Commander William Earl Fanin, Class of 1945, Capstone Essay Contest
Ram-air parachutes, widely used by special forces such as these U.S. Navy SEALs, are more expensive than conventional canopies currently used in ejection seats—but the cost is worth it when pilots' lives are at stake.
Forced ejection from an aircraft is a worst-case scenario for any aircrew member. Fortunately, modern ejection seats make the experience tolerable for most aviators. Unfortunately, although ejection seats have kept pace with technology, the device that ultimately is responsible for the safe return of an aviator to the ground—his parachute—has not. Modern square ram-air parachutes are much better alternatives to the current round parachutes used in naval aircraft ejection seats. Ram-air chutes provide a greater range of control and softer landings, perform at the extremes of the ejection seat operating envelope, and are compatible with existing ejection seat designs.
The main ejection seat in question is the Naval Aircrew Common Ejection Seat (NACES), currently installed in the T-45A/C, F-14D, and F/A-18C/D/E/F. The basic round canopy in this seat is more appropriately termed an aerodynamic decelerator; it will slow the rate of descent of an object, but (in the absence of wind or modifications to the canopy) the object will fall in a straight line to the ground. The GQ Type 5000 Aeroconical parachute in use in NACES is a 21-foot-diameter cone-shaped canopy constructed of 20 sections or gores.1 It is modified from a simple round by the use of Le-Moinge slots, located at two opposing gores, which allow for limited directional control and forward drive.2 If the slots have not been opened, the GQ Type 5000 has a rate of descent of 22 feet per second; when opened, the rate of descent is 20 feet per second.3
A ram-air canopy is more appropriately termed a parafoil. When inflated by ram-air pressure, the canopy takes on the profile of an airplane wing. The upper and lower surfaces are connected by a series of fabric membranes called ribs, which help maintain the proper shape and provide strength to the canopy. Suspension lines are attached to the load-bearing ribs. Two adjacent load-bearing ribs form a cell, which is usually separated into two half-cells by a non-load-bearing rib. Holes cut into the ribs, called crossports, balance the air pressure throughout the inflated canopy. Directional controllability is achieved through the use of steering lines. A ram-air canopy also has the unique ability to flare. This is a maneuver similar to that used by airplanes when landing. Simultaneously depressing both toggles the full range of the control stroke momentarily converts the downward speed of the parachute into lift, thus reducing the rate of descent. When performed correctly, this results in a very gentle landing, similar to stepping off a stair. A round canopy has no equivalent maneuver to slow its rate of descent. A higher rate of descent increases the potential for injuries on landing, as the force of landing is spread out over a shorter period of time.
In the absence of true wind, a ram-air canopy will glide while descending. Because it has a natural horizontal component of velocity, it can be flown into the true wind. If the true wind speed is equal to the forward speed of the ram-air, however, the canopy will descend straight down. If the true wind speed exceeds that of the forward speed of the ram-air, the canopy will be pushed backward at a speed equal to the difference. An important concept in the use of ram-air canopies is wing loading. Wing loading is calculated by dividing an individual's exit weight (weight of the person plus the weight of all equipment) by the area of the canopy. A person weighing 170 pounds and carrying 30 pounds of equipment would have a wing loading of 0.87 Ibs/square feet under a 230-square-foot canopy. Wing loading will affect the speed, both horizontal and vertical, of the canopy. Heavier wing loading will cause a canopy to fly faster when compared to a lighter wing loading of the same canopy.
Greater controllability is a strong argument in favor of using ram-air canopies in ejection seats. An ejected aviator could glide much farther because of the greater forward speed and lower descent rate. This would afford the aviator more options in choosing a landing site, whether to avoid hostile forces or airplane wreckage or simply to find an open field. If an aviator needed to lose altitude quickly, however, that could be accomplished easily by fully depressing one toggle, resulting in a diving spiral. A round canopy does not experience a comparable altitude loss on its much slower turns. In addition, if conscious and able, the aviator could perform a flare to ensure the softest landing and lower the risk of injury.
