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-    from the May 2000 issue - reprinted by permission

Aluminum Diesel Vies to Power Drone Aircraft

In war, the commander who wins is often not the one with the biggest guns or the bravest soldiers. More often than not the winner is the commander who best figures out how to keep an eye on what the enemy is doing.

In the battlefield of the not too distant future, new eye-in-the-sky drone aircraft are going to make combat information gathering a lot better, a lot cheaper, and a lot safer for the troops. Drones have been around almost as long as aircraft, but lacking a dashing pilot to grab attention, they have languished.

Part of the new generation of drones will be even less glamorous. They’ll be diesel-powered just like trucks. Perhaps it’s only fair since turbines migrated from jet planes (and ships) to battle tanks 20 years ago. If all goes well, Rudolf Diesel’s 1890s invention will once again get off the ground under its own power for the first time since the 1930s. The credit goes to Franklin, WI, inventor and developer, Douglas Doers. Vice president of DeltaHawk Inc., Doers and his project team have developed a powerful all-aluminum diesel. For today’s cash-starved military, the DeltaHawk diesel offers a significant cost savings in powering drones for battlefield intelligence.

As a power source for drones, diesels offer numerous advantages. Diesels are simpler and more rugged than the gasoline and turbine engines currently used. There is no valve train and thus no cam shaft. There is no ignition system—a significant battlefield advantage since ignition systems generate electromagnetic radiation which can interfere with on-board navigation systems and is easily targeted by enemy missiles. Also, there is no gear train since the drone’s propeller is directly driven by the crankshaft.

But the biggest advantage is in fuels. First, fuel economy greatly extends the unmanned aerial vehicle’s (UAV) ability to loiter. The DeltaHawk engine burns 35 lb of fuel per hour at the typical loitering mode of 100 hp. A turbine, though lighter in weight, burns 100 to 125 lb of fuel under those conditions. The more data sent back about a potential target, the less chance of a costly targeting error. Second, variable fuels make the engine much more acceptable to the Navy, from whose ships the Predator and other UAVs are launched. Aboard ship, the high flammability of aviation gasoline is a constant worry.

The DeltaHawk engine is a significant advance in small diesels. One of its main features is an integral head and block. Thus it has no head bolts or head gasket, which can present opportunities for failure and maintenance errors. In R&D, of course, progress never comes without a price tag. In the case of the DeltaHawk engine, it is the complexity of the engine block with integral cylinder heads. This is part of the engine’s unusually high power-to-weight ratio, approaching one hp/lb in the V-8 configuration.

Such a design is rare in engines which presented serious challenges to the pattern makers who created the DeltaHawk's tooling. With the exception of the forged steel crankshaft and forged titanium piston connecting rods, virtually all the engine’s major components, regardless of unit volume and range of sizes, are to be made on automated molding equipment. Engines are assembled in a 14,000-sq ft facility at the Racine, WI, airport.

The digital revolution has made aerial surveillance cheap and easy but the platform, the UAV, lacking significant innovations, keeps rising in price. Diesel-powered drones have an appeal to the budget-minded segments of the Pentagon and Congress, officials who prefer readiness to $100 million aircraft.

The value of UAVs was most recently proven in Kosovo when a "giant mechanical bug" called a Predator spotted a dangerous Serb checkpoint almost as soon as it was set up. The Predator UAV flashed images back to NATO commanders in Italy and a bomber was dispatched. Checkpoint eliminated, problem solved.

According to The Wall Street Journal, about two dozen Predators and other UAVs were deployed in Kosovo. Nine were shot down. All told, the newspaper disclosed, the Pentagon’s spending on drones during the past 20 years has added up to $2 billion. That’s roughly the price tag of one B-2 bomber.

One of the biggest problems of new UAVs, as well as DeltaHawk's sole focus, has been engines. Thanks to good design, a hard driving approach to development, and some savvy work by a Wisconsin pattern shop and a leading aluminum foundry, a DeltaHawk diesel is now well along in development. It currently holds more than 100 orders for engines with a value of about $1.9 million from the military and experimental aircraft builders.

The engine is also being tested by the Federal Aviation Administration (FAA). Initial results are due in June 2000 though certification may take two more years. If certified, DeltaHawk will be able to offer its engines to manufacturers of small aircraft. (Certification is not necessary for military and experimental-aircraft.)

