This is a preliminary report for a project on Propeller aircraft, it aims to show the past, present and future technologies used on propeller driven aircraft. The introduction gives a brief history of propeller engine development. After which objectives section explains what this report hopes to achieve by the end of this project. Few of the main objectives include, highlighting the advancements in propeller blade designs and propeller engines, and detailing the future technologies currently in development regarding propeller aircraft. Also it is intends to explain the argument why propeller aircraft are better suited for intercity travel when compared to jet aircraft due to overall lower environmental pollution.
This report then describes the tasks that need to be carried out in order to bring this project to a timely conclusion, the progress that has been made to date and finally limitations regarding this project are outlined and mitigating strategies discussed.
Table of Contents
Word Count = 2133
1 Introduction
Propeller aircraft have come a long way since the early days of fixed pitch wooden propellers that were used by the Wright brothers on the ‘Wright Flyer’. These propellers were not very efficient as they were fixed pitch, which meant that they were only optimum in at one engine speed. I.e. either they were good for takeoff but the angle was not right for cruise or they were optimum at cruise but not efficient during takeoff due to high slippage. Figure 1 shows some examples of fixed pitch propellers o different designs.
Figure 1, Examples of fixed pitch propellers. Available [Online] at http://www.airfieldmodels.com/information_source/model_aircraft_engines/propellers.htm [Accessed: 23rd November 2010]
1.2 Historical Developments
In the late 1920’s we saw the development of ground adjusted metal propeller this allowed for better efficiency as blade angles could be changed due to the local weather conditions and the different type of aircraft they were being used on. Figure 2 shows a ground adjustable metal propeller.
Figure 2, Ground adjustable propeller.
Available [Online] at http://www.legend.aero/options3.asp [Accessed 27th November 2010]
These also became outdated by the development of constant speed propeller system, which allowed you to change the pitch of the propeller blades during ground or in flight and this system continues to be used even today. Other improvements of propeller designs from 1930’s through World War II included the feathering of the propeller for multi engine aircraft in case one engine became inoperative during flight; and reversing propeller systems that allowed for shorter landing distances and greater ground manoeuvrability.
(Delp, 1979)
In recent times we have seen the development of composite blades, which are lighter, stronger and more durable then metal blades and are controlled by constant variable pitch changing mechanism which offer optimum efficiency.
As the design of the propeller blades have been changing constantly so has the way these propellers have been powered, from the early piston engines to the turboprop engines of current times; each change ensuring better performance and more efficient propeller aircraft. Though the development of the ‘Jet engine’ in the 1930’s by Sir Frank Whittle, an RAF serviceman was suppose to change the game plan for propeller aircraft as turbofan engines were perceived to be the only future, turboprop engines have defied those expectations and are still continued to be used till today.
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The reason for this is that they provide maximum efficiency in low altitude, short range flights such as city hopper jets. These are usually operated from smaller airports hence the short takeoff and landing (STOL) characteristic of these aircraft gives them the edge over the turbojets. They are also more fuel economical when compared to their turbofan counterparts as the latter burn high quantity of fuel during takeoff and climb out phases and are usually optimum for long range, high altitude flights, due to this they are also ideal as fright carrier aircraft. So for these reasons turboprops continued to be used by many airlines for short haul flights, and hence therefore continue to defy the prediction of those sceptic people who said that propeller aircraft would die out as turbofans were the clear cut future of civil aviation. Figure 3 shows a modern day constant speed, composite bladed turboprop aircraft, from this we can how the design of the blades and pitch changing mechanisms have evolved from the early wooden and metal props.
http://images.asme.org/MEMagazine/Articles/2009/December/21224.jpg
Figure 3, Constant Speed Propeller, Available [Online] at http://images.asme.org/MEMagazine/Articles/2009/December/21224.jpg> [Accessed] 1st Dec 2010])
2 Aims
The aim of this project is to provide an in depth report of the development of propeller aircraft and their associated benefits over jet aircraft. To highlight why turboprops are best for inter city travel and their relative environmental impact when compared to turbojets, this will be done by analysing the statistical figures for their fuel efficiency, the average fuel emissions per person and the noise emissions of the two types of aircraft; from this one will be able to come to the conclusion that which of these type of aircraft are best to reduce the environmental impact of air travel. Also the past, present and future technologies for propeller aircraft will be discussed and presented to the reader clearly explaining their benefits.
2.2 Objectives
The objectives of this report are listed below and explain the issues that this report is going to investigate and the findings it will show.
To explore the development of the propeller engines from the early piston engines through to the modern day turboprops.
To examine how propeller blades have developed over the years from the early wooden to the composite blades of today, including studying the development of variable pitch changing mechanism that has significantly increased propeller efficiency in each different flight phase.
To highlight the benefits of propeller engines over jet engines for inter city travel aircraft and freight carriers.
To investigate the fuel efficiency and noise emissions of different types of propeller aircraft, in particular turboprop.
To investigate the future technology being developed using propeller aircraft, such as the ‘open rotor’ concept that was first studied in the 1980’s by General Electric’s and NASA due to the last round of high fuel prices.
