Flight Stability & Dynamics, Control · Flight Stability & Dynamics, Control •Airplane Axes •Flight Stability and Control –Static Stability –Dynamic Stability •Flight Control

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Flight Stability & Dynamics, Control

• Airplane Axes

• Flight Stability and Control – Static Stability

– Dynamic Stability

• Flight Control Surfaces – Control along the Longitudinal Axis

– Control along the Vertical Axis

– Control along the Lateral Axis

– (Ref. AC 65-15A)

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Airplane Axes (Sumbu Pesawat Udara)

Longitudinal Axis (sumbu memanjang)

Lateral Axis (sumbu melintang)

Vertical Axis (sumbu tegak/vertikal)

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AXES OF AN AIRCRAFT

Aircraft is completely free to move in any direction

Manoeuvre dive, climb, turn and roll, or perform

combinations of these.

Whenever an aircraft changes its attitude in flight, it

must turn about one or all of these axes.

Axes – imaginary lines passing through the centre of

the aircraft.

AXES ON AIRCRAFT

Sumbu Pesawat Udara – adalah Tiga (3) garis khayal (imajiner) yang melalui titik berat (C.G) pesawat.

• Ketiga sumbu - dapat dipandang sbg sumbu/poros khayal dimana pesawat bebas berputar seperti roda.

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Sumbu Pesawat Udara (Axes of an Aircraft):

Ada Tiga (3) Sumbu pesawat udara,

yaitu :

1. Sumbu Memanjang / Longitudinal Axis (Roll Axis)

2. Sumbu Melintang / Lateral Axis (Pitch Axis) / Cross-wing Axis

3. Sumbu Vertikal / Vertical Axis (Yaw Axis)

Sumbu Pesawat Udara Axes of an Aircraft

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Ke Tiga (3) Sumbu Pesawat –

Melalui titik berat (Center of Gravity, CG) pesawat dan

Berpotongan tegak lurus satu sama lainnya membentuk sudut 90°.

• Apabila pesawat mengubah Sikap Terbang atau Posisi-nya sewaktu terbang (Flight Attitude or Position in flight), – ia berputar/rotasi terhadap satu atau lebih dari ketiga sumbu-sumbu tsb.

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Sumbu Pesawat Udara Axes of an Aircraft

Aircraft Rotations Body Axes

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Center of Gravity (CG)

Gravitasi (Gravity) – adalah gaya tarik-menarik yang cenderung menarik semua benda di-dalam medan gravitasi bumi – menuju pusat bumi.

• CG atau Titik Berat – dapat dipandang sebagai Titik dimana seluruh berat pesawat,W, terpusat (ter-konsentrasi) padanya.

• Jika pesawat udara - ditumpu tepat pada titik beratnya (its exact CG), ia akan seimbang di posisi manapun.

• CG (titik berat) – merupakan hal yang utama bagi sebuah pesawat udara, karena posisi-/letak-nya berperan penting bagi kestabilan pesawat.

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• The CG is determined by the general design of the aircraft.

• The designers estimate how far the CP travels.

• They then fix the CG in front of the CP for the corresponding flight speed in order to provide an adequate restoring moment for flight equilibrium.

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Center of Pressure (CP)


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(Center of Pressure, Cp)

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• Center of Pressure (CP) - The point of intersection of the Resultant force line with the Chord line of the airfoil is called the center of pressure (CP).

• The CP – moves along the airfoil chord as the AOA changes.

(Center of Pressure, Cp)

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Perputaran (rotasi) Pesawat Udara Axes of an Aircraft Rotation

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Sumbu MEMANJANG (Longitudinal Axis) : – Adalah garis lurus khayal yang membentang

sepanjang (lengthwise) fuselage, dari hidung (nose)-ke-ekor (tail) pesawat udara.

–Gerakan berputar terhadap sumbu memanjang (longitudinal axis) – adalah Berguling (Roll) dan dihasilkan oleh pergerakan Ailerons yang terletak di Trailing Edges dari Wing.

• Longitudinal Axis – sering disebut sebagai Roll-Axis (Sumbu-Guling).

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Sumbu Pesawat Udara LONGITUDINAL AXES of an Aircraft

Gerakan berputar thd Sumbu Guling Roll around Longitudinal Axis – ROLL Axis

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Longitudinal or Roll Axis = X - Axis

Figure 1-29 : The Ailerons cause an airplane to Roll about the Longitudinal Axis. The Primary Purpose of the Ailerons is to Bank the wing, causing the airplane to Turn.

