WO1991007315A1

WO1991007315A1 - Aircraft seats

Info

Publication number: WO1991007315A1
Application number: PCT/GB1990/001752
Authority: WO
Inventors: Peter James Sajic
Original assignee: Peter James Sajic
Priority date: 1989-11-15
Filing date: 1990-11-14
Publication date: 1991-05-30
Also published as: GB8925846D0; AU6718990A

Abstract

A seat mounting (20), particularly suitable for an aircraft passenger seat (2), which squashes under impact, thereby absorbing at least part of the loads imparted. In a preferred embodiment, the mounting includes a tubular member (21), formed from composite fibrous material, which incorporates shallow depressions (23) towards one of its ends. The depressions ensure that the member collapses in a concertina-like fashion under axial forces.

Description

A.RCRAFT SEATS ^" Background of the Invention

This invention relates to energy-absorbing mountings suitable for aircraft seats.

Known civil aircraft seats are designed around 9g static strength requirements as laid down by the World's Civil Aviation legislating bodies. These designs came about as demands for more weight-efficient structures increased.

Since the mid 1980's a great deal of work has been carried out on the dynamic response of occupant/seat combination which has lead to the introduction of dynamic test regulations for civil aircraft seats. In order for the seat designer to meet these requirements energy absorption has to be accommodated leading to a crashworthy design. Use of traditional metal design and technology led to more expensive and heavier seats.

An object of this invention is to provide a crash-worthy aircraft seat which is less costly to produce than existing seats.

Further aims of the invention are to alleviate the need for strengthening of seat-track flooring and to allow the use of a torso and shoulder harness (of the car seat belt type). This type of harness gives an increase in occupant safety compared with existing lap seat belt arrangement. Shouluer harnesses are unpopular in civil aircraft passenger seats because the loadings introduced into the aircraft flooring during rapid deceleration are unacceptably high.

The above objects are achieved by virtue of the invention which incorporates an energy absorbing device composed of composite, fibrous material.

One type of known energy-absorbing device suitable for the aircraft seat application is described in US 4,336,868. This device is of tubular form and made from composite materials. The tube is located between an anvil at one of its ends and a force-transmitting structure at its other end.

The composite tube is filament wound using a bundle of fibres impregnated with a resin. The fibres are progressively wrapped at the desired orientation angle until the required wall thickness is achieved. This results in a tube having a brittle composition which disintegrates as it is crushed onto the anvil, thereby dissipating energy.

One disadvantage with the above device is that as the tube disintegrates, particles of material are scattered around the base of the seat, thus constituting a hazard for passengers.

A second disadvantage is that the tube cannot support any reverse tensile load. Summary of the Invention

An energy-absorbing mounting for an aircraft seat in accordance with the present invention has neither of the afore-mentioned disadvantages and thus comprises:

An elongate member of composite fibrous material characterised in that the member incorporates a means for triggering collapse of said member in a concertina - like fashion when a compressive load applied to said member exceeds a pre-determined level.

The elongate member is preferably a hollow cylindrical tube which is easily fabricated by laying fibrous material over a mandrel.

Using a woven fibre cloth of aramid fibre reinforced composite instead of fibre-glass filaments for example is preferred as this gives the tube the desired elastically-deformable properties.

The means for triggering collapse could comprise a taper towards one end of the elongate member. Alternatively, it could comprise a series of shallow depressions in the outer surface of the elongate member. For best results, the depressions should be located adjacent to one end of the member.

The combination of the ability of the member to compress rather than disintegrate under load and the presence of the trigger means results in a seat mounting which collapses progressively, in a controlled manner.

The invention thus allows reduction of high 'g' loadings applied to a seat occupant during crash situations by attenuating forces during energy absorption

Utilising this invention will allow a 9g seat structure to withstand 16g dynamic loadings. This alleviates the need to strengthen seat track flooring which would be an expensive operation for the aircraft manufacturer as well as being a weight increase solution.

In one embodiment a rigid end cap is fitted over one end of the elongate member. The cap has a collar which fits around the outer surface of the elongate member.

It has been found that if the elongate member is of a multi-layer construction, then the orientation of woven fibres in subsequent layers can control (to a certain degree) the load necessary to initiate collapse of the member.

Other parameters which are known by the inventor to affect the strength of the member are the angle of taper and the collar length of an end cap.

Specimen elongate members of composite materials and of tubular form having a taper at one end and fitted with a rigid cap at said end have been constructed by the inventor. The behaviour of these specimens under load are shown in Figs 1 to 5. Table I lists the mechanical properties of sixteen different specimens.

