Design and Simulation of an Electromagnetic Aircraft Launch
System
D Patterson, A Monti, C Brice, R Dougal, R Pettus, D Srinivas, K Dilipchandra
(Department of Electrical Engineering University of South Carolina, Swearingen Center
Columbia, SC 29208 USA )
E-mail 一patters on @ieee? org
Abstract—This paper describes the basic design, refinement and verification using finite element analysis (FEA), and operational Simulation using the Virtual Test Bed (VTB), of a range of can didate lin ear machines for an electromagnetic aircraft launching system (EMALS) for the aircraft carrier of the future ? Choices of basic machine format, and procedures for determining basic dimensions are presented. A detailed design is presented for a permanent magnet version, and wou nd field coil and induetion machine versions are introduced ? The long armature 一short field geometry is discussed, and in particular the impact of this geometry on the scale of the power electronic drive system is preserHed.
I.INTRODUCTION
A.The Project
Moder n ship desig ns are in creasi ngly moving towards the use of elec trici ty to distribute, control, and deliver energy for the multiplicity of on board needs ? This trend has already resulted in large direct drive electric machines for tracti on in commercial shipping ? In some signifies nt cases, includi ng traction, adoption in military applications is rather slower, because of the comparatively low achievable power, energy and torque, per unit volume and per unit mass，of electroechanical energy convers ion systems ?
However the ben efits of controllability, robust ness, reliability, damage management, operational availabilit* reduced manning etc. are undeniable ? Whilst all actuation systems are under continuous investigation, there is a high level of interest in determining the feasibility of an electromagnetic aircraft launch system (EMALS) for aircraft carriers ?
Studies are being carried out at the University of South Carolina (USC) to evaluate alternative design concepts and to determine their feasibility and comparative strengths. Simulation uses the Virtual Test Bed (VTB), a new environment for Simulation and virtual prototyping of power electronic systems that includes not only Simulation of system dynamics, but also solid modeling of the system and visualization of the system dynamics [1].
EMALS also represents a challenging test case for VTB itself ? Models of the different parts of the systems will be built up from the specifications and the characteristics given by U?S. Navy, and from engineering design principles ?
B.The Challenge
The design of an EMALS has many intriguing challenges ? The likely specificatio ns and tech nical features in elude:
Maximum velocity：- 200 kt, TOO m/s
?Maximum power stroke：- 310 ft, T 00 m
?Min braking distanee 一moving member：- 30 ft, TOm
?Maximum Energy:-120 MJ
?Maximum Thrust:~1. 3 MN
?Minimum time between launchings：- 50 s.
Atypical launch might be for a 25000 kg aircraft accelerated to 150 kt in 2. 7 s, at an acceleration of 2.8 g. This represents a total ener gy of 70 MJ ? Acceleration to the maximum velocity requires a more-challenging 2 s stroke, at a constant acceleration of 5 g.
Whilst the overall system design must include storage, power electronics, and control system design, this paper will concentrate on the electrie machine design, and introduce some of the power electronics and control issues ?
II.LINEAR MACHINE DESIGN
A.Background
Asubstantial body of research exists studying large linear motors, however the majority of these are induetion machines, and by far the largest number of these are what are known as short primary 一long sec on dary machines? We will also use the termi no l ogy short armature ? long field for this geometry, a little more apt for machines other than induetion machines? Significant issues in design of these machines are the study of edge effects and end effects?Avery common application of short primary long sec on dary machi nes is for traction in electrie trains, where the energy is delivered to the train via a catenary or third rail system, and applied to an on board armature or primary. The sec on dary, or field member, is some form of complete track length reaction rail ? The Westinghouse Tlectropulf, developed during World War II is an aircraft launching linear induetion machine of this form.
This project is examining an extensive range of possible electrical machines, permanent magnet (PM) machines, machines with wound field (WF) coil structures, (which would in general need to be superconducting), and induction machines, (IM).
