(4) Seat assemblies that provide an energy absorbing system between a seat “bucket or pan” and a seat frame attached to the floor may not perform properly for a pre-loaded seat frame attached to the floor or sidewall. Deformation of the seat frame may cause the energy absorbers to receive unanticipated loads or cause excessive friction in the guides between the seat bucket and seat frame to lock the energy absorber in place.
(5) Restraint system anchorages attached to the airframe structure may be significantly displaced relative to the seat if the seat deforms during the test, and that displacement may inhibit proper performance of the seat/restraint system. This is especially critical for the necessary vertical stroking or displacement.
(B) Floor Deformation. The pitch and roll displacement is intended to evaluate the track or stud and leg fitting joint (axis) tolerance to angular misalignment and not necessarily axis translational displacement.
(1) For the typical aircraft seat. For a multiple or single person seat, with four seat legs mounted in the airframe on two parallel tracks, the floor deformation test fixture may consist of two parallel beams, a “pitch beam” which pivots about a lateral (y) axis, and a “roll beam” which pivots about a longitudinal (x) axis. The beams can be made of any fairly rigid structural form, box, I-beam, channel, or other appropriate cross section. The pitch beam should be capable of rotating in the x -z plane up to +/- 10° relative to the longitudinal (x) axis. The roll beam should be capable of a +/ - 10° roll about the axis of the seat attachment/fitting joint (centerline of floor track or fittings).
(See Figure 29.562-2 for a schematic of an installation.) A means should be provided to fasten the beams in the deformed positions.
(2) Seat and floor interface. The beams should have provision for installing floor tracks or other attachment fittings on their upper surface in a manner that does not alter the above-floor strength of the track or fitting. The track or other attachment fittings should be representative (in above-floor configuration shape and strength) of those used in the rotorcraft. Structural elements below the surface of the floor that are not considered part of the floor track or fitting may be omitted in the installation. The seat having four legs should then be installed on the beams so that the rear seat leg attachment point is near the pitch beam axis of rotation, and the seat positioning pins or locks are fastened in the same manner as specified in the test proposal and as would be used in the rotorcraft, including the adjustment of “anti-rattle” mechanisms, if employed.
(3) Test set-up. The remainder of the test preparations would then be completed (ATD installation and positioning, instrumentation installation, adjustment and calibration, camera checks, etc.). The “floor deformation” would be induced as the final action before the test is accomplished. The roll beam should first be rotated 10° and locked in place, and then the pitch beam should be rotated 10° and locked in place.
The direction of rotation would be selected to produce the most critical loading condition on the seat and floor track or fitting. If the seat is fairly flexible, it may be possible to Page C - 63
AC 29-2C, Chg 1 2/12/03
rot ate the beams by manual effort, perhaps using removable pry bars to gain mechanical advantage. However, rotation of the beams used for tes ting a stiff seat frame is likely to require greater effort than can be accomplished manually, and the use of removable hydraulic jacks or other devices may be necessary. If this condition is expected, provision should be made for appropriate loading points when designing the fixture. This condition is most likely to be encountered when rotating the pitch beam.
The test facility personnel should adhere to appropriate safety provisions during the deformation process. The test fixture may be designed to adjust to fit a wide range of seat designs, including leg spacing, that may be encountered.
Page C - 64
ORIGINAL
POSITION NOTE:
FOR CLARITY, LOAD TRANS
DUCERS ARE
NOT SHOWN
PITCH AXIS
UNDER REAR
LEG ATTACHMENT ., POSITION
AFTER FLOOR
DEFORMATION o/J MINIMUM ~EAT TRACK ~-. 100 ROLL TO BE TlSTED • LEFT OR RIGHT- ~
DETAIL (A)
EXAMPLE OF AIRCRAFT
TRACK BEAM 2/12/03 AC 29-2C, Chg 1 FIGURE AC 29.562-2 – Schematic Floor Deformation Fixture;
Seat Legs Attached at Floor Level Page C - 65
AC 29-2C, Chg 1 2/12/03 (C) Alternative configurations. The preceding discussion described the fixture and floor deformation procedure that would be used for a typical seat that has four seat legs and four attachments to the fuselage floor. These test procedures may be adapted to seats having other designs. Special test fixtures may be necessary for different configurations. The following methods, while not covering all possible seat designs, provide guidance for the more common configurations of seats:
(1) Rotorcraft seats with three legs may have one central leg in front or back of the seat and one leg on each side of the seat. The central leg should be held in its undeformed position as pitch deformation is applied to one side leg and roll to the other.
