Dirt runway testing increases C-17 safety, agility

Published Nov. 27, 2006
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, 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.

Engineers and pilots are testing the aircraft in extreme runway conditions to eventually write the book for landing on dirt runways during dry, wet, and muddy runway conditions.

Phase 2 is scheduled to get under way here Dec. 4. It follows lessons learned from flight tests conducted during Phase 1, which occurred between Sept. 16 and Nov. 8 at Fort Hunter Liggett, Calif.

According to Lt. Col. Bob Poremski, C-17 Integrated Test Force director, the first phase put the C-17 through tests to validate the ability to bring a large force into an airfield without making runway condition corrections.

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 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 zone so there is not as much transit time.

"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," Colonel Poremski 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 Edwards' 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 the Edwards runway, 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 also was a computer modeling issue. Mr. Christou said the performance software that currently is available for the aircraft addresses both take offs and landings on wet and dry conditions for ordinary concrete runways. However, in this particular case there is a mixed condition runway.

"The software cannot predict performance of the airplane on a combination of dry and wet runways," he said. "That existing software had to be blended 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.

"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," Mr. Christou said.

The dust clouds and wet dirt that arose from takeoffs and landings added some unusual aspects to the testing process.

"Through semi-prepared runway operations 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 to where it was eight to 10 inches in 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 also is the maintenance aspect of the aircraft when dealing with so much collected dirt, said 2nd Lt. Mike Mohr, C-17 semi-prepared runway operations, or SPRO, project manager.

"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."

The third and fourth phases are scheduled to take place at Fort Chaffee, Ark., and Fort McCoy, Wis., next year. Officials say all four phases of testing is scheduled to be completed by November 2007.