Takeoff & Climb Performance

Takeoff Performance:

• Takeoff performance is critical to safely departing an airport and can vary daily due to various factors.

Factors Impacting Takeoff Distances:

• Pilot Operating Handbook/Airplane Flying Manuals include takeoff distance charts detailing the factors that impact takeoff performance.
• Factors include:
  • Gross Weight.
  • Center of Gravity.
  • Nose Strut.
  • Power Setting.
  • Flight Profile.
  • Outside Air Temperature.
  • Field Elevation/Density Altitude.
  • Surface Winds.
  • Runway Slope.
  • Runway Surface Condition.
  • Tire Pressure.
  • Wind Shear.
• Once calculated, cross-check the required takeoff distance against runways available to see what is or is not acceptable.

• Gross Weight:

  • Higher gross weights increase takeoff distance as the wings must generate more lift to achieve flight.
    • Takeoff performance, therefore, decreases, aircraft take longer to become airborne, and pitch attitudes decrease.
  • At lower gross weights, takeoff performance increases, causing aircraft to become airborne sooner, climb rapidly, and result in higher pitch attitudes.
    • Student pilots, in particular, will notice lower gross weights when the instructor is not in the aircraft.

• Center of Gravity:

  • The farther forward the CG, the longer the takeoff roll since more authority is required to lift a heavy nose.
    • Higher gross takeoff weights amplify the additional authority required.
  • The opposite is true for farther aft CGs, amplified with lower gross takeoff weights.

• Nose Strut:

  • High oil levels reduce the springboard effect, but the change in the shock absorber effect is minimal (strut compression during takeoff).
  • The reverse is true if the oil level is low; the springboard effect is essentially normal, but shock absorption is poor.

• Power Settings:

  • Applying power too quickly may yaw the aircraft to the left due to torque, most apparent in high-powered engines.

• Flight Profile:

  • The Pilot Operating Handbook/Airplane Flight Manual will specify different configurations and procedures with which to fly.

  • Flaps:

    • Flaps are considered high-lift devices.
    • Flaps allow the aircraft to create more lift on takeoff, allowing quicker rotation into the ground effect and reducing takeoff distance.
      • However, aircraft must accelerate sufficiently in ground effect before continuing a climb.
    • When raising flaps, you change the chord line, decreasing the angle of attack (AoA).
    • This decrease in AoA causes the aircraft's wing to suddenly create less lift, requiring the pitch decrease to maintain stall margin on climb.

• Outside Air Temperature:

  • Temperature is a key variable (among pressure and humidity) in determining density altitude.
  • As temperature rises, so does density altitude.
  • Conversely, density altitude drops with temperature.
  • Engine performance decreases with higher temperatures.

• Field Elevation/Density Altitude:

  • Higher field elevations correlate to starting at a higher density altitude (even if the density altitude is below the field elevation).
  • Higher density altitudes can result in higher engine operating temperatures (they're working harder to obtain performance) and longer takeoff rolls with longer abort rolls when applicable.
  • In some aircraft, maximum tire speed may also be a factor, as the aircraft needs to move faster to achieve the required performance.
  • Consider planning to the 70/50 rule for takeoff, whereby if you haven't achieved 70% of your rotation speed by 50% of the runway, you should abort.

• Surface Winds:

  • The winds impact how air flows over the wing of an aircraft.
  • Headwinds increase flow with the aircraft's motion, while tailwinds push against the normal airflow.
  • As a result, with a headwind, the airplane already feels some airflow over the wings before it starts to roll, generating lift faster and decreasing the takeoff roll.
  • With a tailwind, you would have increased speed to develop minimum lift, causing stress on the tire and increased takeoff distance.
  • Tailwind impacts are often far more detrimental than many realize.
    • Tailwinds increase the runway distance required for takeoff.
    • Tailwinds may decrease directional stability, particularly before control surfaces have the authority to counteract.
  • Once an aircraft is airborne, the effect of winds changes as the aircraft is moving relative to the airmass, not the ground.

