Rail Locks 

for Strategic Brigade Airdrop

by Captain Mark L. Stoddard

In October 1999, Defense Week magazine asked, "What is so important about having a brigade on the ground in 30 minutes?" In response, Colonel John J. Kelly, Director of Operations of the XVIII Airborne Corps at Fort Bragg, North Carolina, said, "Historical studies and recent combat experiences have shown 30 minutes to be the minimum amount of time an enemy would need to adequately respond, following an airborne assault . . . The airborne brigade task force is the lead element of our Army's strategic forced-entry power projection capability."

Successfully putting an airborne brigade task force on the ground in 30 minutes rests on the certification of the revolutionary C-17 dual-row airdrop system (DRAS). Due to the scheduled retirement of the C-141 fleet, the C-17 Globemaster will be the only aircraft available to support strategic brigade airdrop in 2002. To certify the DRAS by 2002, the Department of Defense needs to procure new logistics rail-lock assemblies designed for gravity-release airdrop that will have minimal impact on current airdrop rigging procedures for the 82d Airborne Division.

Dual-Row Airdrop System

The C-17 DRAS uses the dual logistics rail systems within the aircraft instead of the aircraft's conventional airdrop rails. The dual logistics rails were designed for rolling vehicles, equipment, and supplies on and off the aircraft, not for airdrop. The DRAS goal is to maximize C-17 airdrop capabilities by simultaneously dropping eight 16-foot modified equipment or supply platforms (20 inches narrower than the type-5 platforms now used) using a gravity-release system. Currently, the DRAS can release loads only in sequence. According to First Lieutenant Dave Huxsoll of the Air Force Aeronautical Systems Center Public Affairs Office at Wright-Patterson Air Force Base, Ohio, the idea of using C-17 logistics rails for airdrop began with a Boeing loadmaster. Boeing proposed the idea to the Air Force, and the C-17 Support Office conducted initial testing in the spring of 1997 at Edwards Air Force Base, California.

Cargo loaded on aircraft for dual-row airdrop using logistics rails. Cargo loaded on aircraft for dual-row airdrop using logistics rails.

Problems with Logistics Rail Locks

According to Thomas Hammond, Chief of the C-17 Test Division, Airborne and Special Operations Test Directorate (ASOTD), at Fort Bragg, the biggest problem encountered thus far with DRAS is the failure of the logistics rail locks to release the airdrop load when the aircraft is at a nose-up deck angle of about 7 degrees, which is the standard attack angle used for all gravity-release parachute drops. The combination of the high angle and the stress of the load weight (14,500 pounds in many cases) causes the rail locks to bind as the load is released. According to Hammond, "The reason the rail locks are failing is because the rails on the C-17 were designed as logistics rails and not airdrop rails." In support of Hammond's statement, Bill McQuillan of the Air Force Flight Test Center Public Affairs Office at Edwards Air Force Base said during early testing of DRAS, "The testers had to determine the optimum angle of the aircraft's deck for gravity-dropping cargo while allowing the locks to function properly . . . the locks were not designed for airdrop operations."

According to Alec Dyatt, the 418th Flight Test Squadron's DRAS project engineer, "There's a fine line with an aircraft that's gravity-dropping cargo. If the deck angle of the plane is too steep, the locks can't retract back into the deck because the weight of the cargo on the side of the lock keeps the lock from moving. If the deck angle is too shallow, the lock can retract easily, but the cargo falls out too slowly and is dispersed over a wide drop area. The optimum deck angle is as steep as possible while still allowing the locks to retract. This way, the cargo drops quickly and remains close together, making it easier and faster for ground troops to re-cover the equipment."

Effects of Decreasing C-17 Nose-up Angle

When C-17's nose-up angle is lowered to 4 degrees, the logistics rail locks will successfully release all loads using the DRAS. Unfortunately, at a 4-degree nose-up angle, the high center of gravity of the load causes the platform loads to invert past the vertical position upon release from the plane. The platform inversion creates great stress and instability on the platforms and cargo parachutes, causing the loads to turn into each other and become damaged during descent and landing. During initial DRAS testing at Edwards Air Force Base, some platforms broke in half, and about 80 percent of the cargo parachutes were seriously damaged.

With an airdrop using the airdrop rails and a 7-degree nose-up angle on the aircraft, loads do not invert. With an airdrop using the airdrop rails and a 7-degree nose-up angle on the aircraft, loads do not invert.

To allow safe cargo release from a 4-degree angle, the ASOTD has made the following costly, labor-intensive airdrop component changes: adjusted the center of gravity rearward on all 16-foot platform loads to between 81 and 88 inches instead of 96 inches; used a 22-foot ring-slot stabilizing parachute to prevent platform inversion; and used an existing attitude-control bar that is placed in the riser extensions of the cargo parachute to aid in deployment during exit. Using the stabilizing parachute and attitude-control bar has decreased the rollover problem when using 16-foot type-5 platforms on C-130 aircraft. More modifications to the loads may be necessary since no testing has been conducted using these new gravity-release system components with the new modified platforms on C-17's.

Effects of Center of Gravity Changes

Changing the center of gravity on DRAS loads will have the single greatest impact on strategic brigade airdrop, drastically changing the way the 82d Airborne Division rigs its loads for airdrop. The assembly-line technique currently used at the heavy-drop rigging site at Fort Bragg will have to be completely overhauled to accommodate the new DRAS rigging procedures. For example, some loads using cargo parachutes rigged on the front of the load will have to be rigged at the rear of the load. As a result of the center-of-gravity change, riggers in the 82d Airborne Division will have a hard time meeting the exactness of new procedures for the DRAS loads.

The DRAS changes are slowing the certification of DRAS because they are new, unproven, and labor-intensive. At a minimum, a detailed cost analysis is needed to compare the total cost of procuring C-17 airdrop rail locks to the total cost of the DRAS airdrop component changes being developed by ASOTD. Limiting the number of time-intensive departures from current airdrop rigging procedures by using specially designed C-17 airdrop rail locks is the key to meeting the DRAS fielding requirement in January 2002.

Specially designed C-17 rail locks will permit an increase in the deck angle to about 7 degrees, the proven angle for all gravity release static-line-deployed parachute drops. Using the 7-degree angle will eliminate the need to change the center of gravity or to use an attitude-control bar and 22-foot stabilizing parachute for each load.

Raising the C-17 nose-up angle will simplify rigging and logistics and minimize changes in new rigging manuals as they are published. Existing doctrine and procedures will be used as much as possible with new DRAS loads.

Though the existing C-17 logistics rails are being used for airdrop, they are not intended for such use. The changes in equipment and procedures needed to make the rails work effectively will be costly, requiring purchase of new equipment and a change in rigging procedures. Ensuring the success of the Army's strategic forced-entry power projection capability in 2002 requires attacking the DRAS gravity-release problems at the root by developing and procuring C-17 airdrop rail locks to meet both short- and long-term requirements of the strategic brigade airdrop. ALOG

Captain Mark L. Stoddard is serving in the 2d Infantry Division Support Command, Korea. He is a graduate of the University of Utah, the Aerial Delivery Materiel Officers Course, the Jumpmaster Course, the Civil Affairs Course, the Infantry Officer Basic Course, and the Combined Logistics Captains Career Course.