Basiliscus

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About Basiliscus

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    Port Gamble, WA, USA

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  1. Nice trick, making a translucent mast, a mainsail with no battens, and foils with no control surfaces. Maybe it's 3d printed!
  2. No. The FCS only controls the canting of the foils, but no indication yet of of bandwidth, maximum rates, rise time, or any of the typical specifications for a control system. All that's given in the Rule is the physical envelope swept out by the actuator and arm.
  3. I don't think either approach will work. The Design Rule allows the wing design to be totally open to the teams, provided it fits in the envelope. If they tried to restrict the range of flap deflections, the foil could be mounted with negative incidence so as to produce downforce with zero flap deflection and rely on positive flap deflection for positive lift. Requiring both flaps to be set the same would not work because the lift has to transition from one foil to the other during a tack or gybe. With no rake control (and possibly slow cant control), independent flap control is the only way to keep the boat balanced through the maneuver.
  4. I agree with your first sentence. The standardized FCS is indeed the way they are going. The FCS is a supplied item, along with the foil arm structure. It's not clear what parameters the teams will be able to set in the FCS, if any. Even with the standardized FCS, Rule 20.3 allows them to modify the range of motion of the FCS and establish their own fully raised position.
  5. This occurs in every foiling tack or gybe. The Rule says the windward foil can produce downforce up to the weight of the foil when both foils are immersed. But I see no way for the crew to know when the foil is producing downward vs upward hydrodynamic lift. The authors of the rule may be expecting the FCS to be able to tell based on the force provided by the cant actuator. But there are problems with that, too. Let 0 cant angle be the measurement position, as shown in Figure 12.1 of the Design Rule, and the wing has the maximum 4 m span. When the cant angle is 41.4 deg, the foil wings will be horizontal. Figure 12.2 implies the maximum achievable cant angle is 123 deg. Assume the c.g. of the foil and arm is on the Rule's 3.5 m circle for the minimum weight wing. (The possibility of a team designing a much heavier wing is another complication for the FCS designers in limiting the downforce.) Although 123 deg is achievable, the maximum righting moment from the weight of the foil looks to be closer to 90 deg cant because the foil is almost directly under the pivot in the measurement condition. At that angle, the tip of the wing is almost 1.6 m below the measurement waterplane, so depending on the flying height the windward foil may be digging in even when trimmed for maximum righting moment without trying for any hydrodynamic downforce. But my point is to compare the moments about the arm pivot as seen by the FCS. The FCS cannot sense the force on the foil, only the moment about the pivot. Say the windward wing is immersed and horizontal (41.4 deg cant). The pivot moment from gravity is 66% of what it is at 90 deg cant. That means the foil can produce more than 50% of its weight in hydrodynamic downforce and still be within the same pivot moment (and FCS actuator force) as it is at the maximum gravitational moment. By lowering the foil to the wings level position, the righting moment from the foil's weight has only dropped 20%, so there's a big gain in righting moment from lowering the foil and running with hydrodynamic downforce. That gain is doubled because of the lift on the leeward foil that's required to offset the downforce. Of course, it's possible for the FCS to have a maximum pivot moment programmed as a function of cant angle, so the maximum pivot moment may not actually be a fixed value as I've assumed above. But even then, although the Rule says a net downforce is not allowed, I don't see how it's possible for the crew or the umpires to know just what the net downforce actually is. For example, the foil could be set at 51 deg cant and the boat sailed with 10 deg windward heel, leading the FCS to allow 12% more pivot moment that can be taken in downforce. When the crew experiments with different cant and heel angles to see what produces the best performance, I don't see what will keep them from wandering into the negative downforce regime. Especially when you couple that with the fact that maximum gravitational righting moment is not obtained at the envelope maximum of 123 deg cant, but closer to 90 deg cant. That means the teams will want the "fully raised position" to be well below 123 deg cant, and the fully raised position will be anything the teams say it is making any amount of downforce perfectly legal.
  6. In previous matches, the limitations against downforce were enforced by requiring the windward daggerboard to be retracted when established on a tack. Downforce from the daggerboard was allowed for a limited time during maneuvers, and there was no attempt to measure it directly. AC72 Design Rule: 9.9 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC72 Yacht. This rule does not apply: (a) Prior to starting, as defined on RRSAC; (b) when the daggerboards are fully retracted (as per Rule 9.10) (c) when the windward daggerboard does not penetrate the surface of the water for more than 15 continuous seconds; (d) when the AC72 Yacht is within 300m of a mark, as defined in RRSAC; (e) when the AC72 Yacht is within 30 seconds prior to and after tacking or gybing; (f) when an AC72 Yacht is taking a penalty; and (g) when the effect is inadvertent as a result of a breakdown. For a protest against a Competitor under this rule to be upheld, it must be proven to the complete satisfaction of the Jury that this rule has been broken. AC45 