Regional Aircraft/Corporate-General Aviation

Sudarshan KumarAssociate Professor

Aerospace Engineering DepartmentIIT Bombay, India

Regional airline

• A regional airline is a small airline designed to fly up to 100 passengers on short-haul flights,

• Feeding larger carriers' hubs from small markets.

• This class of airliners are typically flown by the regional airlines – that are either contracted– subsidiaries of the larger airlines.

General features

• Regional aircrafts are 40-60 % less fuel efficient than their larger, narrow and wide body counterparts employed for long range

• Regional jets are 10-60 % less fuel efficient than turboprops

• The difference in efficiency largely depends on the differences in operation rather than on technology.

• Operating costs per passenger are 2- 6 times higher for regional transport

Why regional transport

History

• To keep these short routes economical,– Airlines were generally unwilling to spend large

amounts of money on new aircraft;– Used available aircrafts– Slowly new aircrafts models emerged, – In the post-war era

• Douglas DC-3s, • De Havilland Dragon Rapider• Convair 440, • Douglas DC-6 • Vickers Viscount

Duglas DC-3

• Developed in 1935• Fixed wing propeller driven aircraft• More than 16000 planes were built and flown• Early 1950s’ turboprop conversions• It is still being operated by some revenue and cargo

companies• Technical specifications:

– 1200 bhp radial piston engines (PT6 engine variants)– Later P&W engines used with 433 – 1447 kW shaft power– Rolls Royce engines (RB 53 Dart) 1800 bhp shaft power

Bombardier Dash 8

• Two engines, medium range turboprop airliner• Over 1000 planes have been ordered• STOL performance• Improved cruise performance• Low operational costs• Engine (P&W – PW100)• Seating capacity 39 – 80 with a range of engines• Can operate from smaller runways (910 m)

Regional jet

Regional jet

• Although more expensive that the turboprop• Favored for routed not suitable for turboprops• Lower maintenance costs of turbojet engines• 30% more fuel consumption

• According to Bombardier marketing, the aircraft breaks even – For about 1/3rd of its seats filled – Or 1/4 with more closely spaced seats– Making it particularly attractive on routes with varying passenger numbers– For example, Island Air in Hawaii calculated that the use of a 50-seat Regional

Jet would break even at 45 passenger seats compared to the Q400's 35-36 seats (~55% breakeven load factor).

– For most short-haul routes (< 500 km), • time spent on taxiing, • takeoff • Landing

– This eliminates a competing jet's speed advantage. – Q400's 414 mph (667 km/h) cruise speed approaches jet speeds, – Short-haul airlines can easily replace a regional jet with a Q400 without

changing their gate-to-gate schedules.• Bombardier has singled out the Q400 for more aggressive marketing, • Competes in the 90-seat market range• Bombardier commercial aircraft president Gary Scott has affirmed that– By 2013-2014 we are planning to offer a stretched version of the Q400

turboprop.

Indian regional jet

Indian regional jet

Indian regional jet (IRJ)• Jointly proposed by NAL and HAL in 2007• 70 – 100 seater aircraft

– Common platform for turbo prop and turbo fan engines– 95 % of the airframe and other systems same

• The aircraft claimed to offer – 25% lower acquisition costs– 25% lower operating costs– 50% lower maintenance costs than existing turboprop regional aircraft.

• Specifications:• Range: 2,500 km, Runway length: 900m • Aircraft length: 28.6m Wing-span: 29.4m• Service ceiling: 30,000 ft, Cruising speed: 300kt, • Noise level to meet Stage 4 criteria. Composite airframe• 60% lower emissions Ability to operate from ill equipped airfields• Cabin dimensions: Length - 3.01 m and height - 3.35 m. • Cargo version to have 25 m3 volume.• Indigenous fly-by-wire control system, Open distributed modular avionics,• Automatic dependence surveillance Broadcast navigation capabilities, and advanced

displays

ATR-72

ATR 72

• ATR 72 was developed from the ATR 42– To increase the seating capacity (48 to 78) by stretching the fuselage by 4.5 metres (15 ft)– Increasing the wingspan– Adding more powerful engines– Increasing fuel capacity by approximately 10 percent.– The 72 was announced in 1986,[2] and made its maiden flight on 27 October 1988.– One year after that, Finnair became the first airline to put the plane into service– Since then, at least 408 ATR 72s have been delivered worldwide with orders pending on at least 28 more.

• Design– Passengers are boarded using the rear door (quite rare)– The ATR aircraft does not have an auxiliary power unit (APU)– "Hotel Mode") that stops the propeller on the #2 (right) engine, allowing the turbine to run and provide air

and power to the aircraft without the propeller spinning. • General characteristics• Crew: 2• Capacity: 68 to 74 passengers• Length: 27.17 m (89 ft 2 in) Wingspan: 27.05 m (88 ft 9 in)• Height: 7.65 m (25 ft 1 in) Wing area: 61.00 m2 (656.6 sq ft)• Aspect ratio: 12.0:1 Empty weight: 12,950 kg (28,550 lb)• Max takeoff weight: 22,500 kg (49,604 lb) Powerplant: 2 × Pratt & Whitney PW127F turboprops, 1,846 kW

each• Performance• Cruise speed: 511 km/h Range: 1,324 km• Service ceiling: 7,620 m Takeoff Run at MTOW: 1,165 m (3,822 ft)

