Performance and Limitations Flashcards
How is aircraft performance significantly affected as air becomes less dense?
Reduces:
Power as the engine takes in less air
Thurst because the propeller is less efficient
Lift because thin air exerts less force on airfoils
What is the standard atmosphere at sea level?
15C or 59F
29.92”Hg or 1013.2mb
What are standard atmosphere temperature and pressure lapse rate?
2C per 1,000 ft up to 36,000 ft and considered constant up to 80,000 ft
1 “Hg per 1,000 ft up to 10,000 ft
Define the term pressure altitude
Height above standard datum plane (Standard); set barometer to 29.92 to indicate pressure altitude
Why is pressure altitude important?
Used as basis for determining airplane performance as well as assigning flight levels
What are three methods of determining pressure altitude?
Setting the altimeter to 29.92 and reading the indicated altitude
Applying a correction factor to the indicated altitude according to the reported altimeter setting
Using a flight computer
Define the term density altitude
Pressure altitude corrected for nonstandard temperature
How does air density affect aircraft performance?
The denser the air (lower density altitude) the better the airplane performers or vice versa
How is density altitude determined?
Find the pressure altitude then correct it for nonstandard temperature
What factors affect air density?
Altitude, temperature, humidity
What effect does atmospheric pressure have on air density?
Directly proportional to pressure (assuming constant temperature)
What effect does temperature have on air density?
Inverse relationship (assuming constant pressure)
Since temperature and pressure decrease with altitude, how will air density be affected overall?
While temperature and pressure have an inverse relationship with each other the drop in pressure is a much greater factor therefore density typically decreases with altitude gain
What effect does humidity have on air density?
Water vapor is lighter than air therefore moist air is lighter than dry air which means the higher the humidity the higher the density altitude is (less dense); typically, this is not a major factor but it is still a factor nonetheless
What is the definition of relative humidity?
The amount of water vapor the atmosphere (air) can hold expressed in a percentage; this amount varies with temperature
What effect does landing at high elevation airports have on ground speed with comparable conditions relative to temperature, wind and airplane weight?
TAS is faster therefore ground speed is faster throughout all phases of flight
What are some of the main elements of aircraft performance?
T/O and landing distance
Rate of climb
Ceiling
Payload
Range
Speed
Manuverability
Stability
Fuel economy
What is the relationship of lift, weight, thrust, and drag in steady, unaccelerated, level flight?
All forces are equal
What are the two types of drag?
Induced (generated from lift)
Parasitic (“friction” of aircraft surfaces)
Define induced drag
Created by the production of lift; more left more drag
Define parasite drag
Caused by the friction of air moving over the aircraft structure; varies directly with airspeed
Note: Three types - form, interference, skin friction
How much will drag increase as airplane speed increases?
Squared
Climb performance is a result of using the aircraft’s potential energy provided by one, or a combination of two, factors. What are those two factors?
Excess power above that required to sustain level flight
Use of the aircraft kinetic energy
Define the term service ceiling
Maximum density altitude where the best rate of climb airspeed will produce a 100 fpm climb at maximum weight in a clean configuration with maximum power
Will an aircraft always be capable of climbing to and maintain its service ceiling?
No; depends on density altitude
Note: Will always reach its equivalent density altitude service ceiling
What is the definition of absolute ceiling?
Altitude at which a clim bis no longer possible
What is meant by the terms power loading and wing loading?
Power loading - Weight divided by hp (lbs/hp); used for takeoff and climb capabilities
Wing loading - Weight divided by wing area (lbs/sq2); used to determine landing speed
Define the terms maximum range and maximum endurance
Maximum range - Max distance airplane can fly for a given amount of fuel using the best lift/drag ratio
Maximum endurance - Max amount of time an airplane can fly for a given amount of fuel using the least amount of power necessary to maintain level flight
In the event of an engine failure, what airpseed should you use to achieve the most distance forward for each foot of altitude lost?
Best glide ratio which is also the best lift/drag ratio
What is ground effect?
