Deceleration Pulses
Parts 23, 25, 27, 29, and "Commuter"

SaRRSES

Vehicle Deceleration (g's)

a
1

35 F/S)

or + + ‘ H ‘ : i : i
0.00 0.02 0.04 0.06 0.08 010 012 014 016 018 0.20
Time (seconds)

Figure 1

test condition will require an active energy ab-
sorbing system to attenuate vertical forces inthe
seat pan. The design of the EA seat system
should be optimized to limit the dynamic peak
response the pelvic load of the ATD and function
within the physical constraints of the aircraft
interior. The load properties of the EA system
must provide a force-limiting system that will
effect a peak response of less than 1500 pounds
in the pelvic load cell, and the resulting deflec-
tion {or stroke) must be limited to the volume of
space beneath the seat pan in the aircraft instal-
lation.

Acommon characteristic of many commuter
airplane passenger seats is the limited available
space beneath the seat pan. Seats may be at-
tached to the wall of the cabin interior with less
than six inches of vertical clearance between the
outboard seat pan frame and the curved interior
wall of the fuselage. Others may be positioned
with the seat pan directly over raised sections of
the cabin floor with very limited clearance be-
neath the pan. A crashworthy commuter seat
developed to meet the suggested 32 Gs severity

Taust be designed with consideration for the
amount of vertical deflection of the seat pan.

The CAME Seat Pan

Te investigate the dynamic load-deflection
properties of an EA seat intended to providea 32
Gs vertical impact load injury protection, a
Tesearch program was initiated in 1989 by CAMI's
Biodynamics Research Section, with participa-
tion from members of the General Aviation Manu-
facturers Association (GAMA). Tests conducted
with current production seats were not success-
ful in meeting the Part 23 vertical test require-
ments, and attempts to mudify the production
seats did not produce satisfactory results. To
meet the project goal of a satisfactory “32 Gs
seat,” a seat frame was constructed at CAMI to
function as a test fixture for the development of
an EA seat pan system.

The components of the CAMI seat, shewn in
Figure 2, were not modeled after a particular
production seat; rather, the base frame was
designed to accommodate an EA system and


the front of the pan. Then, the rear edge rotated
about the axis of the torsion rod. The peak pelvic
force responses from the other three tests listed
in Table 1 were all within the 1500 pound limit,
and the vertical stroke distance of the seat pan
rear edge ranged from 1.0 to 3.5 inches. As
expected, the amount of seat pan stroke de-
creased as the severity of the impact decreased.
In each test the same sequence of EA actions
occurred: the front EA activated first: then the
wire bender started to stroke.

Because these were not pure vertical tests,
the horizontal component of deceleration re-
sulted ina slight forward translation of the ATD.
It was important to keep the ATD in the normal
position over the cushion because the rear EA
effectiveness decreases as the vertical load trans-
mitted to the seat pan moves forward. The lap
belts were attached to the seat pan to limit
forward movement of the ATD's pelvic section
during seat pan stroking action. Attachment of
the lap belts to the seat pan was also required to
maintain the proper belt path over the pelvis.

RESULTS AND DISCUSSION

Tests A89156 and A89157 were conducted
with impact conditions conforming to the re-
quirement for FAR Part 23 passenger and pilot

seats respectively. The same EA sizeWire ang S

torsion rod, as used in test A89116, were in-
stalled for these tests. Test A89159 was con-
ducted with a peak deceleration of 24.8 Gs to
obtain data frem an impact severity between the
19 Gs of test AS89156 and the 32 Gs of test
A89116.

As shown in Figure 8, the seat pan vertical
displacement during test A89157 was more
than the displacement recorded during the higher
peak deceleration in test A89159. This may be
due to the sled deceleration pulse shapes
achieved in these two tests. Figure 6 shows the
Sled X pulse from A89157 had a rounded peak
with a .040 second plateau at the level of 20 Gs.
The Sled X pulse from A89159 had a shorter
duration peaks around 25 Gs and rapid post-
peak decay.