The issue of the transfer of >120 MJ in 2 seconds to a moving member, (referred to herei nat ter as the shut tie) either t hrough slidi ng con tac ts or some form of moving ham ess, is daunting. The "Electropulf referred to above used sliding contacts; however, the thrust required for this EMALS project is about 20 times greater than that delivered by the ElectropuIt ? An historical d escription of the ElectropuIt says, "???the operational costs were so high that in spite of the encouraging performance, stearn catapuIts held the field” .
The simplicity of the de motor driven flywheel and the linear induction machine with a flat
"'squirrel cage" stator lead one to the conclusion that the operational costs must have been particularly associated with the sliding con tacts? The need to decelerate the shuttle also makes min imization of shuttie mass a strong design constraint. These factors, together with the limited length of travel, have lead to the initial study of long primary ? short secondary, or long armature - short field machines?
B.Basic Machine Sizing
Initial sizing of any machine is often done by considering u Electromagnetic Shear
Stress ： as defined in Fig 1.
Electromagnetic Shear Stress Definition.
Miller quotes numbers for typical machines as being between 0? 7 and 2 kN/m2 for fractional horsepower induetion machines ranging up to between 70 and 100 kN/m2 for very large liquid cooled machines such as turbine gen era to rs, addi ng that peak :rati ng may exceed these values by 2 to 3 times [10]?
The Electropult, which can be considered as an induetion machine with variable resista nee "roto 丿,operated at a stress of a little greater than 50 kN/m2. This makes sense for a machine which was highly inefficient, spending most of its operational time at a slip of greater than 50% ?
It is worth no ting that at 100 kN/m2, for the aircraft launch system to produce 1. 29 MN, the active area of the shuttle would need to be in the order of T3 m2, or 6.5 m2 per side in a double sided strueture ? Early calculations were based on strueture of roughly this size, attempting to keep the moving mass in the order of 1 tonne. 仃 tonne at 100 m/s has 5 MJ of kinetic energy)? The permanent magnet design presented below operates at 200 kN/m2, and the wound field machine at 400 kN/m2.
Similarly electrie machi ne desig n is drive n by current rati ngs in con ductors ? Under intermittent loading maximum workable current densities are between 30 and 50 A / mm2.
C. Basic Machine Format
In order to achieve the surface area determined by achievable stress figures, two geometries were considered, the u
inverted U” and the “blade” as shown in Figs 2 and 3.
Figure 1 ?
Inverted U shuttie Figure 3. Blade shuttle
Figure 2 ?
Whilst for the in ver ted U the overall machine will be lighter, the mass of the shuttle must in elude material for completi ng the mag netic circuit ? There are also issues with supporting the single winding strueture and thermal management of a narrow vertical strueture. In contrast, the blade structure allows the lightest possible shuttle, and a total mass of the two^sided stator which is within the design goal mass, and also has very good thermal paths ?Of course multi-bladed configurations are possible, however a single blade structure is discussed in this paper, on the understending that multi bladed systems are a refinement of, and can be derived from the single bladed system.
1)Pole Pitch
Pole pitch is a very significant determinant of machine performanee?Short pole pitches usually lead to higher efficiencies (less end turn length), thinner back iron on the stator sections, important for total mass, and are usual in high torque / force machines of large size ? Limitations on indefinite reduction of the pole pitch have to do with the fun dame ntal frequency of the drive power, which is also the frequency of flux reversal in parts of the magne tic st rue ture resu lting in core loss, and fringing eff ects betwee n adjace nt poles, which are related to the achievable minimum air gap? A pole pitch of 150 mm is currently under consideration, which results in a maximum frequency of 333 Hz in the magnetic circuit of the synchronous versions of the machine ?
2)Stator, Slot Dimensions
It has been shown that at least for surface PM machines, eddy current loss in the stator teeth is proportional to the number of slots per pole per phase [11]? At the minimum one slot per pole per phase, with a traditional overlapping winding, a stator as shown in fig 4 has been dimensioned for initial FEA study.