(2) Seats that are “integral” with the structure without floor or sidewall attachment devices and with continuous attachments such as rows of rivets or screw, etc., are excluded from the deformation, misalignment, or preload prior to test impact.
Similarly bulkhead-mounted seats, solely mounted to a bulkhead, are excluded from the deformation requirement. The test fixture could represent the seat and structure or a rigid bulkhead or an actual bulkhead panel. If a rigid bulkhead installation is used, the test fixture should transfer loads to the seat restraint system through components equivalent to the seat attachment fittings and surrounding bulkhead panel, which exist in the actual installation. Similar guidelines apply to integral seats.
(3) Seats that are attached to both the floor and a bulkhead would be tested on a fixture that positions the bulkhead surface in a plane through the axis of rotation of the pitch beam. The bulkhead surface should be located perpendicular to the plane of the floor (the rotorcraft floor surface, if one were present) in the undeformed condition or in a manner appropriate to the intended installation. Either a rigid bulkhead simulation or replica or an actual bulkhead panel may be used. If a rigid bulkhead simulation is used, the test fixture should transfer loads to the seat restraint system through components equivalent to the attachment fitting and surrounding bulkhead panel that would exist in the actual installation. The seats would be attached to the bulkhead and the floor in a manner representative of the rotorcraft installation, and the floor, as represented in the test, would then be deformed as described in paragraph b.(2)(ii)(B).
(4) Seats mounted between fuselage sidewalls or to the sidewall and floor of an airplane should be tested in a manner simulating rotorcraft fuselage cross-section deformation (e.g., from circular or rectangular to flattened circular or rectangular or ellipsoidal shape) during a severe impact. The 10° roll would simulate the change in fuselage shape. Brackets should be fabricated to attach the seat to the sidewall test fixture at the same level above the fixture “floor” that would represent the installation above the rotorcraft floor. The sidewall bracket or rail should be located on the “roll” beam. It is envisaged that the sidewall rolls outward 10° about an axis at the floor and sidewall juncture. Then, as the beams are rotated to produce the critical loading condition, the combined angular and translational deformation would simulate the Page C - 66
deformation at the sidewall attachment during a landing impact. (See Figure 29.562- 3 for a schematic of an installation.)
(5) Seats that are cantilevered from one sidewall without connection to another structure would not be subject to floor deformation. However, sidewall deformation is likely, and should be considered by warping the entire sidewall attachment plane, or the attachment points of the seat, 10° to represent the most likely fuselage sidewall deformation. This is intended to evaluate a critical condition for seat attachment or seat and occupant restraint system performance. Either a rigid sidewall simulation or an actual sidewall panel may be used. If a rigid sidewall simulation is used, the test fixture should transfer loads to the seat through components equivalent to the attachment fitting as well as the surrounding sidewall to replicate the actual installation.
(6) Side-facing seats, occupiable for takeoff and landing, are subject to the specified dynamic test conditions. Compliance with the structural requirements should be demonstrated for side-facing seats using the same conditions for the test and pass/fail criteria as for fore- and aft-facing seats. The seat should be loaded in the most critical case structurally. Means of restraining the ATDs may need to be adapted to ensure adequate retention during the test. The application of floor distortion will need to be assessed on an individual basis, depending on the design and the method of attaching the seat.
(7) A seat assembly for multiple occupants may have more than two pairs of legs. If the assembly uses a uniform cross section, deformation of only the outer leg assemblies is sufficient. The inner leg pairs may be maintained in the normal, undeformed position for the dynamic tests.
(D) Multiple Row Test Fixtures. In tests of passenger seats normally installed in rows in a rotorcraft, head impact conditions should be evaluated by tests using at least two rows of seats. This allows direct measurements of the head injury data if secondary head impact occurs and demonstrates the effect of the interaction loads between rows; e.g., due to occupant contact with the front row. (That is, ATD leg contact does not overload the front row.) These conditions are usually critical only on Test 2. The single seat row fixture used for the test should be used to position the front (first) seat row and provide appropriate floor deformation to that row. The test is critical for the first row strength. An additional simple fixture may position the second seat row in the proper location and need not provide floor deformation. The second row should be fully occupied unless it is not as critical a condition for the first seat row.
