418 FLTS testers record highest cargo airdrop

Published July 20, 2011
By Kenji Thuloweit
95th Air Base Wing Public Affairs

EDWARDS AIR FORCE BASE, Calif. -- Testers at the 418th Flight Test Squadron brought another first to Edwards June 24..

A C-17 dropped a 60,000-pound cargo load over the Edwards range from 35,000 feet -- higher than ever before.

The squadron just wrapped up the airdrop portion of on-going testing of the Mode 5 Plus avionics software upgrade for the C-17 Globemaster III. The drop test was part of the "Plus" portion of the software.

"Right now, without major command approval, the highest altitude we can drop cargo from is 25,000 feet," said Capt. Michael Baker, 418th Flight Test Squadron C-17 flight commander. "Because of the areas we are operating in overseas, there seems to be a trend or push to do airdrops from higher altitudes. So we're trying to improve that capability in the C-17."

The upgraded software increases the Globemaster's airdrop capability.

Once a load is released out the back, the aircraft tends to pitch up. As a result the plane wants to climb, which could cause the aircraft to quickly rise 200 to 300 feet of altitude. The software allows a more precise way of doing the airdrop.

"What we're trying to do is reduce the altitude deviation that occurs as the nose pitches up and the climb starts occurring," said Baker. "Mechanically, the spoilers on the aircraft are rising up as the load goes out the back, killing the lift, thus stabilizing the aircraft on a specific altitude and reducing any altitude deviations."

The 418 FLTS chose the 60,000-pound weight because that weight is currently the heaviest weight the C-17 is certified to drop using a single pallet.

"That's really the worst case scenario [60,000 pounds at 35,000 feet]. What we wanted to do was exercise our flight controls to the max extent possible by doing a high altitude drop with a heavy weight," said Baker.

C-17s have dropped heavier cargo at 25,000 feet but not 35,000.

Baker said another unique aspect to the test was controlling the rate the load came out the back of the aircraft. The rate the load rolls out has a huge impact on the pitch rate of the aircraft.

He said engineers designed it so the cargo would release at between three to four seconds, which would force the C-17's flight controls to respond the most. They hit the mark at 3.8 seconds.

With the large weight, engineers were not sure the locks that hold the cargo would hold properly, so loadmasters had to time the release of the locks manually once they received the green light.

"Particularly for this mission the loadmasters were a very integral part," said Capt. Maryann Ehlen, C-17 instructor pilot and co-pilot during the mission.

The loadmasters released the 20 foot long, 8 foot wide, 60,000 pound platform of dirt over the range with success.

Both Ehlen and Baker said the airplane responded the way it should with the Mode 5 Plus software.

Ehlen said the altitude deviation during the drop was within 100 feet.

"It was pretty cool because it's not often in flight test where you actually get to do something for the first time, and being able to drop that high and heavy was pretty cool," said Ehlen.