GENERAL Flashcards
(179 cards)
1
Q
Out of a metal alloy and a carbon fiber reinforced polymer (composite), which material is isotropic ?
A
The metal alloy is isotropic as the composite has preferred orientations for forces to be acted upon, this is related to the directions of the fibres, and thus the composite is not isotropic
2
Q
Young’s modulus
A
represents the materials resistance to deformation
3
Q
what are …
yield strength
failure strength
?
A
the stress at which plastic deformation starts
stress at which material fails
4
Q
Max strain - on material properties table
A
max strain at which the material breaks
5
Q
Specific property
A
gives the value of the property per unit density of the material
6
Q
Thermoplastic
and
Thermoset polymers
A
Thermoplastic: It is one component and softening is reversible
Thermoset: It is made up off multiple components, and curing is irreversible
7
Q
Polymer characteristics
A
isotropic
Low strength & stiffness
Huge variety
Plastic flow & melting
Good processibility
Low cost
8
Q
Composites
A
Composed of more than one material
Fibre reinforced Polymers
Hybrid materials: GLARE
9
Q
Anisotropic
when can they be usefull ??
A
having a physical property which is a different value when measured from different positions
strong and stiff in only one direction
Usefull when composite is tailored fibres, fibres coincide with loads.
10
Q
Which material is stronger and which one strains more ?
Show this quantitatively.
A
To compare both rods you need to use
stress = σ = F/A
strian = ε = ∆L/L
11
Q
Isotropic
A
the properties are independent of the direction the material is tested
12
Q
Metal properties
A
Isotropic
can be strengthened
plastic behaviour ( can melt)
good processibility
often low cost
13
Q
Week 3 Q.
A
thermoplastics can be heated and reshaped
Since composites consists of polymer and (one directional) fibres, composites are anisotropic (almost by definition)
14
Q
Week 3 Q.
A
Because of their relatively thick structure, sandwich structures are difficult to bend (a bending moment is carried by facesheets at “large” distance from each other). Laminates need to be reinforced in order to carry bending loads. So this means only statement 2 is correct.
Though it is true that there is an expensive factor in the use of composites, that factor is not their processability, but the small volume of composites at this moment.
15
Q
A
For fail safe multiple load paths should be created for each force:
(At least) TWO diagonal wires between A-C and also (at least) TWO wires between B-D
OR
(At least) One rod between A-C and also (at least) one rod between B-D
16
Q
A
FOR SAFE Life one load path is assumed sufficient (but this path should have very low probability of failure during entire operational life)
TWO diagonal wires between A-C and also TWO wires between B-D
OR
One rod between A-C
OR
One rod between B-D
17
Q
What can be seen on the primary flight display ?
A
Attitude, heading, airspeed and vertical airspeed
18
Q
What does CDU stand for ?
What does it do ?
A
control and display unit
allows you to select a route or change a route
19
Q
Identify the names of all compenents in this Glare cockpit
A
20
Q
What is this called ?
A
Head-up display (HUD)
Primarily found in fighter jets.
21
Q
KNOTS to M/S converion factor
A
0.5144…
22
Q
ft/min to m/s conversion factor
A
0.00508
23
Q
Why is the EAS used in the cockpit ?
A
the EAS is the measure for total dynamic pressure
24
Q
At an altitude of 24,000 feet a Pitot tube measures a total pressure of 0.5564 bar. Determine the equivalent airspeed (in metres per second) of the aircraft (assuming ISA conditions).
A
25
At an altitude of 24,000 feet a Pitot tube measures a total pressure of 0.5564 bar.
Given the static pressure to be 39264.1 Pa, and the temperature at 24,000 feet altitude to be 240.6 K
What is for this aircraft the true airspeed (in metres per second)?
What is the Mach number this aircraft flies at?
Alternatively you can use the rho/rho\_0 equation which has the -1 in its exponent
26
A commercial aircraft flies at a Mach number of 0.67 at an altitude where the air temperature is -19.15 C. Assume ISA conditions.
