{"id":14470,"date":"2025-06-07T16:16:24","date_gmt":"2025-06-07T10:46:24","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14470"},"modified":"2025-06-09T19:27:38","modified_gmt":"2025-06-09T13:57:38","slug":"machmeter","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/machmeter\/","title":{"rendered":"Machmeter"},"content":{"rendered":"\n<h2>Machmeter<\/h2>\n\n\n\n<h3>Local Speed of Sound<\/h3>\n\n\n\n<ul><li>Speed of sound is not constant but varies with temperature<\/li><li>Sound travels slower in colder air and faster in warm air<\/li><li>Speed of sound decreases with increase in altitude<\/li><li>Local speed of sound (LSS) at sea level, in ISA (+ 15 deg C) is 661 knots<\/li><li>Local speed of sound (LSS) at 30,000 ft, in ISA (-45 deg C) is 589 knots<\/li><\/ul>\n\n\n\n<h3>Calculation of Local Speed of Sound<\/h3>\n\n\n\n<ul><li>Formula for Local speed of sound in knots =<\/li><li>38.95 x Square root of Absolute Temperature In Kelvin<\/li><\/ul>\n\n\n\n<h3>Definition of Mach Number<\/h3>\n\n\n\n<ul><li>Mach Number = True Air Speed \/ Local Speed of Sound<\/li><li>Mach number is the ratio between the speed of aircraft to local speed of sound (or) ratio between the dynamic and static Pressures<\/li><li>0.85 mach means speed of aircraft is 85% of the local speed of sound<\/li><\/ul>\n\n\n\n<h3>Importance of Mach Number<\/h3>\n\n\n\n<ul><li>Shock waves are formed when aircraft reaches local speed of sound<\/li><li>These shock waves would present difficulties in handling<\/li><li>Lift decreases<\/li><li>Drag increases<\/li><li>Pitch changes<\/li><li>Cause buffeting<\/li><li>Loss of controls<\/li><\/ul>\n\n\n\n<h3>Construction of Machmeter<\/h3>\n\n\n\n<ul><li>Machmeter displays the True Air Speed of the aircraft as mach number by determining ratio between dynamic &amp; static pressure<\/li><li>Machmeter has two capsules<\/li><li>Dynamic pressure airspeed capsule<\/li><li>Static fed in altitude capsule<\/li><li>Ratio of static and dynamic is compared<\/li><li>Moves ratio arm and in turn ranging arm which moves pointer<\/li><\/ul>\n\n\n\n<h3>Instrument and Position errors<\/h3>\n\n\n\n<ul><li>Instrument errors are unavoidable due manufacturing imperfections<\/li><li>High error at high altitudes due to smaller pressure changes<\/li><li>Position or Pressure error is caused due to turbulence creating suction around static source<\/li><li>Error is reduced with static vents<\/li><li>Advanced pitot tube on high speed aircraft reduce error<\/li><\/ul>\n\n\n\n<h3>Manoeuvre Induced errors<\/h3>\n\n\n\n<ul><li>Manoeuvre induced error causes short term fluctuations due to changes in pitch or yaw<\/li><\/ul>\n\n\n\n<h3>Density and Temperature Errors<\/h3>\n\n\n\n<ul><li>Machmeter presents the speed as a ratio<\/li><li>Hence, it does not suffer from density and temperature errors<\/li><li>Variation affect both static and dynamic pressures<\/li><li>Cancel out each other<\/li><\/ul>\n\n\n\n<h3>Compressibility Errors<\/h3>\n\n\n\n<ul><li>Machmeter calculates the ratio between the speed of aircraft and that of sound<\/li><li>Therefore, it does not suffer from compressibility errors<\/li><li>Compressibility is a ratio of dynamic and static pressures<\/li><li>Machmeter is designed to read this ratio<\/li><\/ul>\n\n\n\n<h3>Blockage in Pitot Line<\/h3>\n\n\n\n<ul><li>Blockage in pitot line blocks input pitot pressure<\/li><li>Machmeter will not register any change of speed<\/li><li>Indication remains constant in level flight<\/li><li>In a constant speed climb or descent, the mach meter would<\/li><li>Under read in descent due to decrease in static component in pitot capsule (numerator)<\/li><li>Over read in climb due to increase in static component in pitot capsule (numerator)<\/li><\/ul>\n\n\n\n<h3>Blockage in Static Vent<\/h3>\n\n\n\n<ul><li>Blockage in static system makes the static (denominator) to remain constant<\/li><li>Mach number will be correct in level flight<\/li><li>Blockage in static system makes the static (denominator) to remain constant<\/li><li>Over read during constant speed descent due to incorrect low static (denominator)<\/li><li>Under read during constant speed climb due to incorrect high static (denominator)<\/li><\/ul>\n\n\n\n<h3>Leaks in Static Line outside Pressurised Cabin<\/h3>\n\n\n\n<ul><li>Leak in pitot line would reduce the pitot pressure (numerator) sensed by the system makes the machmeter to under read<\/li><li>Leak (outside pressurised hull) in static line will cause no error in the machmeter since the static will be sensed correctly<\/li><\/ul>\n\n\n\n<h3>Leaks in Static Line inside Pressurised Cabin<\/h3>\n\n\n\n<ul><li>Leak (inside pressurised hull) in static line will cause the cabin pressure to be detected as static pressure (denominator)<\/li><li>Cabin pressure is expected to be higher than actual static pressure<\/li><li>Under reads in climb<\/li><li>Over read in descent<\/li><\/ul>\n\n\n\n<h3>Constant CAS Climb in Standard Conditions<\/h3>\n\n\n\n<ul><li>Constant CAS climb increases TAS at higher