A force to be attenuated was applied at the end of the tube via the end cap to progressively buckle the tube like a ¹concertina' .

The deformation V load curves of Figs 1 to 5 can be split into three phases.

The first phase covers the rapid rise of force leading to the peak collapse load followed by a valley. This part of the curve is controlled by the geometry of the taper and the mechanical laminate properties of the composite material.

The second phase, after the initial peak and valley, reflects the travel of the end cap over the tube device during which there is a build up of load force.

Here the tube is initially pushed inside out (like peeling a banana skin); Vertical folding of the material occurs with excess material being pushed up into the collar space.

This part of the curve is controlled by the taper geometry and collar length of the end cap.

The third phase is a transition from the second where the curve turns into a linear portion representative of the constant load. Here controlled progressive horizontal folding of the tube material occurs in a concertina type fashion. Here the maximum absorption part of the curve is controlled by tube geometry and material laminate properties.

The linear portion of the load/deformation curve for this device can be up to 75% of the device length and the load is relativity constant thus absorbing energy efficiently.

Because of the composite materials used the failure is one of fibre buckling which gives rise to a fail-safe design. After the tube collapses the structure is still intact and allows full reverse loads to be carried if required. This is of particular importance in the aircraft seat application since for civil aircraft passenger seats high reverse g loadings are applied to the seat structure as a result of the seat/occupant interaction during high velocity impacts/de-accelerations.

In this case the tube has to resist compression and tension loadings.

Other known energy absorbing members employing composite materials rely on the ability of how fine the material can be broken up during crushing/destruction of the member. For glass and carbon fibre materials powdered fragments are produced which would possibly cause injury to passengers.

Figs 1 to 5 show the effect of varying the taper geometry and collar length.

Table I shows the effect of varying the taper geometry, material types/orientations and collar length. TABLE 1

NOTES

1. AFRP - Woven Aramid/phenolic material

2. CFRP - Unidirectional Carbon fibre/epoxy materials

3. Material Properties:-

AFRP: El-31.7 E2-23.0 MU12-0.2 G12-4.1 (GN/M2) Ften-557.0 Fcomp-182.2 (MN/M2)

CFRP: El-129.3 E2-6.9 MU12-0.3 G12-7.1 (GN/M2) Ften-1977 Fcomp-1216

Tubes 1-14 had collar length - 13mm

Tube 15 had collar length » 7mm (tube construction was the same as tube 11)

As can be seen, different types of deformation V load curves can be produced. Curves exhibiting the distinct three phases absorb energy efficiently while those which combine phases 1 and 2 give a gradual initial load rise rising to the average load representative in phase 3. the latter type of curve provides smoother de-acceleration performance (F max = F mean) at the expense of energy absorbing efficiency.

Also it can be shown that collapse loads can be varied by varying the fibre orientation of the fibre reinforcement ie:- 0 degree plies contribute to higher collapse load values. By incorporating higher strength fibres such as carbon fibre sandwiched between lower strength material such as aramid fibres (forming a hybrid material), higher collapse loads can be achieved.

Also incorporating material at angles of 45 degrees has the effect of producing smoother de-acceleration performance.

Different configurations of energy absorption members displayed values for Specific Energy Absorption which varied between 20 and 25KJ.Kg~ .

Brief Description of the Drawings

Some embodiments of the invention will now be described, by way of example only, with reference to the drawings of which: Figs 1 to 5 are deformation versus load curves for energy-absorption mountings in accordance with the invention;

Fig 6 is a side elevation of an aircraft seat incorporating an energy absorbing mounting in accordance with the invention;

Fig 7 is an enlarged view partly in section of some of the parts seen in Fig 1;

Fig 8 is a section view on the line III-III of Fig 7;

Fig 9 is a view in section on the line IV-IV of Fig 7;

Fig 10 is a scrap view of parts seen in Fig 8, but to a larger scale, and

Fig 11 is a perspective view showing the orientation pattern of fibres in the energy absorbing part of the seat of Fig 6.

