Ch. 11 Aircraft Performance Flashcards
Standard Atmosphere
15 degrees Celsius (59 degrees Fahrenheit)
29.92 in Hg (1013.2 mb)
Standard lapse rate
Temperature decreases at the rate of approximately 3.5 degrees Fahrenheit or 2 degrees Celsius per thousand feet up to 36,000 ft MSL.
Above what altitude is temperature considered constant up to 80,000 feet MSL?
36,000 feet MSL.
Standard pressure lapse rate
Pressure decreases at a rate of 1”Hg per thousand feet of altitude gain to 10,000 feet.
Any temperature or pressure that differs from the standard lapse rate is considered:
Nonstandard temperature and/or pressure.
Height above the standard datum plane.
Pressure altitude
What is the standard datum plane?
A theoretical level at which the pressure of the atmosphere is 29.92”Hg.
What are two reasons pressure altitude is important?
- Basis for determining aircraft performance
2. Assigning flight levels to aircraft operating at or above 18,000 feet MSL.
What are the three ways of calculating the pressure altitude?
- Setting altimeter to 29.92”Hg and reading output.
- By applying a correction factor to the indicated altitude according to the reported altimeter setting.
- Using a flight computer.
The altitude in the standard atmosphere corresponding to a particular value of air density.
Density altitude
Pressure altitude corrected for nonstandard temperature.
Density altitude
As the density of the air increases (lower density altitude), aircraft performance:
Increases.
As air density decreases (higher density altitude), aircraft performance:
Decreases.
Under standard conditions, pressure altitude and density altitude identify:
The same level.
Air density is affected by changes in:
Altitude, temperature, and humidity.
How does density of air vary with temperature?
Inversely. As temperature goes up, density goes down and vice versa.
How does density of air vary with pressure?
Directly. As pressure increases so does density and vice versa.
In the atmosphere, both temperature and pressure decrease with altitude and have conflicting effects upon density. So for us pilots should we expect the density of air to increase or decrease with altitude? Why?
Expect the density to decrease with altitude. The fairly rapid drop in pressure as altitude is increased usually has the dominant effect on density.
Refers to the amount of water vapor contained in the atmosphere and is expressed as a percentage of the maximum amount of water vapor the air can hold.
Humidity or relative humidity.
The amount of water vapor that air can hold is based upon:
Temperature of the air.
The density of air increases or decreases with more humidity?
Decreases.
The ability of an aircraft to accomplish certain things that make it useful for certain purposes.
Performance
The various items of aircraft performance result from the combo of:
Aircraft and power plant characteristics.
The unaccelerated condition of flight is achieved with the aircraft trimmed and powerplant set for:
Lift equal to weight and thrust equal to drag.
Thrust is a:
Force
Power is a:
Measurement of the rate of performing work or transferring energy. (How much work, how fast)
Maximum angle of climb (AOC)
Maximum amount of altitude gain per horizontal distance traveled.
Max angle of climb occurs at the airspeed and AOA combination which allows the maximum excess:
Thrust.
Maximum rate of climb (ROC)
Maximum gain in altitude over a given period of time.
Maximum rate of climb occurs at an airspeed and AOA combination that produces the maximum excess:
Power.
As altitude is increased the max ROC, max AOC, maximum and minimum level flight airspeeds converge at what point?
The absolute ceiling of the aircraft.
Absolute ceiling
Altitude which produces zero ROC.
Service ceiling
Altitude which aircraft is unable to climb at rate greater than 100 fpm.
Total weight of aircraft divided by rated horsepower of engine. Expressed in pounds per horsepower.
Power loading
Total weight divided by wing area. Expressed as pounds per square foot.
Wing loading.
Why is power loading significant?
It is a significant factor in aircraft’s takeoff and climb capabilities.
Why is wing loading significant?
Determines landing speed.
Nautical miles of flying distance versus the amount of fuel consumed.
Specific range.
1/fuel flow
Specific endurance
If maximum endurance is required, the flight condition must provide a:
Minimum fuel flow.
Best endurance speed happens at what power setting?
Minimum power required.
If maximum specific range is desired, the flight condition must provide a:
Maximum of speed per fuel flow.
Where does the maximum speed per fuel flow occur in a propeller driven airplane?
At the L/Dmax. Best glide speed.
The values of specific range versus speed are affected by three principal variables. What are they?
- Aircraft gross weight
- Altitude
- The external aerodynamic configuration of the aircraft.
The control of the optimum airspeed, altitude, and power setting to maintain the 99% max specific range condition.
Cruise control.
Total range is dependent on both:
Fuel available and specific range.
In a propeller-driven aircraft the fuel flow is determined mainly by:
Shaft power put to the propeller rather than thrust.
Region of power curve that while holding a constant altitude, a higher airspeed requires a higher power setting and vice versa.
Region of normal command
Region of power curve while holding a constant altitude which a higher airspeed requires a lower power setting and vice versa.
Region of reversed command
Where does the airplane get into the region of reversed command?
Below the best endurance speed.
The speed at which the lowest brake horsepower sustains level flight.
