7.5 - drag, powerplants

7/29/2019 7.5 - Drag, Powerplants

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Basic Aerodynamics& Theory of Flight

ByAhmad Ahsan


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Winglets Reduce drag and improve aircraft performance Can be installed on various aircraft easily Can be installed after production. Do not need extensive technical

support Small change to aspect ratio and aircraft weight, means negligible effect

on aircraft handling


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Trailing Vortices & Downwash Trailing vortices are by-product of wing lift, their influence changes the air

flow pattern.

They alter the flow direction and speed in the vicinity of the wing and tail

surfaces.

The air behind the wing is drawn downwards, and this is called downwash.

Downwash also influences the approaching air, the flow over the wing, and

causes the air to be deflected downwards as it flows past the wing.

Due to downwash, the angle of attack relative to the local airstream is

reduced. This means that less lift will be generated at certain angles.

It also produces trailing vortex drag

Trailing vortices also produce a large upwash outboard of the wing tips. The

upward momentum change thus produced cancels out the downward

momentum change of the downwash.


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Drag The net aerodynamic force parallel to the relative wind, usually the sum

of two components: induced drag and parasite drag.

Drag is the force that resists movement of an aircraft through the air.

Drag is the aerodynamic force that opposes an aircraft's motion through

the air. Drag is generated by every part of the airplane (even the engines)

Drag is a mechanical force. It is generated by the interaction and contact of

a solid body with a fluid (liquid or gas).

Drag is a force and is therefore a vector quantity having both a magnitude

and a direction. Drag acts in a direction that is opposite to the motion of

the aircraft. Lift acts perpendicular to the motion. There are many factors

that affect the magnitude of the drag.


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Factors that Affect Drag Geometry has a large effect on the amount of drag generated by an object.

Drag depends linearly on the size of the object moving through the air.

The cross-sectional shape of an object determines the form drag created by

the pressure variation around the object.

The three dimensional planform shape affects the induced drag of a lifting

wing.

The amount of drag also depends on the surface roughness of the object; a

smooth, waxed surface produces less drag than a roughened surface. This

effect is called skin friction and is usually included in the measured drag

coefficient of the object.


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Factors that Affect Drag Drag is associated with the movement of the aircraft through the air, and

varies with the square of the velocity of the air.

If the object moves through the air at speeds near the speed of sound,

shock waves are formed on the object which create an additional drag

component called wave drag.

The motion of the object through the air also causes boundary layers to

form on the object. A boundary layer is a region of very low speed flow

near the surface which contributes to the skin friction.

Drag depends directly on the mass of the airflow going past the aircraft.

The drag also depends on viscosity and compressibility of air.

We can gather all of this information through the Drag Equation.


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Drag There are two basic types: parasite drag and induced drag.

The first is called parasite because it in no way functions to aid flight, while

the second, induced drag, is a result of an airfoil developing lift.

Parasite dragis comprised of all the forces that work to slow an aircrafts

movement. As the term parasite implies, it is the drag that is not associated

with the production of lift. This includes the displacement of the air by the

aircraft, turbulence generated in the airstream, or a hindrance of air

moving over the surface of the aircraft and airfoil. There are three types of

parasite drag: form drag, interference drag, and skin friction.


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Drag The second basic type of drag is induced drag. It is an established physical

fact that no system that does work in the mechanical sense can be 100

percent efficient. This means that whatever the nature of the system, the

required work is obtained at the expense of certain additional work that is

dissipated or lost in the system. The more efficient the system, the smaller

this loss.

In level flight the aerodynamic properties of a wing or rotor produce a

required lift, but this can be obtained only at the expense of a certain

penalty. The name given to this penalty is induced drag. Induced drag is

inherent whenever an airfoil is producing lift and, in fact, this type of drag is

inseparable from the production of lift. Consequently, it is always present if

lift is produced.


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Lowest drag, maxgliding dist. Decreasewith weight


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Boundary Layer Prandtl found that the effects of viscosity were only important and

apparent in a very thin layer adjacent to the surface.

He called this the boundary layer. For an aircraft wing in cruising flight, it is,

at most, only a few centimetres thick.

For the purposes of calculations, however, it is necessary to define this

area.


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Propulsion Systems Introduction

Importance and Function

Speed, Reliability, Economics

Compromises

Development to Current Stage

Types


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An air inlet on anaircraft.

On an modern full-sizedaircraft you can have:

1. Carburetor intake2. Cooling intake3. air conditioning intakeIntakes are not limited to

this a wind speedindicator intake is one

unlisted example.


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An engine nozzle isused to expand andaccelerate the gassesfrom combustion.

This is also used inrockets


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A special turbofanengine used primarilyfor lift in VTOL/STOLaircraft and often

mounted in a wing withvertical thrust axis.


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An enclosure on anaircraft.


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4 stroke cycle. Induction Compression

Power Exhaust


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Rotating blades fixedto a shaft.

Can be used for flightor propulsion through

the waterthink of aboat people.


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A propfan is a modifiedturbofan engine, withthe fan placed outsideof the engine nacelle.


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A jet engine without a compressor and has almost nomoving parts.

It can propel objects at 5 times the speed of sound.


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An engine that contains the reaction within itself

needing no external fuel.So this would work in space if you could bring a lot of

fuel with you.


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Definition

A scramjet is asupersonic ramjet.

It can go anywhere frommach 12 to 24.

It is a better ramjet but itdoes not work atsubsonic speeds like aramjetso is it stillbetter?


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Definition

Short takeoff andlanding ability.

This means it can takeoff and land with less

then 1000 feet ofspace.


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Definition

STOVL is short forshort take off andvertical landing.

Can take off within 1500

feet but needs norunway to land.


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Definition

A turbine engine works bycompressing air that moves intothe engine, enriching the air

with fuel, and igniting the air.This forces the air out of theback of the engine, propelling itforward.


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Definition

A turbofan engine is similarto a jet engine in the waythat it ignites fuel enriched

air, but a turbine is used tomove air into the engine


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Definition

A Turbojet engine works onthe same concept as most jetengines, but does not have a

fan, and during the injectionof the fuel, the air is alsocompressed, providinggreater thrust
http://upload.wikimedia.org/wikipedia/commons/e/e3/Turbojet_operation-_axial_flow.png


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Vectored thrust isthe ability to anglethrust in any

direction other thanparallel to theplanes flight path


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VTOL (Vertical TakeOff Landing) is aclassification of

fixed wing aircraftthat can take offand land verticallywithout the use of a

runway.


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http://www.aviation-terms.com/

http://www.britannica.com

http://www.answers.com/

http://dictionary.reference.com/

http://images.google.com/

http://science.howstuffworks.com/military-aircraft-

channel.htm

7.5 - drag, powerplants

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