# Aerodynamics Set 3 – Examination Reviewer

Here are practice Aerodynamics Fundamental Questions for Engineering:

Which is an advantage of flying a jet at high altitudes?
a. Lower engine RPM will result in low SFC
b. Low temperature increases engine efficiency

Answer: Low temperature increase engine efficiency

At high ALTITUDE, V is HIGH. So engine can suck more air without much power needed.

Density decreases, true speed of aircraft increases.

The aircraft needs to move faster to generate the same amount of lift. This relationship is why aircraft fly faster at higher altitudes, where the air is less dense.

Why do helicopters fly nose down?
Answer: To maintain forward flight, the rotor tip-path plane must be tilted forward to obtain the necessary horizontal thrust component from the main rotor. By doing this, it causes the nose of the helicopter to lower which in turn will cause the airspeed to increase.

With an increase in forward velocity of a helicopter, the increase in parasitic drag will cause the fuselage attitude to
a. Nose up
b. Nose down

At forward flight, the helicopter is always naka NOSE DOWN.

The amount of parasite drag increases with increasing airspeed, so that the thrust/parasite drag (nose-down) couple becomes stronger.

Over banking – skid or slip?

With a drop in ambient temperature, an aircraft service ceiling will
a. be lower
b. rise
c. remain the same

T down = Density up = AC performance up

Wing setting angle is also known as

“naka set na”

What happens to air flowing at the SPEED OF SOUND when it enters a converging duct?
Velocity _ Pressure and density _

Answer: AT SONIC SPEED & MACH >1 (high speed)

kabaliktaran

Velocity decreases,
Pressure & density increases

Which flight condition creates the most severe flight hazard by generating wingtip vortices of the greatest strength?
Heavy, slow, gear and flaps down.
Heavy, slow, gear and flaps up

Answer: Heavy, slow, gear and flaps up (CLEAN CONFIGURATION – retracted).

No flaps – High AOA needed.

With flaps, we can fly at a reduced angle of attack. So the vortices reduce in strength due to the lower angle of attack. So a clean aircraft has a higher angle of attack than one with flaps, hence stronger vortices

Rigging angle of incidence of an elevator is

• chord line
• horizontal in the rigging position**

The temperature to which humid air must be cooled at constant pressure to become saturated is called

A two-bladed helicopter rotor on a central gimball is
a. Full articulated rotor
b. Semi-rigid rotor

Central gimball – flap up and down

Which is a characteristic of the constant Mach cruise control procedure?
True airspeed decreases as the outside air temperature (OAT) increases.
Thrust is reduced as the aircraft weight decreases.
EPR is increased as the aircraft weight decreases.

Answer: Thrust is reduced as aircraft weight decreases.

At cruise, W fuel decreases, So V down to maintain cruise = Thrust req down.

Maximum range for a turbojet is achieved at a specific angle of attack that provides the best L/D ratio. This optimum angle of attack is not affected by aircraft weight or altitude.

As fuel is burned and aircraft weight decreases, the speed has to be reduced to maintain the maximum range angle of attack.

It is a setting that increases the resistance to rotation and is a high blade angle
a. Fine
b. Course

Type of propeller
Best for climb

Type of propeller
Best for cruise
a. Constant Speed

An AC is climbing at Mach 0.72. The TAS will
a. Increase with altitude
b. Decrease as temperature decreases

Mach = constant

M = v/a

V low = a low

After a change in collective pitch, the Rotor RPM will rise and fall. This is called
a. Under swing
b. Static droop
c. Transient droop
d. Over swing

The initial total fall in rotor RPM is called
a. Under swing
b. Static droop
c. Transient droop
d. Over swing

The change in stabilized RPM is referred to as
a. Under swing
b. Static droop
c. Transient droop
d. Over swing

The RPM difference between transient droop and static droop is called
a. Under swing
b. Static droop
c. Transient droop
d. Over swing

If a helicopter rotor disc is rotating anticlockwise, viewed from above where would a pitch input be fed into the disc to move the helicopter backward, (90 degrees to what)?
a. Back of the vertical axis.
b. Left of the longitudinal axis.
c. Right of the longitudinal axis

Answer: Right of the longitudinal axis

Why do jets fly at high altitude?
a. Lower engine RPM’s will result in decreased specific fuel consumption.
b. Lower temperatures increase engine efficiency.
c. Thrust increases as the density of the air decreases

Answer: Lower temperatures increase engine efficiency.