Determine the altitude (in metres) this aircraft flies at.
Calculate the equivalent airspeed (in feet per second) of this aircraft.
27
Define safe life
Each element storng enough for entire _life cycle_
28
Fail safe
If one element fails the _system is still able to carry the load_
Redundant elements
29
Where do the arrows for 1 and 2 point ?
1. points left
2. points right
this is because the bottom section of the truss structure is in compression, so the reaction forces are opposing the compression.
30
What is a shell structure
thin _load bearing skin_, with stiffening elements
31
what is a monocoque
a _load bearing skin_ (only skin takes load)
32
Aircraft structure
What is it ?
What does it do ?
- Complex wingbox
- Multiple ribs
- All elements lead to the **Load Path** - which itself _transfers a load_ to the _centre of gravity_
33
What is the failure behaviour of metals?
With force in the y - direction
and displacement in the x - direction
_Yield_ stress ⇒ _Ultimate_ stress ⇒ F**_racture_**
34
What is the failure behaviour of composites ?
Fracture
35
What is a PSE ?
_Principal_ _Structural_ Element
36
What is the Load Factor
n = L/W
37
An aircraft tries to make turn by banking, see the figure below. The angle ϕ is its bank angle. The aircraft makes its turn in such a way that it maintains a constant altitude.
Find an expression for the load factor n in this case.
It isn't jut cos(phi) as the lift is not equal to Lcos(phi) the weight however is equal to Lcos(phi), plug that in for W and you get 1/cos(phi)
38
How is the ultimate load described
39
According to these stress directions were is the load coming from or going to ?
The load is going from left to right.
It is going from left to right as if you can imagine the buckling the arrows going from top left to bottom right are reaction forces opposing the compression of the buckling, while the other arrows are opposing the tension
40
state the hoop stress
and
outline how it is found
The hoop stress is also called the circumferential stress.
It is the stress that wants to make the diameter want to get bigger.
41
Explain longitudinal stress
Longitudinal stress is what wants to make a _cylinder grow longer_.
The force that wants to make the cylinder grow longer is the difference in pressure times the cross sectional area.
Pressure times area equals force.
The force that opposes this expansion is carried by the skin. It is the longitudinal stress times the area of the skins cross section.
42
What do cut outs on a fuselage do to the stresses ?
and how are they dealt with ?
Without any cutouts a fuselage would be a undisturbed cylinder, this is not the case in RL.
Cutouts create _stress concentrations_ and increase local stress.
In order to stay below the maximum allowable stress the skin has to be reinforced.
43
Finish the following statement. "Fatigue is caused by..."
A _**repeated** force **smaller**_ than the _**breaking** force_
44
Which two phases (before a critical crack) do we distinguish in the process of fatigue?
Crack _initiation_ and Crack _growth_
It takes time to start a crack, this phase we call the _'crack initiation'_. Once initiated, the crack will slowly grow due to repeated loading, this phase we call the _'crack growth'_
45
A modern jet flies at an altitude of 6,200 metres, during its climb to cruise altitude. For additional passenger comfort, the cabin pressure is maintained at 80% of the sea level value.
Given that the fuselage radius is 3.2 metres and that the skin thickness is 2.4 mm, compute the circumferential stress in the fuselage skin (in MPa or MegaPascal): (Assume ISA conditions)
Additionally, compute the longitudinal stress in the fuselage skin (in MPa or MegaPascal)
46
Determine the equation for the 'hoop' stress for this square fuselage.
47
A futuristic Aircraft manufacturer has come up with the idea to build a supersonic passenger jet, which is supposed to perform cruise flight at 24 kilometres altitude. For passenger comfort, the cabin pressure should remain at least 72 percent of the sea level value. To give the aircraft an aerodynamic shape its fuselage is rather long and slender, meaning the fuselage diameter is 'just' 4.5 metres.
