# Using TRIZ Tools for Airport Runway Optimization

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## Abstract

Theory of Inventive Thinking (TRIZ) tools are used in the conceptual design and layout of novel runway models (ascending and descending) for the effective use of short length airport runways. When handling bigger aircrafts at smaller airports it is necessary to consider the economic effects and benefits of the larger airliners, and assisting more air travelers of the region.

The process of an aircraft take-off involves acceleration and clearing of a runway by elevating above ground before reaching the point of threshold. The process of an aircraft landing on a runway involves flare and touch down, first free roll, deceleration and a rapid exit runway diversion to stop.

The proposal of ascending and descending runways enables the operation of wide body aircrafts such as the Boeing 747 and the Airbus A380-800 by using the third dimension of a runway with a gradual slope of 2.5 degrees in addition to a rapid exit runway diversion of 18 to 22.5 degrees from the main runway orientation. An optimization solution is accomplished by negotiating the take-off and landing of bigger aircrafts with less than 10,000 feet of runway. This is accomplished through computer-aided design and analysis using the MATLAB (matrix laboratory) and Simulink for Technical Computing.

The conceptual model and theoretical design along with its layout is considered in this paper. Confirming the adequacy of runway length for bigger aircrafts at smaller airports will be addressed in subsequent papers.

## Introduction

Large aircrafts like the Boeing 747 and the Airbus A380-800 are economical for both operators and travelers. The operations of these aircrafts require long runways along with other equipment at airports.

The operation of long haul fights with large aircrafts has had success. For example, India has 128 airports that were mostly built in the middle of the 1900s. When low cost carriers (LCCs) took to the skies in 2003, Indian cities that had never been on active air maps, connected aggressively with many airlines looking for newer markets. The five-year span when domestic airlines could fly international routes brought hope and promise for companies operating long haul flights with large aircrafts.

The Airport Authority of India (AAI) is investing to expand and modernize about 35 non-metro airports. The expansion of several small runways at Indian airports, however, is impossible because the airport locations have become hubs in the last 20 years due to city development. The acquisition of land for existing airport developments has become trivial. It is causing inordinate delays with a long hold for litigation. With those constraints and technical contradictions TRIZ tools can be used to find solutions for enabling large aircrafts to land and take off easily on short length runways. The outcome is the ascending and descending runway model.

## Literature Support

The founder of TRIZ, Genrich Altshuller, and his colleagues developed an algorithm for finding innovative engineering solutions to problems.5 Altshuller's technical literature using TRIZ as a tool offers enough strengths and results for adopting as a tool for airport design.4,7,9 Airport engineering authors, Antonio A. Trani, G.I. Glushkov, S.K. Khanna and M.G. Arora have written documents and textbooks for the design and estimation of runway lengths at airports.1,6,8 In the last few decades runway occupancy time (ROT) in airport design has been the topic of research and development by many expert airport designers and planners. Byung J. Kim, the author of Computer Simulation Model for Airplane Landing Performance Prediction, has designed and prepared extensive documents for the capacity improvement of airports.2 Attention was focused on airport development as a way to reduce runway occupancy time, as in the rapid exit of aircraft from a runway.

The Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO) have stipulated safety regulations for aircraft separation of four to eight nautical miles in the series of a landing process. Under this condition, the rapid exit of the aircraft from the runway within 50 seconds is not substantial. Instead, a rapid exit in combination with a definite stoppage of the aircraft (with the optimum runway length) is required.

Author John-Paul B. Clarke wrote an article about continuous decent where he advocates a constant descent approach of aircrafts to save fuel and to reduce noise pollution.3 His theory also supports the ascending and descending runway theory.

## TRIZ –Theory of Inventive Problem Solving

The Theory of Inventive Problem Solving (TRIZ) is a Russian acronym for the methodology used to identify and define specific problems and elements in a system that needs correcting to reach a solution. The modern theory of TRIZ takes into consideration engineering problems and provides solutions based on a built structure. Part of TRIZ includes technical systems, which evolve through increasing ideality while overcoming contradictions, mostly with minimal resources. These solutions appear as innovations that are the only transpositions of known solutions in the same field(s) of interest.

