Environmental concerns drive power-boat design

Newton, MA-Chariots of the waterways, power boats are racing across the nation's lakes and rivers in unprecedented numbers this summer, ferrying enthusiasts on joy rides that will refresh them for their work-a-day battles.

But, like their four-wheeled cousins that travel the roadways, power boats have run headlong into environmental concerns. The most recent manifestation: a U.S. Environmental Protection Agency proposal that sets forth the first-ever regulations for controlling emissions from outboard motors.

Specifically, the EPA wants outboard engine manufacturers to cut hydrocarbons releases by 75% in the next 10 years. Though the proposed regulations are still in the "public comment" stage and could be changed before the 1998 implementation target, engine manufacturers are already trying out new designs that will cut emissions without affecting performance.

Some manufacturers, such as Yamaha, may replace the traditional two-cycle engines they have been using with four-cycle versions up to about 50hp. But others are experimenting with new direct-injection two-cycle engines, which they say are lighter and more fuel efficient.

Two approaches. Traditional fuel injectors send fuel to an intake manifold where it vaporizes and drains into the cylinders. Direct injection sends the fuel straight to the cylinders without the need for a manifold. Two of the most promising direct injection systems are SEFIS (Small Engine Fuel Injection System), developed by Orbital Engine Corp., Perth, Australia and being used by Mercury Marine, Fond Du Lac, WI; and LEAP3 (Low Emission Advance Propulsion), from the German company FIGHT and being used by Outboard Marine Corp. (OMC), Waukegan, IL.

In SEFIS engines, explains Mercury Marine President David Jones, fuel rushes to the cylinder as a fine spray dispersed by an air blast after the intake and exhaust ports close. Unlike a similar automotive system from Orbital that derives air pressure from an on-board compressor, SEFIS captures a small part of the compressed air/fuel mixture above the piston by keeping the injector open until just before ignition. When it does close, it traps the compressed charge in an accumulator, where it can disperse the fuel spray in the next injection cycle. Jones says SEFIS improves fuel economy by 30%.

High-pressure pump. LEAP3 pressure-surge technology uses a high-pressure pump to blast fuel to the engine's combustion chambers. The pressure surge, at rates up to 100 times per second exceeding 200psi, atomizes the fuel as it enters the cylinder for a clean burn.

OMC engineers repositioned the intake and exhaust ports so both are closed when fuel is injected, and redesigned the piston head to provide more power with every stroke. "Traditional injection methods produce a stratified fuel/air mix-one that's richest at the area of injection and thinner in other areas of the combustion chamber," says Jack Flaig, OMC vice president for engineering and manufacturing. "LEAP3 produces a more homogeneous fuel/air mix throughout the chamber."

OMC President Hank Bowman claims LEAP3 computer-controlled direct injection technology is more sophisticated than that used on most advanced automobiles. He says it will result in a 35% increase in fuel economy.

Both SEFIS and LEAP3 technology have caught the eye of engineers in the general automotive industry. And, says OMC, LEAP3 has potential for use in lawnmowers and snow blowers.

Mercury plans to have SEFIS technology in place in 1996, the same time frame OMC is following for the LEAP3 technology it will put in its Johnson and Evinrude outboard motors.

Smaller wakes. Meanwhile, the need to meet local environmental regulations on wake production is driving other companies to develop new hull designs. Among them is Gallatin, TN-based Boating Corporation of America (BCA), which is experimenting with a new Stolkraft hull for its cruisers.

Developed in Australia, the Stolkraft design uses aerodynamic and hydrodynamic lift to provide what BCA calls an air-lubricated hull. Two geometrically shaped air scoops located at the bow between the hull route the air generated from the forward motion of the vessel to the aft tunnel for aerodynamic lift.

The air lift mixes into an air and water froth at the midship step in the hull, creating a lifting cushion of air and water for the planing hull to ride on this "air-lubricated" tunnel. Engines are located aft to keep the center of gravity on the aft tunnel and to keep the machinery out of the living area.

Clyde Head, BCA executive vice president, says a 26-ft-long Stolkraft hull running at 42 mph in calm water left only an eight-inch-high wake at a distance of 33 ft from the vessel vs the traditional five-ft wake for a so-called "deep V" design.

No spray. Of course, not all enginering work in boat design is for environmental concerns. Vonore, TN-based MasterCraft has just redesigned the hull of its ProStar 190 competition ski boat to dramatically cut down on the spray.

