SCIENCE CONCEPT:
- There is a type of vehicle that depends upon motion to
develop lift, and blends the aerodynamics of an aircraft with the
hydrodynamics of a ship. This vehicle is called a hydrofoil.
STUDENT OBJECTIVE:
- The student will do a comparison study of a hydrofoil
ship and how it operates in the water and a conventional ship and how it
operates in the water.
OVERVIEW:
- The student will compare the hydrofoil ship and the
conventional ship. The comparison will include the structural dynamics
and how Bernoulli's Principle effects the ship's abilities in the water,
usage, speed, comfort, cost, and availability.
TEACHER TEXT:
- The hydrofoil is a cross between the ship it looks like
and the airplane which it is built like. It's raised above the water by
small, wing-like foils. Although the foils move through water, they
operate on the same principle used by an aerofoil. As you recall,
Bernoulli's principle is that the faster a fluid or gas moves, the lower
the pressure it exerts upon objects along which it flows. The curved
upper surface of the hydrofoil causes water to flow at higher speeds
above it than beneath it, causing a difference of pressure between upper
and lower surfaces. The water streaming over the curved upper surface
has to move faster than that flowing beneath, leading to a reduction of
pressure on the upper surface and increased pressure on the lower
surface. The foils are connected to the hull by struts and at a given
speed the lift generated by the foils raises the hull bodily out of the
water.
Not surprisingly, many of the pioneers in aviation were
at the forefront in the development of the hydrofoil. The first
successful hydrofoil was designed and built by the Italian helicopter and
airship leader, Enrico Forlanini, in 1905. His craft was equipped with
foils set like the rungs of a ladder, and could achieve 38 knots.
Forliani's first client was Alexander Graham Bell, who
became so enthused after a ride on Lake Maggiore that he purchased a
license to build and develop the Forlanini ladder-foil system in North
America. One of his craft established a world water speed record of 70
mph in 1918.
It was not until 1953 that commercial value of the
hydrofoil was dramatically demonstrated. Ferries that steamed across
Lake Maggiore, connecting Switzerland and Italy, took nearly 3 hours to
cover the 30 miles. Cars driving around the lake arrived at the
destination in one and a half hours. The 10 ton, 28 passenger von
Schertal hydrofoil took just 48 minutes.
In calm waters the surface-piercing foil performs very
well, but in heavy sea conditions its natural stability turns from a
strength into a weakness. This is because the surface-piercing foil
tends to follow the up and down movement of the waves, which can result
in vertical acceleration that jolts both craft and crew.
The fully submerged foil was designed to limit vertical
acceleration as well as pitch and roll. Instead of following the contour
of waves, the submerged foil design 'platforms' the waves - that is, it
maintains a level flight path. This is accomplished through a complex
system of motion and depth sensing devices that in turn manipulate flaps
and elevators on the foil or change the angle of incidence of the entire
foil. The submerged foil design is in fact very similar to that of a jet
airliner, and like the jumbo jet the submerged foil vehicle is mostly
used for military or large commercial ventures.
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PREPARATION TIME:
- 20 minutes.
LESSON TIME:
- 60 minutes.
TEACHER PREP:
- Gather materials
WORDS TO KNOW:
- hydrofoil
- foils
- Bernoulli's Principle
- surface-piercing foils
- fully submerged foil
- pitch and roll
- flaps and elevators
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