THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE

DEPARTMENT OF MECHANICAL ENGINEERING

ANALYZING EFFECTS OF AIRCRAFT SEAT DIMENSIONS ON PASSENGER ACCOMMODATION WITH REGARDS TO COST OPTIMIZATION

RITWIK BISWAS SPRING 2020

A thesis submitted in partial fulfillment of the requirements for a baccalaureate degree in Mechanical Engineering and with honors in Mechanical Engineering

Reviewed and approved* by the following:

Matthew Parkinson, PhD Professor of Engineering Design and Mechanical Engineering Thesis Supervisor

Anne Martin, PhD Assistant Professor of Mechanical Engineering Honors Adviser

*Signatures are on file in the Schreyer Honors College. i

Abstract

The objective of this work is to quantify how airplane seat dimensions relate to passenger size and shape. Accommodation measures the degree to which a design meets the spatial requirements of a target user population. As the body size of individuals in the US has increased over the years, airplane seat dimensions have either remained constant or decreased. Previous studies have analyzed the effects of airplane seat legroom on passenger comfort and acceptability but few have simultaneously considered seat width. This work uses a virtual study to determine how an increase in seat width and seat legroom can affect levels of accommodation within potential revenue-neutral seating configurations. Results of the virtual study show that 9.1% of military personnel, who tend to be more physically fit than civilians, are not accommodated by the industry standard seat width of 17 inches and seat pitch of 30 inches. As a result, this percentage of people are not able to physically fit in these seat dimensions with their bare anthropometric dimensions. Additionally, it is found that removing a seat per row in order to increase seat width has a greater effect on accommodation levels than reducing a row of seats. However, an increase in seat width comes at a greater ticket cost than an increase in legroom. The optimal solution is to create a smaller separate class such as premium economy that offers larger seats to those dis-accommodated by the standard seat dimensions. ii

Table of Contents

List of Figures iv

Acknowledgements vi

1 Introduction1

2 Background3 2.1 Problems with Current Airplane Seat Design...... 5 2.2 Previous Studies Optimizing Seat Allocation...... 7 2.3 Concept Seat Designs...... 9 2.4 Significance of Airplane Seat Design...... 13

3 Methods 14 3.1 Virtual Study Overview...... 14 3.1.1 Seated Hip Breadth and Buttock to Knee Length...... 15 3.1.2 Equations Used...... 15 3.2 Human Research Study Overview...... 16 3.2.1 Purpose of Experimental Study...... 17 3.2.2 Airplane Seat Model Design...... 18 3.2.3 Experiment Design...... 19

4 Results 25 4.1 Seated Hip Breadth and Buttock to Knee Length Correlation...... 25 4.2 Accommodation Levels in Industry Standard Condition...... 26 4.3 Effects of Increased Seat Width Conditions...... 28 4.3.1 Accommodation Levels in Seating Configuration of 5 Seats across..... 29 4.3.2 Accommodation Levels in Seating Configuration of 4 Seats across..... 30 4.4 Effects of Increased Seat Legroom Conditions...... 32 4.4.1 Accommodation Levels in Seating Configuration of 24 Rows...... 33 4.5 Accommodation Levels in Optimal Seating Configuration...... 35 4.6 Effects on Ticket Cost in Revenue-Neutral Model...... 36 4.6.1 Increase in Ticket Cost with Increased Seat Width Condition...... 36 4.6.2 Increase in Ticket Cost with Increased Seat Legroom Condition...... 37 4.6.3 Increase in Ticket Cost with Optimal Seating Configurations...... 38 iii

5 Discussion 40 5.1 Significance...... 40 5.2 Limitations...... 41 5.3 Future Work...... 43

6 Conclusions 44

Bibliography 45 iv

List of Figures

2.1 Consistent increase in number of flying passengers in several major countries from 2016 to 2036. India, China, Turkey, and Indonesia have the largest increase in the commercial aviation passenger numbers. [1]...... 4 2.2 Average comfort rating for passengers seated in all potential locations with varying features on their sides [2]...... 8 2.3 Aviointeriors has developed this concept seat design called the Skyrider 2.0. This is a saddle seat designed specifically for the ultra-high-density economy cabin. With the seat’s pitch at only 23 inches, it still supports your back and bottom. [3]. 10 2.4 Flying V Airplane Design developed by TU Delft, KLM Airlines, and Airbus. This fuselage design allows for increased flexibility in interior seating design and configuration options. [4]...... 11 2.5 TU Delft has come up with 4 seating options inside the Flying V cabin. 1) facing two-seaters around a flip up table 2) private seats staggered for privacy as well as more shoulder and leg space 3) a three birth bunk bed module that can convert to bench seating for take-off and landing 4) alternating floor and ceiling mounted seats that allow one to take different postures for different tasks [4]...... 12

3.1 Experimental apparatus shown with manikin sitting on the section of the seat bench with varying seat width. The manikin’s right armrest is not permanently fixed and has been designed to move side to side to simulate changing seat width conditions. 19 3.2 Stature measurement is measured from the top of one’s head to the bottom of their feet. In the research experiment, a stadiometer is used to measure the study participant’s stature. [5]...... 20 3.3 a) The seated hip breadth measurement is taken at the widest point of the study participant’s hip b) Bideltoid breadth is measured at the widest horizontal breadth at one’s shoulder level. c) Sitting height is measured from the top of one’s head to the bottom of their buttocks. d) The buttock to knee length measurement is taken from the front point of the subject’s knee to the most rear point of their buttocks. [5] 21 3.4 The survey used in the study is shown here. It is presented on the iPad after every trial and forces study participants to choose whether the condition is acceptable or unacceptable by having a contrasting color scheme. This does not allow for the subjects to choose a neutral reaction. Moreover, the last question asks for the level of comfort the specific situation offers. Research participants use a slider for answering this question and the software program converts this into a relative number from 0-100...... 22 v

3.5 In a), the manikin has access to both the armrests and has a certain degree of shoulder room. For b), the manikin has shoulder room but does not have access to the armrests. In c), the manikin has access to both the armrests but does not have shoulder room. Lastly in trial d), the manikin does not have access to both the armrests and shoulder room...... 24

4.1 The correlation between Seated Hip Breadth and Buttock to Knee Length is shown above. The r value of 0.38 shows that there is a weak relationship between these two variables...... 26 4.2 Accommodation Level under condition of industry standard measurements of 432mm (17in) seated hip breadth and 686mm (27in) buttock to knee length. With these seat dimensions, 90.9% of this data is accommodated...... 28 4.3 Increase in Seat Width when changing seat configuration from 6 seats in each row to 5 and 4 seats across. 5 seats across results in a seat width of 518mm and 4 seats across results in a seat width of 647mm...... 29 4.4 Accommodation Level under condition of 5 seats across in each row. With 5 seats across, the seat measurements are 518mm (20.4in) seated hip breadth and 686mm (27in) buttock to knee length. 98.6% of the data is accommodated in this configu- ration...... 30 4.5 Accommodation Level under condition of 4 seats across in each row. With 4 seats across, the seat measurements are 572mm (22.5in) seated hip breadth and 686mm (27in) buttock to knee length. 98.7% of the data is accommodated in this configu- ration...... 31 4.6 Increase in Seat Width when changing seat configuration from 25 rows of seats to 24 and 23 seats rows. 24 rows of seats results in a seat legroom of 724mm and 23 rows of seats results in a seat legroom of 752mm...... 33 4.7 Accommodation Level under condition of 24 rows of seats as opposed to 25 rows. With 24 rows of seats, the seat measurements are 432mm (17in) seated hip breadth and 724mm (28.3in) buttock to knee length. 91.6% of the data is accommodated in this configuration...... 34 4.8 Accommodation Level under optimal condition of 24 rows of seats and 5 seats in each row. With this seating configuration, the seat measurements are 518mm (20.4in) seated hip breadth and 724mm (28.5in) buttock to knee length. 99.9% of the data is accommodated in this configuration...... 35 4.9 Increase in Ticket Cost with Seat Configuration decreasing from 6 seats in each row to 5 and 4 seats. Maintaining a revenue neutral cost structure, a change to 5 seats in a row results in a 20 % increase in ticket cost per passenger. Similarly, a change to 4 seats in a row causes a 50 % increase in ticket cost per passenger.... 37 4.10 Increase in ticket cost with seat configuration decreasing from 25 rows of seats to 24 and 23 rows. Maintaining a revenue neutral cost structure, a change to 24 rows of seats results in a 4.2 % increase and 23 rows results in a 8.7 %increase in ticket cost per passenger...... 38 vi