Gerakan berputar thd Sumbu Guling

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Sumbu MELINTANG (Lateral Axis) : – Adalah garis khayal yang melintang sepanjang

bentangan sayap (crosswise), dari ujung sayap kiri-ke-ujung sayap kanan (from wing tip - to- wing tip), tegak lurus terhadap sumbu memanjang (longitudinal axis).

– Gerakan turun-naik terhadap sumbu lateral (lateral axis) – adalah Mengangguk (Pitch) dan dihasilkan oleh pergerakan dari Elevators di belakang (T.E) dari Ekor Mendatar (Horizontal tail assembly).

– Lateral Axis – sering disebut sebagai Pitch-axis (Sumbu-Angguk).

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Sumbu Pesawat Udara LATERAL Axes of an Aircraft

Gerakan Mengangguk thd Sumbu Angguk Pitch around the Lateral Axis – PITCH Axis

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Lateral or Pitch Axis = Y - Axis

Figure 1-30 : The Elevators cause an airplane to Pitch about the Lateral Axis. The Primary Purpose of the Elevators is to change the angle of attack (AOA), and thereby control the airspeed.

Gerakan Mengangguk thd Sumbu Angguk

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Sumbu TEGAK ( Vertical Axis ) : – Adalah garis khayal yang secara vertikal

melalui titik berat {center of gravity (C.G)} pesawat udara.

– Gerakan berputar terhadap sumbu tegak (Vertical axis) – adalah Menggeleng (Yaw) dan ini dihasilkan oleh pergerakan dari Rudder yang terletak dibagian belakang (T.E) dari ekor tegak (Vertical tail /Fin assembly).

– Vertical Axis – sering disebut sebagai Yaw-axis (Sumbu-Geleng).

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Sumbu Pesawat Udara VERTICAL Axes of an Aircraft

Gerakan Menggeleng thd Sumbu Geleng Yaw around the Vertical Axis – YAW Axis

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Vertical or Yaw Axis = Z-Axis

Figure 1-31 : The Rudder causes an airplane to Yaw about the Vertical Axis. The Primary Purpose of the Rudder is to counteract Aileron Drag and keep the fuselage streamlined with the Relative Wind. This improves the quality of Turns and Reduces Drag.

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Ringkasan - Gerakan Pesawat Udara terhadap Sumbu Putar

[1] Gerakan thd sumbu Longitudinal (memanjang) pesawat (sumbu-x) – adalah “ber-guling (roll)”;

[2] Gerakan thd sumbu Lateral (melintang) pesawat (sumbu-y) – adalah “meng-angguk (pitch)”, dan

[3] Gerakan thd sumbu vertikal (tegak) pesawat (sumbu-z) – adalah “meng-geleng (yaw)”.

Yaw – adalah gerakan mendatar atau horizontal (ke kiri & ke kanan) dari hidung pesawat (aircraft’s nose).

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Ringkasan - Gerakan Pesawat Udara terhadap Sumbu Putar

[1] ROLL

[2] PITCH

[3] YAW

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Aircraft Design Characteristics

• Each aircraft handles somewhat differently because each resists or responds to control pressures in its own way.

For example : – A Training aircraft – is quick to respond to control

applications, while

– A Transport aircraft – feels heavy on the controls and responds to control pressures more slowly.

• These features can be designed into an aircraft to facilitate the particular purpose of the aircraft by considering certain stability and maneuvering requirements.

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Stability :

• Types of Stability – Static Stability

– Dynamic Stability

• Conditions of Stability – Positive, Negative, and Neutral

• Stability about the Axes – Longitudinal Stability (Pitching)

– Lateral Stability (Rolling)

– Vertical Stability (Yawing)

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Aircraft Stability :

Stability and Control: - is the study of how to control the speed, direction, altitude and other conditions that affect how a airplane flies.

• The engineers - :

– Design The controls that are needed in order to fly, and instruments are provided for the pilot in the cockpit of the airplane.

• The pilot - uses these instruments to control the stability of the plane during flight.

Stability and Control

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http://www.grc.nasa.gov/WWW/K-12/airplane/bmotion.html

Instruments used by the Pilot to Controls the airplane

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STABILITY and CONTROL

♨ Tiga kata yang semuanya merujuk kepada Pergerakan Pesawat Udara terhadap satu atau lebih dari ketiga sumbu rotasi – yaitu:

(1) Stability (Stabilitas / kestabilan),

(2) Maneuverability (kemampuan untuk melakukan gerakan), dan

(3) Controllability (kemampuan mengendalikan / mengemudikan)

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(Kestabilan)

♨ STABILITY (Stabilitas / kestabilan) – adalah karakteristik design utama dari pesawat udara yang :

– Menyebabkan pesawat kembali ke posisi kesetimbangan penerbangan semula (initial equilibrium flight conditions) , atau kondisi terbang stabil (steady flight), sesudah terjadi gangguan.

