Literature review construction project costs

Literature review construction project costs This chapter comprises of literature review, quotes of the various related works done in this area of studies. The duration of construction projects right from inception to completion is assuming great importance in the construction industry. The author of this project work believes that, this shift in attention on constructioin delays is taking it rightful place of importance in the global construction sector. Clients or consumers are no longer content merely with minimal cost and adequate functional performance for their projects; increasing interest rates, inflation and other commercial pressures, among other factors, mean that it is in many instances most cost-effective to complete a project within the shortest possible time.The the current hursh financial climate does not allow for subcontractors not to be prudent with project planning and delivery , hence the reason for chosing to write on this subject. The most significant unbudgeted costs on many construction projects are the financial impacts associated with delay and disruption to the works. Owners and Subcontrcators have one common objective; to complete the project in time and within budget. It is the failure of this objective of time which leads to failure of budget and ultimately gives rise to disputes. There is no consensus in the literature on the identification of factors which affect stipulated, planned or achieved construction times of buildings. One reason for this is that researchers have largely viewed the subject from diverse prospective. Such viewpoints include identification of discrete factors which affect productivity on site and taking a systems view of the construction process and end product (Nkado R.N, 1995) The inherent and often unanticipated risks on construction projects present key challenges to subcontracting firms. For example, if a project is delayed or disrupted, significant resources are engaged and management time consumed. The outcome can have serious consequences on corporate value. One loss-making project can wipe out the profit on 50 successful ones and significantly damage a companys reputation. In the current economic climate, claims and disputes are increasingly more likely. Construction delays are not a modern phenomena.The delays on some of the UKs most famous landmarks, such as St Pauls Cathederal, the Houses of Parliament and the Clifton Suspension Bridge would make the delays on more recent high profile construction projects look distinctly trifling (Lowsley et al, 2006) Delay Ñ-ц¢ generally acknowledged à Ã‚ °Ãƒâ€˜Ã¢â‚¬ ¢ thà Ã‚ µ mà Ã‚ ¾Ãƒâ€˜Ã¢â‚¬ ¢t common, costly, complex à Ã‚ °nd riц¢ky problem encountered Ñ-n construction projectц¢. Becauц¢e à Ã‚ ¾f thà Ã‚ µ overriding ц¢ignificance à Ã‚ ¾f tÑ-me fà Ã‚ ¾r both thà Ã‚ µ proprietor (Ñ-n termц¢ à Ã‚ ¾f performance) à Ã‚ °nd thà Ã‚ µ ц¢upplier (Ñ-n termц¢ à Ã‚ ¾f money), it Ñ-ц¢ thà Ã‚ µ ц¢ource à Ã‚ ¾f frequent diц¢puteц¢ à Ã‚ °nd claimц¢ leading tà Ã‚ ¾ lawц¢uitц¢. Delayц¢ occur Ñ-n almost every construction project à Ã‚ °nd thà Ã‚ µ magnitude à Ã‚ ¾f theц¢e delayц¢ varieц¢ conц¢iderably frà Ã‚ ¾m project tà Ã‚ ¾ project. à Ã¢â‚¬ ¦ome projectц¢ à Ã‚ °re only à Ã‚ ° few dayц¢ behind ц¢chedule; ц¢ome à Ã‚ °re delayed bу over à Ã‚ ° year. à Ã¢â‚¬ ¦o it Ñ-ц¢ eц¢Ãƒâ€˜Ã¢â‚¬ ¢ential tà Ã‚ ¾ define thà Ã‚ µ actual cauц¢eц¢ à Ã‚ ¾f delay Ñ-n order tà Ã‚ ¾ minimize à Ã‚ °nd avoid delay Ñ-n any construction project (Ahmed et al., 2003). Chan et al (2004) Concluded in a research conducted to measure the success of construction projects that, cost, time and quality are the three basic and most important performance indicators in consruction projects.Other measures such as safety, functionality and satisfaction etc. are also currently attracting increasing attention. Chan et al, (2004) accentuated that accurate construction planning is a key factor in ensuring the delivery of a project on schedule and within budget. As almost all projects comprise a large number of interdependent items of work and involve many participants, reliable plans and accurate progress-recording mechanisms become essential to project success. Mbachu, et al(2005) discover the sources of strategies for minimising risks in the construction projects and categorised the results into internal and external sources.The internal sources of risks, which fall under the control of clients ,consultants and Subcontractors , include those risk elements emanationg from their acts or omissions in the project development process. They noted that, the most frequently mentioned risk elements under client sources include frequent and late changes at critical stages of the