1. Fixed wing Flashcards
Define the stratosphere
The stratosphere is the layer of air outside the troposphere. It is from a height of 11km or 36,000ft to a height of 30km.
Define the tropopause
The tropopause is the layer of air where the troposphere and stratosphere meet. It is found at a height of 11km or 36,000ft.
What do the letters ISA stand for?
International standard atmosphere
Why do we have an ISA?
To compare aircraft performance and calibration of altimeters.
What conditions are assumed at sea level in ISA?
+15C. 1013mb. 1.226kg/m(cubed)
Define total or stagnation pressure
Total or stagnation pressure is dynamic pressure + static pressure
Define boundary layer
The boundary layer is the layer of air next to the aircraft that is slowed down by viscosity and surface friction.
Define centre of pressure
The centre of pressure is the point on the chord line which through the total reaction acts.
Define the lift
The lift is the component of the total reaction which acts at right angles to the relative air flow direction.
Define drag
Drag is the component to the total reaction which acts parallel to the relative air flow direction.
Define stall
Stall is when the angle of attack is increased but does not produce an increase in lift.
Describe the boundary layer.
The boundary layer is in 2 forms: laminar layer and turbulent layer. The laminar layer is 0.1mm-0.2mm thick and has a relatively low drag. The turbulent layer is 5mm thick and has a relatively high drag. The transition point is where the laminar layer changes into the turbulent layer. The separation point is the point where the turbulent layer separates from the aerofoil and degenerates into drag.
Define the troposphere
The troposphere is the layer of air next to the earth. It goes from the earths surface to a height of 11km or 36,000ft.
Chord line
A straight line from the leading edge to the trailing edge.
Define mean camber line
A lime drawn midway between the upper and lower surfaces of the aerofoil from the leading edge to the trailing edge.
Define maximum camber line.
The maximum distance between the mean camber line and the chord line.
Define angle of attack.
The angle created between the chord line and relative air flow direction .
Define angle of incidence.
Angle of incidence is the angle between the chord line and the manufactures datum.
Define span.
The distance from wing tip to wing tip.
Define aspect ratio.
The ratio between the wing span and chord length.
Define wash out.
A wash out is a decrease in angle of incidence towards the tip of the wing.
Define wash in.
An increase in angle of incidence towards the tip of the wing.
What is the stalling angle?
15 to 16 degrees
The equation for how lift is calculated.
L = (p x v^2 x s x cl)/2
The equation for how drag is calculated.
D = (P x v^2 x s x cd)/2
List the seven factors that affect lift and drag.
Density Velocity of air flow Plan area Angle of attack Surface finish Aerofoil shape Coefficient of lift/drag
Considering lift augmentation devices, what two factors must they increase (so that the aircraft can fly more slowly without losing too much lift)?
Surface area and/or coefficient of lift.
Name the two devices fitted to the leading edge to allow aircraft to fly more slowly.
Slots and slats.
What is a slat?
A moveable extension to the leading edge which creates a slot when extended.
Why are flaps fitted to an aircraft?
To increase lift at low speeds, particularly at take off And to increase both lift and drag for landing.
What type of flap achieves its object by increasing the area of the wing?
Fowler flap
Why are Krueger leading edges, or nose flaps fitted to some aircraft?
To prevent leading edge separation on thin wings with sharp edges, such as the ones used on very high speed aircraft.
3 things that a fowler flap shows when open.
Increased curvature, increased angle of attack and increased surface area.
The coefficient of lift/drag is made from:
Angle of attack
Surface finish
Aerofoil shape
What is the most effective angle for the highest wing efficiency?
3 to 4 degrees
What is a slot?
The effect of the slot is to re energise the boundary layer.
What types of flaps are there?
Plain, slotted, split, fowler, double slotted fowler, kreuger or nose flap and triple slotted fowler.
What does the slot do to the layers?
It moves the TP on a bit, and moves the SP a lot towards the trailing edge.
Comparison of a thick aerofoil to a thin aerofoil at slow speed.
Thick: lots of lift, lots of drag
Thin: not much lift, very low drag
Comparison of a thick aerofoil to a thin aerofoil at high speed.
Thick: lots of lift, massive drag
Thin: enough lift, some drag
Comparison of a thick aerofoil to a thin aerofoil, what they would be part of in the real world?
Thick: load carrier, short field ops
Thin: high speed fighter, very long runways
Define Mach number
The Mach number is the ratio of the speed of an object to the speed of sound in the same fluid.
Define free stream Mach number
The Mach number of a flow sufficiently removed from an aircraft to be unaffected by it.
Define local Mach number
The ratio of the speed of flow at any point on an aircraft to the speed of sound at the same point.
Define critical Mach number
The free stream Mach number at which any local Mach number becomes 1.
Define subsonic
All ML less than 1.
Define transonic
Mixed flow - some mL less than 1, some mL more or equal to 1.
Define supersonic
All ML equal to 1 or more.
What’s the problem with a shock wave?
Formation of shockwaves on the main plane causes a thickening of the boundary layer which separates from the wing surface at the base of the shockwave.
Name 2 aerofoil sections that are used for supersonic?
Bi convex and double wedge
What type of aerofoil is used for when an aircraft is flying just below the speed of sound?
Supercritical
How can induced drag be minimised?
By having winglets or wings with a high aspect ratio
Symmetrical aerofoil at zero angle of attack
Will not produce a vortex.
Zero lift drag can also be known as the following:
Form skin and drag friction.
The equations for level:
T=D
L=W
P=T x W
The equations for climbing:
RateOfClimb: Vsin€
L = Wcos€
T =D + Wsin€
P=T x V = (D + Wsin€) x V
The equations for diving:
L = Wcos€ D = T + Wsin€ T = D - WSin€ P = T x V = (D - Wsin€) x V
The 2 types of shockwave?
Normal Mach wave
Oblique Mach wave
As aircraft increases in the transonic speed range, what happens to the aircraft pitch attitude?
The C of P goes towards the back of the plane making the nose dive down.
How can a designer increase the value of Mcrit?
Thinner wings and sweepback