– Cenderung menyebabkan pesawat udara (tanpa dikemudikan /hands-off) terbang didalam lintasan lurus dan mendatar (straight and level flight).

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(Stabilitas / Kestabilan)

Stabilitas – adalah suatu kualitas penting dari pesawat udara untuk memperbaiki kondisi yang mungkin mengganggu kesetimbangan-nya, dan untuk kembali ke- atau melanjutkan pada lintasan terbang semula (the original flightpath). Apabila pesawat tersebut stabil, maka pesawat tersebut akan kembali ke posisi kesetimbangan-nya (trim position).

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STABILITY

:

♨ MANEUVERABILITY – Adalah :

• Karakteristik dari pesawat terbang yang memungkinkan Pilot dengan mudah menggerakkan pesawat terbang terhadap ketiga sumbunya, dan

• menahan tegangan (stresses) yang terjadi akibat dari maneuver tsb.

Maneuverability Tergantung kepada :

• Weight (bobot pesawat), Inertia (inersia pesawat), Size & Location of Flight Controls (ukuran & letak pengendali terbang), Structural strength (kekuatan struktur), dan Powerplant (mesin).

Kemampuan Maneuver juga merupakan karakteristik dari rancang-bangun pesawat (aircraft design characteristic).

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:

♨ CONTROLLABILITY— adalah kemampuan Pesawat untuk me-respon/-nanggapi thd pengendalian pilot, terutama yang berkaitan dengan lintasan terbang (flight-path) dan sikap (attitude).

Dapat dikendalikan (controllability) – adalah kualitas / mutu dari respon pesawat terhadap aplikasi pengendalian pilot ketika menggerakan /maneuvering pesawat udara, terlepas dari karakteristik kestabilan pesawat.

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TYPES OF STABILITY

ADA DUA (2) JENIS (TIPE) KESTABILAN :

Kestabilan Statis (Static Stability)

Kestabilan Dinamis (Dynamic Stability)

KESETIMBANGAN (EQUILIBRIUM) - adalah:

Suatu kondisi dimana penjumlahan semua Gaya dan Momen yang bekerja pada benda adalah Nol.

∑ F = 0 ; dan ∑ M = 0

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Pesawat Terbang dalam keadaan Setimbang: Jumlah Semua Gaya dan Momen yang bekerja

pada pesawat = 0 Tidak mengalami Percepatan (no acceleration), Pesawat melaju dengan kondisi terbang stabil

(steady state of flight ).

Hembusan Angin (wind gust) atau defleksi dari Bidang-bidang Kendali (controls) mengusik kesetimbangan (equilibrium), dan pesawat udara mengalami percepatan akibat ketidak- seimbangan (unbalanced) Momen atau Gaya (forces).

TYPES OF STABILITY

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There are Two Main Types of Aircraft

INSTABILITY (KETIDAK STABILAN) :

An aircraft with Static Instability uniformly departs

from an equilibrium condition

An aircraft with Dynamic Instability oscillates about

the equilibrium condition with increasing amplitude.

•There are Two Modes of Aircraft CONTROL : ▪One moves the aircraft between equilibrium states,

▪The other takes the aircraft into a non-equilibrium

(accelerating) state.

►Control is directly opposed to stability.

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Stability and Control

TYPES OF STABILITY : A. STATIC STABILITY (STABILITAS / KESTABILAN

STATIS) :

• Tendensi / kecenderungan awal, atau arah gerakan, untuk kembali ke sikap semula (original attitude), y.i ke kondisi setimbang (equilibrium).

• Dalam penerbangan, hal yang berkenaan dengan respon awal pesawat udara ketika ketika diusik dari AOA (sudut serangan), slip, atau membelok (bank).

B. DYNAMIC STABILITY (STABILITAS / KESTABILAN DINAMIK) :

Menentukan bagaimana caranya kembali.

Mencakup cara bekerjanya gaya restoratif dalam kaitannya dengan waktu.

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A.STATIC STABILITY

• Static stability deals with the tendency of a displaced body to return to equilibrium, that the aircraft displays after being disturbed from its trimmed condition.

• The three types (conditions) of static stability are defined by the character of movement following some disturbance from equilibrium.

