so.

[PAR]

They're just cute . . .

[RHough]

Originally Posted by PAR

They're just cute . . .

and fashionable ...

[Submarine Tom]

...and make people ask questions.

[PAR]

I like to roll up my shirt sleeves for the same reason. It makes me look like I'm doing something when I'm actually standing around dreaming up ways to look like I'm doing something. I'm thinking most see the rolled up shirt sleeves, as the stylish end plates to my wardrobe.

[Chris Ostlind]

The shovel, be it spade or flat end, is the universal signal among all state transportation department workers that "I'm on the job, and gettin' stuff done".

Next time you drive by a road project, take note of how many of these noble tradesmen are fully engaged in the business of leaning on their trusty shovels. Yes sir, they are "on the job and gettin stuff done."

And so we say goodbye and good luck to the noble winglet... always on the job, and getting stuff done.

[sailsocal]

It's interesting to note that the Boeing 787 does not have angled wing tips. Apparently they've discovered a magic profile for the end of the wing that suppresses wing tip vortices as well as an angled wing tip.

[DaveJ]

No, what they do is sell the Winglets later on as an extra to make even more money.

[PAR]

What they've discovered at Boeing (with the 787) is the same thing they already knew and they're back to designing foils with washed out tips and using fences. After Australia II had it's day, everyone that thought they were someone, put wings on their appendages, God it was sickening. Then the smart guys got together and took a good look, eventually settling on what they already knew and the "tits growing on fins syndrome" went away.

[daiquiri]

Winglet design is a tricky job... Winglets are useful in cases where a wing is designed to work under high loading and the wing span is limited by some design or economical requirement.
Otherwise, given two wings - one with a span extension and one with a winglet - and assuming the same root bending moment (which means roughly the same structural weight), a wing with a span increased by an amount equal to just 40-50% of the winglet height gives the same reduction of drag as the wing with the winglet.

[RHough]

Originally Posted by daiquiri

Winglet design is a tricky job... Winglets are useful in cases where a wing is designed to work under high loading and the wing span is limited by some design or economical requirement.
Otherwise, given two wings - one with a span extension and one with a winglet - and assuming the same root bending moment (which means roughly the same structural weight), a wing with a span increased by an amount equal to just 40-50% of the winglet height gives the same reduction of drag as the wing with the winglet.

bingo! we have a winner.