IEA2021 pre-print proceeding "A Human-Centered Design Procedure for Conceptualization Using Virtual Reality Prototyping Applied in an Inflight Lavatory"

1. A Human-Centered Design Procedure for
Conceptualization Using Virtual Reality Prototyping
Applied in An Inflight Lavatory
Meng Li 1,2[0000-0002-7095-0170]
, Doris Aschenbrenner1[0000-0002-3381-1673]
, Daniëlle van
Tol1[0000-0001-5593-8643]
, Daan van Eijk1[0000-0002-5148-0521]
, Peter Vink1[0000-0001-9985-3369]
1
The Faculty of Industrial Design Engineering, Delft University of Technology, Delft 2628CE,
The Netherlands
2
Mechanical Engineering School, Xi’an Jiaotong University, Xi’an 710049, PR China
m-li.4@tudelft.nl
Abstract. For designing large-scale products like an airplane, engaging end-
users in the concept phase is difficult. However, early user evaluation is im-
portant to choose the path which fits the user’s needs best. In particular, com-
fort-related assessments are difficult to conduct with digital models that are
shown on a desktop PC application. Digital Human Modelling (DHM) plays a
role in postural comfort analysis, while the subjective comfort feedback still
largely relied on consulting with end-users.
This paper applies a human-centered design process and analyses the ad-
vantages and disadvantages of using VR prototypes for involving users during
concept design. This study focused on using VR prototypes for concept selec-
tion and verification based on comfort assessment with potential end-users.
The design process started with an online questionnaire for identifying the qual-
ity of the design elements (Step 1 online study). Then, alternative concepts were
implemented in VR, and users evaluated these concepts via a VR headset (Step
2 Selection study). Finally, the research team redesigned the final concept and
assessed it with potential users via a VR headset (Step 3 Experience study).
Every design element contributed positively to the long-haul flight comfort, es-
pecially tap-basin height, storage, and facilities. The male and female partici-
pants had different preferences on posture, lighting, storage, and facilities. The
final prototype showed a significantly higher comfort rate than the original pro-
totypes.
The first-person immersion in VR headsets helps to identify the nuances be-
tween concepts, thus supports better decision-making via collecting richer and
more reliable user feedback to make faster and more satisfying improvements.
Keywords: Virtual Reality, Concept Design, Human-Centered Design, Virtual
Prototyping, First-Person Immersion

2. 2
1 Introduction
Designing a large-scale product like the Flying-V, the next-generation airplane, en-
gaging end-users in the concept phase is difficult. However, early user evaluation is
important in choosing the path which fits the user’s needs best. In particular, com-
fort-related assessments are difficult to conduct with digital prototypes that are shown
on a desktop PC application. Comfort is described as “a feeling of relief or encour-
agement”, “contented well-being” and “a satisfying or enjoyable experience” by the
Merriam-Webster Dictionary [1]. Despite the diverse perspectives on comfort-related
experience, but most studied agree that “comfort is a subjective experience”[2]. Com-
fort plays an important role in boosting a traveler’s well-being, especially during a
long-haul flight. Hence, comfort is becoming increasingly significant in the interior
design of transport systems like airplanes [2, 3]. Digital Human Modelling (DHM)
took the advantages of various anthropometric parameters in postural comfort analy-
sis for transport systems, while the subjective comfort feedback still largely relied on
consulting with end-users [4]. Torkashvand reported that ‘using the bathroom’ is the
second most important activity on board, influencing general satisfaction [5]. Yao and
Vink found that reducing the waiting time for accessing lavatories and maintaining
hygiene and refreshment are key points of improving long-haul flight comfort [6].
Understanding comfortable hygiene experiences in transportation systems is challeng-
ing, not only due to the privacy and safety issues but also due to the diverse demands
of using public lavatories [7]. The co-creation sessions discovered that the activities
around the basin, such as skin-caring, making-up, hair-styling, shaving, and washing
face and hands are key to the comfortable hygiene experience during long-haul flights
[6]. Considering the limited space of airplane lavatories, we found the following de-
sign elements relevant to the comfort of the long-haul flight: posture, lighting, the
height of tap to the bottom of the basin, storage, and facilities.
The Human-Centered Design (HCD) methodology favors VR prototyping, as a tool to
evaluate concepts in a cost-efficient, time-saving way. VR has been used in different
stages of design processes, e.g. design reviewing with the CAVE (Cave Automatic
Virtual Environment) systems [8, 9]. Virtual prototypes enhanced by tactile feedback
have been used in the ergonomic evaluation of cockpit layout and car dashboard de-
signs [10, 11]. A recent study showed that the VR prototype has the same level of
confidence as the visual assessment of real products[12]. However, the suitability of
VR prototypes for selecting design concepts regarding comfort remains unexplored.
This suitability is heavily impacted by whether comfort-related elements like posture,
lighting, height, storage space, and facilities are sufficiently conveyed via VR. This
can be explored by testing which concepts are chosen by users when they are experi-
encing different VR prototypes.