Pelvis Fz Forces
CAM! EA Seat Pan Tests

®
8
t

Pelvis Fz (Ibs)
g

‘ : : —
0.025 0.050 0.075 G.100

0125
TIME (seconds)

0.150 0.175

Figure 7


provide adequate dimensions and strength to
evaluate a range of impact conditions. A seat
back and three-point restraint system were
obtained from a salvaged passenger seat for a
smallaircraft. The seat cushion was constructed
with a two inch thick layer of Ensolite beneath a
one inch pad of soft foam.

The EA system chosen for this project was a
dual mechanism design. A torsional EA device
supported the front of the seat pan and was con-
nected to the seat base frame by pivot arms at
each side of the front of the pan. A wire bending
EA device linked ihe rear comers of the seat pan
to the base frame. These EA mechanisms were
chosen because they were simple to construct
with commonly stocked materials. The seat pan
diaphragm was a rigid aluminum plate. Al-
though no detailed engineering design or model-
ing analysis was performed, laboratory experi-
ence with similar devices provided a rational
basis with which to evaluate these devices. The
torsional EA was comprised of a square sieel rod
secured by a fixed guide in the center of the front
tube of the seat pan. The ends of the steel rod
attach to the pivot arms connected to the base
frame. As vertical forces are reacted at the front
of the seat pan, the pivot arms rotate downward,
twisting the steel rod between the center guide
block and the pivot arms on either end. The wire
bending EA device on the rear of the seat pan

consists of a pair of wire loops routed over rollers
within the rear tube of the seat pan. The left and
right wires are placed over a common roller in
the center of the rear tube, and each wire exits
the rear tube over a roller on each end; from
there the loop on each wire passes through a
shackle attached to the upper rear corner of the
base frame. Vertical forces reacted at the rear of
the seat pan pull the wires through the path over
rollers, bending each wire around the radius of
the rollers. As the wires are pulled through the
rollers, the seat pan moves downward. The force
to maintain the wire bending action is constant
and may be altered by the type and size of wires
installed.

The variables that could affect the force-
deflection parameters of the system were: (a) the
size of the torsion rod on the front of the seat
pan, (b} the diameter and material of the wires in
the wire bending mechanism, (c) the angle ofthe
seat pan (adjusted by the pivot arms attach-
ment), and (d) the seat cushion. Various combi-
nations of torsion rod and wire sizes were evalu-
ated during the trial tests with this seat pan. The
best performance was achieved with a 0.375
inch square torsion bar in combination with
.092 inch diameter welding rod for the wire
bender. Static load deflection curves for this
arrangement are shown in Figures 3 and 4.

r
Force vs Deflection Force vs Deflection
CAMI EA Seat Pan (Rear EA Only) CAMI EA Seat Pan (Front and Rear EAs)
00. -— J val Sper
8 | 8
a1 1 é
3 | 3
$100): Tas
500: a
a 1 2 3 4 5 6 % + 2 3 4 5 6
Verteal Defecnon inches) Verucal De“ection (ncnes }
[Note Load Aoo.ed 6 5 inches Fwe of Aft Eoge on Seat Pan}
Figure 3 Figure 4


ALL DIMENSIONS IN INCHES

PAN FRAME AND SEAT BASE FRAME
CONSTRUCTED WITH 1* SQUARE
STEEL TUBING

SEAT CUSHION MADE
WITH 2° ENSOLITE PAD
AND 1° SOFT FOAM

FRAME ATTACH mi

HYDROLOK
FRAME BASE

1%

| PR
i bE;
| 1 fp
i Pe
| i} log 8
i i 1 3 Z
| il} tg .
It are seer | | rey .
LLL aw REAR TUBE, 7! | ! Z
i | near atl é
le Nil | | é
Tt ¥ (ai i
14
REAR
Figure 2



