Carbon brake tests increase tanker's capabilities

  • Published
  • By 1st Lt. Brooke Davis
  • Air Force Flight Test Center Public Affairs
EDWARDS AIR FORCE BASE, Calif. (AFPN) --  Initial KC-135 Stratotanker carbon brake testing here discovered an increased operational capability over currently used steel brakes.

Test team experts, using a KC-135R from the Alaska Air National Guard, found carbon brakes stopped the aircraft in a shorter distance, allowing the tanker to take off with heavier loads and operate on shorter runways.

"We (used) aircrews from organizations around Edwards to man the aircraft and were able to complete the testing ahead of schedule despite setbacks from the summer heat, the odd testing hours required for brake tests and the busy runway schedule," said Sean Hamilton, a 412th Engineering Directorate flight test engineer.

Test experts accomplished one to two test points a day despite heat reaching 120 degrees in the tanker. The testers completed 24 ground run missions and multiple landings more than two months ahead of the predicted project completion date.

Among the carbon brakes' benefits include increasing the lifespan of the brakes to 1,000 landings from a previous 100 landings with the steel brakes, Mr. Hamilton said. The increased lifespan reduces costs of changing out brakes on the aircraft's 18 wheels every 100 landings.

Wet runway testing evaluated the brake anti-skid system.

"If the wheels 'lock-up' and skid on a wet runway, it reduces the pilot's ability to control the aircraft and bring it to a stop. Therefore, the anti-skid system needs to reduce the speed of the wheels without causing the aircraft to skid," Mr. Hamilton said.

The wet runway tests surpassed experts' predictions and provided adequate control for the pilot and excellent stopping performance, said T.J. Pitsor, a flight test engineer.

The carbon brakes also performed well on medium to high risk testing, experts said. The test experts stopped a heavy, fast-moving tanker in a short distance, putting a lot of energy on the brakes and generating high temperatures.

"High-brake temperatures heat the air inside the tire, causing the air to expand," said Dave Benson, another flight test engineer. "If the air expands beyond what the tire can hold, the tire and wheel can explode like a balloon. Fuse plugs release at certain temperatures, letting air out of the tire to avoid overheating, and the end result is just a flat tire, not an exploded tire and wheel."

During the highest energy test, test experts were able to stop and taxi 4,000 feet before the fuse plugs released, he said.

Another feature of the carbon brakes tested was the auto-brake function, which is designed to automatically engage right after takeoff when the wheels are retracting, Mr. Hamilton said.

"An aircraft is moving extremely fast in order to take off, and you can imagine how fast the wheels are spinning after takeoff," Mr. Hamilton said. "As the wheels spin, they change shape and may not fit into the wheel wells. So, the wheels need to be stopped (before) entering the wheel well, but if the wheels stop too quickly, the momentum could cause the landing gear to 'jerk,' possibly causing damage to the landing gear or wheel well."

He said the auto-brake function performed perfectly, allowing the gear to be retracted without any problems. (Courtesy of Air Force Materiel Command News Service)