Gliding and Soaring Flashcards
How does gliding differ from parachuting
the angle of descent for gliding is less than 45 degrees
the angle of descent for parachuting is more than 45 degrees
Based on energy conversion what is the principle behind gliding
gliders convert potential energy into kinetic energy (trade altitude for forward motion and lift)
Why can’t gliders maintain a horizontal gliding position if the wind is directly blowing on it
because there would be no thrust force that could be generated so even though there is a lift force there is a drag force as a result of the oncoming wind which would result in the lost of airspeed
how do gliders glide?
a positive glide angle is adopted
lift tilts forward to provide a force to balance rearward drag. . the resultant force equals the weight
How do gliders choose their glide angle
Glide angle is chosen based on the lift to drag ratio.
a low L/D ratio means a steep glide angle
a high L/D means a shallow glide angle
How do we calculate the lift to drag ratio
distance travelled/ height lost =lift/ drag = Cl/Cd = 1/tan(theta)
What affects the speed of the glide?
the weight of the object , heavier glides travel faster along the same path as a lighter one, because more lift needs to be produced to offset the weight and drag .
What sets the
a. glide angle
b speed
a. glide angle determined by L/D ratio
b. speed is set by the weight
What is represented in a glide polar plot?
sinking speed over the airspeed
What are the factors that can alter a glider’s air speed and sink speed
- vary angle of attack
- vary the wing camber ( curvature of the wing)
- vary the wingspan
On a graph polar identify where the optimum air speed for maximum distance , and where is the optimum airspeed for maximum time aloft
L20 slide 24
What are the constraints when gliding with a high L/D ratio
shallow glide angles
How can we reduce induced drag ?
have a high aspect ratio by Having long thin wings
What are the 3 most important points on a glide polar plot - identify them on the glide polar plot
- minimum sink speed: maximizes time spent in air
- maximum distance speed: airspeed needed to maximize distance travelled in the air
- minimum airspeed: the slowest speed that can produce lift without stalling the aerofoil
Objects with a high L/D ratio cannot ascend quickly, how can an object ascend quickly if it has a high L/D ratio?
- use of air brakes increase the drag without increasing the lift. to maintain airspeed the glider tilts forward and increase its glide angle. can vary the glide ratio
- birds use their feet and stick out their neck – produces controllable amount of drag,
- steepen your glide angle to hasten your descent