Performance

1
Performance

• Chapter 5
• Lecture 10

2
Performance

• What does performance mean?
• What determines performance?
• How fast will it climb, how quickly will it take
  off, land, or how far will it go.

3
Level of Performance

• Airframe- in-flight performance depends on its
  drag characteristics.
• Remember power is required to move something a
  specific distance per unit or time.
• Power is a force times velocity
• Power required at any given velocity is
  determined by multiplying the drag times velocity.

4
Power Curve

• Plotting power drag a curve appears
• This is the power required curve or the power
  curve
• The power curve has nothing to do with the engine
• The curve is simply the drag curve replotted in
  terms of drag
• The term power required refers to the power
  required for level flight

5
Power Curve

• Figure 5-1 p. 116
• A power required curve for an airplane that
  indicates 200kts to fly, with a 160hp required
• Remember that the rating is given in the brake
  horsepower output of the engine
• The actual power available for thrust is
  determined by multiplying bhp x prop. efficiency

6
Figure 5-2 p. 117

• The dotted line 200 horsepower, the max. bph of
  the 200 horsepower engine
• Not all 200 horsepower overcame drag
• The amount available is the thp, which is the bhp
  x prop efficiency
• Prop efficiency is always less than one, so thp
  is always less than bhp

7
Efficiency

• The efficiency is usually greatest in cruise
  decreases at lower speeds
• Where the power available and the power required
  curves cross is the max level flight speed
• Above that speed more power is required than is
  available

8
Figure 5-3 p. 118

• Power curves showing max power available 75
  power
• Sustaining the speed demands the required amount
  of power being delivered
• Below that speed, increasingly more power is
  required to sustain level flight

9
Back side of the power curve

• The curve changes direction and curls up on the
  low speed side of the speed range
• This effect is due to increased induced drag in
  this region results in a reversed trend in
  power requirement with airspeed

10
Back side of the power curve

• The back side of the power curve is usually very
  short due to minimum power speed is low
• Many airplanes stall before reaching that slow
  speed

11
Climb Performance

• The airplanes ability to climb is also
  determined by the power curve
• Excess power is not used in level flight but is
  used in a climb
• Excess power is also called power differential

12
Excess Power

• The rate of climb at any speed is proportional to
  the amount of excess power
• This is inversely proportional to weight
• Figure 5-4 shows the power required curve the
  maximum power available curve with max power

13
Power Curves

• Figure 5-4 p. 120
• Figure 5-5 p. 121
• Figure 5-6 p. 122
• Figure 5-7 p. 122

14
Vx Vy

• When do you use Vx Vy?
• How are Vx Vy different?
• Figure 5-8 p. 123

15
Terms

• Calibrated Airspeed
• Ceiling
• No more excess power climbing ability is zero
• Absolute Ceiling
• Point where the curves touch is required for
  level flight
• Service Ceiling
• Rate of climb is only 100fpm

16
Power Curves

• Figure 5-9 p. 124
• Figure 5-10 p. 125
• Figure 5-11 p. 125

17
Twin Engine Climb Performance

• The power required is divided into two engines
• Figure 5-13 p. 127
• Twin that looses 50 looses up to 80 of
  performance and up to 90 of climb rate
• This is due to loss of power, asymmetric thrust
  adds to drag climbing even harder

18
Descent Glide Performance

• When there is a negative difference in power we
  get a negative climb rate
• Sinking and the resulting vertical velocity is
  called rate of sink
• Minimum rate of sink does not necessarily mean
  the best overall glide performance.
• At a very low airspeed, the aircraft is moving
  slowly at minimum sink speed

19
Glide

• The maximum glide distance would be obtained at
  the minimum ratio of rate of sink to forward
  speed
• This speed corresponds to the point were power
  velocity touch
• This is best glide speed
• Figure 5-16 p. 130

20
Glide Ratio

• The ratio of horizontal to vertical distance for
  a given amount of altitude
• Glide distance altitude x L/D

21
Time Distance

• Range
• Endurance
• Cruise Efficiency

22
Quiz on Lecture 10Chapter 5

• Please take out a sheet of paper
• Include todays date your name

23
Quiz on Lecture 10Chapter 5

• Describe the back side of the power curve.
• Compare and contrast absolute ceiling and service
  ceiling.
• How do you determine glide distance?