Performance And Limitations Flashcards
How is aircraft performance significantly affected as air becomes less dense?
As air becomes less dense…
- power reduces (less air intake)
- prop is less efficient
- lift reduces (air exerts less force)
What is standard atmosphere at seal level?
15C or 59F and 29.92Hg
Standard temp and pressure lapse rate.
Temp decreases at 3.5F or 2C per 1,000 ft up to 36,000, constant temp up to 80,000
Pressure decreases at 1in Hg per 1,000ft to 10,000 ft
Define pressure altitude
Height above standard datum plane. Altimeter set to 29.92Hg
Why is pressure altitude important?
Basis for determining airplane performance and assigning flight levels above 18,000
2 methods of determining pressure altitude?
Set altimeter to 29.92
Apply correction factor to reported altimeter setting
Define density altitude.
Pressure altitude corrected for non standard temperature
How does air density affect aircraft performance?
Performance increases as density increases. Performance decreases and density decreases.
An increase in air density means a lower density altitude
How is density altitude determined?
Find pressure altitude and correct for non standard temperature
What factors affect air density?
Conditions that result in high/low density altitude?
Air density is affected by changes in altitude, temperature, and humidity.
High density altitude refers to thin air while low density altitude refers to dense air
High density altitude- high elevation, low pressure, high temps, high humidity
Low density altitude- lower elevation, high pressure, low temps, low humidity
What effect does pressure have on air density?
Directly proportional
If pressure doubles, density doubles
This is only true at constant temperature
What effect does temperature have on density.
Inversely proportional
Increase in temp means decrease in density.
Only true with constant pressure
Since temperature and pressure decrease with altitude, how will air density be overall affected?
Density is likely to decrease with altitude gain. The fairly rapid drop in pressure with increasing altitude is usually the dominating factor.
What effect does humidity have on air density?
Water vapor is lighter than air. So moist air is lighter than dry air. As water content of air increases, air becomes less dense. Which increases density altitude and decreases performance. Humidity alone is not considered an important factor in calculating density altitude but it does contribute
Define relative humidity
Amount of water vapor in atmosphere
Varies with temp
Warm air holds more water vapor than cold
What effect does landing at high elevation airports have on ground speed
True airspeed is faster resulting in faster ground speed throughout approach, touchdown, and landing roll.
Which means greater distance to clear obstacles, longer ground roll therefore longer runway.
What are some main elements of aircraft performance?
Take off/landing distance Rate of climb Ceiling Payload Range Speed Maneuverability Stability Fuel economy
Relationship of lift, weight, thrust, drag in steady, unaccelerated flight?
Equal
Name and define 2 types of drag.
Induced drag: total drag created by production of lift. Greater with lower airspeed
Parasite drag: total drag created by form or shape of airplane parts. Greatest at high airspeed. Proportional to square of airspeed. If airspeed is doubles, parasitic drag is quadrupled
Define “service ceiling”
Max density altitude where the best rate if climb speed will produce 100 FPM climb at max weight in clean configuration with max power
Will an aircraft always be able to reach and maintain its service ceiling?
No. Depends On density altitude for any given Day
What is “absolute ceiling”
Altitude at which climb is no longer possible
What is “power loading” and “wing loading”?
Power loading: pounds per horsepower. Divide total weight by engine horsepower. Determines takeoff/landing capabilities
Wing loading: divide total weight by wing area sq ft. Determines landing speed.
Define max range and max endurance
Max range: max distance an airplane can fly for a given fuel supply.
Max endurance: max amount of time the airplane can fly for a given fuel supply.
What is ground effect?
Occurs due to the interference of the ground surface with the flow pattern about the airplane in flight. Aprx one wing span above surface.
What major problems can be caused by ground effect?
Landing: less drag so any excessive speed could cause significant float distance and loss of runway
Take off: less drag so aircraft may try to lift off prior to reach recommended takeoff speed but as it leaves ground effect with insufficient speed, it may loser ability to climb or fly at all.
What does “flight in the region of normal command” mean?
While holding constant altitude, higher airspeed requires higher power setting and lower airspeed requires lower power setting. Most airplane flying is conducted in the region of normal command
What does “flight in region of reversed command” mean?
A decrease in airspeed must be accomplished by en increase in power to maintain steady flight. This happens Jen the low speed phases of flight.
Example: low speed, high pitch, powered approach for short field landing
Soft field takeoff where pilot attempts to climb out of ground effect before attaining normal climb pitch and airspeed
Explain how runway surface and gradient affect performance
Runway surface: any surface that is not hard and smooth will increase take off ground roll.
Braking effectiveness: the amount of power that is applied to the brakes without skidding the tires
Runway gradient: slope. Positive gradient indicates the runway height increases and a negative gradient indicates a decrease. Upslope impedes acceleration and results in longer ground run during take off.
