and Neutral Point Vijay Gaikwad VJTI, Mumbai AE-705 Introduction - PowerPoint PPT Presentation

AE-705: Introduction to Flight Longitudinal Stability and Neutral Point Vijay Gaikwad VJTI, Mumbai AE-705 Introduction to Flight Lecture-15 Capsule-08

Reaction of aircraft when disturbed Stable • Returns to its initial position Static • Departs from equilibrium Instability Dynamic • Oscillates with larger amplitude Instability https://www.nasa.gov/centers/glenn/home/ AE-705 Introduction to Flight Lecture-15 Capsule-08

Initial Reaction on disturbing an aircraft ! STATIC STABILITY AE-705 Introduction to Flight Lecture-15 Capsule-08

Static Stability Definition: When disturbed from an equilibrium position, the aircraft tends to return to its original position, without any action from the pilot Types : I. Positive static II. Neutral static III. Negative static www.boldmethod.com AE-705 Introduction to Flight Lecture-15 Capsule-08

Neutral Static Stability NEUTRAL Ball remains in new position when disturbed AE-705 Introduction to Flight Lecture-15 Capsule-08

Positive Static Stability STABLE Ball returns to starting position when disturbed AE-705 Introduction to Flight Lecture-15 Capsule-08

Negative Static Stability UNSTABLE Ball moves away from starting position when disturbed AE-705 Introduction to Flight Lecture-15 Capsule-08

Flight Conditions http://history.nasa.gov AE-705 Introduction to Flight Lecture-15 Capsule-08

Example of an unstable aircraft https://youtu.be/NciePa8sY_U AE-705 Introduction to Flight Lecture-15 Capsule-08

Final Outcome of disturbing an aircraft ! DYNAMIC STABILITY AE-705 Introduction to Flight Lecture-15 Capsule-08

Dynamic Stability Positive Oscillations decrease in amplitude Neutral Oscillations constant in amplitude Negative Oscillations increase in amplitude www.boldmethod.com AE-705 Introduction to Flight Lecture-15 Capsule-08

A Quick Summary https://www.youtube.com/watch?v=YJ1Tt1zSyH4 AE-705 Introduction to Flight Lecture-15 Capsule-08

Their relative location affects Stability THE 3 CENTRES OF AN AIRCRAFT AE-705 Introduction to Flight Lecture-15 Capsule-08

The Three Key Centers TWO THREE ONE https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf AE-705 Introduction to Flight Lecture-15 Capsule-08

CENTER OF GRAVITY TWO THREE https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf AE-705 Introduction to Flight Lecture-15 Capsule-08

CENTER OF PRESSURE THREE CENTER OF GRAVITY https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf AE-705 Introduction to Flight Lecture-15 Capsule-08

Centre of Pressure https://www.nasa.gov/centers/glenn/home/ AE-705 Introduction to Flight Lecture-15 Capsule-08

NEUTRAL POINT CENTER OF PRESSURE CENTER OF GRAVITY https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf AE-705 Introduction to Flight Lecture-15 Capsule-08

Neutral Point • position of CG where the aircraft would be Neutrally stable . The basics of R/C model Aircraft design . Author – Andy Lennon ,ISBN:0-911295-40-2. chapter -06,page 27. AE-705 Introduction to Flight Lecture-15 Capsule-08

All three Centers together! CENTER OF PRESSURE NEUTRAL POINT CENTER OF GRAVITY https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf AE-705 Introduction to Flight Lecture-15 Capsule-08

Aerodynamic Center THE FOURTH CENTRE ! AE-705 Introduction to Flight Lecture-15 Capsule-08

Aerodynamic Centre https://www.nasa.gov/centers/glenn/home/ AE-705 Introduction to Flight Lecture-15 Capsule-08

Example of a toy plane EFFECT OF RELATIVE LOCATION Source: Understanding Flight , D. F. Anderson, S.Eberhardt , 2 nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965 AE-705 Introduction to Flight Lecture-15 Capsule-08

When CG is ahead of NP Perturbation in flight increase Angle of Attack L wing ↑ but L tail ↓ , hence net Nose down Moment created Aircraft is Stable due to this restoring torque Source: Understanding Flight , D. F. Anderson, S.Eberhardt , 2 nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965 AE-705 Introduction to Flight Lecture-15 Capsule-08