The engineers have asked you, now experts in the field of pressure cabins and fatigue, to determine the required skin thickness to deal with the circular stress (which may not exceed 75MPa) in the fuselage skin. To be on the safe side, they ask you to take into account a safety factor of 1.5.
What will be for this aircraft the skin thickness (in millimetres)?
Go through the steps of solving this.
48
How do ailerons bank a plane ?
By rotating the control wheel or moving the control stick to the left, the left aileron raises and the right left aileron drops.
Doing so causes there to more lift on the right side since dropping a flap down _increases the angle of attack_ of the RHS. Equally raising the aileron on the LHS _decreases the angle of attack_ which accordingly decreases lift.
This imbalance of lift will cause a roll to the left.
So rotating the control wheel _right_ will causes the aircraft to roll to the _right_
49
How does the elevator change the pitch of an aircraft ?
By pulling the control wheel or strick, you raise the elevator. By raising the elevator you decrease the angle of attack of the tail, thus pushing the tail down and correspondingly the nose goes up.
So pulling the control wheel increases pitch, and pushing decreases pitch.
50
How does the rudder change the yaw of an aircraft ?
You should think of the rudder, attached to the vertical stabiliser, as a vertical standing symmetrical wing.
Pushing the right pedal moves the rudder right, as a result this will cause a lift to act to the left moving the tail left, which causes the nose to move right
51
Modern aircraft usually have two sets of ailerons: one 'inboard aileron' (close to the fuselage) and one 'outboard aileron' (further up the wing). Why is this?
The two sets of ailerons are _used for different flight speeds_, here is why:
As you know, the moment caused by a force is given by M=F\*r, where F is the force and r is the moment arm. At low speeds, the force by an aileron is relatively low, so to get a sufficient moment the moment arm should be large. Hence **at low speeds, the outboard ailerons** are used.
At high speeds the force by an aileron is very large, if the outboard ailerons would be used to moment (and loads on the wing structure) would become very big. Hence at **high speeds the inboard ailerons** are used, to keep the banking moment within bounds.
52
For most conventional aircraft the line of action of the engine thrust is situated below the aircraft centre of gravity. This means that in case the engine thrust is altered, the pitching moment of the aircraft will be affected. To prevent the aircraft from pitching, the elevator can be deflected a bit.
Suppose the pilot of a conventional aircraft decides to increase the thrust of this aircraft, but wants to keep the pitch angle (and angle of attack) the same. What kind of elevator deflection should he give to prevent his aircraft from pitching: a positive or negative one?
In case the line of action of the engine thrust is below the aircraft centre of gravity and the thrust is increased, this will result in a nose-up pitching moment, which is positive.
The pilot should thus deflect the elevator such that the nose goes (back) down: **negative pitch**. And since a positive deflection corresponds to a negative aircraft response (and vice versa), the pilot should _apply a positive deflection_ of his elevator.
53
Suppose a passenger aircraft flies with a course of 80 degrees and a heading of 84 degrees (both according to the compass). Determine the angle of sideslip it then experiences.
sideslip = when an aircraft is moving somewhat forward as well as sideways against the incoming wind.
Not equal to yaw as sideslip is only relative to incoming relative wind.
In case the aircraft nose points to 84 degrees on the compass, but the aircraft moves to 80 degrees, then the aircraft experiences the airflow at an angle of 4 degrees from the nose on the left.
Since a flow from the right is defined as positive sideslip, this results in a (negative) sideslip of **-4** degrees.
54
If the pilot would deflect his rudder in this way during flight, what yaw angle will the aircraft get?
A positive yaw angle
55
As an aircraft flies across the globe, it must continuously pitch (with respect to an inertial frame of reference) to keep following the curvature of the Earth.
From that point of view, what must the sign of this continuous (though extremely small) _pitch rate_ be?