On a helicopter, what is vortex ring state?
a. Ground vortex interference when hovering close to the ground.
b. Tip vortex build-up during hover

Answer: Tip vortex build-up during hover.

True airspeed is determined by correcting
Answer: EAS for air density variation from the standard value at SEA LEVEL

The purpose of sweeping wings back approximately 30° to 35° is to
a. Minimize dutch roll.
b. Reduce high-speed drag.
c. Provide aileron control when the root of the wing approaches the critical angle of attack.

Answer: Reduce high-speed drag (WAVE DRAG)

Swept wing – delays shockwave formation & WAVE DRAG.

Sweepback delays the drag rise to a higher Mach number as well as reducing the magnitude of the drag rise.

Which adverse stability characteristic is caused by sweepback?
a. All of the above.
b. Increase of dutch roll tendency.
c. Increase of critical Mach number.
d. Increase of Mach tuck tendency

Answer: Increase of dutch roll tendency.

An excess of lateral stability from sweepback can aggravate Dutch roll tendencies.

At stall, the wingtip stagnation point
a. Moves toward the lower surface of the wing.
b. Doesn’t move.
d. Moves toward the upper surface of the wing.

Density decreases, true speed of aircraft _ Answer: increases

As air density decreases, the true airspeed of an aircraft increases due to the reduced AIR RESISTANCE.

The aircraft needs to move faster to generate the same amount of lift. This relationship is why aircraft fly faster at higher altitudes, where the air is less dense.

8. Which atmospheric conditions will cause the true landing speed of an aircraft to be the greatest?
a. Low temperature with low humidity.
b. High temperature with low humidity.
c. High temperature with high humidity.
d. Low temperature with high humidity.

Answer: C. High temperature with high humidity.

True airspeed (TAS) represents the true speed of an airplane through the air. As air temperature and humidity increase, the density of the air decreases. As air density decreases, true airspeed increases. Therefore, high temperature with high humidity will cause an aircraft’s landing speed to be greatest.

18. Frost covering the upper surface of an airplane wing will usually cause
a. The airplane to stall at an angle of attack that is higher than normal
b. The airplane to stall at an angle of attack that is lower than normal
c. Drag factors so large that sufficient speed cannot be obtained for takeoff
d. Coefficient of drag to increase abruptly

Answer: b. The airplane to stall at an angle of attack that is lower than normal

See CL a curve

24. Recovery from a stall in any airplane becomes more difficult when its
a. Center of gravity moves aft
b. Center of gravity moves forward
c. Elevator trim is adjusted nose down
d. Rudder travel is improperly adjusted

Answer: Center of gravity moves aft

If CG at aft (tail heavy) – tail force cant do downwards

Higher moment (high distance of CP and CG) = mas mahirap macontrol

26. If airspeed is increased during a level turn, what action would be necessary to maintain altitude? The angle of attack
a. And angle of bank must be decreased
b. Must be increased or angle of bank decreased
c. Must be decreased or angle of bank increased
d. And angle of bank must be increased

Answer: c. Must be decreased or angle of bank increased

Va = Vs sqrt n L = V2 CL formula relations

40. If a single rotor helicopter is in forward horizontal flight, the angle of attack of the advancing blade is:
a. Equal to the retreating blade
b. More than the retreating blade
c. Less than the retreating blade

42. It is an airfoil-shaped attachment made of thin sheets of metal, plastic, or composite material. This mounts on the blade shanks and is primarily used to increase the flow of cooling air to the engine nacelle.
a. Slinger ring
c. Townend Ring
d. Collector ring

Which force is not present during gliding?
a. Thrust
b. Weight
c. Lift
d. Drag

Lift is the force that opposes the weight of an aircraft and keeps it in the air.

