Fluid Handling and Fluid Power

Technology Focus part 1

The U.S. Armed Forces are counting on unmanned combat air vehicles to play a bigger role in national defense in the not-too-distant future. There's a lot of upside to using unmanned vehicles in dangerous situations, but one big downside: refueling. Currently, the unmanned vehicles can fly only a very limited distance before needing to return to their base for refueling. Engineers at NASA's Dryden Flight Research Center in Edwards, Calif., are working with the Department of Defense to solve this problem.

NASA, the Defense Advanced Research Projects Agency, the Air Force Research Laboratory, the Naval Air Systems Command, the Naval Air Force-Pacific Fleet, the Canadian Air Force, and aerospace companies Boeing and Northrop Grumman are cooperating to develop a versatile model for the refueling of unmanned aircraft.

NASA Dryden is using two F/A-18 aircraft, one as the tanker and one as a surrogate receiver, to study the performance of the drogue basket during automated aerial refueling of unmanned combat aircraft.

NASA Dryden's piece of the puzzle in the Automated Aerial Refueling project is to model the behavior of the refueling tanker's drogue basket—the connector at the end of the fuel line—during the aerial refueling process.

"Our task is to define the aerodynamic model of the refueling drogue basket when in the receiving aircraft's forebody wake," said Gerard Schkolnik, NASA Dryden's AAR project manager. According to Schkolnik, the wake off the nose of the receiving aircraft affects the behavior and stability of the drogue basket.

To create this aerodynamic model, NASA Dryden is conducting flight tests using two specially outfitted F/A-18 aircraft. One of the older F/A-18 planes, a one-seater, has been outfitted with a Navy aerial refueling store (or tank) and drogue basket to serve as the airborne tanker in the aerial refueling scenario. A second F/A-18, a two-seater, is serving as a surrogate for the unmanned aircraft; it has a pilot onboard who can take over should the need arise. Both aircraft are equipped with special instrumentation and relative guidance control systems, Schkolnik said.

"We're modeling the drogue's behavior in a piecemeal fashion. We're modeling the receiver effect, the characteristics of the drogue, and the hose effect. If we can do that, it's possible for companies like Boeing and Northrop Grumman to substitute their wake effect data and know how the drogue will behave when used near their unmanned aerial receiver vehicles," Schkolnik said. Boeing and Northrop Grumman are very interested in developing automatic aerial refueling capabilities for their unmanned combat air vehicles.

The automated aerial refueling project is intended to run for up to one year. NASA Dryden has completed the first phase of flight testing, which involved developing the in-house tanker capability for serving unmanned vehicles. The second phase of testing, which involves running flight tests with two aircraft outfitted with video instrumentation systems, will run through June. The system uses two video cameras on both the tanker and receiver in order to triangulate the position of the drogue basket relative to the position of the planes.

The flight tests will be run under two sets of conditions. The first condition calls for the tests to be flown at low altitude, to mimic the U.S. Navy's method of refueling an unmanned aircraft near a carrier. The second set of conditions involves refueling at high altitude, to replicate the en-route refueling approach used by the U.S. Air Force.

Schkolnik plans to deliver the aerodynamic model of the drogue's behavior by the end of September.

The Department of Energy's Sandia National Laboratories and the Bureau of Reclamation have released a road map to define a research and development path for desalination technologies. This research, which the plan calls for to continue through 2020, would support finding solutions to the nation's water supply-related needs by advancing water desalination technologies.

Desalination technologies could change the way the nation manages and uses water by providing processes to cost-effectively and efficiently remove salts and other contaminants from impaired waters.

"Cost reduction is the single most important factor necessary to increase the implementation of desalination, which will in turn reduce pressure on our limited fresh water supplies," said John Keys, commissioner of the Bureau of Reclamation.

The desalination road map identifies 10 areas of emphasis, which address ongoing research and economic concerns. Some of these areas include improving membrane processes for treating brackish and salt water; improving thermally driven desalting processes; investigating alternative desalination techniques, and determining if these processes are economically and thermodynamically efficient. In addition, the road map calls for research into innovative methods for treating municipal, industrial, and agricultural wastewaters, and designing, constructing, and testing pilot-scale systems and demonstration plants.

On the economic side, the road map stresses the importance of studying ways to measure the economic efficiency of desalination technologies and for reducing concentrate disposal costs and impacts on the environment.

The Bureau of Reclamation has asked the National Academy of Sciences National Research Council to review the report and comment on it. The Research Council is also being asked to identify general priorities for research investments. A final report that incorporates comments from the Research Council and national desalination experts will be issued later this year.

U.S. Navy aircraft carriers require large quantities of fresh water for drinking, but can't afford the space to carry all the water they need. So, they rely on shipboard desalination systems consisting of reverse osmosis and ultrafiltration membranes.

The 88 40-inch prefilter cartridges on those systems must be manually removed and replaced on a regular basis. To improve system reliability and cut down on manpower required to keep its desal systems running, the Navy is interested in deploying automated, self-cleaning, solid-liquid separation devices. The problem it faced was in deciding which one to choose.

A portable filtration test system, designed for the U.S. Navy by Sigma Design Co., runs a bio-slime mixture through a filtration loop to evaluate the effectiveness of solid-liquid separation devices.

Sigma Design Co. of Springfield, N.J., was subcontracted to design and build a portable filtration test system to evaluate the performance of six different self-cleaning, solid-liquid separation devices. The goal was to see how the filters performed in a marine seawater environment.

To mimic that environment, Sigma used a mixture it calls "bio-slime," a combination of seawater injected with suspended solids, including ISO test dust, silty-clay dirt, plankton, and brine shrimp, according to Jerry Lynch, owner and chief engineer of Sigma. The test system operates unmanned, with automated shutdown controls, and supplies seawater at 40 to 60 gallons per minute at 150 psi. The solids range from 3 parts per million to 225 ppm.

The test system injects the briny bio-slime mix into the inflow of the filter; from there, it washes through the rest of the system, until it reaches the recirculating tank. There are system dead-end filters, so the slime can be removed before the water is discharged, according to Lynch.

The tests, which have been completed, sought to establish how long it took until the separation devices got dirty, and whether they were able to self-clean to their original specs.

One of the tested devices has been selected for further evaluation. Sigma has built a complete filtration system using that device to conduct prototype tests that, it hopes, will validate the lab results.

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