Plane Parachutes

Boris Popov, the founder of Ballistic Recovery Systems Inc. (now known as BRS Aerospace), successfully brought to market a comprehensive aircraft parachute recovery system.2 In collaboration with NASA, Popov’s team secured funding to advance the development of thin-film parachutes, continuous reinforcement manufacturing techniques, and intelligent deployment devices with the aim of achieving optimal parachute strength while reducing weight.2 The weight requirement for the system was set at under 60 pounds.3 To date, the Cirrus Airframe Parachute System (CAPS) has already saved 246 lives.

An activation cable triggers an igniter that launches a solid-fueled rocket motor, propelling the parachute at speeds exceeding 100 mph and deploying it within a second.2 An attenuation device regulates the chute’s opening in accordance with the aircraft’s velocity; at high speeds, the chute opens gradually to 25% to mitigate airspeed, then fully opens to withstand the shock and prevent passengers from experiencing excessive g-forces.2 The aircraft’s descent is halted, and landing on the ground is similar to falling 7-10 feet (with the landing gear and seats absorbing most of the impact).2

The unharmed passengers and plane prompted one US insurance company to offer up to a 10% discount on premiums for aircraft equipped with this system.3 This life-saving technology is useful in cases of plane structural failure, icing, or engine failure and could prevent up to 1,000 lives from being lost annually in general aviation out of the 1,600 accidents that occur. The system is now a standard feature in 4-10 person aircraft models such as the Cirrus SR20 and SR22, Flight Design CT LSA (light-sport aircraft), Piper Aircraft PiperSport LSA, and is an optional addition to the new Cessna 162 Skycatcher.2 Furthermore, retrofitting this system into existing aircraft is possible with minor modifications to the structure to handle the increased forces.

The tragic crash of Air France Flight 447, which resulted in the loss of 228 lives on June 1, 2009, has prompted the aviation industry to consider the feasibility of utilizing parachutes on commercial planes.4 While research into this concept is ongoing, there is a need to explore additional safety measures that could complement the use of parachutes, such as the safety foam seen in the film “Demolition Man” and techniques for water landings.1

However, the current leading technology of parachutes can only withstand up to 4,000 pounds, limiting its application to smaller planes.4 For instance, the CAPS system, which uses a parachute, is only suitable for planes weighing up to 2,000 pounds with a cruise speed of 175 mph.4 Commercial airliners, on the other hand, can weigh anywhere from 37,200 pounds for the ATR 42-500, which seats up to 52 people, to 1,138,000 pounds for the A380-800, which can carry up to 853 passengers.

The classification of aircraft size is rated by the International Civil Aviation Organization, a specialized agency of the United Nations (UN), or the Federal Aviation Administration standards, which are based on qualitative data. Future studies are needed to determine the percentage of aircraft within a certain weight range, which could benefit from the use of a parachute. Despite ongoing research, it is currently not feasible to utilize parachutes on 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 = 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

To derive the equations, we set the drag force on the parachute equal to the weight of the aircraft. This ensures that the aircraft experiences zero acceleration as it falls (dv/dt = 0). For a loaded A380-800 with a mass of 516,188 kg, cruising through air with a speed of 560 mph and a top speed of 634 mph, the air density ρ is 1.229 kg/m3 and the force of gravity g is 9.81 m/s2. We assume a drag coefficient of Cd = 1.5 or Cd = 1.42 [7] for a true domed/hemispherical parachute type.

The parachute’s diameter seems appropriate for the aircraft’s dimensions, with a wingspan of 262 ft and a length of 239 ft. However, it’s important to consider the strength of the material and the load capacity of the suspension lines and harnesses. Zylon is the strongest material, with a 1 mm strand capable of holding up to 450 kg [11] with a yield stress of 815 kips. Using only one Zylon suspension line to lift a loaded A380-800 requires a diameter of 1.40 in². The tearing strength of the fabric depends on its thickness and density, tested through a tensile test as specified in ASTM D2261-13.12 Therefore, determining the wind speed the strongest parachute material can withstand and the load capacity of the suspension lines and harnesses are crucial for determining the parachute’s effectiveness and safety.

To determine the ideal fabric composition for parachutes, including the number and orientation of layers, as well as the size and quantity of voids, studies need to be conducted. After determining the appropriate number and size of parachutes required, further analysis is necessary to understand the force application rate, or impulses, on the aircraft and its passengers. An experiment conducted by a USAF pilot concluded that a person can withstand up to 32 g’s, whereas a Formula One racer survived a crash of 178 g’s, albeit with many broken bones.10 Additionally, modifications must be made to enable commercial jets to float in the event of a water landing as they are not inherently buoyant.

Large engineering programs, such as the Airbus, often experience delays in producing their first article, which can be attributed to various factors. One such factor is the use of composites, which lack natural electrical conductivity. Unlike metal, which offers a natural electrical return path to dissipate electricity in the event of lightning strikes, composites require wire mesh and electrical bonding to establish an electrical return path. The Airbus program faced such challenges, resulting in a delay in the delivery of 97 out of the planned 262 planes between 2001 and 2013.13

Similarly, Boeing’s 787 Dreamliner program has been plagued with various issues, resulting in the grounding of 17 planes and reportedly losing £10M per month. These issues include battery explosions, engine and windshield cracks, faulty wiring leading to electrical problems, fuel line leaks, brake issues, and oil leaks.6 While it may be a tough financial sell, having a safety net in case of life-threatening failures seems worthwhile considering the multitude of problems encountered.

The A380 has major structural sections of the A380 built in France, Germany, Spain, and the UK, so close collaboration is necessary since the parachute(s) would attach to multiple locations on the fuselage.13 Another idea, inspired by NASA, involves incorporating capsules within the body of the plane, situated between the cockpit and the tail, to house the passenger seating area. These capsules would be equipped with the ability to detach from the fuselage.4

References

  1. “50 Fictional Technologies We Wish Existed”. Complex. Pop Culture. 11 Feb 2011.
  2. “Rocket-Powered Parachutes Rescue Entire Planes”. NASA Spinoff. 2010.
  3. Chris Rink. “NASA Helps Create a Parachute to Save Lives, Planes”. 20 Nov 2002.
  4. AirAsia. “Parachutes for Planes?” 1 Mar 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. “A list of Boeing 787 Dreamliner problems”. The Mercury News. 15 Jan 2013.
  7. Giorgio Guglieri. “Introduction to Parachute Subsonic Aerodynamics”.
  8. Tom Harris. “How Aircraft Carriers Work”. Landing on an Aircraft Carrier”. howstuffworks.
  9. “What is the maximum G force a human can survive?” Yahoo Answers.
  10. “Japanese Technology Creates Some of the World’s Strongest, Biggest… and Smallest Products”. Web-Japan.org.
  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)”. 23 Nov 2017.
  12. “Airbus A380″. Wikipedia.
  13. “List of airliners by maximum takeoff weight”. Wikipedia.

Figures

plane velocity during recovery
Figure 1
plane parchute
Figure 2
plane parchute
Figure 3
plane parachute
Figure 4