Fig 12 is a perspective view of part of the energy absorbing part of the seat of Fig 6 illustrating an arrangement for ensuring gradual collapse under impact load;

Fig 13 is a cross-sectional view of an energy-absorbing mounting in accordance with a second embodiment of the invention;

Fig 13a is a cross-sectional view of part of the mounting of Fig 13 on a larger scale;

Fig 14 is a side elevation of part of a seat incorporating the energy absorbing mounting of Fig 13 and

Fig 15 is a sectional view on the line V-V of Fig 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first embodiment, a seat 2 comprises a frame portion 4 to which is pivoted an arm 6 and a cantilever tray arrangement 8. A back support 10 and a seat cushion 12 are provided, all of the above being quite usual and not forming part of the novel invention.

The seat is secured to a support member, generally designated by the numeral 14 and formed as a tubular structure. The member 14 comprises a pair of laterally spaced frames 16 each of which has a substantially horizontal component 18, a vertical compression strut 20 which joins with the horizontal component 18 at one of its ends, and a further component 22 which joins with the component 18 at its other end. The further component 22 extends from its joint with component 18 at an acute angle thereto in an upward direction for a short distance and is then curved sharply to follow a direction at a slight angle to the vertical and to terminate in a flange 24, (see particularly figures 2 and 4). The strut 20 receives within its upper end a tubular component 26 having a flange 28 and an upwardly depending extension 30 (see particularly figure 3).

The rearmost end portion of the component 18 has a connection by means of a pivot pin 32 with a bracket 34 which is bolted to a rail 36 on the aircraft floor 40. The forward end portion of the component 18, where it joins with the vertical strut 20, has a short pivotable arm 42 having a foot 44 which is secured to the rail 36.

The seat frame 4 has a forwardly extending portion 46 and, as seen particularly in figure 7 is formed as a hollow generally triangular section. A pair of laterally spaced brackets 48 having downwardly depending lugs 50 are bolted to the forward part of the portion 46 of the seat frame and are each connected by a pin 52 to the upstanding extension 30 of the tubular component 26 aforementioned.

The rearmost portion of the section 46 rests on the flanges 24 of the component 22 and a bolt 54 passes through the section 46, the flanges 24 and a pair of hollow aluminium tubes 56, being clamped thereto by a nut 58 and washer 59.

The frames 16 are constructed generally of carbon fibre material, having the advantage of strength and lightness, and at least part of the strut 20 is formed so as to be collapsible under high impact stresses.

In the exemplary embodiment, the upper portion 21 of the tubular strut 20 is made from an aramid fibre reinforced composite, the fibre being a polyamide, and the resin is a thermosetting epoxy/phenolic resin or a thermo plastic resin, for example polythermide. As illustrated in Figure 11, the fibres of the collapsible section are orientated, for example, some at 45° and some at 0/90°. The pattern of orientation determines the load at which the tubular portion will collapse in a shock-absorbing manner.

In an experiment, it was found that when three layers each of approximately 0.25mm thickness had their fibres orientated at 0/90° and three further layers of 0.25mm were orientated at 45° and then impregnated with phenolic resin, they collapsed under a load of lOOOKg.

When alternative collapsing strengths are required, the orientation pattern of the fibres is changed accordingly, e.g. the angles of the diagonally woven fibres may be increase or decreased.

In the event of impact, the first effect is to cause the seat to rock in the clockwise direction as seen in Figure 6 about the pivot pin 52 to cause the section 46 to tend to lift away from its seating on the flanges 24. This puts the bolts 54 in tension, resulting in a compressive loading on the aluminium tubes 56 which then collapse under the compressive load imparted thereto, thus absorbing some of the initial shock loads. The next effect is to place the strut 20 in compression and the collapsible part 21 of the strut squashes in a concertina-like manner thus absorbing the shock. .This results in a decrease in the tendency to either tear the retaining bracket 34 from the rails, or to shear the pivot pin at 32.

As illustrated clearly in Figure 11, the collapsible portion 21 of the strut 20 is made form a polyamide fibre reinforced resin, the fibres being so orientated to determine the "collapsing force".

In the specific example, three layers of polyamide fibre of approximately 0.25mm in thickness and having their fibres laid approximately vertically and horizontally and a further three layers of fibres each having approximately 0.25mm in thickness but having their fibres orientated at approximately 45 were impregnated with a phenolic resin which was then allowed to harden.

As illustrated in Figure 10, the portion 21 is moulded with the tubular component 26 in situ, sprags 31 formed on the periphery of the component 26 being provided to ensure an effective key. The lower part of the collapsible portion 21 is moulded in situ with the fibreglass strut 20.

As illustrated in Figure 12, the tubular component 21 is formed with shallow depressions 23 towards its upper end portion. This is found to ensure that upon the application of impact forces in a axial direction, the tube collapses in a concertina-like fashion.