To keep following the curvature of the Earth, the nose must (very slowly) continuously keep going down. This means that (since a nose up movement is positive pitch) the pitch rate of an aircraft must continuously be **negative**.
pitch rate, not deflection rate...
56
Consider a statically stable aircraft in the yaw direction. What direction will the aircraft straight away yaw to after the pilot has pushed his left foot pedal?
The positive yaw direction
57
Go thorugh the steps of calculation
58
What is the relationship between the angle of attack, the horizontal tail AOA and the downwash ?
59
Of this aircraft you are given the following parameters.
Furthermore we will assume that the downwash angle is equal to 10% of the angle of attack of the wing. Given that the centre of gravity of this A340-600 is situated 39.2 metres from the nose, find the static margin (in metres) of this A340.
\*Lengths are measured from nose\*
60
The moment coefficient and longitudinal static stability
How does it work?
As you can see the gradient of the graph is negative (considering the LHS of the x-direction positive, etc.).
If the aircraft pitches up in the positive pitching moment direction, the restorative moment has to be in the negative pitching moment direction.
This translates to a negative moment coefficient as well. Why? Well considering how the moment coefficient is derived, the total moment coefficient is the result of all moments on an aircraft acting on a certain point. If we consider an aircraft with one moment force for the sake of simplicity, this moment has to be in the negative pitching moment direction.
EDIT: basically the moment coefficient oppose the chnge in angle of attack. If there is a positive change in AOA then the moment coefficient is negative
61
What is/are the properties of the Dutch roll? It is:
The Dutch roll motion lets the aircraft return to its equilibrium position following a disturbance (so **statically stable**) and is a damped motion (so **dynamically stable**). It _isn't very well damped_ however (it takes time for the motion to stop, though not as long as with the phugoid), meaning it is quite an unpleasant motion.
62
Equation for measure of average kinetic energy in a gas
KE = 1.5\*k\*T
k = Boltzmann Constant = 1.38 \* 10-23 J/K
63
The Gas Constant R
287
J / (kg\*K)
64
specific volume
1 / ρ
= volume of 1 kg of gas
65
Please finish the following statement:
A streamline is a line that is....
_tangential_ to the velocity at every point
66
Outline where the euler equation comes from
F = m\*a
-(dp/dx)\*(dxdydz) = ρ(dxdydz)\*V(dV/dx)
F= -(dp/dx)\*(dxdydz)
m =ρ(dxdydz)
a = V(dV/dx)
Final Euler Equation: dp = - ρ\*V\*dV
67
During the derivation of the Euler (momentum) equation, three forces were acting on the volume: a pressure force, a gravity force, and a friction force.
Which force or forces is/were neglected during this derivation?
_Friction_ force
_Gravity_ force
68
Suppose it is your job to make a subsonic, incompressible windtunnel. The test section should be square, 2x2m. The conditions in the test section are given to be standard sea level conditions and a flow speed of 50 m/s.
What should be the mass flow (in kg/s)?
The mass flow is given as
ρAV = 1.225\*4\*50 =245 kg/s
69
Go over the steps for deriving the Bernoulli Eq. from the Euler equation
1. Rearrange euler equation - all values on one side
2. Integrate both terms from P1 to P2
3. Rearrange to form Bernoulli equation
70
Consider the following statements:
1. For the work done on the system we can write δw=pdv
2. We can only use cp and cv for a process in which the pressure or the volume, respectively, stays constant.
FALSE or TRUE
The work done on the system can be written as δw=-pdv, since the volume decreases when the boundary is displayed inwards. Therefore, statement 1 is **_false_**.
Although we derived cp and cv for a process in which the pressure or the volume, respectively, stays constant, equations involving these constants can be used even when the pressure and the volume do not remain constant; see for example the Energy equation, where the pressure between the two points will most likely be different.
Statement 2 is also **_false_**.
