Performance III Flashcards
Define “Range.”
Total distance over the ground covered by the AC per unit fuel.
Define “Endurance.”
Total time the AC can stay airborne per unit fuel.
Define specific fuel consumption (SFC).
The weight of fuel consumed per unit power per unit time.
To stay in the air the longest, we need to use ____per unit time.
The minimum number of pounds of fuel
Note: Also known as “minimum fuel burn per unit time.”
The minimum fuel burn rate (lb fuel / hr) is attained when _______is at a minumim.
Horsepower required (hp_R)
Minimum power occurs at the velocity where _____.
(CL^(3/2))/CD is at a maximum.
The maximum endurance of the AC is when it is flying at _______.
Minimum power required.
Note: This also corresponds to the minimum fuel burn per unit time.
To cover the longest distance (range), we must use the minimum ________per unit distance.
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.
The minimum number of pounds of fuel burned per mile occurs when.
The hp_R / V ratio is at a minimum.
With respect to the V vs Pr curve, where is the max range point?
If a line is drawn from the origin to the tangency point, the max range lies at the tangent point.
Slide 6
With respect to the V vs Pr curve, where is the max endurance point?
At the lowest part of the curve.
Slide 6
What is the common manufacturer-provided unit for specific fuel consumption?
(lbs of fuel )/ (hp*hr)
The product cPdt represents ______.
The differential change in weight of the AC due to the consumption of fuel over a short time interval dt.
What do the following variables represent:
w0
w1
wf
w0 = gross weight of the AC w1 = weight of the AC with no fuel wf = weight of the fuel
Does the following equation hold?
w1 = w0 + wf
Yes, the gross weight (w1) is the empty weight (w0) plus the weight of the fuel (wf).
Does the following equation hold? If so, why is there a negative sign?
dt = -dW/(cP)
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.
True or False
The integral equations for range and endurance can be used for any phase of flight, including takeoff, climb, and cruise.
True
What are the assumptions required to use the Breguet range and endurance formulas?
- Engine efficiency, L/D, and c are constant.
2. No acceleration
From the Breguet Formulas for a propeller-driven aircraft, what four items would maximize the range?
- Largest possible prop (greatest prop efficiency)
- Lowest possible specific fuel consumption (c)
- The Highest ratio of w0/w1
- Fly the aircraft at (L/D) max
From the Breguet Formulas for a propeller-driven aircraft, what five items would maximize the endurance?
- Highest prop efficiency (Nu_prop)
- Lowest possible specific fuel consumption (c)
- Highest fuel weight
- Fly at CL^(3/2)/CD
- Fly as close as possible to SLSC
Aviation gasoline weights _______ lb/gal.
5.64
For a jet aircraft, what is thrust-specific fuel consumption?
The weight of fuel burned per unit thrust per unit time.
c_t = (lb of fuel)/(T_lb * hours)
When does max endurance occur for a jet aircraft?
When the aircraft is flying at a velocity that results in (L/D) max.
For a jet, the minimum thrust required occurs when?
When the aircraft is flying at a velocity that results in (L/D) max.
To get the max range in a jet, the fuel weight burn per unit distance needs to be _____.
At a minimum.
For a jet aircraft, the minimum fuel burn rate per unit distance occurs with a minimum _______.
Thrust required / Velocity
Tr/V_infinity
For minimum Tr/V, this corresponds to a maximum of what ratio?
C_L^(1/2) / C_D
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.
C_L^(1/2) / C_D
For maximum endurance in a jet AC, what three traits are most desirable?
- Minimum thrust specific fuel consumption
- Maximum fuel weight
- Fly at L/D max
For the maximum range in a jet aircraft, what four traits are most desirable?
- Minimum thrust specific fuel consumption
- Maximum fuel weight
- Fly at C_L^(1/2) / C_D
- Fly at as high an altitude as possible