A second embodiment of the invention will now be described with reference to Figs 13 to 16. The second embodiment comprises an alternative form of collapsible member suitable for use with the seat of Fig 2.

The collapsible member comprises a cylindrical tube 60 fabricated from composite fibrous material. The tube 60 is of multi-layer construction and is composed of a layer of unidirectional carbon fibre epoxy plies 61 sandwiched between two layers of woven aramid fibre epoxy plies 62.

A metal end cap 63 is bonded to one end of the tube 60 with an epoxy adhesive. The end cap 63 incorporates a cylindrical collar 64.

The tube 60 is provided with a taper 65, towards that end fitted with the end cap 63. The purpose of the taper 65 is to ensure that upon the application of impact forces via the end cap 63, the tube 60 collapses is a concertina-like fashion.

The behaviour of the tube 60 after impact is shown in Fig 14. The tube has moved through a stroke 'S¹ and compressed like a concertina. The tube 60 still has enough strength to stretch out again under any tensile load, if need be.

The tube 60 is shown incorporated into an aircraft seat in Figs 15 and 16. Features common to the first and second embodiments are designated with the same reference numerals. The pair of laterally spaced brackets 48 having downwardly depending lugs and being bolted to the forward part of the portion 46 of the seat frame are each connected by the pin 52 to an upstanding extension 66 of the end cap 63. the lower part of the tube 60 is bonded to the strut 20.

In the event of impact, the seat and tube 60 behave in the same manner as the seat 2 and collapsible portion 21 of the first embodiment. Where ener y absorption, crashworthiness and load limitation are required the invention described can offer low weight, simplicity, low cost, compact design, corrosion resistance, maintenance free and fail safe structure.

The invention will also allow the following design features to be employed: constant or rising collapse load, smooth de-acceleration, controlled collapse over high % of tube length, full structural component prior to collapse, full reverse tensile load carrying capability after collapse, good reliability and incorporation as an integral collapsing section of a larger structure.

Tests have shown that when a passenger uses a diagonal seat belt instead of or as well as the customary lap belt, the effective centre of gravity of the seat becomes much higher than when a lap belt is used alone. The design according to the present invention is found to have great benefits with this type of seat belt.

Although the invention has been described with reference to its use relating to aircraft seats and seat mounting the use of a similar design of collapsible component in a motor vehicle chassis or body in a sea-going vessel, is also envisaged.

Claims

1. An energy-absorbing mounting for an aircraft seat comprising an elongate member (21) of composite fibrous material characterised in that the member (21) incorporates a means (23) for triggering collapse of said member (21) in a concertina-like fashion when a compressive load applied to said member (21) exceed a pre-determined level.

2. An energy-absorbing mounting as claimed in claim 1 in which the elongate member (21) is a hollow cylindrical tube.

3. An energy-absorbing mounting as claimed in claim 1 or claim 2 in which the elongate member (21) is fabricated from a multiplicity of layers of woven fibre cloth, impregnated with resin, said layers having fibres arranged at different orientations.

4. An energy-absorbing mounting as claimed in any preceding claim in which the means for triggering collapse comprises a taper (65) towards one end of the elongate member (60).

5. An energy-absorbing mounting as claimed in any of claims 1 to 3 in which the means for triggering collapse comprises a series of shallow depressions (23) in the outer surface of and located adjacent to one end of the elongate member (21).

6. An energy absorbing mounting as claimed in claim 4 in which a rigid end cap (63) is located at that end of the elongate member (60) having said taper (65) and said end cap (63) incorporates a collar (64) which is bonded to the outer wall of the elongate member (60).

7. An aircraft seat (2) comprising at least one energy-absorbing mounting as claimed in any preceding claim.

8. An aircraft seat (2) having a first collapsible mounting (20) and a second rigid mounting (22), in which the first collapsible mounting (20) includes the energy-absorbing mounting (21) according to any of claims 1 to 6 and in which the second rigid mounting (22) is secured to the seat (2) by a bolt (54) which passes through the base (46) of the seat (2), a flanged part (24) of the second rigid mounting (22) and a hollow metal tube (56), being clamped thereto by a nut (58), so that in the event of impact, the seat (2) tends to lift away from the second rigid mounting (22), putting the bolt (54) in tension and resulting in compressive loading on the metal tube (56) which collapses, thus absorbing initial shock loads, the remainder of the shock loads being absorbed by the first collapsible mounting.