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TYPES OF STABILITY :

OF STABILITY

ADA TIGA MACAM KEADAAN / KONDISI KESTABILAN :

1. POSITIVE Stability

2. NEUTRAL Stability

3. NEGATIVE Stability

• (Lihat Figures 4-18 dan 2-11, untuk jenis/tipe Stabilitas/kestabilan Statik)

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OF STABILITY

KEADAAN / KONDISI KESTABILAN – (samb):

• Kadang-kala turbulensi atau gerakan yang tidak konsistesten menyebabkan Buffeting pada pesawat .

• Buffeting - Turbulent movement of the air over an aerodynamic surface.

– (repeated heavy blows/ hentakan; hantaman)

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A. STATIC STABILITY

1. POSITIVE STATIC STABILITY – exists when the disturbed object tends to return to equilibrium.

2. NEGATIVE STATIC STABILITY, or STATIC INSTABILITY, - exists when the disturbed object tends to continue in the direction of disturbance.

3. NEUTRAL STATIC STABILITY – exists when the disturbed object has neither tendency, but remains in equilibrium in the direction of disturbance.

• These three types of stability are illustrated in Figures 4-18 & 2-11.

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TYPES OF STABILITY :

Types of STATIC Stability

Figure 4-18. Three Types of STATIC Stability 48

Figure 2-11. STATIC Stability

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Penerapan di Pesawat Terbang

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(a) Equilibrium Flight = Neutral Static Stability

(b) Statically Unstable airplane = Negative Static Stability

(c) Neutral Static Stability

http://files.differencebetween.com/wp-content/uploads/2012/08/Static-Stability.png

CONDITIONS OF STABILITY :

1. POSITIVE STABILITY /stabilitas Positif [Fig. 1-32] :

– POSITIVE STATIC STABILITY —the initial tendency of the aircraft TO RETURN TO THE ORIGINAL STATE OF EQUILIBRIUM after being disturbed [Figure 4-18.A &2-11.A.].

• Fig. 1-32 : Positive Static and Dynamic Stability, as illustrated by the ball in a trough, is a desirable characteristic for most airplanes.

• Most airplanes are designed to exhibit the damped oscillation form of stability when disturbed from pitch equilibrium.

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CONDITIONS OF STABILITY

• Pada kondisi Stabilitas Positif – pesawat udara akan kembali ke keadaan semula sesudah turbulensi reda.

• Kondisi stabil positif – merupakan hal yang diharapkan oleh hampir semua pesawat terbang,

• Kecuali pesawat tempur mutakhir yg dilengkapi dgn computer augmented flight controls mungkin memilih menggunakan stabilitas negatif atau netral untuk meningkatkan kelincahan maneouver-nya.

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1. POSITIVE Stability

Figure 4-18. Type of STATIC Stability 53


2. NEUTRAL STABILITY / stabilitas Netral [Fig. 1-34]:

• Neutral static stability—the initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed.

[Figures 4-18 & 2-11.C.]. • Fig. 1-34: An object that has Neutral stability

remain displaced from its original state whenever a force is applied. A neutrally stable airplane would be difficult to control and would probably require computer-augmented flight controls.

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2. NEUTRAL Stability

Figure 4-18. Type of STATIC Stability

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3. NEGATIVE STABILITY /stabilitas Negatif [Fig. 1-33] :

Negative Static Stability (statically Unstable)—the initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed [Figures 4-18 & 2-11.B.].

Fig. 1-33: Negative Stability, as illustrated by a ball rolling off the crest of a hill, is an undesirable characteristic in airplanes. A pilot would be very likely to loose control of an airplane with negative stability.

If the corrective forces increase with time, the body has Negative Dynamic Stability.

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3. NEGATIVE Stability

Figure 4-18. Type of STATIC Stability 57

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B. DYNAMIC STABILITY • Static stability deals with the tendency of an a/c

(a displaced body) to return to equilibrium Occasionally, the initial tendency is different or opposite from the overall tendency, so a distinction must be made between the two.

Dynamic stability – refers to the aircraft response over time when disturbed from a given AOA, slip, or bank.

• Dynamic stability deals with the resulting motion with time.

TYPES OF STABILITY ( Jenis Kestabilan )

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• Pesawat udara apa saja – harus menunjukkan tingkat kestabilan statik dan dinamik yang diperlukan.

• Jika pesawat udara dirancang (designed) – dengan ketidak stabilan statik (static instability) dan tingkat ketidak-stabilan dinamik yang cepat, pesawat akan sangat sulit, jika tidak mustahil, untuk terbang.

