The Aircraft Family Concepts for an Advanced Technology Regional

Aircraft

PRASETYO EDI

Department of Aerospace Engineering

Institut Teknologi Dirgantara Adisutjipto (ITDA)

Lanud Adisucipto, Jl. Raya Janti, Jogjakarta

INDONESIA (55198)

Abstract: - The aim of this work is to make a feasibility study of the aircraft family concepts using a combined

Hybrid Laminar Flow Control - Variable Camber Wing (HLFC-VCW) for a high subsonic Advanced Technology

Regional Aircraft (ATRA). The prediction of ATRA’s performance used computational fluid dynamic and

empirical methods. The aircraft family concept using a combined HLFC–VCW is feasible for the ATRA aircraft

family from an aerodynamic point of view.

Key-Words: - aircraft family concept, advanced technology, regional aircraft, high subsonic, transport aircraft

Received: September 23, 2021. Revised: October 21, 2022. Accepted: November 16, 2022. Published: December 31, 2022.

1 Introduction

Approximately 65% of the world's commercial jet

fleet consists of narrow-body, single-aisle aircraft

with a capacity of 70 to 170 seats. These are

deployed on routes of 1,300 nautical miles or less.

This sector also dominates the current order-book.

More than 60% of aircraft on order are in the short-

haul narrowbody category. The trend since

deregulation in the US has been towards hub-and-

spoke networks and a reduction in average aircraft

size. The liberalization of the European market

could exacerbate this trend.

There are several forecasts for demand for the

above type aircraft in the next 20 years. Bombardier

Aircraft Company believes that there is a demand

for a little over 3,000 aircraft in the 60- to 90-seat

class. According to a DASA market forecast,

published in June 1995, excluding the

commonwealth of Independent States, 2,350 of the

71-130-seat aircraft will be delivered to regional

carriers. IPTN (Indonesian Aircraft Industry) is

forecasting demand for 2,757 passenger aircrafts in

the 80- to 130-seat class. McDonnell Douglas

predicts requirements for 1,700 in that class of

aircraft.

To fulfill the above demand, the regional-jet

manufacturers are trying to attract those airline

carriers with their own designs. Aircrafts that are

already in the market are McDonnell Douglas MD-

87, Fokker-70/-100, Airbus A319, Boeing 737-500/-

600 and BAe-146/Avro RJ-70/-85/-100/-115.

Models that are still under development by regional-

jet manufacturers are Boeing-MD-95-20/-30/-50,

IPTN N-2130, Fairchild Dornier's 728 JET and

Bombardier's Canadair Regional Jet (CRJ) Series

700 programmed.

Only three models of the above aircrafts are

smaller than 120-seats, the Avro RJ-70/-85/-100/-

115, the Fokker-70/-100 and the Boeing 737-500/-

600. The Avro RJ and the Boeing 737 family are 6

abreast seating, while the Fokker family is 5 abreast.

Many Aircraft manufacturers, i.e.: Airbus,

Boeing, McDonnell Douglas, Fokker, British

Aerospace, IPTN/IAe, etc., have developed their

aircraft family based on one wing and one fuselage

cross section to reduce development costs. For one

fuselage cross section aircraft family, alternatives

concepts for Regional Airliner family are:

1. fixed wing geometry on mid-size, then direct

operating cost (DOC) penalties for off-

optimum,

2. fixed wing geometry on mid-size, modification

of wing extension/reduction, then development

costs, and

3. Variable Camber Wing (VCW) which could be

optimum for all families, but will have

increased development costs.

The third concept (VCW) will be used in the

development of the high subsonic Advanced

Technology Regional Aircraft family.

2 ATRA Baseline Design

The following section describes in brief the design

methodology for conceptual sizing of aircraft based

on the author’s experience when he worked as an

aircraft configurator for IAe (Indonesian

Aerospace).

2.1 Design requirements and objectives

As a successor of the regional jet, the baseline

(ATRA-100) will offer 108 seats in two class

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layouts, while the stretched (ATRA-130) and

shortened (ATRA-80) versions accommodate 133

seats in two class layouts and 83 seats in two class

layouts respectively. The cost-economic cruise

speed was set at M = 0.8 at a nominal range of 2,250

nm (ATRA-100), 2,000 nm (ATRA-80) and 2,500

nm (ATRA-130). For all versions the maximum

approach speed will be 127 knots.