• Runway Slope:

  • Airports are not perfectly flat, and they will have some variance in altitude from one end to another, especially at large airfields.
  • Much like when driving a car, moving an airplane uphill requires the engine to work harder to accelerate, which results in a longer time to reach rotation speeds, increasing takeoff roll.
  • Conversely, downhill takeoffs allow for faster acceleration, resulting in a shorter takeoff roll.
  • The FAA publishes airport slope data on the airport diagram or online at FAA.gov.
  • The runway slope is listed only when it is 0.3% or greater.
  • On runways less than 8000 feet, publications provide the slope and direction, e.g., 0.3% up NW.
  • On runways 8000 feet or greater, publications provide the slope (up or down) on the runway end line, e.g., RWY 13: 0.3% up. RWY 31: Pole. Rgt tfc. 0.4% down.
  • Consider adding 10% to your takeoff distance for each percentage of slope.

• Runway Surface Condition:

  • Conditions such as pavement, grass, gravel, water, snow, ice, and rubber slicks impact takeoff performance.
  • Runway surfaces are in the Chart Supplement, U.S.
  • Consider increasing margins for aborting takeoff to avoid losing control during an abort.

  • Snow, Ice, and Slush:

    • Snow, ice, and slushy conditions create a hazardous runway environment.
    • Consider utilizing soft field takeoff and landing procedures, minimizing opportunities to kick up hazards or lose control.

  • Hydroplaning:

    • Hydroplaning risk increases as the aircraft's speed increases and especially if executing a rejected takeoff procedure

    • Dynamic Hydroplaning:

      • Dynamic hydroplaning occurs when standing water on a wet runway is not displaced from under the tires fast enough to allow the tire to make pavement contact over its total footprint area.
      • The tire rides on a wedge of water under part of the tire surface.
      • It can be partial or total hydroplaning, meaning the tire is no longer in contact with the runway surface area.
      • If the tire breaks contact with the runway, the center of pressure in the tire footprint area could move forward.
      • At this point, total spin-down could occur, and the wheel stops rotating, resulting in total braking action loss.
      • The speed at which this happens is called minimum total hydroplaning speed.

    • Viscous Hydroplaning:

      • Viscous hydroplaning can cause complete loss of braking action at a lower speed.
      • Smooth runways or contamination, such as films of oil, dust, grease, or rubber, combined with water create a more viscous (slippery) mixture.
      • Viscous hydroplaning can occur with a water depth less than dynamic hydroplaning, and skidding can occur at lower speeds, like taxiing during light rain, applying the brakes, and rolling over an oil spill.
      • Consider that rubber is found primarily on the approach and departure end of the runway.

    • Rubber Reversion Hydroplaning:

      • Rubber reversion hydroplaning is less known and is caused by the friction-generated heat that produces superheated steam at high pressure in the tire footprint area.
      • The high temperature causes the rubber to revert to its uncured state and form a seal around the tire area that traps the high-pressure steam.
      • Rubber reversion hydroplaning can occur on damp runways or when touchdown occurs on an isolated damp spot of a dry runway, which results in no spin-up of the tires and a reverted rubber skid.

• Tire Pressure

  • Braking effectiveness is a factor of tire pressure.
  • Pressure also impacts the speed at which hydroplaning can occur.
  • Service the aircraft per the Pilot Operating Handbook.

• Wind Shear:

  • Wind shear is a wind speed and direction change over a short distance.
  • It can occur horizontally or vertically and is most often associated with strong temperature inversions or density gradients.
  • Four common sources of low-level wind shear are:
    • Frontal activity.
    • Thunderstorms.
    • Temperature inversions.
    • Surface obstructions.
  • Read more here.
  • If available, utilize information from Low-Level Wind Shear and Microburst Detection Systems.

• Aircraft Engine Age:

  • As aircraft engines age, their power available tends to decrease, resulting in reduced takeoff performance.

