Aircraft Crash Survival Analysis and Design Essay
1. Describe the effect plowing can have on crash forces when the impact surface is soft soil.
Earth gouging and scooping of soil occur when the structure makes initial contact with the ground which minimize the acceleration and force levels to which the structure is subjected. Soft soil can cause plowing and rapid deceleration if there is a large horizontal velocity component. A high-speed longitudinal impact into water can also cause high loads from water plowing as water enters through lower nose transparencies. Reducing the earth scooping effects encountered in longitudinal impacts should include a large, relatively flat surface thereby increasing the aircraft’s tendency to slide over the impact terrain and by minimizing inward buckling of the fuselage nose or engine nacelle to maintain skid surface integrity.
2. Explain the term submarining in respect to the use of lap belt restraints. What human injuries may result?
This is where the lap belt rides over the pelvic brim and compresses the soft tissues of the abdomen resulting in serious abdominal and spinal injuries. Submarining occurs due to the pelvis rotating under the lap belt, usually due to inappropriate location of the lap belt anchors or due to poor design of the seat bottom or a combination of both. Lap belt only restraints so commonly inflicted serious injuries on users in automobile crashes that the medical community coined a new term, “the seat belt syndrome”, to describe the constellation of injuries caused by submarining under the lap belt. ftp://ftp.rta.nato.int/pubfulltext/RTO/EN/RTO-EN-HFM-113/EN-HFM-113-06.pdf
3. Discuss forward and rearward facing passenger seats and explain which you feel may be an advantage in crash survivability.
The rearward-facing seat is optimal for providing maximum support and contact area in longitudinal impacts. The only critical impact sequence for the rearward-facing seat is one that involves a severe lateral component that allows sideward movement of the occupant prior to application of the longitudinal or vertical Pulse. However, lateral torso movement can be minimized by use of a torso restraint system of much lighter weight than that required for other seat orientations. The rearward-facing cabin seat is preferred.
4. Explain the concept and intention of Delethalization of Cockpit and Cabin Interiors.
The delethalization of cockpit and cabin interiors is the design and set up of aircraft cockpits and cabins to prevent injury on impact. This is done by ensuring the occupant’s immediate environment be designed so that when the body parts do flail and contact rigid or semi-rigid structures, injury potential is minimized. This can be done in different manners. First is to relocate the hazardous structure or object out of the occupant’s reach or the hazard might be reduced by mounting the offending structure on frangible or energy-absorbing supports and applying a padding material to distribute the contact force over a larger area on the body member.
The aircraft interior has occupant strike envelopes, meaning that there are hazards that are more conducive to occupant injury than others. Overall the intent is to protect the head and torso first to prevent debilitating injuries or death and then protecting the lower body parts to ensure the area hazards are clear of tripping hazards or anything that could prevent rapid escape. Typical contact hazards in the cockpit area include window and door frames, consoles, controls and control columns, seat backs, electrical junction boxes, glare shields, and instrument panels. Contact hazards commonly found in aircraft cabin areas include window and door frames, seats, and fuselage structure. Use of suitable energy absorbing padding materials, frangible breakaway panels, smooth contoured surfaces, or ductile materials in the typical hazard areas mentioned is recommended to reduce the injury potential of occupied areas. The use of protective helmets is also recommended in certain types of aircraft.
5. Explain the expected advantage frangible fuel system attachments can provide as an aircraft post-crash survival technique.
Frangible Attachment- An attachment possessing a part that is designed to fail at a predetermined location and/or load.
Frangible structures or frangible bolts should be used at all attachment points between fuel tanks and aircraft structure to prevent fuel tank components from being torn out of the tank wall during impact. Frangible attachments should be used at other points in the flammable fluid systems where aircraft structural deformation could lead to flammable fluid leakage. This increases the survivability by containing any remaining fuel to the tank its encapsulated within and reducing the chance of a fire being spread throughout a crash site or into the cabin.
6. What are some of the key concerns when selecting aircraft interior materials form a crash survivability perspective?
All aircraft interior materials such as seat fabrics and cushions, interior wall insulations, and nonmetallic structural components must be flame resistant and produce the least amount of smoke and toxic gases possible.
7. Describe some of the key points of post-crash design criteria associated with oil and hydraulic systems.
Oil and hydraulic fluids are easily ignited and can serve as ready ignition sources for fuel meaning fluid spillage should be prevented. Oil tanks and hydraulic reservoirs should not be located where spilled or sprayed fluid can readily be ingested into the engine or ignited by the engine exhaust. Oil tanks and hydraulic reservoirs should not be located near the bottom of the fuselage, in or above engine compartments, in electrical compartments, in occupiable areas under, in front of, or at the side of heavy masses, such as engines and transmissions, nor above landing gears Oil and hydraulic lines should consist of flexible hoses with steel-braided outer sheaths and for high-temperature; coiled metal tubing should be used. Lines should not be routed, near the bottom of the fuselage, over landing gears, under, in front of, or at the sides of heavy masses, such as engines and transmissions, in the leading edges of wings, in areas of anticipated rotor blade impact, in any area where flammable fluids could be spilled or sprayed onto hot surfaces or ingested into the engine or above electrical wiring
8. Considering aircraft electrical system post-crash survivability design, what are the guidelines concerning routing electrical wires in the vicinity of flammable fluid lines?
Wiring is a prime ignition source for leaking oil, fuel or hydraulic fluid leaks or vapors. To aid in crash survivability wires should be routed above or away from flammable fluid lines and they should never be closely spaced between outer skin and fuel lines. Wires must not be routed near flammable fluid tanks unless the wires are shrouded to prevent arcing. Wires should not be routed near the bottom of the fuselage, over landing gears or in the leading edges of wings.
9. What G forces are experienced if an aircraft impacts the ground at a speed of 120 MPH and skids along the ground 50 feet before coming to rest?
9.8 G’s. 120^2/50 = 14400/50=288288x.034=9.79
10. Explain why you believe passenger airlines do not have to utilize passenger shoulder harnesses as a crash survival precaution.
The passenger shoulder harness is not used for crash survival because: * The cost of the harnesses for one would be huge to retrofit all the airliners in the fleet today and that cost would be put onto the customer. * The need for various sizes; very small through very large would result in further cost. * Comfort, if people are not comfortable then they will not have a good flying experience while others may have a fear or feeling that they are trapped. * The ability to understand how to use the shoulder harness. Most cannot figure out how to wear the harness which would delay taxiing and flight times. The required ability to quickly restrap in bad weather or to unstrap in an egress situation could be deadly. * Americans don’t like to be told what they have to do….they are the paying customer.
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