2.2 Initial sizing

Conceptual design is a “chicken or egg” problem.

The configuration designer cannot draw the aircraft

until he develops some information about the

aircraft, such as takeoff gross weight (TOGW),

wing loading, etc. The performance analyst needs to

know about the geometry of the aircraft before he

can determine the drag, and hence find aircraft

payload-range capability, and hence takeoff gross

weight.

Using a sizing method [1], the main parameters

of initial sizing of the three versions are as follow:

ATRA-80 ATRA-100 ATRA-130

MTOW (kg) 45,538 56,260 69,576

T/W 0.291 0.291 0.291

W/S (kg/m2) 413.2 510.5 631.3

2.3 General arrangement

Designing an aircraft can be an overwhelming task

for a new configurator. The configurator must

determine where the wing goes, how big to make

the fuselage, and how to put all the pieces together.

Based on an existing aircraft there are two main

types of general arrangement for a regional

passenger jet transport aircraft, i.e.:

1. Boeing, Airbus, IAe type: low-wing,

low/fuselage-tail, engine mounted on the wing

and tricycle landing gear attached on the wing

and stowage on the wing-fuselage fairing.

2. Douglas, Fokker, Canadair type: low-wing, T-

tail, engine mounted on the rear fuselage and

tricycle landing gear attached on the wing and

stowage on the wing-fuselage fairing.

The above two types of general arrangement

have several advantages and disadvantages as given

below.

Table 1. Type 1 and 2 general arrangement

Consideration Type 1 Type 2

a. aero. cleanliness wings bad good

b. bending relief yes no

c. cabin noise levels better bad

d. aircraft c.g. management easy difficult

e. one engine out trim difficult easy

f. engine rotor burst critical good

g. engine ground clearance critical good

h. engine accessibility good difficult

I. fuel system lighter heavier

A sound choice of the general arrangement of a

new aircraft design should be based on a proper

investigation into and interpretation of the transport

function and a translation of the most pertinent

requirements into a suitable positioning of the major

parts in relation to each other. No clear-cut design

procedure can be followed and the task of devising

the configuration is therefore a highly challenging

one to the resourceful designer.

The study of possible configurations should

result in one or more sketches of feasible layouts.

They serve as a basis for more detailed design

efforts, and they can therefore be regarded as a first

design phase.

Usually trade studies between several possible

configurations will be required before the choice of

the best configuration is made. The engine mounted

on the wing configuration is typical transport

aircraft and the most common for most airliners. It

is beyond this work to make a trade study, as

described above. For this study, general

arrangement type 1 in section 2.3 is selected for the

ATRA-100 baseline configuration, ATRA-80 and

ATRA-130, as shown in Fig. 1.

2.4 Aircraft family concept.

Fig. 2 shows The ATRA Family concept. Because

of wing fuel tank limitations, the payload-range for

ATRA-130 can not be achieved. There are several

options to solve this problem, namely: (1) increase

the wing area and/or thickness, (2) to reduce the

ATRA-130 range performance, (3) add fuel on

empennage or fuselage tanks, and (4) investigate the

use of winglets to reduce induced drag and therefore

fuel burn.

There are several options to design the low-speed

performances of the ATRA-130, namely: (1) use the

same wing and high lift devices as the ATRA-100

but with increase in take-off and landing field

distance, (2) increase the wing area, and (3) improve

the high lift devices performance.

The ATRA-100 has maximum design

commonality with the ATRA-80 and ATRA-130.

The level of commonality between the members of

the ATRA standard-body aircraft family is such that

the ATRA-80, ATRA-100 and ATRA-130 can

essentially be operated as one aircraft type with

positive effects on crew training, maintenance and

aircraft scheduling. In addition, a mixed fleet of

ATRA-100 aircraft combined with other aircraft in

the ATRA family will allow airlines to better match

capacity to demand whilst reducing operating costs,

increasing crew productivity and simplifying ground

handling.

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Being the reduced/increased size development of

the ATRA-100, the ATRA-80/ATRA-130 key

changes are primarily related to size and capacity as

all aircraft share similar systems and the same flight

deck. Key changes include: derated/uprated engines,

adapted systems and two fuselage plugs

removed/added.