design and construction process, poor leadership and inadequate supervisions on the part of Contractors and subcontractors, low productivity, re-work and lossess, delays in supplying equipment, materials and components. For the consultants, incomplete design information and delay in supplying information required by contractors on site.The external risk sources, which are not within the control of the client and the project team, could be segregated into economic and globalisation dynamics, unforeseen circumstances/force majeue, government, statutory, political controls, health and safety risk elements and socio-cultural issue.smia12010-07-21T16:29:00 Who says this is so? If it5s you then you nned to say what leads you to this concluswionyou Typeц¢ of delay A delay to a construction project generally means delay to the planned completion date or a delay to a particular activity or sequence of activities (Lowsley et al, 2006) Delays can be grouped in the following four broad categories according to how they operate contractually: non-excusable delays; excusable non-compensable delays; excusable compensable delays; and concurrent delayц¢ The Bureau of Engineering Project Delivery Manual version 2 released in October 2006 smia12010-07-21T16:30:00 You need to give a proper reference for this. Who are the Bureau of Engineering Project Delivery?categorised construction delays in three basic types of delays, namely; Excusable-Non-Compensatory (Concurrent), Non-Excusable and Excusable-Compensatory. Non Excusable Delay Non-Excusable delays are events that are within the Subcontractors control or that are foreseeable. These delays might be the results of late performance of Subcontractors, untimely performance by suppliers, faulty workmanship by the subcontractor, underestimate of productivity, inadequate scheduling or mamanagement, equipment breakdowns, staffing problems, a project specific labour strikes caused by either the Subcontractors with the labour representative or by unfair labour practices(Trauner et al,2009) Excusable Non Compensable Delay An excusable delay is caused by factors that are not foreseeable, beyond the Subcontractors control .The implication of the term means that, neither party is at fault under the terms and conditions of the contract and has agreed to share the risk and consequences when excusable events occur. The Subcontractor will not receive compensation for the cost of delay, but he will be entitled for an additional time to smia12010-07-21T16:31:00 Always? Dosent this depend on the terms of his sub-contract? complete his work and is also relieved from any contractually imposed liquidated damages for the period of delay (Ahmed et al, 2003) 2.5 Excusable Compensable Delay (Ahmed et al, 2003) acknowledged that, compensable delays are those that are generally caused by the owner or its agents. If the delay is compensable, then the contractor is entitled not only to an extension of time but also to an adjustment for any increase in costs caused by the delay. Owner-issued contracts specifically address some potential compensable delays and provide equitable adjustments. The usual equitable adjustable clauses in owner issued contracts that apply are: Changes, Dithering Site Conditionsmia12010-07-21T16:32:00 What does this mean?, and Suspension 2.6 Concurrent delays The concept of concurrent delay has become a very common presentation as part of some analysis of construction delays. The concurrency argument is not just from the standpoint of determining the projects critical delays but from the standpoint of assigning responsibility for damages associated with delays to the critical path. Owners will often cite concurrent delays by the contractor as a reason for issuing a time extension without additional compensation.Contractors will often cite concurrent delays by the owners as a reason why liquilidated damages should not be assessed for its delays. Concurrent delays are separate delays to the critical path that occur at the same time. (Lowsley et al, 2006) Rubin et al. (1983) defined concurrent delays as the situation in which two or more delays occur at the same time either of which had it occurred alone, would have affected the ultimate completion date. It means each of the delays must independently affect the critical path. Reynolds et al (2001) argue that to be considered concurrent delays, the delays need not commence precisely at the same time. Arditi et al (1995) had a view that, the delays need not occur in the same activity on the same critical path but may exist in different activities on parallel critical path as well. The SCL Protocol (SCL, 2002) describe a true concurrent delay as the occurrences of the delays, one an employer risk