3. 3
1.1 Research Questions
The research aimed at answering how concept design could improve comfort from
using VR and if it enabled potential users to better compare alternative concepts and
possibly select a better solution. The research questions for this study are:
RQ1: Which design elements of the hygiene experience influence the comfort in long-
haul flight?
RQ2: Which concepts are perceived more comfortable by end-users via showing them
in VR prototyping?
RQ3: Whether VR prototyping helps to improve a comfortable experience?
2 Methodology
In this study, the design process started with an online questionnaire for identifying
the quality of the design elements (Step 1 online study). Then, alternative concepts
were implemented in VR and user evaluation of the selection process was carried out
(Step 2 Selection study). Finally, the resulting concept was designed and assessed
again by potential users via VR (Step 3 Experience study).
2.1 Step 1: Online Study
One hundred and one respondents (including 58 females and 43 males) took part in an
online survey on ten design elements related to hygiene activities in a long-haul flight.
A 7-point Likert scale was developed based on the Kano model [13]. On the scale, 1
means “very dissatisfied” while 7 means “very satisfied”. The design elements in-
cluded larger standing space, sitting in front of mirrors, storage, tap-basin space,
warm lighting, easy-open door, the waiting-queue, open space, facilities, and chang-
ing room. These elements were categorized into five patterns: one-dimensional, must-
be, indifferent, attractive, reverse [13]. The satisfaction differences between males
and females were test via two-tailed T-tests.
2.2 Step 2: Selection Study
Twenty-eight students (including 12 males and 16 females) participated in the concept
selection in the VR Lab of the Delft University of Technology. A 7-point Likert scale
was used for collecting the comfort level (1 means “very uncomfortable”, 7 means
“very comfortable”). Ten concepts were evaluated regarding five design elements.
The concepts were shown in an HTC Vive headset (1080×1200 per eye). A 1:1 card-
board enclosure provided the tactile feedback of the VR space. After filling in the
informed consent, participants rated their comfort level when a concept was shown to
them. Each concept was displayed for 40 seconds and was randomized for each par-
ticipant. After the evaluation, the participants had an oral reflection session for col-
lecting qualitative feedback. The means were calculated. Wilcoxon matched-pair
signed-rank test was applied to compare the concepts.

4. 4
2.3 Step 3: Experience Study
Thirty-three participants joined the final assessment of the lavatory concept at the
same lab. A similar comfort questionnaire, a realistic questionnaire, and the Presence
Questionnaire (PQ) were used for accessing the immersive experience. A predefined
instruction asked participants to imagine that they were in a long-haul flight while
seeking refreshment. They simulated refreshing activities in their preferred ways in
the virtual environment. After the simulated usage, they filled in the questionnaires.
The means and standard deviation were calculated.
3 Results
3.1 Step 1: Online Study
All elements are one-dimensional except open space and facilities while sitting pos-
ture and change room have more diverse distribution (Fig. 1a). Considering the gen-
der differences, the males preferred sitting more and females liked larger standing
space (Fig. 1b).
Fig. 1: (a) design quality for the elements; and (b) for different genders.
3.2 Step 2: Selection Study
In general, lower tap-basin height, more available storage, and high-end facilities
have significantly contributed to a more comfortable experience (Table 1). Warmer
lighting was associated with better comfort. The comfort of females significantly
depended on high-end facilities, while males would be more comfortable when stand-
ing pose and having more storage.
Table 1. The perceived comfort between the two concepts among different genders
Male (12) Female (16) Total(28)
Mean(SD) p value Mean(SD) p value Mean(SD) p value