The algorithm for inventive problem solving, or ARIZ, also is used for solving inventive problems. It is a sequentially structured action for invention. The creative problem solving of ARIZ is divided into three stages:

1. Analytical
2. Operative
3. Synthetic

The various steps bring forth the technical contradiction of a problem to form a matrix. The matrix is primarily used as the database of known solutions for TRIZ principles. The 39 parameters of the matrix, which are described as input, form contradictions that are placed in a 39 x 39 square. This contradiction matrix provides selective solutions among the 40 inventive principles. The algorithm for invention, the contradiction matrix and the 40 inventive principles are all based on the works of Genrich Altshuller and his colleagues. When applied judiciously, those principles help to overcome contradictions and offer ideal solutions.

The parameters that are considered fit for short length airport runways include:

• Area of stationary object
• Loss of time

When these two parameters are used with the contradiction matrix the following four principles emerge as possible solutions:

• Preliminary action
• Parameter changes
• Another dimension
• Asymmetry

When applied meticulously, these four principles will contribute to final innovative solutions for solving a contradiction.

The first principle, preliminary action, suggests:

• Performance of some functions beforehand
• Making a required change in the area of a stationary object
• Prearranging objects

The conditions can come into action from the most convenient place without losing delivery time. As a result, the solutions optimally bring forth the concept of an inclined slope at the end of the airport runway. This offers resistance for increasing the deceleration of aircraft during its ascending slope at the end of the airport runway due to its own mass and gravity, therefore, decelerating the aircraft on its final free and sliding roll.

The second principle, parameter changes, suggests:

• Changing the concentration or consistency
• Providing a degree of flexibility

The suggestions validate the consistent increase of resistance through a constant gradient by a certain degree of slope in the ascending runway. The degree of flexibility means the different diversified runway paths that are available for the aircraft to roll down to ease into its final stop.

The third principle, another dimension, outlines to:

• Move an object in a two or three dimensional space
• Tilt or reorient the object or lay it on its side

This helps the building up of the third dimension to the runway with a gradual slope of 2.5 degrees (upward inclination) in a vertical direction (Z–spatial plane). In addition to a rapid exit runway diversion of 18 to 22.5 degrees from the main runway orientation (with a slope of lesser magnitude such as 2.0 degrees in the vertical direction) it configures the ascending runway.

The fourth principle, asymmetry, dictates:

• Change in shape of the object from symmetrical to asymmetrical

The fourth principle identifies the conceived concept of a level runway changing into an ascending and descending runway model.

## Aircraft Landing and Take-off Sequences

The process of an aircraft landing on the runway is generally classified into four distinct stages.

1. Flare and touch down
2. First free roll
3. Deceleration (brake/thrust reversal)
4. Turn off to rapid exit taxi way and stop

The aircraft take-off process on the runway consists of two stages:

1. Acceleration of the aircraft to the required velocity for air lift
2. Clearing of the aircraft from the runway by elevating to 11 meters above ground level before reaching the point of threshold

Figure 1 illustrates the details of the ascending and descending runway model. The estimation of travel distance and the time for each stage of the landing and take-off processes are theoretical. The calculations made here only pertain to an Airbus A380-800 type aircraft.

 Figure 1: Ascending/Descending Runway Model

## Flare and Touch Down

Aircrafts normally maneuver in air at about 15 meters above ground level with the point of a runway threshold reaching ground level prior to the touch down point of the runway. The flare distance (Sair) is defined as the distance between the threshold point and the touchdown point on the runway. It is determined using a standard equation. The aerodynamic drag on the aircraft is neglected for ease of calculation, shown in Figure 2.

