Performance and Limitations - SGRs Flashcards
As air becomes less dense, aircraft performance is reduced among these 3 factors
Reduced power since engine takes in less air
Reduced thrust since propeller is less efficient in thin air
Reduced lift since thin air has less force on airfoil
Standard day at sea level (F, C, Hg, Mbs)
15C 29.92Hg
59F 1013.12 Millibars
What is the standard temperature lapse rate?
It is accurate to what altitude?
2C/1000 feet
to 36,000 feet
What is the standard pressure lapse rate?
It is accurate to what altitude?
1 in Hg / 1000ft
to 10,000 feet
Pressure altitude is important for…
determining aircraft performance
Pressure altitude is determined by
- Setting Baro to 29.92 and reading indicated altitude
- applying correction factor to indicated altitude according to reported altitmeter
- using a flight computer
Density altitude defined
Pressure altitude corrected for non-standard temperature
Plane performs according to what type of altitude?
Density
Air density is affected by changes in…
altitude
temperature
humidity
At constant temperature air density is _________ to pressure. aka How are air density and pressure related?
Directly proportional
How is density of air and temperature related?
Inversely
Increase in humidity causes a ______ in air density
decrease
Relative humidity defined
Percentage of maximum amount of water vapor the air can hold
Can warm air or cold air hold more water vapor?
Warm air can hold more water vapor
Is water vapor heavier or lighter than air vapor?
Lighter
When landing at high elevation airports the IAS for approach and stall is the same. What is different?
TAS is faster Ground Speed is faster Longer approach, longer rollout Greater distance to clear obstacles Longer runway needed
What are the main aircraft performance characteristics?
Takeoff and Landing Distance Rate of Climb Ceiling Payload Range Speeds Maneuverability Fuel Economy
Induced Drag defined
Induced Drag varies by
Induced drag is the total drag created by production of lift
- increasing with airspeed
- because at lower airspeed higher AOA is required = greater induced drag
Parasite Drag defined
Parasite drag varies
Parasite drag is drag from friction of air over the aircraft structure
varies directly with airspeed
Double the airspeed. What happens to parasite and induced drag
4x greater parasite drag (8x power needed)
1/4 of original value for induced (1/2 power needed)
Service ceiling defined
Can service ceiling always be reached
maximum density altitude where best rate of climb airspeed is 100FPM climb
No. Service ceiling may not be reached due to actual density altitude
Climb performance is a result of what two energy types?
Excess power above that required for level flight.
Aircraft’s kinetic energy (trading airspeed for climb)
Absolute ceiling defined
altitude where climb is no longer possible
Power loading formula
results in ____/_____
weight of plane/ HP of engine
lbs/hp
Wing loading formula
results in ____/_____
weight of plane / wing area (includes ailerons) in sq ft
lbs/sq. feet
Why is power loading important?
Why is wing loading important?
Power loading is important for takeoff and climb capability
Wing loading is important for determining the landing speed.
Maximum range defined
Maximum range obtained at what point?
max distance flyable for a given fuel supply
L/D max
Maximum endurance defined
Maximum range obtained at what point?
max time flyable for a given fuel supply
minimum power (lowest fuel flow)
Ground effect is caused by what change?
Where does ground affect occur?
interference of airflow around the wing caused by the ground
ground effect occurs one wingspan above the surface
Wing in ground effect has reduced upwash, downwash and wingtip vortices. What does reduced wingtip vortices cause?
what happens at 1/4 and 1/10 of the wingspan above the ground?
reduced wingtip vortices reduces induced drag
1/4 span of wing above ground induced drag is reduced by 25%
1/10 span of wing above ground induced drag is reduced by 50%
Ground effect causes what problem in landing and what problems in takeoff?
landing problem - excess speed may result in excess float due to ground effect
takeoff problem - aircraft may takeoff below recommended speed, but out of ground effect induced drag may mean the aircraft isn’t capable of flight and could descend back to ground
What is “flight in the region of reversed command?”
Higher airspeed requires lower power setting to hold altitude
Lower airspeed requires higher power setting to hold altitude
A decrease in airspeed must be accompanied by an increased power setting to maintain steady flight
Where may an airplane encounter the region of reverse command? (2)
- a low airspeed high-pitch attitude powered approach for a short field landing
- soft-field takeoff and climb while attempting to climb out of ground effect with too high of a pitch
What runway surface factors affect performance
not hard surface and unsmooth surfaces increase ground roll.
