Turboprop: And what it means to Nepal???

By Binu ghale

Here I have written about the Turbo-Propeller powered Aircrafts in consortium to Nepal. We’ve got Buddha Airlines, Yeti Airlines, Sita Airlines and others, almost all domestic airlines flying in Nepalese sky falls under the turboprop powered Engines.

Firstly, fuel efficient and cheap operation of turboprop than the Turbojet/turbofan obviously makes it  first choice for us. With this economic comfort, we are certainly making errand for commercialization in our market- but Is it really feasible from the technical view?? Or how it makes good fly for country like Nepal.

One thing is sure. The cheaper operating cost of Turboprop has made Commercial Airlines very much possible for our Economically weak Nation.

As a student of the field and an aware citizen of my Nation, I am interested in how these aircrafts are making for our Nepalese Airline Environment and if I could figure out and emphasize on the true side of the things going around with our Airlines.

MAIN FIGURE

Turboprop and what it means to Nepal???
So what’s the deal with Nepalese Turboprop??. ATR-42-320, ATR-72-500, Beechcraft 1900D of Buddha Air whose -320 and -500 are powered by PW121/127 Twin Turboprop Engines especially designed to perform in hot and high conditions likewise Beechcraft have two PT6A-67D Engines. Also, BAe Jetstream 41 of Yeti Airlines, Dornier Do 228 of Simrik and Tara Airlines along with Beechcraft 1900D of Simrik and PT6A-20 powered de Havilland   Canada DHC-6-300 & Viking Air DHC-6-400 twin otter of Tara Air are the major Turboprop flying in the Nepalese Sky.

Though the prop engines are high in price, they make a good fuel efficiency. A commercial passenger plane is designed for a relatively light load and lots of seating space, with some preference for speed but with definite consideration for fuel efficiency. So, how props make it fuel efficient ?. Unlike the turbofan engines, the propeller has a large diameter that lets it accelerate a large volume of air. This permits a lower airstream velocity for a given amount of thrust. As it is more efficient at low speeds to accelerate a large amount of air by a large degree, low disc loading (thrust per disc area), increases the aircraft’s energy efficiency, and this reduces the fuel use. Besides propeller enables higher thrust in denser air (remember lower the altitude denser the air). Because of the economic advantage of turboprop engines, especially for low speed, low altitude and shorter trip distances which surely is our domestic flight, makes it good economic hit for us.

Let us go with ATR-72 for instance, a 70 seat ATR-72 at a top speed of 317.68 mph and range of 1,300 miles, burns about 810 litres per hour. A Boeing 737-400 seats about 150, has a maximum range of about 2,400miles, and a cruising speed of about 544.42 mph (almost double the range and 1.5 times the speed). But its burn rate is about 3,000 litres per hour. The main reason for preferring turboprop engines over pure jet engines is that turboprop engines deliver more power and greater efficiency at slower flying speeds than jet propulsion. 

The Beechcraft 1900D is designed for all weather conditions, including icing conditions, and for us, this might have made fit for mountain flights. Turboprop are most efficient at flight speeds below 725 km/hr with high performance short-takeoff and landing (STOL) and lower ceiling. In addition, they work better on dirt and gravel runways, having much smaller openings in their engines that dirt and gravel are unlikely to enter. They make less noise pollution on airports, have least environmental chemistry impact from fuel consumption vs payload.

How it works

A turboprop engine is a turbine engine that drives an aircraft propeller. Unlike turbojet, the engine’s exhaust gases do not contain the enough energy to create significant thrust, since almost all of the energy’s power is used to drive the propeller. Propeller is coupled to the turbine via reduction gear that converts the high RPM, low torque output to low RPM, high torque (power equation). The propeller itself is normally at constant.

In its simplest form a turboprop consists of an intake, compressor, combustor, turbine, and a propelling nozzle. Air is drawn into the intake and compressed by the compressor. The fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts. The hot combustion gases expand through the turbine. Some of the power generated by the turbine is used to drive compressor. The rest is transmitted through the reduction gearing to the propeller. Further expansion of the gases occurs in propelling nozzle, where the gases exhaust to atmospheric pressure.

Conclusion 

Seeing the state of our runways, flight trip length, take-off and landing condition and its good economic part, turboprop is a good choice for us. Because we cannot go for high speed, noisy jets to fly for a 20 minute trip from Kathmandu- Biratnagar or Kathmandu-Bhadrapur.