Docstoc

Performance

Document Sample
Performance Powered By Docstoc
					Performance

  Chapter 5
  Lecture 10
               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.
         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.
               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
               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
           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
                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
          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
   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
   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
          Climb Performance
• The airplane’s 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
             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
               Power Curves
•   Figure 5-4 p. 120
•   Figure 5-5 p. 121
•   Figure 5-6 p. 122
•   Figure 5-7 p. 122
                Vx & Vy
• When do you use Vx & Vy?

• How are Vx & Vy different?

• Figure 5-8 p. 123
                    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
             Power Curves
• Figure 5-9 p. 124
• Figure 5-10 p. 125
• Figure 5-11 p. 125
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
  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
                    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
                Glide Ratio
• The ratio of horizontal to vertical distance
  for a given amount of altitude

• Glide distance= altitude x L/D
           Time & Distance
• Range

• Endurance

• Cruise Efficiency
   Quiz on Lecture 10
       Chapter 5
 Please take out a sheet of paper
Include today’s date & your name
         Quiz on Lecture 10
             Chapter 5
• Describe the back side of the power curve.

• Compare and contrast absolute ceiling and
  service ceiling.

• How do you determine glide distance?

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:10
posted:8/9/2012
language:
pages:23