RAVE V - Updated Designer Notes
The winter months have allowed the design team to make great progress in the refinement of the Rave V design. We want to thank the many inputs we have received and recommendations on things we should consider. The feedback has been fantastic and we have taken those inputs along with the more detailed assessments of the foil design and load analysis to make several improvements. I have been particularly pleased with the support we have received from highly professional foiling boat designers that have paved the way for this new generation of foiling boats with America’s cup, and A cat designs to the ground breaking work of the Icarus. In addition many innovators and experimentalists have provided outstanding recommendations.
A lot of work has gone into the design refinement and the model of the current baseline will be on display at the Miami boat show Feb 12th to 16th. Clayton Bader and Jones Machine (Charles Jones) have created an excellent 1/6 scale model that allows the viewers to clearly see the details of the Rave V design. Clayton has updated the design Auto Cad and those are being refined into 3 D models. Please check out the Rave V model at the Miami boat show.
We introduced the University of New Orleans student design team a few weeks ago and they are making great progress with the refinement of the loads analysis and foil designs. Jacob Simon has done an excellent job on the loads assessments which has resulted in several design refinement and simplifications. After several weeks of trying to create a closed solution in 16 equations and variables Jacob was able to come up with a model for the various forces acting on the Rave V that allow us to conduct trades and sensitivity assessments on sail/mast location, sail/mast rake angle, foil placement, pilot/captain and crew placement, aft foil loads, center of gravity, center of sail force and hydrodynamic foil forces at multiple foiling speeds from 8 knots up to 40 knots. Jacob will be adding a separate design assessment to the designer blog to discuss his work.
The key findings from that were, the Rave V will be less sensitive to captain weight and placement than originally thought. This means that the need for the aft ballast may be going away as we found by analysis the movements of the aft cockpit by as much as 3 feet made only minor differences in sail and foil forces. This is great news and should allow for significant simplifications. We will likely still install an aft ballast capability in the prototype so we can validate these results. In addition we were able to change the aft foil to a simple rudder and sonic tube that can be raised and lowered like a simple dagger board. We are keeping a positive lifting force on the aft rudder sonic tube so we can reduce the tendency to pitch pole. At the higher speed the aft foil lifting force is getting below 30 pound up lift required so on strong wind days it may still be desirable to add weight to the aft of the boat to keep the loads higher. At the initial foiling speeds of 8 Knots the aft foil lift force required is closer to 120 pounds which is about where we want the load to be to balance between the forward foils lifting about 650 pound and the aft foil at 120 pounds. The design assessment showed we did not need as much lift on the aft foil as thought in the baseline with an aft V foil so we were able to eliminate that complexity. This was also an early recommendation by many of the reviews and comments we received, so we are quite happy with the design refinement supported by the analysis.
Jacob made an interesting observation that future foiling boats may want to consider. As he did the various sensitivities and trades he observed that these designs may be better suited for a forward rudder and lifting tube (a Bow Rider) concept. My initial reaction was one of emotion and not liking that recommendation. (The rudder is always in the rear). But as I thought about it I was reminded about the WW II German fighter jet story. The Germans had built the Me 262 as early as 1939 and had an effective jet fighter interceptor that would have changed the results of the war had the Germans gotten it fielded earlier. There were a large number of flight tests and design changes but the German high command opposed the use of a nose wheel on the Fighter. As a result the plane was impossible to take off and land do to the thrust reaction of the jet engine. Finally late in the war the engineers prevailed and the nose gear was added and the Me262 went into service. Fortunately for the Allies it was too late to have the impact it would have had if they had gone to a nose gear earlier. It was an emotional decision to try to stick with the tail dragger landing gear and not use the nose gear, much like my initial reaction to a bow rider rudder. We are going to stay with the baseline of an aft lifting rudder but I believe it is worth further study to consider Jacob’s recommendation. I encourage others to consider this option for further improving foiling boat design. I commend Jacob on his analysis and design recommendations. We will keep this in mind for future designs of foiling boats.
As Jacob refined those loads analysis we fed those lift requirements to Tom Cusumano for designing the V foils and sonic tubes to get the desired lift at various speeds. Tom is also preparing a short write up on his design trades and considerations. Tom is doing his graduate thesis on foil designs and has added non planner foil shapes to his research area. We have connected Tom with researchers at NASA Langley and Glenn research centers to gain more insight into supercritical foil shapes and sonic lifting tube non planner foils designs. One key finding is the size of the tube has been reduced from 6 inch diameter to 4 inches to get the desired lift a various speeds. In addition he is trading the sonic tube sizes and angle of attack he has been looking at the supercritical foil shapes and angles of attack along the length of the V foils. Using the lifting forces required at various speeds Tom is assessing what the trades should be. One of the key issues has been getting good supercritical foil and sonic tube data at the high Reynolds numbers the foils will be operating at. NASA Langley and Glenn are looking at the available data bases to see what data they might be able to provide Tom for the final foil selection. The current baseline is a 12% supercritical foil that has a taper form 6 inched cord at the waterline to a 4 inch cord at the sonic tube. His current assessment is that the sonic tube will only be 3 inches below the surface when foiling at max speed so he is trading different angles of attack for the sonic tube and V foils to obtain a good balance and lower the foil a little deeper in the water.
Tom is looking to select a couple configuration that he plans to put in the UNO 120x 16x 6 feet water table in the March time frame. We will build the shapes to be traded in late Feb. with a plan to select the final foil shapes after the water table testing. The prototype foils will be built in April as a result of the trades Tom is making.
The core materials for the Vaka, Amas ad Akas for the prototype have been placed on order and fabrication of the prototype will begin in early March. We are still on track for the prototype making its water debut in mid May on Sandusky Bay.