Aircraft Performance Flashcards
How does density altitude affect aircraft performance?
The density of the air plays a major role in the performance of an AC. The more dense the air, the better performance will be.
Density Altitude is the altitude your AC thinks its flying at.
What are the factors that directly affect the density of the air?
- Temperature
- Altitude
- Pressure
- Humidity
If you have a high density altitude, what does this mean and how will it affect the performance of your AC?
A high density altitude means your AC thinks it is flying higher than it actually is and will behave as such.
A high density altitude means the air is thin (you could be at sea level and have a high density altitude, due to weather conditions)
With a high density altitde, you will have less lift and thrust and in some cases you may not have air dense enough to get off the ground or climb!
How does the temperature at the airport you’re taking off from affect density altitude for your AC?
Even if you are at sea level, if its 30+ outside your AC will perform as if your airport is at say 5000ASL because the air is so thin.
Why does high humidity give us a high density altitude?
Water molecules, less dense and less heavy than air molecules, in the air push air molecules far apart.
So there is less air and more water going into the air intake of your engine, decreasing performance.
Air density (not density altitude) decreases with (4)?
- Increase in the temp of the air
- Increase in altitude
- Increase in humidity
- Decrease in pressure
the aircraft’s Service Ceiling, Absolute Ceiling, and leaning settings are all given in terms of…
Density Altitude!
With a low air density (air is thinner), what effects will this have on the performance of your AC?
Less power from engine
Less thrust from prop
Less lift from wings
This all results in:
Longer takeoff run
Longer landing roll
Poorer climb performance
What is Ground Effect?
It is a decrease in induced drag (drag that is a direct consequence of lift) due to the wing’s proximity to the ground (within one half of a wingspan), which doesnt allow the induced drag to fully form, resulting in more lift.
Due to ground effect an aircraft can become airborn before it is ready to fly. How can this be dangerous?
When you pull out of ground effect you could stall or go back down to the ground.
This is why ground effect should only be used for soft field takeoffs and why it is important to accelerate to the specified speed before pulling out of ground effect
What is Vx?
Best angle of climb. Most altitude gained over a given distance.
This speed changes with altitude. As we climb higher, the numerical value of Vx increases. Eventually it will equal our L/D (lift to drag ratio) speed at the aircraft’s absolute ceiling
What is Vy?
The best rate of climb. Gain the most altitude in a given amount of time
As we climb, the numerical value of Vy becomes smaller.
Like Vx, at the absolute ceiling, Vy speed is the same as L/D speed. So At the absolute ceiling, Vx, Vy, and L/D are all the same speed.
What is Va?
Maneauvering speed. This is the max speed it is safe to make a full and abrupt deflection of the controls (or getting hit by a gust of air) without damaging the AC.
You should be under this speed in rough air/turbulence
Va speed changes with the weight of the AC.
Heavy AC - Higher Va
Lighter AC - Lower Va
What is Vno?
Never Exceed speed except in smooth air.
Bottom of yellow arc on the IAS
Usually higher than Va
What is Vfe?
Max Flaps Extended Speed. White arc on ISA. Self explanitory.
What happens to indicated and true stall speeds as you gain altitude?
IAS stall speed will always be the same regardless of altitude
TAS stall speed will increase with altitude (as will our landing distance) as well as with an increase in density altitude
The only thing that changes the IAS Stall Speed is the load factor
Two AC are being operated at the same angle of bank. What can the faster and slower aircraft expect their turns to look like?
Faster AC has a:
* Smaller rate of turn (takes less time to complete the turn
* Larger radius of turn
Slower AC has a:
* Larger rate of turn
* Smaller radius of turn
So the faster AC will do the turn faster, but has to do a bigger circle. The slower AC will do the turn slower, but can fly in a much tighter circle. The result is they both complete the rate one turn in the same amount of time (1 minute).
Also the faster you turn, the steeper your angle of bank needs to be to maintain a standard rate of turn
If an AC is **tail heavy* (it has a rearward C of G), what characteristics in the AC will this cause?
- Less stable
- Less trim required
- Fly faster (due to less drag from less tail pressure on the stabilizer because the rearward C of G is already providing weight through the tail, and reduced angle of attack)
If an AC is nose heavy, what characteristics will this produce in your AC in flight?
- More stable
- More trim required
- Will fly slower due to more drag from the extra pressure on the stabilizer to counteract the nose-heaviness and the increased angle of attack
Why is landing distance longer at higher density altitudes?
Because our true airspeed is higher (I dunno this was on the quiz)
Quiz Question
With an aircraft flying at it’s endurance speed, and increase in airspeed will increase ________ drag.
Parasite
Quiz questions
When an aircraft is in a level, coordinated turn, lift is ____ than weight
lift
