Performance and Limitations Flashcards
Factors Affecting Performance
Atmospheric conditions Pilot technique Airplane configuration Airport environment Center of gravity CG loading Weight and Balance
Loading CG Forward
- better controllability
- better stability
- worse maneuverability
- recover easier from stalls
- worse fuel burn
- worse range
- worse TAS
Loading CG Aft
- worse controllability
- worse stability
- better maneuverability
- hard to recover from a stall
- better fuel burn
- better TAS
Air Density relative to Altitude
Air density decreases with altitude
At high elevation airports, an airplane
requires more runway to take off. The aircrafts rate of climb will be less and the
aircrafts approach will have to be faster, to stabilize the effects of lower air
density.
Air Density relative to Temperature
Air density decreases with temperature
Warm air is less dense than cold air because there are fewer air molecules in a given volume of warm air than in the same volume of cooler air. As a result, on a hot day, an airplane will require more runway to take off, will have a poor rate of climb and a faster approach and will experience a longer landing roll.
Describe the combination of high temperature and high elevation and how it effects the performance of an airplane
The combination of high temperature and high elevation produces a situation that aerodynamically
reduces drastically the performance of the airplane.
The horsepower out-put of the engines decrease because its fuel-air mixture is reduced.
The propeller develops less thrust because the blades, as airfoils, are less efficient in the thin air.
The wings develop less lift because the thin air exerts less force on the airfoils.
As a result, the take-off distance is substantially increased, climb performance is
substantially reduced and may, in extreme situations, be non-existent
Humidity
Although it is not a major factor in computing density altitude, high humidity has an effect on engine power. The high level of water vapor in the air reduces the amount of air available for combustion and results in an enriched mixture and reduced power
Density Altitude
Density altitude is pressure altitude corrected for temperature. It is the altitude at which the airplane thinks it is flying based on the density of the surrounding air mass.
We relate aircraft performance to density altitude
Calculating Density Altitude
Density altitude in feet = pressure altitude in feet + (120 x (OAT - ISA temperature))
- Pressure altitude is determined by setting the altimeter to 29.92 and reading the altitude indicated on the altimeter.
- OAT stands for outside air temperature (in degrees Celsius).
- ISA stands for standard temperature (in degrees Celsius).
Keep in mind the standard temperature is 15 degrees C but only at sea level. It decreases about 2 degrees C (or 3.5 degrees F) per 1,000 feet of altitude above sea level. The standard temperature at 7,000 feet msl, therefore, is only 1 degree C (or 34 degrees F).
For example, the density altitude at an airport 7000 feet above sea level, with a temperature of 18 degrees Celsius and a pressure altitude of 7000 (assuming standard pressure) would be calculated as follows.
- ) 18 – 1 = 17
- ) 17 x 120 = 2040
- ) 2040 + 7000 = 9040 feet Density Altitude
This means the aircraft will perform as if it were at 9,040 feet.
Calculating Density Altitude (Option 2)
Pressure altitude = (standard pressure - your current pressure setting) x 1,000 + field elevation
That’s a pretty simple formula since two of the variables will always be the same and the other two are easy enough to find. Let’s say our current altimeter setting is 29.45 and the field elevation is 5,000 feet. That means (29.92 - 29.45) x 1,000 + 5,000 = 5,470 feet.
density altitude = pressure altitude + [120 x (OAT - ISA Temp)]
We already have the value for pressure altitude from our last calculation; OAT is degrees Celsius read off our thermometer (let’s say it’s a balmy 35 °C today) and ISA Temp is always 15 °C at sea level. To find ISA standard temperature for a given altitude, here’s a rule of thumb: double the altitude, subtract 15 and place a - sign in front of it. (For example, to find ISA Temp at 10,000 feet, we multiply the altitude by 2 to get 20; we then subtract 15 to get 5; finally, we add a - sign to get -5.)
So, in the example above: density altitude = 5,470 + [120 x (35 - 5)]
Working out the math, our density altitude is 9,070 feet.
Pressure Altitude
Pressure altitude is the attitude displayed on the altimeter when the Kollsman window is set to 29.92 inches of mercury, or 1013.4 millibars.
