The Cruise

Question 1

Max time in the air

Answer 1

Endurance

Question 2

Range

Answer 2

Min fuel per distance

Question 3

Max S+L speed for a prop

Answer 3

Where the Pr meets the Pa curves

Question 4

For a jet, max S+L speeds for both TAS and CAS

Answer 4

TAS - increases with altitude

CAS - remains constant with altitude

Question 5

SAR

Answer 5

Specific air range, relative to the air

= NAM/KG

=TAS/thrust x SFC

As thrust = drag in the cruise it can also be written

=TAS/drag x SFC or = TAS/drag

Question 6

SGR

Answer 6

Specific ground range

= NGM/kg

Question 7

FF for a jet and prop are based on

Answer 7

Prop - power

Jet - thrust

Question 8

Jet FF

Answer 8

=Thrust x SFC

Question 9

Difference in efficiency characteristics between jet and prop

Answer 9

Jet - compresses the air so it is more efficient at alt where the air is colder

Piston prop - less efficient at alt due to lesser molecules

Turbo prop - jet and prop so it is more efficient at mid alt due to them leveling out

Question 10

Design RPM

Answer 10

Where they design the engine to be the most efficient

90 - 95% RPM

Question 11

Vmr for a jet

Answer 11

Best TAS to drag ratio - SR = TAS/drag

Tangent to the drag curve = 1.32 Vmd

Indicated speed

Question 12

Optimum altitude

Answer 12

At a high alt where the Vmr and the 90-95% RPM meet

Question 13

SAR for a prop

Answer 13

=TAS/Pr x SFC

Or

=TAS/Pr

Question 14

Vmr for a prop

Answer 14

Tangent to the Pr curve

At Vmd

Question 15

Long range cruise (Mmlc)

Answer 15

Mmr x 1.04

Flying 4% faster will reduce range by 1% but we can save time for a small fuel penalty

Question 16

Cost index

Answer 16

Ratio between revenue and operating costs

0 = most efficient = 1.32vmd

If operating costs are reduced we can fly faster and reach the dest quicker

Question 17

When to fly at endurance

Answer 17

Rescue duties or holding as we want to stay in the air for the most amount of time

Question 18

Endurance for a jet

Answer 18

= 1/thrust x SFC or 1/drag x TAS (1/FF)

So min drag = min FF

Higher than the max range height due to flying at vmd which requires less thrust than 1.32 vmd

Question 19

Endurance for a prop

Answer 19

= 1/Pr x SFC

Increase in alt - Pr moves along the its tangent = endurance will be lower than its range alt §

Question 20

Effect of wind on endurance

Answer 20

Has no effect