Compared with an oblique shock wave at the same Mach number, a normal shock wave has a:
a. Higher expansion
b. Smaller compression
c. Smaller expansion
d. Higher compression

Kaya malaki pagbaba sa Mach number
Compared to an oblique shock wave at the same Mach number, a normal shock wave has a higher compression, which means the flow is compressed more abruptly and the change in pressure and temperature is greater.

An aerodynamic effect whereby the nose of an aircraft tends to pitch downward as the airflow around the wing reaches supersonic speeds. CP moves aft at high speed.

It refers to the varying of wing chord using a uniform airfoil section
a. Airfoil Tapering
b. Planform Tapering
c. Section Tapering
d. Thickness Tapering

On what instance does negative pressure coefficient occur?
a. When local velocity is higher than freestream velocity
b. When the dynamic pressure is twice the pressure difference.
c. When the freestream velocity is higher than local velocity
d. When the local pressure is greater than freestream pressure.

Answer: a. When local velocity is higher

The minimum speed at which intentional engine failures are to be performed.

Higher induced angle of attack can be obtained by using
a. Lower taper ratio
b. Larger wing area
c. Higher wing aspect ratio
d. Lower wing aspect ratio

Answer: d. Lower wing aspect ratio

Refer to CL vs AR graph CL vs AOA – AR

When an airplane is at constant altitude bank, the stall speed will
a. Remain the same as the level flight condition.
b. Increase as the square of the load factor
c. Increase as the square root of the angle of bank
d. Decrease as the square root of the load factor

Answer: c. Va or Vs turn = Vs sqrt n

In what flight condition are torque effects more pronounced in a single-engine airplane?
a. Low airspeed, high power, high angle of attack.
b. Low airspeed, low power, low angle of attack.
c. High airspeed, high power, high angle of attack.
d. High airspeed, low power, high angle of attack.

Answer: a. Low airspeed, high power, high angle of attack.

Propeller is not generating as much thrust at low airspeed, so the torque effect is more noticeable. The high power also contributes to the torque effect, as the propeller is spinning faster and creating more torque. The high angle of attack further exacerbates the torque effect, as the downwash from the wing is pushing the propeller out of alignment with the engine.

When a blade flaps up, its CG will shift closer to the hub, giving the blade a tendency to?
a. Speed up
b. Slow down
c. Stop
d. Has no effect

Moment = FD When a blade flaps up, its CG will shift closer to the hub and will speed up. This is because the blade is now rotating in a smaller circle, so it needs to move faster to maintain the same angular momentum.

For the maneuvering performance of airplanes, it is advantageous to have the smallest r and the smallest w obtainable by
a. Have the highest load factor and the lowest possible velocity
b. Have the lowest load factor and the highest possible velocity.

Certainly! Here are the remaining items with their formatted questions and answers:

