Desgin Structural 1

8/12/2019 Desgin Structural 1

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Universidad Politcnica Metropolitana

de HidalgoCarrera:

Ingeniera en AeronuticaEstudiante:

Fernando Antonio Herrera Hernndez

Materia:

Structural Design

Trabajo:

Questionary #1Profesor:

Ing. Celedonio Posadas

8 Cuatrimestre Grupo: nico Fecha de Entrega:01/02/2014


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1. - Define and explain the following terms:

A) LOAD FACTOR

Forces acting on an aircraft during a level coordinated turn, like is shown in the next figure

Figure 1

The load factor is a very important structural design parameter of an aircraft, as it

indicates the amount of the load which the structure of an aircraft can bear. For this

reason, the maximum load factor is a maneuvering and performance limit.

The limit of it, is the highest load factor to be expected over the lifetime of the

aircraft. The load factor is not dependent to aircraft weight and size. Whatever the type of

aircraft is, same load factors apply for same bank angles.

The load factor limitations of aircraft are defined by airworthiness regulations such

as, FAR23 for small aircraft, and FAR25 for large aircraft. Load factor limitations of an

aircraft are shown by a graphics called maneuvering envelope or Vn diagram as it shows

the load factor versus airspeed in terms of EAS, An aircraft cannot fly out of the load

factor boundaries given by the maneuvering envelope.


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The FAR25 specifies the limiting load factors of transport category aircraft.

During a steady, coordinated turn the lift required to balance the airplane weight in orderto keep the altitude constant.

L cos = W

Where is the bank angle. Therefore, the ratio of the lift to weight is

+ 1cos (1)Since the lift is greater than the weight in a banked turn because cos < 1, the ratio of liftto weight is the normal load factor

= . . . c o s = 1 (2)Table shows load factor for various types of aircraft:

Table 1


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In the follow figures, is shown Firstable the equations (Figure 3), about the load factor I

terms of weight, and the second the wing load cases (Figure 4) that it may have.

Figure 3 Figure 4


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B) V-n DIAGRAM (FLIGHT ENVELOPE)

In this figures, it shown the V-n Diagram.

A V-n diagram shows the flight load factors that are used for the structural design

as a function of the air speed. These represent the maximum expected loads that the

aircraft will experience. These load factors are called as limit load factors.

The combined V-n diagram is plotted in three steps: 1. Basic V-n diagram, 2. Gust

V-n diagram, 3.Combined V-n diagram. Like in this diagram.

The limit of "A" corresponds to the horizontal line "AD." Point D occurs at higher flight

speed, which is the speed dive. VC point represents cruise. Cruise In, n = 1, shown as the

dotted horizontal line. The intersection that align with the curve "OA" corresponds to the stall

speed, VS, which is the minimum rate at which aircraft can maintain level flight.


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Line HF represents negative loading factor greater for the aircraft, which are

generally less than the maximum load factor positive. The point F corresponds to the

intersection of the load limit and the maximum negative design cruise speed, VC. The

above negative load factor n = 0 point is then closed by the line at the point F in which thediving speed, VD.

C) GUST DIAGRAM

The loads associated with vertical gusts must also be evaluated over the range of

speeds.

The FAR's describe the calculation of these loads in some detail. Because some of the

speeds (VB) are determined by the gust loads, the process may be iterative.

Figure 8


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The gust load may be computed from the expression given in FAR Part 25. This

formula is the result of considering a vertical gust of specified speed and computing the

resulting change in lift. The associated incremental load factor is then multiplied by a load

alleviation factor that accounts primarily for the aircraft dynamics in a gust.

The atmosphere is a dynamic system that encompasses variety of phenomena. In

this point, we concentrate on only gust, since it is not predictable, but is happening during

most high altitude flights. When an aircraft experiences a gust, the immediate effect is an

increase or decrease in the angle of attack. Figure C.2 shows the geometry of an upward

gust. When an upward gust with a velocity of Vg, hits under the nose of an aircraft with the

velocity of V, the instantaneous change (increase) in the angle of attack (), is

determined through.

There are an equation for modeling the "gust induced load factor" as a function of gust

speed:

Where kgis a coefficient that is determined by the following expression:

And gis called the aircraft mass ratio and is calculated through:


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There are an intersections between these three lines respectively with maneuver

speed (VA), cruising speed (VC), and dive speed (VD) must be marked. The gust V-n

diagram is plotted for several altitudes to determine the highest load factor. This diagram

is finally combined; in a special technique; with the basic V-n diagram, to obtain the finalapplicable V-n diagram, like in the Figure C3.