3 Technology Concept for ATRA

The main issue in the application of new

technologies in transport aircraft is the ability to

employ them at low cost without reduction of their

benefits. This cost is reflected in the following

shares of Direct Operating Costs (DOC): fuel,

ownership and maintenance. Laminar flow -

variable camber technology will only produce

acceptable DOC if the penalties due to additional

weight and the complexity of the system do not

exceed those of the fuel savings. Hence the most

important objective in realizing advanced laminar

flow-variable camber technology is to reduce their

additional system costs, weight and minimize

maintainability and reliability costs.

3.1 Initial wing design.

This section describes the initial design of the wing

for ATRA-100 baseline configuration. This wing

design is unique, because it incorporates hybrid

laminar flow control and variable camber wing

technology.

A detailed examination of the very complex wing

design is outside the scope of this work, but it is

considered appropriate to mention some of the

measures which may be taken, although not all of

them are required for each design.

3.1.1 Performance objectives.

For a typical jet aircraft, the equation for cruise

range (R) can be expressed as:





































final

initial0

L M

TSFC

= R

(1)

where:

= speed of sound

 = temperature ratio, T/T0

The equation states that if the thrust specific fuel

consumption, TSFC, is considered to be nearly

constant (which is usually in the cruise region), a jet

aircraft will get the most range for the fuel burned

between weights Winitial and Wfinal by making the

quantity (Mach number)(Lift/Drag), M(L/D), a

maximum. The basic aerodynamic performance

objective is, therefore, to achieve the highest value

of M(L/D)max at the cruise Mach number. Climb and

descent performance, especially for short range

missions, is also important and may suggest the

“cruise” design conditions be compromised.

The aerodynamic advantages of the combined

laminar flow - variable camber wing stem from two

considerations [2 - 4]:

a. Laminar-flow is a potential means of reducing

viscous drag in cruise, by up to 15 - 20%.

Aircraft components such as wings, fin,

tailplane, engine nacelle are candidates for

laminar flow treatment.

b. Variable-camber is a potential means of

increasing lift/drag ratio in cruise and climb, by

up to 4% (in cruise) due to cruise and climb

always at optimum lift coefficient. Theoretically

the aerodynamic advantages of variable camber

wing stem from four considerations:

1. A reduction in profile drag, resulting from the

obtaining of lift by the use of an optimum

amount of section camber.

2. Operation with the minimum induced drag,

due to the achievement of an elliptical lift

distribution at all lifts coefficients.

3. A reduction in wing/fuselage interference drag

and fuselage drag, stemming from operation

at a near constant angle of attack over a wide

range of lift coefficients.

4. A higher buffet onset Mach number, resulting

from minimal wing twist and minimal wing

camber at high speeds/modest lifts

coefficients. This creates the potential for a

higher maximum cruise and limit Mach

numbers.

However, the off-design considerations must not

be neglected. The off-design characteristics should

show no drop in lift or (L/D)max at Mach numbers

below cruise. The variation of L/D with lift at cruise

Mach number should provide at least 95 % of

(L/D)max for a (+/-) 0.1 variation in lift about cruise

[3 - 5].

3.1.2 Wing area, planform and airfoil design.

With maximum take-off weight (MTOW) of

ATRA-100 = 56,260 kg and wing loading (W/S) =

510.5 (kg/m2), wing area (S) for ATRA-100 =

110.21m2.

Wing planform selection is based on a

combination of criteria that require constant review

during the design phase. Planform span, aspect ratio,

sweep, and taper will be revised based on the trade’s

studies taking place during the design. As sweep

increases, the MTOW, operating empty weight

(OEW), mission fuel and engine size increase for a

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constant aspect ratio and wing loading. As aspect

ratio increases, OEW and MTOW increase while

engine size and fuel burn decrease.

A detailed trade off study of planform parameters

is outside the scope of this work. For ATRA-100

Baseline, sweep and taper ratio are taken based on

comparison with existing aircraft data, (Fig. 3) i.e.:

 A quarter chord sweep (



c/4) = 25 deg.

 Taper ratio (



) = 0.274

 Aspect ratio (AR) = 9.5

Selection/design of the outboard wing sweep and

outboard aerofoil section are made at the same time.