event and the other a contractor risk event, at the same time, and their effects felt at the same time. This occurrence is, however, extremely rare in practice since time is infinitely divisible. For instance, two delay events occurring on the same day would not necessarily be true concurrent delays because one may have occurred in the morning while the other in the afternoon. Concurrent delay is also rather misleadingly used to refer to the occurrence of two or more delay events at different times but their effect are felt (in whole or in part) at the same time. As a summary, Figure 1 classifies the different types of delays based on their various attributes. Figure 1: Delay Classifications (Nuhu Braimah 2008) 2.7 Primary Causes of Delay There are two kinds of reason for delay in construction project: external causes; and internal cauц¢eц¢.Internal causes of delay include the causes arising from four partià Ã‚ µÃƒâ€˜Ã¢â‚¬ ¢ involved in the project. These partià Ã‚ µÃƒâ€˜Ã¢â‚¬ ¢ include the proprietor, designers, contractorц¢, and conц¢ultantц¢. Other delays, which do not arise from these four partià Ã‚ µÃƒâ€˜Ã¢â‚¬ ¢, are based on external factors for example from the government, material suppliers, or the weather (Ahmed et al., 2003). Semple et al. (1994) found that making provisions in a construction programme for events such as weather delays reduces disputes. Cost and time claims, especially those which are difficult to quantify, regularly result in disputes between the contractual parties. Weather contingencies are very seldom adequate, in terms of progress and cost, due to the use of varied methods used in the industry for weather contingency calculations. This results in adverse client-contractor relationships. Caenell.N.J, C2005) Cited the appropriateness to look at the matters which actually cause delay during the works themselves. The Contractor/Subcontractors responsibly for delays arise due to a failure on the part of the contractor to carry out the planning stages of the works properly, others will be due to an inability to perform in the manner agreed in the contract.This is in line with the authors believes that, most delays are caused by inefficiencies on the part of the Subcontractors. Employers responsibility or neutral events are caused through an act or omission of the employer or his team or by a matter which does not arise through the fault of the contractor. These are governed by the contract conditions. A useful list according to Carnell N.J (2005) is listed in Clause 25.4 of JCT 98 and includes: Force majeure,Exceptionally adverse weather conditions,Clause 22 perils(flood and the like),Civil commotion, strike or lock out,Compliance with architects instructions,Non-receipt of essential information,Delays by nominated suppliers or sub-contractors, artisans and tradesmen,Government action,Restrictions on the availability of labour or materials,Delays by,statutory undertakers,Delays in giving access to the works Ahmed et al, (2003) also mentioned the following as some possible causes of delays in construction project in nowadays: Possessive decision-making mechanism, highly bureaucratic organization, insufficient data collection and survey before design Site topography is changed after design,Lack of coordination at design phase,Inadequate review,Improper inspection approach,Different attitude between the consultant and contractors/subcontractors,Financial difficulties,Inexperience personnel,Insufficient number of staffs,Deficiency in project coordination,time spent to find sub contractors,company who is appropriate for each task,Often changing Sub -contracting company,Inadequate and old equipment,Lack of high-technology equipment and Harvest time. Ahmed et al (2003) cited Ogunlana et all (2001) as having studied the delays in Thailand, as an example of developing economies.They concluded that the problems of the construction industry in developing economies could be nested in three layers:(1) Problem of shortages or inadequacies on industry infrastructure, mainly supply of resources, (2) Problems caused by clients and consultants and (3) Problems caused by incompetence of Contractors. Assaf et al (1995) Listed 56 extensive causes of disputes over delay and identified them as : shortage of construction material, changes in types and specifications during construction, slow delivery of material, damage of material in storage, delay in the special manufacture of the building material, shortage of labour, labour skills, nationality of labourers, equipment failure, equipment shortage, unskilled operators, slow delivery of equipment, equipment productivity, financing by Contractor during construction, delays in Contractors progress payment by