Crash Load Attenuator for Water Ditching and Floatation
An apparatus comprising a float bag comprising an air bladder configured to inflate when an aircraft lands in the water, a girt coupled to the air bladder and configured to attach the air bladder to the aircraft via at least one airframe fitting, and a load attenuator coupled to the girt and configured to be positioned between the girt and the airframe fitting when the float bag is attached to the aircraft.
1 . An apparatus comprising:
a float bag comprising:
an air bladder configured to inflate when an aircraft lands in the water;
a girt coupled to the air bladder and configured to attach the air bladder to the aircraft via at least one airframe fitting; and
a load attenuator coupled to the girt and configured to be positioned between the girt and the airframe fitting when the float bag is attached to the aircraft.
2 . The apparatus of claim 1 , wherein the load attenuator is a textile load attenuator having a “T” configuration.
3 . The apparatus of claim 1 , wherein the load attenuator is a textile load attenuator having a “Z” configuration.
4 . The apparatus of claim 1 , wherein the load attenuator is a textile load attenuator comprising a fold and a plurality of stitches in the fold, and wherein a density of the stiches is varied across the fold.
5 . The apparatus of claim 1 , wherein the load attenuator is a textile load attenuator comprising a fold and a plurality of stitches in the fold, wherein the stitches comprise a plurality of thread types, and wherein the thread types are varied across the fold.
6 . The apparatus of claim 1 , wherein the load attenuator is a textile load attenuator comprising tear-fabric, and wherein the fabric is comprised of a fabric woven together.
7 . The apparatus of claim 1 , wherein the load attenuator is a frangible load attenuator comprising:
a casing having a first strength;
a frangible support material positioned within the casing and having a second strength less than the first strength; and
a fastener positioned within the frangible support material and having a third strength greater than the second strength, wherein the fastener is configured to deform the frangible support material when a tensile load is applied to the frangible load attenuator.
8 . The apparatus of claim 1 , wherein the load attenuator is a mechanical load attenuator comprising a material that deforms but does not break when the aircraft lands in water.
9 . The apparatus of claim 1 , wherein the load attenuator is a mechanical load attenuator comprising a compression load attenuator.
10 . The apparatus of claim 1 , further comprising an airframe comprising the airframe fitting, an engine, and landing gear.
11 . The apparatus of claim 10 , wherein the float bag is configured to attach to the airframe.
12 . The apparatus of claim 10 , wherein the float bag is configured to attach to the landing gear.
13 . The apparatus of claim 1 , further comprising:
an upper load girt comprising two upper arms, wherein the upper load girt is coupled to the air bladder and configured to attach the air bladder to the aircraft via the two upper arms and a pair of upper load girt airframe fittings;
a pair of upper load girt load attenuators coupled to the upper load girt arms and configured to be positioned between the upper load girt arms and the upper load girt airframe fittings when the float bag is attached to the aircraft;
a lower load girt comprising two lower arms, wherein the lower load girt is coupled to the air bladder and configured to attach the air bladder to the aircraft via the two lower arms and a pair of lower load girt airframe fittings; and
a pair of lower load girt load attenuators coupled to the lower load girt arms and configured to be positioned between the lower load girt arms and the lower load girt airframe fittings when the float bag is attached to the aircraft,
wherein the girt is a drag girt comprising only one drag girt arm, and
wherein the load attenuator is a drag girt load attenuator.
14 . An aircraft comprising:
an airframe comprising an airframe fitting;
landing gear coupled to the airframe,
wherein the airframe fitting is configured to couple to a float bag via a load attenuator,
wherein the airframe fitting is sized to allow the float bag to stay connected to the aircraft when the aircraft makes a water landing, and
wherein the airframe has less mass than the mass that is needed in another airframe when there is no load attenuator positioned between the other airframe and the float bag.
15 . The aircraft of claim 14 , wherein the airframe fittings and the load attenuator are both sized based upon characteristics of the aircraft and an expected sea state.
16 . The aircraft of claim 14 , wherein the airframe comprises a cavity, and wherein the airframe fitting is positioned within the cavity.
17 . The aircraft of claim 16 , further comprising a cover plate configured to cover the cavity and provide an aerodynamic shape to the aircraft near the cavity.
18 . The aircraft of claim 17 , wherein the cover plate does not cover the float bag when the float bag is inflated on the aircraft.
19 . The aircraft of claim 14 , wherein the float bag comprises:
an air bladder;
an upper load girt comprising two upper arms, wherein the upper load girt is coupled to the air bladder and configured to attach the air bladder to the airframe via the two upper arms and a pair of upper load girt airframe fittings;
a pair of upper load girt load attenuators coupled to the upper load girt arms and configured to be positioned between the upper load girt arms and the upper load girt airframe fittings when the float bag is attached to the airframe;
a lower load girt comprising two lower arms, wherein the lower load girt is coupled to the air bladder and configured to attach the air bladder to the airframe via the two lower arms and a pair of lower load girt airframe fittings; and
a pair of lower load girt load attenuators coupled to the lower load girt arms and configured to be positioned between the lower load girt arms and the lower load girt airframe fittings when the float bag is attached to the airframe;
a drag girt comprising only one drag girt arm, wherein the drag is coupled to the air bladder and configured to attach the air bladder to the airframe via the airframe fitting; and
wherein the load attenuator is coupled to the drag girt arm and the airframe fitting and is configured to be positioned between the drag girt arm and the airframe fittings when the float bag is attached to the airframe.
20 . A method comprising:
selecting a sea state and an aircraft, wherein the aircraft comprises an airframe fitting;
sizing at least one float bag for the aircraft, wherein the float bag is configured to keep the aircraft afloat and allow crew egress when the aircraft makes a water landing; and
selecting a load attenuator to be positioned between the aircraft and the float bag,
wherein the airframe fittings are configured to couple to the float bag via the load attenuator,
wherein the airframe fitting is sized to allow the float bag to stay connected to the aircraft when the aircraft makes the water landing, and
wherein the airframe has less mass than the mass that is needed in another airframe when there is no load attenuator positioned between the other airframe and the float bag.
21 . The method of claim 20 , wherein selecting a load attenuator comprises:
calculating a load that the aircraft will experience when the aircraft makes the water landing; and
selecting a load attenuator that has a tensile strength greater than the load.