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2. - Describe 3 situations where the airplane will perform symmetric maneuver

and 3 others situations where each will perform an asymmetric maneuver.

a) Symmetric maneuver.

Is symmetric when a maneuver is performed on the main longitudinal axis (roll,pitch or yaw).

1) Loop

2) Yaw

3) Take off


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B)Asymmetric maneuver.

Is asymmetric when there are more than two movements in the principal axes the

entry into loss, the auger.

1)

2)

3)


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3- Explain applicability of FAR-23 and FAR-25 define the design velocities and

the limit load factors for the different airplane categories contain in FAR-23

and FAR-25 for symmetric maneuvers and gust conditions.

The FAR 23:

Contains the airworthiness standards for aircraft, utility, acrobatic among

others, the airplane must be safely controllable and maneuverable under all

phases of flight such as takeoff, descent climb and level flight. It must be possible

to make a gradual transition from one flight regime to another (including turns and

slips) without danger of exceeding the limit load factor.

The FAR 25:

Except where limited by maximum (static) lift coefficients, the airplane is

assumed to be subjected to symmetrical maneuvers resulting in the limit

maneuvering load factor prescribed this section. Pitching velocities appropriate to

the corresponding pull-up and stead turn maneuvers must be taken into account.

4. - Derive the equations for the load factor experience by an airplane while

performing the following maneuvers:

a. Turn

The load factor is the ratio between the total load supported by the wings and the

gross weight of the aircraft with its contents:

(Load Factor = Load supported / Gross weight of the aircraft).

As the weight is due to the force of gravity, the load factor is usually expressed in terms of

relation to it: in "g". So a load factor of 3 "manage" means that the load on the airframe is

3 times your current weight.

This factor can be positive or negative. Is positive (positive g) when the force is down, and


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is negative (negative g) when it is up, in the positive g increases the rider's weight being

"stuck" to the seat, while negative g weight decreases and the pilot "floats" on the seat.

The load factor is important for two reasons: On the structural load imposed on the wings,you might get to break them, and because the rate of loss increases in proportion to the

load factor.

During the flight, the wings of the airplane must bear the full weight of this, to the

extent that it moves at a constant speed and in straight flight, the load imposed on the

wings is constant and a velocity change in this situation does not occur appreciable

change in the load factor.

Therefore any change of aircraft trajectory implies a greater or lesser extent a

centrifugal force that increases the load factor. Any force applied to an aircraft (Like in the

next picture) to take him out of his path produce stress on its structure, the total of which

is the load factor.


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The load factor in turns. In any aircraft, at any rate, if stays a constant altitude during a

coordinated turn, the load factor for a given pitch is the same, like in the following diagram.

Categories. All airplanes are designed fulfilling some requirements of effort,

depending on the intended use to do the same. The classification according to theserequirements are called categories. To get certified by the competent authorities, the

structural stress (load factor) must conform to the prescribed standards. The categories and

the maximum load factor for each are as follows (according to the FAA):

Normal: 3.8 G.

Utility: 4.4 G

Acrobatic 6 G.

b. Dive Recovery (Dicovering)

The load factor in the recovery is up to approximately 4 Gs and Gs in 3 ascent (Figure

1.8.9). The plane will end in same way, but inevitably to a lower height. This maneuver is

especially difficult orientation and energy inefficient to be the initial point of reference

hidden at the beginning and middle of the maneuver.


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c. Circular ascend and descend

ASCEND:

The rise is a basic maneuver during which a suitable combination of

power and attitude makes the plane gain altitude. It means two keys, power

and speed. The power is needed to overcome the drag of the aircraft. The

amount of resistance is dependent on the beat rate of a graphic form whose

expression is shown in Figure 5.5.1.

This figure shows the evolution of resistance with speed through the curve of powerneeded to counter it. In another power available curve shown, which owes its form to the

gradual loss of efficiency of the propulsion system. The intersection of the two curves

indicates the maximum speed, one in which all the power consumed in overcoming

resistance not being available quantity for promotion.

From the above figure we can get:

To maintain a given speed requires sufficient power to overcome resistance.

Fly with a higher or lower strength to lower the speed requires more power.

For any given speed, climb requires more power to maintain level flight.

If more power is applied, the excess of overcoming resistance causes the air to rise.


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This graph shows that for a constant power

you can get the same rate of climb at low speed

(v) or with a much higher speed (v ').

In an extreme case of low (z) or high speed

(z '), all the power is consumed in overcoming

resistance precluding the rise of the aircraft.

In summary, the keys to promotion are:

Ascender requires more power than level flight.