As the combat numbers indicate, most UAVs have a short life expectancy. This is due to the simple fact that drones are sent into places too dangerous for manned aircraft. Considering the prevalence of small wars, drones may be needed in large numbers on short notice. It is this scenario that brings many of the Pentagon’s famous "-ilities" into play: manufacturability, durability, reliability, maintainability and survivability.

DeltaHawk entrusted its components to the expertise of two nearby firms: Central Pattern Corp., North Prairie, WI, which designed and built tooling for a dozen engine components, and Waterford Aluminum Co., the foundry which made the sand castings. Among their most pleasant surprises was the performance of Central Pattern’s new CAD and CAM software, PowerSHAPE and PowerMILL from Delcam International Inc. Based in Windsor, Ontario, Canada, Delcam is a developer of software for complex surfaces and tooling.

"When we checked the geometry, everything was right where it was supposed to be," said Doers. "There were a couple of minor problems, of course, but much less than could be expected with jobs of this size and complexity."

High praise came from the foundry, too. "The whole thing went really well and a lot of it was due to the modeling and machining software used by Central Pattern," said Darryl Slak, president of Waterford Aluminum. "The geometric models they created made it very simple and easy to cut some scaled patterns and half-sized models to verify the core assembly."

The quality of the design and machining of the tooling showed in the precision, which foundrymen describe in terms of tolerance "stack-up" in the cores. Cores allow foundrymen to create hollow places inside cast parts. Stack-ups in core tolerances, however, are the bane of the foundryman’s existence. "We had to hold ten to fifteen thousandths (0.010 to 0.015 in.) on each unit. The tooling Central Pattern created let us do it."

As always with well designed tooling, the components went together on the third try, Slak said. "The first try," he explained, "is just to look at the way the tools run. The second try is for real. On the DeltaHawk engine block, we had to go back to Central Pattern for just one modification, out of all those surfaces on all those parts. The third set of components we cast was sent to the FAA for certification," he added. This four-cylinder V-block design generates 200 hp at 2,700 RPM with a turbo-supercharger. Eight-cylinder and two-cylinder versions are also under development.

What’s critical to the foundry is the close-over, the fit of the molding tools for the outside of the engine when closed over the mold and cores for the inside. The DeltaHawk engine required "stacking up" more than a dozen cores. Despite the complexity, the tooling held together tightly, with no "crushes"—where two pieces are jammed too tightly together—and no "fin-outs"—where two pieces didn’t quite close. "All those surfaces have to just kiss together," Slak said.

"There was no room for errors in alignment or stack-up," said Mark Patrick at Central Pattern, who did some of the tooling design and CAM programming. "If any errors occurred, it would have meant excess metal that has to be ground away by hand," he explained. "It would also mean that parts would have to be spot-matched for proper fit during assembly. Though cast separately, cored ports in the cylinders must align perfectly with those in the sleeve liners inserted after machining."

Misfits could mean a great deal of hand work for assemblers as well as reliability and maintainability problems later in the engine’s life cycle, especially with field replacements.

"For CAD we used PowerSHAPE, which was created for this kind of work," Patrick said. "For something like the DeltaHawk, we couldn’t rely on the traditional methods—modeling large portions of the job with several other types of software and allowing the machinists to create the proper fillets through their choice of cutters or modifying toolpaths. This tooling had to be done right to the data. No interpretation was allowed, not even on the smallest fillets. If we had tried that," he added, "we would end up with a scabby model full of miscellaneous information."

"We probably could have designed this tooling with other software packages," Patrick continued. "But it would have taken 15% to 20% longer and we would have had to do a lot of hack and patch work. Before PowerSHAPE, when the software we were using couldn’t generate a surface or a fillet as required, we would hack out the problem geometry, create the surface some other way, and patch the new surface back in. This is very time consuming," he noted. "And if the new surface is not blended very carefully, machining marks will be left on the surfaces at the edges of the patch."

Time was also of the essence. The patterns for the DeltaHawk engine were designed and built over a period of 10 weeks ending in July. Having spotted the potential market, several other firms are racing DeltaHawk to develop competing engines.

