Longitudinal Stability and Neutral Point
Transcript of Longitudinal Stability and Neutral Point
AE-705 Introduction to Flight Lecture-15 Capsule-08
AE-705: Introduction to Flight
Vijay Gaikwad
VJTI, Mumbai
Longitudinal Stability
and
Neutral Point
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 positionStable
• Departs from equilibriumStatic
Instability
• Oscillates with larger amplitudeDynamic
Instability
AE-705 Introduction to Flight Lecture-15 Capsule-08
STATIC STABILITY
Initial Reaction on disturbing an aircraft !
AE-705 Introduction to Flight Lecture-15 Capsule-08
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
AE-705 Introduction to Flight Lecture-15 Capsule-08
Ball remains in new position when disturbed
Neutral Static Stability
NEUTRAL
AE-705 Introduction to Flight Lecture-15 Capsule-08
Positive Static Stability
STABLE
Ball returns to starting position when disturbed
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Ball moves away from starting position when disturbed
Negative Static Stability
UNSTABLE
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Flight Conditions
http://history.nasa.gov
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https://youtu.be/NciePa8sY_U
Example of an unstable aircraft
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DYNAMIC STABILITY
Final Outcome of disturbing an aircraft !
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
https://www.youtube.com/watch?v=YJ1Tt1zSyH4
A Quick Summary
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THE 3 CENTRES OF AN AIRCRAFT
Their relative location affects Stability
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https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf
The Three Key Centers
TWO
THREEONE
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
AE-705 Introduction to Flight Lecture-15 Capsule-08
https://zh.scribd.com/document/334413404/XFLR5-and-Stability-analysis-pdf
CENTER OF PRESSURE
THREECENTER OF GRAVITY
AE-705 Introduction to Flight Lecture-15 Capsule-08
https://www.nasa.gov/centers/glenn/home/
Centre of Pressure
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
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.
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 POINTCENTER OF GRAVITY
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THE FOURTH CENTRE !
Aerodynamic Center
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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
AE-705 Introduction to Flight Lecture-15 Capsule-08
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
AE-705 Introduction to Flight Lecture-15 Capsule-08
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
AE-705 Introduction to Flight Lecture-15 Capsule-08
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 ??
AE-705 Introduction to Flight Lecture-15 Capsule-08
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 !
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
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
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
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 FLIGHT
Effect of CG on Longitudinal Stability of plane
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Longitudinal stability
Payload position CG Position
BOTTOM VIEWTOP VIEW
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BOTTOM VIEWTOP VIEW
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Payload Location CG Location
CG Position at 1
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BOTTOM VIEWTOP VIEW
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Payload Location CG Location
CG Position at 2
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BOTTOM VIEWTOP VIEW
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Payload Location CG Location
CG Position at 3
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BOTTOM VIEWTOP VIEW
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Payload Location CG Location
CG Position at 4
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Payload Location CG Location
CG Position at 5
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Flights with different CG position
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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
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Comparison of Flight Path with Graph
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CG at 1
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CG at 3
CG at 4
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Different CG positions Corresponding α positions
𝛼
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NEUTRAL POINT
Longitudinal stability concept explanation
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Longitudinal stability
Payload position CG Position
BOTTOM VIEWTOP VIEW
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Comparison of flights (CG at 1)
without Vertical Gust with Vertical Gust
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Comparison of flights(CG at 3)
without Vertical Gust with Vertical Gust
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Comparison of flights (CG at 4)
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Comparison of flights (CG at 4)
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Comparison of flights (CG at 5)
without Vertical Gust with Vertical Gust
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Comparison of flights (CG at 5)
Back
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Flights with changing AOA
Angle of attack = 4°
Angle of Attack = 8°
Angle of Attack = 12°
Angle of attack = 0°
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Comparison of flights