Twin strakes in the new hull knock down the spray before it becomes a problem, says MasterCraft's David Wilson. Then, deep slots in the hull channel it toward the back of the boat, where stepped chines flatten it and keep it close to the boat--and away from skiers.

Other developments on the horizon in power-boat design include multihulls, LCDs to display real-time engine data, fiber-optic cables to replace the hundreds of feet of corrosion-prone wires and connectors, and digital compasses with fluxgate technology to drive automatic pilots and sound "off-course" alarms.

Best of all, says boating author Gordon West, Costa Mesa, CA, marine electronics will have "off switches to shut everything down so boaters can just scan the horizon, take in the smell of the water, and enjoy life until an electronic alarm announces the dinner hour."

Strakes that deflect spray away from water skiers, as in this MasterCraft MarisStar, are among the recent advances in power-boat design.

SEFIS technology captures a small part of the compressed air/fuel mixture above the piston by keeping the injector open until just before ignition. When it does close, it traps the compressed charge in an accumulator, where it can disperse the fuel spray in the next injection cycle.

What this means to you

GM engineer wins Lemelson prize

Washington, DC-William J. Bolander, a 34-year-old engineer with GM's Power train Group, received the first $500,000 Lemelson-MIT Prize for Invention and Innovation during a ceremony held at the Smithsonian's National Museum of American History in late March. A distinguished committee, led by Professor Lester Thurow of MIT, selected Bolander.

Presently employed as corporate algorithm technical resource leader with GM's Powertrain Group, Bolander is the inventor of the Cadillac Northstar's "limp-home" system. It enables a driver whose vehicle has lost coolant to travel to a service facility without experiencing engine damage. His engineering career has resulted in ten patents to date.

In an exclusive interview, Design News asked Bolander what significance the Lemelson-MIT award might hold for the design engineering profession. "I hope that it will raise the awareness in young people of what engineers are," he responded. "I've been shocked at the ignorance of most of the media people that I've been talking to. They don't know what engineers are and what we do. And if these adults don't know, our young people certainly don't."

In addition to Bolander's award, a Lifetime Achievement award was presented to William R. Hewlett and David Packard, founders of Hewlett-Packard Corp.

These awards were established by Jerome H. Lemelson, who was recently chosen "Engineer of the Year" by readers of Design News. The award received by Bolander will be given annually to an outstanding American inventor/innovator. It is reportedly the world's largest single prize of its kind. The Lifetime Achievement Award honors Americans whose careers as engineers and innovators have had a major impact on industry and society.

Lemelson funded the awards program, which is administered by MIT, in 1994. His purpose in doing so is to draw the attention of society, and particularly young people, to the importance of technology, and to make careers in engineering and science more attractive. "We glorify Michael Jordan and Tom Cruise," says Lemelson, "but the true heroes of our society are the men and women who solve our social and technological problems.

Aircraft-design winner sails into world championships

Sugar Land, TX-Last fall, Design News challenged readers to submit their aircraft designs to the Unique Airplanes contest. At stake: a Texas Instruments calculator-and pride.

Over the succeeding months, the postal carrier delivered a surprising number of entries. They ranged from rough conceptual sketches to multi-view CAD drawings. But one, Peter Masak's Scimitar glider, soared above the competition.

Many entries approached its creativity. Several very unusual proposals were more unique. However, none, save Scimitar, showed any promise of production.

A racing sailplane in the 15m class, Scimitar matches an advanced composite wing and empennage to a Schempp-Hirth Ventus fuselage. The result is an affordable, world-class competitive glider. Since most good fuselages affect overall aircraft performance insignificantly, Masak focused his effort where it counts-on the wing.

He began with a proven Wortmann airfoil section. To it he added an electronic boundary-layer control system (BLC) and winglets. An innovator in sailplane design-by day he's a mechanical engineer at Schlumberger-Anadrill-Masak developed the first successful winglets for gliders several years back.

The BLC consumes less than 15W and dramatically improves performance. "It's reduced drag in flight tests, at both low and high speed, by 15 percent," he says. "At the airfoil's design point there is no gain or loss, but a sailplane spends 99 percent of its time at the low or high end." He hopes to patent the BLC this year.