Increase power by keeping the angle of attack (speed) makes the plane climb.

With the same power, for all possible speeds the best rate of climb is obtained with specific.

This corresponds to an angle of attack.

The best rate of climb is not obtained with a higher angle of attack (attitude steep climb) but

with the right mix of power and speed.

DESCEND:

Falling should adjust both pitch attitude, as power. Declines assisted engine

performed when precise control of the rate of decline and the distance traveled during the

same is necessary.

The decrease in plan requires greater control of the flight path, then provide power to

the engine not only has the attitude to control the airplane and do not provide many variations

on the rate of descent speed or distance traveled. Basically we define the descent as a basicmaneuver in which the airplane loses altitude flying in a controlled manner in a downward

(forward and down) path, with or without power applied.


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Drop the keys are:

Descend requires less power to fly level.

Reduce power maintaining speed (angle of attack) causes the plane descends.

With the same power, all the best speeds possible rate decrease (less sag) is obtained with

a specific, corresponding to a particular angle of attack.

The best rate of descent is obtained (the same as climbing) with a suitable combination of

power and speed.

5. - Describe the differences between the following: True airspeed, Indicated airspeed,

Calibrated airspeed and Equivalent airspeed.

TRUE AIRSPEED INDICATED AIRSPEED CALIBRATED AIRSPEED EQUIVALENT AIRSPEED(TAS) of an aircraft is a

relative measurement. The

actual flight speed of an

airplane relative to an air

mass is termed as true

airspeed, and it is primarily

used for navigational

purposes. In short:

-Flight speed shown on the

instrument (notcorrected for

instrument error, altitude,

density and temperature) is

called indicated airspeed.

-The actual speed of an

aircraft through the air is

termed as true airspeed.

(IAS) of an aircraft is simply

the value that an airspeed

indicator denotes on its scale.

The value is obtained through

a pitot-static system which

includes a pitot tube and two

static vents. Indicated

airspeed is used

aerodynamically, and is

important to aircraft

performance.

This Speeds related to take-

off, stall, lift, turns, etc. are all

in terms of IAS

.

Calibrated airspeed (CAS)

is the speed shown by a

conventional airspeed indicator

after correction for instrument

error and position error.

When flying at sea level

under International Standard

Atmosphere conditions

calibrated airspeed is the same

as equivalent airspeed and true

airspeed.

If there is no wind it is also the

same as ground speed.

Equivalent airspeed (EAS) is

the airspeed at sea level in the

International Standard

Atmosphere at which the

dynamic pressure is the same

as the dynamic pressure at the

true airspeed and altitude at

which the aircraft is flying.In low-speed flight, it is the

speed which would be shown

by an airspeed indicator with

zero error.

It is useful for predicting

aircraft handling, aerodynamic

loads, stalling etc.


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= = 126.95 /N min = 1.5

= = 98.33 / = 1 . 4 = 767.95 /Then, the next step is to make the table, for we can graphic the Diagram.

Vs (ft/s) 80.29

Positivo Negativo

n Vs n Vs

0 0 0 0

0.25 40.145 -0.25 40.145

0.5 56.7736035 -0.5 56.7736035

0.75 69.5331797 -0.75 69.53317971 80.29 -1 80.29

1.25 89.766949 -1.25 89.766949

1.5 98.3347657 -1.5 98.3347657

1.75 106.213686 -1.75 106.213686

2 113.547207 -2 113.547207

2.25 120.435 -2.25 120.435

2.5 126.949637 -2.5 126.949637


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-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500 600 700 800 900

n

V

V-n Diagram

VA

VG

VCVS

VD


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7. - Describe the concepts of gust and its effects on the loads experienced by the

airplanes.

Whether due to discrete gusts or continuous turbulence, are ordinarily considered tobe the result of a change in angle of attack due to a component of gust velocity at right angles

to the flight path. Vertical and lateral gusts fall into this category. The change in angle of

attack, in radians, is equal to the gust velocity divided by the forward speed.

If we consider, for example, a vertical gust, the change in lift due to the gust is:


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Head- On gust

This case can also be important. Here all that changes is the dynamic pressure. (The angle of

attack is simply the constant pitch attitude of the airplane).


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Ratio of Lifts, Headon to vertical Gust

Values of this ratio for typical situations are shown in the next to last column of the following

table:

8. - Derive the equations used to sketch the gust envelope and mention the 3 different

velocities for gust use in this diagram.

The gust can be considered as if the plane goes into a vertical air stream instant:

To adapt the theoretical instantaneous gust to reality, the rules include an attenuation factor of

bursts, kg, where:

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