Performance III

Question 1

Define “Range.”

Answer 1

Total distance over the ground covered by the AC per unit fuel.

Question 2

Define “Endurance.”

Answer 2

Total time the AC can stay airborne per unit fuel.

Question 3

Define specific fuel consumption (SFC).

Answer 3

The weight of fuel consumed per unit power per unit time.

Question 4

To stay in the air the longest, we need to use ____per unit time.

Answer 4

The minimum number of pounds of fuel

Note: Also known as “minimum fuel burn per unit time.”

Question 5

The minimum fuel burn rate (lb fuel / hr) is attained when _______is at a minumim.

Answer 5

Horsepower required (hp_R)

Question 6

Minimum power occurs at the velocity where _____.

Answer 6

(CL^(3/2))/CD is at a maximum.

Question 7

The maximum endurance of the AC is when it is flying at _______.

Answer 7

Minimum power required.

Note: This also corresponds to the minimum fuel burn per unit time.

Question 8

To cover the longest distance (range), we must use the minimum ________per unit distance.

Answer 8

number of pounds of fuel burned (fuel burn)

(you need high fuel efficiency— low burn rate)

To fly a large distance you need a very fuel-efficient aircraft.

Question 9

The minimum number of pounds of fuel burned per mile occurs when.

Answer 9

The hp_R / V ratio is at a minimum.

Question 10

With respect to the V vs Pr curve, where is the max range point?

Answer 10

If a line is drawn from the origin to the tangency point, the max range lies at the tangent point.

Slide 6

Question 11

With respect to the V vs Pr curve, where is the max endurance point?

Answer 11

At the lowest part of the curve.

Slide 6

Question 12

What is the common manufacturer-provided unit for specific fuel consumption?

Answer 12

(lbs of fuel )/ (hp*hr)

Question 13

The product cPdt represents ______.

Answer 13

The differential change in weight of the AC due to the consumption of fuel over a short time interval dt.

Question 14

What do the following variables represent:
w0
w1
wf

Answer 14

w0 = gross weight of the AC
w1 = weight of the AC with no fuel
wf = weight of the fuel

Question 15

Does the following equation hold?

w1 = w0 + wf

Answer 15

Yes, the gross weight (w1) is the empty weight (w0) plus the weight of the fuel (wf).

Question 16

Does the following equation hold? If so, why is there a negative sign?
dt = -dW/(cP)

Answer 16

Yes, the equation holds.
As the aircraft flies it burns fuel consistent with the power of the engine multiplied by the specific fuel consumption (c). The negative is necessary to show that the weight of the aircraft decreases over time.

Question 17

True or False
The integral equations for range and endurance can be used for any phase of flight, including takeoff, climb, and cruise.

Answer 17

True

Question 18

What are the assumptions required to use the Breguet range and endurance formulas?

Answer 18

1. Engine efficiency, L/D, and c are constant.

2. No acceleration

Question 19

From the Breguet Formulas for a propeller-driven aircraft, what four items would maximize the range?

Answer 19

1. Largest possible prop (greatest prop efficiency)
2. Lowest possible specific fuel consumption (c)
3. The Highest ratio of w0/w1
4. Fly the aircraft at (L/D) max

Question 20

From the Breguet Formulas for a propeller-driven aircraft, what five items would maximize the endurance?

Answer 20

1. Highest prop efficiency (Nu_prop)
2. Lowest possible specific fuel consumption (c)
3. Highest fuel weight
4. Fly at CL^(3/2)/CD
5. Fly as close as possible to SLSC

Question 21

Aviation gasoline weights _______ lb/gal.

Answer 21

5.64

Question 22

For a jet aircraft, what is thrust-specific fuel consumption?

Answer 22

The weight of fuel burned per unit thrust per unit time.

c_t = (lb of fuel)/(T_lb * hours)

Question 23

When does max endurance occur for a jet aircraft?

Answer 23

When the aircraft is flying at a velocity that results in (L/D) max.

Question 24

For a jet, the minimum thrust required occurs when?

Answer 24

When the aircraft is flying at a velocity that results in (L/D) max.

Question 25

To get the max range in a jet, the fuel weight burn per unit distance needs to be _____.

Answer 25

At a minimum.

Question 26

For a jet aircraft, the minimum fuel burn rate per unit distance occurs with a minimum _______.

Answer 26

Thrust required / Velocity

Tr/V_infinity

Question 27

For minimum Tr/V, this corresponds to a maximum of what ratio?

Answer 27

C_L^(1/2) / C_D

Question 28

With respect to the lift and drag coefficients, the maximum range for a jet occurs when the plane is flying at a velocity so that _______ is a maximum.

Answer 28

C_L^(1/2) / C_D

Question 29

For maximum endurance in a jet AC, what three traits are most desirable?

Answer 29

1. Minimum thrust specific fuel consumption
2. Maximum fuel weight
3. Fly at L/D max

Question 30

For the maximum range in a jet aircraft, what four traits are most desirable?

Answer 30

1. Minimum thrust specific fuel consumption
2. Maximum fuel weight
3. Fly at C_L^(1/2) / C_D
4. Fly at as high an altitude as possible