Foiling, food for thought

[Jim Caldwell]

After watching all the available foiling videos, I wonder;

1 Most of the foiling video attempts, when they look like they should have the speed, end up pitch poling.
Looks like the foil lift is too far aft. Why not move them forward?

2 Hulls are not lifting up on the foils until 8 to 10 knots, why not increase the cord to say 8mm, it will increase the drag and lower cavitation speed, but we are nowhere near cavitation speed and lower take off speed to 5 to 6 knots?

3 Most of the V foil boats have heave problems and the one that doesn't has spent a looong time getting it to work in a narrow range. Since the V foils generally have the foil shaft going thru the hull with a stub sticking out, why not install the Bradford Ride height control system because it would be an easy mod?

https://docs.google.com/viewer?a=v&...WFpbnxoeWRyb3NhaWx8Z3g6NjU0NDdkNmI0ZDFmOGM2ZA

 

[IOMchen]

It's like the Moth are doing it. At about 2 to 3 Bft. it works. An the speed between with or without foils is incredibly.

 

[mij]

Hello Jim,

Interesting thread on the boatdesign site, seems to support your choice of T-foils:

http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/lowest-drag-hydrofoil-designs-48716.html

Jim.

 

[Jim Caldwell]

Thanks Jim, I saw it and yes it does. Lohring is another Fast Electric boat racer like myself who was influenced by the America's Cup. He also helped set the world Electric out board record, its on YouTube.

 

[mij]

Jim, I've been thinking about your point #2, and it brings me back to a suggestion that I raised earlier on this forum. I think that the ultimate goal for foils is to be able to change the shape of the foil in response to factors such as boat speed/height etc. This would also allow a boat to perform in both foiling and non-foiling conditions. What do you think of this proposition? I'm not suggesting that it would be easy to do, but I suggest that it is possible. There is a plane wing for which the lift is adjusted in this way, I think it works by pumping a fluid into a deformable section of the wing.

 

[Jim Caldwell]

Your right, it does not sound easy to do! LOL
However, I have been thinking, always dangerous!, small high lift wing just below the hull 1" to get the hull up to speed and the main foil would take over. I think I will leave that for down the road and finish the molds then the wing sail and test.

 

[mij]

Jim, I agree that it would be difficult. but what I am trying to do is identify what would be ideal, and then work backwards to what is possible.

Another possibility might be to use a rotating leading edge device. The amount of lift could then be controlled by the speed of rotation. However, I don't know if this approach will translate from air to water applications. Interesting ref:

http://kimerius.com/app/download/5782402961/A+review+of+current+leading+edge+device+technology+and+of+options+for+innovation+based+on+flow+control.pdf

 

[Jim Caldwell]

Just remember water is 800 times denser than air and every time you change the flow direction you increase drag. That is one of the reasons I am not using a flap on the foils, I am changing the angle of the foil. Example, when you are in an airplane and the pilot is flying along and pulls the nose up 5 degrees you can feel some lift but no drag. Now when he is coming in for a landing and lowers the flaps you suddenly feel large amounts of lift AND drag.

 

[mij]

My (perhaps simplistic) understanding of foiling is that a foil will always have more drag than non-lifting profile. The trade off is that by lifting the hull the foil reduces the overall drag of the boat, and hence it doesn't matter that it has more drag itself. Am I missing something here?

What I am proposing is that there are different means of controlling the lift associated with a foil, and that some of these foil types will produce less drag when in a non-foiling configuration.

What do you think about the rotating edge? This seems to me to have some potential. It should be possible to use feedback between hull speed and/or height above the water line to control the speed of a rotating edge. This seems to be even more elegant than the Bradford system, which in itself will have drag associated with it. It seems to me that the main question is whether the rotating edge approach will work in a dense fluid? But I don't see why it wouldn't.

 

[mij]

Here is an answer to my rotating edge questions:

http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/moving-surface-boundary-layer-control-hydrofoil-48886.html

 

[Jim Caldwell]

It doesn't get any better than Tom Speer, several decades of engineering at Boeing.