Usually for most swept wings, the outboard aerofoil

section defines the wing Mach number capability.

This is a result of the higher outboard wing section

loading compared to the inboard wing. The lower

inboard wing lift is due to wing taper and the lower

lift curve slopes near the side of the fuselage. The

outboard wing aerofoil is selected/designed based

not only on the design Mach number but also on the

aerofoil off-design characteristics. Good low Mach

number lift capability is required for climb

performance and for aircraft gross weight growth

capability. High Mach number characteristics

should exhibit low drag creep below cruise Mach

number and still maintain gentle stall buffet

characteristics. Shock position should remain fairly

stable with small changes in Mach number or angle

of attack to maintain good ride quality and handling

characteristics.

The introduction of laminar flow represents an

additional design criterion that must be satisfied

along with all existing considerations. The issues

raised for NLF section design are also relevant to

Hybrid Laminar Flow Control (HLFC) sections

although leading edge suction reduces the severity

of the constraints imposed for NLF. Typically,

transonic HLFC airfoil sections have been designed

with pressure distributions having a small peak

close to the leading edge, followed by a region of

increasing pressure (an adverse pressure gradient)

over the suction region, after which the ‘roof-top’

has a mildly favorable pressure gradient. Such a

pressure distribution has been found to maximize

the extent of laminar flow.

Development of an airfoil is concerned mainly

with the selection of the desired pressure

distribution. Once this is done, the shape can be

computed by a mathematical procedure. However,

not all pressure distributions correspond to

physically meaningful airfoil shapes; real flow

constrains the pressure distribution to have a

leading-edge stagnation point, low pressure forward,

and gradually rising pressure aft, ending somewhat

above ambient at the trailing edge. Within these

constraints, details must be tailored to meet the

specific requirements of HLFC and of low drag rise

due to compressibility.

For this study, three airfoils were designed, i.e.,

root, inboard and outboard, as shown in Fig. 4.

3.2 The application of combined HLFC-

VCW

Practical use of HLFC requires that laminar flow be

maintained through a range of cruise lift coefficients

and Mach numbers. Variations in lift coefficient and

Mach number will change the wing pressure

distributions from the optimum and may result in

some loss of laminar flow. Therefore, it was decided

to investigate a HLFC wing together with a VC-

flap. Deflection of the VC-flap permits controlling

the pressure distribution over the forward part of the

airfoil, keeping it similar to the design pressure

distribution, even when the lift coefficient and Mach

number differ considerably from the design values.

With careful design of VC-flap, it would be possible

to reduce the wave drag penalty, and to sustain

attached flow in turbulent mode. Flow control on

such a wing is shown schematically in Fig. 5.

3.2.1 Candidate laminar flow – variable camber

section

Section views of the two wing configurations

considered in this study are shown in Fig. 6.

Configuration I have both upper and lower surface

suction, from the front spar forward with leading

edge systems as proposed by Lockheed [6]. Because

it has no leading-edge device, it requires double-

slotted fowler flaps to achieve

CLmax

requirements.

Configuration II replaces the lower surface suction

with full-span Krueger flaps, which, combined with

single-slotted fowler flaps, provide equivalent high

lift capability. The Krueger flaps also shield the

fixed leading edge from insect accumulation and

provide a mounting for the anti icing system. Only

the upper surface, however, has suction panels. The

leading-edge system used on configuration II is

similar to leading edge systems as proposed by

Douglas [6]. A summary of the advantages, risks,

and disadvantages are:

 Configuration I: The advantages are (1) a simple

system with no leading-edge device and (2)

upper and lower surface laminar flow for least

drag. The disadvantages and risks are (1) more

potential for insect contamination on the suction

device which may cause boundary-layer

transition, (2) high approach speeds and landing

field lengths and/or a more complex trailing-

edge high lift system, (3) longer take-off field

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lengths, particularly for hot, high-altitude

conditions, and (4) a trim penalty due to higher

rear loading (when the flaps are deployed).

 Configuration II: The advantages are (1) less

potential insect contamination on the suction

device, hence laminar boundary layer will be

more stable, (2) simpler trailing-edge high lift

devices, (3) lower approach speeds and shorter

take-off and landing field lengths, and (4) less a

trim penalty (when the flaps are deployed). The

disadvantages and risks are (1) less drag

reduction due to laminar flow only on the upper

surface and (2) a more complex leading-edge

system.