Owner, cash problems during construction, design changes by Owner or his agent during construction, design errors made by designers, foundation conditions smia12010-07-21T16:35:00 These would be far better rpesented as a bullet pointed listencountered in the field, mistake in soil investigation, water table conditions on site, geological problems on site, obtaining permits from municipality, obtaining permits for labourers, excessive bureaucracy in project Owner operation, building code used in the design of the project, preparation and approval of shop drawings, waiting for sample material approval, preparation of scheduling networks and revisions, lack of training personnel and management support, lack of database in estimating activity duration and resources, judgement of experience in estimating time and resources, project delivery systems used, hot weather effect on construction activities, insufficient available utilities on site, the relationship between different subcontractors schedule, the conflict between the consultant and the Contractor, uncooperative Owners, slowness of the Owner decision making process, the joint ownership of the project, poor o rganization, insufficient communication between Owner and designer at the design phase, unavailability of professional construction management, inadequate early planning of the project, inspection and testing procedures used in the projects, errors committed during field, application of quality control based on foreign specification, controlling subcontractors by general Contractors in the execution of the works, the unavailability of financial incentives for Contractor to finish ahead of schedule, negotiations and obtaining of contracts, legal disputes between various parties, social and cultural factors, accidents during construction . Ahmed et al. (2003) maintained that the iц¢Ãƒâ€˜Ã¢â‚¬ ¢ue of responsibility for delay Ñ-ц¢ related to whether the supplier Ñ-ц¢ awarded or Ñ-ц¢ liable for costs and additional time to complete the project. The categories of reц¢ponц¢ibilitieц¢ are: proprietor (or agent) responsible supplier will be granted à Ã‚ ° time extension and additional costs (indirect), where warranted; supplier (or subcontractor) responsible supplier will not be granted time or costs and may have to pay damages/penalties; neither party (e.g. act of God) responsible supplier will receive additional time to complete the project but no costs will be granted and no damages/penalties aц¢Ãƒâ€˜Ã¢â‚¬ ¢eц¢Ãƒâ€˜Ã¢â‚¬ ¢ed; and both partià Ã‚ µÃƒâ€˜Ã¢â‚¬ ¢ responsible supplier will receive additional time to complete the project but no costs will be granted and any damages/penalties aц¢Ãƒâ€˜Ã¢â‚¬ ¢eц¢Ãƒâ€˜Ã¢â‚¬ ¢ed. smia12010-07-21T16:36:00 Always? Dosent this depend on the risk allocation in the contract? Ying et al (2005) acknowledged five factors that influence time performance as; Long project scope identification, low speed of decision making, inadequate managerial skills during the planning phase, insuffiecient contractor completion and Lack of a strong organasational culture. Okumbe et al (2008) researched on Construction Industry perpestive on causes and effects of delays in South Africa and highlighted causes of dealy in payment as consultants inefficiency,lack of professionalism by the government employees,incompetence caused by insufficient staff,bureaucratic procedures experienced by government/client,late processing by project quantity surveyors ,late prepartion of payment certificate,claiming problems,late approval of work by architect and engineers,continous formulation of new policies by The Public Procurement and Asset Disposal Board (PPADB),poor budgeting by the client,late submission of cost reports by projects quantity surveyors,lack of understanding of contractual obligations and lack of funding,late project delivery,delays, in materials supply,labour stoppage as employess may go on strike if not paid on time,cash flow problems faced by contractors,contractors claiming extension of time with costs,risk of poor workmanship,poor contract deli very and default in paying suppliesrs and employers. In addition to causes of delays and who is responsible for them, there are other delay-related effects that may occur. High on the list is a decrease in the Contractors efficiency caused by the delays. The delays may directly cause the inefficiency or be caused by the inefficiency. Gorse (2004) Suggested that a well-evidenced claim, supported by an appropraite documentation, that properly establishes cause and effect and reasonably quantities the losses for each event will probably succeeds. Frimpong et al (2003)Conducted a survey on the causes of delay and cost overruns in construction of groundwater