What factors affect performance of an aircraft during takeoff and landing?
Air density Surface wind Runway surface Upslope or downslope of runway Weight Power plant thrust
What effect does wind have on aircraft performance?
Takeoff landing cruise
Takeoff: headwind increases performance by shortening takeoff distance and increasing angle of climb, tailwind decreases performance by increasing takeoff distance and reducing angle of climb.
Landing: headwind increase performance by steepening approach angle and reducing landing distance. Tailwind decreases performance by decreasing approach angle and increasing landing distance
Cruise: winds aloft have opposite effect. Headwind decreases performance by reducing ground speed which increases fuel requirement. Tailwind increases performance by increasing ground speed which reduces fuel required
How does weight affect takeoff and landing performance?
Increased gross weight produces
- higher liftoff and landing speed required
- slow acceleration/deceleration
- increases drag and ground friction
- longer takeoff and ground roll
What effect does an increase in density altitude have on take off and landing performance?
- increases take off distance
- reduced rate of climb
- increases TAS on approach/landing
- increases landing roll
Define following V speeds
Vso Vsi Vy Vx Vle Vlo Vfe Va Vno Vne
Vso- power off stall speed or minimum steady flight at which airplane is controllable in landing configuration
Vsi- same ^ but in specified configuration
Vy- best rate of climb (max alt per time) fastest
Vx- best angle of climb (max alt per horizontal distance) furthest
Vle- max CAS with landing gear down
Vlo- max CAS at which landing gear can be safely extended or retracted
Vfe- max CAS with flaps extended
Va- design maneuvering speed. Max CAS at which limit load can be imposed without structural damage
Vno- max Structural cruising speed. Exceeding limit load factor may cause permanent damage
Vne- CAS that should never be exceeded.
At speeds below 200kts, how is TAS computed?
Correct CAS for pressure altitude and temperature
What performance characteristics will be adversely affected when an aircraft has been overloaded?
Higher takeoff speed Longer takeoff run Reduced rate/angle of climb Lower max altitude Shorter range Reduces cruise speed Reduced maneuverability Higher stalling speed Higher landing speed Longer landing roll Excessive weight in nose wheel
If weight and balance of an aircraft has changed due to addition or removal of fixed equipment, what responsibility does owner or operator have?
Ensure that maintenance personnel make appropriate entries in aircraft records. Weight changes must be accounted for. “Major Repairs and Alterations” form
Define “center of gravity”
Point at which the aircraft would balance if it were possible to support it at that point. The mass center.
What effect does a forward center of gravity have on flight characteristics?
Higher stall speed
Slower cruise speed
More stable
Great back pressure required
What effect does aft CG have on flight characteristics?
Lower stall speed
Higher cruise speed
Less stable.
Define the following…
Arm Basic empty weight (GAMA) Center of gravity limits CG range Datum Floor load limit Fuel load Licensed empty weight Max ramp weight Max weight Max zero fuel weight (GAMA) Mean aero dynamic chord Moment Moment index Payload (GAMA) Standard empty weight (GAMA) Station Useful load
Arm- horizontal distance in inches from reference datum line to CH of an item
Basic empty weight- standard empty weight plus optional and special equipment installed
CG limits- forward and aft points behind d which the CG must not be located
CG range- distance between CG limits
Datum- imaginary vertical line from which all arm measurements are taken
Floor load limit- max weight floor can sustain per square inch
Fuel load- only usable fuel.
Licenses empty weight- Airframe, engine, unusable fuel, undrainable oil plus standard and optional equipment installed
Max ramp weight- total loaded aircraft and al fuel. Greater than takeoff weight due to fuel burned during taxi
Max weight- max authorized weight of aircraft and all equipment
Max zero fuel weight- max weight excluding usable fuel
Mean aerodynamic chord- avg distance from leading edge to trailing edge of wing
Moment- product of the weight multiplied by arm
Moment index- moment divided by a constant like 100. Used to simplify weight and balance computations
Payload- weight of occupants, cargo, baggage
Standard empty weight- airframe, engines, all operating equipment permanently installed, hydronic fluid, unusable fuel, full oil
Station- location which is identified as a number designating its distance from datum in inches
Usable load- max weight of pilot, co pilot, pax, baggage, usable fuel, drainable oil. Empty weight subtracted from max allowable takeoff weight
How do you find CG?
Divide moment by weight
Explain the term percent of mean aerodynamic chord
Expression of CG relative to MAC. An aircraft will have acceptable flight characteristics if the CG is located near the 25% average chord point. The CG would be located one-fourth of the totally distance back from leading edge
Why would fuel economy be better or have better cruise with AFT CG?
The horizontal stabilizer requires less lift to keep the nose up. Less lift = less drag
Why would an AFT CG make the plane less stable?
The controls have less authority the further back the CG is.
