Cruise Power And Performance

Question 1

Four forces of flight

Answer 1

All OPPOSING forces are equal in unaccelerated straight and level flight.
Thrust is the force that pushes our aircraft forward.
Normal piston engines don’t create thrust by themselves.
They create power more specifically known as Brake horsepower (BHP).
They need the help of a propeller to turn that power into thrust.
These terms are used interchangeably but it’s important to distinct between the two.

Question 2

Power and power curve

Answer 2

Power required = Thrust required x airspeed since power is work /time
“Power is the force required to move something a specific distance per unit of time”
Power required = Thrust required x airspeed since power is work /time

Question 3

Range

Answer 3

The maximum distance an aircraft can fly from takeoff to landing

Question 4

Endurance

Answer 4

The maximum time an aircraft can spend aloft from takeoff to landing.

Question 5

What factors affects range and endurance?

Answer 5

1.Altitude
2.Weight
3.Configuration

Question 6

Cruise speeds

Answer 6

Higher power settings = high cruise speed + more fuel burn + less range
Lower power settings = better economy + longer range + slower cruise speed
There are many different ways to get the best possible combination. It is up to the pilot on what they actually want from their aircraft.

Question 7

Cruise efficiency

Answer 7

You can run the engine at max power all day and be fine but that isn’t the best for most piston engines if they were run at that power setting.
Manufacturers recommend between 55% - 75% of rated BHP as a max.

Question 8

Cruise optimum speed

Answer 8

Dr. Bernard Carson at U.S. Naval academy wanted to find a similar speed to max L/D but just at a higher speed. Instead of producing the minimum fuel per mile traveled he wanted to find the minimum fuel per unit of speed (knot). This is known as max V/D.

Even though cruise optimum isn’t the most “optimum” speed for best range. It is the best increase in airspeed for more excess fuel consumption.
Carson refers to it as, “the least wasteful way of wasting fuel”

Question 9

Region of reverse command

Answer 9

The slower your go below Vbe (best endurance/minimum power required) the more power that is required.
Slower below Vbe = More power due to induced drag increasing.
Pitch for airspeed and power for altitude

Question 10

Effects of CG

Answer 10

More aft CG = Higher TAS
More forward = lower TAS
This is due to less tail down force required at more aft CGs to maintain equilibrium in steady flight.