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Thrust is the force which moves any aircraft through the air. Propulsion system is the machine that produces thrust to push the aircraft forward through air. Different propulsion systems develop thrust in different ways, but all thrust is generated through some application of Newton's third law of motion. A gas (working fluid) is accelerated by the engine, and the reaction to this acceleration produces the thrust force. Further, the type of power plant to be used in the aircraft depends on four important factors, namely: the aircraft mission, over all weight, flying range and endurance and altitude of flight. This assignment work was partitioned into three different parts (A, B and C respectively). In Part-A, a debate was made on the viability of implementation of twin engine propulsion system for long range civil aircrafts. Logical arguments based on literatures collected from various internet and text book sources were made and the conclusion of the usage of twin engine propulsion system for long range civil aircrafts was drawn. In Part-B, for the given mission of the aircraft, suitable power plant was chosen (Turbo fan engine) and corresponding cycle analysis calculations was done. The calculations were repeated for a range of flying altitudes and performance plots drawn were critically examined. Also, for the given Turbo prop engine data, cycle analysis calculations were done. The calculations were repeated for a set of Mach numbers and performance plots drawn were critically examined. The different engine installation techniques for a turboprop engine was also discussed. In Part-C, flow over an axial gas turbine cascade was analysed in Ansys-FLUENT software package. The blade geometry was created in Ansys-BladeGen and then imported to CATIA to create the flow domain. Meshing of the geometry was done in Fluent-ICEMCFD. The total momentum thrust and propulsion efficiency for the selected turbofan engine for the extreme altitudes of 4km & 18km was estimated as 73541N & 9375N and 47% & 40% respectively. The percentage of cold thrust generated at 4km & 18km was 60% & 45% respectively. Both momentum thrust and propulsion efficiency of the engine was observed to decrease with increase in altitude. The propeller thrust and power for the given turboprop engine for flight Mach corresponding to 0.1 & 0.8 was estimated to be 191669N & 25546N and 6074467W & 6477144W respectively. With increasing Mach number of flight, propeller thrust and power was observed to decrease and increase respectively. For the flow analysis over the axial turbine cascade, maximum static pressure value occurs for +150 (2.67*105 Pa) and minimum for 00 (2.5*105 Pa) flow incidence angles respectively. The maximum Mach number value occurs for +150 (1.89) and minimum for -150 (1.57) flow incidence angles respectively. Further the pressure loss was observed to be minimum for -150 (0.1118) flow incidence angle and maximum for +150 (0.2538) flow incidence angle.
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M. S. Ramaiah University of Applied Sciences
1Faculty of Engineering & Technology
Session delivered by:
Dr. H. K. Narahari
Aircraft Requirements Analysis
Session 1
M. S. Ramaiah University of Applied Sciences
2Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
3Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
4Faculty of Engineering & Technology
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)
M. S. Ramaiah University of Applied Sciences
5Faculty of Engineering & Technology
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.
M. S. Ramaiah University of Applied Sciences
6Faculty of Engineering & Technology
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.
M. S. Ramaiah University of Applied Sciences
7Faculty of Engineering & Technology
Overall Process Flow (Sadrey)
M. S. Ramaiah University of Applied Sciences
8Faculty of Engineering & Technology
Configuration Options
M. S. Ramaiah University of Applied Sciences
9Faculty of Engineering & Technology
A/C Components and function
M. S. Ramaiah University of Applied Sciences
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Configuration options 2
M. S. Ramaiah University of Applied Sciences
11Faculty of Engineering & Technology
Wing and Tail Configurations
Engine Layouts
Tail Layouts
Wing types & Layouts
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What do the specification influence?
M. S. Ramaiah University of Applied Sciences
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Components & impact on design
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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.
M. S. Ramaiah University of Applied Sciences
15Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
16Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
17Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
18Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
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Reason
M. S. Ramaiah University of Applied Sciences
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Design Models : NASA General
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Design Models : Boeing Commercial
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Design Models : Military Function Driven
M. S. Ramaiah University of Applied Sciences
23Faculty of Engineering & Technology
Design Cycle Another view
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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
M. S. Ramaiah University of Applied Sciences
25Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
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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
M. S. Ramaiah University of Applied Sciences
27Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
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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)
M. S. Ramaiah University of Applied Sciences
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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
M. S. Ramaiah University of Applied Sciences
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Dream but flawed aircraft
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Weight Estimation
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Mission Profile Types (Sadraey)
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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
M. S. Ramaiah University of Applied Sciences
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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.)
M. S. Ramaiah University of Applied Sciences
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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.
M. S. Ramaiah University of Applied Sciences
36Faculty of Engineering & Technology
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.
M. S. Ramaiah University of Applied Sciences
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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
M. S. Ramaiah University of Applied Sciences
38Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
39Faculty of Engineering & Technology
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.
M. S. Ramaiah University of Applied Sciences
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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.
M. S. Ramaiah University of Applied Sciences
41Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
42Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
43Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
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Case Study 3 : Mission
M. S. Ramaiah University of Applied Sciences
45Faculty of Engineering & Technology
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
M. S. Ramaiah University of Applied Sciences
46Faculty of Engineering & Technology
Thank you !