Speed of Sound Flashcards
What is a sound wave?
A LONGITUDINAL PRESSURE WAVE/DISTURBANCE which TRAVELS through a MEDIUM
What equations make up the speed of sound (m/s) equation?
EULER equation:
CONTINUITY equation:
IDEAL GAS LAW:
ADIABATIC PROCESS (Ideal gas)
What are the equations for speed of sound?
What does each component represent?
a = √yRmT OR a = √y(p/ρ) OR a = 39√T; y: ADIABATIC INDEX of AIR Cp/Cv = 1.4; Rm: GAS CONSTANT of AIR = 287J/kg.K; T: ABSOLUTE TEMPERATURE of AIR LOCALLY (Degrees Kelvin); p: PRESSURE of AIR LOCALLY; ρ: DENSITY of AIR LOCALLY
What function(s) affect the speed of sound?
ONLY TEMPERATURE, however, if there are CHANGES to the PRESSURE and DENSITY which RESULT in a CHANGE in TEMPERATURE then SPEED of SOUND will CHANGE
What is Mach number?
A DIMENSIONLESS QUANTITY that is a PROPERTY of AIR lthat is a FUNCTION of TEMPERATURE;
The RATIO of FLOW SPEED to the LOCAL SPEED of SOUND M = v/a
What values determine the category of speed of an air particle?
M < 1: SUBSONIC;
M = 1: SONIC;
M > 1: SUPERSONIC
What are the special Mach numbers?
FREE STREAM Mach number (Mfs): RATIO of TAS/FREE STREAM AIRSPEED of an AIRCRAFT to the FREE STREAM SPEED of SOUND Mfs = TAS/afs;
LOCAL Mach number (ML): RATIO of SPEED of AIRFLOW/PARTICLES at a LOCATION around the AIRCRAFT to the LOCAL SPEED of SOUND ML = v local/a local;
CRITICAL Mach number (Mcrit): FREE STREAM Mach number when a LOCAL Mach number reaches 1. Marks the FIRST LOCAL AIRFLOW SPEED to become SONIC
What makes a subsonic flight?
What are the characteristics of the air?
FREE STREAM Mach number is LESS THAN CRITICAL Mach number Mfs < Mcrit;
AIRFLOW is always SUBSONIC and can be TREATED as INCOMPRESSIBLE if TAS is LESS than 250kts (LOW SUBSONIC) otherwise it is COMPRESSIBLE
What makes a flight transonic?
What are the characteristics of the air?
The FREE STREAM Mach number is GREATER THAN the CRITICAL Mach number but LESS THAN 1.2 Mcrit < Mfs < 1.2;
AIRFLOW is SUBSONIC and SUPERSONIC even when Mfs < 1, AIR is DEFINITELY COMPRESSIBLE and SHOCKWAVES may FORM
What makes a flight supersonic and hypersonic?
What are the characteristics of the air?
FREE STREAM Mach number is GREATER THAN 1.2, Mfs > 1.2;
FREE STREAM Mach number is GREATER THAN 5, Mfs > 5;
AIRFLOW is SUPERSONIC apart from AIRFLOW BEHIND normal SHOCKWAVE and within BOUNDARY LAYER, HIGHLY COMPRESSIBLE and KINETIC HEATING is significant CONCERN
What is the mathematical principle behind the Mach meter?
(TOTAL PRESSURE - STATIC PRESSURE)/STATIC PRESSURE;
Compares RELATIONSHIP between DYNAMIC and STATIC PRESSURE
What is the simple operation of Mach meter?
STATIC PRESSURE in chamber;
PITOT PRESSURE is in IAS CAPSULE;
SET PRESSURE is in ALTITUDE CAPSULE;
CAPSULES EXPAND/CONTRACT which are geared to the MACH METER INDICATOR
What is Vmo?
Why is this important?
Vne;
Beyond this point LOCAL SHOCKWAVES may be CREATED, INDICATED by RED/WHITE POINTER on MACH METER
Does density and compressibility error affect Mach meter? Why?
No it OPERATES on the basis of the RATIO of DYNAMIC pressure to STATIC pressure and CHANGES to DENSITY and TEMPERATURE affect BOTH sides of EQUATION so it has NO DENSITY ISSUES. It is CALIBRATED for COMPRESSIBILITY ERROR to be COMPENSATED for
What errors is the Mach meter susceptible to?
INSTRUMENT ERROR;
BLOCKAGES in PITOT tube/STATIC pressure
LEAKS in ALTITUDE capsule or AIRSPEED capsule;
POSITION ERROR