• Inoperative Equipment:

Calculating Takeoff Performance:

• FAR 91.103 mandates pilots be familiar with all available information concerning that flight, which includes takeoff performance
• Performance charts are contained in the Pilot Operating Handbook and generally consist of the following:
  • Normal (and crosswind) takeoff performance
  • Short-field takeoff performance
  • Soft-field takeoff performance

• Determining Normal & Crosswind Takeoff Performance:

  • 

  • Normal & Crosswind Takeoff Performance Conditions:

    • Pressure Altitude: 2,000 feet.
    • OAT: 22°C.
    • Takeoff Weight: 2,600 pounds.
    • Headwind: 6 knots.
    • Obstacle Height: 50-foot obstacle.

  • Normal and Crosswind Takeoff Performance Chart:

    • From the outside air temperature (at the surface), follow the chart until reaching the airport's pressure altitude.
    • From where the OAT intersects the airport's pressure altitude, move right to the beginning of the gross weight section and trace down the lines until intersecting the aircraft's gross takeoff weight.
    • Moving straight across, do the same for the headwind or tailwind components.

    • Crosswind Component Conditions:

      • Runway: 17 (170°)
      • Wind: 140° at 25 knots

    • Crosswind Component Chart:

      • 

      • The difference between runway and wind direction is 30° (170-140=30) at 25 knots.
      • Marking off the 30° point at 25 knots, draw a line straight across and straight down to determine headwind (or tailwind) and crosswind component.
      • In this example, the headwind component is 22°, and the crosswind component is 13°.
      • While the crosswind component may be relevant to aircraft limitations, if a correction is not specified in the PoH, it is not relevant to the performance calculation.

      • 

    • With the head/tailwind component traced (use 6 knots of headwind per original conditions), continue to the right of the chart and complete the same for any obstacles present.
    • For the given conditions, this normal takeoff requires ~800 feet of runway with no obstacles and 1,400 with obstacles (almost double!).

  • 

• Determining Short-Field Takeoff Performance:

  • 

  • Use the chart for all performance data specific to an aircraft, in this example, a Cessna 172.
  • Typically, there will be more than one chart for the same thing, separated by weight or aircraft configuration conditions.
  • Always round up if your weight is not close to the reference weights they provide; this is because takeoff data will never improve with weight, and therefore, your numbers will be more conservative and provide a safety margin.

  • Short-Field Takeoff Performance Conditions:

    • Aircraft Weight: 2300lbs.
    • Altitude: 3,000' MSL.
    • 20°C Outside Air Temperature.

  • Short-Field Takeoff Performance Chart:

    [Figure 4]

    • Starting at the left with the altitude, continue right across the chart until you reach the appropriate temperature.
    • We expect a 1,100' takeoff without obstacles and 1,970' with a 50' obstacle.
      • With a headwind of 9 knots, we can expect 990' takeoff without obstacles and 1,773' with a 50' obstacle.
      • With a tailwind of 4 knots, we can expect 1,320' takeoff without obstacles and 2,364' with a 50' obstacle.

  • 

• Determining Soft-Field Takeoff Performance:

  • Soft-field takeoff performance is calculated using a normal takeoff chart; however, corrections will apply
  • Check the notes for the chart and apply the appropriate correction.

• Determining Aborted/Rejected Takeoff Performance:

  • An aborted takeoff, also known as a rejected takeoff, is it's own deliberate procedure; however, all planning and decision points are detailed before ever walking to the aircraft.
  • Every takeoff could potentially result in a rejected takeoff (RTO) for a variety of reasons, including:
    • Engine failure.
    • Fire or smoke.
    • Foreign debris or unsuspected equipment on the runway.
    • Bird strikes.
    • Blown tires.
    • Direct instructions from the governing ATC authority, or.
    • Recognition of a significant abnormality (split-airspeed indications, activation of a warning horn, etc.).

  • Determining Accelerate-Stop Distance:

    • 

    • Many aircraft pilot operating handbooks, specifically twin-engine aircraft, publish accelerate-stop distance charts.
    • Accelerate-stop distance is the distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and abort the takeoff and bring the airplane to a stop using braking action only (use of thrust reversing is not considered)

    • 

Takeoff Performance Case Studies:

Climb Performance:

• For the initial climb, however, we are concerned with our aircraft's performance to escape the ground.
• Climb performance is a measure of excess thrust or power, which generally increases lift to overcome other forces, such as weight and drag.
  • Some high-performance aircraft can function like rockets for a limited time, utilizing thrust to lift away from the earth vertically, requiring no lift.
• Power and thrust are not the same, despite their incorrect use as such.