projects in a developing countries;Ghana as a case study and the main conclusions of the survey were;monthly payments difficulties from agencies,matarial procurement,poor technical performance,escalation of matarial prices accordinging to their degree of influence and theses were considered as major factors.The other factors that emerged as not very important ,but of interest were,bad weather,unfavorable geological conditions. Ahmed et al (2003) carried out a research which revealed the ranking of design related key delays.The most general design related caused delay was found to be taking place during the inspection phase followed by material/fabrication period, poor subcontract performance, material procurement and construction mistake as shown on figure 2. Source: Ahmed et al. ;( 2003) Figure 2: Ranking of design related key delays Effects of Delay on Construction Cost A brief review of text books and reports smia12010-07-21T16:38:00 What books and reports? You should at least give some example referencesreveal that construction excellence has not only become an option but a necessity, if the UK construction industry is to survive economics dynamics and changing social needs. Considering the industry is one of the pillars of the domestic economy making approximately 10 percent of Gross Domestic Product (GDP) and employing considerable number of workers, it is important to note that construction excellence is critical for the UK economy and its future. When a project is delayed, the owner, Contractor, or both may incur added costs. The determination of the amount of these costs is based on the results from the delay analysis and the determination of liability once the critical delays have been identified. (Trauner et al, 2009) More importantly, the construction industry needs to improve itself in order to increase profitability, quality of deliverables and client needs before it can contribute to the economy. There are many possible factors that can cause actual labour costs to exceed estimated costs such as engineering errors and omissions, excessive changes, delay and acceleration and weather. These factors may require contractors to work out of sequence, hire more manpower than planned, work scheduled overtime and utilize more costly methods of construction. (Borcherding et al, 2006). Trauner et al (2009) listed the following as examples of how delays can lead to inefficiencies. Shifts in construction sections-A delay to a project can shift work originally scheduled for one season into a different season. Availability of resources-Delays can affect the availability or resources in the areas of manpower, subcontracts or equipment. Manpower levels and distribution-Changes may be needed in terms of additions manpower, erratic staffing or variations in preferred/optimum gang size. Lowe et al (2006) described disputes as being the source of possible time and cost overrun and possible adversarial relationships between the different parties. This is not welcome to either the Owner or the Contractor. Cost overrun might lead to the project being unsuccessful, unfeasible or invalidate any benefits. Although avoiding disputes has been suggested, this is not usually possible and where disputes cannot be avoided efforts should be made to manage and contain the consequences. It is to the benefit of both the Employer and the Subcontractor to manage disputes towards a resolution as this will safeguard the success of the project. Cormican (1985) observed that the construction industry in UK is always at the top of the bankruptcy league and the most dangerous of all sectors. These unhealthy developments underpin the prevailing abandonment of projects and undermine the viability and sustainability of the construction industry. Akinci et al (1998) categorised risk factors affecting cost performance into organisation specific, global and acts of God. The organisation specific risks are internal risks related to the organisations resources and management including labour skills and availability, material delivery and quality, equipment reliability and availability, and managerial efficiency. Global risks are those that transcend the boundaries of the contracting organisation yet having large impact on it. These include estimating related, design related, level of competition, fraudulent practices, construction related, economic related and political relatedsmia12010-07-21T16:40:00 This is OK as far as it goes, but the literature revierw is supposed to be a CRITICAL review yours is really just a list of someone said thisà ¢Ã¢â€š ¬Ã‚ ¦. You really need to summariuse at the end what the key issues are from your literature review, and how they relate to your particular problem..