1. Increase in Air Viscosity:
• An increase in which of the following will result in an increase in air viscosity?
• A. Pressure
• B. Density
• C. Temperature
• D. Weight
2. True Airspeed (TAS):
• The true airspeed (TAS) is _.
• A. Higher than the speed of the undisturbed airstream about the aeroplane.
• B. Equal to the indicated airspeed (IAS) at ISA conditions and altitudes below sea level.
• C. Lower than the speed of the undisturbed airstream about the aeroplane.
• D. Lower than the indicated airspeed (IAS) at ISA conditions and altitudes below sea level.
• Answer: D. Lower than the indicated airspeed (IAS) at ISA conditions and altitudes below sea level.
3. Effect of Curved Deflecting Angles:
• Regarding curved deflecting angles, what happens to the vertical component of force as the angle of deflection increases? Assuming that all the other parameters remain constant.
• A. Increases
• B. Decreases
• C. No relationship
• D. Remains the same
4. Start of Flow Separation on Typical Aerofoil:
• Where on the surface of a typical aerofoil will flow separation normally start at high angles of attack?
• Answer: Upper side trailing edge.
5. NACA Airfoil Construction:
• NACA 4412 was used in the construction of the airfoil. Determine the chord (in inches) if the camber equals 9.12 cm.
• Answer: 89.76 inches (1 cm = 0.393701 inches).
6. Elliptical Planform Wing:
• An elliptical planform wing has a span of 12 m and a chord of 2 m. What is the induced drag coefficient when the lift coefficient is 0.8?
7. Identical Aeroplanes in Horizontal Steady Turns:
• Two identical aeroplanes A and B are flying horizontal steady turns. Further data are: Condition A W= 1500 kg Bank= 20 deg TAS= 130 kt Condition B W= 1500 kg Bank= 20 deg TAS= 200 kt Which of the following statements is correct?
• Answer: D. The rate of turn A is larger than the rate of Turn B.
8. Exterior View Change During Speed Decrease:
• How does the exterior view of an aircraft change when the trim is used during a speed decrease?
• Answer: D. The elevator is deflected upwards by means of a downwards deflected trimtab.
9. High-Speed Limitation:
• The maximum speed at which maximum elevator deflection up is allowed.
• Answer: C. The maximum speed at which maximum elevator deflection up is allowed.
10. Predicting Compressibility Effects:
• To be able to predict compressibility effects, you have to determine the _.
11. Oblique Shock Wave with Pressure Ratio:
• Consider an oblique shock wave with β = 35 deg and pressure ratio of P2/P1=3. What is the upstream Mach number?
12. Density Altitude Effect on IAS and TAS:
• Effect of high density altitude to IAS and TAS.
• Answer: Indicated airspeed (IAS) remains the same, the true airspeed (TAS) increases.
13. Incorrect Statement about Density Altitude:
• Which among the statements about Density Altitude is incorrect?
• Answer: D. None, all statements above are correct.
14. Shock Stall:
• Shock stall is _.
• Answer: Separation of the boundary layer behind the shock wave.
15. First Shockwaves in Straight and Level Flight:
• When the Mach number is slowly increased in straight and level flight, the first shockwaves will occur at _.
• Answer: B. At the wing root segment, upperside.
16. Symmetrical Airfoil Acceleration to Supersonic Speed:
• If a symmetrical aerofoil is accelerated from subsonic to supersonic speed, the center of lift will move _.
• Answer: C. Aft to the mid chord.
17. Fineness Ratio:
• Fineness ratio is _.
• Answer: Fuselage length / Max diameter.
• Upon which factor does wing loading during a level coordinated turn in smooth air depend?
• Answer: C. Angle of Bank.
19. Span-wise Component of Flow:
• The span-wise component of flow over the top surface of the wing flows _.
• Answer: A. From wing-tip to root.
20. Quarter-Chord Moment Coefficient for Cambered Airfoil:
• The quarter-chord moment coefficient for a cambered airfoil depends on _.
• Answer: B. The shape of the airfoil.
1. Predicting Compressibility Effects:
• To be able to predict compressibility effects, you have to determine the __.
2. Oblique Shock Wave with Given Parameters:
• Consider an oblique shock wave with β = 35 deg and pressure ratio of P2/P1=3. What is the upstream Mach number?
3. Density Altitude Effects on IAS and TAS:
• Effect of high density altitude on IAS and TAS.
• Answer: Indicated airspeed (IAS) remains the same, the true airspeed (TAS) increases.
4. Incorrect Statement about Density Altitude:
• Which among the statements about Density Altitude is incorrect?
• Answer: D. None, all statements above are correct.
5. Shock Stall:
• Shock stall is __.
• Answer: Separation of the boundary layer behind the shock wave.
6. First Occurrence of Shockwaves during Acceleration:
• When the Mach number is slowly increased in straight and level flight, the first shockwaves will occur __.
• Answer: B. At the wing root segment, upper side.
7. Effect of Symmetrical Aerofoil Acceleration:
• If a symmetrical aerofoil is accelerated from subsonic to supersonic speed, what will happen to the center of pressure?
• Answer: C. It will move aft.
8. Shock Wave Angle Calculation:
• Calculate the Mach angle for a Mach number of 2.5.