When CG is at NP Position of AC is independent of angle of attack Moments due to ↑ L wing & ↑ L tail balance There is no restoring torque Aircraft is neutrally stable due to this balance of moments Source: Understanding Flight , D. F. Anderson, S.Eberhardt , 2 nd ed, McGraw-Hill, Ch-4, pp. 102, ,ISBN-13: 978-0071626965 AE-705 Introduction to Flight Lecture-15 Capsule-08

When CG is behind NP WHY ?? As the nose pitches up, ↑ L wing > ↑ L tail The aircraft nose pitches up further Aircraft is unstable due to unbalanced moments Source: Understanding Flight , D. F. Anderson, S.Eberhardt , 2 nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965 AE-705 Introduction to Flight Lecture-15 Capsule-08

w.r.t. AC and NP EFFECT OF CG POSITION AE-705 Introduction to Flight Lecture-15 Capsule-08

CG ahead of AC and NP Aircraft is HIGHLY stable ! Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2 AE-705 Introduction to Flight Lecture-15 Capsule-08

CG at AC but ahead of NP Aircraft is stable ! Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2 AE-705 Introduction to Flight Lecture-15 Capsule-08

CG behind AC but ahead of NP Aircraft is LESS stable ! Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2 AE-705 Introduction to Flight Lecture-15 Capsule-08

CG behind AC and at NP Aircraft is NEUTRALLY STABLE ! Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2 AE-705 Introduction to Flight Lecture-15 Capsule-08

In summary : Effect of CG Position Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2 AE-705 Introduction to Flight Lecture-15 Capsule-08

Effect of CG on Longitudinal Stability of plane EFFECT OF CG ON FLIGHT AE-705 Introduction to Flight Lecture-15 Capsule-08

Longitudinal stability Payload position CG Position BOTTOM VIEW TOP VIEW 5 4 3 2 1 1 2 3 4 5 AE-705 Introduction to Flight Lecture-15 Capsule-08

CG Position at 1 TOP VIEW BOTTOM VIEW 1 Payload Location CG Location 300 200 100 BACK 0 0 100 200 300 400 500 600 AE-705 Introduction to Flight Lecture-15 Capsule-08

CG Position at 2 TOP VIEW BOTTOM VIEW 2 Payload Location CG Location 300 200 100 0 0 100 200 300 400 500 600 BACK AE-705 Introduction to Flight Lecture-15 Capsule-08

CG Position at 3 TOP VIEW BOTTOM VIEW 3 Payload Location CG Location 300 200 100 0 0 100 200 300 400 500 600 BACK AE-705 Introduction to Flight Lecture-15 Capsule-08

CG Position at 4 TOP VIEW BOTTOM VIEW 4 Payload Location CG Location 300 200 100 0 0 100 200 300 400 500 600 BACK AE-705 Introduction to Flight Lecture-15 Capsule-08

CG Position at 5 TOP VIEW BOTTOM VIEW 5 Payload Location CG Location 300 200 100 0 0 100 200 300 400 500 600 BACK AE-705 Introduction to Flight Lecture-15 Capsule-08

Flights with different CG position 300 200 CG at 1 CG at 2 CG at 3 CG at 4 CG at 5 100 0 0 100 200 300 400 500 600 BACK AE-705 Introduction to Flight Lecture-15 Capsule-08

Why ?? Lets see ! AE-705 Introduction to Flight Lecture-15 Capsule-08

Vs α graph 3 2 1 4 5 𝛽 𝛽 AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of Flight Path with Graph Corresponding α positions Different CG positions 3 300 2 CG at 1 200 CG at 2 1 CG at 3 4 CG at 4 100 CG at 5 0 0 100 200 300 400 500 600 5 𝛽 AE-705 Introduction to Flight Lecture-15 Capsule-08

Longitudinal stability concept explanation NEUTRAL POINT AE-705 Introduction to Flight Lecture-15 Capsule-08

Longitudinal stability  Payload position  CG Position TOP VIEW BOTTOM VIEW 5 4 3 1 1 3 4 5 AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights (CG at 1) without Vertical Gust with Vertical Gust 300 300 200 200 100 100 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights(CG at 3) without Vertical Gust with Vertical Gust 300 300 200 200 100 100 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights (CG at 4) without Vertical Gust with Vertical Gust 300 300 200 200 100 100 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights (CG at 4) 300 200 100 0 0 100 200 300 400 500 600 Back AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights (CG at 5) without Vertical Gust with Vertical Gust 300 300 200 200 100 100 0 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 AE-705 Introduction to Flight Lecture-15 Capsule-08