Atmosphere Flashcards
Static pressure is the result of _______.The unit for static pressure is _____
the weight of the atmosphere pressing down on the air beneath, N/m2
Density varies with _________.
static pressure, temperature and humidity
Density decreases with increasing altitude because of _______. However, with increasing altitude temperature also decreases, which would tend to ______, but the effect of ____________.
decreasing static pressure, increase density , decreasing static pressure is dominant
The ICAO standard atmosphere assumes the following mean sea level values:
Temperature
Pressure
Density
Temperature 15°C
Pressure 1013.25 hPa
Density 1.225 kg/m3
The temperature lapse rate is assumed to be uniform at a rate of ________. from mean sea level up to a height of _________ above which the lapse rate becomes ____and the temperature remains constant at ______.
2°C per 1,000 ft (1.98°C), 36,090 ft (11,000 m) , zero, -56.5°C
At 40000 ft the relative density is
one- fourth that at sea level
If a cubic metre of moving air is completely trapped and brought to rest by means of an open ended
tube the ________, but by being brought completely to rest the
kinetic energy will become __________, for all practical purposes, is equal to:
total energy will remain constant, pressure energy which , Dynamic Pressure = ½ ρ V2 N/m2
An air flowing at 100 kts. What is the Dynamic pressure ?
Consider air flowing at 52 m/s (100 kt) with a density of 1.225 kg/m3
(100 kt x 6080ft = 608000 ft/hour ÷ 3.28 = 185366 metres/hour ÷ 60 ÷ 60 = 52m/s)
Dynamic pressure = 0.5 x 1.225 x 52 x 52 = 1656 N/m2 (16.56 hPa)
If speed is doubled, dynamic pressure will be four times greater
0.5 x 1.225 x 104 x 104 = 6625 N/m2 (66.25 hPa)
Indicated Air Speed
The speed registered on the Air Speed Indicator.
Calibrated Air Speed:
When IAS is corrected for this ‘position’ or ‘pressure’ error, as it’s called, the resultant is Calibrated Air It is affected by
1. Position of the Pitot and static port- particularly the static port
2. Configuration of the ac - Flaps, UC, spoilers, airbrakes etc.
3. Attitude to the airflow - the AOA and sideslip
4. Presence or absence of Ground Effect
Equivalent Air Speed:
When the IAS is corrected for ‘position’ AND ‘compressibility’ error, the resultant is Equivalent Air Speed.
True Air Speed:
The actual speed of the aircraft relative to the free stream is called true airspeed (TAS), and denoted by (V).The speed of the aircraft through the air. THE ONLY SPEED THERE IS - All the other, so called, speeds are pressures.TAS = EAS/√ б.
Speed of sound is proportional to
The speed at which pressure waves propagate is proportional to the square root of the absolute temperature of the air.
Why is that the ASI indicates the EAS rather than TAS ?
Many of the handling characteristics of an aircraft depend mainly on the dynamic pressure, i.e. on the equivalent airspeed, so it is often more useful to have a direct reading of EAS than TAS. Like stalling speed
Taking-off from an airfield with low atmospheric pressure and/or high air temperature and/or high humidity, will require a ____ TAS to achieve the same dynamic pressure (IAS).
higher
A constant IAS will give ____ dynamic pressure. As altitude increases, a higher TAS is required to maintain ________. Maintaining a constant IAS will compensate for _______.
constant, a constant dynamic pressure, changes in air density
Aircraft ‘V’ speeds are ____, except VMO which is an ____, but all are presented to the pilot in the Flight Manual as ____.
CAS, EAS, IAS
When considering air:
1 - Air has mass
2 - Air is not compressible
3 - Air is able to flow or change its shape when subject to even small pressures
4 - The viscosity of air is very high
5 - Moving air has kinetic energy
The correct combination of all true statements is:
a. 1, 2, 3 and 5
b. 2, 3 and 4
c. 1 and 4
d. 1, 3, and 5
D
Why do the lower layers contain the greater proportion of the whole mass of the atmosphere:
Because air is compressible
With increasing altitude, up to about 40,000 ft, the characteristics of air change:
1 - Temperature decreases continuously with altitude
2 - Pressure falls steadily to an altitude of about 36,000 ft, where it then remains constant
3 - Density decreases steadily with increasing altitude
4 - Pressure falls steadily with increasing altitude
The combination of true statements is:
a. 3 and 4
b. 1, 2 and 3
c. 2 and 4
d. 1 and 4
A
When considering static pressure:
1 - In aviation, static pressure can be measured in hectopascal=s
2 - The SI units for static pressure is N/m2
3 - Static pressure is the product of the mass of air pressing down on the air beneath
4 - Referred to as static pressure because of the air’s stationary or static presence
5 - The lower the altitude, the greater the static pressure
The correct statements are:
a. 2, 4 and 5
b. 1, 2, 3, 4 and 5
c. 1, 3 and 5
d. 1 and 5
B
When considering air density:
1 - Density is measured in millibar=s
2 - Density increases with increasing altitude
3 - If temperature increases the density will increase
4 - As altitude increases, density will decrease
5 - Temperature decreases with increasing altitude, this will cause air density to increase
The combination of correct statements is:
a. 4 only
b. 4 and 5
c. 5 only
d. 2, 3 and 5
A
Air density is:
a. Mass per unit volume
b. Proportional to temperature and inversely proportional to pressure
c. Independent of both temperature and pressure
d. Dependent only on decreasing pressure with increasing altitude
A
When considering the ICAO International Standard Atmosphere and comparing it with the
actual atmosphere, which of the following statements is correct:
1 - Temperature, pressure and density are constantly changing in any given layer of the actual
atmosphere
2 - A requirement exists for a hypothetical ’standard’ atmosphere
3 - The values given in the International Standard Atmosphere exist at a the same altitudes in
the actual atmosphere
4 - The International Standard Atmosphere was designed for the calibration of pressure
instruments and the comparison of aircraft performance calculations
a. 1, 2 and 3
b. 2, 3 and 4
c. 1, 2, 3 and 4
d. 1, 2 and 4
D