Pilots cannot use pressure altitude below 18,000 feet, because then the aircraft’s true altitude would change depending on temperature. That is why every time a pilot checks in with a new air traffic controller, the local altimeter calibration is necessary. The altimeter indicates how high the airplane is above sea level by calculating the difference between the pressure in the aneroid wafers and the atmospheric pressure fed into the static port.
How do you calculate pressure altitude?
The pressure altitude can be determined by any of the three following methods:
1. By setting the barometric scale of the altimeter to
29.92 “Hg and reading the indicated altitude
2. By applying a correction factor to the indicated
altitude according to the reported “altimeter setting,”
3. By using a flight computer
OAT
Outside Air Temperature
Calibrated Airspeed (CAS)
Indicated airspeed corrected for instrument and position error.
When flying at sea level under International Standard Atmosphere conditions (15 °C, 1013 hPa, 0% humidity) calibrated airspeed is the same as equivalent airspeed (EAS) and true airspeed (TAS). If there is no wind it is also the same as ground speed (GS). Under any other conditions, CAS may differ from the aircraft’s TAS and GS.
True Airspeed (TAS)
Calibrated Airspeed (CAS) corrected for density altitude
True airspeed is the speed of your aircraft relative to the air it’s flying through.
As you climb, true airspeed is higher than your indicated airspeed. Pressure decreases with higher altitudes, so for any given true airspeed, as you climb, fewer and fewer air molecules will enter the pitot tube. Because of that, indicated airspeed will be less than true airspeed. In fact, for every thousand feet above sea level, true airspeed is about 2% higher than indicated airspeed. So at 10,000 feet, true airspeed is roughly 20% faster than what you read off your airspeed indicator.
Groundspeed (GS)
The movement of your airplane relative to the ground is called groundspeed.
It’s true airspeed corrected for wind.
With a true airspeed of 100 knots and a tailwind of 20 knots, you’d be flying a groundspeed of 120 knots
Loss of RPM During Cruise Flight (Non-altitude engines)
Probable Cause: Carburetor or induction icing or air filter clogging
Corrective Action: Apply carburetor heat. If dirty filter is suspected and non-filtered air is available switch selector to unfiltered position.
High Oil Temperature
Probable Cause/Corrective Action:
Oil congealed in cooler - Reduce Power. Land. Preheat engine
Inadequate engine cooling - Reduce Power, increase airspeed
detonation or preignition - Observe Cylinder Head Temps (CHT) for high reading, reduce manifold pressure, enrich mixture.
forth coming internal engine failure - Land as soon as possible or feather propeller and stop engine
Defective thermostatic oil cooler control - Land ASAP. Consult Maintenance Personnel
Low Oil Temperature
Probable Cause/Corrective Action:
Engine not warmed up to operating temperature - Warm engine in a prescribed manner
High Oil Pressure
Probable Cause/Corrective Action:
Cold Oil - Warm engine in prescribed manner
Possible internal plugging - Reduce power, land ASAP
Low Oil Pressure
Probable Cause/Corrective Action:
Broken Pressure Relief Valve - Land ASAP or feather propeller and stop engine
Insufficient Oil - same as above
Burned out bearings - same as above
Fluctuating Oil Pressure
Low oil supply, loose oil lines, defective pressure relief valve - Land ASAP or feather propeller and stop engine
High Cylinder Head Temperature
Probable Cause/Corrective Action:
Improper cowl flap adjustment - adjust cowl flaps
Insufficient airspeed for cooling - increase airspeed
Improper Mixture Adjustment - Adjust Mixture
Detonation or Preignition - Reduce power, enrichen mixture, increase cooling airflow
Low Cylinder Head Temperature
Probable Cause/Corrective Action:
Excessive Cowl flap opening - Adjust cowl flaps
Excessively Rich Mixture - Adjust mixture control
Extended glides without clearing engine - clear engine long enough to keep temps at minimum range
Ammeter Indicating Discharge
Probable Cause: Alternator or generator failure
Corrective Action: Shed unnecessary electrical load. Land as soon as practicable.
Load Meter Indicating Zero
Probable Cause: Alternator or generator failure
Corrective Action: Shed unnecessary electrical load. Land as soon as practicable.
