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Senior Design > CH3: Performance > Flashcards

CH3: Performance Flashcards

1
Q

For level, unaccelerated flight, the thrust required is simply equal to __________.

A

Drag.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 73

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2
Q

Plotting the thrust required as a function of velocity and observing the global minimum gives what important information?

A
  1. The airspeed at which L/D will be maximized.
  2. The approximate velocity for maximum endurance for a turbine-powered aircraft.

Fundamentals of Aircraft and Airship Design, Nicolai, 73

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3
Q

Explain the discrepancy between the magnitude of the Oswalt efficiency factor and the spanwise efficiency factor.

A

The spanwise efficiency factor only considers induced drag, while the Oswalt efficiency factor considers both the induced and parasite drag.

Mechanics of Flight, Phillips, Pg. 262

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4
Q

If the aircraft is flown at an airspeed such that the induced drag is equal to the parasitic drag at zero lift, the lift-to-drag ratio will be ___________.

A

At its maximum value.

Mechanics of Flight, Phillips, Pg. 264

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5
Q

True or False
For an aircraft at high altitudes (low ambient density) and high wing loading, the airspeed for max L/D will be slower than at a lower altitude.

A

False. The required airspeed will be faster under these circumstances.

Extra Notes: See Eq. (3.2.14) in the reference.

Mechanics of Flight, Phillips, Pg. 264

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6
Q

The maximum possible lift-to-drag ratio for a given aircraft is only a function of __________.

A

The aircraft’s design (geometry).

Mechanics of Flight, Phillips, Pg. 264

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7
Q

The maximum L/D ratio for a given aircraft can be increased by:
a) Decreasing parasite drag
b) Increasing the aspect ratio
c) Increasing the Oswalt efficiency factor
d) All the above.

A

d) All the above

Mechanics of Flight, Phillips, Pg. 265

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8
Q

The maximum L/D ratio for a given aircraft can be increased by:
a) Decreasing parasite drag
b) Increasing the aspect ratio
c) Increasing the Oswalt efficiency factor
d) All the above.

A

d) All the above

Mechanics of Flight, Phillips, Pg. 265

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9
Q

True or False
To completely minimize the thrust required, the thrust vector must be aligned with the direction of flight.

A

False. The thrust vector should be tilted upward slightly, at an angle equal to the arctangent of (1/(L/D)).

Mechanics of Flight, Phillips, Pg. 266

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10
Q

True or False
Like thrust required for steady level flight, the power required is a strong function of airspeed.

A

True.

Mechanics of Flight, Phillips, Pg. 270

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11
Q

The minimum power required for a given aircraft weight can be made smaller by:
a) decreasing parasite drag
b) Increasing the Oswalt efficiency and/or increasing the aspect ratio.
c) Increase wing loading
d) Decrease air density

A

a & b

Note: c and d would increase the power required. See Eq. (3.3.11) in the reference.

Mechanics of Flight, Phillips, Pg. 272

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12
Q

An aircraft with high wing loading will have a ________ power requirement than a different aircraft with a lower wing loading (all things held equal).

A

Higher

Mechanics of Flight, Phillips, Pg. 272

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13
Q

The minimum power airspeed and the minimum power required both increase with _________.

A

Altitude (a decrease in air density)

Mechanics of Flight, Phillips, Pg. 273

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14
Q

True or False
The lift on an aircraft in climbing flight is greater than the same aircraft in straight and level flight.

A

False. The lift for climbing flight is less than the lift for level flight (all other things held equal).

Mechanics of Flight, Phillips, Pg. 278

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15
Q

Define specific excess power (give the equation).

A

(Pa - Pr) / W
Pa = Power available
Pr = Power Required
W = Weight

Mechanics of Flight, Phillips, Pg. 279

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16
Q

How is the maximum airspeed at a constant altitude determined?

A

The airspeed at which the full throttle power available matches the required power.

Mechanics of Flight, Phillips, Pg. 279

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17
Q

As altitude increases, the power required __________, and power available ________.

A

Increases
Decreases

Mechanics of Flight, Phillips, Pg. 281

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18
Q

All things held equal, the rate of climb possible will ______ with altitude.

A

Decrease.

Mechanics of Flight, Phillips, Pg. 281

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19
Q

What is the difference between absolute and service ceilings?

A

The absolute ceiling is the altitude at which the available rate of climb is zero.

The service ceiling is the altitude at which the available rate of climb is ~ 100 ft/min.

Mechanics of Flight, Phillips, Pg. 281-282

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20
Q

Define aircraft “endurance.”

A

The total time an aircraft can stay aloft under its own power on a single tank of fuel.

Mechanics of Flight, Phillips, Pg. 287

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21
Q

True or False
In steady-level flight with no acceleration, the power available must equal the power required.

A

True.

Mechanics of Flight, Phillips, Pg. 288

22
Q

For flight at a constant altitude (constant density), how does the L/D curve vary as a function of airspeed?

A

L/D increases with airspeed to a global maximum, then decreases with increasing airspeed.

Extra Notes: See Fig. 3.2.2 in the reference.

Mechanics of Flight, Phillips, Pg. 263

23
Q

The global minimum on the Thrust Required vs. Airspeed curve will shift _________ on the plot as the density is increased.

A

Rightward.

Mechanics of Flight, Phillips, Pg. 265

24
Q

True or False
For flight in an airplane at a constant altitude (constant density), the power required at a large airspeed will be greater than the requirement at stall.

A

True. Lower airspeeds require a lower power requirement, all things held equal.

Extra Notes: See Fig. 3.3.1 in the reference. At a constant altitude, the power required increases parabolically with airspeed.

