Cruise (aeronautics): Difference between revisions
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With aircraft, other factors affecting optimum cruise altitude include payload, [[center of gravity]], air temperature, humidity, and speed. This altitude is usually where the higher [[ground speed]]s, the increase in [[aerodynamic drag]] power, and the decrease in engine thrust and efficiency at higher altitudes are balanced. |
With aircraft, other factors affecting optimum cruise altitude include payload, [[center of gravity]], air temperature, humidity, and speed. This altitude is usually where the higher [[ground speed]]s, the increase in [[aerodynamic drag]] power, and the decrease in engine thrust and efficiency at higher altitudes are balanced. |
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For jet aircraft, "long-range cruise" speed (LRC) is typically chosen to give 1% less [[fuel efficiency]] than maximum range speed (the speed which covers the greatest distance for a given amount of fuel), because this results in a 3-5% increase in speed. However, fuel is not the only marginal cost in airline operations, so the speed for most economical operation (ECON) is chosen based on the cost index (CI), which is the ratio of time cost to fuel cost.<ref name="Boeing pg2">{{cite web |title=AERO - Fuel Conservation Strategies: Cruise Flight 2|url=https://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_2.html |website=www.boeing.com |publisher=Boeing |access-date=28 January 2022}}</ref> Cost index can be given in "Boeing" or "English" units as {{math|($/hr)/(cents/lb)}}, equivalent to {{math|100 lb/hr}}.<ref name="Airbus">{{cite web |title=Getting to grips with cost index |url=https://ansperformance.eu/library/airbus-cost-index.pdf |publisher=Airbus |access-date=31 January 2022}}</ref><ref name="Openairlines">{{cite web |title=Top 10 facts or myths about Cost Index |url=https://blog.openairlines.com/top-10-facts-or-myths-about-cost-index |website=blog.openairlines.com |language=en-us}}</ref> A typical cost index in these units might be anywhere from 5 to 150.<ref name="Boeing pg3">{{cite web |title=AERO - Fuel Conservation Strategies: Cruise Flight 3 |url=https://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_3.html |website=www.boeing.com |publisher=Boeing |access-date=28 January 2022}}</ref> Alternatively cost index can be given in metric or "Airbus" units of {{Math|kg/min}}.<ref name="Airbus"/><ref name="Openairlines"/> In the presence of a tailwind, ECON speed will be reduced to take advantage of the tailwind, whereas in a headwind, ECON speed will be increased to avoid the penalty of the headwind. In a strong tailwind, the aircraft can fly at a low speed to conserve fuel, while the tailwind does most of the work getting the aircraft to its destination. In an area of strong headwind, the aircraft should fly faster to pass through that region sooner.<ref name="Boeing pg3"/> |
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The typical cruising airspeed for a long-distance commercial passenger aircraft is approximately {{cvt|880–926|km/h|kn mph|lk=on}}.{{cn|date=January 2022}} |
The typical cruising airspeed for a long-distance commercial passenger aircraft is approximately {{cvt|880–926|km/h|kn mph|lk=on}}.{{cn|date=January 2022}} |
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For propeller aircraft, maximum range speed is typically achieved when the [[lift-to-drag ratio]] is maximised. However, this is typically regarded as too slow, so propeller aircraft typically cruise at a significantly faster speed.<ref name="BoldMethod">{{cite web |title=Why You Rarely Fly At Best Range Speed In A Prop, But You're Close To It In A Jet |url=https://www.boldmethod.com/learn-to-fly/aerodynamics/best-range-speed-prop-vs-jet/ |website=www.boldmethod.com |access-date=31 January 2022}}</ref> |
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== See also == |
== See also == |
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Revision as of 11:19, 31 January 2022
Cruise is a flight phase that occurs when the aircraft levels after a climb to a set altitude and before it begins to descend. [1]
Cruising usually consumes the majority of a flight, and it may include changes in heading (direction of flight) at a constant airspeed and altitude.
For most passenger aircraft, the cruise phase consumes most of the aircraft's fuel. This lightens the aircraft and raises the optimum altitude for fuel economy. For traffic control reasons it is usually necessary for an aircraft to stay at the cleared flight level. On long-haul flights, the pilot may ask air traffic control to climb from one flight level to a higher one, in a maneuver known as step climb.
Cruise speed
Commercial or passenger aircraft are usually designed for optimum performance at their cruise speed (VC). Combustion engines have an optimum efficiency level for fuel consumption and power output.[2] Generally, gasoline piston engines are most efficient between idle speed and 30% short of full throttle. Diesels are most efficient at around 90% of full throttle.[3][better source needed]
With aircraft, other factors affecting optimum cruise altitude include payload, center of gravity, air temperature, humidity, and speed. This altitude is usually where the higher ground speeds, the increase in aerodynamic drag power, and the decrease in engine thrust and efficiency at higher altitudes are balanced.
For jet aircraft, "long-range cruise" speed (LRC) is typically chosen to give 1% less fuel efficiency than maximum range speed (the speed which covers the greatest distance for a given amount of fuel), because this results in a 3-5% increase in speed. However, fuel is not the only marginal cost in airline operations, so the speed for most economical operation (ECON) is chosen based on the cost index (CI), which is the ratio of time cost to fuel cost.[4] Cost index can be given in "Boeing" or "English" units as ($/hr)/(cents/lb), equivalent to 100 lb/hr.[5][6] A typical cost index in these units might be anywhere from 5 to 150.[7] Alternatively cost index can be given in metric or "Airbus" units of kg/min.[5][6] In the presence of a tailwind, ECON speed will be reduced to take advantage of the tailwind, whereas in a headwind, ECON speed will be increased to avoid the penalty of the headwind. In a strong tailwind, the aircraft can fly at a low speed to conserve fuel, while the tailwind does most of the work getting the aircraft to its destination. In an area of strong headwind, the aircraft should fly faster to pass through that region sooner.[7]
The typical cruising airspeed for a long-distance commercial passenger aircraft is approximately 880–926 km/h (475–500 kn; 547–575 mph).[citation needed]
For propeller aircraft, maximum range speed is typically achieved when the lift-to-drag ratio is maximised. However, this is typically regarded as too slow, so propeller aircraft typically cruise at a significantly faster speed.[8]
See also
References
- ^ "Glossary". CAST/ICAO Common Taxonomy Team. Retrieved 2016-06-19.
- ^ Cruising speed definition
- ^ Thiel, Richard. "How to Find the Best Cruising Speed for Your Boat". Power & Motoryacht. Retrieved 29 January 2022.
- ^ "AERO - Fuel Conservation Strategies: Cruise Flight 2". www.boeing.com. Boeing. Retrieved 28 January 2022.
- ^ a b "Getting to grips with cost index" (PDF). Airbus. Retrieved 31 January 2022.
- ^ a b "Top 10 facts or myths about Cost Index". blog.openairlines.com.
- ^ a b "AERO - Fuel Conservation Strategies: Cruise Flight 3". www.boeing.com. Boeing. Retrieved 28 January 2022.
- ^ "Why You Rarely Fly At Best Range Speed In A Prop, But You're Close To It In A Jet". www.boldmethod.com. Retrieved 31 January 2022.
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