The wing consists of a fairly flexible S-glass spar and stiff kevlar skins. Masak tailored the structure to be soft in bend- ing but stiff in torsion. "We get superior twist characteristics as a function of speed," he explains. And the soft bending "reduces the local angle of attack during gusts to better keep the airfoil in the laminar-flow range." The wing is also the first to employ an optimized planform. Instead of easy-to-build straight-tapered sections, Scimitar's wing-geometry changes in three dimensions.

The design process consisted of classic techniques-an FAA requirement-followed by verification with advanced computer tools. Masak used Swanson Analysis' ANSYS to verify the wing structure. Several aircraft-specific programs, such as Stanford University's LinAir, assisted with wing-loading calculations and stability and control computations.

In January, Scimitar ventured to New Zealand for the 1995 world glider championships. "We were the first American team in almost 30 years to fly a glider built in this country," Masak says. Even more surprisingly, not one composite sailplane has ever been designed and certified in the U.S. Teething problems prevented Scimitar from placing, but even without the BLC system Masak says his aircraft equaled the best European machines.

Scimitar USA in Woods Cross, UT, will manufacturer and sell the new glider. The wings will be molded by Contour Composites (Salt Lake City). Following two years of testing, a Scimitar can be had for roughly $50,000-30 percent less than an equivalent German sailplane. Interested parties can call John Neel at (801) 298-2001, ext. 109.

Design News' Unique Airplane design winner Peter Masak poses at the 1995 world championships in New Zealand with his 15-meter class sailplane, Scimitar.

Scimitar's wing is flexible in bending and stiff in torsion due to a unique combination of an S-glass spar and Kevlar skins. It is the first sailplane to employ an optimized planform that changes in three-dimensions from root to tip. All other sailplanes use straight-tapered sections, which are easier to build.

-Mark A. Gottschalk Western Technical Editor

Brake-light design focuses on materials

Lisle, IL-Long before Design for Manufacturability became popular, Tricon Industries, Inc. simplified designs and reduced part counts by integrating components and connectors into a single, insert-molded part. The process, plus the selection of the right materials, paid big dividends when Inland Fisher Guide, Anderson, IN, asked Tricon to design and produce a new center-high-mount stop light (CHMSL) for Chevrolet and GMC full-size truck platforms.

Tricon's CHMSL design addressed a problem inherent in vehicle light assemblies. Over time, excessive heat buildup caused by multiple bulbs in a confined space can damage the polycarbonate (PC) fasia and cause warpage or twisting of the assembly. To prevent this, an open, rather than airtight, design was implemented to provide convective cooling. Extended metal back plates, which function as electrical conductors and as heat sinks, provide added heat dissipation. Molded-in "eyebrow" extensions above the bulbs further shield the PC lens from the heat source.

Key to the design is a 4-way integral connector and interconnecting stamped circuits, instead of four separate light assemblies. Power and signal lines are provided through a single plug-in cable connector. The 12-inch-long, single-shot molded component encompasses complex interior stamping and exterior interface geometries. Due to the complexities and tight tolerances, stampings are final-formed on demand at the insert molding machine.

Don Paul, Tricon's director of technical service and the company's Advanced Product Design Group, determined that heat deformation, warpage, and other performance problems could be prevented by careful material selection. The most common problems encountered in vehicle light assemblies: short circuits caused by water leakage and poor part fit, and part deformation resulting from moisture absorption.

Tricon consulted with Amoco Polymers, Alpharetta, GA, to find an easily molded, high-temperature plastic that would allow the 12-inch-long part to remain perfectly flat and stable. The resin selected: a 33% glass-filled custom blend of Amodel(R) PPA, a high-temperature engineering thermoplastic. The material's heat-deflection and temperature-resistance testing, Paul reports, proved it better than glass-reinforced nylon and other engineering-grade resins in its ability to remain stable despite heat buildup and moisture.

For the CHMSL's injection-molded bulb sleeves, Tricon chose high-temperature Ryton(R) PPS, Grade R-4XT, from Phillips Petroleum Co., Bartlesville, OK. This resin, says Paul, also offers the mechanical, thermal, electrical, and physical properties needed to withstand heat, moisture, vibration, and temperature extremes.

"These days, low part weight and long service life are high priorities for automotive manufacturers," Paul explains. "These materials allowed us to produce a part that satisifies GM's quality and performance standards, while assuring cost-effective, high-volume production."