Figure 4. S WBJ Dimensions
The steel of the PM and induction stator has a total mass of 100 tonnes, and for the wound field coil version 75 ton nes ? The max allowable to tai sys tem mass in the design specif ica tion is 530 tonnes, and the goal mass is 270 tonn es, so t hese st rue tu res are comfortably in side these specificati ons? The thermal mass of the 100 tonne structure is such that an energy dump of 40 MJ, for a very in efficient machi ne, will resuIt in less than one degree Celsius temperature rise per shot. Thus active cooling will not be necessary?
As will be seen below, the induetance of the winding is a primary determinant of the complexity of the power electronic drive svstem, so that the stator is designed with open slots to minimize winding inductanee. The stator winding scheme, using the traditional three phases, which is not obligetory, but gives a good starting position for a first design, is as summarized in figure 5.
D.Driving the Armature
Using the permanent magnet machine stress of 200 kN/m2 as discussed above, yields a shuttle length of 3 metres ? Assuming standard 6 step servo drive, a pole pitch of 150 mm, an achievable flux density in the air gap of 0.9T, and a totai thrust of 1. 29 MN, a slot current of 18 kA results ?
If this is in a single conductor in the slot, of 20 * 40 mm (64% fill factor), a current density of 22.5 A/mm2 resuIts, yielding an estimated total copper loss of 2. 2 MW for the complete launcher? Since the machine rating is 61 MW the efficiency, considering copper loss only, is thus over 96%?
The more important issue is that, confirmed by FEA, the induetanee of the single con duetor in the slot is ' 2.6 pH/metre ? Of course the single con duetor can be divided, reducing the in dividual conductor current and the switch current, using more than 1 turn for the winding without affecting the copper loss (providing the same fill factor resuIts) but the induetanee of course goes up as the number of turns2? Even at 1 turn, the induetanee of a single phase 200 metres in length for both sides, pole pitch 150 mm, without considering end turns (where the induetanee is negligible, not being in iron) computes to 3.5 mH. In order to commutate from +18 kA to 一18 kA at 333 Hz rate a supply voltage of 250 kV would be required? Clearly driving the track in sections is the only feasible option.
E.Simulation
Discussion so far has indicated the very large range of possibilities that need to be compared and considered when conceiving of a system of this complexity ? Most comm only, promising research directions are deduced from data from existing operation systems ? Without operational systems to guide research, recourse must be had to very powerful cross- disciplinary system Simulators.
III.DETAILED MACHINE DESIGN
In t his research projec t, the major ity of effort has so far been direc ted to the permanent magnet version of this machine, which has resulted in a surprisingly simple and achievable design.
Some effort has been expended to explore the wound field coil, which has some intriguing implications, and less effort on the in duetion versi on, since this is an area where a substa ntial body of expertise exists.
IV.INDUCTION MACHINE
Following the completion of the wound field coil machine analysis a more traditional induetion versi on will be designed, analyzed, and Simulated ? The induction motor system will be substantially more difficuIt to drive, since the magnetic circuit must be designed to maximize the flux in the airgap from current in the armature. Thus the induetanee of the armature winding w 川be significantly higher, and the mutual induetanee between windings will not be negligible ? The resuIts of this work will be reported at a later date.
V.CONCLUSIONS
The initial conclusion is that the PM machine is a very good solution, being surprisingly small and simple, with a manageable power electronics switching system. The wound filed coil machine does not appear to provide sufficient advantage to make the extra complexity worthwhile, unless weight becomes a much more significant concern than has so far appeared ? However there will be adva ntages in the power electr onic system. The in duction machi ne desig n will be very complex, and the cost of the power electronics is liable to be substantially higher because of the much higher induetances?
