Airplane exam 1

When was the first flight and why was the weather important?

Dec 17th, 1903 and it was a cold day so the air was denser which gives the plane more power

Pros and cons of the Strut/wire Biplanes

Pro: high strength to weight ratio

Cons: high drag caused by wires

Mature Propeller driven

Streamlining, retractable landing gar, pressurization

What was the first Jet-propelled plane to reach mach1 and when?

In Oct. 14, 1947 chuck yeager flew the bell X-1

Flying wings design

No fuselage, tail, drag, volume, or leverage

Stealth design

Angular bc of early computer code, originally a Russian design

Tilt rotor design

HelicopterXjet, crashed a lot

Absolute altitude

Measured from the center of the earth, good for orbital mechanics

Geometric Altitude

Measured from sea level, MSL in hg

Pressure Altitude

Corresponds to a given pressure using standard atm, altimeter in an airplane is just a pressure gauge, Keeps airplanes from crashing

Density altitude

Corresponds to density, important bc will affect aircraft performance

Standard atmosphere pressure

2116lb/ft² = 101kPa = 29.92”

Standard atmosphere temperature

519 R = 59F =15 °C = 288K

Standard atmosphere density

.002377 slugs/ft³ = 1.225 kg/m³

Explain the altitude vs. temp graph

From 0-36,000ft is the troposphere and it has a steady decrease in temp

From 36,000-82,000ft is the stratosphere and it has a constant temp

Lapse rate

Slope of a altitude vs temp graph, we will use -3.56F/1000ft

Standard viscosity (μ)

3.74e-7 lbs/ft² = 1.79e-5 Ns/m²

Ideal gas law

P=ρRT

Ideal gas constant for air

1716 ftlbf/slugR = 287 J/kgK

Airfoil

Infinitely long slice of wing

Leading edge

The left most point on an airfoil

Trailing edge

The rightmost point on an airfoil

Chord line

A straight line from the trailing edge to the leading edge, defines orientation

Angle of attack

The angle between the relative wind and the chord line

What does the sign of the moment say about the nose

Positive means nose, negative means nose down

For a steady flight, lift is equal to

Weight of the plane

What is the equation for the coefficient of lift

= L/(1/2ρV²S)

What is the equation of the coefficient of drag?

Cd= D/(1/2ρV²S)

What is the equation for the coefficient of momentum?

Cm= M/(1/2ρV²SC)

Dynamic pressure

Also called Ram pressure: q=1/2ρV²

Reynolds Number

Re= ρVC/M, C=wing length, bigger with higher speed

Re=ρVc/μ

Mach number

M=V/a, a=speed of sound

What is the speed of sound equation?

a= sqrt(γRT), γ= 1.4

Reference area

Also called planform area, denoted by “S”

What is CFD?

Computational fluid dynamics=approximate solution to viscous flow

What does NACA stand for?

National Advisory Committee for Aeronautics, ran tests on airfoil sections

Lift curve

Lift coefficient vs angle of attack (in radians)

What is the max value of the lift curve slope?

2π 1/rad

What is the equation for the lift coefficient on a lift curve slope?

C_l= a_0(α-α_L=0)

What is the Prandtl-Glavert equation?

C_lsubsonic/sqrt(1-M²)

What is the mean camber line

A line that follows the curve of an airfoil from trail edge to leading edge

What is the camber?

The distance between the chord line and the mean camber line

How would you analyze a NACA 2412?

12% chord thickness, 2% max camber @ 40% chord position

Laminar flow

Reduces drag, ordered flow

Turbulent flow

Applies more drag than laminar, flow rolls around

Planform area (S)

The area of a finite wingspan plus the area of the fuselage

Wingspan (b)

Length from tip to tip of the wings

Tip chord

Ct, the height of the tip of the wing

Root chord

Cr, the height where the wing meets the fuselage

What is the planform area equation?

S=b(Ct+Cr)/2

What is the taper ratio?

λ=Ct/Cr

What is he equation for the aspect ratio?

AR=b²/S

Downwash

Deadly drag created in the vortexes behind the engines, acts to reduce the effective angle of attack, lowering our C_L

High Aspect Ratio

AR>0.4, long slender, less induced drag, weak tho

Low aspect ratio

Pros: agility, strong, high speed

Cons:high drag, poor fuel efficiency

Straight wings

Pro: massive lift at slower speeds, stability

Cons: bad with higher speeds

Swept wings

Pros: high speeds, jet standard

Cons: not enough lift at flow speed

Define e

Efficiency factor, function of AR, typically .95 or higher

High AR, incompressible, straight

Slope: a=a_0/1+(a_0/πeAR)

High AR, compressible, straight

Slope: a=a_0/[sqrt(1-M²)+(a_0/πeAR)]

Low AR, incompressible, straight

Slope: a=a_0/[sqrt(1+(a_0/πAR)²)+(a_0/πAR)]

Low AR, compressible, straight

Slope: a=a_0/[sqrt{1-M²_0+(a_0/πAR)²}+(a_0/πAR)]

What is the finite drag equation?

C_D=C_Do + C_Di

What is the induced drag coefficient for high AR?

C_Di=(C_L)²/πeAR=k_3(C_L)²

How can you get e from the tables?

1/(1+δ)

Fuselage drag

A combination of skin friction and pressure drag (mostly friction)

Interference drag

The combined drag from the wing and fuselage

Drag total

Fuselage drag + wing drag + interference drag

Transonic drag

Mach exceeds 1 which produce shock waves that increase the pressure drag

Area rule

The peak transonic drag rise can be reduced by having a smooth cross-sectional area distribution

What is the drag polar?

Describes the aerodynamics of the whole airplane

Zero lift parasite drag

D_0=1/2pV²S_wetC_fe

What is C_fe

Equivalent skin friction, includes form skin friction, and interference. Found from data, must be assumed based on type of plane

What is S_wet?

Wetted surface of the entire plane, like surface area

C_Do?

C_fe(S_wet)/S_ref

What is total drag?

C_D=C_De+C_Dw+C_Di

What is C_Dw?

Wave drag, compressibility, supersonic

1hp

550ftlb/s

1 mile

5280

Total drag equation

C_D=C_Do+(k_1+k_2+k_3)C_L²=C_Do+K(C_L)²

Thrust flow equation

T=m(Vj-V)

How dos a reciprocating engine/propeller work

Produces power

Turbojet

Produces thrust

Turbo fan

Hybrid, most common

Turbo prop

Jet engine drives propeller

What is Vj?

The velocity of the air leaving the propulsion device

What is the exhaust?

The wasted energy you feel from a propulsion device

What is the power available equation?

P_A=(T_A)V

What is the power dissipated equation?

P=1/2m(Vj-V)²

Total power generated equation

P=(T_A)V+1/2m(Vj-V)²

Define Efficiency

Useful power/total power

Efficiency equation

η_P=2/1+(Vj/V)

Propeller

Large diameter= high m, low ΔV, high efficiency

Jet engine

Small diameter=low m, high ΔV, less efficient