Aircraft Performance And Drag Sciences Essay

There are 4 basic forces that act on an aircraft in flight ; push, lift, weight and retarding force.

Of these forces the most complex is drag. A thorough apprehension of how drag affects the flight of an aeroplane is necessary if one is to exert complete control over their aircraft. Drag can be broken down into 2 different types, induced and parasitic. It affects both the lift and push of the aircraft, and determines best glide velocity every bit good as power required for an aeroplane. Drag in itself is non so hard to understand, but every bit is so frequently the instance, it is how drag interacts with the other forces that make it alone and complex.

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Aircraft Performance and Drag

There are four basic forces that act on an aeroplane in flight ; push, lift, weight, and retarding force. Of these forces, it is of import to take a deeper expression into what retarding force is and how it truly affects the aircraft. The entire retarding force moving on an aeroplane in flight can be divided into two specific types ; Induced retarding force and parasitic retarding force. Induced retarding force is produced by the wings and is merely a by-product of lift. Parasitic retarding force is caused by traveling an object through a fluid ( such as air ) . In order to to the full understand what is go oning during flight and through different angles of onslaught, we must to the full understand how retarding force is formed and the relationship between retarding force, power and airspeed.

Parasitic Drag

Parasitic retarding force is chiefly made up of signifier retarding force and skin clash, and is the easier of the two to understand. As the aircraft moves through the air, air atoms nearby absorb some of the energy from the aircraft through clash. So the one time comparatively still air atoms now are being accelerated as the aircraft passes. This transfers some of the aircrafts energy to the environing country.

This is merely friction and specifically, skin clash. Form retarding force is break of air atoms as a peculiar form base on ballss through them. Obviously an aerodynamic form will necessitate less energy to travel through a fluid ( air ) than something non so aerodynamic. An illustration could be a sleek new Lamborghini compared to an old school Volkswagen hippy new wave. The Lamborghini will be more efficient and require less energy to travel through the air.

In the existent universe, parasitic retarding force non merely comes from less aerodynamic aircraft designs, but chiefly from set downing cogwheel, flying prances, aerials, or fundamentally anything attached to the aircraft that disrupts the air flow over it. The expression for ciphering parasitic retarding force is:Parasitic Drag = CD * ? P V2 * S

    Cadmium = Coefficient of DragP = Air DensityV2 = Velocity squaredS = Frontal surface country

Since the coefficient of retarding force, air denseness, and frontal surface country can non be changed ( for a peculiar aircraft already manufactured ) , they are considered invariables and are non of import to us right now. The of import thing to notice is V2. It can hence be stated that Parasitic Drag is straight exponentially relative to the aircraft ‘s velocity. In other words, as the velocity of the aircraft additions, the parasitic retarding force of the aircraft additions. This is chiefly due to the sheer figure of air atoms that come in contact with the aircraft. The higher the airspeed, the more molecules the aircraft comes in contact with, therefore the more retarding force is imposed on the aircraft.

Induced Drag

Lift can be defined as the force that acts perpendicular to the comparative air current, and in the plane of symmetricalness.

Bernoulli ‘s rule fundamentally states that the force per unit area and speed of a fluid are reciprocally related. So as the speed of a fluid additions, the force per unit area decreases. This is true of an aerofoil. The speed of the fluid ( air ) flowing over the longer, curving form of the top of the aerofoil must increase.

Therefore the force per unit area over the top of the aerofoil must diminish. The consequence is a comparative low force per unit area country over the aerofoil or wing of an aircraft. This in bend produces a comparative high force per unit area country under the aerofoil. The high force per unit area country found beneath the wing is what we refer to as lift. As the aircraft velocity or speed is increased, the lift on the wing is besides increased ( See figure 1 ) .Induced retarding force can be defined as the force that acts parallel to the comparative air current, but in the opposite way of push. It is a by-product of lift, as stated earlier, and is slightly related to the angle of onslaught of an aerofoil. In its simplest signifier, one can believe of it as this ; at slower airspeeds, it is necessary to increase angle of onslaught to keep adequate lift to keep a changeless height.

As the aircraft additions in velocity the angle of onslaught is decreased due to the aerofoil bring forthing more lift, therefore cut downing induced retarding force.What is really go oning is the airflow in front of the wing undergoes what is called upwash. As a effect, the air that flows over the wings arrives at that place at a deflected angle, or is forced up. The air behind it is so forced downward. Since lift it created perpendicular to the comparative air current, the attendant lift now is somewhat deflected backward ( see figure 2 ) . This adds to the retarding force vector of the aircraft and is the induced retarding force. Factors that affect this induced retarding force are weight of the aircraft, design of the aerofoil, aspect ratio of the wing ( chord compared to the length ) and angle of onslaught.

Ultimately the finding factor is lift. The more lift the wings have to bring forth, the greater the force per unit area difference between the top and underside of the wing. The greater this force per unit area difference, the more induced retarding force will be present.

Populating with Drag

Now that we have a steadfast appreciation of what retarding force is we can discourse how it will impact the aircraft in flight, and what the pilot can anticipate ( see figure 3 ) . As you see in the Total Drag chart, parasitic retarding force additions with velocity of the aircraft and induced retarding force lessenings. The consequence is a entire retarding force curve that decreases as airspeed additions to a point, so increases as airspeed continues to increase. It is of import to understand this because the entire retarding force curve and the needed power are the same. If you think back to the definition of push, you will remember that it is the force required to travel the aircraft frontward through the air, or merely, the antonym of retarding force. If drag so is increased, push must besides increase to stay traveling in a forward way.

Then once more looking at the Total Drag chart, you will detect the power required to prolong flight at slower airspeeds is greater than the power required at faster airspeeds, to a certain point. This part of the graph is referred to as the back side of the power curve. It is necessary for pilots to be adept in the stage of flight because these airspeeds are typically the encountered during takeoff and landing. In the instance of instrument conditions, or a fouled track, the pilot may be force to put to death a lost attack or travel about. The pilot so has to acquire the aircraft to mount at low airspeeds, while avoiding an aerodynamic stall. This is non so difficult to carry through in itself, but add the emphasis of a long flight in instrument conditions, tonss of yak on the wireless, at a big airdrome, among a myriad of other possible distractions, and you begin to see the danger.

In Flight Emergencies

Suppose for a 2nd that you are winging about in a Cessna 172.

You are merely taking in the sights, seting along at 3000 pess. All of the sudden the engine quits… What do you make? Again mentioning back to the Total Drag chart you can see that someplace in the center of the curve is the minimal drag velocity. This is the velocity at which the sum retarding force exerted on the aeroplane is the least. There are two of import things to take away from this. First, this is the velocity that will give the greatest fuel economic system.

Second, this is the Best Glide velocity of the aeroplane. A Cessna 172 has a best glide velocity of 65 knots indicated airspeed ( KIAS ) . This airspeed will give you a glide ratio of approximately nine to one. That is for every 1000 pess of height ; you have about one and one half stat mis of forward distance. Notice, I did state forward.

Turning the aircraft causes more burden on the wing which requires more lift. And we know more lift peers more drag. So in the old illustration, you would hold about four and one half stat mis to either acquire the engine restarted, or acquire the aircraft safely on the land.


It goes without stating that it is of import for a pilot to cognize every facet of the aircraft he is winging. I would presume merely about every pupil at Embry Riddle could province the four forces that act upon an aircraft in flight. However, as I have discussed, something every bit simple as the force of retarding force could hold black effects if non to the full understood and respected.

Drag is both good and bad, but understanding retarding force is all good.


Skinner, Craig, The Wonderful World of Drag. Retrieved from hypertext transfer protocol: //