Surging RPM and Overspeeding
Probable Cause/Corrective Action:
Defective propeller - Adjust propeller RPM
Defective engine - consult maintenance
Defective propeller governor - Adjust propeller control. Attempt to restore normal operation
Defective Tachometer - Consult Maintenance
Improper Mixture Setting - Adjust mixture for smooth operation
Loss of airspeed in cruise flight with manifold pressure and RPM constant
Probable Cause: Possible loss of one or more cylinders
Corrective Action: Land as soon as possible
Rough Running Engine
Probable Cause/Corrective Action:
Improper mixture control setting - Adjust mixture for smooth operation
Defective ignition or valves - consult maintenance
Detonation or preignition - Reduce power, enrich mixture, open cowl flaps to reduce cylinder head temp. Land ASAP.
Induction Air Leak - Reduce Power. Consult maintenance
Plugged Fuel Nozzle (Fuel Injection) - Same as above
Excessive fuel pressure or fuel flow - Lean mixture control
Loss of Fuel Pressure
Probable Cause/Corrective Action:
Engine driven pump failure - Turn on boost tanks
No Fuel - Switch tanks, turn on fuel
An abnormally high engine oil temperature indication may be caused by:
The oil level being too low
Excessively high engine temperatures will:
Cause loss of power, excessive oil consumption, and possible permanent internal engine damage
For internal cooling, air cooled engines are especially dependent on:
The circulation of lubricating oil
If the engine oil temperature and cylinder head temperature gauges have exceeded their normal operating range, the pilot may have been operating with:
Too much power and with the mixture set too lean
What action can a pilot take to aid in cooling an engine that is overheating during a climb?
Reduce rate of climb and increase airspeed
What is one procedure to aid in cooling an engine that is overheating?
Enrich the fuel mixture
A precaution for the operation of an engine equipped with a constant speed-propeller is to:
Avoid high manifold pressure settings with low RPM
What is an advantage of a constant-speed propeller?
Permits the pilot to select the blade angle for the most efficient performance
One purpose of the duel ignition system on an aircraft engine is to provide for:
Improved engine performance
If the ignition switch ground wire becomes disconnected, the magneto:
May continue to fire
The presence of carburetor ice in an aircraft equipped with a fixed-pitch propeller can be verified by applying carburetor heat and noting:
A decrease in RPM and then a gradual increase in RPM
Generally speaking, the use of carburetor heat tends to:
Decrease engine performance
Generally speaking, the use of carburetor heat tends to:
Decrease engine performance
Applying carburetor heat will:
Enrich the fuel/air mixture
What change occurs in the fuel/air mixture when carburetor heat is applied?
The fuel/air mixture becomes richer
The basic purpose of adjusting the fuel/air mixture at altitude is to:
Decrease the fuel flow in order to compensate for decreased air density
While cruising at 9,500 feet MSL, the fuel/air mixture is properly adjusted. What will occur if a descent to 4,500 feet MSL is made without readjusting the mixture?
The fuel/air mixture may become excessively lean
The uncontrolled firing of the fuel/air charge in advance of normal spark ignition is known as:
Pre-ignition
If the grade of fuel used in an aircraft engine is lower than specified for the engine, it will most likely cause:
Detonation
Should it be necessary to hand-prop an airplane engine, it is extremely important that a competent pilot:
Be at the controls in the cockpit
An electrical system failure (battery and alternator) occurs during flight. In this situation, you would experience?
Avionics equipment failure
What are the handling Characteristics of an airplane with a Forward CG?
- Generally more stable
- Fly at a slower TAS (true airspeed) due to more drag
- Stall at a higher indicated stall speed
What are the handling Characteristics of an airplane with an AFT CG?
- Generally unstable aircraft
- Fly at a higher TAS (true airspeed), less drag, better
fuel burn - May be impossible to recover from a stall or spin
What are some of. The main elements of aircraft performance?
A. Take off and landing distance B. Rate of climb C. Ceiling D. Payload E. Range F. Speed G. Fuel economy
What factors affect the performance of an aircraft during takeoff a and landings?
A. Air density B. Surface wind C. Runway surface D. Upslope or downslope of runway E. Weight