Design Rule: 11.14 Daggerboards shall not be used to generate force for the purpose or effect of increasing righting moment when used on the windward side of an AC Class Yacht. This Rule 11.14 does not apply: (a) when the daggerboards are fully retracted (in accordance with Rule 11.6); (b) prior to starting, as defined in RRSAC; (c) when the windward daggerboard inadvertently penetrates the surface of the water for less than 10 continuous seconds; (d) when the AC Class Yacht is within 10 seconds prior to and after tacking or gybing; or (e) when the AC Class Yacht is taking a penalty. Downforce from the rudder elevators was implicitly limited by the restrictions on elevator movement. This led to tactics like slack lower shrouds to increase racking of the hulls and unstable bending-twist coupling of the elevators to increase the downforce as much as possible. The AC75 is different from the catamarans because it depends on using gravitational downforce on the windward foil for stability. This puts the authors of the Rule in the position of having to distinguish between gravitational downforce and hydrodynamic downforce, which is a very difficult thing to do, considering all the dynamic situations that occur when tacking and gybing. You can bet that teams will be taking every opportunity to increase righting moment as much as possible within the Rule.
  7. If you want to see what can result from a control system designed to move a control surface in an uncommanded manner, the crash of the Lockheed High Technology Testbed provides a cautionary tale. There were seven fatalities. The accident report says: PROBABLE CAUSE: "Disengagement of the rudder fly-by-wire flight control system resulting in a total loss of rudder control capability while conducting ground minimum control speed tests. The disengagement was a result of the inadequate design of the rudder's integrated actuator package by its manufacturer; the operator's insufficient system safety review failed to consider the consequences of the inadequate design to all operating regimes. A factor which contributed to the accident was the flight crew's lack of engineering flight test training." It doesn't take a huge leap of imagination to substitute the FCS operating under Rule 26.5 into this paragraph.
  8. Per the Design Rule: 26.4 The foil shall not intentionally be used to generate net downforce (combining gravitational and hydrodynamic loads) unless: (a) the foil is at its fully raised position (maximum cant angle); (b) the foil is at its fully lowered position (minimum cant angle); or (c) the FCS is being commanded to drive the foil to a prescribed cant angle. If the foil is not in one of these conditions and generates a net downward moment, the FCS shall not support the foil at a fixed cant angle and shall move the foil downwards. Downforce is allowed, provided the foil is at its fully raised position. The Rule does not specify what the "fully raised position" is. Rule 20.3 allows the use of stops to alter the range of motion of a control system: 20.3 Stops or locks acting on a single control function may be permanently in place (e.g. in the case of end stops on a hydraulic actuator), or if not permanently in place, may only be engaged and/or disengaged: (a) directly by the crew; (b) through a mechanically connected force input device; or (c) by an ECC and/or HCC, providing the device is only capable of locking the control function: (i) in a maximum of two defined positions; or (ii) from moving at all, regardless its position. The combination of Rules 26.4 and 20.3 mean the team can sail with a restricted value for the fully raised position, allowing the windward foil to dip into the water for hydrodynamic downforce. A foil section designed for a high incipient cavitation speed is almost symmetrical for the front half of the section, with nearly all of the lift at high speed coming from the aft half of the section. It would be entirely feasible to create hydrodynamic downforce using flap deflection on such a section and still have good characteristics with positive flap deflection for takeoff. They plan to use the FCS to enforce the restrictions on downforce: 26.5 If an FCS is frequently being commanded to drive the foil to a more raised position, and that foil is generating net downforce, the FCS may: (a) reduce the operation of the cant movement, or drive the foil to a lowered position; and/or (b) provide information to the Media System for the provision of racing penalties. It will be interesting to see what happens when the FCS moves the foil to a lesser cant position than commanded by the crew, putting Rules 26.5 and 20.3 in conflict. The crew may be operating the boat in a perfectly legal manner according to 20.3, but have the FCS invoke 26.5. False positive indications in the FCS are a definite possibility as the heavy foil wing bobs up and down at the end of the foil arm, causing oscillating loads on the FCS actuator and requiring frequent compensation from the FCS to maintain position. Uncommanded motion by design is a safety issue. Since the FCS is a supplied item, it leaves the supplier open to a protest, lawsuit, or even criminal liability should injury or death result from the uncommanded motion.
  9. Yes, although the force on the stern wing could be downward instead of upward. It depends on where the c.g. is and how much pitching moment is created by the rig. I think you have the heel angle exaggerated, though. If you consider the intersection of the arm and the 3.5 m circle, the c.g. of the foil and arm will be near that location and there's no point in raising that point higher than the arm pivot point, because that gives the maximum righting moment when the boat is upright. I'd use that as the baseline max cant angle. That should let you take out 15 deg or so of heel. You should also put the pivots at the same height in the hull, and that will take out a little more heel.
  10. Basiliscus