航母的基本常识介绍 ☆舰岛 早期航母，象英国“百眼巨人”号和美国的“兰利”号等整个舰面是平坦的飞行甲板，没有突出部分。而现代航母基本上是把舰桥、烟囱等集中在飞行甲板的一侧，好象一个小岛，它就是“舰岛”。 从飞机起降的要求上讲，航母的飞行甲板上空空无物是最理想的。但是，航母的指挥塔、飞行控制室、航海室、雷达和通信天线等又是需要高耸在甲板上的。所以，现代航母都是把这些上层建筑设计得很紧凑，集中在飞行甲板右舷的“舰岛”上，空出甲板的绝大部分来方便飞机起降。 ☆飞行甲板 飞行甲板就是航母舰面上供舰载机起降和停放的上层甲板，又称为舰面场。早期飞机由于起降速度不大，可以从军舰首部或主炮塔上部铺设的小型甲板上起飞，从舰尾的短小甲板上着舰。但现代航母都是贯通全舰的大面积的上层甲板。需要指出的是，航母的飞行甲板要比舰体宽得多。从正面看，飞行甲板从舰体上面向两舷张出，形状很
怪异。 飞行甲板要承受飞机着舰时的强烈冲击载荷，所以要用高强度钢板制成。二战时航母飞行甲板表面要铺设一层木质甲板，而现代航母的飞行甲板表面都是金属的了。 ☆直式和斜角式飞行甲板 从航母出现直到50年代初，航母的飞行甲板都是直式的。其形状为矩形，防冲网把甲板分成前后两部分；前部供飞机起飞、停放用，后部则是飞机降落区。当防冲网放下时，前后两区合二为一，舰载机就能从舰尾向前做不用弹射器的自由测距滑跑起飞了。 随着喷气式飞机的上舰，直式甲板的局限性就显露出来了。50年代初，英国海军上校卡梅尔提出了斜角甲板设想，经试验后证明它有许多优点，遂成为现代航母的标准甲板样式。 斜角甲板分为两部分。舰前部直甲板为起飞区，后半部斜角甲板为着舰区，斜直相交处形成三角形停机区。斜式甲板的斜度以斜角甲板中线与航母首尾中线夹角来表示。斜角甲板的优点是着舰飞机未能钩住拦阻索时，可马上拉起复飞而不致于与前甲板停放的飞机相撞。另外，舰载机起飞和降落可同时进行。 ☆弹射器的工作 早期的螺旋桨式飞机由于起飞速度不大，可以轻易从甲板上自行滑跑起飞，但喷气式舰载机的重量和起飞速度急剧增大，只能通过弹射器起飞了。 1950年8月，英国在“英仙座”航母甲板中线上安装了一台动
弹射模型飞机的调整试飞 一、弹射飞行原理 弹射模型飞机是利用橡筋的弹性能量作为初始动力来放飞模型的。当模型获得橡筋的弹性能量后就会被弹射出去，模型爬升到最高点后在重力作用下转为下滑，模型在下滑时由于机翼翼型的作用，可以产生一定的升力，因此，会慢慢地滑翔飞行，在滑翔过程中若遇到上升气流，则可获得较长的留空时间。 二、航空模型技术常用术语 1.翼展——机翼（尾翼）左右翼尖间的直线距离。（穿过机身部分也计算在内） 2.机身全长——模型飞机最前端到最末端的直线距离 3.重心——模型飞机各部分重力的合力作用点称为重心 4.尾力臂——机翼后缘到水平尾翼前缘的距离 5.翼型——机翼或尾翼的横剖面形状 6.前缘——翼型的最前端 7.后缘——翼型的最后端 8.翼弦——前后缘之间的连线 9.展弦比——翼展与平均翼弦长度的比值。展弦比大说明机翼狭长 三、模型飞机受力分析 1.升力——由机翼产生的向上作用力 机翼的升力是机翼上下空气压力差形成的。当模型在空中飞行时，机翼上表面的空气流速加快，压强减小；机翼下表面的空气流速减慢压强加
大。这是造成机翼上下压力差的原因。 造成机翼上下流速变化的原因有两个： (1)不对称的翼型； (2)机翼和相对气流有迎角。翼型是机翼剖面的形状。机翼剖面多为不对称形，如下弧平直上弧向上弯曲(平凸型)和上下弧都向上弯曲(凹凸型)。对称翼型则必须有一定的迎角才产生升力。 2.重力G——与升力相反的向下作用力 3.拉力P——由发动机产生的向前作用力 4.阻力Q——由空气阻力产生的向后作用力 四、试飞前的检查 组装完成后，检查重心的位置,两边上反角是否对称，机翼、水平尾翼是否扭曲。垂直尾翼是否垂直，水平尾翼是否扭曲变形，机翼的安装角是否正确 五、测定重心位置 用两手指顶在两片机翼之间，找出能使飞机平衡的某点，再对照力学中重心位置。（机翼后缘向前，在机翼的40%处左右）如发现飞机的重心不在规定的位置上，应该进行重心调整。如果整机前（后）倾，应在机身尾部（头部）粘上电工胶布（配重）。如果整机左（右）倾，应将左（右）翼磨削。 六、试飞、分两个步骤 1 手掷试飞：也就是手投模型飞机，方法是用两手指抓住机身上重心稍靠后的位置，机头稍低于水平线，逆风，沿机身方向，将模型轻轻掷出（注意手掷模型时手臂不能划弧线，而是沿机身方向的直线方向，轻轻掷出）