TEST PEAK AVERAGE | VELOCITY PELVIC SEAT PAN

NUMBER | SLED X SLED X (f/s) FZ (Ibs.) STROKE
(G.) \Gs) (inches)

ABST1E 33.4 19.1 31.0 1371 63

A89155 15.6 84 8.4 826 1.0

AR9157 21.8 145 145 1093 35

A89159 24.8 11.8 118 1178 24

Table i

Table 1 lists four of the tests conducted with
“his seat. Figures 6, 7, and 8 present the perti-
nent data acquired during the impact tests. Test
A89116 was conducted with a peak deceleration
of 33 Gs and a velocity of 31 ft/sec. The peak
pelvic compressive force measured 1371 pounds,
and the rear edge of the seat pan stroked 6.3
inches downward. The motion of the seat pan
during the impact resembled the sequence that

occurred during the static force-deflection test.
First, the torsional EA activated, allowing the
front of the seat pan to rotate down approxi-
mately 3 inches, followed by the wire bending EA
action as the rear of the seat pan moved down
6.3 inches. This sequence of actions by the front
and rear EAs resulted in a rotational motion by
the seat pan. The front edge rotated through an
are with a radius defined by the pivot arms on

Sled Deceieration
CAMI EA Seat Pan Tests
4
g
3 -107-
x]
3 -154
DS 20 rannsceeerenfecenenceceel panne nell geri cceeesesesccodeee BOR fb anaceeneeerbecceeecencee
a
re ee
BOferro $ Erorsecrseecnefecanecaneennedbeeeetnene
i ~i—i— AB9116} i i
000 0.025 0.059 0075 0.400 0125 oiso ove oxoo 0225 0.250
TIME (seconds)
Figure 6

6


TIE FILE COPY

DOT/FAA/AM-90/11 Development of a
Crashworthy Seat for
Wakiogon Die. 20591 Commuter Aircraft
Van Gowdy
Civil Aeromedical Institute

Federal Aviation Administration
Oklahoma City, OK 73125

September 1990

AD-A227 486

DTIC '

Final Report ELECTE
OCT 101990

(%
This document is available to the public through

the National Technical Information Service,
Springfield, Virginia 22161.

@

US. Department
of Transportation

tree


CAMi EA Seat Pan Tests

Seat Pan Displacement vs Energy Pulse

Seat Pan Displacement (inches)

‘4000 2 6000 p00 12000)
((Gavg * 7) /2))/T (ft/sec) /sec
Figure 9
CONCLUSIONS pulse shape or a method to measure pulse

1. The maximum seat pan vertical displace-
ment was 6.3 inches during the 32 Gs impact
with this seat pan design. It should not be
inferred that this dimension is to be used as a
design facior. Rather, the vertical displacement
can be as much as 6.3 inches with EA systems
that perform in a similar manner. If commuter
seats are to be developed to meet a 32 Gsvertical
4mpact test condition, the volume available for
seat pan stroke into the space beneath the seat
pan should conform to the dynamic deflection
characteristics of the EA system.

2. Seat pan performance, as measured by
stroking distance and peak pelvic force, is sen-
sitive to pulse shape. The peak deceleration Gs
of an impact test are not necessar‘’y the primary
indicator of the test severity. Impact test facili-
ties can only approximate an ideal pulse shape.
Therefore, a careful definition of an acceptable

severity should be addressed if further research
or regulatory activities occur.

3. The resuits from the dynamic tests with
this seat indicate the need for an active energy
absorbing system in orderto meet th * pelvicload
criterion when a seat is subjected to the vertical
test orientation of the FARs at a pulse severity 32
Gs and an impact velocity of 32 ft/sec. This
project did demonstrate a EA seat pan can be
constnucted with common materials and per-
form satisfactorily during impact conditions
ranging from 15 to 32 Gs.

