- Predicting performance
- Your ability to predict the performance of an airplane is very important
- It allows you to
- Takeoff distance
- If you can safely clear obstacles in your departure path
- How long it will take to reach a destination
- Fuel requirements
- Landing distance
- Most of this information can be found in the POH
- Aircraft performance and design
- When developing performance charts, the manufacturer's make certain assumptions about conditions of the airplane and ability of the pilot
- The pilot
- Expected to follow normal checklist procedures
- Perform each of the required tasks correctly and at the appropriate time
- The airplane
- Assumed to be in good conditions, with a properly tuned engine and all systems operating normal
- With the aid of these assumptions, the manufacturers develop performance data based on actual flight tests
- Chart presentations
- All performance charts apply to specific aircraft's
- You should only refer to the aircraft's POH for the model you are going to fly
- Generally present their info in either table or graph format
- Table format
- Find row and column that most closely match the conditions, and read the value
- Graph format
- Has more variables built into it, making it faster and accurate
- Factors affecting performance
- Two main factors are weight and wind
- The heavier you are, the more lift you need → giving you less power for thrust
- Wind can help or also hinder performance
- Airplanes taking off or landing in strong wind have reduced ground roll
- In cruising flight, the groundspeed and time en route vary depending on the direction and speed of the wind
- Atmospheric conditions can decrease air density, Increasing the apparent altitude
- As pressure decreases, there are fewer air molecules in a given volume, so air density decreases
- When air is warm, it contains fewer air molecules than colder air
- Air containing water vapor is less dense than dry air
- Since aircraft performance decreases with altitude, it follows that decrease in air density due to temperature, pressure, or humidity will also reduce performance
- When the air is less dense, the wings must move thru the air faster to produce enough lift for takeoff
- Lower air density also reduces engine power, since the engine must take a larger amount of air for combustion
- Takeoff and landing performance
- Depends on several factors you can measure and calculate in advance such as
- Weight
- Wind
- Runway conditions
- Aircraft weight and configuration
- To generate sufficient lift for flight, a heavily loaded airplane must accelerate to a higher speed than the same airplane with a lighter load.
- Since the acceleration will also be slower, more runway will be needed
- You can see the effects of weight on the takeoff/landing distance chart
- Surface winds
- takeoff/landing distance can be influenced by direction and speed of wind
- Runway configurations
- Aircraft performance data generally specify a paved and level runway with a smooth dry surface
- If any of these conditions are different, you must adjust the takeoff/landing distance
- Climb performance
- The POH lists airspeeds for a variety of climbing flight conditions
- Two of the most important are best angle-of-climb airspeed(Vx) and the best rate-of-climb airspeed(Vy)
- Climbing speeds
- The Vx is usually used for obstacle clearance immediately after takeoff
- Should be used to gain the maximum amount of altitude in the minimum horizontal distance
- Vy is usually used after you cleared all obstacles during departure
- Gives the best altitude gain in a given time
- Cruise performance
- Manufacturers of light airplanes provide cruise performance charts to indicate rate of fuel consumption, true airspeed, range, and endurance.