    Luna Rossa Challenge. AC 36

    The Challenger Selection Series has no place in the Deed. It is a separate regatta, organized by the CoR. The prospective challengers agree among themselves that if the CoR is not the winner of the CSS, the CoR will withdraw its challenge, thus satisfying the Deed requirement, "when a challenge from a Club fulfilling all the conditions required by this instrument has been received, no other challenge can be considered until the pending event has been decided." The winner of the CSS that goes forward to meet the Defender is actually the next challenger for the AC. If the CoR wins the CSS then it's as if the CSS never occurred, as far as the Deed is concerned. No mutual consent is required to freeze out the other challenging clubs - they were never in the AC to begin with. It's only through the mutual consent of the Defender that the regatta organized by the CoR uses the same venue and management structure as the AC regatta so as to give the appearance that the two are parts of one event.
  11. Yes, that's what I had in mind. Now, consider what it looks like if the windward foil isn't raised so high - more of it will be in the water and it will be more effective. Probably immersed up to the arm/wing junction would be best. The Rule doesn't allow for much positive dihedral in the wing, but giving it as much as possible allowed by the envelope would help to generate more downforce. AFAIK, there is no definition in the Rule of just what the maximum cant angle is. The Rule only talks about downforce being allowed when the foil is at max [26.4(a)]. The Rule also says mechanical stops are permitted [20.2(ii)]. So, if one inserted a mechanical stop (which may need to be movable to meet the requirement of 12.7(b)), one could reduce the maximum cant angle. That would allow less windward heel and move the leeward foil more to leeward for better righting moment. Less heel also puts the stern foil deeper in the water. The leeward foil can be set at any angle because it creates an upward force. So the FCS can be commanded to put the leeward foil at its optimum position, whether that be with the wing horizontal or with more cant so the leeward wing contributes to side force. It sounds crazy, but if the leeward wing were given less cant than horizontal, it would create a side force to leeward, requiring more side force to be generated by the windward foil and thus more downforce from the windward foil and more righting moment. Whether this makes any sense at all would have to be determined by the VPP.
  12. I don't follow why you think flaps are slower than rudder elevator - I would think it's the other way around. The Design Rule allows flaps up to 50% chord. Each degree of deflection of a 50% chord flap produces a change in lift that is 80% of what you'd get with a one degree change in angle of attack of the entire surface, so flaps can produce a large amount of lift. Flaps can be moved much faster than raking the rudder, and the elevator needs to change the pitch angle of the entire boat to change the lift on the main foil. For controlling ride height, I would use foil flap as the primary height control, and command elevator angle with flap command passed through a limited integrator. This would use the flap for quick response and the elevator for long-term pitch trim. The integral control of the elevator would drive the steady state flap deflection to zero, resulting in the foil being driven to the angle of attack needed for trimming at the desired flying height, while preserving the entire flap authority for short-term control.
  13. You're not taking it far enough. The Design Rule makes no distinction between gravity and hydrodynamic down force on the windward foil. It says the foil can only produce down force when fully down, fully up, or moving to a commanded position. So take the windward heel further until the windward wing digs in while in the fully raised position. Then the vertical lift comes from the wing, shaft of the leeward foil and rig, while the windward wing is producing side force and down force for additional heeling moment. It's not clear from the Rule whether the teams will be able to tailor just what the fully raised position is, but they may be able to insert a mechanical stop to make the fully raised position favorable for creating additional heeling moment.
  14. Basiliscus

    AC36 CLASS RULE

    Wands have been considered an appendage under previous AC rules, and thus would not be allowed because the three appendages are specified.
  15. Basiliscus

    AC36 CLASS RULE

    You could use mechanical sensors, like a bobweight, in the control system. The Monitor used mechanical feedback of shroud tension to foil incidence, and feedback like that (although to the flap rather than incidence) would be allowed.