• Power vs. Thrust:

  • Power is a measure of output from the engine, while thrust is the force that moves the aircraft.
    • In a piston aircraft, power converts to thrust through the propeller.
    • In a jet aircraft, the engine produces thrust directly from the engine.
  • When moving the throttle controls inside the aircraft, cables control the engine; therefore, controlling engine power output is where the term power levers originate.
  • Aircraft angles and climb rates are due to excess power and thrust.

• Best Angle of Climb vs. Best Rate of Climb:

  • Certain conditions will call for a specific climb profile, generally the best rate (V_y) or angle (V_x) of climb.

  • Best Angle-of-Climb:

    • 

    • Max excess thrust results in the best angle of climb.
    • The best angle of climb occurs below L/D_max for a prop but at L/D_max for a jet [Figure 2]
    • The best angle of climb occurs below L/D_max for a prop.
    • Reduced distance to climb to the same altitude as V_y, but reaches that altitude slower

    • 

  • Best Rate-of-Climb:

    • 

    • The best rate of climb, or V_y, maximizes velocity to obtain the greatest gain in altitude over a given time.
    • It is the point where the largest power is available.
    • Pilots pitch for V_y when obstacles are not present or when cleared.
    • The best rate of climb occurs at L/D_max for a prop but above L/D_max for a jet [Figure 3]
    • The lower pitch provides more visibility over the cowling.
    • Increases airflow over the engine while at high power.
    • The best rate provides an additional buffer from stall speeds.
    • While V_y takes more distance to reach the same altitude as V_x, it will reach the desired altitude faster than V_x.

    • 

  • 

• Propulsion vs. Drag:

  • The relationship between propulsion and drag is such that it takes a certain amount of power/thrust to overcome drag both on the high end (the faster you go) and also on the low end (the slower you go)
  • This is noticeable during slow flight, where you find yourself adding extra power to overcome all the increases in drag that are necessary to sustain lift
  • If you fall "behind the power curve," however, you're in a position where you cannot generate immediate performance by simply increasing power
    • The increase in power must first overcome the increased drag, and then the expected performance will occur
  • You can learn more here: https://www.aopa.org/news-and-media/all-news/2013/november/pilot/proficiency-behind-the-power-curve

Factors Impacting Climb Performance:

• There are several factors which can impact climb performance:

  • Aircraft Weight:

    • One of the most basic considerations with regard to aircraft performance is weight, as it is a principle of flight.
    • The higher the weight of an aircraft, the more lift will be required to counteract.
    • Climb performance airspeeds are published at mass gross takeoff weight unless otherwise indicated.
      • V_y and V_x decrease by about 1 knot for each 100 pounds below mass gross takeoff weight.

  • Temperature:

    • Ambient air temperatures impact an aircraft's performance based on its physical properties.
    • Engines don't like to run hot; if they do, reducing throttle settings reduces temperature.
    • Temperature is also a leading factor in determining the effect of air density on climb performance.
    • Consider utilizing a cruise climb once practical to increase airflow over the engine.

  • Air Density:

    • Air density, specifically density altitude, is the altitude at which the aircraft "thinks" it is.
    • Performance does not depend on the physical altitude but rather the density altitude; the higher the temperature, the higher that altitude.
    • As the engine and airframe struggle to perform, expect changes to characteristics like a reduced climb attitude.
    • For each 1,000' increase in density altitude from sea level, V_y will reduce by 1%.
      • As a rule of thumb for GA aircraft, V_y decreases by 1 knot of indicated airspeed for each 1,000' increase in density altitude.
    • For each 1,000' increase in density altitude from sea level, V_x will increase by 0.5%.
      • As a rule of thumb for GA aircraft, V_x increases by 1 knot of indicated airspeed for each 2,000' increase in density altitude.

  • Winds:

    • Headwinds increase performance by allowing wind flow over the wings without any forward motion of the aircraft.
    • Tailwinds do the opposite.