Acknowledgements

I would like to thank Professor Matt Parkinson for supervising my research and providing incredibly valuable guidance during my thesis project. He has truly helped me grow as a researcher and engineer over the past four years. I would like also to thank my peer OpenDesign Lab members who assisted in running the research study and providing their expertise along the way. Lastly, I want to acknowledge my parents, professors, and friends for their unwavering support during my college career. 1

Chapter 1

Introduction

The objective of this paper is to explore the relationship between airplane seat dimensions and percentage of passenger accommodation. Accommodation level measures the percentage of fit for passengers in airplane seats. Some airlines have been increasing passenger density with the use of slimline seats which is potentially impacting people’s flying experiences negatively [6]. Slimline seats are new popular designs that both weigh less and have less padding than full size seats [7]. As a result, these seats allow airlines to place seats closer together in order to increase passenger capacity and revenue. The experiment conducted for this research is based on a virtual model that shows the percent- age of the US population sample data that is accommodated in airplane seats of certain dimensions. This paper then analyzes the data received from this study and makes conclusions about the rela- tionship between seat dimensions and levels of accommodation. Alternative seating configurations and their cost effects are also discussed in detail assuming a revenue neutral cost structure for the airline. Human variability refers to the range of physical and mental characteristics of people. Design for human variability can be a challenging field as it analyzes how designs can accommodate the human population. With human bodies having such a wide variety of shapes and sizes, developing a product with fixed dimensions can potentially be an intensive process. Engineers guide design practice based on anthropometry, the science of analyzing and defining different proportions of the human body, to determine certain measurements they need to account for. Within this process, engineers strive to make their product ergonomic by ensuring it can be used safely and efficiently. Design for human variability (DfHV) can be implemented for a wide array of products ranging 2 from wearable electronic devices to handheld tools to even healthcare equipment such as surgical beds. One other example of DfHV that this work specifically focuses on is designing airplane seats. The population that flies in airplanes today consists of people that are of all sizes and shapes physically. As a result, those prescribing the interior of an airplane are faced with the daunting task of designing a product that can fully accommodate almost all of the human population regardless of their height and weight while simultaneously trying to make money. They do this by using accurate anthropometric data that effectively meets the relationship between potential human body characteristics and the parameters of the seat design. Airplane seats should allow people of all sizes to physically fit in the seat and ensure that passengers experience a certain level of comfort. Especially with an increase in the number of long haul nonstop flights lasting up to 19 hours, airplane seat comfort is becoming more significant in the aviation community [8]. However, as airlines prioritize increasing their profit margins by maximizing the number of seats they can fit in an aircraft, passenger comfort is greatly forfeited [9]. Awareness of these cramped seating situations while flying is growing at such a rapid rate that even the US Congress has stepped in by developing a Seat Act of 2017 that grants the FAA the authority to set minimum airplane seat requirements by which airlines must abide [10]. The FAA plans to analyze how passengers interact with the space they are given as well as how comfortable they are in different seat dimensions. The research presented in this paper does exactly this by using a virtual model to explore the relationship between airplane seat dimensions and level of ac- commodation. Although acceptability is an aspect that can be difficult to quantify, the experiment offers valuable insights into how levels of passenger accommodation ranges in different physical situations. This work goes a step further by discussing optimal seating configurations that benefit both passenger comfort and airline profit potential. 3

Chapter 2

Background

In 2017, over 4 billion passengers flew on scheduled airline flights between more cities than ever setting a new global travel record [1]. As seen in Figure 2.1, the International Air Transport Association (IATA) expects the number of global flying passengers in several countries, especially developing nations, to increase from 2016 to 2036. This growth in flying passengers is due to current and expected improvement in global economic conditions as well as lower airfares around the world [1]. However, as aircraft reach full capacity and load factor (ratio of seats occupied to the total number of seats on an airplane) increases, passenger comfort can become significantly compromised. It also reflects on how efficiently airlines operate with regards to filling the number of seats they offer on a particular airplane or route. 4

Figure 2.1: Consistent increase in number of flying passengers in several major countries from 2016 to 2036. India, China, Turkey, and Indonesia have the largest increase in the commercial aviation passenger numbers. [1]

Although humans are increasing in size, airplane seats are only becoming smaller and offering less legroom as well as seat width. Researchers such as Vasquez et al. [11] analyzed changes in human dimensions from 1975 to 2014 using data from the United Nations and found that the average adult was 14% heavier and 1.3% taller in 2014 compared to 1975 [11]. As a result, passenger comfort is being affected and will potentially continue to diminish in the near future if the standard aircraft seat design is not revised. 5

2.1 Problems with Current Airplane Seat Design

Over the past several decades, researchers have looked into the problems with the current air- plane seat design through a variety of studies and experiments. It has been found that seat comfort is one of the major sources of dissatisfaction that airline passengers have with their flying experi- ence. Vink et al. [12] evaluated passenger comfort by conducting a study of more than 10,000 internet-based trip reports and 153 passenger interviews. From this research, legroom and per- sonal space received the lowest ratings and that they had a strong correlation of 0.72 with comfort score. There was also a consensus that passengers disfavored the cramped seating conditions with respect to legroom and seat width. Moreover, an analysis of passenger interviews indicated that there is a significant need for more room and further separation from their seated neighbors. Not only do the current airplane seat designs cause widespread passenger discomfort, but they can also lead to multiple health complications. Hinninghofen and Enck [13] discovered that cramped seating makes it extremely difficult for passengers to leave their seat and gain the routine exercise they need, especially on long haul flights. Sitting in one position for extended periods of time negatively affects respiration and restricts normal blood circulation. As a result, a fixed seated posture has the potential to cause deep vein thrombosis (DVT), oedema, and pulmonary embolism of the lower limbs. Mastrigt, Hiemstra-van et al. [14] found that regardless of one’s height, people tend to adhere to one specific posture during a flight but change where their body makes contact with the cushion and backrest of the seat. Mastrigt, Hiemstra-van et al. [14] also concluded that seat designs which support a wide variety of postures will offer the highest comfort to passengers. Current airplane seats do not support more than a few body postures and as a result need to be redesigned to do so. Additionally, Hinninghofen and Enck [13] determined from their research that women are at higher risk than men for developing DVT, oedema, and pulmonary embolism. However, it was found that leg oedema specifically is usually benign and tends to subside after landing. 6

Porta et al. [15] claims that researchers in the field often refer to these health problems as the “economy class syndrome”. With the majority of people flying in economy class over first and business, most of the flying population is thus exposed to these major health complications. In fact, there has been a significant increase in passengers flying on low cost airlines equipped only with economy class seats [1]. As a result, worldwide airplane passenger discomfort becomes of greater importance. Porta et al. [15] also discusses how these health issues can be aggravated by a multitude of attributes such as old age, obesity, use of certain medications, arterial hypertension, and taking long haul flights. From this study, it was concluded that seat pitch and seat width dimensions should be designed to accommodate at least the 95th percentile of the population at hand. Similarly, Bouwens et al. [16] experimentally determined that being confined to one sitting position for a flight longer than four hours poses severe risk for DVT, oedema, pain in buttocks, leg numbness, and lower back pain. Bouwens et al. [16] also states that the total localized muscu- loskeletal discomfort (LMD) increases over time for all humans regardless of shape and size. The participants of this study reported that they had the highest discomfort in their neck, buttocks, and lower back. However, the words “comfort” and “discomfort” are not affected just by physical stresses. Ahmadpour et al. [17] defines comfort as being a subjective state that is determined by physical, physiological, and psychological factors. Therefore, it is vital to also explore the emotional aspects of the airplane seat experience that passengers face. Ahmadpour et al. [17] conducted a study to find the most important factors affecting passenger comfort and determined that there are six main areas: proxemics, pleasure & satisfaction, aesthetics, social association, physical well-being, and peace of mind. One can clearly see that the majority of these areas are in fact emotional states. Proxemics refers to the amount of space that people need from each other. This aspect was found to be the most important area affecting comfort from this study. Ahmadpour et al. [17] states that eighty percent of the study participants responded with seat proxemics being extremely vital for them when determining seat comfort. This research suggests that future aircraft seat designs 7 should enhance proxemics by increasing the personal space that passengers receive when seated on an airplane. Moreover, an increase in proxemics was found to increase people’s feelings of “peace of mind” resulting from a greater sense of relaxation and security.