Design and Simulation of an Electromagnetic Aircraft Launch System D Patterson, A Monti, C Brice, R Dougal, R Pettus, D Srinivas, K Dilipchandra (Department of Electrical Engineering University of South Carolina, Swearingen Center Columbia, SC 29208 USA ) E-mail 一patters on @ieee? org Abstract—This paper describes the basic design, refinement and verification using finite element analysis (FEA), and operational Simulation using the Virtual Test Bed (VTB), of a range of can didate lin ear machines for an electromagnetic aircraft launching system (EMALS) for the aircraft carrier of the future ? Choices of basic machine format, and procedures for determining basic dimensions are presented. A detailed design is presented for a permanent magnet version, and wou nd field coil and induetion machine versions are introduced ? The long armature 一short field geometry is discussed, and in particular the impact of this geometry on the scale of the power electronic drive system is preserHed. I.INTRODUCTION A.The Project Moder n ship desig ns are in creasi ngly moving towards the use of elec trici ty to distribute, control, and deliver energy for the multiplicity of on board needs ? This trend has already resulted in large direct drive electric machines for tracti on in commercial shipping ? In some signifies nt cases, includi ng traction, adoption in military applications is rather slower, because of the comparatively low achievable power, energy and torque, per unit volume and per unit mass，of electroechanical energy convers ion systems ? However the ben efits of controllability, robust