ASTM E-17 Seminar – December 6, 2006 – Page 1 ROUGH RUNWAY ANALYSIS Aircraft Dynamic Response...
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Transcript of ASTM E-17 Seminar – December 6, 2006 – Page 1 ROUGH RUNWAY ANALYSIS Aircraft Dynamic Response...
ASTM E-17 Seminar – December 6, 2006 – Page 1
ROUGH RUNWAY ANALYSIS
Aircraft Dynamic ResponseJack Hagelin
Boeing Technical FellowASTM E-17 SeminarDecember 5, 2006
2
Types of Runway Roughness Impact on Aircraft
Three Types of Runway Roughness Impact on Aircraft:
1) Limit Loads – Single Discrete Bump Events
2) Fatigue Loads – Continuous Long Wavelength Bumps
3) Truck Pivot Joint – Continuous Short Wavelength Bumps
Each type imposes a different runway roughness criteria.
Current standards address mainly first two types.
Third type is not directly addressed in current standards.
3
Limit Load Dynamic Taxi Analysis
Limit Load Critical Conditions Constant speed taxi Accelerated Takeoff Decelerated Landing Rollout Ride Comfort
Runway profile used as direct input Goal is to use roughest runway reasonably expected in normal operation (FAR 25.235). In absence of other data, AC 25.491-1 provides SF28R profile data. Analyze both forward and reverse directions, and multiple tracks if available. Discrete bump conditions also analyzed (Boeing single bump and FAR double bumps) Runway crown effect for airplanes with more than two main gears
Important input parameters: Airplane weight, cg, pitch inertia, speed, aerodynamic forces, and thrust Landing gear location (wheelbase), number of gears, shock strut air curve, tire stiffness, brake
force Tail aerodynamic force affects nose gear load Airplane on-the-ground natural frequencies (usually from 0.5 to 1.5 Hz)
Important output parameters: Landing gear vertical loads, airplane cg acceleration, forward fuselage, and engine loads
4
Bump Height vs. Length Diagram FAA Certification Runway (AC 25.491-1) – SFO 28R
3
2
1
5
Limit Load Dynamic Taxi AnalysisResults – San Francisco (SFO) Runway 28R
6
Bump Height vs. Length Diagram Sample Recently Measured CIS Rough Runway
7
Sample Rough Runway 200m section with critical bump
Smooth line is curve fit used to flatten profile
8
3D Power Spectral Density (PSD) Plot Sample CIS Rough Runway
1 2 3
Airplane Speed of 60 knots
9
Limit Load Dynamic Taxi AnalysisSample CIS Rough Runway
10
Bump Height vs. Length Diagrams Russian Certification Runways (A, B, C, D)
11
3D PSD Diagrams Russian Certification Runways (A, B, C, D)
1 2 3
12
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Airport
CG
Ver
tica
l Lo
ad f
acto
r (g
's)
Limit Load Dynamic Taxi AnalysisCG Vertical Acceleration Comparison
Limit Load Factor = 1.7g per AC 25.491-1
13
Fatigue Dynamic Analysis
Fatigue Critical Conditions Preflight taxi Takeoff roll Landing rollout Post-flight taxi
Runway profile used as direct input ‘Typical’ runway/taxiway profiles used to match in-service statistical data
Important input parameters: Airplane weight, cg, pitch inertia, speed, aerodynamic forces, and thrust Landing gear wheelbase, number of gears, shock strut air curve, tire stiffness Airplane on-the-ground natural frequencies (usually from 0.5 to 1.5 Hz)
Important output parameters: Landing gear vertical loads Airplane cg acceleration Engine loads Fuselage, wing, and horizontal tail incremental loads
14
Sample Taxiway which may be rough for Fatigue
Critical Taxi Speed = 24 knots for 1 Hz airplane
response
15
Main Gear Pivot Joint Analysis
Current runway standards do not adequately address this issue
On rough runways, the bogie pitch mode exhibits low damped resonant response at 10 to 20 Hz range due to short wavelength roughness (~2 to 7 m)
Important parameters for pivot joint analysis:
Pivot pin diameter
Friction coefficient in joint
Bearing pressure due to post load
Bearing surface velocity
PV (Pressure * Velocity)
Heat energy generated in the joint
Time duration of heating
16
Pivot Joint Heat Calculations
dtFRdtVFFdsE
AFR|PV
||||
/|
Friction Energy =
Pressure-Velocity =
Pivot Pin
= friction coefficient at bushing surface
F / 2 F / 2
F / 2 F / 2 Inner Cylinder
Bogie Beam
R
FA
F = Post Load
FF
Bogie Pivot Joint
17
Short Wavelength Runway Profile AnalysisPower Spectral Density (Overall Runway)
• Shows bump height intensity versus bump wavelength
Acceptable
Threshold
18
Runway Profile Analysis3D Relative Power Spectral Density
Acc
epta
ble
Ro
ug
hR
un
way
Dis
tan
ce (
m)
Rel
ativ
e R
un
way
Hei
gh
t P
SD
(d
B)
Bump Wavelength (m)
2 7
1500m
19
Runway Profile Analysis RMS of PSD Sorted by Airport
0
0.5
1
1.5
2
2.5
3
3.5
4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Runway
RM
S o
f P
ow
er S
pec
tral
Den
sity
[m
m]
Potential Heat Damage
Probable Heat Damage
20
Pivot Joint Dynamic Takeoff AnalysisResults – Typical International Runway
21
Pivot Joint Dynamic Takeoff AnalysisResults – Borderline Runway
22
Pivot Joint Dynamic Takeoff AnalysisResults – Rough Runway
23
Dynamic Analysis Results –Takeoff RollPivot Joint Heat per Unit Bearing Area (Normalized) vs. Runway
0
0.5
1
1.5
2
2.5
3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Runway
Piv
ot
Join
t H
eat
(No
rmal
ized
)
Potential Heat Damage
Probable Heat Damage
24
Dynamic AnalysisRunway RMS vs. Pivot Joint Heat
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.5 1 1.5 2 2.5 3
Pivot Joint Heat (Normalized)
RM
S o
f P
ow
er S
pec
tral
Den
sity
[m
m]
Potential Heat Damage
Probable Heat Damage
Acceptable
25
Dynamic AnalysisCG Vertical Load Factor vs. Pivot Joint Heat
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0 0.5 1 1.5 2 2.5 3
Nornalized Pivot Joint Heat
CG
Ver
tica
l Lo
ad F
acto
r (g
's)
Correlation of CG Acceleration with Pivot Joint Heat
is not strong.
(Due to widely different response
frequencies)
26
Summary
Three types of airplane response to runway roughness require three different acceptance criteria.
Airplane dynamic analysis is necessary to evaluate effects of rough runways on aircraft design, however, runway profile analysis can be used to determine acceptable roughness levels.
For limit loads, single bump height vs. length chart is good criteria. (This criteria is not adequate for fatigue or pivot joint).
For fatigue loads, a PSD criteria may be used in the 10 to 75 m range.
For pivot joint, PSD approach works well (2 to 7 m range).
RMS value in this range is a good measure of pivot joint impact.
Work is in progress with FAA to establish short wavelength runway roughness standard to address pivot joint friction.