2.2 Previous Studies Optimizing Seat Allocation

While passengers greatly value seat comfort, airlines on the other hand strive to maximize the number of seats in order to optimize revenue. This in turn however decreases passenger comfort by making the seats smaller and closer to each other. People from both academia and industry have attempted to find the perfect balance between passenger seat comfort and airline profit potential. This section describes the seat configuration solutions these researchers have presented in their respective works. For instance, Butt [18] developed a patent that outlines a seat allocation strategy that maximizes both airline revenue and passenger comfort. It was found that passenger comfort can be increased by decreasing the number of seats one is located from the aisle. As a result, this work incorporated the concept that commercial airplanes should have enough aisles to make sure there are no more than two contiguous seats next to each other. Butt [18] also made a simplified assumption that airline revenue = price per ticket * number of seats. This shows that revenue can only increase if airlines either increase the cost per ticket or squeeze more seats into an airplane with fixed dimensions. Over the last decade, airlines have consistently chosen to do the latter which has resulted in decreased passenger comfort. Butt [18] sets up the seat allocation strategy as having a total of five seats per row as opposed to the conventional six seats that narrow body aircraft such as the Airbus A320 and Boeing 737 have installed today. This model places only five seats per row in order to add a second aisle thereby resulting in a 2/2/1 or 2/1/2 seat layout where the / refers to where the aisle is located. Butt [18] claims that because this would decrease a significant number of economy class seats, airlines should remove business class to only have economy class seats throughout the airplane to make up 8

Figure 2.2: Average comfort rating for passengers seated in all potential locations with varying features on their sides [2] for the decrease in the number of seats. Because economy class seats would be more comfortable with this new layout, Butt [18] believes that more people would pay higher ticket prices offsetting the removal of business class and thus maximizing revenue. In the end, increasing airline revenue is a significant step towards making airlines profitable. While this invention has great merit, it can only be successful if the assumption is true that most people would pay higher ticket prices for more comfortable economy class seats. Brauer [2] similarly claims that conventional airplane seat layouts have failed to maximize both passenger comfort and the number of seats that can be fitted on an aircraft with fixed dimensions. Brauer [2] developed a patent with a goal of providing a way to maximize the number of seats installed on an airplane while still maintaining the average passenger comfort rating. Brauer [2] 9 achieved this goal by conducting in-flight studies and calculating the APCL or average passenger comfort level. As shown by Figure 2.2, Brauer [2] found that passengers experience vastly different comfort levels depending on their seating position and what features they are located between. For instance, passengers seated between an empty seat and a sidewall have the highest level of comfort while passengers on a middle seat seated between two other passengers have the lowest level of comfort. The data also shows that the comfort of passengers seated next to the sidewall or furthest from the aisle experience the greatest levels of comfort. This directly contradicts the previous belief that comfort can be increased by minimizing the number of seats a passenger is located from an aisle. Note that Brauer [2] only researched these variations because the FAA has mandated a policy that an airplane passenger cannot be seated more than two seats away from the nearest aisle. Brauer [2] also concluded that a useful measure of comfort is analyzing the spatial area of passengers’ shoulder level since anthropometric data shows humans are widest at their shoulder breadth. By analyzing the spatial area of the horizontal plane at the shoulder level, Brauer [2] could find the total amount of useful additional area enjoyed by passengers (UAAP) which is an important parameter to consider when attempting to qualify comfort. It is argued that passenger comfort can be significantly increased by increasing the UAAP parameter. Brauer [2] looked into reducing the dimensions of the airplane itself to maximize airline revenue and profit since smaller dimensions result in less aerodynamic drag and weight which leads to less fuel consumed. Reducing operating costs for an airline while still maintaining certain levels of passenger comfort is a vital step towards finding the ideal balance between airline profit potential and comfort.

2.3 Concept Seat Designs

In the last decade, several conceptual seat designs have been developed that are aimed either at increasing passenger capacity on airplanes or increasing passenger comfort. This section describes both of these approaches and the designs that have resulted. Increased competition between airlines can lead to making airfares cheaper for the increasing 10

Figure 2.3: Aviointeriors has developed this concept seat design called the Skyrider 2.0. This is a saddle seat designed specifically for the ultra-high-density economy cabin. With the seat’s pitch at only 23 inches, it still supports your back and bottom. [3]

flying population. Over the last decade, airlines across the world have been competing to offer the lowest fare possible to entice both leisure and business travellers that are budget minded [3]. These airlines have realized that if they want to lower airfares without affecting their bottom line, they need to increase the number of seats. They can either do this by decreasing legroom and making the seats closer or utilizing a brand new seat design all together. In fact, some airlines have begun to look into a standing seat design which will allow airlines to place seats much closer and have significantly more seats in the airplane. This way, airfares can fall and profit is unaffected. According to Noor and Romli [19], Spring Airlines projected that a standing cabin concept would increase the passenger capacity of their airplanes by roughly 40 percent. The airline seat manufacturer, Aviointeriors, has already developed a standing seat concept called the Skyrider [3]. Aviointeriors believes that they have a design that can successfully trans- port passengers in their upright position. With the Skyrider seat shown in Figure 2.3, passengers would not be fully standing but instead would feel like they are sitting on a saddle. This firm claims that passengers would be comfortable in this position for up to three hours. In fact, Ryanair 11

Figure 2.4: Flying V Airplane Design developed by TU Delft, KLM Airlines, and Airbus. This fuselage design allows for increased flexibility in interior seating design and configuration options. [4] has already operated a hundred trial flights where 50 standing seats replaced the last five rows of seats. They tested these flights by having passengers in these standing seats for one hour flights. However, safety is of utmost importance in any airplane seat design and no standing seat concept has been approved for commercial use [3]. On the other hand, not all concept seat designs are solely focusing on maximizing the number of seats that can be squeezed into a fuselage. Some industrial designers have been tasked with developing unique seat designs that prioritize comfort for future commercial travel. In partnership with Airbus, researchers from the Delft University of Technology have had a new vision for the design of commercial airplanes: The Flying V [4]. It promises to use 20 percent less fuel than modern commercial aircrafts due to its aerodynamic shape. With this new fuselage design shown in Figure 2.4, Yao and Vink [4] have been creating different cabin designs that can be smoothly incorporated with this structure. Figure 2.5 shows multiple economy class seating options Yao and Vink [4] have developed. 12

3) 2)

4)

1)

Figure 2.5: TU Delft has come up with 4 seating options inside the Flying V cabin. 1) facing two-seaters around a flip up table 2) private seats staggered for privacy as well as more shoulder and leg space 3) a three birth bunk bed module that can convert to bench seating for take-off and landing 4) alternating floor and ceiling mounted seats that allow one to take different postures for different tasks [4]