The complexity of the DeltaHawk engine block with its integral cylinder heads led to what Patrick termed "a great deal of in-house engineering." The integral heads added several degrees of complexity to what would normally have been a relatively simple core and mold assembly. The cores now had to incorporate passages to and from the cylinders. But this saved as much as one-third of the weight of more conventionally designed, so-called light-weight diesels.

The first thing Central Pattern did was physically model the block’s components, cutting them from Ren. "Doing this with PowerMILL was essential because not all the fillets were in place," Patrick said, noting that PowerMILL will skip right over the missing geometry (below a preset tolerance). The toolpaths can be easily manipulated to get some of the results that previously had to be developed on the model.

For this tryout work, a pattern maker need not have every last fillet in place to get usable parts. "We actually cut several physical test models and machined their core passages," Patrick added. "We literally played with them like a kid’s building blocks to see how all the engine mold and all the necessary cores would best go together." This was done with a block split down the center, a symmetrical half engine.

"As we stacked all these together, we got a basic idea of how the tooling would work," Patrick explained. "Then we plotted out a series of wireframe drawings and sent them to Waterford Aluminum. They added comments and adjustments for things like the cores and core prints." Core prints ensure there is enough room inside the mold’s cavity and core halves for the core’s necessary movement. "On the block, there was a lot of coring work to do internally to core things like cross-drilled holes for cooling."

Unlike most aircraft engines, the DeltaHawk is liquid cooled, another DeltaHawk advantage over the four-cycle air-cooled gasoline engines powering most UAVs. Being a diesel, DeltaHawk's engine actually runs hotter so liquid cooling is essential to a long service life, among other advantages.

Liquid cooling also extends the drone’s life. A cooler engine is harder to track with heat-seeker missiles. Another DeltaHawk advantage is simple toughness, the ability to survive battle damage. Even without coolant, the DeltaHawk can run almost indefinitely at half power. This gives it a far better "limp home" capability than conventional engines.

When these 2D drawings came back with the necessary manufacturing details, Central Pattern got to work with PowerSHAPE.

"The engine block and its integral components had a total of 1,400 surfaces," Patrick said.

These surfaces, the majority of the engine’s internal workings, were deleted because they were not directly formed by the tooling. Central Pattern deleted a few too many surfaces and had to regenerate them. Working with the software, however, this was done quickly, easily and accurately.

"At this point we used PowerSHAPE to draft all the model’s components to accommodate the 11 core boxes, 14 cores," Patrick said.

"Drafting" molded components means that any surfaces parallel to the opening of the mold must be angled one or two degrees. Undrafted components will not come out of the mold.

The software has several functions to help automate this critical work, beginning with a capability of assigning every surface in the original part geometry to half of the mold or the other. It also automatically creates a mold split or parting line between the mold halves. Note that the fingers sizes change as they step around the cylinder to accommodate air flows.

"PowerSHAPE was also invaluable in designing all the core prints, making sure everything that had to mate during molding had sufficient clearance to do so," Patrick added.

"This is also where we added the extra metal to allow for areas to be machined," Patrick said.

By adding metal in surfaces to be machined, the foundry assures there will be no porosity and inclusions which can force the part to be scrapped (and wreck machine tool cutters).

Two of the more challenging areas of tooling design are shown in the accompanying images. 

• Tooling the water jackets of the block. Water jackets are below the "fingers" visible in the cylinder head area of the block. The fingers’ precise location, shape, orientation, twist, and surface to surface blendings proved very difficult to model. The fingers hold nickel - silicon - carbide alloy cylinder sleeve liners in place. The design is essential to the engine’s ability to develop its high horsepower, a robust 1 hp/lb.

• Tooling the tops of the cylinder heads, the areas closest to the combustion, to keep them cool. A thin-section wall—the dark straight line in the image—was inserted to make sure the water circulates completely and efficiently.

"We were helped a great deal by getting good geometry in from DeltaHawk as files and models from I-DEAS (the mechanical design software of Structural Dynamics Research Corp, Milford, OH)," he added. "They designed the engine very well but did not try to add draft angles and similar things that are strictly needed for tooling and molding. They left that to us."

"We worked very closely with Central Pattern," said Doers. "The quality of their work and the speed and power of their software tools were really good. We got what we expected—high quality tooling—and that was what we had to have."
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