• Biasanya, stabilitas dinamik positif diperlukan dalam suatu rancang-bangun pesawat udara - untuk mencegah osilasi /goyangan terus-menerus yang tidak disukai dari pesawat.

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• Any aircraft must demonstrate – the required degrees of static and dynamic stability.

• If an aircraft were designed with static instability and a rapid rate of dynamic instability, the aircraft would be very difficult, if not impossible, to fly.

• Usually, positive dynamic stability is required in an aircraft design to prevent objectionable continued oscillation of aircraft.

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DYNAMIC STABILITY also has Three Subtypes: [Figure 4-19] 1. POSITIVE DYNAMIC STABILITY— the motion of the

displaced object decreases in amplitude with time and, because it is positive, the object displaced returns toward the equilibrium state.

2. NEUTRAL DYNAMIC STABILITY— once displaced, the displaced object neither decreases nor increases in amplitude. A worn automobile shock absorber exhibits this tendency.

3. NEGATIVE DYNAMIC STABILITY (or DYNAMIC INSTABILITY)—the motion of the displaced object increases with time, and becomes more divergent.

CONDITIONS OF DYNAMIC STABILITY :

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DYNAMIC STABILITY :

Dinamik Positif

Dinamik Netral

Dinamik Negatif

Conditions of Dynamic Stability :

Figure 4-19. Damped vs Undamped Stability

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Damped vs Undamped Stability :

Static Stability Dynamic Stability Oscillation

Positive Static Positive Dynamic Damped Oscillation

Positive Static Neutral Dynamic Undamped Oscillation

Positive Static Negative Dynamic (Dynamic Instability)

Divergent Oscillation

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*Damped (extingusihed): meredam, memadamkan, mematikan.

Penerapan di Pesawat Terbang

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http://files.differencebetween.com/wp-content/uploads/2012/08/Dynamic-Stability.png

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STABILITAS DAN GERAKAN PESAWAT UDARA,

(Stability and Motions of an Aircraft)

•Stabilitas terhadap Sumbu Pesawat Udara

(Stability about the Axes)

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Motion of an Aircraft about its Axes

69 FIGURE 2-10

Stabilitas & Gerakan Pesawat Udara

STABILITAS (STABILITY) – adalah kemampuan pesawat memperbaiki sendiri gerakan penyimpangan yang disebabkan oleh turbulensi udara tanpa pengendalian oleh Pilot.

• Apabila pesawat tersebut stabil, maka pesawat tersebut akan kembali ke posisi kesetimbangan-nya (Trim Position).

• Stabilitas pesawat sangat ditentukan oleh posisi pusat massa (C.G) pesawat.

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Tiga (3) jenis Gerakan - yang perlu diperbaiki sendiri oleh KESTABILAN / STABILITAS pesawat, y.i :

1. Mengangguk (Pitch) – rotasi terhadap sumbu-Y (Sumbu Lateral)

2. Berguling (Roll) – rotasi terhadap sumbu-X (Sumbu Longitudinal)

3. Berputar (Yaw) – rotasi terhadap sumbu-Z (sumbu Vertikal / Vertical)

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Stabilitas terhadap sumbu pesawat udara (stability about the Axes of the aircraft), ada Tiga:

– Longitudinal Stability (pitch) / stabilitas membujur;

– Lateral Stability (roll) / Stabilitas melintang;

–Directional Stability (yaw) / Stabilitas arah.

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Stabilitas terhadap sumbu pesawat udara (stability about the Axes of the aircraft), kombinasi gerakan :

–Dutch Roll – stability : A Dutch Roll is an aircraft motion consisting of an out-of-phase combination of yaw and roll.

• Dutch roll stability can be artificially increased by the installation of a yaw damper.

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FIGURE 2-10: View A

Motion of an aircraft about its axes.

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A. Banking (roll) control affected by Aileron movement

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FIGURE 2-10: View B

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B. Climb and Dive (pitch) Control affected by Elevator .

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FIGURE 2-10 : View C


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C. Directional (Yaw) control affected by Rudder movement


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Illustrates the roll, pitch, and yaw motion of the aircraft along the longitudinal, lateral, and vertical axes, respectively.

[1] ROLL

[2] PITCH

[3] YAW

Kesetimbangan ditentukan dari letak Pusat Massa Pesawat (CG).

• Posisi pusat massa ditentukan dari bagaimana berbagai macam kontributor ke berat pesawat diletakkan di dalam pesawat. Dalam hal ini berarti pengaturan siapa duduk di mana, juga pengaturan letak muatan bagasi.