One seating strategy is where the rows alternate between floor and ceiling mounted to utilize the interior space more efficiently. This design allows passengers to take different positions during flight and lay almost flat even in economy class. Another seating concept is having a combination of a bench and 3 lie flats in a bunk bed design so passengers can also lie down during the flight with the exception of take off and landing when they will be seated on the bench. The bottom two bunk beds can easily convert to a bench for take off and landing purposes. Yao and Vink [4] conducted surveys of 128 participants and found from their research that most passengers value the feeling of privacy on a long haul flight. Moreover, it was found that 60 percent of passengers want to be able to lie down and sleep on a long haul flight in economy class. However, these are only conceptual designs and the research team does not expect this form of commercial travel to revolutionize for another 20-30 years after the Flying V has been fully developed. 13

2.4 Significance of Airplane Seat Design

Understanding the implications of airplane seat design can be vital for several groups including airlines and airplane manufacturers. It is of upmost importance for airlines specifically to invest in better seat design since passenger comfort is a significant aspect of the overall flying experience with that airline. In fact, Vink [20] found that there is a strong correlation between seat comfort and flying again with the same airline. Moreover, Brauer [2] found that higher comfort levels are extremely desirable for airlines since it has been proven that passengers are willing to pay higher fares for a more comfortable seat. This will especially hold true in a greater competitive environment when airlines with higher comfort levels start attracting more passengers willing to pay higher fares. From the 10,032 internet trip reports that Vink [20] analyzed, it was found that passengers flying on newer aircrafts experienced a higher level of comfort as opposed to older aircrafts. In fact, Hinninghofen and Enck [13] state that one of the newest aircrafts on the market, the Boeing 787 Dreamliner, has economy seats that are more spacious, being 4 cm wider than previous versions of the airplane. This shows that both aircraft manufacturers and airliners have already begun to realize the significance of seat design and the widespread effects it can attribute to. However, Hinninghofen and Enck [13] also concluded from their research that 30 percent of commercial aircraft seats in use today are narrower than the recommended 42 cm seat width pre- scribed by Airbus in 2013. As a result, there is still an urgent need for the entire industry to pivot with regards to aircraft seat design in the upcoming years and redesign the conventional airplane seat to offer higher levels of comfort to paying passengers. 14

Chapter 3

Methods

This section includes the methods used for a model-based study that was conducted to complete this thesis. It also describes the study it replaced: an experimental study that was taking place in the OPEN Design Lab prior to the COVID-19 interruption. It remains so the reader understands the context in which the remaining work was done.

3.1 Virtual Study Overview

This model-based study leverages a certain data set and R software program to compare anthro- pometry with certain seat dimensions and configurations. While any population data can be used for this work, the data that is used here for finding accommodation levels is from a comprehensive anthropometric survey of US military personnel taken in 2012, ANSUR II [5]. This data provides an initial glimpse into how human anthropometry can vary from person to person. ANSUR II stands for The Anthropometric Survey of US Army Personnel and it is the most comprehensive publicly available data set on body size. A total of 93 bare body feature sizes were taken for 6068 military personnel including 4082 males and 1986 females [5]. Note that the comparison between available seating space and certain body dimensions to determine accommodation levels is made without considering the thickness of clothing. In this work, a seating configuration of a popular narrow body aircraft, the Boeing 737, is employed. According to SeatGuru [21], the Boeing 737-800 is commonly used by major US airlines such as United, Delta, American, and Southwest. In addition, the Boeing 737 was found to have a seating configuration of 3-3 and an average of 25 rows of economy class seats. As a 15 result, this seating configuration is used for as the industry standard for the rest of this section. However, take note that the Airbus A320 family has a very similar seating configuration and can also be applied to this analysis.

3.1.1 Seated Hip Breadth and Buttock to Knee Length

The two anthropometric variables that are used to determine accommodation levels are seated hip breadth and buttock to knee length. Seated hip breadth directly corresponds to the width of the airplane seat available while buttock to knee length is related to the space available from the seat- back to where the knees contact the seat in front. If one’s seated hip breadth is greater than the seat width available, this person will not be able to fit in the seat physically and as a result will not be accommodated. Similarly, if one’s buttock to knee length is greater than the seat legroom available, this person will also be referred to as dis-accommodated. A person is referred to accommodated if they would be able to physically fit in the airplane seat. Variability due to posture, which can have a large effect on buttock to knee length, is not considered.

3.1.2 Equations Used

As different seating configurations will be analyzed in the results section, it is important to understand the equations that are used to calculate new seat dimensions when modifying seating layouts. Both an increase in seat width and seat legroom will be studied by either removing a certain number of seats per row or removing a certain number of rows of seats respectively. Eq. 3.1 shows the equation that is used to determine the new seat widths of these modified seating configurations. It is assumed that the width of the armrests is constant and the width of the armrests that are removed due to the removal of seats is added to the aisle width. As a result, the original given amount of seat width between armrests is distributed evenly to the new number of seats in each row during these calculations. Note that one armrest is removed for 5 seats across and two armrests are removed for 4 seats across. 16

(Original # Seats per Row) ∗ (Original Seat W idth) New Seat W idth = (3.1) New # Seats per Row

Similarly, Eqn. 3.2 shows the equation that is used to determine the new seat legroom lengths of the modified seating configurations. This equation makes sure to account for the discrepancy between seat pitch and seat legroom by subtracting the thickness of the seat. The Recaro slimline seat with a seatback thickness of 3 inches is chosen as an average seat design model for this calculation [7]. As a result, an average seatback thickness of 3 inches is used for all legroom calculations in future analysis.

(Original # Rows of Seats) ∗ (Original Seat P itch) New Seat Legroom = −Seatback T hickness New # of Rows (3.2) The analysis in this work also explores increases in ticket cost per passenger for each seating configuration. A revenue neutral cost model is used to ensure that airlines are still reaping the same level of profit regardless of seating configuration. Eqn. 3.3 shows the equation that is used to determine the percent increase in ticket cost for each situation. A simplified assumption is made that airline revenue = price per ticket ∗ number of seats and the number of seats = rows of seats ∗ seats/row.

(Original # Rows) ∗ (Original # Seats/Row) P ercent Inrease = ( − 1) ∗ 100 (3.3) (New # of Rows) ∗ (New # Seats/Row)

3.2 Human Research Study Overview

This is the study that was being conducted prior to the COVID-19 shutdown

Previous research and models of airplane seat accommodation that have attempted to quantify 17 seat comfort are mostly purely theoretical. Since comfort is a subjective measure, it is crucial to obtain experimental data to provide additional insight. Airlines provide transportation to a wide variety of people, requiring passengers of all sizes to sit in seats of fixed dimension for extensive amounts of time. Airlines are constantly trying to find new ways to fit more passengers on planes for commercial travel. In many cases, this is at the cost of space and comfort. While several factors including seat width, legroom, and the proximity between passengers contribute to reported comfort levels, the study in this work focuses specifically at the width of the seat. As the width of aircraft seats decreases to make room for more passengers, the comfort level of passengers decreases and a lower fraction of individuals is properly accommodated. The experiment ignores other factors that potentially can affect comfort such as legroom and environmental concerns like cabin temperature, crew service, air pressure, and social interactions. Over 50 human participants would have participated in the study and filled in multiple surveys with their perceived level of comfort. A varying seat width airplane seat model was also built and used for this experiment. This allows researchers to employ a seat with varying width discussed in detail in the upcoming sections. Moreover, the experiment uses physical barriers on the sides of the participant to analyze how comfort and acceptability vary in different physical situations.

