Posted on February 10, 2012 - 13:58 by Trent Nouveau
Did you know that top-heavy structures are actually far more likely to maintain their balance while hovering in the air compared to those with a lower center of gravity?
According to Jun Zhang, a Professor at NYU’s Courant Institute, the recent findings are indeed counter common perceptions that flight stability can be achieved only through a relatively even distribution of weight - and may offer realistic new design principles for hovering aircraft.
As the Wright brothers demonstrated 100 years ago, the key challenge of flight is maintaining balance.
Yet, while insects took to the air 400 million years earlier, their flight stability remains a mystery because of the complex aerodynamics of their flapping wings.
The NYU researchers approached this enigma by creating experimental conditions required to achieve stable hovering in mechanical flyers.
To do so, they designed a range of pyramid-shaped "bugs" constructed from paper that hover when placed in an oscillating column of air - essentially mimicking the effect of flapping wings. The team then captured the experiment with high-speed videos to analyze the nature of the airflow around the bugs.
To gauge which types of structures best maintained their balance, the researchers created paper bugs with various centers of mass. Top-heavy bugs were made by fixing a weight above the pyramid, and low center-of-mass bugs bore this weight below.
Surprisingly, results indicate that the top-heavy bugs hovered stably while those with a lower center of mass could not maintain their balance.
The team also demonstrated that when the top-heavy bug tilts, the swirls of air ejected from the far side of the body automatically adjust to keep it upright.
"It works somewhat like balancing a broomstick in your hand," Zhang explained. "If it begins to fall to one side, you need to apply a force in this same direction to keep it upright."
For bugs, it is aerodynamical forces that provide this stability. Yet, as noted above, the lessons learned from these studies could definitely be put to good use in designing more stable and maneuverable flapping-wing robots.
New study finds hovering airplanes could become a reality; Military use possible
The State Column | Sunday, February 12, 2012
Hovering airplanes? Hover boards? It could all become commonplace, according to a study released Saturday, which finds that weight distribution contributes to the hovering ability of insects and other creatures.
A new study led by Jun Zhang, a Professor at NYU’s Courant Institute, finds that hovering in mid-air may depend more on weight distribution that once thought. Hovering in midair is easier for structures that are top-heavy, contrary to common perceptions about flight stability, U.S. researchers say.
To gauge which types of structures best maintained their balance, the researchers created paper bugs with various centers of mass. Top-heavy bugs were made by fixing a weight above the pyramid, and low center-of-mass bugs bore this weight below.
The results show that the most top-heavy bugs hovered stably while those with a lower center of mass could not maintain their balance.
“It works somewhat like balancing a broomstick in your hand,” said Mr. Zhang in a statement. “If it begins to fall to one side, you need to apply a force in this same direction to keep it upright.”
The results of the study could ultimately lead to the creation of a number of hovering prototypes, including military airplanes. Currently, there are a few airplanes that hover in calm air such as the AV-8 Harrier, and the V-22 Osprey, as well as a couple of others that have been built over the years. Some military aircraft either have vectorized thrust from their engines and/or enough thrust to hover on that alone, but this tends to be very inefficient from a fuel-consumption standpoint, and the amount of time during which the aircraft can hover is quite limited.
Electromagnetic Railgun World Record Shot on December 10, 2010
Uploaded by baesystemsinc on Dec 13, 2010
BAE Systems, along with partners IAP Research and SAIC, participated in a record-setting shot measuring 33-megajoules (MJ) of muzzle energy set by the Office of Naval Research's (ONR) experimental Electromagnetic Railgun launcher on December 10, 2010. The shot broke ONR's previously held world record of 10.64MJ of muzzle energy achieved in Jan. 2008.
A MJ is a measurement of energy associated with a mass traveling at a certain velocity. For example, a one-ton vehicle moving at 100 mph equals a MJ of energy.
The experimental Electromagnetic Railgun launcher used for the demonstration was developed through a team led by BAE Systems, after which BAE Systems showcased their advanced composite prototype railgun to Navy leaders.
BAE Systems received a $21 million contract from ONR in February 2009 to design and develop an advanced containment railgun prototype.
The ‘‘railgun’’ uses electricity to fire shells at over 5,000miles per hour. JOHN F. WILLIAMS/US NAVY
Shells fired from the railgun, developed by BAE Systems, could travel more than 100 miles, and the Navy could steer the missiles in flight to ensure they hit their targets. JOHN F. WILLIAMS/US NAVY
By Hiawatha Bray February 13, 2012
The Navy will soon test a futuristic weapon developed by BAE Systems, a defense contractor with operations in Massachusetts and New Hampshire, that uses electricity rather than gunpowder to hurl shells over 100 miles at more than 5,000 miles per hour.
BAE has delivered the weapon, called a railgun, to the Navy’s surface warfare center in Dahlgren, Va., for tests that are expected to begin this month.
Another defense contractor, Raytheon Co. of Waltham, won a $10 million contract to build a vital component for the railgun: a “pulsed power’’ system to enable the weapon to fire multiple shots without overheating.
“We’re looking at the railgun as something to put on a Navy ship,’’ said Roger Ellis, the Navy’s railgun program manager, adding it would eliminate the need for warships to carry large quantities of gun propellant and reduce the risk of onboard explosions.
Shells from such a gun could travel much farther than those from existing artillery, Ellis said. Because of the great distances, the gun would fire shells that could be steered in flight to ensure they hit their targets.
“You could do multiple missions with the same weapon,’’ said retired Admiral Nevin Carr, former chief of naval research. The same railgun could be used in attacks on enemy ships or shore targets that now require guided missiles. And railgun rounds would be relatively cheap.
“They don’t cost nearly what a Tomahawk or a Standard missile would cost,’’ Carr said.
A railgun works by sending powerful electric pulses through electromagnets in the barrel of the gun. The system generates an intense magnetic field that flings the shell down the barrel.
A pulsed power system builds up the energy needed to fire the gun, then releases it in a fraction of a second. Ellis compared it to the capacitor in a point-and-shoot camera, which slowly charges up and then releases its energy in a split-second to fire the flashbulb. But, he added, “We charge up about 50 million times larger than your typical camera.’’
Still, like a photographer, a naval captain needs the ability to fire again and again, with little delay between shots. The Navy’s goal is six to 10 shots every minute. Raytheon, BAE Systems, and a third defense contractor, General Atomics of San Diego, are working to develop a pulsed power system that can meet that challenge.
In addition, General Atomics will deliver a railgun system of its own to compete with the one from BAE Systems at the Dahlgren test site.
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