Hannover Fair pavilions feature American innovation

Hannover, Germany-World class: It may qualify as one of the most over-used terms of the '90s, but it fits many of the exhibitors that lined the aisles of this year's Hannover Fair in Germany.

More than 7,000 international firms displayed their technology at the world's largest industrial fair, held the first week of April. Included in that group were seven American pavilions, representing 151 U.S. firms.

American exhibitors at the fair felt their presence there gave them a deeper understanding of the global market. "If you're not competing worldwide, saying that you're world class is a hollow mission statement," notes Ronald Bullock, president and CEO of Bison Gear & Engineering Corp., a motor manufacturer based in St. Charles, IL. "Here, you learn more about your global customers and your competitors."

Bison was one of 13 American companies exhibiting at the Power Transmission Distributor Association's (PTDA) Pavilion. Firms there introduced a multitude of new products, most aimed at the global market. Reliance Electric, for example, rolled out its IEC Metric Motor, which employs metric mounting dimensions and shaft diameters. Bison also introduced a global product: Its G-line of gearmotors, also offering metric mounting dimensions and shaft configurations.

Twenty American firms displayed their wares at the National Fluid Power Association Pavilion, including Auburn Gear, Bimba Limited, Fabco-Air, Firestone Industrial Products, Hobbs Corp., and Sun Hydraulic, among others. Most saved their global product introductions for the Fair. Fabco-Air, Gainesville, FL, for example, rolled out its Global Series of pneumatic cylinders. The firm also did a brisk business with its Multi-Power pneumatic cylinders, which already enjoy widespread use in the U.S., but are relatively new to Europe.

Exhibiting in a European show is critical for companies that want to forge business alliances abroad, says William H. Prueser, director of exhibitions for the NFPA. "The business culture is different in Europe," he explains. "You can't make cold calls on customers at their facilities. You have to get to know them first. At the Hannover Fair, you have a chance to make that initial introduction. That's why it's important to have shows like these."

Most exhibitors said they left Hannover with a better feel for the meaning of the term "global market." "You might come here thinking that you have only four or five competitors," notes Leslie G. Hennessy, vice president of marketing for Lovejoy, Inc., Downers Grove, IL. "But when you leave, you realize that you have 40 competitors."

The Hannover Fair, which attracted more than 300,000 attendees from around the world this year, highlights innovations in fluid power and motion control every other year. The Fair will again focus on those disciplines in 1997.

The Hannover Fair attracted more than 300,000 attendees from around the world.

Fabco-Air introduced its Global Series pneumatic cylinders at the Hannover Fair. Global Series cylinders incorporate special surfaces for mounting of stroke-sensing switches.

-Mark A. Gottschalk Western Technical Editor

Government plans to bolster 'green' design

Washington,DC-The White House has launched a nationwide program aimed at encouraging engineers to develop more environmentally sensitive designs.

Called the National Environmental Technology Strategy, the plan calls for promoting innovation, cutting red tape, "reinventing" regulations, and improving availability of information. It also seeks to shift emphasis away from costly cleanups and toward long-term pollution prevention.

By November, federal, state, and local governments are to join with private industry to update R&D priorities and demonstrate "green" technologies. A three-year goal: establishing a "market-based" process for verifying the technologies.

As part of the program, the U.S. government will let American companies use federal sites to test and demonstrate the effectiveness of environmental innovations.

Parts of the Strategy already are underway. The federal government recently launched a Rapid Commercialization Initiative to stimulate business use of environmental know-how. Over the coming year, program officials expect to commercialize ten technologies.

Also, the U.S. Environmental Protection Agency now runs a voluntary program called Design for the Environment. It encourages businesses to incorporate environmental considerations into designs.

"We will move from discrete technologies tackling particular problems to the integrated design of large systems," according to the Strategy report, recently unveiled by Vice President Al Gore.

One long-term goal: holding down use of resources in the design of every product and manufacturing process. As work unfolds, government planners believe, radically new products will feature longevity and "reusability." And, information needed for critical design tradeoffs will be widely available.

"In the end," the Strategy document predicts, "environmental technologies will virtually disappear as distinct pieces of hardware, and environmental concerns will become more fully integrated in the fundamental design of all products and processes."

Plasma source ion implantation (PSII)-a cleaner, longer-lasting alternative to chrome plating-is an environmental offspring of defense research at Los Alamos National Laboratory.