3.2.1 Purpose of Experimental Study

The objective of the research study is to determine the relationship between aircraft seat width and level of acceptability in different physical situations. It has been hypothesized that as space decreases, comfort also decreases. Conversely, we anticipate that there will be a point at which increased space no longer improves the passenger experience. In addition, we strongly believe that when seated next to physical barriers, people experience lower but varying levels of comfort. As the perception of comfort is subjective, theoretical research discussing seat comfort does not definitively describe how comfort or acceptability can be affected by different factors. These studies simply assess a person’s accommodation by comparing seat width and hip breadth. For in- 18 stance, Miller [22] explains how a person is accommodated as long as their hip breadth is less than the width of the seat. Her research was running an algorithm in MATLAB to fill a virtual airplane seat configuration with randomly selected passengers of varying size. This program was designed to then calculate how many of the passengers were properly accommodated by comparing the seat width, seat pitch, and bideltoid breadth available with the respective dimensions of the passenger. However, accommodation does not necessarily have a direct relationship with the feeling of com- fort. Virtual fit trials run on a computer are not designed to be able to quantify a sense of comfort. As a result, this paper discusses a human research study that was to be conducted by our research lab. With regards to the application of this study, it informs the aviation community of how exactly comfort is valued by the flying population. Airlines will be able to use and analyze this data to understand the demand for comfort as well as the potential benefits of increasing seat width. This study explores the significance of airplane seat width as well as analyzes the effects of how different physical barriers and individuals placed next to the study participant can alter their perception of comfort.

3.2.2 Airplane Seat Model Design

This experiment uses a custom-built mock airplane seat with seats that can be adjusted for width. The main features of the model are a sliding armrest and the ability to install physical barriers on the sides of the seat to simulate different real world conditions. The model shown in Figure 3.1 is designed to have the participants sit in the middle seat of the model. The human subject’s left armrest is fixed into position but the right armrest is free to move along the whole length of the seat model. This allows for complete flexibility and the scope to test at any seat width desired. Regarding both the armrests, they have been designed in such a way to be able to accommodate potential physical barriers used in the study. The types of physical barriers employed will be discussed later in this chapter. 19

Figure 3.1: Experimental apparatus shown with manikin sitting on the section of the seat bench with varying seat width. The manikin’s right armrest is not permanently fixed and has been de- signed to move side to side to simulate changing seat width conditions.

3.2.3 Experiment Design

This section focuses on how the experiment was designed to receive valuable data about the relationship between airplane seat width and acceptability. We made sure to pre-screen potential participants before allowing them to be involved in the experiment. Since the study examines the relationship between body size and perceived comfort, a wide range of sizes is considered. The study uses a sampling strategy that incorporates stature and mass for both men and women. As a result, nine bins were created for each gender, with a target enrollment of: 3 participants per bin * 9 bins * 2 genders = 54 participants. Potential study participants are asked to self report their height and weight in order to decide if they could be placed in an open bin which is a fixed range of BMI values as well as stature measurements. If a participant’s associated bin is full, that individual is excluded from the study. The study is advertised through posters on bulletin boards in Penn State University Park campus. Participants 20 of this study are mostly college students studying at Penn State University.

Figure 3.2: Stature measurement is measured from the top of one’s head to the bottom of their feet. In the research experiment, a stadiometer is used to measure the study participant’s stature. [5]

The first step of the study is to collect data on each participant’s anthropometry. These measures included stature, body mass, sitting height, seated hip breadth, bideltoid breadth, and buttock to knee length. Figures 3.2-3.3 illustrate some of these measurements. Stature and body mass are obtained through the use of a stadiometer while a calibrated wall-mount height rod measures the person’s sitting height. In addition, calipers are used to collect data regarding seated hip breadth, buttock to knee length, and bideltoid breadth. Participants are also asked how often they fly on average per year. This question is asked to potentially reveal how anthropometric measures and flying experience affect a person’s own sensitivity to comfort. We also hope that the data allows us to better understand the significance of seat width in addition to allowing us to find better designs for aircraft seats that prioritize passenger comfort. The main portion of the study is split into two parts: independent seating and seating with 21

b)

c)

a) d)

Figure 3.3: a) The seated hip breadth measurement is taken at the widest point of the study par- ticipant’s hip b) Bideltoid breadth is measured at the widest horizontal breadth at one’s shoulder level. c) Sitting height is measured from the top of one’s head to the bottom of their buttocks. d) The buttock to knee length measurement is taken from the front point of the subject’s knee to the most rear point of their buttocks. [5] other passengers and physical barriers. The presentation of these two is fully randomized through a computer program. In the individual phase, the participant is seated in the middle seat with no physical barriers or individuals next to them. As a result, the participant has complete access to both armrests and also has unrestricted shoulder room. During this phase of the study, the research assistant changes the seat width dimensions by sliding the right armrest from side to side. After each configuration, the participant completes the online survey on an iPad that asks them about their perceived comfort levels. The survey shown in Figure 3.4 asks the participants questions regarding their perception of seat width, personal space, and overall comfort level. The iPad designated for the study participants is connected to a computer that is running a MATLAB program developed specifically for this experiment. This MATLAB program outputs the instructions step by step as well as runs all the trials and randomly generates the combinations and orders of the seat configuration. The research lab assistants only know the order of the experiment by referring to the MATLAB output. This process is repeated several times with different armrest 22

Figure 3.4: The survey used in the study is shown here. It is presented on the iPad after every trial and forces study participants to choose whether the condition is acceptable or unacceptable by having a contrasting color scheme. This does not allow for the subjects to choose a neutral reaction. Moreover, the last question asks for the level of comfort the specific situation offers. Research participants use a slider for answering this question and the software program converts this into a relative number from 0-100. positions controlling the width of the seat. The study participant is asked to stand up and look away between each trial. The five seat width dimensions that are tested for the individual section of the study are 17 inches (industry average), hip breath, hip breadth + 15mm, hip breadth + 30mm, and hip breadth - 15mm. Throughout this phase, the research assistant continues to change the seat width dimensions and with each position, the participant completes the comfort level survey. We are unable to measure at “hip breadth -30mm” as most participants would not be able to physically seat themselves at this constrained width. In the other physical barrier portion of the study, the research assistant similarly changes the 23 seat width dimensions by moving the armrests. There is now either an individual (one of the re- search lab members) or a physical divider placed on either side of the armrests. The participants are again asked to complete the online survey in each configuration. This process is repeated sev- eral times with different armrest positions controlling the width of the seat. During this section of the study, the order of either person or divider wall setup is also fully randomized by the MATLAB program. The goal of the divider wall as a physical barrier is to simulate either the sidewall that someone in a window seat experiences or a large person with broad shoulders sitting next to them. There are four potential physical barriers shown in Figure 3.5 that the study participant en- counters. Note that these figures only show potential physical barriers on the right side of the participant. A participant also encounters trials where there are some of these barriers placed on both left and right armrests. The first represented by a) in Figure 3.5 is when they have access to the armrest and shoulder room but still are aware that there is a person or sidewall next to them. The wall on the right of the manikin simulates a sidewall or an adjacent person with a narrow bideltoid breadth. The second situation in b) of Figure 3.5 is where they are not able to use the armrest but have unrestricted shoulder room. This situation simulates a condition where the study participant is seated next to a passenger who is not extremely broad but is occupying the armrest. The third condition in c) of Figure 3.5 is the opposite where they have access to the armrest but have severely restricted shoulder room representing a broad shouldered individual. This situation simulates a condition where the study participant is seated next to a broad shouldered passenger. Lastly, the fourth situation shown by d) in Figure 3.5 is where they do not have access to either the armrests or shoulder room. This situation simulates a condition where the study participant is seated next to a broad shouldered passenger who is fully using the armrest between them. We have concluded that this fourth situation would result in the lowest comfort ratings but wish to analyze exactly how much worse this situation is compared to the others. The goal of having different individuals being placed next to the study participant is to analyze how different genders can have an effect on the perception of comfort as well. We have hypothe- sized that fellow male passengers will cause a slightly lower level of comfort in certain situations. 24

a) b) c) d) Figure 3.5: In a), the manikin has access to both the armrests and has a certain degree of shoulder room. For b), the manikin has shoulder room but does not have access to the armrests. In c), the manikin has access to both the armrests but does not have shoulder room. Lastly in trial d), the manikin does not have access to both the armrests and shoulder room.

