Flashcards in Commercial PTS performance and limitations 1/F Deck (16)
How is performance affected as air becomes less dense?
Power because the engine takes in less air
Thrust because the prop is less efficient in thin air
Lift because thin air exerts less force on airfoils
What is the standard atmosphere at sea level?
Temp 15* c or 59* f
Pressure 29.92 in. Hg or 1013.2 millibars or hectopascals (hPa)
What is standard temperature and pressure lapse rate?
Temp 2*c or 3.5* f every 1000 ft up to 36,000(tropopause)
Pressure decreases 1 in.Hg every 1000 ft up to 10,000
If your altimeter setting correction is high, that means you have low pressure.
Standard pressure for KVGT (2000 ft) should be 27.92". An altimeter setting higher is a correction for lower pressure in the area.
Standard temp for KVGT would be 11*c or 52*f
Describe the term pressure altitude?
It's the altitude above the standard datum plane of 29.92"
Sensitive altimeters are calibrated for standard pressure of 29.92". So, if you set 29.92 at your local field and the reading is higher than the field elevation, you are in an area of low pressure because the pressure anaroid wafer (29.92) is greater than the outside pressure and causing the needle to increase essentially making your airplane perform as if it were at a higher altitude. Pressure altitude, along with temperature make up density altitude.
Describe Density Altitude?
DA is pressure altitude corrected for non standard temperature. You must find pressure altitude first. It gives you an idea of air density.
Lower than standard pressure and higher than standard temps cause higher than standard density altitude.
High altitudes and high humidity (water vapor is lighter than air) also contribute to high density altitudes.
If your field elevation is 2000' but DA is 3400' then your plane will perform worse because the air is less dense.
What is true of the forces of flight in steady, unaccelerated flight?
Weight = lift
Talk about Drag
2 types, induced and parasitic. Together they make total drag
Induced comes from the wings during production if lift. The slower the airspeed, greater lift is needed to stay level which created more induced drag.
Conversely, Parasitic drag, all the stuff hanging off the airplane and varies depending on configuration, increases as airspeed increases. In fact, it is the square of airspeed in the equation. So, if airspeed is doubled, parasitic drag is quadrupled.
This is the chart that the two drags cross and the total drag line forms a U shape where at the bottom of the U is your best glide ratio.
Service, cruise and absolute ceilings?
Service ceiling is defined as the DA will allow the best rate of climb of 100 ft/min
Cruise is 300 ft/min
Absolute=can't climb any higher
Power loading and wing loading?
Power loading= total weight/rated horsepower
3000/180= 52.7 pounds per horsepower.
Factors into takeoff and climb capes
Wing loading= total weight/wing area
3000/45=67 pounds per sq foot
Determines landing speed
What's the difference between max range and max endurance?
Max range is the farthest a plane can fly on a given amount of fuel and is known as L/D max. Based on AOA for particular configuration and coefficient of lift.
Max endurance is the longest a plane can fly on a given amount of fuel. Located at a lower airspeed than l/d max on the graph (power required). Will change with weight.
Talk about ground effect
Ground effect occurs when the ground interferes with the flow pattern of air around the airplane reducing drag. Drag is reduced 25% when the wing is 1/4 the span above the surface.
Ground effect can cause one to float too long on landing or make one feel they have more performance on takeoff which can be dangerousness if heavy and high.
Define flight in the region of normal command and reverse command
This region is where the majority of phases of flight takes place. It means while holding a constant altitude, a higher airspeed requires more power and and a slower airspeed requires less.
Conversely, when an aircraft is operating in the region of reverse command, a higher airspeed will require less power and a slower airspeed will require more power. This typically is seen in slow flight which airspeed occurs below the max endurance speed and just above stall speed or min control.
During a short field landing that requires high pitch and low airspeed will be in region of reverse command. Another is a soft field takeoff where the pilot attempts to climb out of ground effect before normal airspeed and pitch attitude is attained.
Talk about runway surface and gradient
The rougher the surface the longer the take off roll. Slippery conditions increase landing distance and braking effectiveness.
Upslope or positive gradient increases takeoff roll but decreases land roll and a negative gradient decreases takeoff roll and increases land distance.
What does brake horsepower mean?
It's the same concept of how much wheel horsepower you get in a car.
If you are operating at 75 brake horse power, you are getting 75% of that engines rated horsepower on a standard day and at sea level.
The POH gives you different manifold and rpm settings to give you power options or endurance options. Simply set the manifold pressure and rpm accordingly to get the results you want.
When would you lean a normally aspirated engine?
Rules of thumb
When the power setting is 75% or less at altitude
High altitude airport ops( taxi, takeoff, pattern,land)
High, hot or humid