Dynamic Stability

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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 (Axes of an 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)
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Sumbu Pesawat Udara
Axes of an Aircraft
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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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 (terkonsentrasi) 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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Center of Gravity (CG)
• 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.
Center of Pressure (CP)
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Center of Gravity (CG)
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(Center of Pressure, Cp)
• 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.
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(Center of Pressure, Cp)
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Perputaran (rotasi) Pesawat Udara
Axes of an Aircraft Rotation
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Sumbu Pesawat Udara
LONGITUDINAL AXES of an Aircraft
 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 RollAxis (Sumbu-Guling).
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Gerakan berputar thd Sumbu Guling
Roll around Longitudinal Axis – ROLL Axis
Longitudinal or Roll Axis = X - Axis
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Gerakan berputar thd Sumbu Guling
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.
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Sumbu Pesawat Udara
LATERAL Axes of an Aircraft
 Sumbu MELINTANG (Lateral Axis) :
– Adalah garis khayal yang melintang sepanjang
bentangan sayap (crosswise), dari ujung sayap
kiri-ke-ujung sayap kanan (from wing tip - towing 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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Gerakan Mengangguk thd Sumbu Angguk
Pitch around the Lateral Axis – PITCH Axis
Lateral or Pitch Axis = Y - Axis
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Gerakan Mengangguk thd Sumbu Angguk
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.
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Sumbu Pesawat Udara
VERTICAL Axes of an Aircraft
 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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Gerakan Menggeleng thd Sumbu Geleng
Yaw around the Vertical Axis – YAW Axis
Vertical or Yaw Axis = Z-Axis
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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
[2] PITCH
[1] ROLL
[3] YAW
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


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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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Aircraft Stability :
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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Stability and Control
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.
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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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TYPES OF STABILITY
 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).
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Stability and Control
 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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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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TYPES OF STABILITY :
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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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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TYPES OF STABILITY :
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 STATIC Stability
Figure 4-18. Three Types of STATIC Stability
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Figure 2-11. STATIC Stability
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Penerapan di Pesawat Terbang
(a) Equilibrium Flight =
Neutral Static Stability
(b) Statically Unstable
airplane = Negative
Static Stability
(c) Neutral Static
Stability
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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 maneouvernya.
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1. POSITIVE Stability
Figure 4-18. Type of STATIC Stability
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CONDITIONS OF STABILITY :
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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CONDITIONS OF STABILITY :
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
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TYPES OF STABILITY ( Jenis Kestabilan )
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.
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TYPES OF STABILITY ( Jenis Kestabilan )
• 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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TYPES OF STABILITY ( Jenis Kestabilan )
• 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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CONDITIONS OF DYNAMIC STABILITY :
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.
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DYNAMIC STABILITY :
Dinamik
Positif
Dinamik
Netral
Dinamik
Negatif
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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
Positive Static
Negative Dynamic
(Dynamic Instability)
Undamped
Oscillation
Divergent
Oscillation
*Damped (extingusihed): meredam, memadamkan, mematikan.
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Penerapan di Pesawat Terbang
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TYPES OF STABILITY ( Jenis Kestabilan )
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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
FIGURE 2-10
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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 kesetimbangannya (Trim Position).
• Stabilitas pesawat sangat ditentukan oleh posisi
pusat massa (C.G) pesawat.
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Stabilitas & Gerakan Pesawat Udara
 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 & Gerakan Pesawat Udara
 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 & Gerakan Pesawat Udara
 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-ofphase combination of yaw and roll.
• Dutch roll stability can be artificially increased
by the installation of a yaw damper.
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Motion of an Aircraft about its Axes
FIGURE 2-10: View A
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Motion of an aircraft about its axes.
A. Banking (roll) control affected by
Aileron movement
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Motion of an Aircraft about its Axes
FIGURE 2-10: View B
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Motion of an aircraft about its axes.