This hypothesis will be tested by this experiment since both genders are randomly chosen to be seated next to the participant throughout the study. At the end of the experiments during the last 9 trials, we ask the participant to fill out the survey once again with no one or no barriers beside them as they had done at the beginning of the study to analyze whether their perception of comfort changed during the course of the experiment. 25

Chapter 4

Results

This section presents the results of the virtual study and shows how accommodation levels are affected with different seating configurations. The impact of increasing seat legroom, seat width, or both are thoroughly discussed.

4.1 Seated Hip Breadth and Buttock to Knee Length Correla-

tion

Figure 4.1 shows that seated hip breadth and buttock to knee length are correlated only to a certain degree. While there is a positive association, the correlation coefficient of 0.38 suggests a weak correlation. As a result, it is determined that these two variables do not have a significant impact on each other. 26

r = 0.38

700

650

600

550 Buttock to Knee Length (mm)

500

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.1: The correlation between Seated Hip Breadth and Buttock to Knee Length is shown above. The r value of 0.38 shows that there is a weak relationship between these two variables.

4.2 Accommodation Levels in Industry Standard Condition

This section discusses the accommodation level of an industry standard seating configuration. SeatGuru [23] offers airplane seating data of all the major US airlines and it is determined that the industry average seat width is 432mm (17 in) and the seat pitch is 762mm (30 in). The industry standard seat width here is referring to the distance between the armrests. It does not include the width of the armrest itself as the seated hip breath must fit in the space available between the armrests. Similarly, the seat pitch refers to the length between one point on a seat to the same 27 point of the seat in front of it. However, this dimension does include the thickness of the seat back. Since the buttock to knee length must be accommodated by the space between the seats not including this thickness, a new dimension must be referred to. In this work, seat legroom refers to the space available to passengers and does not include the thickness of the seat-back (Seat Legroom = Seat P itch − T hickness of Seat). Note that as mentioned in Chapter 3, a seat-back thickness of 3 inches is employed. As a result, a seat legroom of 27 inches or 686mm is used as the industry standard for this work. Figure 4.2 shows that the accommodation level of this population seated in these seat dimen- sions is 90.9%. The horizontal and vertical lines on the plot are referring to the average dimensions of airplane seats. All the data points to the bottom and to the left of these cutoff lines are considered to be accommodated individuals. In this scenario, almost 10 percent of the population would not be able to physically fit in these seats and would potentially have to purchase two seats or switch to a different cabin such as business class that offer larger seats. Note that the majority of the individuals are disaccommodated here because of their seated hip breadths being wider than the width of the seat. This issue will be discussed in further detail during a later analysis. 28

accommodation = 90.9%

700 686mm

650

600

550 Buttock to Knee Length (mm)

500 432mm

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.2: Accommodation Level under condition of industry standard measurements of 432mm (17in) seated hip breadth and 686mm (27in) buttock to knee length. With these seat dimensions, 90.9% of this data is accommodated.

4.3 Effects of Increased Seat Width Conditions

This section provides results of modifying the standard seating configuration from 3-3 and 6 seats in each row to two different configurations: 5 seats across or 4 seats across. These new seating configurations of fewer seats in each row are designed to increase the seat width and be able to accommodate a greater percentage of this population. Using Eq. 3.1, it is determined that the seat width with 5 seats in each row increases to 518mm (20.4in). Similarly, for 4 seats in each row, the seat width increases to 647mm (25.5in). Figure 4.3 shows the increase in seat width for each new seating configuration. By analyzing this plot, it can 29 be concluded that the increase in seat width is not linear and the change in width increases during each occurrence that a seat is removed in each row. A change from 6 to 5 seats in each row offers a seat width increase of 19.9% while a change from 5 to 4 seats in each row provides an increase of 24.9%.

700

650

600

550

500 Seat Width (mm)

450

400 6.0 5.0 4.0 Number of Seats in Each Row

Figure 4.3: Increase in Seat Width when changing seat configuration from 6 seats in each row to 5 and 4 seats across. 5 seats across results in a seat width of 518mm and 4 seats across results in a seat width of 647mm.

4.3.1 Accommodation Levels in Seating Configuration of 5 Seats across

Figure 4.4 shows that the accommodation level with the modified seating configuration of 5 seats across in each row increases from 90.9% to 98.6%. The increase in seat width and space available for the seated hip breadth makes a significant impact on the level of accommodation. If airlines switch to a 3-2 seating configuration, they can increase their level of accommodation by 30

7.7%. Most of the individuals that are still not accommodated by this seating configuration are being restricted by the legroom space available, not the seat width.

accommodation = 98.6%

700 686mm

650

600

550 Buttock to Knee Length (mm)

500

518mm

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.4: Accommodation Level under condition of 5 seats across in each row. With 5 seats across, the seat measurements are 518mm (20.4in) seated hip breadth and 686mm (27in) buttock to knee length. 98.6% of the data is accommodated in this configuration.

4.3.2 Accommodation Levels in Seating Configuration of 4 Seats across

Figure 4.5 shows that the accommodation level with the modified seating configuration of 4 seats across in each row increases to 98.7%. The accommodation level increase is small because as mentioned above, the individuals that are not accommodated in this configuration are restricted by the legroom space available. In this seating configuration, a seat width of 572mm or 22.5in 31 is used. As a result, the vertical line is not present on the plot as this dimension fails to dis- accommodate any individuals in this population. The 647mm (25.5in) seat width value presented earlier for this configuration assumes that the thickness of the armrest remains constant. A 572mm seat width is used by assuming that the armrest between the two seats on each side of the aircraft will double in width as there is now no effect of dis-accommodation with regards to seated hip breath.

accommodation = 98.7%

700 686mm

650

600

550 Buttock to Knee Length (mm)

500

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.5: Accommodation Level under condition of 4 seats across in each row. With 4 seats across, the seat measurements are 572mm (22.5in) seated hip breadth and 686mm (27in) buttock to knee length. 98.7% of the data is accommodated in this configuration. 32

4.4 Effects of Increased Seat Legroom Conditions

This section provides results of modifying the standard seating configuration 25 rows of econ- omy class seats to either 24 or 23 rows of seats. Reducing the number of rows in a seating config- uration is aimed at increasing the seat legroom to be able to accommodate a greater percentage of the data population. Using Eq. 3.2, it is determined that by removing one row of seats, the seat legroom increases by 4.7% to 724mm (28.3in). Similarly, by removing another row of seats (two rows total), the seat legroom increases also by 4.7% to 752mm (29.6in). The physical increase in legroom space (38mm) from removing a row of seats is significantly smaller than the increase in seat width (86mm) one can achieve by removing a seat per row. However, Figure 4.6 shows that the increase in legroom space proves to be more linear than the change in seat width discussed earlier. 33

800

750

700 Seat Legroom (mm)

650

25.0 24.0 23.0 Number of Rows of Seats

Figure 4.6: Increase in Seat Width when changing seat configuration from 25 rows of seats to 24 and 23 seats rows. 24 rows of seats results in a seat legroom of 724mm and 23 rows of seats results in a seat legroom of 752mm.

4.4.1 Accommodation Levels in Seating Configuration of 24 Rows

Figure 4.7 offers the accommodation level of passengers being seated in 24 rows as opposed to 25 rows. The decrease in one row of seating increases the accommodation level from 90.9% to 91.6%. In this case, 8.4% of the population is dis-accommodated because of the restriction to their seated hip breadth by the standard seat width of 432mm in a 3-3 seating configuration. As a result, a seating configuration with 23 rows is not discussed since it will lead to an insignificant increase to accommodation levels. 34

accommodation = 91.6%

724mm

700

650

600

550 Buttock to Knee Length (mm)

500

432mm

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.7: Accommodation Level under condition of 24 rows of seats as opposed to 25 rows. With 24 rows of seats, the seat measurements are 432mm (17in) seated hip breadth and 724mm (28.3in) buttock to knee length. 91.6% of the data is accommodated in this configuration.

