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Aircraft Landing Dynamics Facility Demonstration
09.14.05
 

NASA will fire one of the world's largest water guns on Saturday, Sept. 17, to celebrate the facility's 50th anniversary and test aircraft landing gear. The event will be open to the public.

It's a rush… literally. But don't blink. In less than two seconds, thousands of gallons of water and pressurized air propel a 54-ton (49-metric-ton) steel carriage mounted on rails to race car velocity.

The Aircraft Landing Dynamics Facility carriage rumbles down its track

Whoosh!

Image to right: The Aircraft Landing Dynamics Facility (ALDF) test carriage hurtles down the track. Credit: NASA
+ View Video (Quicktime)

But the fun isn't over yet. For our next trick we answer the equally difficult question of "How do you stop a semi going 200 mph in less than 600 feet?"

NASA's solution? We use cables, a lot like how jets land on aircraft carriers.

NASA calls this "water gun" the Aircraft Landing Dynamics Facility, or ALDF for short. As the world's fastest water-powered test facilty, it's a lot of fun, for sure. But it has also served an important role for five decades developing safer landing gear and tires for airplanes and the space shuttle.

We're celebrating that milestone by inviting everyone to see the unique facility at work.

NASA's Langley Research Center will open its gates at 9 a.m. on Saturday, Sept. 17. Test runs are scheduled for 10 a.m., noon and 2 p.m. Food, beverages and NASA merchandise will be on sale.

The rain date of the event is Saturday, Sept. 24. Visit Langley's web site for updates on the status of the event.

+ NASA Langley Research Center
+ Directions to NASA Langley
 

How It Works

The major components of the ALDF are the pressurized air and water propulsion system, a 54-ton (49-metric-ton) tubular steel carriage and the arresting gear at the end of the railroad-like tracks the carriage runs along.

The landing gear and tire to be tested are bolted inside the tubular steel carriage. This combined assembly runs over an 1,800-foot (549 meters) simulated runway. As the carriage passes over this test surface, the landing gear mounted inside it is slammed into the the runway to mimic an aircraft landing. Dozens of sensors radio real-time test data from the carriage to the researchers.

Launch of a test run at the Aircraft Landing Dynamics Facility

Image to left: Thousands of gallons of water and pressurized air catapult the Aircraft Landing Dynamics Facility test carriage down the track. Credit: NASA

The "water gun" that propels the carriage is comprised of an L-shaped container that holds 26,000 gallons (98,410 liters) of water, three air tanks pressurized at up to 3,150 pounds per square inch (2,214,669 kg/m2) and a high-speed shutter valve that controls the water jet.

At the beginning of each test, the shutter valve snaps open in less than half a second. The speed of the carriage is controlled by the length of time the shutter remains open. Operating at full capacity, the shutter stays open for two seconds, producing an 18-inch-diameter (46 cm) water jet and over 2,000,000 pounds of thrust! All that concentrated power results in a peak acceleration of 20 times the force of gravity and propels the carriage to 250 mph (402 kph) within 400 feet (122 meters)!

Unfortunately, you can't ride it.
 

About the Facility

The ALDF was called the Landing Loads Track when it was completed in 1956. Back then, the facility's maximum speed was about 125 mph (201 kph), and the test track was 2,200 feet (670 meters) long.

In 1985, it was upgraded to increase the test speed of the facility. The improvements doubled the maximum carriage speed and extended the track to 2,800 feet (853 meters). The test carriage was also redesigned to accommodate larger test items and withstand the higher acceleration loads. The upgrade allowed the facility to test experimental space shuttle landing gear and tire modifications.
 

All In A Day's Work

Research performed at the facility has led to a number of improvements in landing gear, aircraft tires, runways and even our highways.

In 1962, NASA Langley's hydroplaning program was looking for ways to increase aircraft tire traction and decrease braking distances on water-covered runways. The researchers concluded that the best way to help aircraft tires get a grip was to cut thin "grooves" into the runway pavement that would let the excess water drain off of the runway.

Results of tire test at the Aircraft Landing Dynamics Facility

Image to right: Some tires don't survive their time at the Aircraft Landing Dynamics Facility. Credit: NASA

After these tests were validated in the late 1960s and early 1970s, safety grooving was adopted for use on hundreds of airport runways around the world. Soon, the practice was adopted for use in highways, too. Today, every state in the U.S. has grooved at least some of its highway system. If you look carefully, you can even see this safety grooving at work in pedestrian walkways, ramps, steps, swimming pool decks and playgrounds.

ALDF tests have helped develop new tires for the space shuttle that are more maneuverable and durable, as well as more capable of landing on wet surfaces and carrying greater loads.

Commercial industries also use the facility to help make public transportation safer. Tire and brake manufacturers test prototypes here before moving ahead with production.

Boeing tested radial tires for use on its 777 wide-bodied passenger jet at the ALDF. Almost all cars use radial tires, but before the 777 nobody knew if they would work for airplanes.

The ALDF has even been used to research how well skids and air cushions would work as aircraft landing gear.

At only $50 per run, the facility provides an affordable way to perform safety tests that gives researchers an opportunity to detect and identify problems in an environment with no risk to pilots or aircraft.

 
 
Bob Allen
NASA Langley Research Center