Aircraft Stability and Performance 2nd Year, Aerospace Engineering. Dr. M. Turner

Transcription

1 Aircraft Stability and Performance 2nd Year, Aerospace Engineering Dr. M. Turner

2 Basic Info Timetable Monday Physics LTA Monday Physics LTA Exam hour exam 6 questions 2 from first semester; 4 from second Answer 4 questions

3 What this module covers A brief introduction to various concepts of (winged) flight First aero module - some basics required Some coverage of appropriate notation, terminology and conventions The basic (approximate) principles and techniques used to calculate various aspects of an aircraft s performance Extensive use of point mass approximation Focus on steady flight conditions The basics of trimmed flight Longitudinal static stability Attention focused on conventional aircraft

4 What this module does not cover A comprehensive account of all aspects of aircraft performance (subject too big for a first course) Flight dynamics - covered in 3rd year Aerodynamics - some covered already, more covered in other modules A comprehensive account account of aircraft stability Only static stability is covered Dynamic stability (and control) covered elsewhere This module does not teach you to be a pilot!

5 Teaching Lectures Lecture notes - available for download Pictures - used extensively for illustrating concepts Demonstrating - useful for demonstrating dynamic behaviour of aircraft Lectures split between theory and problem classes Attendence of lectures highly recommended Labs - no labs directly associated with module, but various 1st/2nd year labs relevant Private study - Very important. Aim to spend a couple of hours a week reading notes, attempting example questions etc.

6 Study Aids - Online lecture notes Online lecture notes: Those associated with this course: Lectures posted as course progresses Exercises and exam info Prof. Jonathan How, MIT. Look at Aircraft Stability and Control course First few lectures give a good summary.

7 Study Aids - Books Course roughly based on this book First four chapters very relevant Easy to read BUT a lot of typos Useful for reference esp. for trim/stability Really a flight dynamics book First three chapters useful and interesting Comprehensive Quite mathematical & difficult to read

8 Structure of typical aircraft PLAN VIEW WING FUSELAGE FIN SIDE VIEW TAILPLANE Control surfaces Ailerons Flaps Elevator Control surfaces Rudder FUSELAGE Wing Primary device for lift generation Fuselage Payload, guidance, control, communications Elevator primary device for altering aircraft pitch Ailerons Responsible for aircraft roll Rudder Responsible for aircraft yaw Flaps For increasing lift at low velocities Turbofan/jet/propeller Thrust generation

9 Notes Some aircraft have other (different/extra) control surfaces More manoeuvrability, better efficiency Larger flight envelope Control surfaces used differentially (roll) & collectively (pitch)

10 The wing A type of airfoil - device specially shaped to produce lift when it passes through the air Dominant device for producing lift on most aircraft (main rotor is equivalent for helicopter) Simplified principle behind winged flight 1. Coanda effect bends air around airfoil 2. Bending of air implies there is a force acting on it. 3. Displacement of air implies reaction force on wing 4. Net reaction force upwards gives lift

11 Geometry of the wing h maximum camber: maximum distance from chord-line to camber line c chord length: straightline connecting leading edge to trailing edge t maximum thickness α angle between chordline and airstream Useful quantities: τ = t/c thickness chord ratio γ = h/c camber ratio Large lift, low speed: thick leading edge Small drag, high speed: thin leading edge Design of appropriate wing geometry is a subject in its own right

12 Wing cross-section

13 Wing Planform leading edge Fuselage λ kc c t b trailing edge c = (c t +c 0)/2 b S = cb A = span b2 = = meanchord b c S mean chord span gross wing area Aspect ratio c 0 NB: Gross wing area includes more than the physical wing - fuselage and air! Wing sweep = Λ k : angle wing makes to fuselage at chord fraction k (normally k = 1/4). Wing sweep lower drag at higher velocities...lower lift at lower velocities (stall) Drag function of aspect ratio: C d = C d0 + C2 L πea (e efficiency factor = constant) But high aspect ratios not always possible...(why?)

14 Different aspect ratios High aspect ratio: long, thin wings Low aspect ratio: short, wide wings (low induced drag) (structural limits) (low parasitic drag, C d0 )