1. POF Unit 2 Review

2. Review Unit Two – LTA Flight - Mini-Lessons H to K
Five multiple choice questions
Example: Lift is generated in an airship as a result of the INSIDE gas having a ______ density than the surrounding OUTSIDE atmosphere.
Greater
Lesser
Equal
No change
One SHORT ANSWER
Example: Explain Charles’ Law, and give an example of how it might affect a balloon’s flight. (Use diagrams to illustrate your answer.)
Review
Unit Two – Lighter Than Air (LTA)
A complete answer will include: CHARLES’ LAW states that as the temperature of a gas increases, so does its volume, too. A balloon should fly better as the temperature of its lifting gas goes up because as volume increases, density decreases.

3. Mini-Lesson H: Lighter-than-Air (LTA) Introduction
Lighter-than-Air flight is based on principles of AEROSTATICS
Balloons are the earliest machines invented capable of manned flight (1783)
Lift is generated by a of DIFFERENCE in DENSITY between gases
Warm air is less dense than cold air – hot air is MUCH less dense than cold air
Certain gases – Hydrogen (H) and Helium (He) are naturally less dense than the surrounding Nitrogen (N) atmosphere
Balloon - shape due to internal air pressure; does not have means for thrust (depend upon wind for direction)
Blimp - shape due to internal air pressure; has a means for thrust and directional control
Dirigible - shape due to internal structure; has thrust and directional control.
Goodyear's Latest Airship

4. Mini-Lesson I: LTA Fundamentals
Measurements and calculations will be in metric. Mass (grams, g); Linear distance (centimeters, cm); Volume (liters, l, and cubic centimeters, cm3 or cc)
Density is the key measurement in understanding LTA flight – if the density of the gas INSIDE the aircraft is significantly lower than the density of the atmosphere OUTSIDE the aircraft, the aircraft will have lift. Density = mass/volume.
LTA aircraft can be thought of in three basic shapes: rectangular cubes (“boxes”), cylinders (“tubes”) and spheres (“balls”)
The volume of a rectangular cube (“box”) = length x width x height. (l x w x h)
The volume of a cylinder (“tube”) = πr2h, where “h” is the height (or length) of the cylinder, and “r” is the radius (or, ½ of the diameter) of the cylinder
The volume of a sphere (“ball”) is: 4/3πr3, and “r” is the radius (or, ½ of the diameter) of the sphere.
Notice that the shape of the USS Los Angeles approximates a cylinder…a very, very BIG cylinder.

5. Volume Applications Estimating Volume (1)
Rectangular cube (“box”) = length x width x height. (l x w x h)
Round data to nearest whole numbers
Do multiplication
Add “zeros” and units
Example: l = 23 m, w = 43 m, h = 56 m
20 x 40 x 60
2 x 4 x 6 = 48
48,000 m3
Volume Applications
LTA Unit Review

6. Volume Applications Estimating Volume (2)
Cylinder (“tube”) = πr2h, where “h” is the height (or length) of the cylinder, and “r” is the radius (or, ½ of the diameter) of the cylinder
Round data to nearest whole numbers
Do multiplication
Add “zeros” and units
Example: π = 3.14 (3), r = 7.3 m, h = 42 m
3 x 72 (49) x 40
3 x 5 x 4 = 60
6000 m3
Volume Applications
LTA Unit Review

7. Volume Applications Estimating Volume (3)
Sphere (“ball”) is: 4/3πr3, and “r” is the radius (or, ½ of the diameter) of the sphere.
Round data to nearest whole numbers
Do multiplication
Add “zeros” and units
Example: 4/3 = 1.3, π = 3.14 (3), r = 1.7 m
1.3 (1) x 3.14 (3) x 23
1 x 3 x 8 = 24
24 m3
Volume Applications
LTA Unit Review

8. Mini-Lesson J: Helium vs. Hydrogen
Certain gases – Hydrogen (H) and Helium (He) are naturally less dense than the surrounding Nitrogen (N) atmosphere
Hydrogen is VERY chemically reactive (combustible). Helium is completely chemically non-reactive (does NOT burn or explode)
Airship designers often conservatively estimate helium’s lift at 27.2 kgs per 28.3 m3 and hydrogen’s lift at 38.4 kgs per 28.3 m3.

9. Mini-Lesson K: Three Gas Laws
Boyle's Law: The pressure of a gas is inversely proportional to its volume.
When the VOLUME gets smaller, the PRESSURE gets higher
Charles' Law: the volume of a gas is proportional to its temperature.
When the TEMPERATURE gets higher, the VOLUME gets higher
Gay-Lussac's Law: The temperature of a gas is directly proportional to its pressure.
When the TEMPERATURE gets higher, the PRESSURE gets higher