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# System prepended metadata

title: Terminology

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# Terminology
**Maximum takeoff weight (lb):** The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is gross lift-off mass, or GLOW. MTOW is usually specified in units of kilograms or pounds. MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it. MTOW of an aircraft is fixed and does not vary with altitude, air temperature, or the length of the runway to be used for takeoff or landing.

**Wing reference area (ft):** The reference wing area is defined as the plan area of an aircraft's wing.
![](https://i.imgur.com/nnHMonk.png)

**Wing aspect ratio:** Aspect ratio is the ratio of the span of the wing to its chord.
![](https://i.imgur.com!/XoFaO6b.png)

 
**Wing taper ratio:** The tapering ratio (taper ratio, commonly used symbol λ), indicates the ratio of the length of the wing tip (wing tip, ct) to the wing root (wing root, cr) of the aircraft wing (λ≡ct/cr). 
![](https://i.imgur.com/A5xwIEv.png)


**Wing span (ft):** The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip.

**Wing leading edge sweep (deg):** Leading edge sweep (Leading edge sweep) refers to the wing whose leading edge is swept backward. The index that characterizes the degree of wing sweep is the sweep angle, which is the angle between the leading edge of the wing and the horizontal line.
![](https://i.imgur.com/UU5rYox.png)

**Wing tip/root thickness-to-chord ratio:** In aeronautics, the thickness-to-chord ratio, sometimes simply chord ratio or thickness ratio, compares the maximum vertical thickness of a wing to its chord. It is a key measure of the performance of a wing planform when it is operating at transonic speeds. The section positions of tip and root are different
 
 ![](https://i.imgur.com/uW4tANe.png)
a=chord, b=thickness, thickness-to-chord ratio = b/a

**Wing location along fuselage:** The wing may be mounted at various positions relative to the fuselage.
- Low wing: mounted near or below the bottom of the fuselage.
- Mid wing: mounted approximately halfway up the fuselage.
- Shoulder wing: mounted on the upper part or "shoulder" of the fuselage, slightly below the top of the fuselage. A shoulder wing is sometimes considered a subtype of high wing.
- High wing: mounted on the upper fuselage. When contrasted to the shoulder wing, applies to a wing mounted on a projection (such as the cabin roof) above the top of the main fuselage.
- Parasol wing: raised clear above the top of the fuselage, typically by cabane struts, pylon(s) or pedestal(s).

![](https://i.imgur.com/USFCaK7.png)

**Horizontal tail area (ft):**
root chord             = "Cr"
tip chord              = "Ct"
mean aerodynamic chord = "MAC"
horizontal tail span   = "b"
Tail area              = "SHT"
SHT                    = (Ct+Cr) *0.5*(b/2) *2
 
![](https://i.imgur.com/FRH52Ju.png)
 
**Horizontal tail leading edge sweep (deg):** The definition can be known from the leading edge sweep angle.

**Horizontal tail thickness-to-chord ratio:** Comparison of the maximum vertical thickness of a wing to its chord.

**Vertical tail area (ft):** The vertical tail area is the area of the surface of the vertical tail, including the submerged area to the fuselage centerline.
 
 ![](https://i.imgur.com/kFiGFyU.png)

**Engine takeoff thrust (lb):** Engines can give out a constant amount of thrust up to a particular temperature. This thrust, called TOGA (Takeoff Go Around) thrust, is the maximum thrust the engines can generate without breaking something.

**Engine bypass ratio:** The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core.

![](https://i.imgur.com/O2BMdK3.png)

**Engine fan pressure ratio:** The engine pressure ratio (EPR) is the total pressure ratio across a jet engine, measured as the ratio of the total pressure at the exit of the propelling nozzle divided by the total pressure at the entry to the compressor.

![](https://i.imgur.com/AhVeTfU.png)

**Engine LPC/HPC pressure ratio:**
- LPC: Low pressure compressor, 
- HPC: High pressure compressor, 
- LPT: Low pressure turbine, 
- HPT: High pressure turbine, 
- N1: Turbine axis and 
- N2: Turbine shaft

**Engine turbine inlet temperature (R):** Turbine Inlet Temperature (TIT) is the temperature of the combustion chamber exhaust gases as they enter the turbine unit. The gas temperature is measured by a number of thermocouples mounted in the exhaust stream and is presented on a flight deck gauge in either degrees Fahrenheit or degrees Celcius.
Cruise Mach number: Mach number (M or Ma)  is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound.
 