- Must compensate for nonstandard conditions
- Using performance charts
- Charts are provided for determining takeoff, landing, climbing, and cruising information
- Importance of weight
- Almost every aspect of performance is influenced by weight of the aircraft and its content
- An overweight aircraft has a
- Longer takeoff run
- Higher takeoff speed
- Reduced angle and rate climb
- Reduced cruising speed
- Shorter range
- Higher stalling speed
- Longer landing roll
- Loading an aircraft too heavily can dangerously decrease its performance, and increase risk of structural damage if you encounter turbulence or make a hard landing
- Aircraft manufacturers do extensive testing to establish safe limits for aircraft loading
- Importance of balance
- You can check the balance conditions of an airplane by locating its center of gravity(CG)
- Imaginary point where the aircraft would balance if suspended
- The location of this point is critical for the aircraft's stability and elevator effectiveness
- Improper balance of the airplanes load can result in serious control problems
- You can avoid these problems by locating the CG before each flight and making sure it stays within limits
- Terminology
- Empty weight
- aircraft itself
- Avionics
- Unusable fuel
- Gross weight
- Sum of the empty weight and useful load
- Max gross weight
- Maximum allowed weight to fly
- Useful load
- People
- Cargo
- Fuel
- Payload
- Load that pays → passengers, cargo, baggage
- Ramp weight
- Airplane loaded for flight prior to engine start up
- Takeoff weight
- Maximum weight at which the pilot is allowed to attempt to take off
- Landing weight
- Maximum aircraft gross weight due to design or operational limitations at which an aircraft is permitted to land
- Center of gravity
- The theoretical point where the weight is concentrated
- CG moves when weight shifts
- Datum
- A fix from where measurements are taken
- Principles of weight and balance
- Arm of an object
- Horizontal distance from the datum to any point
- Total moment / total weight = total arm
- Moment of an arm
- Is the result of a multiplication made between an object and weight
- Force acting on an object weight from a distance
- Total moment
- All moments from an object added together
- Calculating the position of the CG
- Moment divided by weight
- Cg allowable range
- A range of position within an object where Cg is allowed
- Lateral
- Left or right of the vertical plane through the mast
- From nose to tail
- Left is “-“, right is “+”
- Longitudinal
- Forward or aft of the datum line
- Forward is “-“. aft is “+”
- Weight and balance management
- Adding/ subtracting objects changes the weight and balance calculations
- Cg change of an object
- Change of equip. , payload, fuel, changes the cg of the aircraft
- During flight, fuel is consumed, passengers are dropped, cg will shift
- Computation method
- Multiply weight and arm to get moment
- Add weights and moments
- Divide total moment by total weight
- Table method
- Uses a series of tables provided by the manufacturer to eliminate the multiplication and division
- Moment table provided for each of the most common payload areas
- Front seat
- Rear seat
- Usable fuel
- Baggage area
- The manufacturer has taken many weights and multiplied them by the arm for that location
- Graph method
- Allows you to use values between increments published in a table
- Loading graph used to find the moment for the loads you intend to put into the airplane
- CG moment envelope tells you if your proposed loading is within the weight and balance limits
- Weight-shift formula
- Weight moved/weight of airplane = distance CG moved/ distance between arms
- Effects of operating at high total weights
- Wing must fly faster or at higher AoA to generate additional lift
- Takeoff roll is longer - landing distance is longer
- Angle and rate of climb is reduced
- In cruise, range is reduced and speed is lowered at any given power setting
- Closer to stalling angle, and stalls at higher speed
- Flight at various CG positions
Flight computers
- Mechanical flight computers
- Flight planning and enroute navigation require solutions to several different types of mathematical problems
- The mechanical flight computer makes these common calculations easier
- Has two sides
- Computer side
- For ratio type problems, such as time, speed, distance, fuel, conversions
- Wind side
- For wind drift calculations
- Time, speed, and distance
- If you have two variables , you can find the third
- A scale is for distance, B scale represents time in minutes
- Speed index always points to the speed
- Airspeed and density altitude computations
- As air density decreases, indicated airspeed will be lower than true airspeed by about 2% per 1000 feet of altitude
- Use windows marked with pressure altitude/temperature
- For TAS calculation, use the scale on the right of the DA window
- To calculate DA, use the same scale, and set the pressure altitude opposite the OAT, read the DA in the center window
- Wind problems
- Correcting for wind drift
- Pointing the nose slightly towards the wind will keep you on course
- Conversions
- Multi-part problems
- Sometimes you may have to solve a series of related problems to to obtain a particular solution
- Example: to find the fuel required for a proposed flight, you must first find the true airspeed, then ground speed and time enroute, then fuel required
- Electronic flight computers