4. The EA system developed for this project
may not provide optimal performance, and other
systems may be capable of meeting the injury
criterion with greater efficiency. One feature
that might enhance the performance of the
system would be a deformable seat pan dia-
phragm, that absorhs some ofthevertical energy.


The relationship between seat pan stroke and
deceleration pulse shape for these tests can be
demonstrated by analyzing the time period for
the energy applied to the system. These tests
were conducted with approximately the same
sled velocity; therefore, the total energy dissi-
pated by the seat /occupant test specimens was
similar, As the peak Gs of the triangular shaped
Sled X pulse increased, the time period of the
pulse decreased. The Sled X puises achieved
during these tests were not perfectly symmetri-
cal triangles; therefore, the average rate at which
the eneigy was dissipated during the impact
interval was calculated by using the following
equation:

AER = ((Gavg x T)? /2) /T
AER = Average Energy Rate
T = Period of Deceleration (sec.)

Figure 9 shows the relationship between this
calcutated energy dissipation rate and the seat
pan vertical displacement for these four tests.
The calculated average energy rates for tests
A89116 and ASY156 were the upper and lower
bounds, as shown. Note the average energy rate
for test A89159 is less than the rate calculated
for test A89157, even though the peak sled
deceleration from test A89159 is greater. This
supports the qualitative analysis of pulse shape
differences discussed above. Thus, average
energy rate was a significant factor in the per-
formance of the seat pan tested in this series.

Seat Pan Vertical Displacements
CAMI EA Seat Pan Tests

ce coe

Seat Pan Z Displacement (in)

7 + +
0.000 0.08 0.075 4.100

“Time lag in sensor on AS89116

0.025

0.125 0.180 0175 0.200 0225 0.250

TIME (seconds)

Figure 8

8


The force required to stroke the wire bending
EA was approximately 1400 pounds with the
load applied at the aft edge of the seat pan. With
a static force applied at a point 6.5 inches
forward of the aft edge of the seat pan, the force
deflection curve for the seat pan exhibits a two
step action. An initial plateau occurs at around
1200 pounds for the first two inches of pan
stroke as the torsional EA activates, allowing the
front of the pan to rotate down. Then the wire
bending EA starts stroking and a second force
plateau at approximately 2200 pounds is main-
tained as the static load point moves vertically
beyond 3.5 inches for the remaining seat pan
stroke. Since the initial pitch of the seat pan was
about 20 degrees above horizontal, the vertical
displacement of the front edge of the pan was not
considered to be as significant as the rear edge
movement into the volume within the seat base
frame.

Dynamic Tests

Dynamic impact tests of the CAMI EA seat
were conducted on the CAMI impact track.

Figure 5 shows the impact sled setup with this
seat for the vertical impact test specified in the
FARs and proposed for con-muter seats. This
facility uses a horizontal deceleration system to
implement controlled impact tests. The sled is _
accelerated to the desired velocity on parallel
circular rails using a cable and pulley system
attached to a falling weight. The tension in the
cable becomes slack as the sled nears the brake
device, which consists of a set of 0.235 inch
diameter steel wires placed across the track
rails. As the sled coasts at a constant velocity
into contact with the wires in the brake, the
wires are pulled through rollers fixed on each
side of the track. The action of pulling the brake
wires through the rollers creates a deceleration
force; and the deceleration pulse shape is con-
trolied by the number, spacing, and length of
wires placed in the brake. The pitched fixture,
shown in Figure 5, positioned the seat in a 30
degrees nose down orientation relative to the
velocity and deceleration vector of the sled. A
fiftieth percentile Hybrid II ATD was used as the
occupant.