  • Aircraft Condition:

    • Smooth, parasite-free wings produce the best lift.
    • Anything interrupting the smooth flow of air or increasing drag will require additional forward movement, or thrust, to overcome.

  • Icing:

    • Increased drag will require increased power and, therefore, may decrease climb performance during the climb.

  • Aircraft Engine Age:

    • As aircraft engines age, their power available tends to decrease, resulting in reduced climb performance.

Calculating Climb Performance:

• Determining Top-of-Climb:

  • 

  • Given:
    • Departure Airport: 900 ft
    • Cruise Altitude: 5,500 ft
  • From Sea Level to 5,500' we calculate 9 minutes, 2.0 Gal, 13 NM
  • Assuming 1,000' for the departure altitude we calculate: 1 minute, 0.4 Gal, 2 NM
  • Subtract the difference: (9-1)=8 Min, (2.0-0.4)=1.6 Gal, (13-2)=11 NM
  • Pay attention to the notes at the bottom of the chart, especially to add 1.1 Gal for taxi and takeoff
  • To add wind, calculate ground speed and use that distance instead

  • 

• Determining Climb Gradient:

  • Formula:

    • Climb Rate ÷ (Ground Speed (GS) ÷ 60)

  • Example:

    • Ground Speed = 75 knots
    • Climb Rate = 250 feet per minute

  • Calculate:

    • 250 ÷ (75 ÷ 60) = 200 feet per mile required

• Determining Rate-of-Climb Requirements:

  • Used to determine rate of climb for a given departure/climb out

    • Formula:

      • Ground Speed (GS) (knots) ÷ 60 * Climb Gradient (Feet Per Mile)

    • Example:

      • Ground Speed = 75 knots
      • Climb Gradient Required = 200 feet per mile

    • Calculate:

      • 75 ÷ 60 * 200 = 250 feet per minute climb rate required

Constant-Speed Propeller Climb Considerations:

• As an aircraft with a constant-speed propeller climbs, the manifold pressure decreases.
• Since the RPM is constant, an aircraft can exceed maximum power limitations and become "oversquared."
  • Oversquaring is when the manifold pressure is higher than RPM in hundreds of feet.
  • For example, RPM is 2500 in a climb, but the manifold pressure is 26" (vs. 25" or lower).
• Pilots must, therefore, decrease the throttle position with a decrease in RPM to maintain the pressure in hundreds of feet.
• The Airplane Flight Manual is the guiding document and may suggest an oversquared parameter.

Published vs. Realized Performance:

• Although general aviation charts found in the POH/AFM do not consider every variable, it is vital to understand the various conditions that may exist.
  • If not published, the conditions were likely ideal, with a new engine flown by an experienced test pilot.
  • It is highly recommended to add up to a 50% safety margin to any performance number before pushing the performance limits of an aircraft.

Conclusion:

• Note from the takeoff performance charts that as OAT, aircraft gross weight, tailwind, and obstacle height increase, so does the takeoff distance required
• Takeoffs are optional, but landings are mandatory
  • Make decisions early as to whether or not a takeoff under existing conditions is wise
• POH numbers require POH technique, which may not be the type of takeoff (normal, short, soft, etc.) which you plan to execute
• Takeoff distances per the book are performed under test conditions, and therefore, applying a margin of safety is recommended
  • Margins should be higher as more variables apply, such as more baggage, more passengers, etc.
• Pay attention to winds before takeoff - save tailwinds for cruise
• Pilots must be familiar with their aircraft's performance per Federal Aviation Regulations
• Climb performance is governed by FAR Part 23, depending on aircraft weight
• Pilots may always deviate from climb numbers for factors like cooling or the ability to locate and follow traffic
• Remember, when flying under instrument conditions, minimum climb gradients are expected unless a deviation is communicated and authorized as applicable
• Check out the AOPA's density altitude quiz
• Review your seaplane safety knowledge by taking the Air Safety Institute's "Invasive Species" quiz
• Still looking for something? Continue searching:

References:

• Bold Method - The 3 Types Of Hydroplaning, And How To Prevent Them
• Federal Aviation Administration - Pilot/Controller Glossary