Plane Parachutes

Boris Popov, founder of Ballistic Recovery Systems Inc. (now BRS Aerospace), has commercialized a complete aircraft parachute recovery system.2 By partnering with NASA, they received funding to help develop thin-film parachutes, continuous reinforcement manufacturing methods for parachutes, and smart deployment devices.2 The goal is to reduce weight while maintaining parachute strength.2 The weight requirement is less than 60 pounds.3 The Cirrus Airframe Parachute System (CAPS) has already saved 246 lives.2

An activation cable leads to an igniter that fires a solid-fueled rocket motor that shoots out at more than 100 mph and extracts the parachute in less than a second.2 An attenuation device constrains the chute to open according to the speed of the aircraft.2 At high speeds, the chute opens at 25% for a few seconds to reduce the airspeed, and then is opened fully, at which point it can withstand the shock, and the passengers do not experience extreme g-forces.2 The descent of the plane is arrested, and landing on the ground is equivalent to falling 7 -10 feet (a force largely absorbed by the landing gear and seats).2 The unscathed plane and people have led one US insurance company to offer up to 10% discount on premiums for aircraft with such a system.3 Situations where this could save lives are plane structural failure, icing, or engine failure. This could save 1,000 lives lost yearly in general aviation out of the 1,600 accidents that occur. This system is already standard on 4-10 person aircraft, such as the Cirrus SR20 and SR22, Flight Design CT LSA (light-sport aircraft), the Piper Aircraft PiperSport LSA, and as an option on the new Cessna 162 Skycatcher.2 In addition, existing aircraft can be retrofitted to include this system, with minor modifications to strengthen the structure to cope with the added forces.

The crash of Air France Flight 447, Airbus A330-200, on June 1, 2009, in which 228 people were killed, has the aviation industry taking a serious look at using this concept on commercial planes.4 The feasibility of using parachutes on larger commercial planes will be investigated. Future research is needed to assess whether other safety ideas could be used in conjunction with a parachute, such as the safety-foam shown in the movie “Demolition Man”.1 In addition, for water landings, breaking surface tension just before impact or gliding along the water surface helps stop the plane’s momentum in stages. The current leading technology allows a parachute to withstand around 4,000 pounds.4 The CAPS is used for planes weighing up to 2,000 pounds and having a cruise speed of 175 mph.4 The weight of an A380-800 airliner, which carries 853 people, weighs 1,138,000 pounds. The weight of commercial airliners vary depending on the make and model, and goes down to 37,200 pounds for the ATR 42-500, which seats 40 to 52 people. Qualitative data is used to rate the size of an aircraft in either International Civil Aviation Organization (an agency of the United Nations) or Federal Aviation Administration standards. Further studies are needed to examine the percentage of aircraft falling in a certain weight range to determine the percentage of aircraft for which the parachute could be used. It is not yet possible to lower the heaviest jets, such as the Airbus A380-800 and Boeing 747-8I.

Equations

  1. F = m *a (sum the forces on the plane)
  2. W – D = m *a
    • W = m *g (weight of plane)
    • D = ½ *Cd *ρ *v2 *A (drag equation)
    • m *a = m *(dv/dt) = 0 (acceleration of plane)
  3. m *g = ½ *Cd *ρ *v2 *A
  4. A = (2 *m *g) / (Cd *ρ* v2) = (2 *516,188 *9.81) / (1.5 *1.229 *(560)2) = 17.51 m2
  5. d = √ (4 *A /pi) (diameter of chute)
  6. d = 4.72 m

The equations are derived by setting the drag force on the chute equal to the weight of the aircraft, because we want zero acceleration of the aircraft as it is falling (dv/dt = 0). The cruising speed of the air (v) is 560 mph, with a top speed of 634 mph. The mass (m) of a loaded A380-800 is 516,188 kg. The air density ρ = 1.229 kg /m3 and the force of gravity g = 9.81 m/s2. The drag coefficient of chute is Cd = 1.5 or Cd = 1.42 [7] for a true domed / hemispherical parachute type.