Preliminary estimates [3 - 5] indicated cruise

drag reductions of about 11% for HLFC having

laminar flow on the upper and lower surface, while

the reduction for HLFC having laminar flow only on

the upper surface was only 7%. The deficiencies

noted for configuration I are related to low-speed

performance and insect contamination problems.

The potential exists for high lift performance

improvements if wings were specifically designed

for the HLFC task. Although it has an inherently

lower drag reduction, configuration II is more likely

to provide a stable laminar boundary-layer due to a

lower likelihood of being contaminated by insects.

Taking into account the above considerations,

configuration II was selected for this study.

3.2.2 Hybrid laminar flow – variable camber

section baseline configuration

The Hybrid Laminar Flow Control - Variable

Camber Wing (HLFC-VCW) section baseline

configuration for use on the ATRA-100’s wing is

shown in Fig. 7.

Ideally the change in section profile at aft of the

rear spar should not cause separation of airflow,

which would otherwise give rise to higher profile

drag. To overcome the problem of separation, the

radii of local curvature must be greater than half the

chord, but not too high, as the section will have a

higher pitching moment, and hence higher trim

drag, which then will reduce the benefit of variable

camber itself. The radii should be optimized

between these two constraints. The radius is

inherent to the trailing-edge upper surface of the

aerofoil, so when the aerofoil is used for a VC

concept, the aerofoil should be designed with taking

into account the above considerations from the

beginning.

The concept of variable camber used for the

ATRA-100’s wing is quite similar to traditional

high lift devices. The camber variation is achieved

by small rotation motions (in two directions for

positive and negative deflections). In VC-operation

the flap body slides between the spoiler trailing edge

and the deflector door. The radius of flap rotation is

picked-up from the radius of curvature of the

aerofoil trailing edge upper surface at about 90%

chord. Camber variation is therefore performed with

continuity in surface curvature at all camber

settings. During this process the spoiler position is

unchanged.

4 Aircraft Performance

The computational design analysis and revision of

the ATRA-100 aircraft due to lift/drag improvement

from the application of HLFC on the ATRA-100

aircraft compared to the turbulent version will be

described in the following section.

4.1 Design analysis for ATRA-100’s wing

Many aircraft operate at transonic speed, where part

of the flow field is subsonic and part is supersonic.

At these speeds shock waves form on the wings,

which cause an increase in drag and variable

changes in the lift. Multiple shock waves can

develop and interact in ways that are difficult to

predict, but that have a large influence on lift and

drag.

With detailed knowledge of the flow field and

shock wave locations designers can shape the wing

to delay the transonic drag rise and increase the lift

to drag ratio. The results are higher transonic

cruising speeds and reduced fuel consumption.

Fig. 8 and 9 show the contours of static pressure

and Mach number in fully turbulent flow, while fig.

10 and 11 show the contours of static pressure and

Mach number in fully laminar flow, both for

variable-camber flap deflected respectively, for

detailed flow analysis see Reference [3].

4.2 Revision of the ATRA-100 aircraft

Technically, the application of the combined HLFC-

VCW to the civil transport aircraft appears to

provide significant performance gains in terms of

fuel consumption and payload range performance.

However, in order to justify the implementation of

the technology economically, it is necessary to

consider the associated costs throughout the entire

program.

It was judged that the most appropriate method

of examining the cost implications of the combined

HLFC-VCW would be to examine its effects on the

direct operating costs (DOC) of the aircraft. For the

purposes of this research, aircraft weight reductions

and increased range performance due to the

application of the combined HLFC-VCW would be

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examined rather than DOC, with the assumption that

if the aircraft weight is reduced DOC would also

reduce.

The aircraft lift/drag improvement at cruise

(Mach 0.8, 10,668 m and RN = 6.28e6/m) was 7.675

% of total cruise drag [3 - 4].