Mechanics of Flight, Phillips, Pg. 271

25
Q

True or False
The power required for a prop-driven aircraft is inversely proportional to the drag.

A

False.
Pr = DV

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 73

26
Q

True or False
On the velocity vs. Power Required curve, the velocity for L/D Max is slower than the speed for minimum power required.

A

False. The velocity for minimum Pr is less than that required for L/D max.

Extra Notes: See Fig. 3.3 in the reference.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 75

27
Q

What is the relationship between the drag due to lift and the parasite drag when flying at the minimum power airspeed?

A

The parasite drag is 1/3 of the drag due to lift when flying at this airspeed.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 77

28
Q

How does an increase in weight affect the velocity vs. thrust required (TR) curve?

A

It shifts the curve upward and slightly to the right. The result is a faster airspeed requirement for L/D max.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 78

29
Q

True or False
The location of the minimum point on the velocity vs. TR curve is invariant with altitude.

A

False
An increase in altitude (decrease in density) shifts the velocity vs. TR curve to the right. This forces the aircraft to fly faster and expend more fuel to reach the L/D max point.

Extra Notes: See Fig. 3.6 in the reference.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 79

30
Q

Explain why maximum endurance does not necessarily occur at the velocity for L/D max.

A

An aircraft’s endurance is a function of (L/D)(1/C), where C is the specific fuel consumption.

C is dependent upon Mach number and altitude, which can sometimes negate the max (L/D) to max endurance relationship.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 79 & 80

31
Q

True or False
The horsepower required for a prop-driven aircraft is directly proportional to the power required and inversely proportional to the propulsive efficiency.

A

True.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 82

32
Q

The maximum endurance for a reciprocating engine aircraft will occur at what power setting?

A

The minimum power required (Pr).

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 83

33
Q

Define “Specific range.”

A

The distance traveled per pound of fuel consumed.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 83

34
Q

The rate of change of the total energy of the aircraft is the rate at which an aircraft can _____________.

A

Climb and accelerate.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 91

35
Q

Define “energy maneuverability.”

A

The aircraft’s ability to change its energy state.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 91

36
Q

What is the physical analog of specific energy (what is it used to describe)?

A

The specific energy has units of feet and represents the theoretical height that an aircraft could reach if all of its kinetic energy were converted to potential energy.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 91

37
Q

A large value of specific power implies that the aircraft exhibits what characteristic?

A

It can rapidly accelerate.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 92

38
Q

What is the primary performance measure of an aircraft’s air-to-air combat effectiveness?

A

Turn rate performance.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 94

39
Q

The most efficient production of thrust is attained by using a large ______ and a small _______ increment.

A

Mass flow rate
velocity

Mechanics of Flight, W. Phillips, Pg. 155

40
Q

For low-speed subsonic flight, why is the prop the most efficient method of propulsion?

A

Because due to their relatively large diameters, the mass flow rate is large while the velocity change is relatively small.

Mechanics of Flight, W. Phillips, Pg. 155

41
Q

True or False
The thrust required is independent of wing loading.

A

True

Extra Notes: See Eq. 3.2.4 in the reference.

Mechanics of Flight, W. Phillips, Pg. 261

42
Q

The aircraft velocity required for minimum drag ______ with increasing wing loading.

A

increases

Extra Notes: See Eq. 3.2.14 in the reference

Mechanics of Flight, W. Phillips, Pg. 264

43
Q

Assuming a small thrust angle, an increase in wing loading will cause the power required at a given altitude to ______.

A

Increase.

Extra notes: See Eq. 3.3.4 in the reference

Mechanics of Flight, W. Phillips, Pg.

44
Q

The minimum power required for a given aircraft at a set altitude will _______ if the wing loading is increased.

A

increase

Extra Notes: See Eq. 3.3.11 in the reference

Mechanics of Flight, W. Phillips, Pg. 272

45
Q

Select the performance items that will increase for a corresponding increase in wing loading:
a) Thrust Required
b) Power Required
c) The airspeed for minimum power required

A

b and c

Mechanics of Flight, W. Phillips, Pg. 272

46
Q

For most aircraft flying at a constant altitude (constant density), the specific fuel consumption will _____ with increasing airspeed.

A

Decrease.

Extra Notes: See Fig. 3.5.3 in the reference

Mechanics of Flight, W. Phillips, Pg. 290

47
Q

As the gross weight of the aircraft increases, the maximum endurance airspeed will _____.

A

Increase.

Extra Notes: See Fig. 3.5.6 in the reference

Mechanics of Flight, W. Phillips, Pg. 291

48
Q

Define aircraft “range.”

A

The total distance that an aircraft can travel on a tank of gas.

Mechanics of Flight, W. Phillips, Pg. 295

49
Q

True or False
The range of the aircraft depends not only on the airspeed but also on the ground speed.

A

True

Mechanics of Flight, W. Phillips, Pg. 295

50
Q

The airspeed required for maximum range is ______ than that required for maximum endurance with the same engine performance and airframe configuration.

A

considerably higher

Mechanics of Flight, W. Phillips, Pg. 300

51
Q

The airspeed for minimum power required is always _______ the airspeed for minimum drag.

A

less than

Mechanics of Flight, W. Phillips, Pg. 301

52
Q

Why is wing loading so important to an aircraft designer?

A

The aspect ratio, Oswalt efficiency factor, CL/CLmax, and CD0 all have (relatively) set ranges of values they can take. Wing loading is the only design parameter that can be varied widely to control the design speed of a particular airplane.

Mechanics of Flight, W. Phillips, Pg. 318

Senior Design (13 decks)

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