Reduction of drag (increase performance) due to the interference of the ground; typically within one wingspan of the aircraft
What major problems can be caused by ground effect?
Landing - Excess speed may result in significant float
Takeoff - Rotation before Vr which means the aircraft is not producing enough lift to start a climb
What is flight in the region of normal command?
Power for altitude, pitch for speed
What is flight in the region of reversed command?
Pitch for altitude, power for speed
What are examples of where an airplane would be operating in the region of reversed command?
Short field (low airspeed, high pitch attitude)
Soft field take off and climb
Explain how runway surface and gradient affect performance
Runway surface - If not hard and smooth increase forces acting against aircraft therefore longer ground roll
Braking effectiveness - See above
Runway gradient or slope - Upslope reduces acceleration but increases braking and the opposite for downsloping runway
What factors affect the performance of aircraft during takeoffs and landings?
Air density (density altitude)
Surface wind
Runway surface
Upslope or downslope
Weight
Powerplant
What effect does wind have on aircraft performance?
Takeoff - Headwind greater lift generated and vice versa for tailwind
Landing - Headwind greater performance at lower air speeds thereby increasing approach angle and lowering landing distance, opposite for tailwind
Cruise - Headwind slower ground speed and vice versa for tailwind
How does weight affect takeoff and landing performance?
Weight direction proportional to total inertia which requires more forces to overcome
What effect does an increase in density altitude have on takeoff and landing performance?
Results in overall reduction in performance
Increased takeoff distance
Reduced rate of climb
Increased TAS on approach and landing
Planning for a rejected takeoff is essential to the safety of every flight. What calculation must be made prior to every takeoff?
Have a point in mind at which the airplane should be airborne and reject the takeoff immediately if past that point
Why does the manufacturer provide various manifold pressure/prop settings for a given power output?
Gives pilot a choice between the aircraft at best efficiency or best power/speed
What does the term 75 percent brake horsepower mean?
75% of the engine’s HP available at sea level on a standard day
Explain how 75 percent BHP can be obtained from your engine
Set the throttle (manifold pressure) and propeller (rpm) to the recommended values found in the performance chart of the POH
When would a pilot lean a normally aspirated direct drive engine?
Any time power is 75% or less
High altitude airports
When density altitude is high (hot, hight, humid)
Landings at airports below 5,000 ft density altitude
Consult POH for recommended procedure
What are the different methods available for leaning aircraft engines?
Tach method - Leaned until rpm drops from peak rpm
Fuel flowmeter method - Lean to the publish (POH) or marked fuel flow
EGT method - Lean mixture to peak EGT then enrich down by 50 degrees
Explain the difference between the best glide speed and minimum sink speed
Best glide - provides the greatest forward distance for a given loss of altitude
Minimum sink speed - Maximize the time the airplane remains in flight (losing altitude at the lowest rate); not often published but generally a few knots less than best glide
Define the following airplane performance speeds
VS0 - Stall speed or minimum flight speed in landing configuration
VS1 - Stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration
VY - Best rate of climb
VX - Best angle of climb
VLE - Max landing gear extended speed
VLO - Max landing gear operating speed
VFE - Max flaps extension speed
VA - Manuvering speed
VNO - Max structural cruising speed
VNE - Never exceed speed
How man miles can you glide in your aircraft per 1,000 feet of altitude lost?
Rule of thumb for 152 and 172s is 1.5 NM per 1,000 ft
What performance charactertistics will be adversely affected when an aircraft has been overloaded?
Less overall performance
If the weight and balance of an aircraft has changed due to the addition or removal of fixed equipment in the aircraft, what responsibility does the owner or operator have?
Ensure appropriate entries are made in the weight and balance records; FAA Form 337, “Major Repairs and Alternations”
Define center of gravity (CG)
The point about which an aircraft weight would balance on
What effect does a forward center of gravity have on an aircraft’s flight characteristics?