 Figure 2: Flair Distance Equation

Where:

• Sair = runway (air) distance to touch down
• HT = aircraft height at threshold point
• tan = descent angle of the aircraft (usually 2.5 degrees for the normal approach)

The time taken for the flare stage is calculated using the following equation:

 Figure 3: Flare Stage Time Equation

Where:

• Vfl = landing speed of the aircraft (usually taken as 1.1 to 1.15 times the stalling speed of the aircraft; for the Airbus A380-800 it is about 240 to 253 kmph or 67 to 70 m/sec)

The stalling speed of the various aircrafts with the maximum landing weight (MLW) at sea level can be found in an aircraft manufacturer's manual. The changing atmospheric conditions from the international standard atmosphere (ISA) and the location altitude determine the stall speed Vstall, shown in Figure 4:

 Figure 4: Stall Speed Equation

Where:

• Vstall = stalling speed (m/sec)
• m = MLW minus maximum landing mass of the aircraft with payload and fuel (kg)
• g = acceleration due to gravity (9.81 m /sec2
• r = air density (kg/ m3) (depends on the temperature and altitude of the airport)
• CL = lift co-efficient developed by the aircraft
• S = aircraft gross wing area (m2)

## First Free Roll

The first free roll is the tangential (arc) distance of transition to touch down of the aircraft with minimum sink rate added with the slope run. Upon touch down the aircraft is allowed to make a free roll to get stabilized after the sinking and retrieval effect of the landing gears. The term Vfl, (the flaring velocity) is closely related to the stalling speed of the aircraft where pilots try to maintain a safe margin with the stalling speed for the stability and assurance of the aircraft landing process.

At the end of the flare phase the speed of the aircraft is supposed to be maintained at 95 percent of the stalling speed of the aircraft. In the case of the Airbus A380-800 the stall speed is estimated to be 220 kmph or 61 m/sec. When the instrumental landing system (ILS) is used to make 2.5 degrees of approach inclination in the descending path of the aircraft, the first free roll distance of the aircraft (neglecting the aerodynamic drag) is estimated by using the following formula:

 Figure 5: First Free Roll Distance Equation

Where:

• nf = flare load factor (recommended value ranges from 1.1.to 1.3)
• FR= rolling and frictional resistance of the runway (assumed as 220N/ton mass of the aircraft)
• a = runway inclination (2.5 degrees)

The time taken for the first free roll phase is estimated by the following equation:

 Figure 6: Equation for Time Taken for First Free Roll

Figure 7 shows the various stages of the aircraft landing process.

 Figure 7: Various Stages of Aircraft Landing

At the end of the first free roll (approximately five seconds from touch down) the aircraft velocity (u) should be equivalent to 90 to 95 percent of the stalling speed. For the Airbus A380-800 it is estimated as 55–58 m/sec. The aircraft has the capacity to apply brakes to decelerate at the rate of 3 to 5 m/s2. For the safety and comfort of passengers, pilots will decelerate the aircraft well below the maximum braking capacity of the aircraft depending on the length of the available runway. The terminal velocity (v) of the aircraft (if choosing to follow the rapid exit taxi way) should be around 20 m/s. The minimum and the maximum distance and time required for this phase (up to the point of termination of brake/thrust reversal) is determined as follows:

## Deceleration (Brake/Thrust Reversal)

The long landing run (distance) is determined using the following equations when the initial velocity (u) and the final velocity (v) of the aircraft are known.

• v2 = u2 + 2as (8 a)
• v = u + at (8 b)
• a = gFR (ground level) (9)
• a = g (FR cos a + sin a) (ascending runway stretch) (10)
• a = g (FR cos a - sin a) (descending runway) (11)

Where:

• u = initial velocity in m/s
• v = terminal velocity in m/s
• s = distance in meters
• a = acceleration in m/s2
• t = time in seconds
• FR = coefficient of runway friction (0.15 to 0.2 for rolling) (0.7 for sliding)

## Final Roll

The final roll of the aircraft is subjected to pure frictional resistance due to the paved main runway or the rapid exit runway. The rolling and sliding frictional resistance that comes from the paved runway surface would be 0.15 to 0.2 and 0.7, respectively. The distance and time taken for the final roll is determined by taking into account the initial and final velocities as 20 m/sec and zero m/sec and then applying the two previous equations (8a and 10).

