AVIATION HISTORY Lecture 8: Speeds of Flight

Introduction  After the invention of the airplane, designers and engineers created new aircraft for a variety of uses.  Airplanes became a part of daily life.  They were used regularly to ship cargo and to transport people.  Over time, the speed of aircraft has increased.

Introduction  Aircraft can be grouped based upon how fast they can fly.  These groups called as speeds of flight or regimes of flight  There are three basic speeds of flight which are Subsonic (low, medium and high), Supersonic and Hypersonic.  These include the earliest aircraft to the most modern.

Speed of sound and Mach No.  Speed of sound means how fast the sound waves travel.  Roughly speaking, the speed of sound is 343 m/s (or 1236 km/h, or 768 mph).  When we refer to the speed of sound, we measure it in Mach numbers.  In the late 19 th century, physician named Ernst Mach developed Mach Number theory.  Mach number are used to show the pilot’s speed in comparison to speed of sound. Mach

Speed of Sound and Mach No.  If an airplane is flying slower than the speed of sound, we say it is moving at subsonic speed.  If it is flying faster than the speed of sound, it is traveling at supersonic speed.  So, if an airplane is traveling at the speed of sound, we say it is flying at Mach 1.  If it is traveling at two times the speed of sound, we say it is flying at Mach 2.

Subsonic (0-700 MPH )  Subsonic aircraft travel below the speed of sound.  The Mach number M is much less than one, M << 1.  Subsonic aircraft can be divided into three: low speed, medium speed and high speed Low speed Medium speed High speed

Subsonic (Low speed)  Low speed aircraft travel at speeds between 0 and 100 miles per hour (mph).  They were lightweight vehicles with a small engine or no engine at all.  The aircraft in this group include the earliest types of aircraft, such as kites, balloons and early airplanes.  Modern aircraft in this speed regime are hang gliders and ultra lights aircraft.

Subsonic (Medium speed)  Medium speed aircraft fly between 100 and 350 mph.  These vehicles are usually airplanes with straight, thick wings.  This category includes biplanes, propeller planes, helicopters, small plane like the modern Cessna

Subsonic (High speed)  High speed aircraft are the powerful jet planes that fly between 350 and 700 mph.  The Boeing 747 Jumbo Jet, the Lear Jet, the Sikorsky Blackhawk helicopter and many fighter planes fly within this speed regime.

Supersonic ( MPH )  Supersonic aircraft can go faster than speed of sound.  The range of Mach No. is between Mach 1 and Mach 5 (1.0<M<5.0).  These vehicles have high- powered jet engines, a sleek fuselage and super thin wings.  The Concorde, the F-15 Eagle, and the SR-71 Blackbird are some examples of airplanes that can fly at supersonic speeds.

Hypersonic ( MPH )  Hypersonic aircraft has Mach No. greater than 5 (M>5).  This is more than five times the speed of sound.  These vehicles have high- powered rocket engines with short, thin wings.  The best known examples of hypersonic aircraft are the X- 15 and the space shuttle

What is SST (Supersonic Transport) aircraft?

SST: Supersonic Transport  A Supersonic Transport (SST) is a civil aircraft designed to transport passengers at speeds greater than the speed of sound.  The only SST to see regular service was the Concorde, and the only other design built in quantity was the Tupolev Tu-144.  The last passenger flight of the Tu-144 was in June 1978, and the Concorde's last flight was on 26 November 2003.

Tu-144, first supersonic transport aircraft (SST), The Tupolev Tu-144 was the first supersonic transport aircraft (SST), constructed under the direction of the SovietSoviet

Concorde: Fastest Commercial Aircraft. Primary Users: British Airways & Air France First flown in 1969, Concorde service commenced in 1976 and continued for 27 years. It flew regular transatlantic flights from London Heathrow (British Airways) and Paris Charles de Gaulle (Air France) to New York JFK and Washington Dulles, flying these routes at record speeds, in under half the time of other airliners.Washigton Dulles

Advantages of Supersonic Transport Aircraft  High Speed  Special shaped wings- to gain more lift.  Droop-nose section for improved visibility in landing  Weight Saving  Aircraft skin was made from Aluminium  Fully electrically controlled fly-by-wire flight controls systems, no hydraulic system.

Why Airliners have failed to go Supersonic?  However, as of 2005, there are no more SSTs used in regular commercial service.

Challenges of Supersonic Transport Aircraft 1. High Costs – high fuel consumption 2. Narrower fuselage-limited passenger 3. Takeoff Noise – environmental issues 4. Poor Range – uneconomical

High Costs  The faster the speed the higher the air resistance, thus the higher the drag.  As the drag increases, more power/fuel require to overcome the drag which lead to high fuel cost.  As, SST consume higher fuel, this leads to higher ticket costs.  As a results, only low passengers demand on this aircraft services

Narrower fuselage  SST demand narrower fuselage designs.  Therefore, capacity for passengers on this aircraft are very limited.  Both Concorde and the Boeing 747 use approximately the same amount of fuel to cover the same distance, but the 747 can carry more than four times as many passengers.  This factor will not give profit to the airlines.

Takeoff noise  SST has very high engine noise levels, associated with very high jet velocities used during take-off.  This noise disturbing the communities near the airport.  This is an environmental hazard – Noise pollution

Poor range  Range means how far can the aircraft fly with a tank of fuel.  SST can only carry lesser fuel due to airline trying to increase passenger volume.  This means that SST can not cover many routes.

Conclusion  The cost of operating supersonic aircraft do not outweigh the benefits that airlines could get from them.  Thus, today supersonic transport aircraft services has stopped.  Only the military consistently use supersonic aircraft these days.

Question Bank a) Write the equation of Mach number and define the speed of sound.(3M) b) Explain the CHARACTERISTICS of subsonic, supersonic and hypersonic aircraft. Give examples for each type. (12M)

Question Bank a) Define SUPERSONIC TRANSPORT (SST) Aircraft. Provide examples. (5M) b) Explain four (4) REASONS why airliners have failed to go supersonic? (10M)