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In a tight spot, you need zoom to maneuver.

By Jim Mathews
Air & Space Magazine, July 01, 2008

Remember the scene in the movie Top Gun when Navy pilot Pete “Maverick” Mitchell gets the upper hand on his instructors by slowing down, pulling up the nose of his F-14 Tomcat, and watching his opponent fly right by? The idea was to get a quick, unexpected position behind the bad guy, putting Maverick (played by Tom Cruise) and his trusty sidekick Goose into place to win the Engagement.

Real fighter pilots will tell you that what Maverick does is a showoff move that bleeds off so much energy that you’re vulnerable to getting shot down yourself. What a pilot really needs is a way to quickly get in the right position to fire at the enemy. Today’s most maneuverable fighters use thrust vectoring, which can make a jet turn faster and more tightly.

Powered by Pratt & Whitney F119 turbofans, each with 35,000 pounds of thrust, the F-22A—the Air Force’s newest fighter—sports a nozzle that can direct exhaust thrust up or down as much as 24 degrees.

The advantage to pilots is superior low-speed and high angle-of-attack maneuverability, compared to conventional-thrust aircraft, says Second Lieutenant Aaron Hoke, a propulsion engineer on the U.S. Air Force team that manages the Lockheed Martin F-22A Raptor program at Wright-Patterson Air Force Base in Ohio.

Continue reading ‘How Things Work: Thrust Vectoring’ »

By Joe Pappalardo

Air & Space Magazine, August 01, 2007

These days, fighter pilots’ helmets are nearly as complex as their airplanes. And with good reason: If the helmets can’t tell where the pilot is looking, many of the airplane’s systems, including weapon targeting, are useless.

The folks at Vision Systems International of San Jose, California, who have designed advanced U.S. military helmets for the F-15, F-16, and F/A-18, make their living at the nexus between man and machine. VSI’s flagship program is the Joint Helmet Mounted Cueing System. It uses a magnetic field in the cockpit to sense the orientation of the helmet, then feeds information on the current line-of-sight to the aircraft’s flight computer. VSI’s helmet has an accuracy of about four milliradians, an angular measure commonly used in the world of shooting and targeting. One milliradian equates to one one-thousandth the distance to the target. So if the target is 1,000 feet away, you’d be accurate to within a foot.

Determining where a pilot is looking by tracking eye movement is a much taller order. “You would not believe some of the human factor issues you have to overcome to have a successful eye tracker,” says Louis Taddeo, VSI marketing director. “Although we have research projects into eye tracking, it is a very difficult task both from a technical [standpoint] and the physiology.”

So for now, VSI uses helmet position to achieve that four-milliradian accuracy. Pilots need only turn their heads to aim their weapons, even during high-G maneuvers, freeing their hands for other tasks.

The head-up displays (HUDs) currently used in fighter aircraft are sophisticated, but they have a single, fixed point of view. Future helmets will include virtual displays projected across the visor, where the pilot can see information and targeting prompts. The F-35 Lightning II helmets due to enter service in 2012 will offer what Taddeo calls “extreme off-axis targeting.” Instead of having to turn the airplane toward the target to frame it in a fixed-view HUD, the pilot will be able to see targets that are off-axis, or not in the direction of flight. Like its predecessors, the Lighting II helmet will use magnetic head tracking, but VSI says the accuracy will be greater, courtesy of software upgrades that combine head position with eye location and data from the HUD.

Lockheed Martin test pilot Jon Beesley took the new helmet for a test drive last April in the first pre-production F-35. It was the first time a pilot in a tactical fighter had flown without a HUD in at least three decades. Expect more flights if the reviews are good.

Got a nagging question we can help you answer? Send an email to Joe Pappalardo at needtoknow@airspacemag.com

Some keep flying for decades, while others end up on the scrap heap.

By Rebecca Maksel

airspacemag.com, March 01, 2008

Source:  Air & Space Magazine

A reader asks: “Two articles in the Feb./Mar. 2007 issue of Air & Space raised a question. One was about the last flying examples of a number of classic planes (”And Then There Was One”). The other was about newer jetliners, too old to fly, being chopped up to make skateboards and soft drink cans (”We Recycle“). It struck me as odd that the old planes are still airworthy, while the jetliners are fit only for the scrap heap. Why can some planes seemingly keep flying forever, while other, newer ones are already used up?”

An aircraft’s lifespan is measured not in years but in pressurization cycles. Each time an aircraft is pressurized during flight, its fuselage and wings are stressed. Both are made of large, plate-like parts connected with fasteners and rivets, and over time, cracks develop around the fastener holes due to metal fatigue.

“Aircraft lifespan is established by the manufacturer,” explains the Federal Aviation Administration’s John Petrakis, “and is usually based on takeoff and landing cycles. The fuselage is most susceptible to fatigue, but the wings are too, especially on short hauls where an aircraft goes through pressurization cycles every day.” Aircraft used on longer flights experience fewer pressurization cycles, and can last more than 20 years. “There are 747s out there that are 25 or 30 years old,” says Petrakis.

How do airlines determine if metal fatigue has developed in their passenger-liners? Bob Eastin, an FAA specialist on aircraft fatigue, says, “[Airlines] are really relying on the manufacturer’s maintenance programs. The manufacturers design the aircraft to be trouble-free for a certain period of time. There are maintenance actions to preclude any catastrophic failures, but that’s not to say that the aircraft might not [experience metal fatigue] before those times…. When you get to a certain point [in the aircraft’s lifespan], you need to inspect or replace certain parts.”

Nondestructive evaluation (NDE) inspections are used both during production (to ensure that components start out free of defects) and during an aircraft’s service life to detect cracks as small as 0.04 inch. Inspectors might, for example, take a close look at fastener holes located at the wing and spar junction.

We contacted NDE experts Deborah Hopkins of Lawrence Berkeley National Laboratory and Guillaume Neau, of Bercli, LLC, who together answered in an e-mail: “The challenge in developing an easier and less expensive inspection strategy is to design a technique that can be used from the skin side (of the wing), that does not require removal of the fastener, and that provides the same or better resolution than the conventional method of removing the fastener.” Not having to remove the fastener is a big money-saver.

One commonly used method of NDE is ultrasonic phased-array testing, which analyzes the echoes from ultrasonic waves to reveal imperfections inside a material. By using several ultrasonic beams instead of just one, then varying the time delays between the beams, inspectors can look inside a material at different locations and depths, thereby determining the size and shape of any defects.

At present, million-dollar robotic inspection systems equipped with phased arrays are being used to inspect wings and composite fuselages for large commercial aircraft and jetfighters before they fly. “Most aircraft manufacturers and service providers—Dassault Aviation, Airbus, and Boeing, for instance—ensure the quality of their production with large-scale non-destructive testing systems,” Neau wrote in an e-mail. And while a million dollars may sound like a lot, “when put in perspective, the number is not so large,” he says. “If manufacturers discover a problem after assembly, the cost of dismantling and redoing the part or the scrappage waste is much higher than the inspection cost.”

Got a nagging question we can help you answer? Send an email to Rebecca Maksel at rmaksel@si.edu