Wing Design

Question 1

Give 5 advantages of using high wing

Answer 1

1. Loading/unloading
2. water landing
3. more lift
4. good engine location
5. avoid high temperature gases (take-off / landing)

Question 2

Give 4 disadvantages of using high wing

Answer 2

1. More frontal area then mid-wing
2. lower ground effect
3. pilot reduced vision
4. more drag

Question 3

Give 5 advantages of using low wing

Answer 3

1. Better ground effect
2. lighter
3. lower drag
4. shorter landing gear
5. higher lateral control

Question 4

Give 2 disadvantages of using low wing

Answer 4

1. less lift

2. needs more landing run

Question 5

Give 2 advantages of using mid-wing

Answer 5

1. features stand between high and low wing

2. cut wing for fuselage

Question 6

Give 2 disadvantages of using mid-wing

Answer 6

1. more expensive

2. more drag than low wing

Question 7

Define aerodynamic centre

Answer 7

The point where moment is independent of angle of attack

Question 8

Define centre of pressure

Answer 8

point where resultant pressure forces act on the body

Question 9

How inaccurate can initial iteration be for calculating maximum takeoff weight

Answer 9

20%

Question 10

Give equation for Wto

Answer 10

Wto = (Wc + Wp) / ( 1 - Wf/Wt - We/Wt)

Question 11

Give equation for fuel fraction ratio

Answer 11

Wf/Wt = 1.05(1 - sum(Wi+1 / Wi))

1.05 : 5% extra fuel

Question 12

Give equation for pitching moment

Answer 12

Cm = M/q(c^2)

c^2 = S probably

Question 13

Give thickness ranges for various flight dynamics

Answer 13

15-18%:
low speed, high lift cargo

9-12%;
high speed, low lift high subsonic passenger aircraft

3-9%:
supersonic aircraft

Question 14

Explain 6-series NACA aerofoil

Answer 14

example: 65(1) - 212

6: 6 series
5: minimum pressure at 50%c
(1) : low drag for a Cl range +/- 0.1
2: Cl desirable is 0.2
12: thickness

Question 15

Explain 5-series NACA aerofoil

Answer 15

example: 23012

2: Control camber (L=2, Cl = L x 3/20)
3: position of max camber divided by 20
0: 0-normal camber line, 1-reflex camber line
12: thickness

Question 16

Give advantages and disadvantages of a tapered wing

Answer 16

Ad:

• elliptical lift distribution
• reduces wing weight
• improves lateral control

Dis:
- increases production cost

Question 17

What are raked wingtips

Answer 17

tip of the wing has a higher degree of sweep than the rest of the wing

• improves fuel efficiency, climb performance and shorten takeoff
• this is because it reduces induced drag

Question 18

What does Dihedral wings achieve

Answer 18

• better lateral stability
• this is due to a greater lift force being produced on one wing when aircraft slips during manoeuvre
• increases drag however as lift is not perfectly normal to fuselage

Question 19

Give thrust equation

Answer 19

T = m(dot)(Ve - Vi) + (Pe - Pi)Ae

m(dot) = mass flow rate = ρVA

Question 20

Give propeller diameter equation

Answer 20

Dp = Kn x SQRT( 2 x np x P x AR / ρ x Vav^2 x Vc x Clp)

Question 21

What is the use of frames and stringers in fuselage structure

Answer 21

Frames:
resist hoop stress

Stringers:
resist bending stress

Question 22

Give equation for wing box

Answer 22

Wing box volume = Tr x Cr x intersection length

Cr = 3/2 x C x ( 1 + λ)/(1 + λ x λ^2)

C = mean chord length
λ = taper ratio

Tr = (t/c),max x C

Question 23

How to calculate gear box ratio

Answer 23

GR = np / ns

np = propeller rotational speed
ns = engine shaft rotational speed

Question 24

Define divergence

Answer 24

when deformation-dependent aerodynamic forces exceed the elastic restoring capability of the structure

Question 25

Define control surface reversal

Answer 25

control loss or reversal of expected response due to structural deformation (stiffness) of the primary surface

Question 26

Define flutter

Answer 26

an oscillatory instability where one ‘mode of motion’ is driven to resonance by a second mode. Both modes have coalesced to the same frequency