B. Climb and Dive (pitch) Control affected by Elevator .
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Motion of an Aircraft about its Axes
FIGURE 2-10 : View C
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Motion of an aircraft about its axes.
C. Directional (Yaw) control affected by Rudder movement
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Stabilitas & Gerakan Pesawat Udara
[1] ROLL
[2] PITCH
[3] YAW
Illustrates the roll, pitch, and yaw motion of the aircraft along the
longitudinal, lateral, and vertical axes, respectively.
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Stabilitas & Gerakan Pesawat Udara
 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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Stabilitas & Gerakan Pesawat Udara
 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
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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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1. Logitudinal Stability (Pitching)
• 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 (counteracted) 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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1. Logitudinal Stability (Pitching)
 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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1. Logitudinal Stability (Pitching)
 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.
88
1. Logitudinal Stability (Pitching)
 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.
89
1. Logitudinal Stability (Pitching)
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.
90
Horizontal Stabilizer – Elevator
91
1. Logitudinal Stability (Pitching)
• 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.
92
Elevator Controls Pitch
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.
93
2. Lateral Stability (Rolling)
94
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
Dihedral
Sweepback
STABILITY
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).
97
2. Lateral Stability atau Rolling
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.
98
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.
99
2. Lateral Stability atau Rolling
• 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.
100
Fig. 2-14. Contribution of Dihedral to
Lateral Stability atau Rolling
 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.
101
Fig. 2-14. Contribution of Dihedral to
Lateral Stability atau Rolling
Fiigure: RIGHT –
Aileron DOWN
102
Fig. 2-14. Contribution of Dihedral to
Lateral Stability atau Rolling
• 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].
103
2. Lateral Stability atau Rolling
Illustrates the rolling motion of the aircraft
along the longitudinal axis
104
Ailerons
Figure: LEFT –
Aileron- DOWN
105
Effect of Sweepback on Lateral Stability
106
Effect of Sweepback on Lateral
Stability
 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.
107
Effect of Sweepback on Lateral
Stability
 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.
108
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.
109
3. Directional Stability (Yawing)
(Stabilitas Arah)
110
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.
113
3. Directional Stability (Stabilitas Arah)
Illustrates the yaw motion of the
aircraft along the vertical axis
114
3. Directional Stability (Stabilitas Arah)
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.
115
3. Directional Stability
(Stabilitas Arah)
116
Vertical Stabilizer – Rudder
117
Rudder Controls Yaw
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.
118
Airplane Controls, Movements, Axes of Rotation, and
Types of Stability
119
Airplane Controls, Movements,
Axes of Rotation, and Types of
Stability
120
Mengendalikan Pesawat
Terbang
121
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).
122
CONTROL (KENDALI) :
• 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).
123
Mengendalikan Pesawat Terbang
• 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).
124
Mengendalikan Pesawat Terbang
• 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).
125
Bidang Kendali Terbang
(Flight Control Surfaces)
• PRIMARY (Utama) : Aileron, Elevator, Rudder
• SECONDARY ( Kedua) :
• AUXILIARY (Tambahan. Bantuan) :
126
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
127
Pitching (mengangguk)
128
Rolling (berguling)
129
Yawing (menggeleng)
130
Definisi Pilihan
131
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.
132
Selected Definitions :
• 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.
133
Selected Definitions :
•Angle of attack – The acute angle formed between
the chord line of an airfoil and the direction of the air
striking the airfoil
134
Selected Definitions :
135
Selected Definitions :
• 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.
136
Selected Definitions :
• Angle of incidence – The angle formed by the
chord line of the wing and a line parallel to the
longitudinal axis of the airplane.
137
References / Rujukan
1.
2.
3.
4.
5.
FAA-H-8083-31: AMA Ch.02
FAA AC 65-15A, Ch.2
JSAT, Ch. 1, Section B.
FAA PHAK, Chapter 04.
EASA Part 66.
138