# Presentation: 056173

## ROUGH RUNWAY ANALYSIS

- Aircraft Dynamic Response

- Jack Hagelin
- Boeing Technical Fellow
- ASTM E-17 Seminar
- December 5, 2006

## Types of Runway Roughness Impact on Aircraft

**Three Types of Runway Roughness Impact on Aircraft:**
- Limit Loads – Single Discrete Bump Events
- Fatigue Loads – Continuous Long Wavelength Bumps
- 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.  **

## 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

## Bump Height vs. Length Diagram FAA Certification Runway (AC 25.491-1) – SFO 28R

- 3
- 2
- 1

## Limit Load Dynamic Taxi AnalysisResults – San Francisco (SFO) Runway 28R

## Bump Height vs. Length Diagram Sample Recently Measured CIS Rough Runway

**Bump Height vs. Length Diagram**** ****Sample Recently Measured CIS Rough Runway**

## Sample Rough Runway 200m section with critical bump

- Smooth line is curve fit used to flatten profile

## 3D Power Spectral Density (PSD) Plot Sample CIS Rough Runway

- 1

- 2

- 3

- Airplane Speed of 60 knots

## Limit Load Dynamic Taxi AnalysisSample CIS Rough Runway

## Bump Height vs. Length Diagrams Russian Certification Runways (A, B, C, D)

## 3D PSD Diagrams Russian Certification Runways (A, B, C, D)

**3D PSD Diagrams**** ****Russian Certification Runways (A, B, C, D)**

## Limit Load Dynamic Taxi AnalysisCG Vertical Acceleration Comparison

**Limit Load Dynamic Taxi Analysis****CG Vertical Acceleration Comparison**

- Limit Load Factor = 1.7g per AC 25.491-1

## 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

## Sample Taxiway which may be rough for Fatigue

- Critical Taxi Speed = 24 knots for 1 Hz airplane response

## 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

## Pivot Joint Heat Calculations

**Friction Energy =**

**Pressure-Velocity =**

**Pivot Pin**

-  = friction coefficient at bushing surface

## Short Wavelength Runway Profile AnalysisPower Spectral Density (Overall Runway)

**Short Wavelength Runway Profile Analysis****Power Spectral Density (Overall Runway)**

-   Shows bump height intensity versus bump wavelength

- Acceptable
- Threshold

## Runway Profile Analysis3D Relative Power Spectral Density

**                                                                                                                                         **

**                                                                                                                                          **

**Runway Profile Analysis****3D Relative Power Spectral Density**

**Acceptable**

**Rough**

**Runway Distance (m)**

**Relative Runway Height PSD (dB)**

**Bump Wavelength (m)**

**2**

**7**

- 1500m

## Runway Profile Analysis RMS of PSD Sorted by Airport

## Pivot Joint Dynamic Takeoff AnalysisResults – Typical International Runway

## Pivot Joint Dynamic Takeoff AnalysisResults – Borderline Runway

## Pivot Joint Dynamic Takeoff AnalysisResults – Rough Runway

## Dynamic Analysis Results –Takeoff RollPivot Joint Heat per Unit Bearing Area (Normalized) vs. Runway

## Dynamic AnalysisRunway RMS vs. Pivot Joint Heat

## Dynamic AnalysisCG Vertical Load Factor vs. Pivot Joint Heat

- Correlation of CG Acceleration with Pivot Joint Heat is not strong.
- (Due to widely different response frequencies)

## 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.