Landing Gear

Not all landing gear tests require facilities the size of small towns or the ability to land the 787 Dreamliner, which is discussed in the March 2009 cover story of Cutting Tool Engineering magazine. As impressive as Boeing's landing gear tests are (visit the Boeing Web site to view a brief overview of Boeing's landing gear technology), CTE Plus takes a look at the other end of the spectrum.

Carter Aviation Technologies, Wichita Falls, Texas, is an aerospace R&D company, that has has invented and patented an ultra-high-energy-absorbing landing gear system. Carter, which has been flying on a prototype since1998, said, "The gear was designed to greatly improve safety margins duringlandings and should be scaleable to fit any aircraft."

The landing gear system uses a "Smart Strut," a hydraulic cylinder with a mechanical smartvalve, according to the company. "During the first inch of travel, the valve determines the impactvelocity, and automatically adjusts the pressure to provide a nearconstant deceleration for the remainder of the travel, with no rebound," the company Web site explained.

Carter noted, too, that the landing gear is designed to absorb as much impact from a crash landing as possible before it fails. Reported Carter, "The maximum pressure is kept below that which would cause yield untilthe gear bottoms out, which keeps the gear from failing until the maximumenergy possible has been absorbed."

The prototype system being flown onthe CarterCopter Technology Demonstrator uses an 18-inch stroke, and has been tested to absorb a1,200 feet-per-minute (fpm) landing impact with no damage to theaircraft or occupants. It will absorb a 25 fps impact with only minimumdamage, Carter reported.

The accompanying video shows tests of the original gear design as well as testing of the company's next generation landing gear design. Carter tested one gear toan impact velocity of 24 fps (1440 fpm) with 3,000 lbs. of weight.The drop height was 134" (107" until first impact, plus 27" of landing gearstroke).

What follows is a summary of the results from the Carter Web site:

The landing gear did not exceed the design limits, which were themselves only two-thirds of the load applied during the static proof test. The peak decceleration during the 24 fps test was 5g.

Depending on the weight being supported by the gear, the impact velocity could be varied accordingly, as long as the total energy being absorbed by the gear remains the same. For a 2,000 lb weight, that would be an impact velocity of 30.4 fps (1,824 fpm) and a drop height of 197". The total weight of the gear, including the rim, tire, brake and attachment hardware, but not including the pump used for retraction/extension, was less than 70 lbs. Note that these tests were for one gear supporting 3,000 lbs. For a typical airplane with two main gear, this translates to a 6000 lb gross weight.

Carter now has an improved version of its landing gear system that uses a hydraulic fluid that changes viscosity based on anapplied electrical charge. Using a 3' stroke, the new gear shouldabsorb up to 2,000 fpm landing impacts with no damage to the aircraft oroccupants, according to Carter.