71
Select all that applies about enthalpy (more than one answer may be correct!):
Enthalpy ...
is defined as h=e+pv
can be either positive or negative
is a measure of the total energy of the system
is zero at T = 0 K
In the lectures, we defined enthalpy as h=e+pv, and as a measure of the total energy of the system; hence, the _first_ and _third_ statements are correct.
Although the change in enthalpy can be both positive or negative, depending on the type of process, the enthalpy itself can not be negative. The second statement is therefore incorrect.
We defined _h=0 at T=0_ K, so the last statement is correct.
72
What are two things yo have to remember about bernoulli's equation
Bernoulli equation only for _inviscid_ = frictionless, incompressible flow
Bernoulli equation is valid along a _streamline_
73
What is the First Law of Thermodynamics ?
and the different form
de= δq + δw
δq is heat per unit mass
δw is work done per unit mass
de= δq - pdv
74
Enthalpy eq.
dh= δq + vdp
75
What is the specific heat defined as ?
defined as the added _heat per degrees temp_ rise
c= δq/dT
76
Thermodynamics: General Equations for a perfect gas
de = cvdT
dh=cpdT
e=cvT
h=cpT
77
What are the values for cp and cv for processes with T\<600k
For air:
cv = **720** J/(kg K)
cp = **1008** J/(kg K)
78
What is a process with no heat addittion or extaction called ?
_adiabatic_ δq = 0
79
What is process with no frictional or dissipative effects called ?
_reversible_ _process_
80
What do you call a process that is both adiabatic and reversible ?
_Isentropic_
81
What are the isentropic relations ?
82
For steady, isentropic compressible flow: Energy equation
with temp
83
What are all the names for the the equations "For steady, isentropic compressible flow (adiabatic and frictionless)":
_Continuity_ equation
_Isentropic_ relations
_Energy_ equation
Equation of _state_
84
what is the ratio of specifc heats ?
**cp** / **cv**
85
Consider an aircraft flying at 250 m/s and -20 C. At one point on the wing, the temperature is 240 K. (compressible flow)
What is the velocity at this point?
Suppose the free-stream pressure is 38794 Pa.
Calculate the pressure in the point on the wing, in Pa
If it is also given that the free-stream density is 0.53396 kg/m3, we can calculate the density.
Calculate the density at this point on the wing
86
What are the second form of isentropic relations ?
when are they valid ?
only valid for flow to or from V=0
87
Consider the following statements:
1. Going through the speed of sound is an isentropic process
2. The second form of the isentropic relations are only valid for flow to or from a station where the velocity is zero.
True or False ?
Going through the sound wave there is _no heat addition_, and friction is negligible. This makes this an isentropic process, and hence statement 1 is **true**.
During the derivation of the second form of the isentropic relations, it was explicitly assumed that the speed in station 0 was zero. Hence statement 2 is **true**.
88
Consider the following statements:
1. If there is a throat in a windtunnel, the flow at that point will always be sonic (M = 1)
2. To get a supersonic flow in the test section, there should always be a throat.
The area-velocity relation only dictates that when there is a sonic flow in a nozzle involving a throat, the sonic flow must be at that throat. But you could also have an entirely subsonic windtunnel with a throat in it. Hence, statement 1 is **false**.
The area-velocity relation shows that the way to speed up the flow is dictated by the Mach regime. For subsonic flow, the only way to increase the velocity is for dA/A to be negative - the cross-sectional area should become smaller. At one point the flow becomes sonic; according to the previous reasoning, this must be in the throat. If we then want to increase the velocity, the area must increase; if we decrease the area, the flow will likely choke and stop flowing. Hence, statement 2 is **true**.
89
In the combustion chamber of a rocket engine, kerosene is burned, resulting in a hot, high-pressure gas mixture with the following properties:
T0 = 3000 K
p0 = 15 atm
R = 378 J/kg K
γ=1.26
This gas flows from the combustion chamber through the rocket nozzle. The pressure at the exit of the rocket nozzle is: 1 atm, and the area of the throat of the rocket nozzle is: 0.08 m2. Assume isentropic flow.
