Takeoff distance is calculated using performance charts, which can be found in your Pilot Operating Handbook/Airplane Flying Manual
Once calculated, cross-check the required takeoff distance against runways available to see what is or is not acceptable
Takeoff Distance Variables:
Gross Weight:
As gross weight increases, the difference between nose-wheel lift-off and takeoff speed decreases
When an instructor is not in the plane, the pitch attitude may differ
The aircraft will be airborne sooner, climb more rapidly, and have higher performance
Center of Gravity:
The farther forward the CG, the longer the takeoff roll
More authority is required to lift a heavy nose
This can be amplified with heavy takeoff weight
As CG moves forward, the difference between nose-wheel lift-off and takeoff speed decreases
Nose Strut:
If the nose-wheel is improperly serviced:
If the oil level is high, the springboard effect is reduced, but the change in shock absorber effect is minimal (strut compression on landing)
If the oil level is low, the reverse is true; springboard effect is essentially normal, but shock absorption is poor
Power Settings:
Applying power to quickly may yaw the aircraft to the left due to torque, most apparent in high-powered engines
Flight Profile Flown:
The Pilot Operating Handbook/Airplane Flight Manual will specify different configurations and procedures with which to fly
Flaps:
Flaps are considered high-lift devices
The use of flaps allows for the aircraft to create more lift on takeoff, allowing quicker rotation into the ground effect, and reducing takeoff distance
Aircraft must accelerate sufficiently in ground effect, however, before continuing a climb
When lowering flaps, you are changing the chord line, which increases the angle of attack (AoA)
This increase in AoA causes the aircraft's wing to suddenly create more lift, and therefore the aircraft will "balloon"
When lowering flaps, anticipate this balloon effect by being ready to lower the nose
Outside Air Temperature:
Temperature is a key variable 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:
The field elevation is irrelevant besides the fact that it correlates to starting at a higher density altitude
While density altitude can actually be lower than field elevation, an aircraft on that same day at a lower altitude would almost definitely experience a lower density altitude as well, barring any environmental phenomena
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 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 work with the motion of the aircraft to increase flow, while tailwinds push against the normal flow of air
As a result, with a headwind, the airplane already feels some airflow over the wings before it starts to roll, thereby generating lift faster and decreasing the takeoff roll
With a tailwind you would have increased speed to develop minimum lift, causing stress on tire, and increased takeoff distance
Tailwind impacts are often far more detrimental than many realize
They the increase runway distance required for takeoff
They also may decrease directional stability, particularly before control surfaces have the authority to counteract
Once an aircraft is airborne, the effect of winds change 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, taking off downhill allows for faster acceleration, resulting in a shorter takeoff roll
When available, runway slope data will be provided. Runway slope will be shown only when it is 0.3 percent or greater. On runways less than 8000 feet, the direction of the slope up will be indicated, e.g., 0.3% up NW. On runways 8000 feet or greater, the slope will be shown (up or down) on the runway end line, e.g., RWY 13: 0.3% up., RWY 31: Pole. Rgt tfc. 0.4% down
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:
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
It is possible that as 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, which results in total loss of braking action
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 if the wet runway is contaminated with a film of oil, dust, grease, rubber, or the runway is smooth
The contamination combines with the water and creates a more viscous (slippery) mixture
It should be noted that 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
With regards to rubber, 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
It is theorized that this condition would 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
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
Conditions:
Aircraft Weight: 2300lbs
Altitude: 3,000' MSL
20°C Outside Air Temperature
Chart:
[Figure 1]
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
Short Field Takeoff Performance
Soft-Field Takeoff and Climb
Abort Planning:
Consider how much distance is required to stop the aircraft from rotation speed
Based on stopping distance, pick a point on the runway as an abort point
Make the abort point part of takeoff checks to ensure it is not reached before obtaining the desired performance
Published vs. Realized Performance:
Although general aviation charts found in the POH/AFM do not consider every variable, it is important to have an understanding of the various conditions that may exist
If not published, the conditions were likely most ideal, with a new engine and 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
Climb Planning:
Climb Planning is necessary for several reasons, which include flight planning and obstacle clearance
Takeoff Performance Case Studies:
Climb Performance:
Climb performance is a measure of excess thrust, which generally increases lift to overcome other forces, such as weight and drag
This is true for most aircraft, although some high-performance aircraft can function like rockets for a limited time, utilizing thrust to lift away from the earth vertically, with no lift required
Excess power or thrust, terms that are incorrectly used interchangeably, allow for an aircraft to climb
Power vs. Thrust:
Power and thrust are not the same, despite their use as such
Power is a measure of output from the engine, while thrust is the force that actually moves the aircraft
In a piston aircraft, power is converted to thrust through the propeller
In a jet aircraft, the engine produces thrust directly from the engine
When you are moving the throttle controls inside of the aircraft, you're controlling the engine, and that is why they are referred to as power levers
Therefore, the best angle of climb (produces the best climb performance with relation to distance, occurs where the maximum thrust is available
The best rate occurs where the maximum power is available)
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
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
