Design Criteria
Design Criteria
Affordable - Durable - Easy to ride
Initiate and maintain stable , lower speed foiling over a wide range of open surf conditions
High foil maneuverability and control at these lower speeds to enable surf and swell riding
Safer surf-friendly profiles and parts
Rigid Aluminium mast , pedestal and fuselage. Polyurethane , Epoxy and Carbon flying surfaces.
Kite , Surf , Modular Electric
Stepped Wing
Wing Design
KFM Windtunnel Test
Wing Design
- KFM Modified Wing Profile: Increased pitch and height control , Ability to ride and turn extremely slowly on foil , Increased foiling wind range using the same kite , Enhanced ability to ride through wind gusts , Enhanced speed control when riding on swell , Smaller wing areas are required.
- Drooped Wingtips : The wing not only imparts downward momentum on the fluid but also a lateral, or sideways, component. The lateral momentum is hence deflected downward, and lift is further increased.
- Anhedral : Reduces ventilation of the wingtips , adds compression lift , and adds lateral stability against an upward force (kite etc)
- Blunted Profile Surf edges
KFM Airfoil
KFM Windtunnel Test
Wing Design
- The concept behind the Kline-Fogleman airfoil used in our hydrofoil design may be hard to understand because it is so different from present aerodynamics. The KF concept uses a vortex, which attaches itself to the KF airfoil behind the step and becomes part of the airfoil. This means that at least one quarter of the KF airfoil is air against air. This also means less friction and greater efficiency penetrating the air.
- The Kamm Effect is something that is very much in use. You can see it applied to sedans virtually everywhere. It is a flat or blunted rear end of a car and the reason for it is efficiency. In the 1930s, a German aerodynamacist named Wunibald Kamm shocked the auto racing world when he chopped off the rear end of his tear-dropped shaped racing car. At that time it was thought that the tear-drop shape was most efficient aerodynamically. But it turned out that the blunted rear end created a more aerodynamic shape. Some of the drag created by the car collects at the back end of the car and becomes part of the shape of the car. It is vortex attachment.
KFM Windtunnel Test
KFM Windtunnel Test
KFM Windtunnel Test
- The KF airfoil handles a wide range of speed from very slow to very fast.
- Normal airfoils are designed to either generate a lot of lift in order to carry more weight, which means they must be thicker to produce more lift, or they need to be thinner in order to fly faster thus sacrificing lifting heavier loads. The KF airfoil can do both of these jobs extremely well.
- The KF airfoil has a much greater range for its center of gravity. A conventional airfoil would normally have a CG about 33% back. The KF airfoil can be moved back as much as 40%, thus allowing it to carry a heavier load. The further back the center of gravity is the more desirable it is, because of the center of balance. It can also handle a shifting CG and still give you control authority.
- At higher angles of attack, the KF airfoil remains unstallable. The center of gravity and center of pressure appear to move backward thus preventing a loss of lift.
Empennage
Stabilizer
Vertical Fin or Strakes
Vertical Fin or Strakes
- KFM modified airfoil profile , inverted and spaced with profile tuned nose-up incidence.
- The trailing edge curves are copied from dolphin flukes. This increases stability , upwind performance and offers better pumping action.
- The stabilizer was initially positioned above the fuselage offset to the wing to escape induced downwash. However, during water testing, maneuverability, speed and stabilizer effectiveness was increased by positioning them in-line.
- Positioning the stabilizer and fin below the fuselage ensures ventilation will not normally occur before the wing.
Vertical Fin or Strakes
Vertical Fin or Strakes
Vertical Fin or Strakes
- Using Strakes , or a single Vertical Fin , will primarily add directional stability.
- Strakes keep airflow attached underneath the aft fuselage and reduce form drag. High pressure air flowing underneath the fuselage interacts with the low pressure air flowing over the top of the wing. A vortex forms at the aft wing root and runs along the fuselage, moving and separating uncontrollably. The separation causes drag , vibration and wake. The Dual Aft Body Strakes capture these vortices in between each surface (Coanda Effect), and tuck the flow closer to the fuselage. This relieves the problem of separation, or drag and, in effect, produces thrust.
- During water testing however, upwind-ability and speeds on foil were improved greatly by using a single thin Vertical Fin. Yaw stability in larger surf remained unaffected.
Hydrobat
Slots & Slats
Slots & Slats
Slots & Slats
Aircraft leading edge Lift Augmentation devices :
https://www.boldmethod.com/learn-to-fly/aircraft-systems/leading-edge-slot-lift-device/
https://www.boldmethod.com/learn-to-fly/aircraft-systems/leading-edge-slat-lift-device/
T-Can
Slots & Slats
Slots & Slats
A “T Canaliser” is sometimes used on pattern model RC aircraft. They have wide chords and short spans.
They limit the amount of air moving from one side of the fuselage to another, improving the efficiency of the fuselage in "knife edge" flight.
The canaliser also limits the spanwise flow on the vertical tail, improving rudder efficiency.
Another theory suggests that as the wing angle of attack increases, the wing begins to stall at the root (where the wing and fuse meet) first, and then moves spanwise outwards towards the wingtip. The canaliser helps maintain the boundary airflow over the wing, and inhibits the stall onset for longer at these higher attack angles.
Hydrobat
Slots & Slats
Hydrobat
The Hydrobat combines both the "Slot & Slat" and the "T-Can" proven concepts. So too does it act as a Bi-Wing, creating slightly more lift than the lower, carrying wing, on its own.
Extensive water testing took place in flat water but particularly in the open ocean and surf. It was here, in the turbulence of our sea conditions, where the results became particularly interesting......
- Marked stability increase
- Far greater pitch control
- Increased lift and maneuvering time whilst remaining on foil
- Enhanced ability to remove and control foil speed when riding a wave
- Enhanced control relationship between the kite and the foil
- Faster, more controlled turning with a smaller turn radius
- Better control through wind gusts
- Increased high end wind handling ability
- Better low end wind range
There is a very slight decrease in average and top speeds, however this is far outweighed by the massive gain in stability and control.
Riding On Rails !!
Hence the name: “Hydrobat” (Greek origin)
“Hydro” - Water , “Bates” - Walker / Dancer