Homelessness and Solutions Homeless People

Let’s all help the homeless During the past decade there may have been an increase in homelessness due to the struggles of daily life. People have many ideas on ways that the government or communities can help improve these situations. It is not easy to help the homeless but any help can improve their lives and our streets. It may not take them completely off our streets but it can help them to get back on their feet.In a New York Times article, â€Å"Rooms of Their Own† on January 21, 1990 by Anna Quindlen, she reports that after observing people on the streets that all they want it a safe place to live to call home where they can have some privacy. She describes that many are mentally ill that the government cannot support any longer. Some homeless are former inmates that just need a little help getting back into society. Anna argues that the government should have to help by housing them in small studio like room to help them get back on their feet.By doing this it m ay get them back in the community and working soon to be on their own and not need the help any longer. Stuart D. Bykofsky complains in Newsweek, â€Å" No Heart for the Homeless†, on December 1, 1986 that he is fed up with the homeless laying around in the streets and making his community disgusting and unsafe to walk. He argues that why should individuals settle for these kinds of people living on there property for free and get away with it. He believes that it is not fair that they get to live on the streets for free and whileRivas 2 tax payers are getting fined for any reason. Stuart explains that the homeless need no excuse to live on the streets if there is a shelter to go to. It is their choice to go but if they choose not to then they should be fined for it as well. Not all homeless are the same because they all have different situations on why they have become homeless. Some of them have gotten laid off and simply cannot find w a job to support their families. This is all a part of Steven’s Vanderstaaty claim in his book, â€Å"Solutions Homeless People Seek†.He reveals that these unemployed people just want to work so they can get back into the community, but believe they shouldn’t have to go through all different kinds of training and programs for a job that they already have experience in. He points out that what homeless need is help getting back to society by their certain situations they may face of drug and alcohol programs or resources to help each individual that may need help mentally, physically or financially.After reading all three essays I find that any help would it be, donating time or money would help the homeless. It would show that the community does care for them as well as their surroundings to make it a cleaner and a safer place to live. Homeless or not everyone needs help may it be financially, emotionally or physically the government should have resources to help everyone!

Educational Policies For Inclusive Education - 1701 Words

â€Å"There is a direct correlation between the strength of inclusive education in schools and the values held by its leaders† (Porter AuCoin, 2012, p.146). The issue of inclusion is education is one that is surrounded by different ideological perspectives. In order to examine the policies surrounding inclusive education in Canada it is first necessary to understand the specific question at hand, who will be affected by the policy issue, as well as who has the power to make changes to this policy issue. Once there is a clear understanding of the issue and stakeholders, digging deeper into the opposing ideologies that surround the issue present the state of Canadian inclusion policies in education today. 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How Flight Control Systems Stabilize Rockets

Building an efficient rocket engine is only part of the problem. The rocket must also be stable in flight. A stable rocket is one that flies in a smooth, uniform direction. An unstable rocket flies along an erratic path, sometimes tumbling or changing direction. Unstable rockets are dangerous because its  not possible to predict where they’ll go – they may even turn upside down and suddenly head directly back to the launch pad. What Makes a Rocket Stable or Unstable? All matter has a point inside called the center of mass or â€Å"CM, regardless of its size, mass or shape. The center of mass is the exact spot where all the mass of that object is perfectly balanced. You can easily find the center of mass of an object — such as a ruler — by balancing it on your finger. If the material used to make the ruler is of uniform thickness and density, the center of mass should be at the halfway point between one end of the stick and the other. The CM would no longer be in the middle if a heavy nail was driven into one of its ends. The balance point would be nearer the end with the nail. CM is important in rocket flight because an unstable rocket tumbles around this point. In fact, any object in flight tends to tumble. If you throw a stick, it will tumble end over end. Throw a ball and it spins in flight. The act of spinning or tumbling stabilizes an object in flight. A Frisbee will go where you want it go to only if you throw it with a deliberate spin. Try throwing a Frisbee without spinning it and youll find that it flies in an erratic path and falls far short of its mark if you can even throw it at all.   