Air Transportation: Low, Slow And Out The Back Door


June 22, 2011: The U.S. Department of Defense is currently spending some $11 million a month for one-use, low altitude cargo parachutes. These low velocity parachutes were developed by the U.S. Army five years ago as a cheaper alternative to the more expensive low altitude parachute the air force was already using. These parachutes are also quite accurate when delivered from aircraft (or helicopters) flying low (under 400 meters/1200 feet) and slow. Coming like that puts less stress on the cheap parachutes and insures an accurate drop.

This type of parachute was a timely development because, in Afghanistan, there's a growing crises with supplying the troops. This is especially true because in the last year more and more American troops arrived and were dispatched to remote bases and outposts. There are over 300 American bases that have to be supplied either by truck, or by air. There aren't enough helicopters to do this, and it's often too dangerous (because of the Taliban, the terrain or the weather) to do it by road. So air drops are increasingly favored. But even here, there are problems that have to be taken care of.

Often, accuracy is needed for the drops (because of the presence of hostile forces or very rough terrain). Air dropped supplies have landed, on average, within 185 meters of the aim point when dropped from higher altitudes. This is often necessary when there is a risk of enemy fire. For that, there are GPS guided pallets can land within 50 meters of the aim point. So when greater accuracy is needed (or it has to be done at night), a GPS guided parachute rig is used. But there is now a problem with getting these GPS parachute guidance systems back. The rigs are built to survive 20-30 drops, and even though helicopters visit the isolated troops periodically, and can bring back the several hundred pounds of equipment that comprises each GPS rig, there are still too many of them stranded out there. The army is in the process of obtaining helicopter UAVs to carry cargo, and to land and recover GPS parachute rigs.

Another problem is the many mountain peaks and ridges. The GPS guided rigs go for the spot on the ground. The GPS sees only a straight line, between where the GPS chute was dropped, and the GPS location down there. There is no way to to detect and avoid any mountainous terrain that's in the way. Because of this, airdrop supervisors and pilots have to carefully plan the drops. There are several solutions to this in the works, including flight planning software that will calculate the optimum altitude and location for making a drop. There are still problems with unpredictable winds (that overwhelm the guided parachute's ability to compensate.)

In most cases, the low altitude drops, get the job done. For other jobs, the GPS guided rigs are still available. The air force has developed JPADS (Joint Precision Airdrop System) and ICDS (Improved Container Delivery System). Both of these systems work by using parachuted pallets of supplies equipped with GPS, and mechanical controls, to guide the direction of the descending parachute to a pinpoint landing.

Before the development of GPS guided air drops, a large percentage of air dropped supplies were lost, either by falling into enemy hands, or into things that destroyed them (especially water). With the GPS delivery systems, it's possible to do night drops, which is preferred when you don't want to alert nearby enemy troops. Often, you can accurately drop pallets without the GPS systems, if you have a large flat drop zone, daylight, and calm winds. But if conditions are difficult, you now have GPS guided drops. Otherwise, a low level, day time drop from a C-130, will get the job done.

There are other alternatives. Last year, the U.S. Army conducted tests of a helicopter UAV parachuting supplies. The K-MAX UAV was originally designed as a single seat helicopter that could carry sling loads of 2.8 tons (6,000 pounds) at sea level, or two tons (4,300 pounds) at 4,800 meters (15,000 feet). The recent tests involved using the army low altitude parachute, which can deliver loads of 36 kg (80 pounds) to 273 kg (600 pounds) at heights of 48-100 meters. The K-MAX had a special rig that could carry and release four different payloads, and demonstrated its ability to drop each one at a different location. The low altitude drops are more accurate than higher altitude ones, and useful where the troops getting the stuff are on hilly ground that has few good helicopter landing zones. The army is also planning to test using K-MAX to drop loads from higher altitudes, using GPS guided parachutes. The army and marines are planning to obtain their helicopter UAVs to drop supplies via parachute to troops in isolated areas.





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