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Kondisi kesetimbangan yang stabil dipenuhi apabila pusat massa pesawat di depan titik yang disebut Titik Netral (Neutral Point) .

Neutral Point (Aerodynamic Center atau Center of Pressure). Angka tipikal untuk titik netral adalah sekitar 0.25 (sekitar 1/4 panjang chord sayap).


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1. Logitudinal Stability (Pitching)

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1. Logitudinal (Pitch) Stability

Illustrates the pitch motion of the aircraft along the lateral axis

1. Longitudinal Stability or Pitching (Stabilitas Membujur)

1. Mengangguk (Pitch): ini adalah gerakan hidung pesawat (nose) naik atau turun oleh gangguan udara.

• Pesawat harus memiliki Stabilitas

Membujur (Logitudinal Stability atau Pitching) – untuk mengembalikan hidung pesawat ke posisi datar seperti semestinya,

• Ekor pesawat (Elevator/Horizontal Tail)- adalah bagian utama yang bertugas melakukan pekerjaan ini.

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• Fig. 4-20: Karena wing’s center of lift (CL)/center pressure berada dibelakang titik berat (center of gravity CG), wing pesawat terbang menghasilkan nose-down pitching moment.

• Pitching moment tsb di-imbangi/lawan (counter-acted) oleh gaya kebawah (down-load) yang dihasilkan oleh horizontail tail surface.

• Elevator trim dapat diatur oleh pilot untuk menghasilkan down-load yang diinginkan pada sembarang kecepatan, dengan demikian mengimbangi pesawat agar tetap terbang lurus dengan sedikit atau tanpa dikemudikan.


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The Horizontal Stabilizer – is the Primary Surface which Controls Longitudinal Stability.

• The action of stabilizer depends upon –

♦ The Speed and

♦ The Angle of Attack (AOA) of the aircraft.

A longitudinally unstable aircraft - has a tendency to dive or climb progressively into a very steep dive or climb, or even a stall.

• Thus, an aircraft with longitudinal instability becomes difficult and sometimes dangerous to fly.


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The aircraft is said to have Longitudinal Stability :

• When an a/c has a tendency to keep a constant an angle of attack (AOA) with reference to the relative wind – that is, when it does not tend to put its nose down and dive, or Lift its nose and stall.

• Longitudinal stability – is the quality that makes an aircraft stable about its lateral axis.

• Longitudinal Stability – refers to Motion in Pitch as the aircraft’s nose moves up and down in flight.

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STATIC LONGITUDINAL STABILITY OR INSTABILITY in an aircraft, is Dependent upon Three Factors:

1. Location of the wing with respect to the CG;

2. Location of the horizontal tail surfaces with respect to the CG;

3. Area or size of the tail surfaces.

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Fig.2-12 :

• Illustrates the contribution of Tail Lift to stability. If the a/c changes its AOA, a change in Lift takes place at aerodynamic center (center of pressure, Cp) of the Horizontal Stabilizer.


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Horizontal Stabilizer – Elevator

• Under certain conditions of Speed, Load, and Angle of Attack (AOA), – the flow of air over the Horiz. Stabilizer creates a Force which pushes the Tail Up or Down.

• When conditions are such that the airflow creates Force Up = Force Down, the forces are said to be in Equilibrium.

• This condition is found in Level Flight in calm air.


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The ELEVATOR

controls PITCH.

On the horizontal tail

surface, the Elevator

tilts up or down,

decreasing or

increasing lift on the

tail. This tilts the nose

of the airplane up and

down.

Elevator Controls Pitch

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2. Lateral Stability (Rolling)

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Lateral Stability

Stability about longitudinal axis rolling motion

Laterally stable aircraft tend to return to the original attitude from rolling motion

Lateral stability is maintained by the wing (design)

a. Dihedral – the upward inclination of the wings from their point of attachment

b. Sweepback – wing leading edges are inclined backwards from their points of attachment

STABILITY

Lateral Stability

STABILITY

Dihedral Sweepback

2. Lateral or Roll Stability

2. Berguling ( Roll ): gerakan Pesawat Udara berguling kalau ujung sayap dipaksa naik atau turun.

• Dalam gerakan ini pesawat akan slip /tergelincir kearah ujung sayap yang lebih rendah, kecuali jika diperbaiki oleh stabilitas melintang (Lateral Stability).

• Kecenderungan (tendency) untuk kembali ke sikap/attitude semula dari gerakan berguling (roll motion) thd sumbu longitudinal – disebut Stabilitas Lateral (Lateral Stability).

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2. Berguling (Roll) . . . .