Roll, Pitch and Yaw Spinning or tumbling takes place around one or more of three axes in flight: roll, pitch and yaw. The point where all three of these axes intersect is the center of mass. The pitch and yaw axes are the most important in rocket flight because any movement in either of these two directions can cause the rocket to go off course.  The roll axis is the least important because movement along this axis will not affect the flight path. In fact, a rolling motion will help stabilize the rocket the same way a properly passed football is stabilized by rolling or spiraling it in flight. Although a poorly passed football may still fly to its mark even if it tumbles rather than rolls, a rocket will not. The action-reaction energy of a football pass is completely expended by the thrower the moment the ball leaves his hand. With rockets, thrust from the engine is still produced while the rocket is in flight. Unstable motions about the pitch and yaw axes will cause the rocket to leave the planned course. A control system is needed to prevent or at least minimize unstable motions. The Center of Pressure Another important center that affects a rockets flight is its center of pressure or â€Å"CP.† The center of pressure exists only when air is flowing past the moving rocket. This flowing air, rubbing and pushing against the outer surface of the rocket, can cause it to begin moving around one of its three axes. Think of a weather vane, an arrow-like stick mounted on a rooftop and used for telling wind direction. The arrow is attached to a vertical rod that acts as a pivot point. The arrow is balanced so the center of mass is right at the pivot point. When the wind blows, the arrow turns and the head of the arrow points into the on-coming wind. The tail of the arrow points in the downwind direction. A weather vane arrow points into the wind because the tail of the arrow has a much larger surface area than the arrowhead. The flowing air imparts a greater force to the tail than the head so the tail is pushed away. There is a point on the arrow where the surface area is the same on one side as the other. This spot is called the center of pressure. The center of pressure is not in the same place as the center of mass. If it were, then neither end of the arrow would be favored by the wind. The arrow would not point. The center of pressure is between the center of mass and the tail end of the arrow. This means that the tail end has more surface area than the head end. The center of pressure in a rocket must be located toward the tail. The center of mass must be located toward the nose. If they are in the same place or very near each other, the rocket will be unstable in flight. It will try to rotate about the center of mass in the pitch and yaw axes, producing a dangerous situation. Control Systems Making a rocket stable requires some form of control system. Control systems  for rockets keep a rocket stable in flight and steer it. Small rockets usually require only a stabilizing control system. Large rockets, such as the ones that launch satellites into orbit, require a system that not only stabilizes the rocket but also enables it to change course while in flight. Controls on rockets can be either active or passive. Passive controls are fixed devices that keep rockets stabilized by their very presence on the rockets exterior. Active controls can be moved while the rocket is in flight to stabilize and steer the craft. Passive Controls The simplest of all passive controls is a stick. Chinese fire arrows  were simple rockets mounted on the ends of sticks that kept the center of pressure behind the center of mass. Fire arrows were notoriously inaccurate in spite of this. Air had to be flowing past the rocket before the center of pressure could take effect. While still on the ground and immobile, the arrow might lurch and fire the wrong way.   The accuracy of fire arrows was improved considerably years later by mounting them in a trough aimed in the proper direction. The trough guided the arrow until it was moving fast enough to become stable on its own. Another important improvement in rocketry came when sticks were replaced by clusters of lightweight fins mounted around the lower end near the nozzle. Fins could be made out of lightweight materials and be streamlined in shape. They gave rockets a dart-like appearance. The large surface area of the fins easily kept the center of pressure behind the center of mass. Some experimenters even bent the lower tips of the fins in a pinwheel fashion to promote rapid spinning in flight. With these spin fins, rockets become much more stable, but this design produced  more drag and limited the rockets range. Active Controls The weight of the rocket is a critical factor in performance and range. The original fire arrow stick added too much dead weight to the rocket and therefore limited its range considerably. With the beginning of modern rocketry in the 20th century, new ways were sought to improve rocket stability and at the same time reduce overall rocket weight.  