What should be the Mach number in the throat?
What is the speed of sound in the exit? (in m/s)
What is the Mach number in the exit?
What is the flow speed in the exit? (in m/s)
90
What is shear stress on an airfoill defined as ?
91
What does the boundary layer velocity profile look like ?
92
What is laminar flow defined as ?
streamlines are smooth and regular and a fluid element moves smoothly along a streamline
93
What is turbulent flow defined as ?
streamlines break up and a fluid element moves in a random irregular way
94
What is the max. limit for incompressibility defined as ?
How is it defined ?
For M \< 0.3 the flow can be treated
Why?
For M \< 0.3 the change in density is less than 5 %
95
What is the 'area velocity relation' for a 'Supersonic wind tunnel'
96
What is the change of pressure, temperature and density in a supersonic wind tunnel starting from a reservoir starting at V =0 ?
97
Local skin friction coefficient
98
Total aerodynamic force, skin friction drag Eq.
99
Total skin friction drag coefficient
100
What is the Reynolds Number
101
What is e. for boundary layer thickness ?
102
What is the eq. for pressure distribution ?
103
What does a Pressure distribution graph look like ?
With correct labels.
104
What is Cp in terms of velocities ?
105
At what Re number does turbulent flow become more _important-dominant_ than laminar flow ?
**500,000**
At _low_ Reynolds number (\<500,000 for airfoils) _laminar_ flow dominant
High Re: turbulent flow more important
106
What is drag due to viscous effects defined as ?
Cd = **Cdpressure + Cdfriction **
Cd = profile drag
107
What is the effect of turbulence on flow separation ?
Turbulent boundary layer has _more flow kinetic energy_ near the surface.
Thus _flow separation may be postponed._
Remember the boundary velocity profile for turbulent flow. It sticked to surface a lot longer. There were greater shear stresses, and this is beneficial in postponing a flow separation.
108
What are bluff bodies ?
Cylinders and spheres are considered bluff bodies because at large Reynolds numbers the drag is dominated by the pressure losses in the wake.
109
What can different Reynolds numbers tell us about how the flow is going to act ?
Low Reynolds number: influence of viscosity (friction) is high
- for bluff bodies this may often lead to laminar separation with high pressure drag as a result
Increasing the Reynolds number:
influence of viscosity decreases
the transition location moves forward on an airfoil / object
the boundary layer thickness and Cf decrease
drag goes down (3 wins over 2 for an airfoil)
lift slope goes up (less de-cambering {flow separation decambers} of the airfoil)
110
What does a CL - AOA graph tell us about the flow around an airfoil ?
When Cl start to _deviate from a straight line to the origin **flow separation starts** at the trailing edge_.
At the maximum lift coefficient the boundary layer flow separation is around 85-90% of the chord.
Further increasing angle of attack moves the separation forward until the boundary layer separates from the leading edge.
111
What does a drag coefficient graph tell us about the flow separation ?
The drag coefficient increases so drastically for both positive and negative angles of attack because the _transition location_ _moves forward_ with respect to the _leading edge_. Which means a larger part of the wing has a turbulent boundary layer.
Because of its shape the drag curve is sometimes called the drag bucket.
112
How does a Cl - Cd graph gives us the optimal Cl/ Cd
The tangent to the drag lift curve
113
Laminar and turbulent airfoils ?
Laminar airfoil 10% higher Cl/Cd
114
What does increasing the camber line do to CL-Cd graphs and Cl-AOA graphs ?
Increases lift curve and this results in a larger Cl/Cd ratio
115
Normal coefficient in terms of Cp
116
Lift coefficient in terms of Cp with compressibility correction
117
How do you obtain the lift coefficient from the normal and tangential components
118
How do the critical pressure coefficient and mach numnber change with different thicknesses for airfoils
\*Also shown is the effect of compressibility according to the Prandtl-Glauert correction, so with increasing Mach number the Cp and obviously also the minimum Cp goes to more negative values.\*
Thicker airfoils, reach critical pressure coefficients for lower mach numbers.