Best endurance speed.
What formula relates our landing distance to the amount of energy our plane has when touching down?
Work energy formula.
Fd=0.5m*V^2
The amount of power that is applied to the brakes without skidding the tires is referred to as:
Braking effectiveness
A positive runway gradient means the runway is sloping
Upwards
A negative runway gradient means the runway is sloping:
Downwards
A condition in which the aircraft tires ride on a thin sheet of water rather than on the runway’s surface.
Dynamic hydroplaning.
Minimum speed at which hydroplaning begins formula.
9*SQRT(Main gear tire pressure)
Increased gross weight can be considered to produce a threefold effect on takeoff performance:
- Higher lift-off speed
- Greater mass to accelerate
- Increased retarding force (drag and ground friction)
The effect of a headwind is to allow the aircraft to reach the lift-off speed at a lower:
Groundspeed
The effect of a tailwind is to require the aircraft to achieve a greater:
Groundspeed to attain lift-off speed.
Does wind effect landing distance in the same way that it affects takeoff distance?
Yes.
An increase in density altitude can produce a twofold effect on takeoff performance:
- Greater takeoff speed
2. Decreased thrust and reduced net acceleration force
Regardless of density altitude the aircraft requires what two conditions to always be the same for takeoff?
- Dynamic pressure
2. Lift Coefficient
Does the indicated airspeed for takeoff change with altitude?
No. Indicated airspeed remains the same.
The minimum landing distance is obtained by landing at:
Some minimum safe speed
Landing is accomplished at some particular value of:
Lift coefficient and AOA.
The particular lift coefficient and AOA for landing are independent of:
Weight, altitude, and wind.
By creating a continuous peak deceleration of the aircraft; that is, extensive use of the brakes for maximum deceleration you can achieve:
Minimum landing distance
Considerable excess runway may allow extensive use of aerodynamic drag to minimize wear and tear on the tires and brakes. This results in what kind of landing roll?
Ordinary landing roll
The use of aerodynamic drag is applicable only for deceleration to:
60-70% of touchdown speed.
At speeds less than 60-70% of touchdown speed, aerodynamic drag is so slight as to be of little use. Therefore, how is deceleration continued?
Brakes.
One of the principal items determining the landing distance is:
Gross weight
One effect of an increased gross weight is that a greater speed is required to support the aircraft at the landing:
AOA and lift coefficient
Landing distance increases approximately by how much for every 1000’ altitude gain?
4% per 1000’ gain
Landing distance is proportional to velocity how?
Proportional to the square of velocity. A 10% increase in landing speed increases landing distance by 21%.
The most critical conditions of landing performance are combinations of what three things?
- High gross weight
- High density altitude
- Unfavorable wind
The speed of the aircraft in relation to the air mass in which it is flying.
True airspeed (TAS)
The speed of the aircraft as observed on the ASI. It is the airspeed without correction for indicator, position (or installation) and instrument errors. (Equal to TAS at sea level in standard atmosphere)
Calibrated airspeed
The ASI reading corrected for position (or installation), for instrument error, and for a diabetic compressible flow for the particular altitude. Equal to CAS at sea level in standard atmosphere.
Equivalent airspeed (EAS)
The calibrated power-off stalling speed or the minimum steady flight speed at which the aircraft is controllable in the landing configuration.
Vso
The calibrated power-off stalling speed or the minimum steady flight speed at which the aircraft is controllable in a specified configuration.
Vs1
The speed at which the aircraft obtains the maximum increase in altitude per unit time.
Vy
The speed at which the aircraft obtains the highest altitude in a given horizontal distance.
Vx
The maximum speed at which the aircraft can be safely flown with the landing gear extended. This is a problem involving stability and controllability.
Vle
The maximum speed at which the landing gear can be safely extended or retracted. This is a problem involving the air loads imposed on the operation mechanism during extension or retraction of the gear.
Vlo
The highest speed permissible with the wing flaps in a prescribed extended position. This is because of the air loads imposed on the structure of the flaps.
Vfe
The airspeed below which you can move a single flight control, one time, to its full deflection for one axis of airplane rotation (pitch, roll, yaw) in smooth air without risk of damage to the airplane.
Va
The maximum speed for normal operation or the maximum structural cruising speed. This is the speed at which exceeding the limit load factor may cause permanent deformation of the aircraft structure.
Vno
The speed that should never be exceeded. If flight is attempted above this speed, structural damage or structural failure may result.
Vne
Information the manufacturer provides on their performance charts has been gathered from:
Flight tests conducted in a new aircraft, under normal operating conditions while using average piloting skills, and with the aircraft and engine in good working order.
Should you compensate performance numbers if the aircraft or engine isn’t in good working order, or if the pilot flying doesn’t have average skill?
Yes.
Taking known information from performance charts and computing intermediate information.
Interpolating
When interpolating performance numbers that reflect slightly more adverse conditions provides what two things?
- A reasonable estimate of performance information.
2. Slight margin of safety.
Charts whose information is based on actual flight tests conducted in an aircraft of the same type.
Climb and cruise charts
