acd506_ day 1 aircraft requirements analysis

M. S. Ramaiah University of Applied Sciences

1Faculty of Engineering & Technology

Session delivered by:

Dr. H. K. Narahari

Aircraft Requirements Analysis

Session 1



At the end of this session the students will be able to:

Analyse Customer requirements : Types and differences between them

Break down the total weight into components and estimate individual weights: Payload, Fuel, Structure, and Total Weight Could be through correlations from old data

Or from estimation from individual mission components

Start the Design Process

Session Objectives



Overview

A new design is launched when it is perceived that there is a requirement to fulfil a need beyond the capability of existing aircraft.

In many aeronautical applications the need arises because an existing aircraft is coming towards the end of its useful life

or its design has been overtaken by developments in technology

As result of operational experience

or-when a potentially exploitable, unfulfilled, need is identified



Overview 2

The statement of the need may be defined as a basic requirement or a target to be achieved

The identification of the need may originate from within a manufacturing organisation or from a potential operator. former is more usual for large civil aircraft

Later is often the case of military a/c or niche areas ( ambulance , remote high altitude operation etc)



Overview 3

Potential manufacturers of a civil type will consult with operators to enable the requirement to be refined to give maximum market potential.

Military types most frequently result from a target established by defense organizations.

In many cases the initial statement of the basic requirement may be brief, essentially identifying the class of aircraft needed together with

its dominant performance characteristics.



Overview 4

It is usual for this basic requirement to be considered widely by interested parties.

The originators may discuss their concepts with relevant branches of their own organisations as well as with potential manufacturers.



Overall Process Flow (Sadrey)



Configuration Options



A/C Components and function



Configuration options 2



Wing and Tail Configurations

Engine Layouts

Tail Layouts

Wing types & Layouts


12Faculty of Engineering & TechnologyM. S. Ramaiah University of Applied Sciences

12

What do the specification influence?



Components & impact on design



Meeting User requirements

There are usually various ways of meeting a basic requirement each of which must be analysed at the feasibility stage.

These may be identified as: Modify / upgrade an existing aircraft. This is most likely to

involve a change in equipment and the cost of airframe alterations is often relatively small.

A major modification or direct development of an existing type. This may well involve expensive major changes to the airframe such as an extended fuselage, new wing or alternative powerplants, equipment update.



Meeting User Requirements

A completely new design. Most expensive option and with greatest risk.

Completely new designs not very frequent

New designs are likely to emerge with Radical new requirements : Stealth or ultra-lite or ultra-long range etc



Requirements Breakup

Performance

Range, or sortie pattern, with basic payload mass; probably also altemative range/payload combinations and fuel reserves

Maximum, Minimum and cruise operating speed

Take-off and landing field length limitations

Climb performance, such as time to a given height, and service ceiling or operating altitude

Point performance covering manoeuvre / acceleration requirements



Requirements Breakup

Operational considerations

Size limitations, such as for naval aircraft

Mass limitations including runway loading

Crew , passenger complement

Payload variations and associated equipment Bombs, Missiles, Drop Tanks

Geographical environment requirements Operate from Leh or Saichen strips

Low observability (stealth) aspects for combat aircraft

Extended engine failed allowances for civil transports



Reason for Design

Fills a need (mission or market niche) identified by Sales team or Air force projection

New aircraft may Fill a new need, or

Replace an old product that filled a need

In the latter case, the new aircraft may perform the same function Better and Cheaper

Have new features : State of the art

Satisfy changing conditions in the market or threat scenario



Reason



Design Models : NASA General



Design Models : Boeing Commercial



Design Models : Military Function Driven



Design Cycle Another view



Overview : Conceptual Design

Conceptual design

Competing concepts evaluated What drives the design?

Is it Range driven ? Passenger, long range bomber planes

Is it maneuver driven? Rate of climb, Turn rates, acceleration etc

Performance goals established Will it meet the requirement ?

Run CFD codes to verify the performance of selected concept



Conceptual Design

Select a concept which meets the requirements

Build CAD models Visualize its looks

Run CFD codes to evaluate its performance

If there are shortfalls in some areas, modify the concepts till convergence



Conceptual Design

No right or unique answer in Aircraft design only a best answer at a point in time.