Muddy + Wet surfaces reduce friction and act as obstructions to reduce landing distance
Runway gradient or slope
Braking effectiveness is defined as
the amount of power that is applied to the brakes without skidding the tires
Takeoff and Landing performance is affected by:
air density surface wind runway surface runway gradient (slope) weight powerplant and thrust
Increased density altitude on takeoff and landing causes
increased takeoff distance (greater TAS required)
reduced rate of climb
increased TAS on approach and landing
increased landing distance roll
What calculation is made before a flight prior to every takeoff in regards to a rejected takeoff?
point along the runway at which the airplane should be airborne or discontinue the takeoff (need remaining runway using normal measures to safely stop aircraft)
Why are there various manifold pressure and prop settings for a given power output?
so pilot can choose between best efficiency and best power for given conditions.
Higher RPM causes what issue regarding oil and fuel?
more friction and more fuel
What happens to manifold pressure of a non-turbo aircraft operating at higher alititudes?
constant power output will decline due a drop in manifold pressure
What is brake horsepower?
power delivered to the propeller shaft of an aicraft engine. In % of normally rated power available at sea level on standard day
How do you set 8165C to 75% brake horsepower?
well…
When to lean normally-aspirated direct-drive engine?
- lean anytime power is 75% or less
- at high altitudes
- at high-altitude airports lean for taxi/takeoff/pattern/landing
List 3 methods for leaning aircraft engines
Tachometer Method
Fuel Flowmeter Method
Exhaust Gas Temperature Method
Describe Tachometer Method of leaning engine
for best economy - lean from full rich to maximum power (peak RPM)
then lean until engine starts to run rough and enrich mixture slightly until engine runs smoothly
Describe Fuel Flowmeter Method of leaning engine
use the fuel flowmeter to lean the mixture to the POH marked fuel flow
Describe Exhaust Gas Temperature Method of leaning engine
Lean slowly to peak EGT then enrich it 50 degrees rich (cooler) of peak EGT
What is the CG equation?
CG = total moments / total weight
weight x arm = moment
Aft CG causes (5 things)
lower stall speed (due to less wing loading)
Higher cruise speed (due to less drag)
Less stability (spin and stall recovery is difficult)
Less fuel burn (from less drag)
Increased range
CG change equation
(weight shifted X distance moved) / aircraft gross weight = CG change
Assumed weight (if unknown) for Crew + Pax Gas Oil Water
Crew + Pax = 190lbs
Gas = 6lbs/gal
Oil = 7.5 lbs/gal
Water = 8.35 lbs/gal
3 ways to control lift during flight
AoA
airspeed
flaps
In %MAC, approximately where is the CG located?
near 25% average chord point (aka 25% back from leading edge of the average wing section)
Performance chart data assumes what important items (which may not exist)?
paved, level smooth, dry runway surface
age of aircraft, pilot skill and proper technique
Maximum ROC (Vy) and Maximum AOC (Vx) converge where?
at the aircraft’s maximum ceiling
Does horizontal stabilizer produce lift?
Yes. horizontal stabilizer produces lift downwards
Thrust hits top of horizontal stabilizer. With less thrust there is less lift on wings and less downforce on horizontal stabilizer
What could cause the CG to move aft during flight?
fuel burn
passenger movement
What happens to elevator effectiveness while in ground effect?
elevator is much less effective in ground effect
Define payload
weight of occupants, cargo, and baggage
Define useful load
the maximum amount of weight the aircraft can carry in people (including the crew), baggage, cargo, useable fuel and oil.
Define basic operating weight
the empty weight plus the weight of the crew, ready for flight. This does not include payload and fuel.
Define empty weight
the weight of the airframe, engines, and all other items which have fixed locations and are permanently installed in the aircraft. It includes hydraulic fluid, unusable
Can warm or cold air hold more water vapor?
warm
What is the definition of the term “relative humidity”?
percentage of the maximum amount of water that a sample of air can hold.
What effect does humidity have on air density?
water vapor is lighter than air, so moist air is lighter than dry air. As the water content of the air increases, the air becomes less dense, increasing density altitude (lowering density) and decreasing performance.
Since temperature and pressure decrease with altitude, how will air density be affected overall?
the decrease in temperature and pressure have conflicting effects on density as you go up in altitude, but the fairly rapid drop in pressure with increasing altitude is usually the dominating force. Hence, the density is likely to decrease with altitude gain.
What effect does temperature have on air density?
Air density and temperature are inversely proportional
What effect does atmosphere pressure have on air density?
Air density is directly proportional to pressure. If air pressure gets lower, density gets lower which will yield a higher density altitude.
What factors affect air density?
by changes in altitude, temperature, and humidity. High density altitude refers to thin air while low density altitude refers to dense air.
Aircraft performs better in lower ________ altitude.
density
How is density altitude determined?
find pressure altitude and then correct it for nonstandard temperature variations.
