CRASH ATTENUATION SYSTEM FOR AIRCRAFT

Technical Field

The present invention relates generally to crash attenuation systems and specifically to crash attenuation systems for use in aircraft.

Description of the Prior Art

Currently internal airbags are used in the automotive industry within the occupied volume to mitigate occupant injuries. Similarly, external airbags have been used to attenuate decelerative loads to air and space vehicles, such as escape modules, upon contact with the ground or water. Examples include the NASA Mars

Rovers and the crew module of the General Dynamics/Grumman F-1 1 1.

During impact, the gas in the airbag must be vented to prevent gas pressurization and subsequent re-expansion, which may cause the occupant to accelerate backward. This effect is commonly known as rebound. In addition, the gas may be vented to prevent over-pressurization, which can cause failure of the airbag. Venting may be accomplished, for example, through discrete vents or through a porous membrane that forms at least a portion of the skin of the airbag.

One shortcoming of prior external airbag systems is that they fail to prevent post-impact pitch-over, or "tumbling," of an aircraft having a forward and/or lateral velocity at impact with a hard surface. For example, referring to Figures 1 a-1e, an aircraft 10 that is equipped with a prior external airbag system 12 is shown at different points during a crash sequence from (a) to (e). The crash sequence involves the aircraft 10 having both forward and downward velocities at (a) and (b). The airbag system 12 properly deploys its airbags 14 at (b), but still incurs serious damage due to pitch-over of the aircraft 10 as shown at (d) and (e). Thus, improvements are still needed in external airbag systems, particularly improvements to the pitch-over stability of an aircraft equipped with an external airbag system.

Brief Description of the Drawings

For a more complete understanding of the present invention, including its features and advantages, reference is now made to the detailed description of the invention taken in conjunction with the accompanying drawings, in which: Figures 1 a-1e show a crash sequence for a helicopter equipped with a prior external airbag system;

Figure 2 is a perspective view of a helicopter equipped with an external airbag system;

Figure 3 is a perspective view of an airbag used with the external airbag system shown in Figure 2;

Figures 4a-4c are a cross-sectional views of a vent valve in full-open, partially-open, and closed configurations;

Figure 5 is a diagram of the vent plate shown in Figures 4a-4c; Figure 6 is block diagram of the helicopter shown in Figure 2;

Figure 7 is a block diagram illustrating the operation of the crash attenuation system of the helicopter shown in Figure 2;

Figure 8 shows a chart of exemplary data representative of a relationship between airspeed of the helicopter and open vent area;

Figures 9a-9d show a crash sequence for a helicopter equipped with an external airbag system according to the present disclosure;

Figure 10 shows a cross-sectional view of an airbag of the external airbag system of the present disclosure; and

Figure 11 shows a perspective view of a helicopter equipped with an alternative external airbag system.

Description of the Preferred Embodiment

The present invention provides for an inflatable crash attenuation system for aircraft. The system comprises an airbag that is inflated prior to impact and controllably vented during impact so as to prevent aircraft pitch-over. The present invention may be used on all models of aircraft, for example, helicopter, fixed wing aircraft, and other aircraft, and in particular those that are rotorcraft. The system of the invention improves on the prior art by providing automatic control of the venting valves based on sensed crash conditions, thereby effectively shifting the center of impact pressure and preventing aircraft pitch-over. Figure 2 shows a helicopter 100 incorporating the crash attenuation system according to the present invention. Helicopter 100 comprises a fuselage 102 and a tail boom 104. A rotor 106 provides lift and propulsive forces for flight of helicopter 100. A pilot sits in a cockpit 108 in a forward portion of fuselage 102, and a landing skid 1 10 extends from a lower portion of fuselage 102 for supporting helicopter 100 on a rigid surface, such as the ground.

^• A problem with rotor 106 or the drive system for rotor 106 may necessitate a descent from altitude at a higher rate of speed than is desirable. If the rate is an excessively high value at impact with the ground or water, the occupants of helicopter 100 may be injured and helicopter 100 may be severely damaged by the decelerative forces exerted on helicopter 100. To reduce these forces, an airbag assembly 1 11 comprising inflatable, non-porous airbags 112, 114 is installed under fuselage 102. Though not shown in the drawings, airbags 112, 114 are stored in an uninflated condition and are inflated under the control of a crash attenuation control system (described below). Figure 3 is an enlarged view of airbag 1 12, which has a non-porous bladder

116, which is sealed to a housing 1 17 having a plurality of discrete vents 1 18. Airbag 1 12 is shown in Figure 3, but it should be noted that airbags 112 and 1 14 can have generally identical configurations. In a preferred embodiment, the bladder 1 16 is formed of a fabric that comprises Kevlar and/or Vectran. Vents 118 communicate with the interior of bladder 1 16, allowing for gas to escape from within the airbag

112. In the embodiment shown, vents 118 are open to the ambient air, though vents 118 may be connected to a closed volume, such as another airbag or an accumulator (not shown). Also, while a plurality of vents are shown in the embodiment illustrated in Figure 3, alternative embodiments can include only a single vent 118.