-Walt Wingo, Washington Editor

System pinpoints biopsy needles

Princeton, NJ-Five million people undergo needle biopsies each year in the United States, and some patients must retake the test due to inaccurate results the first time around. These needle biopsies are often performed through an image-guided method that uses ultrasound technology. The problem with ultra-sound biopsies: It is often difficult to see the needle in the ultrasound image. Now EchoCath, Inc., Princeton, NJ, has developed a system that eliminates this problem.

The ColorMark(TM) system features a small device that, when attached to a biopsy needle, causes the needle to vibrate at almost undetectable levels. The device is used with a color-flow Doppler ultrasonic system that projects an all-black-and-white image, with the exception of anything that moves; those portions appear in color.

Because the ultrasound machine can detect the slightest movement, the needle's vibrations provide a colored image of the needle on the screen. This makes the needle clearly visible to the technician.

The most critical part of the ColorMark system is the driver, which causes the needle to vibrate. Engineers used Algor software to determine the optimal size and shape for the driver, to enable it to vibrate at a number of natural frequencies to accommodate various needle sizes.

Engineers also needed to determine the natural frequencies at which a variety of needle sizes would vibrate. Using Algor's Beam Design Editor, engineers examined different needle sizes with various driving forces imposed on them. "The information about the driver and needle frequencies enabled us to develop the optimal design for the system," says Bayard Gardineer, vice president of engineering at EchoCath. "Overall, we built dozens of models to create the system. But with Algor software we avoided building hundreds more."

Algor software enabled engineers at EchoCath to locate natural frequencies without having to build new models for every design change. Shown is the modal analysis of the clip of the ColorMark system.

Workstation makers boost graphics power, speed

Newton, MA- Hewlett-Packard has unveiled its next-generation of graphics workstations, featuring several hardware innovations that offer up to a three-fold boost in performance.

"I was pretty impressed," says Peter Lowber, senior analyst at Datapro, Lexington, MA. "The graphics are outstanding. HP has really leapfrogged."

Sun Microsystems, meanwhile, announced a new system that roughly doubled the company's desktop graphics performance. "The SPARCstation 20TurboZX has performed beyond our expectations in tests with the I-DEAS Master Series," according to William Carrelli at SDRC.

HP's new "J-class" workstations incorporate a redesigned system bus running up to three times faster than its predecessor. Engineers speeded up throughput via custom-designed silicon, including a chip to perform texture-mapping. There are 13 patents pending on the new system, HP officials say.

The chip for hardware texture-mapping dramatically increases speed for such graphics, the company says. Texture mapping is a technique for photo-realistic graphics, and is extremely compute-intensive. HP's new design features texture caching, so if memory overflows while texture-mapping a large image, the cache allows the system to operate at almost full speed. Conventional systems rely on software texture-mapping when the memory is full, slowing the system.

"We believe this is going to change the face of design applications," says HP's Pete Dubler-hastening the day when engineers can model full systems, such as complete autos and airplanes, with realistic graphics on their desktops.

The VisualEyes-48 graphics accelerator, at $16,000, scales up to 235 PLFsurf 93, a measure of 3-D graphics speed developed by the National Computer Graphics Association. "That's absolutely unprecedented in the industry," claims Mark Pacelle at Hewlett Packard. HP's design also substantially increases graphics speeds if the CPU is upgraded to a faster model. Prices for the workstations start at $32,775. Engineers using HCRX-8Z and HCRX-24 graphics can upgrade to new VisualEyes 3D graphics accelerators for a $1,500 price differential.

Sun's SPARCstation 20TurboZX workstations prices range from $32,795 to $41,495, depending on CPU and configuration.

Plastics address semiconductor ESD, heat, and chemicals

Reading, PA-The Polymer Corp. has introduced five new plastic materials designed especially for use in the semiconductor manufacturing process. The materials are said to offer superior chemical and wear resistance, dimensional stability, and high purity.

"With this range of high-performance plastics, design engineers can select a material that best meets a design involving the use of semiconductor processing and test equipment," says Fred Sanford, Polymer Corp. industry manager. The materials, all of which come in rod, bar, and plate stock shapes, include:

Semitron(TM) ESD 225, ESD 410, and ESD 500 electrostatic dissipative polymeric materials.