• Stabilitas melintang (Lateral atau Roll Stability) – dipasok terutama oleh wing dihedral (Fig.2-14 & Fig. 4-25).

• Lateral or roll stability – biasanya diperoleh dengan memiringkan sayap sedikit keatas dari tubuh pesawat ke ujung sayap, pada waktu pesawat dibuat.

• Sudut pemasangan sayap demikian disebut Sudut Dihedral dan tidak dapat diubah oleh pilot.

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2. Lateral Stability atau Rolling

• Motion about its longitudinal (fore and aft) axis is – a Lateral or Rolling motion.

• Lateral stability of an airplane – involves consideration of rolling moments due to sideslips. A sideslip – tends to produce both a Rolling and a Yawing motion.

• If an airplane has a favorable rolling moment, a Sideslip will tend to return the airplane to a level-flight attitude.

• The Principal Surface contributing to the Lateral Stability of an airplane is the Wing.

• The Effect of the geometric Dihedral of a Wing (Fig. 2-14) – is a powerful contribution to Lateral Stability.


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• With the Relative Wind from the side, the Wing into the wind is subject to – an increase in AOA and develops an increase in Lift.

• The Wing away from the wind is subject to – a decrease in AOA and develops less Lift.

• The Changes in Lift – effect a rolling moment tending to raise the windward wing.

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DIHEDRAL (FIGURES 2-14 & 4-25) • The most common procedure for producing

lateral stability is to build the wings with an angle of one (1°) to three (3°) degrees above perpendicular to the longitudinal axis. (Fig. 2-14).

• The wings on either side of the aircraft join the fuselage to form a slight V or angle called “dihedral.”

• The amount of dihedral is measured by the angle made by each wing above a line parallel to the lateral axis.

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Fig. 2-14. Contribution of Dihedral to Lateral Stability atau Rolling


Fiigure: RIGHT – Aileron DOWN

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• Dihedral involves a balance of lift created by the wings’ AOA on each side of the aircraft’s longitudinal axis.

• If a momentary gust of wind forces one wing to rise and the other to lower, the aircraft banks.

• When the aircraft is banked without turning, the tendency to sideslip or slide downward toward the lowered wing occurs. [Figure 4-25].

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Illustrates the rolling motion of the aircraft

along the longitudinal axis

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Ailerons

Figure: LEFT – Aileron- DOWN

Effect of Sweepback on Lateral Stability

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Sweepback • Sweepback is an addition to the dihedral that increases

the lift created when a wing drops from the level position.

• A sweptback wing is one in which the leading edge slopes backward.

• When a disturbance causes an aircraft with sweepback to slip or drop a wing, the low wing presents its leading edge at an angle that is perpendicular to the relative airflow.

• As a result, the low wing acquires more lift, rises, and the aircraft is restored to its original flight attitude.

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Sweepback – (continued) • Sweepback also contributes to directional (yaw)

stability. • When turbulence or rudder application causes

the aircraft to yaw to one side, the right wing presents a longer leading edge perpendicular to the relative airflow.

• The airspeed of the right wing increases and it acquires more drag than the left wing.

• The additional drag on the right wing pulls it back, turning the aircraft back to its original path.

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Ailerons Control Roll

The AILERONS control

ROLL.

On the outer rear edge of

each wing, the two

Ailerons move in

opposite directions, up

and down, decreasing lift

on one wing while

increasing it on the other.

This causes the airplane

to roll to the left or right.

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3. Directional Stability (Yawing) (Stabilitas Arah)

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Directional Stability

Stability about the vertical axis

Directionally stable aircraft tends to remain on its course in straight and level flight

Directional stability is maintained by keel surface of the vertical stabilizer

Sweptback wings also aid in directional stability (frontal area)

STABILITY

Directional Stability

STABILITY

Effect of Sweepback on Directional Stability

• When an airplane with swept-back wing is flying straight into the wind, the Lift and Drag on both sides are equal.

• When an airplane yaws to the left, the right wing produces more induced drag than the left, and the airplane tends to straighten into the relative wind.

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3. Directional Stability (Stabilitas Arah)

Illustrates the yaw motion of the aircraft along the vertical axis


3. Berputar (Yaw) : dalam gerakan ini hidung pesawat berputar kekiri atau kekanan, dan pesawat akan Membelok.

• Untuk memperoleh Stabilitas Arah (Directional Stability) dipasang sirip ekor (vertical fin/ stabilizer), supaya pesawat tetap pada arah lurus seperti yang dikehendaki.

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Vertical Stabilizer – Rudder

The RUDDER controls

YAW.