Referring to Figures 4a-4c, each vent 1 18 has a vent valve 120 for controlling the flow of gas through vent 118. Vent 118 and vent valve 120 together form a vent passage 122 for channeling gas flowing out of airbag 112. Each vent valve 120 is sealiπgly mounted in housing 117 (or bladder 116 in some embodiments) to prevent the leakage of gas around vent 1 18, which forces venting gas to flow through passage 122. A vent plate 124 is configured to be moveable between an open position, for example shown in Figure 4a, at least one intermediate position, for example as shown in Figure 4b, and a closed position, for example as shown in Figure 4c. Figure 4a shows vent plate 124 in the open position, or open state, in which a maximum amount of gas is allowed to flow through passage 122 from within airbag 112. Figure 4b shows vent plate 124 in an intermediate position, or intermediate state, in which a selected amount of gas less than the maximum is allowed to flow through passage 122 from within airbag 1 12. Figure 4c shows vent plate 123 in the closed position, or closed state, in which gas is prevented from flowing out of airbag 112 through the passage 122. Though only a single intermediate position is shown, it should be understood that various additional intermediate positions can be selected in order to control the amount of gas that is allowed to escape from within the airbag 1 12 through the vent 1 18. Also, while the vent valve 120 is shown as a sliding valve, it will be understood by one skilled in the art that vent valve 120 may alternatively be other suitable types of valves. Control of vent valves 120 may be accomplished though any number of means, including, for example, electrorheological means. In some embodiments, the vents 1 18 can be sealed with an optional pop-off pressure release mechanism, preferably a pressure sensitive fabric 125. In such embodiments, once the fabric 125 pops off, the vent valve 120 controls release of the pressurized air inside the airbag 1 12, 1 14.

. Referring next to Figure 5, as will be discussed in greater detail below, each vent plate 124 can be selectively positioned to any position between a full open position and a full closed position. In the view shown in Figure 5, the hatched area 127 represents the open vent area, through which gas can escape from within an airbag 112 or 1 14 through passage 122. The vent plate can be moved a distance A according to a desired amount of open vent area 127. The open vent area 127 will be a total open vent area "S" if there is only one vent 118; otherwise, the open vent area 127 of each vent 118 is summed to be a total vent area "S." The total vent area S is a function of crash conditions:

S = f{x,z,θ,φ,θ,φ, .. )

where x represents forward velocity, i represents downward or sink velocity, θ represents pitch angle, ψ represents roll angle, θ represents pitch rate, and φ represents roll rate.

Figure 6 shows airbags 1 12 and 114 mounted to a lower portion of fuselage 102 and show additional components of the crash attenuation system according to the present disclosure. A computer-based control system 126, which is shown mounted within fuselage 102, is provided for controlling the operation of components associated with airbags 112, 114. Each airbag 1 12, 114 has a gas source 128, such as a gas generator, for inflation of the airbags 1 12, 114. In some embodiments, a secondary gas source, such as compressed gas tank (not shown), can be provided for post-crash re-inflation of airbags 1 12, 1 14 so that the airbags 112, 114 can be used as floatation devices in the event of a water landing. The gas source 128 may be of various types, such as gas-generating chemical devices or compressed air, for providing gas for inflating airbags 1 12, 114. In addition, the crash attenuation system has a sensor system 130 for detecting crash conditions used to determine the total vent area S, such as rate of descent and/or ground proximity. Airbags 112, 114 can also have a water-detection system (not shown), which may have sensors mounted on fuselage 102 for detecting a crash in water. Gas source 128, vent valves 120, and sensor system 130 are in communication with control system 126, allowing control system 126 to communicate with, monitor, and control the operation

of these attached components. In addition, control system 126 may be in communication with a flight computer or other system for allowing the pilot to control operation of the crash attenuation system. For example, the pilot may be provided means to override, disarm, or arm the crash attenuation system. The sensor system 130 is shown in Figure 6 as a discrete component for the sake of convenience. However, it should be noted that actual implementations of the sensor system 130 can comprise a number of components that are located at various locations on the helicopter 100. For example, the sensor system 130 can include, for example, sensors for detecting pitch and roll attitude, pitch and roll rate, airspeed, an altitude, and rate of descent.

Referring next to Figure 7, an exemplary embodiment of the sensor system 130 is configured to detect various crash conditions, which can include, for example, one or more of the sink speed, forward speed, pitch and roll attitude, pitch and roll rate, and proximity to the ground of the helicopter 100. The control system 126 receives data from the sensor system 130 representative of the detected crash conditions. In a preferred embodiment, the control system 126 is a microprocessor- based system configured to operate as a crash predictor. When excessive oncoming velocity of the ground within a certain altitude range is detected by the control system 126, the gas source 128 is triggered to inflate the airbags 112, 1 14 (indicated at box 126A) prior to impact of the helicopter 100 with the ground. At the same time, the control system 126 activates the vent valves 120 to adjust the open vent area based on an active vent valve algorithm as indicated at box 126B.