Traditional technologies for achieving static dissipative performance in plastics include: conductive reinforcement (steel and carbon fiber and carbon black), hygroscopic salts, special antistats, and chemical enhancement. However, conductive reinforcements can prove unreliable, since microarcing can occur when a static charge exceeds 500V, creating a permanent conductive path to ground. On the other hand, hygroscopic salts fail to provide a permanent solution, since they rely on moisture to be effective. And, topical antistats tend to wear away over time.

Chemical enhancement provides the only reliable permanent solution for producing static dissipative plastics, according to Sanford. Both Semitron ESD 225 and ESD 500 are "permanently ESD [electro-statically dissipated] and not susceptible to microarcing," he adds. Typical uses include IC inspection station material for making wafer combs, flat finders, and vacuum wand tips.

Duratron HP can be machined to form dimensionally stable, structural parts for continuous use at temperatures up to 580F. The material also exhibits low outgassing based on the ASTM E595 test. And it resists aromatic hydrocarbons, acids, and bases. Typical uses include "fingers" for handling hot glass and insulators and connectors.

Celazole PBI has a continuous-use temperature of 750F, a heat-deflection temperature of 800F, and can be exposed short-term to 1,000F. Other major properties include: 50,000-psi compressive strength, flexural modulus of 950 kpsi, and a low coefficeint of thermal expansion.

Insulating blocks made from Polymer Corp.'s Semitron ESD 500 plate dissipate static electricity in test-handling equipment.

3-D modeling helps design advanced spinal implants

Cleveland, OH-Thousands of people report back problems to their physicians annually. Not all require surgery, but when they do, there is little room for error. AcroMed, manufacturer of spinal implants, uses 3-D modeling to keep the risk of error to a bare minimum.

Using both AutoCAD design and SDRC's I-DEAS solid modeling software, engineering service's Frank Byers and his colleagues create 3-D images of discs and surgical devices.

"Recently," says Byers, "I-DEAS helped me completely redesign an artificial vertebral disc." Byers then uploaded the solid model files to an outside stereolithography service to generate a prototype part. "It was a three-day turnaround time between conceptual design and part-in-hand."

Byers notes that 3-D computer models prove to be the best visualization tool when physicians visit AcroMed.

"The 3-D solid model serves as an accurate representation of the actual part," Byers says. "Doctors generally do not understand 2-D drawings."

Byers says I-DEAS also assists in defining part details and contours-a critical consideration.

Parametric Technology buys Rasna Corp.

Waltham, MA-Parametric Technology Corp., developer of the Pro/ENGINEER family of mechanical CAD products, has purchased Rasna Corp. of San Jose, CA, developer of the MECHANICA family of analysis products. Pending approval of Rasna's stockholders, the sale will be finalized by mid-August.

The acquisition brings together two of the most dynamic players in the computer-aided engineering industry. International Data Corp. rates PTC as the top mechanical CAD/CAM vendor in terms of software revenue. Inc. magazine last year rated Rasna as the third fastest-growing private company in the U.S. But, there are differences between the companies, as the Gartner Group's Dave Burdick points out. "Rasna is technology centric, and PTC is sales centric, with the lowest R&D expenditures vs sales in the industry," he says. Still, he says, there are synergies that make the merger good for the companies and their customers.

Primary among the synergies: Rasna's analysis software fills out PTC's product offerings. The integration will make it easier for engineers to do the form, fit, and function of design in one package, says Rasna President David Pidwell. Adds PTC Chairman Steven Walske, the combination is critical to PTC's plans "to architecture the industry's first digital design automation toolset encompassing product concept through manufacturing."

I-DEAS can illustrate the placement of artificial discs between spinal vertebrae.

CAD delivers variable-pitch propeller

Spokane, WA-Thanks to CAD and 13 years of engineering perseverance, recreational boat owners can replace their fixed-pitch propellers with "two-speed", auto-shifting models. Produced by Aerostar Marine, the Power Pitch and Switch Blade Pro series of props increases off-the-line acceleration by 30 to 40% without sacrificing top speed.

The propeller's secret lies in a patented shifting mechanism that combines inertial weights, springs, and hydrodynamic forces to change blade-pitch by six inches. Out of the hole, the center of pressure (CP) on each blade lies forward of the blade shank, producing a moment about the shank. In this situation, an over-center mechanism locks the blades into the low-pitch position.