ness, reliability, damage management, operational availabilit* reduced manning etc. are undeniable ? Whilst all actuation systems are under continuous investigation, there is a high level of interest in determining the feasibility of an electromagnetic aircraft launch system (EMALS) for aircraft carriers ? Studies are being carried out at the University of South Carolina (USC) to evaluate alternative design concepts and to determine their feasibility and comparative strengths. Simulation uses the Virtual Test Bed (VTB), a new environment for Simulation and virtual prototyping of power electronic systems that includes not only Simulation of system dynamics, but also solid modeling of the system and visualization of the system dynamics [1]. EMALS also represents a challenging test case for VTB itself ? Models of the different parts of the systems will be built up from the specifications and the characteristics given by U?S. Navy, and from engineering design principles ? B.The Challenge
航空母舰的主要装置
起飞装置
蒸汽弹射起飞使用一个平的甲板作为飞机跑道。起飞时一个蒸汽驱动的弹射装置带动飞机在两秒钟内达到起飞速度。目前只有美国具备生产这种蒸气弹射器的成熟技术。在工作原理上，蒸汽弹射器是以高压蒸汽推动活塞带动弹射轨道上的滑块，把与之相连的舰载机弹射出去的。它体积庞大，工作时要消耗大量蒸汽，功率浪费严重，只有约6%的蒸汽被利用。为制造和输送蒸汽，航母要备有海水淡化装置、大型锅炉和无数管线，工作维护量惊人。它的最大缺陷在于因为弹射功率太大而无法发射无人机，现役的无人机因为重量轻，在弹射时机体会被加速度扯碎。
?? 蒸汽弹射起飞
蒸汽弹射有两种弹射方式：
一种是前轮牵引式弹射，美国海军1964年试验成功。舰载机的前轮支架装上拖曳杆，前轮就直接挂在了滑块上，弹射时由滑块直接拉着飞机前轮加速起飞。这样就不用8－10甲板人员挂拖索和捡拖索了。弹射时间缩短，飞机的方向安全性好，但这种舰载机的前轮要专门设计。美国海军核动力航母都采用了这种起飞方式。&nb sp;
另一种是拖索式弹射，顾名思义，就是用钢质拖索牵引飞机加速起飞，这种弹射方式比较老，各方面都不如前者好，目前只有法国的“克莱蒙梭”级航母使用。拖索式弹射时，甲板人员先用钢质拖索把飞机挂在滑块上，再用一根索引释放杆把其尾部与弹射器后端固定住。弹射时，猛力前冲的滑块拉断索引释放杆上的定力拉断栓，牵着飞机沿轨道迅速加速，在轨道末端把飞机加速到直起飞速度抛离甲板，拖索从飞机上脱落，滑块返回弹射器起点准备下一次工作。& nbsp;
斜板滑跳起飞
??
斜板滑跳起飞