DEVELOPMENT OF A CRASHWORTHY SEAT
FOR COMMUTER AIRCRAFT

INTRODUCTION

Crashworthy seat requirements in the Fed-
eral Aviation Regulations (FARs) were amended
in 1988 and 1989 for aircraft defined in FAR
Parts 23, 25, 27, and 29 (1,2,3,4*}. Each of these
regulations contains a pass-fail criterion for a
vertical test condition, which states the “maxi-
mum compressive load measured between the
pelvis and the tumbar column of the anthropo-
morphic dummy (ATD) must not exceed 1500
pounds.” Dynamic tests for seats in normal,
utility, and acrobatic aircraft as defined in Part
23 include a test condition that represents a
vertical impact with the pitch axis of the aircraft
oriented in a 30-degree nose-down configura-
tion, The dynamics of the impact test specify the
velocity must be 31 feet per second {it/sec) with
a peak deceleration of 19 Gs for pilot seats or 15
Gs for passenger seats. Requirements in Part 25
of the FARs for seats in transport category
aircraft contain a test in the same vertical im-
pact orientation with the impact velocity of 35 ft/
sec and a peak deceleration of 14 Gs. Rotorcraft
seat performance requirements in Parts 27 and
29 specify the same vertical impact test orienta-
tion with a velocity of 30 ft/sec and a peak
deceleration of 30 Gs.

Dynamic impact test programs conducted at
the Federal Aviation Administration’s (FAA) Civil

Aeromedical Institute (CAMI), have evaluated
various techniques to meet the pelvic load re-
quirement with seats developed for Parts 23 and
25 categories of aircraft as well as military
rotorcraft (5,6). Based on the results of these
tests, three of tre main factors that influence the
pelvic load response are: (a) the deceleration
pulse severity, (b) the energy absorbing (EA)
properties of the vertical Joad paths through the
cushion, seat pan, and seat legs, and (c} the
available clearance for unimpeded deformation
or controlled stroking beneath the seat pan. Part
25 aircraft seats (passenger, pilot, and crew)
have met the 14 Gs requirement with “passive
EA” components such as a dense foam cushion
on a sheet metal seat pan with two inches of
clearance beneath the pan. Passenger seats for
FAR Part 23 have passed the 15 Gs vertical test
‘by incorporating a dense foam cushion and
deformable or flexible seat pan with three inches

of free space beneath the pan. Part 23 pilot seats
have met the 19 Gs requirement with designs
that included energy absorbing cushions/seat
pans and “active EA” components such as
curved legs that attenuate vertical forces by
bending or stroking downward three to four
inches {5). In comparison, military rotorcraft
pilot seats designed to meet the 50 Gs vertical
impact test specification of MIL-S-58095 {7,8)
require elaboxate energy absorbing mechanisms
with as much as 14 inches of vertical stroke
capability. Thus, seats tested at a higher sever-
ity than the 15 Gs condition for Part 23 passen-
ger seats have required vertical-displacement
active EA components that limit the forces re-
acted at the seat pan in order to enab’e it to pass
tne pelvic load specification.

Commuter Aircraft Seats

Commuter aircraft are categorized as those
with 19 passenger places and weighing 19,000
pounds. Although the airworthiness stavidards
for commuter aircraft are currently provided in
FAR Part 23, the size and flight performance
characteristics of commuter airplanes are in
most cases different from the characteristics of
smaller aircraft (weighing less than 12,500
pounds with seating capacity of nine passengers
or less) also regulated in Part 23. Concerns have
been raised within the FAA to address the verti-
cal test severity for commutes seats as a sepa-
rate requirement from the Part 23 regulations
adopted in 1988. Analysis of commuter acci-
dents and ongoing research may determine the
need ic change the vertical impact test severity
for commuter aircraft, on the basis of higher
crash loads experienced by occupants in a
commuter aircraft. One proposal ier a com-
muiter seat vertical test condition is a 32 Gs peak
triangular dec'aration pulse with a rise time of
0.030 seconds and an impact velocity of 32 ft/
sec. The deceleration pulse shape for this impact
condition is shown in Figure 1. along with the
three vertical test pulses defined in the FARs.

