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Basiliscus last won the day on October 24 2020

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541 F'n Saint

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    Port Gamble, WA, USA

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  1. I don't know what shape they used, either. However, it's likely they would have been trying to achieve as high a speed as possible without cavitation, and that severely constrains what the shape could be. Here are a couple of sections that I designed that have near constant pressure on top and bottom. The upper surface is basically at the cavitation limit everywhere. Prof. Mark Drela joined in the discussion with his own design: He used aft loading to get the lift. However, the velocity in the middle of the lower surface had to increase in order to provide the thickne
  2. What you've shown is a supercavitating section. I've read Sailrocket used a base ventilated section. Those have a blunt trailing edge, too, but the leading edge is rounded, not sharp. A sharp leading edge would lead to separation and cavitation. With a base ventilated section you want the flow to remain attached at the leading edge.
  3. I was a flight test engineer in a previous life.
  4. No, the shift in aerodynamic center between subsonic and supersonic flow doesn't have an analog with cavitation.
  5. The big advantage of the oblique wing is the structure is continuous from tip to tip, so it carries the bending loads across the pivot. th This makes the pivot a lot easier to implement. You still get some shift in the center of lift, and moment across the pivot, because the aft half of the wing is in the upwash from the wake shed by the forward half of the wing and this makes it more heavily loaded. But it's not as much as with symmetrical sweep. In an airplane, oblique wings have some interesting handling qualities. There is a pitching moment due to roll rate, and a rolling momen
  6. Here's the basis for simple sweep theory. Imagine an unswept wing with infinite span, in inviscid flow (no boundary layer). Now pull on the wing so it is sliding sideways in the spanwise direction. The flow over the wing hasn't changed (no boundary layer, remember) because the fluid still follows the same contour over the wing. But if you consider the fluid velocity relative to the wing, it is now flowing over the wing at an angle. So the unswept wing sliding sideways is equivalent to a stationary swept wing. What this means is simple sweep theory says ignore the spanwise component o
  7. You might find this paper useful. Modest amounts of sweep are effective at extending the cavitation speed. Larger amounts of sweep, on the order of 30 - 45 deg, can perform better at high speed but their performance suffers at lower speeds. AIAA-48104-766_EffectsOfSweep.pdf
  8. I think it helps to consider the non-foiling example of a gybing centerboard. Picture the centerboard, rudder, and rig sailing to windward all by themselves without any hull. The angle of attack of the centerboard is whatever is required so that the lift on the board exactly matches the applied load from the sail rig. The angle of attack on rudder is determined by the yawing moment from the sail rig. Now place the hull on top of the board and rudder. For a normal centerboard, the hull will be aligned with the chord of the board and see a leeway angle. If the board is gybed to weather, th
  9. Leeway in itself is irrelevant to performance. Leeway only determines which way the bow is pointed, not which way the boat is moving. It is of interest when dealing with the wake of a daggerboard impinging on the rudder, and it affects sail trim. But camber and cant do not drive the boat to windward because the boat's heading angle is not fixed.
  10. Defining camber as the angle between the flap and main element chords also has the advantage that it is easily measured onboard. You can use a lifting line or vortex lattice to get the induced drag of the L foil, including both side force and vertical force. It's the surface velocities that require a panel code. If you look around you may be able to find free panel codes. I've written a plug-in in Java that I use to create PMARC formatted input files directly from a Rhino CAD model. Most CAD packages have a command for creating a surface by sweeping along one or two curves, interp
  11. FWIW, judging camber in that manner is not very useful. SailGP uses the main element chord as the reference and measures flap deflection as the angle between the main element chord and the flap chord. If you want to visualize the effect of flap deflection on lift, it is much better to simply look at where the flap trailing edge is pointed. Since the whole purpose of the wing is to bend the flow, the flap chord points in the direction the flow will be moving when it leaves the trailing edge. For a wing with a 50% flap chord, the change in lift due to a change in flap angle (measured bet
  12. I doubt it. I suspect the AC75 shaft section is symmetric all the way down. They can use cant to adjust the ratio of vertical to horizontal lift so as to maintain near zero load on the shaft and maximize the effective span. With regard to the L foil sections, it would be typical to use many different sections along its length, as you've indicated. You have about the right number of sections, too, although you probably need to have some more closely spaced near the elbow and maybe one or two more along the wing. At the top, the sections are thick because of the need to react the
  13. Why do you think nothing was holding the film to the ribs? IIRC, they used double-sided tape to attach the film. I was wondering about the scalloping, too. When I viewed the lee side of the AC72 wingsail from the chase boat, I was surprised to see how smooth it was. There was just a hint of convex scalloping visible when the light was glancing off it. So the shape was pretty close to the designed shape. The windward side was pushed in significantly. That may have been helpful, as it added camber and reduced thickness. I think of more significance were all the water droplets
  14. Here you go - knock yourself out. AIAA-1984-347_Optimization_and_application_of_riblets_for_turbulent_drag_reduction.pdf AIAA-1988-138_Drag_reduction_for_external_and_internal_boundary_layers_using_riblets_and_polymers.pdf AIAA-1999-3402_Riblets_on_airfoils_and_wings-A_review.pdf AIAA-45821_Effects_of_contamination_on_riblet_performance.pdf AIAA-48695_Turbulent_Boundary-Layer_Modification_by_Surface_Riblets.pdf AIAA-60126-754_Riblets_as_a_Viscous_Drag_Reduction_Technique.pdf
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