119
How do you find the Mcr for an aircraft in consideration ?
The intersection of this curve with the airfoil CP,min will give the value of the Mcr specific for the airfoil under consideration.
120
What does sweeping wings do to the mach number?
By sweeping the wings of subsonic aircraft,
the **drag divergence** is _delayed_ to _higher_ **Mach** numbers
121
What does the _induced_ drag do ?
It lowers the angle of attack
122
Difference between drag polars for wings and that for complete airfract ?
The difference is the 'e'
For a wing it is written as e1 and it is called the _span efficiency factor_
For complete airfract it is called the _oswald efficiency factor_
123
The induced angle of attack in terms of Cl and k?
i think you can also use it without 57.3
124
What does the induced angle of attack do?
It reduces the local effective angle of attack
125
Graphically show how the induced angle of attack effects the effective angle of attack, Cl - AOA graph.
126
What is the main purpose of a main flap ?
An increase in effective angle of attack
An increase in camber
127
What are the equations for the lift curve slope in terms of radians and degrees ?
128
What is the longitudinal stability of a canard ?
129
How do you calculate min airspeed ?
130
Easy eq. for Cloptimal
131
How do you maximise range ?
Maximising V/F
= (nj/Cp)\*(1/D)
find optimal V
with Cl/Cd max
132
maximise endurance
minimise fuel consumption
so Pr minimum
look at image attached
133
What is the progression of the combustion cycle ?
what does the enclosed volume represent ?
Intake → Compression → Combustion → Expansion → Exhaust
134
How does the propellor pitch vary on a 'non fixed pitch' propellor ?
1. By large twist they mean that with respect to the airplane it is more twisted. Essentially it is more pointed towards the airspeed. This has to do with the fact that the rotation speed decreases as you move closer to the centre of rotation.
2. Here the blade element has to be pointed closer to the plane of rotation, hence a smaller twist
135
Pa is equal to...
T\*V
Thrust \* Airspeed
136
What is the propulsive efficiency of a propellor engine written as ?
137
What is the net work done (in Joule) by this cylinder during one cycle?
138
139
What mistake did you make ?
You mistook A (aspect ratio) with surface area....
140
What is the concept behind turbofan engines ?
Turbo fans decrease the airfoil but they increase the mass flow to maintain the sam thrust. However, by decreasing the jet speed you can increase the efficiency so turbofans are more efficient.
141
Difference between EAS and TAS ?
EAS - equivalent airspeed on the ground
TAS - True airspeed
EAS is used in the cockpit as it is measure of total dynamic pressure.
142
143
When you're calculating the EAS at a certain height what air density do you use ?
sea level air density
144
What's the equation for Vstall ?
145
If the sea level temp is lower than 288.15 what does that mean for the value for VSTALL ?
when it is colder the air is more dense so the stall speed can be lower
146
The stall limit is a performance limit of the aircraft which varies with altitude. Besides performance limits, there are also operational limits which define the flight envelope. List 3 of those operational limits.
_Altitude_ limit – pressurized cabin
Maximum _operating speed_ VMO
Maximum operating _Mach_ number MMO
147
Why is the 'Earth fixed referance frame' actually not an inertial frame of reference ?
Because earth is a sphere and not flat so there is a centripetal acc. acting towards the earth.
Secondly the earth is rotating, so an aircraft supposedly flying at in a straight path is actually on a curved path.
148
Flight mechanics equations of motion
149
Flight Mechanics: FBD
E is for 'moving earth axis system'
B is for 'Body axis system'
A is for 'Air path axis system'
gamma angle is 'flight path angle'
Alpha is ofc AOA
Theta is 'pitch attitude'
Alpha T is angle between airspeed vector and Thrust vector
150
Describe how these flight conditions affect equations of motion or other variables associated with aircrafts?
