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

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

Mar 30, 2024 199 likes •746 views

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

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AE-705 Introduction to Flight Lecture-15 Capsule-08

AE-705: Introduction to Flight

Vijay Gaikwad

VJTI, Mumbai

Longitudinal Stability and Neutral Point

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Reaction of aircraft when disturbed

https://www.nasa.gov/centers/glenn/home/

  • Returns to its initial position

Stable

  • Departs from equilibrium

Static Instability

  • Oscillates with larger amplitude

Dynamic Instability

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AE-705 Introduction to Flight Lecture-15 Capsule-08

STATIC STABILITY

Initial Reaction on disturbing an aircraft !

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Definition:

When disturbed from an equilibrium position, the aircraft tends to return to its original position, without any action from the pilot

Static Stability

Types :

I. Positive static

  • II. Neutral static
  • III. Negative static

www.boldmethod.com

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Ball remains in new position when disturbed

Neutral Static Stability NEUTRAL

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Positive Static Stability STABLE

Ball returns to starting position when disturbed

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Ball moves away from starting position when disturbed

Negative Static Stability UNSTABLE

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Flight Conditions

http://history.nasa.gov

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AE-705 Introduction to Flight Lecture-15 Capsule-08 https://youtu.be/NciePa8sY_U

Example of an unstable aircraft

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AE-705 Introduction to Flight Lecture-15 Capsule-08

DYNAMIC STABILITY

Final Outcome of disturbing an aircraft !

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Dynamic Stability

Positive

Oscillations decrease in amplitude

Neutral

Oscillations constant in amplitude

Negative

Oscillations increase in amplitude

www.boldmethod.com

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

A Quick Summary

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AE-705 Introduction to Flight Lecture-15 Capsule-08

THE 3 CENTRES OF AN AIRCRAFT

Their relative location affects Stability

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

The Three Key Centers

TWO THREE ONE

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

CENTER OF GRAVITY

TWO THREE

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

CENTER OF PRESSURE

THREE CENTER OF GRAVITY

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

Centre of Pressure

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

NEUTRAL POINT

CENTER OF PRESSURE CENTER OF GRAVITY

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AE-705 Introduction to Flight Lecture-15 Capsule-08

  • position of CG where the aircraft would be Neutrally stable.

Neutral Point

The basics of R/C model Aircraft design . Author–Andy Lennon ,ISBN:0-911295-40-2. chapter -06,page 27.

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

All three Centers together!

CENTER OF PRESSURE NEUTRAL POINT CENTER OF GRAVITY

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AE-705 Introduction to Flight Lecture-15 Capsule-08

THE FOURTH CENTRE !

Aerodynamic Center

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

Aerodynamic Centre

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EFFECT OF RELATIVE LOCATION

Example of a toy plane

Source: Understanding Flight, D. F. Anderson, S.Eberhardt , 2nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965

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Perturbation in flight increase Angle of Attack Lwing ↑ but Ltail ↓, hence net Nose down Moment created Aircraft is Stable due to this restoring torque

Source: Understanding Flight, D. F. Anderson, S.Eberhardt , 2nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965

When CG is ahead of NP

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Position of AC is independent of angle of attack Moments due to ↑ Lwing & ↑ Ltail balance There is no restoring torque Aircraft is neutrally stable due to this balance of moments

Source: Understanding Flight, D. F. Anderson, S.Eberhardt , 2nd ed, McGraw-Hill, Ch-4, pp. 102, ,ISBN-13: 978-0071626965

When CG is at NP

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As the nose pitches up, ↑ Lwing > ↑ Ltail The aircraft nose pitches up further Aircraft is unstable due to unbalanced moments

When CG is behind NP

Source: Understanding Flight, D. F. Anderson, S.Eberhardt , 2nd ed, McGraw-Hill, Ch-4, pp. 102 ,ISBN-13: 978-0071626965

WHY ??

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EFFECT OF CG POSITION

w.r.t. AC and NP

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CG ahead of AC and NP

Andy Lennon, The basics of R/C model Aircraft design, Chapter-06, pp. 27, ISBN:0-911295-40-2

Aircraft is HIGHLY stable !

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

Aircraft is stable !

CG at AC but ahead of NP

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

Aircraft is LESS stable !

CG behind AC but ahead of NP

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

Aircraft is NEUTRALLY STABLE !

CG behind AC and at NP

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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

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EFFECT OF CG ON FLIGHT

Effect of CG on Longitudinal Stability of plane

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Longitudinal stability

Payload position CG Position

BOTTOM VIEW TOP VIEW 5 4 3 2 1

1 2 3 4 5

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AE-705 Introduction to Flight Lecture-15 Capsule-08 1 BOTTOM VIEW TOP VIEW

BACK

Payload Location CG Location

CG Position at 1

100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08 2 BOTTOM VIEW TOP VIEW

BACK

Payload Location CG Location

CG Position at 2

100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08 3 BOTTOM VIEW TOP VIEW

BACK

Payload Location CG Location

CG Position at 3

100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08 4 BOTTOM VIEW TOP VIEW

BACK

Payload Location CG Location

CG Position at 4

100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08 5 BOTTOM VIEW TOP VIEW

BACK

Payload Location CG Location

CG Position at 5

100 200 300 100 200 300 400 500 600

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Flights with different CG position

BACK

100 200 300 100 200 300 400 500 600 CG at 1 CG at 2 CG at 3 CG at 4 CG at 5

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Why ??

Lets see !

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Vs α graph

𝛽

2 3 4 5

𝛽

1

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of Flight Path with Graph

100 200 300 100 200 300 400 500 600 CG at 1 CG at 2 CG at 3 CG at 4 CG at 5

Different CG positions Corresponding α positions

𝛽

1 3 4 5 2

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AE-705 Introduction to Flight Lecture-15 Capsule-08

NEUTRAL POINT

Longitudinal stability concept explanation

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Longitudinal stability

Payload position CG Position

BOTTOM VIEW TOP VIEW 5 4 3 1

1 3 4 5

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Comparison of flights (CG at 1)

without Vertical Gust with Vertical Gust

100 200 300 100 200 300 400 500 600 100 200 300 100 200 300 400 500 600

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Comparison of flights(CG at 3)

without Vertical Gust with Vertical Gust

100 200 300 100 200 300 400 500 600 100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights (CG at 4)

without Vertical Gust with Vertical Gust

100 200 300 100 200 300 400 500 600 100 200 300 100 200 300 400 500 600

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100 200 300 100 200 300 400 500 600

Comparison of flights (CG at 4)

Back

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Comparison of flights (CG at 5)

without Vertical Gust with Vertical Gust

100 200 300 100 200 300 400 500 600 100 200 300 100 200 300 400 500 600

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Comparison of flights (CG at 5)

Back

100 200 300 100 200 300 400 500 600

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AE-705 Introduction to Flight Lecture-15 Capsule-08

Flights with changing AOA

  • Angle of attack = 4°
  • Angle of Attack = 8°
  • Angle of Attack = 12°
  • Angle of attack = 0°
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AE-705 Introduction to Flight Lecture-15 Capsule-08

Comparison of flights