Representative seat cushions and torso restraint systems should be used on both seat rows. The allowable seat pitch (longitudinal spacing) can be determined by analysis of previous test data or limited by type design data and information for the most critical condition for head or leg impact against relatively stiff structure in the first seat row.
Operational limitations that specify the allowable seat pitch of the seats in rotorcraft may be considered also. No impact surface such as seats, bulkheads, etc., may be needed Page C - 67
AC 29-2C, Chg 1 2/12/03 for the ATD in the first seat row unless such a surface is within the expected head strike envelope whenever the seats are installed in rotorcraft.
Page C - 68
ORIGINAL
POSITION NOTE:
FOR CLARITY,
LOAD TRANSDUCERS
ARE NOT SHOWN
PITCH AXIS
UNDER REAR
LEG ATTACHMENT "' POSITION
AFTER FLOOR
DEFORMATION
REPRESENTATION
SEAT TO SIDEWALL AT'fACHMENT
IGID TEST
STRUCTURE 2/12/03 AC 29-2C, Chg 1 FIGURE AC 29.562-3 – Schematic Test Fixture;
Side Wall Mounted Seat Page C - 69
AC 29-2C, Chg 1 2/12/03 (E) Other fixture applications. Test fixtures should provide a flat footrest for an ATD used in tests of passenger and attendant seats. Flightcrew seats associated with special foot rests or foot-operated controls may use simulated footrests. The surface of the footrest should be covered with carpet (or other appropriate material) and be at a position representative of the undeformed floor or control. Test fixtures may also be necessary to provide guides or anchors for torso restraint systems or for holding instrument panels or bulkheads if necessary for the proposed tests. If these provisions are necessary, the installation should represent the configuration of the installation and be of adequate structural strength to withstand the expected test loads.
(iii) Instrumentation. Electronic and photographic instrumentation systems are essential to properly record the information for the tests discussed in this AC.
Electronic instrumentation is used to measure accelerations and forces required for verifying the test environment and for measuring most of the pass/fail criteria and the floor (seat) attach loads. Photographic instrumentation is used for recording the overall qualitative results of the tests, for confirming that the lap safety belt remained on the ATD’s pelvis (no submarining), and that the upper torso restraint straps remained on the ATD’s shoulder, and for recording the relative deformation of the seats as it may influence rapid evacuation of the rotorcraft by the occupants. Paragraph d.(10), of this guidance contains allowable seat deformation information related to an aisle, passageway, access to exits, and so forth.
(A) Electronic instrumentation. Electronic instrumentation should be accomplished in accordance with the Society of Automotive Engineers Recommended Practice SAE J211, Instrumentation for Impact Tests. In this practice, a data channel is considered to include all of the instrumentation components from the transducer through the final data measurement, including connecting cables and any analytical procedures that could alter the magnitude or frequency content of the data. Each dynamic data channel is assigned a nominal channel “class” equivalent to the high frequency limit for that channel, based on a constant output/input ratio vs. frequency response plot which begins at 0.1 Hz (+1/2 to –1/2 db) and extends to the high frequency limit (+1/2 to – 1 db). Frequency response characteristics beyond this high frequency limit are also specified. When digitizing data, the sample rate should be at least five times the –3 db cutoff frequency of the pre-sample analog filters. Since most facilities set all pre- sample analog filters for Channel Class 1,000 and since the –3 db cutoff frequency for Channel Class 1,000 is 1,650 Hz, the minimum digital sampling rate would be about 8,000 samples per second. For the dynamic tests discussed in this guidance, the dynamic data channels should comply with the following channel class characteristics:
(1) Sled or drop tower vehicle acceleration should be measured in accordance with the requirements of Channel Class 60, unless the acceleration is also integrated to obtain velocity or displacement, in which case, it should be measured in accordance with the Channel Class 180 requirements.
(2) Belt restraint system loads should be measured in accordance with the requirements of Channel Class 60.