The difficulty in designing any canopy for use in an ejection seat is the wide operating envelope required. A canopy must safely land an aviator ejecting from the zero-zero condition (when the aircraft is on the ground with zero knots of airspeed and zero altitude) as well as during high-speed ejections (the current recommended maximum ejection speed for NACESequipped aircraft is 600 knots indicated airspeed).4 Designing a ram-air canopy to perform reliably at these two extremes is challenging, but not impossible. The concept was first explored by the Navy during the 1970s and 1980s at Naval Weapons Center China Lake, culminating in an in-flight test of a ram-air canopy in an ejection seat that demonstrated the feasibility of the concept.5 More recently, the idea of using ram-air canopies in the Air Force's Advanced Concept Ejection Seat II was studied by Performance Designs, Inc., one of the leading manufacturers of canopies for both civilian and military use. In tests conducted in 1998-99, Performance Designs demonstrated that a ram-air canopy could be deployed at speeds up to 285 knots and still satisfy the zero-zero deployment criterion.6 A 335-square-foot, seven-cell canopy constructed of low porosity nylon, the TR335, already in use as a military ram-air reserve canopy, was used as a base for further development of a canopy suitable for an ejection seat.7 It had a rate of descent of about 12 feet per second when flown by test pilots with exit weights of about 230 pounds.8
The wide range of weights of aviators also presents difficulties in designing a suitable ram-air canopy for ejection seats. For a smaller aviator, the benefit of having a ram-air would be the greater decrease in the rate of descent due to the lighter wing loading. In addition, the TR335 tested by Performance Designs easily scales down to a 305-square-foot model.9 In light of the wing-loading parameters, the smaller size may be advantageous. It would provide the smallest aviators with a higher wing loading, resulting in more forward drive, while still being docile enough to land the heaviest aviators safely.
Despite its noted advantages, one design concern must be overcome before a ram-air canopy could be placed in an ejection seat. At both ends of the operating envelope, line sail is a significant problem. Line sail occurs when the suspension lines become slack before the canopy is fully inflated. This is dangerous because it could lead to a malfunction if a suspension line were to pass and remain over the uninflated canopy. This type of malfunction can result in a fast turn leading to a high rate of descent.10 Although it has yet to be tested in a crosswind environment, the reefing system developed by Performance Designs on the TR335 performed well on the high-speed deployment, and it is believed that with slight modifications such a system could be capable of controlling line sail on zero-zero deployments as well.11
It would not be difficult to train aviators in the proper use of ram-air canopies. Static line training is ideally suited to teaching basic canopy control. Such training could be a part of every aviator's four-year swimming and survival training. Installing a ram-air canopy in the current head box container used in NACES could be accomplished with little difficulty as well. The TR335 tested by Performance Designs would fit in the current container.12
The notion that "round is sound" must be abandoned. The ram-air canopy is a better alternative, and its feasibility for use in ejection seats is proven. It is likely a ram-air would be more expensive than a round canopy, but considering its sole purpose is to save the life of an ejecting aviator, the cost should not be the primary concern. Millions of dollars have been spent to train aviators and billions spent to develop the systems they fly and employ. The system with the ultimate responsibility of returning them safely to the ground deserves greater attention.
1 Naval Air Systems Command, Organizational, intermediate, and Depot Level Maintenance with Illustrated Paris Breakdowns: Emergency Personnel and Drogue Parachute Systems, NAVAIR 13-1-6.2 Change 10, 1 December 2003, WP 026 00, p. 2.
2 Organizational, Intermediate, and Depot Level Maintenance, p. 2.
3 Naval Air Training Command, Naval Aircrew Common Ejection Seat (NACES) Lecture Guide, CNATRAP-1286, September 1999, 1-29.
4 Naval Air Systems Command, NATOPS Flight Manual: Navy Model FIA-18E1F 165533 and Up Aircraft, A1-F18EA-NFM-000, 1 March 2001, V-17-2; Peter Yost, senior engineer, Martin-Baker Support America, e-mail to author, 31 March 2004.
5 Manley C. Butler, In-Flight Ejection Seat Test Using the Aircrew Gliding Escape System (AGES) Parachute, NWC TP 6741, Naval Weapons Center China Lake, September 1986, p. 5.
6 Bill J. Coe, Square Canopy for the ACES (Advanced Concept Ejection Seat) Il Ejection Seat: Project Phase I Final Report, SBIR Contract No. F41624-98-C-5056, 14 April 1999, p. 42.
7 Coe, Square Canopy for the ACES 11, p. 8.
8 Coe, Square Canopy for the ACES 11, p. 8.
9 Coe, Square Canopy for the ACES II, p. 8.
10 Coe, Square Canopy for the ACES 11, p. 9.
11 Coe, Square Canopy for the ACES II, p. 43.
12 John LeBlanc, vice president, Performance Designs, Inc., telephone communication with author, 1 April 2004.
In August, Ensign Reese will report to flight school for training to become a naval flight officer. She hopes to fly in the F/A-18F Super Hornet. She is an avid civilian skydiver with more than 160 jumps. The author wishes to thank lieutenant David Benhke, USN; Aviation Structural Mechanic (Safety) First Class Scott Oram, USN; John LeB lane; and Peter Yost for their valuable assistance.