For Video Lecture of this presentation: https://youtu.be/yO0IPxVZmwE The topics covered in this session are pressure, density and temperature altitude. The practical significance of pressure altitude is discussed along with a real case example. An alternative method is also briefed Attention! "Gate Aerospace Engineering aspirants", A virtual guide for gate aerospace engineering is provided in "Age of Aerospace" blog for helping you meticulously prepare for gate examination. Respective notes of individual subjects are provided as 'Embedded Google Docs' which are frequently updated. This comprehensive guide is intended to efficiently serve as an extensive collection of online resources for "GATE Aerospace Engineering" which can be accessed free of cost. Use the following link to access the study material https://ageofaerospace.blogspot.com/p/gate-aerospace.html

1. FLIGHT MECHANICS
PRESSURE ALTITUDE
Presented by - Ganesh Natarajan S
Target Audience: Gate Aerospace, Aerospace and Aeronautical Engineering Students, etc.

2. CORE TOPICS:
Basics: Atmosphere: Properties, standard atmosphere. Classification of aircraft. Airplane (fixed
wing aircraft) configuration and various parts.
Airplane performance: Pressure altitude; equivalent, calibrated, indicated air speeds; Primary
flight instruments: Altimeter, ASI, VSI, Turn-bank indicator. Drag polar; takeoff and landing;
steady climb & descent; absolute and service ceiling; cruise, cruise climb, endurance or loiter;
load factor, turning flight, V-n diagram; Winds: head, tail & cross winds.
Static stability: Angle of attack, sideslip; roll, pitch & yaw controls; longitudinal stick fixed &
free stability, horizontal tail position and size; directional stability, vertical tail position and size;
dihedral stability. Wing dihedral, sweep & position; hinge moments, stick forces.
SPECIAL TOPICS:
Dynamic stability: Euler angles; Equations of motion; aerodynamic forces and moments,
stability & control derivatives; decoupling of longitudinal and lateral-directional dynamics;
longitudinal modes; lateral-directional modes.
SYLLABUS

3. Outline
Let’s Start
PRESSURE ALTITUDE
Previous Lessons Basics
Types of Altitudes
• Pressure
• Density
• Temperature
Practical Significance
• General method
• Unit conversion
Alternative Method
• Altitudes - ISA equations

4. Types of Altitude
ByCmglee-Ownwork,CCBY-SA3.0
 Geometric
 Absolute
 Geopotential
• Pressure
• Density
• Temperature
Altitude

5. PRESSURE
• Pressure is the force applied in a perpendicular direction to
the surface of an object.
• Air has mass and is affected by the attraction of gravity
(weight), and because of its weight, it has force.
• Since air is a fluid substance, this force is exerted equally in
all directions. Its effect on bodies within the air is called
pressure.
• The pressure of the atmosphere varies with time and location.
• Thus a standard atmosphere model (ISA) was developed and
is referred.

6. ALTITUDES DEFINITION
Pressure Altitude:
 Pressure altitude is the height above a standard datum plane (SDP), which is a theoretical
level where the weight of the atmosphere is 29.92 "Hg (1,013.2 mb) as measured by a
barometer.
Density Altitude:
 Density altitude is the vertical distance above sea level in the standard atmosphere at which
a given density is to be found. Density altitude is pressure altitude corrected for nonstandard
temperature.
 A decrease in air density means a high density altitude; an increase in air density means a
lower density altitude.
Temperature Altitude:
 The altitude measured by knowing the temperature is known as temperature altitude.

7. Altitude Pressure Temperature
feet metre (Hg) Pascal (°C) Kelvin (°F)
0 0 29.9 101309 15 288.2 59
1,000 304.8 28.9 97720 13 286.2 55.4
2,000 609.6 27.8 94198.5 11 284.2 51.9
3,000 914.4 26.8 90812.5 9.1 282.3 48.3
4,000 1219 25.8 87494.2 7.1 280.3 44.7
5,000 1524 24.9 84277.5 5.1 278.3 41.2
6,000 1829 24 81196.3 3.1 276.3 37.6
7,000 2133 23.1 78182.7 1.1 274.3 34
8,000 2438 22.2 75236.9 -0.9 272.3 30.5
9,000 2743 21.4 72392.7 -2.8 270.4 26.9
10,000 3048 20.6 69650 -4.8 268.4 23.3
11,000 3353 19.8 67008.9 -6.8 266.4 19.8
12,000 3657 19 64401.7 -8.8 264.4 16.2
13,000 3962 18.3 61929.9 -11 262.4 12.6
14,000 4267 17.6 59492 -13 260.5 9.1
15,000 4572 16.9 57155.7 -15 258.5 5.5
16,000 4877 16.2 54887.1 -17 256.5 1.9
17,000 5181 15.6 52686.2 -19 254.5 -1.6
18,000 5486 14.9 50586.8 -21 252.5 -5.2
19,000 5791 14.3 48521.4 -23 250.6 -8.8
20,000 6096 13.7 46523.6 -25 248.6 -12
ISA CHARTPractical Significance?
• Let’s consider a real case example
Imagine that you are in an airplane
flying at some real, geometric altitude.
 You measure the actual outside air
pressure to be 20.6 Hg
 You measure the actual outside air
temperature to be 260.5 K
By using the ISA Chart
 You are flying at a pressure altitude of
10,000 ft (3 km).
 You are flying at a temperature
altitude of 14,000 ft (4.3 km).

8. How to determine the pressure altitude?
pressure altitude = (standard pressure - your current pressure setting) x 1,000 + field elevation
Field elevation: The officially designated elevation of an airport above mean sea level, in
international usage denoted by the symbol Ha. (It can be neglected if you are referring mean
sea level i.e. Field Elevation = 0)
For Example:
Let’s say we measure 24.92"Hg at some geometric altitude. So what is the pressure altitude?
• (29.92 – 24.92) x 1,000 = 5000 feet.
Higher Pressure = Lower Altitude
Lower Pressure = Higher Altitude
• Feet to metre conversion: 5000 x 0.3048 = 1524 metre.

9. Alternative Method

12. Book Reference
• Pilot's handbook of aeronautical knowledge 2016 - Chapter 4:
Principles of flight (4-1, 4-4) Pg No: (90-93/524)
• Introduction to Flight - John David Anderson (7th Edition) Section:
3.5, Pg No: (125-133/945)
PRESSURE ALTITUDE

13. Summary
Types of
Altitude
Determination
of pressure
altitude
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