Roy's Gun project: Old Faithful 9'5" pintail

If the leading edge is bumped then the trailing edge doesn't need the undulations as the flow has already been organised.

My tunnels are foiled inside and out.

The opposite is the case, the tunnel lifts the tail. We set the tunnels at a postive angle of attack in relation to the bottom of the surfboard and the water flow. Even if the tunnels are foiled only on the outside they still liftt the tail if set at a positive effective angle of attack, the angle has to be greater if the tunnel isn't foiled on the inside. Even if the tunnel is set up parallel to the bottom and is symmetrically foiled it will still lift the tail slightly especially if used on an extreme pintail 'displacement tail, due to the tunnel producing more planing lift than the tail and due to changes in the angle of the water flow at depth compared with flow at the hull surface.

It's helpful to visualise the tunnel as a water flow direction unit rather than just assuming that lift is entirely dependent upon whether or not the wing is foiled more on the top ( i.e. the inside of the tunnel) than on the bottom. Keep in mind that symmetrically foiled wings produce lift, they are often used on aerobatic aircraft. Even assymetrically foiled wings produce lift when flying upside down.

No, and it's not what happens. the tunnels could pull the tail down if set up at a negative angle of lift, and have been used that way but not by me.

There's a widespread misunderstanding of the 'Bernoulli effect'. It's often assumed that lift is entirely dependent upon the top of the wing having more foil than the bottom (i.e. the wing having camber) but that's not the case.

Associated with this is the mistaken 'equal transit time' assumption which is often taught in high school... this is the idea that flow over the top of the wing and beneath the wing will take the same amount of time, and that therefore there will be lower pressure on top of the wing.

In fact if there is a positive effective angle of attack there will be lower pressure on top of the wing, but the flow on top takes longer to reach the trailing edge than the flow underneath does.

Visualising flow using the ' water redirection' or Newtonian method is usually easier and clearer than visualising the pressure differences via Bernoulli's theorem, it's important to know also that both methods give exactly the same answer when calculated.

More explanation of these points is probably needed.

 

Here's number one the 16-021 9'5" with 3D glass:

http://www.roystuart.biz/2015/01/the-gun-project-resin-tint-on-16-series.html



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