有些航空母舰在其甲板前端有一个“跳台”帮助飞机起飞，即把甲板的前头部分做成斜坡上翘，舰载机以一定的尚未达到其飞速度的速度滑跑后沿着上翘的斜坡冲出甲板，形成斜抛运动，在刚脱离母舰的一段（几十米）距离内继续在空中加速以达到起飞速度。这种起飞方式不需要复杂的弹射装置，但是飞机起飞时的重量不如蒸汽弹射起飞，使得舰载机的载油量、载弹量、航程以及作战半径等受到一定的制约。英国、意大利、印度和俄罗斯等国由于技术限制，无法研制真正在技术和工艺上过关的蒸汽弹射器，所以只能在本国航母上采用滑翘甲板。采用滑跃起飞舰载机的航空母舰在载机起飞时都必须以20节（36公里/小时）以上的速度逆风航行，以加大载机相对速度来帮助舰载机起飞。
垂直起飞
垂直起飞技术顾名思义就是飞机不需要滑跑就可以起飞和着陆的技术。它是从20世纪50年代末期开始发展的一项航空技术。英国、美国、俄罗斯的一些航空母舰采用这种技术。
使用垂直起降技术的飞机机动灵活，具有常规飞机无可比拟的优点：
首先，具有垂直起降能力的飞机不需要专门的机场和跑道，降低了使用成本。其次，垂直起降飞机只需要很小的平地就可以起飞和着陆，所以在战争中飞机可以分散配置，便于伪装，不易被敌方发现，大大提高了飞机的战场生存率。最后，由于垂直起降飞机即使在被毁坏的机场跑道上或者是前线的简易机场上也可以升空作战，所以出勤率也大幅提高，并且对敌方的打击具有很高的突然性。
但使用垂直起降技术的飞机同时也有许多重大的缺点：
首先是航程短，由于要实现垂直起降，飞机的起飞重量只能是发动机推力的83%-85%，这就使飞机的有效载荷大大受到限制，影响了飞机的载油量和航程。同时，飞机垂直起飞时发动机工作在最大状态，耗油量极大，也限制了飞机的作战半径。例如“鹞”式飞机的载重量为1060千克时，作战半径只有92公里。所以在实际使用中，“鹞”式飞机尽量使用短距起飞的方式，以延长飞机的航程。因此，垂直起落
即将登场的航母电磁飞机弹射系统 这是名为《即将登场的航母电磁飞机弹射系统》一文摘录，配图也是里面的，来源网上。有兴趣的自己去搜全文，极好的科普文章 从线圈电磁炮的发展历史来看，其实阻碍电磁弹射器的现实化并不是线性电机本身，而是强大而稳定的瞬发能源。美国航母上采用90年代nasa为电磁炮，激光类武器发展的惯性储能装置发展而来的盘式交流发电机。新设计的盘式交流发电机重约8.7吨，如果不算附加安全壳体设备重量只有6.9吨。盘式交流发电机的转子采用绕水平轴向的旋转，转子重约5177公斤，使用镍铬铁的铸件经热处理而成，上面用镍铬钛合金箍固定2对扇形轴心磁场的钕铁硼永磁体，镍铬钛合金箍具有很大的弹性预应力，确保稳定固定高速旋转中的磁体。转子旋转速度为6400转/分，一个转子可存储121兆焦的能量，储能密度比蒸汽弹射器得储气罐高一倍多，一台弹射器由4台盘式交流发电机供电，安装时一般采用成对布置，转子反向旋转，减小因高速旋转飞轮带来的陀螺效应和单向扭矩。弹射一次仅使用每一台发电机所储备的能量的22.5%，让飞轮转盘的转动速度从6400转/分下降到5200转/分，能量消耗可以在弹射循环的45s间歇中从主动力输出中获得补充。4蓄能发电机结构可以允许弹射器在其中一台发电机没有工作的情况下正常使用，由于航母装备4台弹射器，每两台弹射器的动力组会安装到一起，集中管理并允许其动力交联，出现6台以上发电机故障而影响弹射几率每300年才会重复一次。盘式交流发电机采用双定子设计，分别处于盘的两侧，每一个定子由280个线圈绕组的放射性槽构成，槽间是支撑结构和液体冷却板，由于采用双定子结构，每台发电机输出电源是6相的，最大输出电压1700伏，峰值电流高达6400安培，输出的匹配载荷为8.16万千瓦，输出为2133-1735赫兹的变频交流电。盘式储能交流发电机的设计效率为89.3%，这已经通过缩比模型验证，也就是说每一次弹射将会有127千瓦的能量以热量形式消耗掉了，发电机的定子线圈的电阻仅有8.6毫欧，这么大的功率会迅速将定子线圈加温数百度，所以设计了定子强制冷却。冷却板布置在定子的外侧，铸铝板上安转不锈钢管，内充WEG 混合液，采用流量为151升/分的泵强制散热，根据1/2模型试验测试所知，可以保证45s循环内铜芯温度稳定在84摄氏度，冷却板表面温度61度。 