altitude<\/li><li>Reduced density at higher altitude<\/li><li>Density affected by atmospheric pressure<\/li><\/ul>\n\n\n\n<h3>Constant TAS Climb in Standard Conditions<\/h3>\n\n\n\n<ul><li>Constant TAS climb increases Mach number at higher altitude<\/li><li>LSS reduces with altitude<\/li><li>Speed of sound is lower in cold air (altitude)<\/li><\/ul>\n\n\n\n<h3>Climb Planning for High performance Aircrafts<\/h3>\n\n\n\n<ul><li>High performance aircrafts would climb at<\/li><li>Constant CAS at lower level<\/li><li>Constant Mach number at higher levels<\/li><\/ul>\n\n\n\n<h3>Descent in Standard Conditions<\/h3>\n\n\n\n<ul><li>Constant mach number descent increases TAS at lower altitude<\/li><li>TAS will have to increase to match with increase in LSS<\/li><li>CAS will increase due to higher density at lower levels<\/li><\/ul>\n\n\n\n<h3>Descent Plan for High Performance Aircrafts<\/h3>\n\n\n\n<ul><li>High performance aircrafts would descend at<\/li><li>Constant mach number at higher levels<\/li><li>Constant CAS at lower level<\/li><li>In ISA conditions CAS &lt; TAS &lt; Mach Number<\/li><\/ul>\n\n\n\n<h3>Mach Number and TAS in Isothermal Layer<\/h3>\n\n\n\n<ul><li>Mach Number remains constant with height<\/li><li>Temperature remains constant with height<\/li><li>Ratio of TAS &amp; LSS would remain constant<\/li><\/ul>\n\n\n\n<h3>Constant TAS Climb and Descent in an Isothermal Layer<\/h3>\n\n\n\n<ul><li>At a constant TAS<\/li><li>CAS will reduce during climb due to reducing density<\/li><li>CAS would increase during descent due to increasing density<\/li><\/ul>\n\n\n\n<h3>Constant CAS Climb and Descent in an Isothermal Layer<\/h3>\n\n\n\n<ul><li>At a constant CAS<\/li><li>TAS will increase during climb due to reducing density<\/li><li>TAS would reduce during descent due to increasing density<\/li><\/ul>\n\n\n\n<h3>Local Speed of Sound in an Inversion Layer<\/h3>\n\n\n\n<ul><li>Local speed of Sound increases with height due to higher temperature<\/li><li>Constant TAS climb decrease Mach number at higher altitude<\/li><li>Constant TAS descent increase Mach number at higher altitude<\/li><\/ul>\n\n\n\n<h3>Constant CAS Climb in Inversion Layer<\/h3>\n\n\n\n<ul><li>Constant CAS climb increases TAS at higher altitude<\/li><li>Reduced density at higher altitude<\/li><li>Density affected more by atmospheric pressure<\/li><\/ul>\n\n\n\n<h3>Summary of CAS and TAS<\/h3>\n\n\n\n<ul><li>Relation between CAS and TAS<\/li><li>During a constant CAS climb, TAS will always increase<\/li><li>During a constant TAS climb, CAS will always reduce<\/li><li>Pressure has a greater effect on air density than temperature.<\/li><\/ul>\n\n\n\n<h3>Summary of CAS, TAS and Mach Number<\/h3>\n\n\n\n<ul><li>Pressure has a greater effect on air density than temperature.<\/li><li>Relation between CAS and Mach Number<\/li><li>During a constant Mach No climb, CAS will always reduce<\/li><li>During a constant CAS climb, Mach No will always increase<\/li><\/ul>\n\n\n\n<h3>Mach \u00e2\u20ac\u201c Air Speed Indicator<\/h3>\n\n\n\n<ul><li>Combines functions of Mach meter and Air Speed Indicator<\/li><li>Analogue instrument indicates Air speed on fixed scale and Mach number on a movable scale<\/li><li>Digital readout Instrument displays Mach No and Air speed from an Air Data Computer<\/li><\/ul>\n\n\n\n<h3>Use of Mach \u00e2\u20ac\u201c Air Speed Indicator<\/h3>\n\n\n\n<ul><li>Provides Calibrated (Rectified) Airspeed instead of Indicated Air Speed<\/li><li>Speed limiter pointer is a manually controlled needle for speed limits<\/li><li>Maximum operating Mach number M no<\/li><li>Maximum operating speed V no<\/li><\/ul>\n\n\n\n<h3>Errors of Mach \u00e2\u20ac\u201c Airspeed Indicator<\/h3>\n\n\n\n<ul><li>Errors of both Air Speed Indicator and Mach Meter<\/li><li>Instrument errors<\/li><li>Position (pressure)<\/li><li>Manoeuvre induced<\/li><li>Density<\/li><li>Temperature<\/li><li>Compressibility<\/li><\/ul>\n\n\n\n<h2>Share this Page<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>Machmeter Local Speed of Sound Speed of sound is not constant but varies with temperature Sound travels slower in colder air and faster in warm air Speed of sound decreases with increase in altitude Local speed of sound (LSS) at sea level, in ISA (+ 15 deg C) is 661 knots Local speed of sound (LSS) at 30,000 ft, in ISA (-45 deg C) is 589 knots Calculation of Local Speed of Sound Formula for Local speed of sound in knots = 38.95 x Square root of Absolute Temperature In&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false},"categories":[345],"tags":[],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14470"}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14470"}],"version-history":[{"count":0,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14470\/revisions"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14470"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14470"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14470"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}