Based on the results from dynamic tests of
seats developed to pass existing impact require-
ments, acommuter seat that will meet the pelvic
force criteria when subjected to a 32 Gs vertical


Technical Report Documentation Page

1. Report No.
DOT/FAA/AM-90/11

2. Government Accession No. 3. Recipient's Catclog No.

4. Title and Subtitle 5. Report Date

Development of a Crashworthy Seat for Commuter September 1990
Aircraft 6. Perfsrming Organization Code
8. Performing Organization Report No.
7. Author! s)
Van Gowdy
9. Performing Orgenizetion Name ond Address 10.” Wark Uni: No. (TRAIS)
FAA Civil Aeromedical Institute
P.O. Box 25082 1. Contract or Grant No.

Oklahoma City, OK 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address
Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, S.W. 14, Sponsoring Agency Code
Washington, D.C. 20591

15. Supplementary Notes

16. Abstract

A series of dynamic impact tests were conducted using a prototype seat with an
energy absorbing mechanism as part of the seat pan. The seat frame was designed
to represent a typical commuter aircraft passenger seat. Tests were conducted in
an orientation simulating a vertical impact with a 30-degree nose-down aircraft
attitude. “The impact severity for these tests ranged from 15 to 33 Gs. Seat pan
stroke and occupant lumbar reaction forces were measured. Results indicate the
axial force measured in the lumbar spine of a fiftieth percentile Hybrid II dummy
can be limited to a peak value less than 1500 pounds during vertical impact tests
of 33 G with a seat pan stroke distance of 6.3 inches. K.. +

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ede13) lpi
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17. Key Words 18. Distribution Statement
yf Commuter Aircraft- Document is available to the public
Energy Absorbing Seat - through the Nationas Technical Information
Vertical Impact - 7.7" — Service, Springfield, Virginia 22161.
19. Security Classif. (of this report) T2. Security Classif. (of this poge) 21. No. of Pages | 22. Pree
UNCLASSIFIED UNCLASSIFIED 12

Form DOT F 1709.7 (8-72)

Reproduction of completed page authorized


NOTICE

This document is disseminated under the sponsorship of
the U.S. Department of Transportation in the interest of
information exchange. The United States Government
assumes no liability for the contents or use thereof.


REFERENCES

1. Title 14 U.S. Code of Federal Regulations, Part 23, Amendment 23-39, Section 23.562,
published in the Federal Register of August 15, 1988, effective date of September 14, 1988.

Nn

. Title 14 U.S. Code of Federal Regulations, Part 25, Amendment 25-64, Section 25.562,
published in the Federal Register of May 17, 1988, effective date of June 16, 1988

3. Title 14 U.S. Code of Federal Regulations, Part 27, Amendment 27-25, Section 27.562,
published in the Federal Register of November 13, 1989, effective date of December 13,
1989.

4. Title 14 U.S. Code of Federal Regulations, Part 29, Amendment 2¢-29, Section 29.562,

published in the Federal Register of November 13, 1989, effective date of December 13,
1989.

5, Rathgeber, Ronald K, and Parker, Paul E., Preliminary Design Research for the Caravan 1 Crew
Seat. Proceedings of 1985 SAE General Aviation Aircraft Meeting and Exposition, SP-622,
April 16, 1985.

6. Coltman, J.W., Design and Test Criteria for Increased Energy-Absorbing Seat Effectiveness,
FAA-AM-83-3, U.S. Department of Transportation, FAA Office of Aviation Medicine,
March, 1983.

x

. Gowdy, R.V., Dynamic Tests of the ARA Blackhawk Crew Seat for the U.S. Army, Memorandum
Report AAC-119-82-2, FAA Civil Aeromedical Institute, February, 1982.

8. MIL-S-58095A, Military Specifica*ion for Seat System: Crash-Resistant, Non-Ejection, Aircrew.
U.S. Army Aviation Systems Command, Dept. of the Army. August, 1986.

*U.S. GOVERNMENT PRINTING OFFICE: 1990-761-020/20330 Regica 7.

10