Dirt runway testing increases C-17 safety, agility

  • Published
  • By Tech. Sgt. Eric M. Grill
  • 95th Air Base Wing Public Affairs
EDWARDS AIR FORCE BASE, Calif. --  In an effort to expand the capability of the C-17 Globemaster III, engineers and pilots are testing the aircraft in extreme runway conditions to eventually write the book for dirt runways during dry, wet, and muddy runway conditions.

About 40 people from the C-17 Integrated Test Force are in the midst of a four-phase test program to determine the C-17 takeoff and landing performance on non-paved surfaces.

The first phase of the flight tests was performed at Fort Hunter Liggett, Calif., where the C-17 was put through tests to validate the ability to bring a large force into an airfield without making runway condition corrections, said Lt. Col. Bob Poremski, C-17 Integrated Test Force director. Additional tests are to be performed here, as well as Fort Chaffee, Ark., and Fort McCoy, Wis.

Testing at Fort Hunter Liggett started with a dry landing zone "without re-grooming or re-preparing the runway to see if it's able to sustain rapid deployment operations with enough aircraft," Colonel Poremski said. "Once that phase was done, we progressively wet the ground in a controlled manner to correlate how much rainfall would happen if something like a thunderstorm rolls by and drops a quarter-inch of rain to see the effect it has on the braking action of the aircraft."

The purpose of the testing is to open up the capability to bring warfighters and equipment closer to the combat so there is not as much transit time, Colonel Poremski said.

"The C-17 was designed to deliver forces and cargo from an initial pick-up point and directly to the battlefield. This is called the direct delivery concept," he said. "But the original testing only cleared a small portion of the types of surface the earth is made out of. Our testing is expanding the types of surfaces the C-17 can operate in and out safely."

Performing tests on wet-semi-prepared runways proved to be a challenge, said Gus Christou, a mechanical subsystems engineer with the 418th Flight Test Squadron.

"The biggest concern we had was executing this test on a relatively short runway," Mr. Christou said. "Most of the runways with the exception of here are 5,800-feet long. For the wet-testing we proposed in the test plan, we really didn't have enough room to execute on a fully-wetted runway. So, we split the runway into a partial wet section and a partial dry section to ensure the aircraft could perform stopping as well as takeoff (again)."

There was also a computer modeling issue as well, he said.

The performance software that is currently available for the aircraft addresses both take offs and landings on wet and dry conditions for ordinary concrete runways, but in this particular case, there is a mixed condition runway, Mr. Christou said.

"The software that is available cannot predict performance of the airplane in that combination of dry, wet runways, he said. "That existing software had to be blended to be able to accommodate a dry and wet runway. It was very time-consuming."

In the end of the testing at Fort Hunter Liggett, the upgraded software models were able to accurately predict the aircraft performance.

"Performance was very-well predicted from the blending of the software for existing routines that were there," he said. "But it's quite a spectacular site to see this huge cloud of dust chasing you when you're taking off and then the same thing happening when you're landing - a dust cloud chasing you as you come to a stop.

The dust clouds and wet dirt, while spectacular to look at when the aircraft is taking off and landing, caused added some unusual aspects to the testing process.

"Through SPRO testing and weighing the aircraft after the take-offs and landings, we've seen anywhere from 1,200 to 1,500 additional pounds of dirt collected in the aircraft," Colonel Poremski said. "We've seen enough dirt collect in the wheel wells where it was eight to 10 inches of depth.

"However, those sorts of operations are not going to be typical with the aircraft in the field, because they might operate into a field and depart again," he said. "We've been up there with the dirt being wet, and we've repeated the landings multiple times throughout the day, thus helping to force the dirt up into the wheels."

There is also the maintenance aspect of the aircraft when dealing with so much collected dirt, said 2nd Lt. Mike Mohr, C-17 SPRO project manager.

"Our maintenance folks pulled off a tremendous job with the SPRO project," he said. "We're out there beating the plane up every day, landing in the dirt, landing in the mud and these guys are working 24-hours to get this plane ready for (the next-days flying).

"Well after we got into the mud, these guys had to fire hose (the aircraft) down to get the mud off," Lieutenant Mohr said. "Some of the instrumentation on the (landing gear) were kind of epoxied on, and we were having some calibration issues. There were all kinds of things pretty much all throughout the C-17 test the maintenance folks were dealing with, from the nose to the tail."

Colonel Poremski said the tests being performed have a special meaning.

"Having come from Air Mobility Command and being in the operational Air Force," he said, "and knowing how the men and women that operate the C-17 in combat day in and day out, are still using semi-prepared runway operations. It's acutely very satisfying and gratifying that I've been a part of the test and development of the charts that will allow them, my friends that are still operating the aircraft in combat, to operate more safely and more informed with how the runways affect their conditions, and ultimately, bring more supplies to the warfighter and conduct war operations."

The second phase of testing, taking place at Edwards, is set to begin after Thanksgiving, Colonel Poremski said. The entire four phases of testing is scheduled to be completed in November 2007.