Page C - 70
(3) ATD head accelerations used for calculating the HIC should be measured in accordance with the requirements of Channel Class 1,000.
(4) ATD femur forces may be measured if desired in accordance with Channel Class 600.
(5) ATD pelvic/lumbar spinal column force should be measured in accordance with the requirements of Channel Class 600.
(6) The full-scale calibration range for each channel should provide sufficient dynamic range for the data being measured.
(7) Digital conversion of analog data should provide sample resolution of not less than 1 percent of full-scale input.
(B) Photographic instrumentation. Photographic instrumentation is used for documenting the response of the ATD and the test items to the dynamic test environment. Both high speed motion picture and still systems are used.
(1) High-speed motion picture cameras that provide data used to calculate displacement or velocity should operate at a nominal speed of 1,000 pictures per second. Photo instrumentation methods should not be used for measurement of acceleration. The locations of the cameras and of targets or targeted measuring points within the field of view should be measured and documented. Targets should be at least 1/100 of the field width covered by the camera and should be of contrasting colors or should contrast with their background. The center of the target should be easily discernible. Rectilinearity of the image should be documented. If the image is not rectilinear, appropriate correction factors should be used in the data analysis process.
A description of photographic calibration boards or scales within the camera field of view, the camera lens focal length, and the make and model of each camera and lens should be documented for each test. Appropriate digital or serial timing should be provided on the image media. A description of the timing signal, the offset of timing signal to the image, and the means of correlating the time of the image with the time of electronic data should be provided. A rigorous, verified analytical procedure should be used for data analysis.
(2) Cameras operating at a nominal rate of 200 pictures per second or greater can be used to document the response of ATD and test items if measurements are not required. For example, actions such as movement of the pelvic restraint system webbing (lap safety belt) off of the ATD pelvis or movement of upper torso restraint webbing off of the ATD’s shoulder can be observed by documentation cameras placed to obtain a “best view” of the anticipated event. These cameras should be provided with appropriate timing and a means of correlating the image with the time of electronic data.
Page C - 71
AC 29-2C, Chg 1 2/12/03
(3) Still image cameras can be used to document the pretest installation and the posttest response of the ATD’s and the test items. At least four pictures should be obtained from different positions around the test items in pretest and posttest conditions. Where an upper torso restraint system is installed, posttest pictures should be obtained before moving the ATD. For the posttest pictures, the ATD’s upper torso may be rotated to the approximate upright seated position so that the condition of the restraint system may be better documented, but no other change to the posttest response of the test item or ATD’s should be made. The pictures should document that the seat remained attached at all point of attachment to the test fixture. Still pictures can also be used to document posttest yielding of the seat for the purpose of showing that it would not impede the rapid evacuation of the airplane occupants. The ATD’s should be removed from the seat in preparation for still pictures used for that purpose.
Targets or an appropriate target grid should be included in such pictures, and the views should be selected so that potential interference with the evacuation process can be determined. For tests where the ATD’s head impacts a fixture or another seat back, pictures should be taken to document the head contact areas.
(iv) ATD. The tests discussed in this guidance were developed using modified forms of the ATD specified by the United States Code of Federal Regulations, Title 49, Part 572 Anthropomorphic Test Dummies, Subpart B – 50th Percentile Male.
These “Part 572B” ATD’s were developed for automobile impact testing and have been shown to be reliable test devices capable of providing reproducible results in repeated testing. However, since ATD development is a continuing process, the standards allow use of “equivalent” dummies. See paragraph c.(2)(iv)(D) of this guidance. Dummy types should not be mixed when the tests discussed in this guidance are performed.
(A) Modification for measuring pelvic/lumbar column load. Since ATD’s have been developed for use in automobile testing to evaluate injury protection in forward, rearward, and sideward impacts, the ATD’s must be modified to measure the spinal load to comply with the § 29.562(c)(7). This load is influenced by a vertical direction component and by upper torso restraints which may produce a downward force component on the shoulders. To measure the load, a load (force) transducer is inserted into the ATD pelvis just below the lumbar column. This modification is shown in Figure 29.562-4. A commercially available “femur” load cell with end plates removed has been adapted to the modified ATD to measure the compression load between the pelvis and the lumbar spine column of the ATD. A “femur” load cell is commonly available to most test facilities and (according to specifications) is insensitive to bending and twisting moments. This feature prevents load transmission through the load cell as it measures the ATD lumbar/pelvis compression forces. To maintain the correct seated height of the ATD, the load cell is fixed in a rigid cup inserted into a hole bored in the top surface of the ATD pelvis, the top flange of which is bolted to the pelvis. If necessary, ballast should be added to the pelvis to maintain the specified weight of the assembly.