On the vertical tail fin, the

rudder swivels from side

to side, pushing the tail in

a left or right direction.

A pilot usually uses the

rudder along with the

ailerons to turn the

airplane.

Rudder Controls Yaw

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Airplane Controls, Movements, Axes of Rotation, and Types of Stability

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Airplane Controls, Movements, Axes of Rotation, and Types of

Stability

Mengendalikan Pesawat Terbang

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CONTROL (Pengemudian/Pengendalian) :

Pengemudian /Pengendalian (Control) – adalah tindakan yang dilakukan untuk membuat pesawat udara mengikuti lintasan terbang yang diinginkan.

• Ketika pesawat terbang disebut “controllable” (dapat dikendalikan) – artinya bahwa pesawat menanggapinya/me-respon dengan mudah dan cepat terhadap gerakan kemudi (controls).

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• Menggerakkan bidang kendali (control surfaces) pada pesawat – akan mengubah aliran udara diatas permukaan pesawat udara.

• Hal ini menimbulkan perubahan pada keseimbangan gaya-gaya yang bekerja untuk mempertahankan pesawat terbang lurus dan mendatar (straight & level flight).

CONTROL (KENDALI) :

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• Pilot harus dapat mengendalikan pesawat terbang – walaupun sebagaimana stabilnya sebuah pesawat terbang.

• KONTROL MEMBUJUR (Lateral Control): digunakan untuk menaikkan dan menurunkan hidung (nose) pesawat, dan ini diperoleh dengan Elevator terletak di bagian belakang ekor mendatar (Horizontal Tailplane, Horizontal Stabilizer).

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• KONTROL MELINTANG (Longitudinal Control): digunakan untuk memiringkan pesawat. Hal ini diperoleh dengan kemudi guling (Aileron) pada trailing edge sayap.

• KONTROL ARAH (Directional Control):

• Digunakan untuk membelokkan kemudi pesawat kekiri atau kekanan. Diperoleh dari kemudi arah (Rudder) pada sirip ekor pada Vertical Tail (Vertical Stabilizer/ Vertical Fin).

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Bidang Kendali Terbang

(Flight Control Surfaces)

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• PRIMARY (Utama) : Aileron, Elevator, Rudder • SECONDARY ( Kedua) : • AUXILIARY (Tambahan. Bantuan) :

Flight Control Surfaces (Bidang Kemudi/Kendali Terbang)

• Bidang Kendali Terbang (Flight Control Surfaces) – adalah airfoil yang ber-engsel atau bergerak yang dirancang untuk mengubah sikap (attitude) pesawat udara selama penerbangan.

• Bidang /permukaan Kendali Terbang dibagi menjadi tiga kelompok :

– Primary

– Secondary

– Auxiliary

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Pitching (mengangguk)

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Rolling (berguling)

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Yawing (menggeleng)

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Definisi Pilihan

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Selected Definitions : • Buffeting – is a high-frequency instability, caused by airflow

separation or shock wave oscillations from one object striking another. – It is caused by a sudden impulse of load increasing. – It is a random forced vibration. – Generally it affects the tail unit of the aircraft structure due to

air flow down stream of the wing.

• Slipping turn – An uncoordinated turn in which the aircraft is banked too much for the rate of turn, so the horizontal lift component is greater than the centrifugal force, pulling the aircraft toward the inside of the turn.

• Sideslip — A slip in which the airplane’s longitudinal axis remains parallel to the original flight-path, but the airplane no longer flies straight ahead. Instead, the horizontal component of wing lift - forces the airplane to move sideways toward the low wing.

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• Dihedral – The positive acute angle between the lateral axis of an airplane and a line through the center of a wing or horizontal stabilizer. Dihedral contributes to the lateral stability of an airplane.

• Directional stability – Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state.

The Vertical Tail is the primary contributor to directional stability, causing an airplane in flight to align with the relative wind.

Selected Definitions :

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•Angle of attack – The acute angle formed between the chord line of an airfoil and the direction of the air striking the airfoil

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• Angle of incidence – The angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.

• Swept Wing — A wing planform in which the tips of the wing are farther back than the wing root.


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• Angle of incidence – The angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.


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References / Rujukan

1. FAA-H-8083-31: AMA Ch.02

2. FAA AC 65-15A, Ch.2

3. JSAT, Ch. 1, Section B.

4. FAA PHAK, Chapter 04.

5. EASA Part 66.

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Flight Stability & Dynamics, Control · Flight Stability & Dynamics, Control •Airplane Axes •Flight Stability and Control –Static Stability –Dynamic Stability •Flight Control

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