Higher stall speed - Increased wing loading, higher AOA therefore closer to the critical AOA
Slower cruise speed - Increased drag, greater AOA to maintain altitude
More stable - CG forward of CL which increases longitudinal stability, elevator more effective
Great back elevator pressure required - Longer takeoff roll, higher approach speeds and problems with flaring
What effect does an aft center of gravity have on an aircraft’s flight characteristics?
Lower stall speed - Less wing loading, less AOA therefore reaching stalling AOA is achieved at lower speeds
Higher cruise speed - Reduced drag, lower AOA needed
Less stable - Stall and spin recovery more difficult, elevator less effective
Will the center of gravity be forward or aft of the center of pressure?
Foreward; designers fix CG in front of CL to maintain a pitch down tendency
Define the following:
Arm
Basic empty weight
Center of gravity
Center of gravity limits
Center of gravity range
Datum
Floor load limit
Fuel load
Licensed empty weight
Maximum landing weight
Maximum ramp weight
Maximum takeoff weight
Maximum weight
Maximum zero fuel weight
Mean aerodynamic chord
Moment
Moment index
Payload
Standard empty weight
Station
Useful load
Arm - horizontal distance from the reference datum line to CG of an item
Basic empty weight - Standard empty weight plus optional equipment
Center of gravity - Point about which the aircraft would balance if it were suspended at that point
Center of gravity limits - Specified forward or aft or lateral points beyond which the CG must not be located
Center of gravity range - Distance between the forward and aft CF limited
Datum - Imaginary vertical plane or line from which all measurements of arm are taken; established by manufacturer
Floor load limits - Maximum weight the floor can sustain per inch/foot; provided by the manufacturer
Fuel load - Useable fuel
Licensed empty weight - empty weight including airframe, engine, unusable fuel, and undrainable oil plus optional equipment (term used prior to GAMA standardization)
Maximum landing weight - Max weight at which aircraft can normally be landed
Maximum ramp weight - Total weight of a loaded aircraft including fuel
Maximum takeoff weight - Max allowable weight at the start of the takeoff run
Maximum weight - Max authorized weight of the aircraft and its equipment specified in the TCDS
Maximum zero fuel weight - Max weight, exclusive of useable fuel
Mean aerodynamic chord (MAC) - Average distance from the leading edge to trailing edge of the wing
Moment - Weight of an item multiplied by its arm
Moment index - Moment divided by a constant; simplifies weight and balance computations
Payload - Weight of occupants, cargo, and baggage
Standard empty weight - Weight of airplane and all standard equipment including unusable fuel and engine oil
Station - Location in the aircraft which is identified by a number designating its distance from the datum
Useful load - Empty weight subtracted from max takeoff weight
What basic equation is used in all weight and balance problems to find the center of gravity location of an airplane and/or its components?
Weight x arm = Moment;
CG = Moment/weight
What basic equation is used to determine center of gravity?
Total Moment/Total Weight
Explain the term percent of mean aerodynamic chord (MAC)
CG that is expressed as a percent MAC; typically around 25% MAC meaning CG is CG is located around 1/4 of the distance away from the leading edge
If the weight of an aircraft is within takeoff limits but the CG limit has been exceeded, what actions can the pilot take to correct the situation?
Shift the weight aft so CG falls within limits
What simple and fundamental weight check can be made by all pilots before flight?
Check if useful load has been exceeded
What factors would contribute to a chage in center of gravity location during flight?
Consult POH to effects of changes in variables such as fuel use and movement of passengers
If actual weights for weighrt and balance coputations are unknown, what weights may be assumed for weight and balance computations?
Crew and passengeres = 190 each
Gas - 6 lbs/gal
Oil - 7.5 lbs/gal
Water - 8.35 lbs/gal
Note: These are only rule of thumbs weights, actual may be much different
How is the CG affected during flight as fuel is used?
As fuel is consumed the weight and thereby CG will change however most aircraft have fuel tanks close to CG therefore there is a minimal amount of change; lateral balance may be off due to uneven fuel loading