Alternative approaches to measuring the axial force transmitted to the lumbar spinal column by the pelvis are acceptable if the method— Page C - 72
(1) Accurately measures the axial force but is insensitive to moments and forces other than that being measured;
(2) Maintains the intended alignment of the spinal column and the pelvis, the correct seated height, and the correct weight distribution of the ATD; and
(3) Does not alter the other performance characteristics of the ATD.
FIGURE AC 29.562-4 – Installation of Pelvic—Lumbar Spine Load Cell In Part 572B Anthropomorphic Dummy.
(B) Figure 29.562-4 shows an acceptable installation of a femur load cell
(d) at the base of the ATD lumbar spine (a). The load cell is in line with the centerline of the lumbar spine and set below the top surface of the pelvis casting to maintain the seated height of the ATD. A rigid adapter cup (e) is fabricated to hold the load cell, and a hole is bored in the ATD pelvis to accept the cup. Provide clearance between the walls of the adapter cup and the load cell and the wires leading from the cell to avoid possible interference loads. The bottom of the load cell is bolted to the adapter cup.
Adapter plates having similar hole patterns in their periphery are fabricated for the lower surface of the lumbar spine (b) and the upper surface of the load cell (c). These plates are fastened to the lumbar spine and load cell with screws through holes matching threaded holes in those components and are then joined together by bolts through the peripheral holes. The flange on the adapter cup has a bolt hole pattern matching that on the pelvis. The cup is fastened to the pelvis using screws to the threaded holes in the pelvis. Spacers (f) may be placed under the flange of the cup to obtain the specified ATD seating height. Additional weight should be placed in the cavity below the adapter Page C - 73
AC 29-2C, Chg 1 2/12/03 cup to compensate for any weight lost because of this modification. The instrument cavity plug (g) is cut to provide clearance for the adapter cup and added weight.
(C) Other ATD modifications. Flailing of the ATD arms often causes the “clavicle” used in the Part 572B ATD to break. To reduce the frequency of this failure, the clavicle may be replaced by a component having the same shape but made of higher strength material. This may increase the ATD weight slightly, but it would be acceptable for the tests discussed in this guidance. Another useful modification is the use of “submarining indicators” on the ATD pelvis. These electronic transducers are located on the anterior surface of the ilium of the ATD pelvis without altering its contour and indicate the position of the lap safety belt as it applies loads to the pelvis. Thus they can provide a direct record that the lap safety belt remains on the pelvis during the test and eliminates the need for careful review of high-speed camera images to make that determination.
(D) Equivalent ATD. The continuing development of ATD for dynamic testing of seat restraint/crash-injury-protection systems is guided by goals of improved biofidelity (human-like response to the impact environment) and reproducibility of test results. The following criteria can be used to assess whether or not an ATD is equivalent to the present Part 572B ATD:
(1) Fabrication in accordance with design and production specifications established and published by a regulatory agency responsible for crash injury protection systems;
(2) Capability of providing data for the measurements discussed in this guidance or of being readily altered to provide the data;
(3) Evaluation by comparison with the Part 572B ATD and shown to generate similar response to the impact environment discussed in this guidance; and
(4) Any deviations from the Part 572B ATD configuration or performance are representative of the occupant of a civil aircraft in the impact environment discussed in this guidance.
(E) Temperature and humidity. Since extremes of temperature and humidity can change the performance of ATD, the tests discussed in this guidance should be conducted at a temperature from 66° F to 78° F, and at a relative humidity from 10 percent to 70 percent. The ATD should have been maintained under these conditions for at least 4 hours prior to the test.
(3) Test Preparation. Preparations for the tests should include selection of the test articles to be used in the tests, determination of the “most critical” conditions for the tests, and installation of the test articles, instrumentation, and ATD on the test fixture.
Preparations pertaining to the normal operation of the test facility, such as safety Page C - 74