The plots so far show that a decrease in the number of seats in each row has a significantly greater impact to accommodation level than decreasing the number of rows. For instance, increas- ing seat width by decreasing from 6 to 5 seats in each row resulted in a 7.7% increase of percent accommodated while increasing seat legroom by decreasing the number of rows from 25 to 24 rows resulted in an increase of only 0.7%. However, in later sections, it is discussed that removing a seat in each row is much costlier to passengers than removing a row of seats. 35

4.5 Accommodation Levels in Optimal Seating Configuration

When analyzing increases in seat width, accommodation level is mostly restricted by seat legroom and vice versa. As a result, this section aims to describe the accommodation level in an optimal seating configuration where there are 5 seats in each row instead of the standard 6 and 24 rows of seats as opposed to 25. In this scenario, the new optimal seat dimensions are 518mm (20.4in) for seated hip breadth and 724mm (28.3in) for legroom. Figure 4.8 shows that the ac- commodation level increases to 99.9%. This seating configuration is designed to accommodate the most number of people possibly by removing restrictions to both seat width and legroom.

accommodation = 99.9%

724mm

700

650

600

550 Buttock to Knee Length (mm)

500

518mm

300 350 400 450 500 550 Seated Hip Breadth (mm)

Figure 4.8: Accommodation Level under optimal condition of 24 rows of seats and 5 seats in each row. With this seating configuration, the seat measurements are 518mm (20.4in) seated hip breadth and 724mm (28.5in) buttock to knee length. 99.9% of the data is accommodated in this configuration. 36

4.6 Effects on Ticket Cost in Revenue-Neutral Model

The analysis switches focus here from accommodation levels to increases in ticket cost per passenger for each seating configuration.

4.6.1 Increase in Ticket Cost with Increased Seat Width Condition

Figure 4.9 displays how the percent increase in ticket cost is related to the number of seats in each row. 6 seats in each row is used as the standard benchmark in this analysis. Note that Eq. 3.3 is used to calculate the ticket cost percent increases. Decreasing the seating configuration to 5 seats per row results in a 20% increase in ticket cost. Similarly, changing the configuration to 4 seats per row causes the ticket cost to increase by 50%. This plot shows that the percent change in ticket price is not linear and increases with each seat that is removed per row. 37

50

40

30

20

Percent Increase in Ticket Cost (%) 10

0 6.0 5.0 4.0 Number of Seats in Each Row

Figure 4.9: Increase in Ticket Cost with Seat Configuration decreasing from 6 seats in each row to 5 and 4 seats. Maintaining a revenue neutral cost structure, a change to 5 seats in a row results in a 20 % increase in ticket cost per passenger. Similarly, a change to 4 seats in a row causes a 50 % increase in ticket cost per passenger.

4.6.2 Increase in Ticket Cost with Increased Seat Legroom Condition

Similar to the previous section, Figure 4.10 shows a relationship between the number of rows of seats and the increase in ticket cost. In this analysis, 25 rows of seats is used as the standard benchmark value. Reducing the configuration by one row to 24 rows causes a 4.2% increase in ticket cost. Removing two rows of seats will inflate the ticket cost by 8.7%. Similar to the increase in legroom with every row that is removed, this relationship also seems to be more linear than that of seat width. It can also be concluded that the increase in ticket cost when increasing legroom is significantly lower than when increasing seat width. This shows that although increasing seat 38 width can offer a higher increase in accommodation, it is 15.8% more expensive per ticket than increasing legroom by removing one row of seats. The ticket cost increase for more legroom is relatively lower because it offers a lower increase in accommodation when compared to seat width.

10

8

6

4

Percent Increase in Ticket Cost (%) 2

0 25.0 24.0 23.0 Number of Rows of Seats

Figure 4.10: Increase in ticket cost with seat configuration decreasing from 25 rows of seats to 24 and 23 rows. Maintaining a revenue neutral cost structure, a change to 24 rows of seats results in a 4.2 % increase and 23 rows results in a 8.7 %increase in ticket cost per passenger.

4.6.3 Increase in Ticket Cost with Optimal Seating Configurations

This section provides a discussion on how ticket cost increases are affected by optimal seating configurations such as the one offered earlier. In fact, with the optimal configuration of 24 rows of seats and 5 seats per row, it is calculated that the ticket cost increase for each passenger is 25%. While this configuration proves to accommodate 99.9% of the population, charging everyone 25% more may prove to be an unrealistic option. 39

It was first found that 90.9% are accommodated by the industry standard seat dimensions in service today. If it is assumed that 90.9% find their seats to be acceptable, very few will be willing to pay more for a larger seat. In this situation specifically, only 9.1% would be forced to pay more since they are not accommodated properly. As a result, offering an “economy plus” or “premium economy” section for these passengers can potentially prove to be effective. If approximately 10% of the passengers find industry standard airplane seats to be unacceptable, a premium economy section should have enough seats for these passengers. If there are 150 seats in economy, roughly 15 seats should be dedicated as premium economy. These seats would offer larger seat widths and seat legrooms. With this alternative, the 90% people who find their seats to be acceptable do not need to pay a higher amount and the 10% who are dis-accommodated can find acceptable seats in the premium economy section. It is calculated that these passengers in premium economy would need to pay a 20% increase in ticket cost for their larger seats assuming that this section has 15 seats. SeatGuru [21] provides several seat maps where US airlines have done exactly this by offering premium economy sections that do not necessarily offer wider seats but do ensure an increase in seat legroom. Additionally, airlines often do charge 20% or more for these larger seats. 40

Chapter 5

Discussion

The purpose of this work is to determine how accommodation levels are affected by a variety of different seating configurations as well as optimal seating configurations based on ticket cost per passenger. This research accomplishes these goals by applying a sample data of the US population to different seat dimensions in order to find the percent of passengers that would be accommodated. Analyzing and comparing these percentages provides a thorough understanding of the effect of seat dimensions on passenger accommodation as well as the cost incurred to passengers with an increase in accommodation percentage.

5.1 Significance

The ability to understand how accommodation levels are affected by seating configurations can prove to be useful to airlines, aircraft manufacturers, researchers, and the overall aerospace community. As airplane seats continue to diminish in size, accommodation levels are potentially being impacted negatively. With a decrease in the number of seats per row, it is determined that passenger accommodation increases significantly when there are 5 seats in a row but plateaus when there are 4 seats in each row. 4 seats in each row is the point of diminishing returns as passengers are not restricted by seat width any longer but seat legroom. However, this attempt to increase seat width also causes the ticket cost per passenger to significantly increase as well. Note that the 50% increase in ticket cost for 4 seats in a row reflects on why business and first class seats need to be priced significantly higher as these sections often encompass 4 seats per row [23]. Ignoring other factors such as higher quality seats, in flight service, baggage allowance, etc, premium classes are 41 cost structured the way they are mostly due to the fact that the seating configuration forces the airline to lose substantial revenue if no ticket cost increase is implemented. On the other hand, by increasing legroom space, the effect on accommodation level is relatively small. But now this increase in legroom can be offered at a much smaller increase in ticket cost. For passengers, increased seat legroom is cheaper than increased seat width due to the inherent design of an aircraft fuselage being significantly longer than wider. While removing both one row and one seat per row causes a 99.9% accommodation, the majority of passengers would not be willing to pay the 25% price increase for this configuration. In fact, for all of the alternate seating configurations discussed, note that every passenger would need to pay these increases in ticket price if the entire aircraft’s economy class configuration is being modified. Many people would potentially not be willing to pay these significant increases in ticket price. As a result, other avenues must be explored. During the last decade, several airlines have altered their economy class seating configuration to now include an “economy plus” or “premium economy” section. For instance, according to SeatGuru [23], all of the three major US airlines (United, Delta, and American) have a dedicated section on both their narrow-body and wide-body airplanes that resembles a premium economy class. This separate area offers seats with either an increase in seat legroom, seat width, or even both to further accommodate larger passengers or passengers who desire more space. The re- sults from this work can be used by airlines to fully understand both the accommodation and cost implications of a variety of seating configurations for narrow body aircraft.