Figure 8 shows an example of a relationship that can be used by the control system 126 for adjusting the open vent areas at 126B. In Figure 8, a chart is shown that illustrates a relationship between open vent area and forward velocity of a helicopter for a given sink velocity of 36 feet per second. The line 134 maps open vent areas to forward velocities for the forward airbag 112, while the line 136 maps open vent areas to forward velocities for the aft airbag 114. It should be appreciated that the relationship will vary for different sink velocities. The relationship will also vary depending on a number of other factors, for example aircraft characteristics, such as aircraft weight and balance, and the number and characteristics of the

airbags. The data can be determined using known flight simulation techniques, for example simulation software, for simulating crash results. Using such techniques, data can be collected based on simulation of crash results for various crash conditions and open vent areas. Figures 9a through 9d illustrate operation of the crash attenuation system. In operation, if an impending crash is sensed by sensor system 130, for example, by excessive oncoming rate of the ground within a certain attitude range, control system 126 triggers gas source 128 to inflate airbags 112, 114 at the appropriate time to allow inflation just as airbags 1 12, 1 14 contact the impact surface (ground or water). ' Figure 9a shows an impending crash onto ground 132, which is sensed by the control system 126 based on data received from the sensor system 130. At Figure 9b, gas source 128 is triggered, causing airbags 1 12 and 114 to inflate just prior to contact with ground 132. The control system 126 also calculates the open vent areas for each of the airbags 112, 114. In this case, the control system 126 determines that the crash conditions correspond to the line 138 shown in Figure 8, which requires the open vent area of aft airbag 1 14 be greater than the open vent area of forward airbag 112. Accordingly, at Figure 9c the open vent area of aft airbag 1 14 is set to an area of about 0.0205 square meters and the open vent area of forward airbag 1 12 is set to an area of about 0.0145 square meters. Thus, as shown in Figure 9c, the aft airbag 1 14 deflates faster than the forward airbag 112. As a result, as shown at Figure 9d, the helicopter 100 comes to a stop without experiencing a pitch-over.

• Referring next to Figure 10, a cross-section of a preferred embodiment of an airbag 112, 114 is shown. The hatched area 140 represents the portion of the airbag 1 12, 114 that is adjacent to the underside of the fuselage 102. The arrow 142 points towards the forward end of the helicopter 100. The broken line 144 is the widest portion of the airbag 1 12, 1 14 between the top (hatched area 140) and bottom 146 of the airbag 1 12, 1 14. As shown in Figure 10, for a width W of the airbag at line 144, the distance D1 , which is the distance between the top 140 and the line 144, and the distance D2, which is the distance between the bottom 146 and the line 144, are equal and determined based on the following relationship:

W

£1, 1 ⁾ 2 =

This geometry maximizes crush distance for optimal energy absorption management. Also, the curved region 148 provides anti-plow, anti-scooping geometry to assist in preventing pitch-over of the helicopter 100. Referring next to Figure 1 1 , an alternative embodiment of the helicopter 200 is shown. As mentioned above, while the present crash attenuation system has been discussed primarily in connection with two airbags 1 12, 114, alternative embodiments can have additional airbags. For example, the helicopter 200 shown in Figure 11 has an airbag assembly 21 1 comprising four airbags 212, 213, 214, and 215. Like the helicopter 100, the helicopter 200 comprises a fuselage 202 and a tail boom 204. A rotor 206 provides lift and propulsive forces for flight of helicopter 200. A pilot sits in a cockpit 208 in a forward portion of fuselage 202, and a landing skid 210 extends from a lower portion of fuselage 202 for supporting helicopter 200 on a rigid surface, such as the ground. . A problem with rotor 206 or the drive system for rotor 206 may necessitate a descent from altitude at a higher rate of speed than is desirable. If the rate is an excessively high value at impact with the ground or water, the occupants of helicopter 200 may be injured and helicopter 200 may be severely damaged by the decelerative forces exerted on helicopter 200. To reduce these forces, inflatable, non-porous airbags 212, 213, 214, and 215 are installed under fuselage 202. Though not shown in the drawings, airbags 212, 213, 214, and 215 are stored in an uninflated condition and are inflated under the control of a crash attenuation control system.

The crash attenuation system of the helicopter 200 can operate as discussed above in connection with the helicopter 100. In addition, compared to the helicopter 100, the helicopter 200 provides additional lateral roll-over prevention capabilities. Each of the airbags 212, 213, 214, and 215 is independently actively vented during a crash sequence. Thus, if the helicopter 200 is approaching the ground with a lateral velocity, the airbags 212 and 214, which are located along one side of the helicopter

200, can be vented more or less than the airbags 213 and 215, which are located along the other side of the helicopter 200, as necessary based on detected crash conditions in order to prevent the helicopter 200 from rolling over after impact with the ground The above disclosure describes a system and method for actively controlling the venting of external airbags based on sensed crash conditions, such as airspeed, sick speed, pitch attitude, roll attitude, pitch rate, and roll rate This active venting of the external airbags causes different airbags located at different locations of an aircraft exterior to deflate at different rates upon impact, thereby shifting an aircraft's center of impact pressure

While this invention has been described with reference to at least one illustrative embodiment, this description is not intended to be construed in a limiting sense Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description