Aircraft Design Final

Tendency of forces acting on an aerodynamic object to rotate it about an axis. Aerodynamic moment is mainly important for aircraft stability and control. DO NOT USE THE WORD "TORQUE" OR "MOMENT" IN YOUR ANSWER

Define aerodynamic moment

Center of pressure - location where all aerodynamic forces effectively act, centroid of all distributed aerodynamic load, changes with AOA Aerodynamic center - Point about which moments are independent of AOA

Define center of pressure and aerodynamic center

AR: ratio of wingspan to chord length -> b^2 / S Has an impact on the lift-induced drag K and the lift curve slope a_lift. "induced effects" due to lift is stronger with lower AR

Define wing aspect ratio, what is its impact on the aerodynamics?

Thrust is a net reaction force due to the force exerted by air on the propulsive device. Still caused by pressure and shear forces.

Describe engine thrust

Slat: high lift device at the leading edge of an airfoil Flap: high lift device at the trailing edge of an airfoil; increases the effective wing platform area

Describe the difference between a slat and a flap

Turbojet engine - There is no bypass section. Allows the pressure to escape out the back of the engine to produce thrust Turbofan engine - has a bypass air section that produces thrust and also cools the engine off. Uses pressure from expanding gas to turn a crankshaft which turns large fan blades to provide thrust

Describe the main difference between a turbojet and turbofan engine.

The fuel efficiency of an engine design with respect to thrust output. It does vary with operating conditions. TSFC increases with Mach #

Describe thrust specific fuel consumption. Does it vary with operating conditions? If so, how?

Delta wings cause primary and secondary vortices on their sharp wing edges. These vortices create a region of low pressure on the upper wing surface, therefore increasing the differential pressure between the upper surface of the wing and the lower surface of the wing which in turn provides more lift

Describe vortex lift in delta wings

First digit: max camber in % chord Second digit: location of max camber in tenths chord Last two digits: max thickness in % chord

Explain the 4-digit NACA airfoil nomenclature

The compressor slows down the flow rate to sustain a flame, increases pressure which helps combustion, and conditions the flow for efficient combustion

Explain the role of the compressor in a turbojet engine?

Propeller/reciprocating engine - low T, High E Turbojet - Higher T, Lower E Rocket - Substantial T, Poor E

Explain the thrust-efficiency trade-off in aircraft engines.

Fuel injector: spray nozzles that inject fuel into the primary zone Primary zone: has recirculation zones where the fuel and air mix to start combustion Intermediate zone: Air is injected here Dilution zone: reduce the temp of the combustion products to a temp that will not damage turbine blades

Explain the various zones in a jet engine combustor and their roles

Make the airfoil thinner and the surface smoother

How can you mitigate drag?

Plain flap split flap leading-edge slat single-slotted slat double-slotted flap triple-slotted flap - most used today

Name some types of high lift devices and the setup that is most commonly used today

Delta wings are triangular shaped wings that dramatically increase the sweep of an aircraft wing. Supersonic aircraft benefit from these wings.

What are delta wings? What kind of aircraft need it?

High lift devices - added mechanical components to a wing to temporarily increase CLmax during takeoff and landing without having to re-design the entire wing You need them for takeoff and landing to increase lift

What are high lift devices and why do you need them?

A turbo shaft is basically a turboprop but without a propeller for horizontal propulsion.

What are similarities and differences between a turboshaft and a turboprop?

AOA Re # viscosity

What are some independent fundamental parameters that affect aerodynamic quantities?

Max camber Max thickness chord length

What are the design parameters of an airfoil?

Pressure and skin friction. Pressure acts perpendicular to the surface, skin friction of shear stress acts parallel to the surface

What are the fundamental contributors to all aerodynamic forces? How do these contributors act on an airfoil?

Fan Guide vanes Compressor Combustion Chamber HPT LPT Nozzle

What are the stages of a turbofan engine

Compressor Diffuser Combustion Chamber Turbine Exhaust unit and jet pipe Propelling nozzle

What are the stages of a turbojet engine?

Cold stream reversers Actuator bucket doors

What are the types of thrust reversers?

Ailerons: turn the aircraft Flaps: increase effective AOA, used during takeoff and landing Elevators: pitch up and pitch down, mainly used in takeoff rotation

What do ailerons, flaps, and elevators do?

First of all, Mach # is a measure of compressibility. It decreases a_lift.

What effect does Mach # have on wing aerodynamics?

It is a thermodynamic cycle that describes the thermodynamic operation of a gas turbine engine it is useful because one can quickly estimate engine conditions at all stages and it can be used for sizing engine components.

What is the Brayton Cycle and why is it useful?

AOA density speed platform area Temperature - speed of sound - mach # viscosity

What parameters do aerodynamic forces and moments depend on?

Modifies flow on top surface and mitigates flow separation by delaying adverse pressure gradient; delays stall, increases stability, effectively increases CLmax

Why are slats good?

They delay flow separation, therefore increasing CLmax

Why are slots good in flaps?

Wing sweep in aircraft lowers the effective Mach # the wing experiences. This improves transonic aerodynamics because it decreases the magnitude of the flow speed acting perpendicular to the edge. Transonic and supersonic aircraft need this.

Why do we need sweep in aircraft wing configurations? What type of aircraft need it?

GET THIS ANSWERED

Why does the zero lift AOA not change with AR?

At lower Mach #'s, you have less compressibility loss in lift curve slope. You can also decrease the drag divergence Mach # and delay transonic flow

Why is it better for an aircraft wing to see a lower Mach #?

Efficiency can be improved by Noise increases as efficiency increases

Write an expression for engine propulsive efficiency. What are some means to improve efficiency? Are there unintended effects of improving propulsive efficiency? What are they?

max camber is 2% chord length max camber is at 0.4x chord length (or 40% chord) max thickness is 12% chord

Write out what NACA2412 means in words