![](https://i.imgur.com/DmdpzV2.png)
![](https://i.imgur.com/VJZkjVh.png)
![](https://i.imgur.com/6AlYXMu.png)



**Initial cruise altitude (ft):**
This definition is the condition of the aircraft at the top of climb. By the time the aircraft arrives at this point it has lost about 2-3% of its take-off weight because of the fuel used. Initial cruise altitude capability is defined as the ability to sustain a certain rate of climb at this altitude, at typical cruise speed and with the engines operating at maximum climb rating. A 300ft/min rate of climb is the usual requirement although airlines may specify other levels (e.g. 500ft/min). In this calculation we will assume a 300ft/min requirement. The initial cruise altitude is set at a minimum of 2000 ft above the optimum cruise altitude. This margin is required because in the current air traffic control environment it is not possible to follow the optimum cruise altitude schedule (i.e. approximately a constant CL technique). Such a procedure would lead to a gradual increase in altitude as fuel is burnt and the aircraft becomes lighter. Air traffic control requires aircraft travelling in the same direction to fly at discrete flight levels separated by 4000 ft in altitude. This means that a minimum of 2000 ft margin above the optimum is required to enable the aircraft to fly a stepped cruise technique.

**Final cruise altitude (ft):** I think final cruise altitude is equal to optimum cruise altitude.

**The optimum cruise altitude** is that at which a given thrust setting results in the corresponding maximum range speed. The optimum altitude is not constant and changes over the period of a long flight as atmospheric conditions and the weight of the aircraft change. A large change in temperature will significantly alter the optimum altitude with a decrease in temperature corresponding to an increase in altitude. At the optimum altitude, operating costs will be minimum when operating in the most economical (ECON) mode; it is also the cruise altitude for minimum fuel burn when in the Long Range Cruise (LRC) mode. In both cases, optimum altitude increases with reducing aircraft weight. If the aircraft is at its maximum certified level or the altitude is operationally capped, speed reduction as weight decreases will help to maintain a minimum fuel burn profile.

**Top Level Aircraft Requirements(TLAR)**
Aircraft design is a complex large-scale system engineering involving multi-disciplinary and multi-technical fields. Aircraft design work is generally divided into three stages: conceptual design, preliminary design, and detailed design. The first two stages are also called overall design. The top-level/detailed design technology of aircraft is an important content of the comprehensive technology adopted by modern countries to develop advanced aerospace vehicle systems, and it is also the development trend of future aircraft design and research. The top level is a higher level than the conceptual design, which is to study the aerospace vehicle system to be designed from the perspective of a higher level and a large system in the initial stage of the design, aiming at the situation that the amount of information in the early stage of the design is less. Top-level design is the initial planning phase of the design of complex systems such as aerospace vehicle systems. It uses the principles and methods of systems engineering to conceive system solutions and determine system technical requirements under given mission objectives and constraints, and meet schedule requirements at an affordable cost. In general, the top-level design of aircraft is to consider and study relevant issues from the perspective of top-level and large-scale system, starting from user requirements/needs, in the case of less information in the early stage of design, and to evaluate the feasibility of aircraft design in the early stage of design. The key content in the research and design is studied and weighed, and the **top-level design is the initial stage beyond the conceptual design stage.
![](https://i.imgur.com/oYGxl4C.png)

**Thrust-to-weight ratio**
Thrust-to-weight ratio is a dimensionless ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine that is an indicator of the performance of the engine or vehicle. The instantaneous thrust-to-weight ratio of a vehicle varies continually during operation due to progressive consumption of fuel or propellant and in some cases a gravity gradient. The thrust-to-weight ratio based on initial thrust and weight is often published and used as a figure of merit for quantitative comparison of a vehicle's initial performance.**The thrust-to-weight ratio is calculated by dividing the thrust (in SI units – in newtons) by the weight (in newtons) of the engine or vehicle.**

**Take-off-weight-to wing area ratio**
Wing loading is a measurement that relates the mass of an aircraft or bird to the total wing area. The relationship between wing area and body weight is given in kilograms per square metre (or grams per square centimetre). To calculate wing loading, divide the mass of the bird or plane by the total area of the upper surface of its wings: wing loading = body mass (kg)/wing area (m2).

**Swet and Sref**
![](https://i.imgur.com/WPCMTFs.png)
![](https://i.imgur.com/RnVsdnI.png)

**Pitch Yaw Roll**
![](https://i.imgur.com/WdSIp2T.png)

