Chapter 2,4 and 5

The weight of an aircraft is determined during the design process, which can take years and resources.

For designing a fighter jet, consider an F-15 with a take-off gross weight of 44,500 lbs. For a mid-range airliner, consider Boeing 777 with a take-off gross weight of 545,000 lbs.

An estimate of the total weight involves dividing it into major weight groups: crew, payload, fuel, and empty weight.

Rearranging terms, the weight of fuel and empty weight can be expressed as fractions of the total weight.

To estimate empty weight fraction, use historical trends and adjust the statistical value for advanced composite material aircraft.

Fuel weight fraction cannot be estimated using historical trends, as an aircraft does not use all its fuel during the mission.

Fuel weight is dependent on the type of aircraft, engine, and mission requirements.

Mission profiles consist of several numbered segments, with vehicle weight changing at each segment.

Weight fraction at the end of the mission is calculated by multiplying weight fractions at each mission segment.

For calculating the weight fraction of a cruise segment, use the lift-to-drag ratio and specific fuel consumption.

Lift to drag ratio depends on the aircraft configuration and is influenced by wing span and wing reference area.

Wing efficiency is expressed using aspect ratio, which may affect the drag and lift of the wing.

Maximum lift-to-drag ratio varies with altitude and velocity.

For a jet aircraft, most efficient loiter speed is the speed for maximum lift-to-drag ratio, but most efficient cruise speed is the speed for 86.6% of maximum lift-to-drag ratio.

For a propeller aircraft, most efficient loiter speed and cruise speed have the same requirement of maximum lift-to-drag ratio.

Fuel fractions are estimated using historical trends and the simplified sizing method does not account for payload drops.

To calculate the take-off gross weight, an iterative process is used, starting with an initial guess, then calculating the fuel and empty weight fractions, and adjusting the initial guess accordingly.

The text outlines the process of designing an aircraft, specifically focusing on mission segment weight fractions, sizing, and engine considerations.

For climbing and accelerating, approximate weight fractions can be calculated using the given equation, where M is the ending Mach number and W1, W2, W3, and W4 are the weight fractions at different Mach numbers.

For cruise flight, the equation from lecture 2 is used to calculate weight fractions for jet aircraft and propellers.

During loiter, the equation is similar to that of climb conditions.

For specified-duration fuel burn segments (combat, aerobatics, etc.), the weight fractions are calculated based on time duration, thrust, and engine specific fuel consumption.

To size an aircraft, the design process begins with objectives and mission, followed by deciding on wing geometry and initial layout, and estimating thrust-to-weight ratio, wing loading, and using an engine specific fuel consumption to calculate mission segment weight fractions.

The takeoff gross weight is guessed, and the weight is calculated after each mission segment. The total fuel burned is added to the empty weight to calculate the new W0, and the process is iterated until convergence.

When the power supply is fixed, the designer must consider either range or performance as a dependent parameter.

If range is dependent, the performance capabilities can be calculated using the thrust-to-weight ratio and engine data.

If range is a design parameter, then performance must be dependent, and the fuel burned is calculated by specific fuel consumption times thrust times duration.

The fuselage length can be estimated based on the takeoff gross weight using a table.

The tail generates moments to overcome wing moments, and the effectiveness of the tail is related to the tail moment arm length times tail area, called tail volume coefficient.

Tail areas can be calculated using typical values for volume coefficients and their formulas, and tail arms can be estimated based on fuselage length.

The text mentions various tail designs and their effects on volume coefficients.

Primary control surfaces are ailerons for roll, elevators for pitch, and rudders for yaw.

Aileron area can be estimated based on wing span, wing mean chord, and the figure on the left, and ailerons extend from 50% to 90+% of span.

Other control surfaces such as flaps, spoilers, and elevators and rudders are also discussed, as well as their sizes and locations.

High-speed aircraft may experience a problem called aileron reversal, where the air loads on the aileron are so high that the wing itself is twisted, causing the aircraft to roll in the opposite direction.

To avoid aileron reversal, transport jets use additional inboard ailerons for high-speed control, and spoilers can also be used.

Elevators and rudders begin near the fuselage and extend to 90% of tail span, as shown in Table 6.