Some of the advantages and disadvantages of the

application of the combined HLFC-VCW to civil

transport aircraft compared to the turbulent version

are [3 - 6]:

 HLFC systems weight = 0.373 % MTOW,

 VCW systems weight = 0.5 % wing weight,

 Lift/drag increment due to VCW application =

2.5 %,

 The increment in fuel flow to maintain the

specified net thrust due to power off-take of

HLFC suction systems = 0.2 %,

 Assumption: the reduction of wing sections t/c

due to the application of the HLFC is eliminated

by the application of VCW and wing sweep is

unchanged.

The above values are taken from aircraft which

do not closely match the ATRA aircraft types

included in this study, preventing any direct

comparisons. However, the benefits and/or

drawbacks associated with the various HLFC and/or

VCW applications are provided. In the absence of a

detailed investigation, it was decided to use the

above values.

With the above predictions and assumptions

using sizing method [1], it is reasonable to conclude

that the benefits of the combine HLFC-VCW to the

ATRA-100 aircraft compared to the turbulent

version are: (1) for constant DR&O: MTOW

reduction = 4.25 % and (2) for constant MTOW:

range performance increased by 7.6 %.

5 Conclusions

The aircraft family concept using variable camber

wing technology to manage the lift requirement is

feasible from technical point of view

The combined HLFC–VCW as a flow control

concept is feasible for a transport aircraft from an

aerodynamic point of view. With the same

reservations that apply to the feasibility of any

laminar flow control (LFC) and variable camber

flap (VCF) aircraft, i.e., the economic aspects

depend on material, manufacturing and operational

data. Before HLFC and VCW technology can be

applied to the transport aircraft, a large

multidisciplinary research effort is needed in order

to master the technology and demonstrate it on

flying test-beds and in-service operational tests.

Acknowledgement:

The author is grateful to ITD Adisutjipto Jogjakarta

and Indonesian Aerospace (IAe/PT. DI/IPTN) for

supporting this research.

References:

[1] Dr. Jan Roskam. Airplane Design Parts I-VIII.

Roskam Aviation and Engineering

Corporation. Ottawa, KS. 1989.

[2] Greff, E., (Deutsche Airbus GmbH, Bremen,

FRG). Aerodynamic design and technology

concepts for a new ultra-high-capacity aircraft.

ICAS, 96-4.6.3. (1996).

[3] Edi, P. Investigation of the application of

hybrid laminar flow control and variable

camber wing design for regional aircraft. PhD

thesis, AVT/CoA/Cranfield University,

Cranfield - UK (1998).

[4] M. Abdul Raheem, Prasetyo Edi, Amjad A.

Pasha, Mustafa M. Rahman and Khalid A.

Juhany. Numerical Study of Variable Camber

Continuous Trailing Edge Flap at Off-Design

Conditions. Energies: Special Issue Modelling

of Aerospace Vehicle Dynamics, Vol. 12(16),

No. 3185, pp. 1-22, 20/8/2019.

https://doi.org/10.3390/en12163185.

[5] Boeing Commercial Airplane Company.

Hybrid laminar flow control study final

technical report. NASA CR 165930 (October

1982).

[6] Conceptual Design Staff. ATRA-100

Multinational Project Aircraft (Boeing, MBB,

Fokker, IPTN). Wing Design Doc. 1987.

Figure 1. ATRA-100, with additional side views of

ATRA-130 (centre) and ATRA-80

(below)

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Payload-range concept

trio regional airliner

103

108

113

118

123

128

133

138

1950

2000

2050

2100

2150

2200

2250

2300

2350

2400

2450

2500

2550

RANGE (NM)

ATRA-80

ATRA-100

ATRA-130

Fuselage concept

two fuselage plugs removed/added

2-25

Lift management concept

2-25

optimum cruise/climb management

constant altitude cruise management

Figure 2. The ATRA Family concept

Figure 3. ATRA wing concept

Figure 4. Airfoil for ATRA wing (root, inboard and

outboard)

Figure 5. Flow control on the win

Figure 6. Cross sections of candidate combine

HLFC-VCW configurations

Figure 7. HLFC-VCW section baseline

configuration

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Figure 8. Configuration II: contours of static

pressure, Pascal (fully turbulent flow)

Figure 9. Configuration II: contours of Mach

number (fully turbulent flow)

Figure 10 Configuration II: contours of static

pressure, Pascal (fully laminar flow)

Figure 11 Configuration II: contours of Mach

number (fully laminar flow)

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