Embraer jet

Embraer- ERJ family• The aircraft ERJ 135-145 family is powered by two turbofan engines (Rolls-Royce AE 3007)

– Thrust: 30 – 42 kN– Pressure ratio 20: 1– Turbine inlet temperature: 1300 K– Thrust to weight ration : 5: 1

• Capacity 37 – 122 passengers• Sold around 1800 jets in last 15 years• Service ceiling: 11278 m• Cruise speed: 828 kmph• Range: 3200 km

• The ERJ E-170-195 family employs GE CF34- 8E/10E engine series– Thrust: 63 – 89 kN thrust– Range – 4000 km– Cruise speed: 890 kmph– 80-122 passengers

Energy efficiency and load factor

U

I

EE EI = Energy intensity – energy consumed per ASK (available seat per km)

EU = Energy usage- energy required per kma = load factor

•EI– energy consumed per ASK Constant for all the aircrafts

•EU = Varies from one aircraft to another• Depends on

• Technological advancement• Size• Mission• Propulsion system type• Operational efficiencies

EU of regional aircraft and their yearly average

EU of regional aircraft and their yearly average

• EU of regional jets has improved with an annual rate of about 2 % per year

• EU of turboprops has improved by ~1.5 % per year.• Although regional jets are ~ 50 % less efficient than turboprops• But the technological advancement has helped in catching up with

turboprops.• Reason: More investment into improving the fuel efficiency of jet

engines.– Long range aircrafts most lucrative field– Technology developed for those engines is simply transferred to regional jets– Not much investment into the turboprops because of their limited application

• regional transport• lower speed as compared to regional jets

EU comparison of large and regional aircrafts

Drastic decrease in the E indicates technological advancement due to demand for long distance travel

Specific fuel consumption of Engines

Specific fuel consumption• TSFC is 10-25% higher for regional jet as compared to large jet because

of delay in implementation of new technology to regional jets• For smaller size the gap remains as efficiency of a system can not be

improved when size of the engine is reduced …e.g. regional transportation

• Due to limitation of engine size, smaller jet engines employ smaller lower pressure ratio engine and hence reduced efficiency.

• Hence lesser compressor stages and less efficient than centrifugal compressors

• Turboprops are 10-30 % more efficient than regional jets.• Turboprops deliver 85% of the total thrust from propellers.– Due to their ability to accelerate large amount of air at small speeds.– Advantageous for takeoff, climb operation and low speed operation

Structural efficiencies

• 1% reduction in the gross weight reduces the specific fuel consumption by 0.25 – 0.75%.

• Despite availability of best materials i.e. composites, most of the aircrafts contains ~ 97% metallic with very few composite components

• Reduction in the component weight is offset by integration of new passenger facilities i.e. personal entrainment systems

• For smaller engines, thrust to weight ratios are typical lower• Turboprops are quite poor because of high weight of engine

components (e.g. Speed reduction gearbox; mechanisms to alter propeller pitch)

Trends in structural efficiency

Aerodynamic efficiencies

Energy usage for various aircrafts

Energy usage

• EU for large aircrafts is approximately 1.6 times to that of EU,CR

• For regional aircrafts, the number is app. 2.6• For turboprops, it is approximately 2.5 times

Operational sequence influence

Ground Efficiencies

Airborne efficiency

Energy usage Vs ground and airborne efficiencies

Operating costs

Pilot salaries and fuel costs

Turboprop Regional jet Large jet0

10

20

301975 1999

Turboprop Regional jet Large jet0

10

20

30

40

501975 1999

Pilot salaries (% of total cost) Fuel costs (% of total cost)

Operational cost Vs Stage length

Regional Daily flights distribution in 2002

Comparison of fuel consumption

Turboprop

Propulsive efficiency

Turboprops and Turbofans

Why regional transport• For regional

transport– Many hubs located

around the many centers

– Delhi, Mumbai, Bangalore, Chennai, Hyderabad

– Distance ~ 600 km– Importance of

connectivity

Conclusions• Regional aircrafts have value of energy use 1.5 - 2 times greater than larger aircraft• The difference is due to operational sequence rather than technological

sophistication• Regional aircraft fly short lengths and spend large fraction of time in climbing to

altitude than cruise.• Turboprops have inherent advantage than regional jet as they can cruise efficiently

at a much lower altitude than regional jets and at much lower speed.• Fuel costs are– ~ 26% for larger aircrafts– ~ 20% for regional jets– ~ 13% for turboprops• Regional jets appear to be as good as turboprops because of their higher load

factors.• If strategies are evolved to increase the load factors in Turboprops, they are the

best option of economical transport at regional levels.

References

• Smirti and Hansen, “The effect of fuel prices on comparative aircraft costs,” National center of Excellence for Aviation Operations Research

• Babikian et al., “The historical fuel efficiency characteristics of regional aircraft from technological, operational, and cost perspectives,” Journal of air transportation management, 8(6) 2002, 389-400.

• ATR- Optimum choice for friendly environment, www.fc.fi/data/files/ATR_TheOptimumChoice.pdf

• The green power of tomorrow, The latest generation turboprops, www.avantiair.com/.../The%20green%20power%20of%20tomorrow.pdf