The parachute diameter is reasonable when it comes to the size of the aircraft: wingspan of 262 ft (80 m) and length of 239 ft (73 m). The question remains, what wind speed can the strongest parachute material withstand (high porosity will help prevent failure, but result in less drag) and what is the load capacity of the suspension lines and harnesses (attaching at the chute and the aircraft). The strongest fabric in the world is Zylon, and a strand 1 mm thick can hold 450 kg [11] (yield stress: 814.937 kips or 3,625.02 kN). If only one suspension line made of Zylon was used, the required diameter to lift a loaded A380-800 is 1.40 in2. The tearing strength of the fabric depends on the thickness and density, and is tested using a tensile test (per ASTM D2261 – 13).12

Studies must be carried out to determine the optimal fabric makeup: layer quantity and orientation, as well as the size and quantity of voids. Once the number and size of parachutes are determined, further analysis is needed to understand the rate at which forces are applied (impulses) to the plane and thus to passengers. A USAF pilot experimentally determined that 32 g’s is something a person can walk away from, even though a Formula One racer survived a crash of 178 g’s, but this led to many broken bones and would certainly kill many on board the plane.10 Finally, commercial jets cannot float on water, so modifications would have to be made to allow them to float in the event of failure over the water.

Engineering marvels like the Airbus had delays producing the first article, and this is common for large programs. One cause was using composites which are not electrically conductive. Metal has a natural electrical return path, so that the electricity is dissipated through the structure if lightning strikes the plane. The groundbreaking solution was to add wire mesh and electrical bonding, so there is an electrical return path. Airbus is behind schedule delivering 97 of the planned 262 planes for 2001 to 2013.13 Boeing’s 787 Dreamliner is reportedly losing £10M a month because 17 Dreamliner planes are out of service. Problems include battery explosion and fire, engine crack, windshield crack, electrical problems due to faulty wiring, faulty fuel lines that cause leaks, brake problems, and oil leaks.6 This could be a tough sell financially, but with all these problems it seems worth having a safety net in case of a life-threatening failure.

The A380 has major structural sections of the A380 built in France, Germany, Spain, and the UK, so close collaboration would be required, since the parachute(s) would attach to the fuselage in multiple locations.13 There are other ideas, one that has NASA’s clear influence, which was previously developed for rockets that split the cabins.4 The body would have a few capsules between the cockpit and the tail.4 The capsule would house the passenger seating area and be equipped with the ability to detach itself from the fuselage.4 I predict parachutes will be implemented on commercial airliners and involve several chutes that are not launched at once, but staggered. The technology for using parachutes on commercial planes has been around for 30 years. Many solutions are currently available, but are not being implemented due to the cost of building and integrating parachutes into the planes.

References

  1. “50 Fictional Technologies We Wish Existed”.
  2. “Rocket-Powered Parachutes Rescue Entire Planes”.
  3. Chris Rink. (November 20, 2002). “NASA Helps Create a Parachute to Save Lives, Planes”.
  4. AirAsia. “Parachutes for Planes?” (March 1, 2012).
  5. Steven C Chapra. Applied Numerical Methods with MATLAB, “For Engineers and Scientists. The McGraw-Hill Companies, Inc., 2008.
  6. San Jose Mercury News. (January 15, 2013). “A list of Boeing 787 Dreamliner problems”.
  7. Giorgio Guglieri. “Introduction to Parachute Subsonic Aerodynamics”.
  8. Tom Harris.“How Aircraft Carriers Work”.
  9. Yahoo Answers. “What is the maximum G force a human can survive?”.
  10. Web-Japan.org. “Japanese Technology Creates Some of the World’s Strongest, Biggest… and Smallest Products”.
  11. “ASTM D2261 – 13 Standard Test Method for Tearing Strength of Fabrics by the Tongue (Single Rip) Procedure (Constant-Rate-of-Extension Tensile Testing Machine)”.
  12. Wikipedia. “Airbus A380”.
  13. “List of airliners by maximum takeoff weight”.

Figures

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