## Take-off

The aircraft take-off includes two processes. The acceleration required for the aircraft to be airborne is around 1.2 to 1.25 times the stalling velocity of the aircraft. The descending runway helps the aircraft to accelerate faster and to reach the required velocity to break contact with the runway and to airlift at the shortest spell. This velocity would range from 264 km/hr to 275 km/hr for the Airbus A380-800. The aircraft (after clearance from air traffic control) is lined up to its position to reach the stop way area of the paved runway to commence its take-off run. The aircraft is placed at the elevated plane of a descending runway (2.5 degrees of inclination) it starts moving down initially with minimum startup velocity. As the aircraft moves down it gains great momentum due to its own mass and steady acceleration. Gradually it picks up acceleration and attains the required velocity to break contact with the runway surface for airlift. The runway length required for the successful take-off is calculated using the equation 8a coupled with equation 11. Even in the event of an aborted take-off, the aircraft will have sufficient runway length to decelerate and will subsequently take advantage of the ascending runway at the other end for a definite stop.

## Results

 Estimation and Comparison of Runway Lengths Process Flare Free roll Deceleration Final roll Total length (in meters) Available length (in meters) Landing 344-514 30-45 670-755 90-136 1450 2950 Take-off 1935 + 125 2060 2950

The minimum runway length required for the ascending and descending runway is invariably 15 to 20 percent less of the statutory minimum length required of the level runway.

## Conclusion

The innovative concept of ascending and descending runway models provides multiple benefits, such as optimizing the runway lengths, saving fuel during landing and take-off, and subjecting the landing gear to less impact while extending its life. Fulfilling the FAA's and ICAO's regulatory allowances of 15 percent extra on take-off length and 67 percent extra on landing length of the runway is also assured with varied runway options for safety. The conceptual design and the model arrived through the identified four principles of TRIZ is a workable solution for modern aircraft as well as older airports worldwide.

## Acknowledgements

I am deeply indebted to my institution, Dr. Mahalingam College of Engineering & Technology, for its support and for the ability to carry out this project during extended hours at the college. I wish to express my thanks to Mr. K. Senthil Kumar of MIT and Dr. J. Shanmugam, principal at Velammal Engineering College and Chennai, for their support of extending the simulation facilities to conduct the second part of the studies on this research.

## References

1. Dr. Antonio A. Trani, Aircraft Runway Length Estimation, Part 1, Virginia Tech, USA.
2. J. Kim Byung, Computer Simulation Model for Airplane Landing Performance Prediction, Transportation Research Record, 1996.
3. John-Paul B. Clarke, Continuous Descent Approach: Design and Flight Test for Louisville International Airport, Journal of Aircraft, Vol. 41, No.5, p.1054-1066, 2004.
4. Ellen Domb, The 39 Features of Altshuller's Contradiction Matrix, The TRIZ Journal, November 1998.
5. Genrich Altshuller, The Innovation Algorithm, Technical Innovation Center, Inc. Worcester, MA, 2000.
6. G.I. Glushkov, Airport Engineering, Mir Publishers, Moscow, 1988.
7. James Kowalick, Technology Forecasting With TRIZ, The TRIZ Journal, January 1997.
8. S.K. Khanna and M.G Arora; Nemchand, Airport Planning and Design, 2005.
9. Nikolay Shpakosky, TRIZ in the World of Science, The TRIZ Journal, March 2008.

Professor K. Venkata Rao's interests are in aeronautics and aero-model building. He works as an associate professor in the Mechanical Engineering Department of Dr. Mahalingam College of Engineering and Technology in India. He has also worked as a scientist at the Indian Space Research Organization in Trivandrum, India over the span of three decades. Contact K. Venkata Rao at k_venkatarao (at) hotmail.com.

Dr. V. Selladurai professor and head of the Department of Mechanical Engineering at Coimbatore Institute of Technology, Coimbatore.

Dr. R. Saravanan professor and head of the Department of Mechanical Engineering at Karpagam University, Coimbatore.

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