NAV - Speed Flashcards
What units is speed expressed in? (5)
- Mph
- Kts
- Fps or ft/sec
- Kph
- Mach
What does a Pitot tube do? (1)
Projects forward of the aircraft sufficiently to sample the undisturbed air (= PITOT PRESSURE)
What is undisturbed air known as? (1)
Pitot pressure
What is Dynamic pressure? (1)
The pressure generated by the aircraft’s movement
What is the Static pressure? (1)
The natural pressure that is exerted by the atmosphere
How is Pitot pressure calculated? (1)
Pitot Pressure =
Static Pressure + Dynamic Pressure
How is Dynamic pressure calculated? (1)
Dynamic Pressure =
Pitot Pressure - Static Pressure
Pitot pressure diagram
The simple Airspeed Indicator removes Static Pressure by allowing it to impinge on the outside of a flexible metal capsule that is fed with Pitot Pressure air
What errors is an ASI subject to? (6)
- Instrument error
- Pressure error
- Position error
- Manoeuvre error
- Density error
- Compressibility error
What types of instrument errors do ASIs suffer from? (3)
- Due to small manufacturing imperfections and the need to generate a large needle movement from a small capsule movement
- Any error is noted when the instrument is tested and calibrated prior to use
- An error card is mounted in the aircraft cockpit near the indicator
What is Pressure error divided into? (2)
- Position error - static vent not being able to accurately sample static pressure throughout the aircraft speed range
- Manoeuvre error - Likely at low speeds
What is Density error? (1)
When ASI’s deviate from ISA conditions
(ASI’s are calibrated to to ISA)
What is Compressibility error? (2)
- At speeds above 300kts the air is compressed and temporarily brought to a halt in front of the pitot tube
- This causes a false pressure to enter the pitot tube and causes the airspeed indicator to over read
What types of airspeed are used? (1)
IAS - Indicated Air Speed
What other types of airspeed is avaialble?
- RAS - Rectified Air Speed
- TAS True Air Speed
- GS - Ground Speed
- M - Mach number
What is RAS? (2)
RAS - Rectified Air Speed
The IAS after correction for Pressure and
Instrument Errors
What is TAS? (2)
- The RAS after correction for Density Error
- The actual speed of the aircraft through the air
What is GS? (2)
- The actual speed of the aircraft over the surface of the Earth
- TAS corrected for the effects of wind
What is Mach Number? (2)
- TAS expressed as a fraction of the local speed of sound
- Mach 1 depends on temperature: “The colder, the slower”
How is the Mach Number calculated?
What 3 conditions does Mach Number have? (3)
- Subsonic - Conditions exist when Mach number is less than one (M < 1 )
- Transonic - when some part of the aircraft is above Mach 1
- Supersonic - when all of the airframe is above Mach 1
What is the speed of sound known as? (1)
Mach 1.0
What is Mcrit? (2)
Mcrit - Critical mach Number
- Dependent on the aerodynamic shape of the airframe
Mcrit example diagram
For instance, if the air flowing over a wing reaches Mach 1 when the wing is only moving at Mach 0.8, then the wing’s critical Mach number is 0.8. At this point a shock wave is generated on the wing’s upper and lower surfaces
What are the Mach classification of speeds? (4)
- Subsonic Flight: less than M 0.8
- Transonic Flight: M 0.8 to M1.2
- Supersonic Flight: M1.2 to M 5.0
- Hypersonic Flight: above M 5.0
What happens when an aircraft achieves Mcrit? (1)
A Shockwave is formed
Where must all medium & high-level supersonic flights be made within the EU? (4)
- Over the sea
- May accelerate to supersonic speed:
- 10nm> at sea
- On flight path of 20° from mean line of coast
When may supersonic flights take place with the aircraft facing / parallel / turning to land? (1)
- 35nm> from the nearest coastline
What does a Mach meter allow a pilot to do? (3)
- Fly speeds just below Mcrit
- Have optimum performance
- Minimum discomfort & fatigue
Speed graph of TAS & IAS diagram
Speed graph of Mach & FL diagram