To highlight the benefits and drawbacks of distinctive propeller A/C designs, such as the tilt-rotor technology that is employed on the Boeing-Bell V22 Osprey.
To analyse future methods and procedures that could be used to reduce the environmental impact of propeller aircraft such as external noise suppression, synchrophasing of propeller blades and active noise control.
To investigate the different fluid dynamic studies that have been carried out on various different propeller designs to show which design is the most efficient and why.
3 Analysis of tasks
To achieve the objectives of this report extensive research on propeller aircraft will be carried out, especially regarding turboprops. A performance database listing all the appraisals for major turboprop aircraft that are being used in commercial and military environments will be constructed. This will make it easy to compare the performances of different turboprop aircraft against one another of different category and weight i.e. their fuel consumption, ceiling height, max speed etc. In order to highlight the benefits of turboprops for intercity travel, turbojets used for the same routes will also be looked at, in order to give a direct comparison.
To investigate the development of propeller engines, propeller blades and the pitch changing mechanism the following textbooks will be used amongst others:
Aircraft Propellers and Controls, Delp, Frank, 1979
Powerplant Textbook, Jeppesen, 2002
Jet and Turbine Aero engines, Gunston, Bill, 1997
As well as these books other sources such as the internet and aircraft magazines are to be used. The internet will be the main source of information for this report as it contains vast amount of data and archives related to propeller aircraft and their development, information that otherwise would be hard to find. After the research is completed into each part it will be collated into one report. The main findings from this report are expected to show whether propeller aircraft or jet aircraft have lower environmental impact during short haul flights.
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Future technologies involving turboprop engines will also be included; in particular the development of the General Electric’s ‘GE36’ open rotor engine of the 1980’s which gave us increased fuel efficiency. Figure 4 shows a ‘GE36 on a NASA test rig. The major drawbacks for this design such as noise, vibration issues will also be discussed in the view of reducing environmental pollution.
(Open rotor engine, 2008)
Photo
Figure 4, Open Rotor Engine [Online] Available at:
http://www.greencarcongress.com/2008/07/cfm-introduces.html
[Accessed] 3rd December 2010)
The fluid dynamic studies involving different propeller designs will be looked at to see which blade design is the most efficient and to explain the reason behind this. If time permits ‘Solidworks’ will be used to simulate fluid dynamics on at least two different blade designs to confirm these findings.
4 Gantt Chart
5 Current status of the project
Research has been carried out using various internet sites and information has been gathered on the development of propeller engines, the blades construction and the pitch change mechanism used on propeller aircraft. Also a database appraisal of different props that are currently in use around the world is being constructed, detailing information such as range, max payload, max ceiling etc; this will be used to validate why propeller aircraft are more economical for short haul flight when compared to jet aircraft.
Research on the ‘ultra high bypass’ (prop fan) open rotor concept has shown that the new designs by using titanium, lightweight stainless steel and composite materials offer 15 percent better fuel economy then some leading turbofan engines. The designers for this engine have achieved 30:1 bypass ratio, by employing single or dual propellers with composite blades that have 12 to 15 feet diameter. As composite blades are lighter, they allow for safer operation at higher speeds. But the disadvantages of noise, vibration and maintenance issues cannot be simply overlooked. This information has helped to clarify why this design has the potential for success but also why it is still a long way to becoming a reality.
(Jeppesen, 2002)
The Bombardier Q400 (‘Q’ standing for Quiet) was looked at and shows that this new generation turboprop aircraft produces 30 percent less fuel emissions and is said to be more efficient then an average car, when calculated on per passenger basis. It also employs a revolutionary ‘Active Noise and Vibration Suppression’ system; that prevents noise and vibration from entering the cabin.
(Bombardier’s Greener Turboprop, 2008)
6 Discussion & Conclusion
The research that has been conducted up to now is generic to say the least, but it does cover most of the objectives that are listed for this report. Nonetheless, more specific research is needed regarding points such as the future development of propeller engines especially the open rotor concept; and the potential noise suppression techniques being studied for turboprop aircraft. Research regarding the last two points will have to be conducted over the Christmas holidays as much more information is needed, whilst it is to be ensured that enough time is also taken out for revision for end of semester exams straight after the holidays.
In view of the time constraints the study on fluid dynamics of propeller blades using computer software ‘Solidworks’ will be carried out towards the end of the project, this is to ensure that main objectives of this project are covered as it is assumed that it will take time to get used to operating this software. The purpose of this part is to show which propeller blade shape is most efficient and why.
Due to the secrecy of manufacturers regarding their new and exclusive products, especially in the aircraft industry; it is presumed that it will be difficult to get up to date information such as figures and stats for developing technologies such as the open rotor engine being developed by GE and NASA. Along with the already developed tilt-rotor military AC from Boeing-Bell, so therefore general information that is available in the public domain such as on the internet will be used, but the drawback to this is that this information might not be 100% accurate and sometimes cannot be verified. Finally if this report is to be completed on schedule to meet its set objectives then the above mentioned points in this section should be sufficiently addressed on the earliest opportunity to allow time for the fluid dynamic research.
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