As the boat increases speed, the CP shifts aft until it nearly aligns with the shank. This action releases the over-center lock and allows the propeller to shift into the high-pitch configuration. "It senses the loads on the blade and changes gears like an automatic transmission in a car," says Steve Speer, Aerostar Marine's president.

The shift point varies dynamically with propeller speed and loading; if the boat planes early, the prop shifts early as well. Originally, engineers toyed with creating an infinitely variable propeller. But variable, unpredictable loading produced uncontrollable flutter, and they switched to the two-speed design.

To expedite the design process, engineers turned to Intergraph's (Huntsville, AL) EMS computer-aided engineering system. Its 3-D solid- modeling allowed them to lay out aerodynamic sections in a plane, and then wrap sections to a radius to create the blades.

EMS let engineers prepare patent drawings, fit the propeller's 80 some-odd parts together on screen, and send CAD data to vendors. "We needed a package that could do a variety of functions including mechanism analysis, finite-element analysis, and also be able to get into NC machining of the blades," says Speer. Intergraph emerged as Aerostar's choice after two years of in-depth evaluation of CAD packages.

Speer drew inspiration for the variable-pitch propellers from his firm's experience with aircraft design. "They are almost a standard with aircraft," he says. "We wondered why not with boats?"

-Mark A. Gottschalk, Western Technical Editor

Software trims gas-spring design time

Leicester, UK-Engineers at Camloc Products are using a PC-based statics an-alysis software package from Saltire Software, Beaverton, OR, to quickly simulate mechanical designs that use gas springs.

Analytixa software combines a parametric sketching engine with mechanical simulation and analysis, and can be used for a variety of mechanical designs. Embedded equations allow the software to perform kinematic, inverse dynamic, and force analyses.

For example, with gas-spring design, the geometry and applied load vary considerably based on the application, explains Camloc Project Engineer Andy Bools. "So rather than doing laborious hand calculations to get the optimum geometry, rotation, and spring force, we set up the application details in Analytix, and from there we can quite simply modify mounting positions or applied loads without having to start from scratch."

Camloc engineers have used the package to simulate automotive tailgates, tanning booths, and other applications. "It lets us show the customer how well the spring would match their requirements before they go to the expense of testing," says Bools.

The software saves time during concept trials, he adds, "but the biggest benefit is that you get away from trial-and-error before tests. Using Analytix, we can match spring performance with the customer's requirements. We're getting 95% of the design on the first go."

Other users have applied the software to the design of hinges, folding seats, hydraulic actuators, linkages, conveyor systems, and printed-circuit-board assembly machines.

t0> Analytix starts at $895; a combination of that package and the Dynamixa option for forward dynamic simulations such as trajectories or impacts costs $1,350.

Analytix software simulates movement for mechancial design analysis.

CAE tool aids chip-holder design

Dallas, TX-When Texas Instruments' Corporate Research and Development Division was charged with designing a semiconductor sample holder that could withstand liquid-helium temperatures, TI engineers called on ANVIL-500(R) CADD/CAM/CAE software from Manufacturing and Consulting Services (MCS) of Scottsdale, AZ.

The customer, another TI division, needed the holder for the interior chamber of an analytical spectrometer. In addition to withstanding -272C, the product had to fit within a specified cubic area and be of low mass.

Tool- and instrument-builder Craig Fischer received the preliminary design on disk. He imported AutoCAD geometry into ANVIL-500, which he says easily translates DXF files. The TI Model Shop team used the design and drafting portions of ANVIL-5000 to build a 3-D wireframe model of the sample holder.

Once he was satisfied with the model, Fischer brought the customer in to view it on the shop's workstation. "I made changes on the fly using the software while the customer was there watching." Together, they could examine the design on screen and see immediate results or get answers to "what-if" scenarios.

When Fischer completed the prototype sample holder, it weighed less than one pound and was 6.25 inches in diameter. After design approval, he broke the finished design into components so he could generate individual drawings for its assembly. Fischer gave the drawings to other shop workers to begin CAM procedures for making the part. The Tool Shop used ANVIL-500 again to create the tool paths necessary for manufacturing.

Fischer credits NCPost, a new post-processor, with making it simple for machinists to create customized code when needed instead of having to hire someone to write the code for them. "I find that being able to go directly from design to NC without having to convert anything helps tremendously and saves time," Fischer says. "I don't have time to be redrawing things because of a conversion problem."