Aircraft design is a balance between the following competing requirements: Technical. Performance, survivability

Signature. Survivability, appearance

Economic. Cost, LCC

Political. Policy, payback, risk, and so on

Schedule. When needed? First mover to market

Environmental. Limited energy source, noise, hydrocarbon emissions



Mission requirements

The mission requirements identify the following:

Purpose. Commercial transport; B747, B727, B777, A320, A380

air-to-air fighter, air-to-ground , fighter, bomber; , F14 Tomcat, F15, F16 , B52, B1

general aviation; intelligence, surveillance, and reconnaissance (ISR); trainer, and so on

Crew. Manned or unmanned



Mission requirements

Payload. Passengers, cargo, weapons, sensors

Speed. Cruise, maximum, loiter, landing

Distance. Range or radius

Duration. Endurance or loiter (time-on-station)

Field length. Vertical, short, or conventional takeoff and landing ( VTOL, STOL, CTOL)

Signature level. Radar cross section ( RCS); infrared ( IR); visual; and acoustic (noise)



Assessment of Requirements

Designer must study, understand, evaluate, and question them Sometimes negotiate them with the customer

Customers try to generate a consistent set of requirements sometimes they can be flawed, there ae example for it awed

Some flawed requirements are discovered and changed some flawed requirements prevail and designs are produced



Dream but flawed aircraft



Weight Estimation



Mission Profile Types (Sadraey)



Design Process

Estimate weight (TOW or Wo) based on known payload GTOW :Gross Take-Off Weight

Estimate wing loading and size based known speed and lift coefficient

Select wing shape and aspect ratio based upon type of aircraft



Design Process

Select C.G location based on static margin requirements (stability) as given distance from a.c. C.G.: center of gravity

A.C.: aerodynamic center, also called neutral point

Select wing sweep, taper, twist, as required Decide on Planform and airfoil

Size control surfaces based upon tail distance

Iterate

Verify against baseline data - use benchmarking and basic physics (L=W & T=D, etc.)



Military Aircraft Design Process

Guess the MTOM from (statistical value) for the payload, range for the class.

Pick a wing area for the MTOM. Decide on a single surface, two-surface, or three-surface design. The decision needs aircraft control analysis

Next, decide wing geometry (e.g., sweep, taper ration, and t/c for the high-speed Mach number capability).

Decide on high wing, midwing, or low wing, based on customer requirements.



Process 2

Decide on wing dihedral or anhedral based on wing position.

Decide on number of engines required. For fighter aircraft, this number is unlikely to exceed two

engines.

The engine is invariably housed in the fuselage.

Shape the fuselage to house the engine and fit the wing and empennage.

Guess H-tail and V-tail sizes for the wing area.



Constraint Analysis This is a basic analytical tool which relates Excess Power to

change in Total energy

Used to highlight constraints on the design and related them to T/W and W/S



Case Study 1 : Basic Military Trainer

Need a Military Trainer with following characteristics :

W TOM < 2800 kg

Load factor : +6 / -3

Ceiling : > 6 km

Endurance > 3 hours

ROC > 10000 ft/min ( >50 m/s)

Glide angle



Case Study 2 : Long Range Civil Jet

The following design requirements and research studies are set for the project:

Design an aircraft that will transport 80 business-class passengers and their associated baggage over a design range of 7000nm at a cruise speed equal or better than existing competitive services.

To provide the passengers with equivalent, or preferably better, comfort and service levels to those currently provided for business travelers in mixed-class operations.

To operate from regional airports.



Case Study 2

To use advanced technologies to reduce operating costs.

To offer a unique and competitive service to existing scheduled operations.

To investigate alternative roles for the aircraft.



Case Study 3 : Advanced Military Trainer

Performance

General Atmosphere max. ISA+20C to 11 km (36 065 5 ft) , min. ISA 20C to 1.5km (4920 ft) Max. operating speed, Vmo = 450 kt @ SL (clean)

Vmo = 180 kt @ SL (u/c and flaps down)

Turning Max. sustained g @ SL = 4.0

Max. sustained g @ FL250 = 2.0

Max. sustained turn rate @ SL = 14/s

Max. instantaneous turn rate @ SL = 18 /s



Case Study 3

Takeoff & Landing Field Approach speed = 100 kt (SL/ISA)

TO and landing ground runs = 610m (2000 ft)

Cross-wind capability = 25 kt (30 kt desirable)

Climb Service ceiling > 12.2 km (40 000 ft)

Climb 7 min SL to FL250, (note: one flight level, FL = 100 ft)

Descent 5 min FL250 to FL20 (15 max. nose down)

Ferry range = 1000nm (2000nm (with ext. tanks))

FL : Flight Level. FL250 means 25000ft altitude, ISA/SL = 15 degrees C



Case Study 3

Structural

Flight envelope n1 = +7, n3 = 3

Max. design speed M0.8

VD > 500 kt CAS

Operational Hard points = 2 @ 500 lb (227 kg) plus 2 @ 1000 lb (453 kg), all

wet

Consideration for fully armed derivatives

Consideration for gun pod installation

Provision for air-to-air refuelling



Case Study 3 : Mission



Session Summary

In this session the following topics were dealt with :

Design Models as applicable to end use

User Requirements and how they impact the design

How to derive Crucial parameters for design : Weights, T/W, W/S

Drag polar, CL max, Cd 0



Thank you !

acd506_ day 1 aircraft requirements analysis

Documents

basic requirement

potential manufacturers

military types

potential operator

class of aircraft

large civil aircraft

individual mission components

total weight