5. 5
Male (12) Female (16) Total(28)
Mean(SD) p value Mean(SD) p value Mean(SD) p value
With seat 3.83(1.403) 0.077 3.87(1.727) 0.309 3.85(1.562) 0.056
No seat 4.75(1.545) 4.56(1.459) 4.64(1.471)
Light3000k 4.42(1.621) 0.357 4.25(1.342) 0.070 4.32(1.442) 0.053
Light3500k 4.75(0.965) 4.00(1.088) 4.82(1.020)
Tap-basin28cm 5.00(1.279) 0.083 4.69(1.448) 0.163 4.78(1.368) 0.036*
Tap-basin24cm 5.58(0.996) 5.27(0.884) 5.41(0.931)
Storage shelves 5.08(1.443) 0.055 4.69(1.448) 0.171 4.86(1.433) 0.021*
Storage box 4.08(1.240) 4.06(1.389) 4.07(1.303)
More facilities 5.58(1.505) 0.224 5.69(1.078) 0.004** 5.64(1.254) 0.002**
Fewer facilities 4.75(1.422) 4.25(1.183) 4.46(1.290)
*indicates that p value <0.05; **indicates that p value <0.01.
The participants thought tactile feedback created a believable perception of being
inside the lavatory but did not influence their comfort level. The participants had viv-
id feedback, such as sharp edges, postures during turbulence, and bend angle when
using the basin.
3.3 Step 3: Experience Study
Participants rated every design element of the final prototype significantly higher than
the prototypes in the selection study except the comfort of using water (Fig. 2a). The
VR prototyping was realistic for the participants except using water and no significant
differences between the people with or without VR experience (Fig. 2b). No signifi-
cant simulation sickness symptoms were perceived by the participants.
Fig. 2: (a) the comfort perception and (b) the realistic level of the final prototype. “*” indicates
that p-value <0.05; “**” indicates that p-value <0.01; “***” indicates that p-value < 0.001.
4 Discussion and Conclusion
Regarding the research questions, every design element contributed positively to the
long-hula flight comfort, especially tap-basin height, storage, and facilities. The male
and female participants had different preferences, e.g. comfortable standing posture

6. 6
and storage are key for males, while high-end facilities and lighting are more critical
to females. Lavatories provide a private bubble for many people during long-haul
flights [6,14], thus some participants wanted to remove the seat to limit the duration
of each user. The shelves, providing more options for storing passengers’ belongings
were preferred. Kuijt-Evers also mentioned that storage space can be an element for
improving the comfort of wheel loaders and excavators [15]. The basin improved
comfort by providing sufficient space for cleaning hands and faces. This need is con-
firmed by a study showing the larger environments for washing hands increase user-
friendliness [16].
The final prototype showed a significantly higher comfort rate than the first round.
The first-person immersion provided by VR prototyping encouraged the participants
to be more interactive and explorative during concept evaluation [11, 17]. The miss-
ing interaction of virtual objects like the tap might influence the perception of realism
and thus alter the comfort perception, as we observed on the comfort of using water
[18]. The knowledge on using a VR headset was mainly new to most of the partici-
pants, thus a formal practice session is needed [19]. The potential risk of prototyping
using a VR headset is some individuals might experience severe simulation sickness
symptoms and quit the evaluation [20].
The first-person immersion in VR prototyping helps to identify the nuances between
concepts, thus supports better decision-making via collecting richer and more reliable
user feedback to make faster and more satisfying improvements. The next step of this
study is comparing the VR prototyping with the physical prototyping within the Fly-
ing-V project to find out how to take advantage of both of them to create more effec-
tive and efficient human-centered design processes.
Acknowledgment
The authors wish to thank Ms. Xinhe Yao for her assistance in developing the VR
prototyping and conducting the tests. The authors thank all the participants who
shared their feedback about the prototyping and VR experience.
Funding
Meng Li’s doctoral research is sponsored by a grant from China Scholarship Council
(CSC) (No. 201706280020). The contents of this paper are solely the responsibility
of the authors and do not necessarily represent the official views of CSC.
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