Straight flight
Steady flight
Horizontal flight
Symmetric flight
151
MAXIMUM RANGE
Go through the different forms you can use.
152
Optimal lift coefficient for Max Range
153
MAX ENDURANCE
154
Optimal lift coefficient for maximum endurance
155
Optimal Speed for maximum range and endurance
156
Fill in the table
157
Maximum Climb Angle
158
Minimum Descent Angle
159
Rate of Climb (ROC)
160
Time to climb
161
Maximum rate of climb in steady flight
162
Minimum rate of descent in gliding flight
163
Performance diagram of ideal Jet
Force vs. Airspeed
so.. the minimum point is also the Cl for Max climb angle and min descent angle
164
Performance diagram of an ideal propeller
Power vs. Airspeed
165
When can you use the attached isentropic relations ?
How would you apply this to a nozzle question ?
When one of the points has a zero velocity.
The stagnation point would be po and p1 and M1 would be related to the point which is isn't zero velocity.
166
What should you always remember to put behind an answer...?
Units..
167
What is the difference between a 0 and a
a 0 is the profile lfit gradient - basically when you take the gradient between two given points.
to find the actual lift-gradient you need to use one of the eq attached.
168
What is the pitot-static tube formula ?
169
Glide Ratio
170
What do you have to remember about the prandtl-glauret ?
INSTEAD OF Cl USE CD for the eq.
171
For longitudinal stability problems, when dividing to find the coefficients, which equation out of moments and lift has the chord in it as one of the variables.
And what implications does that have.
The moment eq.
This means when you divide by the said value the chord gets elimanated for the moment coefficients and it stays for lift coefficients.
172
Do q. b)
What are important things you have to remember about how you did this q. ?
First, when they show and alpha in the coefficient subscript then they probably differentiated with respect to AOA.
Lw1 doesn't have a differential as one of its terms as it has an AOA that is alpha the differential of alpha over alpha is just 1.
Because wing 1 and 2 are the same type of wing they have the same Cl.
173
c) Based on this equation for Cmα , what is the required area of the horizontal tail surface to ensure longitudinal static stability?
d) In reality a slightly larger tail surface area is chosen. Why and what would be the operational advantage the user will experience when using this aircraft?
c) REMEMBER to DOUBLE the surface area
d) this means that there will be a distance between the centre of gravity and neutral point. So there will be a _static margin_. This allows the user a larger range of center of gravity positions of the aircraft.
174
When they ask you to take into account the lift-induced angle of attack, what eq. do you have to use ?
How would this calue change a angle of attack ?
It takes away from it.
175
In the FBD for flight mechanics what is the LIFT perpendicular to ?
To the velocity vector
or in other words the xA coordinate.
176
When they say simplify the eq. of motion because the aircraft is in steady, horizontal flight, what do you do ?
horizontal acc is eqaul to zero
and vertical acc as well.
177
Difference between Climb Angle and ROC ?
First of all max climb angle is measured in degrees
ROC units are m/s
Importantly ROC is just the climb angle equation multiplied by V ⇒ Vsin(γ) and this is then termed as ROC.
On the RHS of the eq T-D are converted into Pa and Pr respectively.
178
Difference between Max Climb Angle and Min descent angle
Max climb angle is
(T-D)MAX / W
While min descent angle is dervid from the same eq, however, since it is a state of gliding the thrust is set to 0.
The resulting eq. is - Cd/Cl
negative because D was negative, and the Cl comes from W which itself is equal to L.
179
Difference between ROC max and min
First, the numerators for max ROC are set to MAX while the numerator for min is set to Min
Next, beacuse it is a state of glide, there is no Pa and thus Pr/W is left to be minimised
Or in other terms (DV)/W
Also note that ROCMAX can be written as (DV)MAX which can further be manipulated.
