Basic Aeronautics and Aerodynamics

Forces of Flight

Four Forces of Flight 4 fundamental forces act in an aircraft in flight Forces have a magnitude and direction which makes them “vectors” Vectors can be added and subtracted to give resultant or net force When forces add to zero, aircraft is in steady flight When a force is unbalanced, aircraft accelerates in direction of net force

All Forces Balance in Steady Flight

Forces in a Turn

LIFT

Showed that pressure of a fluid decreases as velocity increases Daniel Bernoulli (1700 - 1782) His work described the relationship between pressure and velocity in a fluid Bernoulli did the pioneering work on fluid dynamics which forms the basis for aerodynamics Showed that pressure of a fluid decreases as velocity increases

Airfoil Design

How an Airfoil Works The shape of an airfoil generates lift when air flows over it Relatively low pressure force downward Higher speed flow (relatively low pressure) Lower speed flow (relatively high pressure) Relatively high pressure force upward

Wingtip Vortices

Vortices From Large Aircraft Are Very Dangerous

THRUST

Propellers

Propellers Convert Engine Revolutions to Thrust Increasing speed Notice the pitch decreases further away from the hub This keeps the load even The faster moving tip doesn’t need as much pitch as near the hub A propeller is a spinning airfoil Spinning propeller produces thrust First successful aircraft propeller invented by the Wright Brothers

DRAG

Drag is Air Resistance to Motion Flat plate Sphere or Cylinder Which has the most drag? Which has the least drag Airfoil

Laminar Flow Laminar flow is smooth Turbulent flow has a lot of swirling and mixing Laminar flow is desirable for aircraft as it has lower drag than turbulent flow however there are other considerations we shall see later

Turbulence Notice how strings are not in straight lines Turbulent flow results when airflow is no longer laminar and becomes “swirly” Straight streamlines become unsteady and mix BUT turbulence isn’t all bad……it “sticks” to a surface better than laminar flow

Highly Turbulent Becomes Separated Flow Separated flow is highly turbulent flow that is no longer “attached” to the surface Separated flow results in a HUGE increase in DRAG In the case of an Airfoil it results in a STALL

Stalls Stall occurs when flow over wing separates Separated flow results in high pressure Result is loss of lift (and life if not corrected!)

Using Turbulence for Advantage Turbulent flow remains “attached” better than laminar flow Sometimes it’s better to have a turbulent flow than a laminar flow For example, do you know why a golf ball has dimples??

Aircraft in Motion

Center of Gravity The center of gravity is the average location of the weight of an object. In flight, both airplanes and rockets rotate about their centers of gravity.

Aircraft Move in 3 Axes

Longitudinal (Roll) Axis Roll controlled by ailerons on the wings

Vertical (Yaw) Axis Yaw controlled by the rudder on the vertical stabilizer

Lateral Axis Pitch controlled by the elevator on the horizontal stabilizer

Flight Maneuvers Use all Three Axes

Aircraft Engines

Reciprocating Engines Reciprocating engines are used in many aircraft Same type of engine used in cars and trucks Based on 4 stroke cycle also known as Otto cycle 1 power stroke for every 4 strokes Nicolaus Otto Germany 1832 -1891

#1 Intake Stroke Valves Fuel/air mix Intake valve opens and piston drops down and sucks in a mixture of air and fuel Start

Valves close and piston moves upward compressing the fuel/air mixture #2 Compression Valves close and piston moves upward compressing the fuel/air mixture

#3 Ignition and Power Spark plug fires at top of compression stroke Exploding gas pushes piston downward

Exhaust valve opens and piston pushes burned gases out of the cylinder Hot exhaust gases Exhaust valve opens and piston pushes burned gases out of the cylinder

Review Can you follow the four stroke cycle??

Turbine Engines

Why Turbines?? Turbines (jets) are: Simpler (higher reliability) Recip TBO 1500 to 2000 hrs Jet TBO 5000+ hrs Smoother running Produce much higher thrust at high speed Capable of very high speeds (much higher than propeller engine) Props loose efficiency at high speeds due to tip speed approaching Mach 1 Much higher power per unit weight (as much as almost 4:1) But Require special high temperature materials High fuel consumption Not efficient for low speed operations Very loud (environmental issue)

A Quick Comparison Pratt & Whitney JT-9 Wright 3350 Characteristic   A Quick Comparison Pratt & Whitney JT-9 Wright 3350 Characteristic Lockheed 1049G Boeing 747 Weight, W, lb 112 000 700 000 Speed, V, mph 330 530 Altitude, ft 23 000 35 000 Lift-drag ratio, L/D 15 16 Number of engines 4 Total cruise power, hp 6 585 59 934 Power per engine, hp 1 646 14 984 Dry engine weight, lb 3 675 8 600 Power to weight ratio 0.45 1.74  

Turbojet Engines

Turbofan Engines Turbofan has some of the good properties of a propeller engine such as better low speed efficiency but retains high speed jet performance

Turboprop Engines Turboprop is more like a propeller engine with high low speed efficiency but lower top speed compared to pure jet

Ramjets and Scramjets Instead of compressor turbines, ramjets use the “ram” pressure of inlet air for compression Ramjets are very simple with no moving parts But they can only operate at very high speeds

Structures and Other Systems

Fuselage Structure 3 main types of aircraft structures: Truss Monocoque 3 main types of aircraft structures: Truss (used in early fabric covered airplanes) Semi-monocoque Loads carried by frame and skin Monocoque Loads carried by skin Semi-monocoque

Landing Gear Conventional (“Tail dragger”) Tricycle Tandem Fixed and Retractable - why is retractable gear a good thing??

Fuel Systems Fuel usually stored in wings Fuel “Feed” Gravity Force (pumped) Wing higher than engine Fuel tanks in wings Wing lower than engine