5.2 Limitations

It is important to note that there are several limitations to this work. The first being that these results are based on data of US army personnel, not civilians. The anthropometry of military personnel may not necessarily reflect exactly the anthropometric data for either the US population as military personnel train heavily and tend to be more fit. Similarly, the seat data used for this 42 work relies only on statistics provided for the major US airlines. Airplane seat measurements can vary greatly from airline to airline. Moreover, the concept of accommodation does not necessarily translate to comfort and accept- ability. For instance, although an individual could be accommodated in a seat, he or she may not find the seat to be acceptable as it is a very tight fit or they simply desire more room. In this situation, this passenger would want to upgrade to a seat that offers more legroom or width even though he or she was previously accommodated. Acceptability is a qualitative factor that can only be explored qualitatively with tools such as surveys and questionnaires. Additionally, seat legroom in this work can be impacted by a variety of factors that are ignored such as location of reading material pocket, tray table, degree of seat recline, and posture. All of these variables have the potential to impact the space available for one’s buttock to knee length. For example, if the seat in front is reclined and the reading material pocket is located where the knee impacts the seat in front, the legroom space significantly decreases. In fact, several airplane seat manufacturers such as Recaro [7] have begun to offer modern seat designs that have the reading material pocket behind the tray table to avoid the negative impact on legroom space described above. Similarly, accommodation with regards to seat width can also be impacted by variables such as the relationship between seated hip breadth and bideltoid breadth. Brauer [2] states that anthro- pometric data shows humans are widest at their shoulder or bideltoid breadth. As a result, even though one’s seated hip breadth could be smaller than the width of the seat and thus be “accom- modated” by this research, this person if seated next to a relative broad shouldered person would be dis-accommodated. An adjacent passenger’s bideltoid breadth could protrude past the armrest and into one’s seated area. 43

5.3 Future Work

While this work solely focuses on seating configurations for a narrow body aircraft such a Boeing 737, further work can be done on effects of varying seat configurations on wide body airplanes such as the Boeing 777. As wide body aircrafts tend to fly for longer periods of time, people potentially place more importance on their levels of comfort and acceptability. In addition, with these larger airplanes having two aisles and nine or ten seats per row, a more diverse variety of optimal seating configurations can be studied in the future. Further studies are also necessary to understand variables such as acceptability previously dis- cussed. It would be valuable to develop a study that analyzes effects on perceptions of comfort and acceptability. Since these are subjective measures, it is crucial to obtain experimental data to provide additional insight. For instance, a physical model of an airplane seat with varying seat widths and legroom could be built and used in a human based experiment such as the one described in Chapter 3. Interested participants would be asked to seat themselves in varying physical con- figurations and fill in questionnaires with their perceptions of comfort and acceptability. Physical barriers such as restrictions to the armrest, shoulder room, as well as varying genders could also be introduced to offer more robust data showing effects on acceptability and comfort levels. More studies need to take place that discover relationships between airplane seat design and perceptions of acceptability and comfort. The study described in the latter half of the methods section that was unable to be conducted does exactly this. 44

Chapter 6

Conclusions

As air travel increases around the world and airlines squeeze more seats on their airplanes, the experience of flying that was once highly regarded is continuing to be soured. McCartney [6] discusses how many economy class passengers feel like they are “sardines packed in a can”. Airlines should strive to provide a higher quality user-product experience for its paying customers. They can do this be re-evaluating their seat configurations and offering more options to customers who need or desire more space. Particularly with a rise in the size of US body measurements, seat width and legroom must be highly considered to ensure a certain level of accommodation, acceptability, and feeling of comfort. By using a virtual sample population that resembles US anthropometric data, this work exam- ines quantitative relationships between percentage of accommodation and varying seat configura- tions. The variables of seated hip breadth and buttock to knee length are leveraged to simulate the space required for seat width and seat legroom. According to this work’s results, increasing seat width by removing one seat per row has a greater impact on accommodation level than increasing seat legroom by removing a row of seats. However, when increasing space in one dimension (seat width), it is found that most of the dis-accommodated people are restricted by the other dimen- sion (seat legroom) and vice versa. Additionally, by using a revenue neutral cost model, it can be concluded that an increase in seat width is more expensive per passenger than in increase in seat legroom. A significant portion of passengers will not deem it necessary to pay more for increased space. As a result, a solution of a separate economy class section is offered that potentially contains more spread out and larger seats. Future studies might seek to further this research by exploring relationships between seat configurations and acceptability, not just accommodation. 45

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Education:

The Pennsylvania State University, College of Engineering University Park, PA Schreyer Honors College Graduation: May 2020 -Bachelor of Science in Mechanical Engineering -Minor in Entrepreneurship & Innovation

Relevant Experience:

The Boeing Company: Payloads Design Engineering Intern Everett, WA -Developed a 777X payloads configuration package that will accelerate the airplane configuration process May ’19 - Aug ’19 by streamlining decision making and setting expectations for design development -Collaborated with several suppliers to identify lead times and manufacturing methods for custom options -Improved the configuration experience for airline customers by allowing them to not only visualize all the commodity offerings but also be aware of lead times and design limitations

Volvo Group Truck Technology: Mechanical/Systems Engineering Intern Hagerstown, MD -Analyzed and documented failures in prototypes for the 11 and 13-liter engine projects at the powertrain May ’18 - Aug ’18 headquarters for Volvo Group North America -Administered flow tests to determine nominal leakage rates for the exhaust gas recirculation valve and

correlated these tests with suppliers such as Borg Warner Inc. -Led and coordinated a prototype engine build with part suppliers and mechanics as well as documented assembly instructions for an 11-liter diesel engine

OPEN Design Lab: Undergraduate Research Assistant University Park, PA -Conducting a human research study to quantify the effects of aircraft seat width on passenger comfort Dec ’1 8 - Present under several scenarios involving load factor, demographics, and seating allocation strategies -Leveraging the data from the study to explore the tradeoffs between passenger comfort and airline profit potential

Engineering Ambassadors: Veteran Ambassador University Park, PA -Mentor middle and high school students to challenge conventional ideas about engineering through Mar ’17 - Present College of Engineering Tours, Presentations, and Outreach Events promoting careers in STEM -Communicate the importance of engineering and how engineers better the world by giving a variety of technical presentations to younger audiences

Leadership & Activities:

Infusion: Executive Board – Sponsorship Director University Park, PA -Managed a committee of 40 to host an intercollegiate, fusion dance competition for students across the Oct ’16 - May ’19 United States -Raised approximately $2000 by reaching out to local and corporate businesses to ask for monetary and food donations as well as sponsorship for the weekend of the event

THON Rules & Regulation Committee: Finance Chair University Park, PA -Worked in a team of 35 to ensure the safety and security of everyone at THON, a 46 hour dance marathon Sep ’16 - M ay ’18 -Oversaw all committee finances and work with Merchandise Chairs and Fundraising Specialists to track committee fundraising totals

Honors: Dean’s List Penn State / ’16 - ’1 9 Academic Excellence Scholarship Penn State / Mar ’16 Ferguson Honors Engineering Scholarship Penn State / Mar ’16 Arthur M. Wilcox Memorial Award for Mechanical Eng. Scholarship Penn State / Jun ’16

Skills:

Proficient in: CATIA, ENOVIA, SolidWorks, Java, MATLAB, Siemens NX, Creoview, ATI Vision, German

Relevant Courses Taken: Fluid Dynamics, Vibration Mechanics, Mechanical Design, Thermodynamics, Statics, Strength of Materials, Dynamics, Advanced Engineering Communication, Ordinary & Partial Differential Equations

Interests/Hobbies: Traveling, Airplanes, Cars, Tennis, Badminton, Biking, Running, Guitar