The answer was the development of active controls. Active control systems included vanes, movable fins, canards, gimbaled nozzles, vernier rockets, fuel injection and attitude-control rockets.   Tilting fins and canards are quite similar to each other in appearance — the  only real difference is their location on the rocket. Canards are mounted on the front end while tilting fins are at the rear. In flight, the fins and canards tilt like rudders to deflect the air flow and cause the rocket to change course. Motion sensors on the rocket detect unplanned directional changes, and corrections can be made by slightly tilting the fins and canards. The advantage of these two devices is their size and weight. They are smaller and lighter and produce less drag than large fins. Other active control systems can eliminate fins and canards altogether. Course changes can be made in flight by tilting the angle at which the exhaust gas leaves the rocket’s engine. Several techniques can be used for changing exhaust direction.  Vanes are small finlike devices placed inside the exhaust of the rocket engine. Tilting the vanes deflects the exhaust, and by action-reaction the rocket responds by pointing the opposite way.   Another method for changing the exhaust direction is to gimbal the nozzle. A gimbaled nozzle is one that is able to sway while exhaust gases are passing through it. By tilting the engine nozzle in the proper direction, the rocket responds by changing course. Vernier rockets can also be used to change direction. These are small rockets mounted on the outside of the large engine. They fire when needed, producing the desired course change. In space, only spinning the rocket along the roll axis or using active controls involving the engine exhaust can stabilize the rocket or change its direction. Fins and canards have nothing to work upon without air. Science fiction movies showing rockets in space with wings and fins are long on fiction and short on science. The most common kinds of active controls used in space are attitude-control rockets. Small clusters of engines are mounted all around the vehicle. By firing the right combination of these small rockets, the vehicle can be turned in any direction. As soon as they are aimed properly, the main engines fire, sending the rocket off in the new direction.   The Mass of the Rocket The mass of a rocket is another important factor affecting its performance. It can make the difference between a successful flight and wallowing around on the launch pad. The rocket engine must produce a thrust that is greater than the total mass of the vehicle before the rocket can leave the ground. A rocket with a lot of unnecessary mass will not be as efficient as one that is trimmed to just the bare essentials. The total mass of the vehicle should be distributed following this general formula for an ideal rocket:   Ninety-one percent of the total mass  should be propellants.Three percent should be tanks, engines and fins.Payload can account for 6 percent. Payloads may be satellites, astronauts or spacecraft that will travel to other planets or moons. In determining the effectiveness of a rocket design, rocketeers speak in terms of mass fraction or â€Å"MF.† The mass of the rocket’s propellants divided by the total mass of the rocket gives mass fraction:  MF (Mass of Propellants)/(Total Mass) Ideally, the mass fraction of a rocket is 0.91. One might think that an MF of 1.0 is perfect, but then the entire rocket would be nothing more than a lump of propellants that would ignite into a fireball. The larger the MF number, the less payload the rocket can carry. The smaller the MF number, the less its range becomes. An MF number of 0.91 is a good balance between payload-carrying capability and range. The Space Shuttle has an MF of approximately 0.82. The MF varies between the different orbiters in the Space Shuttle fleet and with the different payload weights of each mission. Rockets that are large enough to carry spacecraft  into space have serious weight problems. A great deal of propellant is needed for them to reach space and find proper orbital velocities. Therefore, the tanks, engines and associated hardware become larger. Up to a point, bigger rockets fly farther than smaller rockets, but when they become too large their structures weigh them down too much. The mass fraction is reduced to an impossible number. A solution to this problem can be credited to 16th-century fireworks maker Johann Schmidlap. He attached small rockets to the top of big ones. When the large rocket was exhausted, the rocket casing was dropped behind and the remaining rocket fired. Much higher altitudes were achieved. These rockets used by Schmidlap were called step rockets. Today, this technique of building a rocket is called staging. Thanks to staging, it has become possible not only to reach outer space but the moon and other planets, too. The Space Shuttle follows the step rocket principle by dropping off its solid rocket boosters and external tank when they’re exhausted of propellants.