真正最为关键，技术难度最大的部件是高功率的循环变频器，这个技术是电磁弹射器的真正技术瓶颈，EMALS现在正处于关键性部件工程验证阶段，循环变频器仅仅是完成了计算机模拟，还没有开始发展工程样品，从设计而言，循环变频器是一个多路的桥式电路通过串联或者并联多路桥式电路来获得叠加和控制功率输出，他不使用开关和串联电容器，省略了电流分享电抗器，实现了完全数字化管理的无电弧的电能源变频管理输出。她每一相的输出能力为0到1520伏，峰值电流6400安培，可变化频率为0-644赫兹。循环变频器设计非常复杂，它不仅需要将4台交流发电机的24相输入电能准确的将正确的相位输入到正确的模块端口，还必须准确的管理298个直线电机的电磁模块，在滑动组运行到来前0.35秒内让电磁体充电，而在滑组经过后0.2秒之内停止送电并将电能输送到下一个模块。循环变频器工作时间虽然不长，每次弹射仅需工作10-15秒，但热耗
美军研发新航母电磁弹射器概况 2010年12月18日，美国海军在莱克湖海军基地使用电磁弹射器成功弹射1架F/A-18E型战斗机 建设中的试验用电磁弹射系统(左) 以及试验用电磁弹射系统的跑道(右) 2010年底，美国海军在多年研制的基础上，使用试验型电磁弹射系统，成功弹射了1架F/A-18E型战斗机，并将继续进行多次试验。这表明电磁弹射系统项目进展得比较顺利，有望于今年前后向"福特"号航母交付首部电磁弹射器。按此发展进度，到2014年，"福特"号航母便能正式使用电磁弹射器。 美国海军为何放着已十分成熟的蒸汽弹射器不用，偏要花费大量人力物力研制风险较大的电磁弹射器?此举将对世界海军产生什么样影响? 进一步扩大与他国的差距 航空母舰的战斗力主要来自舰载机，而弹射技术则是舰载机起飞的关键技术。美军现役航母主要采用蒸汽弹射器，虽然技术成熟可靠，但也存在不少缺陷：一是效率低，配套设施多，系统繁琐；二是要频繁更换密封条，维护成本高，且非常麻烦；三是必须耗费大量淡水。 为了克服上述缺陷，美军决心研制电磁弹射器。与蒸汽弹射器相比，电磁弹射器有许多优点： 能弹射多种舰载机， 包括无人机"尼米兹"级航母上的蒸汽弹射器每天最多出动120架次舰载机，而电磁弹射器可以使舰载机的每日出动量达到160架次。电磁弹射器还可以弹射不同重量的舰载机，甚至几十公斤重的无人机。 另外，电磁弹射器的构成组件较少，体积约425立方米，重225吨，不到蒸汽弹射器的一半。 大幅延长战机寿命 电磁弹射器具有匀速平稳，过渡柔和等特点，因而可以大幅减少对舰载机机体及各部件的撞击，使舰载机的受损度明显降低。实验证明，采用电磁弹射器后，将使舰载机的机体寿命延长31%。 操作简单，15分钟即可待用
航母弹射飞机起飞 目前，航母弹射飞机起飞的装置，使用最多的还是蒸汽弹射装置。考虑弹射问题，做了一点点初步的估算。这仅仅是一个粗线条的概算，有关结果，可能提供参考。 1，弹射过程加速度估算： 弹射末速度80 米/ 秒，相当时速288公里（160节），假设弹射加速长度100米（美国C—13—2弹射器）， 按照V = (2aS)EXP0.5公式计算， 80 米/ 秒＝（2a100米）EXP0.5 加速度 a ＝32 米/ 秒2＝3.26 g （此处的g代表重力加速度，g ＝9.8米/ 秒2） 2，弹射运动时间估算： S = 0.5at2 S = 100米，a = 32 米/ 秒2 ，t = 2.6 秒 3，弹射过程功率估算： 30吨飞机，加速度为1g情况下需要30吨即30000公斤弹射力，100米弹射距离，做功3000000公斤米。弹射时间粗略视为3秒，则功率1000000公斤米/ 秒＝13300马力（9790千瓦）。实际上弹射需要的加速度超过3g（按照前面1的估算），相应的功率约为3万千瓦。
一艘航母配备两条到四条弹射道，2－4个弹射器，最紧张时，四个弹射器都要投入工作。 4，弹射力估算： 弹射加速度a = 32 米/ 秒2 ，被弹射飞机起飞重量30吨情况下，由于弹射加速度a = 32 米/ 秒2 = 3.27 g，弹射力为30吨X 3.27 = 98吨。 5，美国C—13—2弹射器，轨道长度324英尺（99米），冲程306英尺（93米），气缸直径21英寸，冲程容积1527立方英尺，活塞与牵引器重量6350磅，里根号航母装备四套。蒸汽弹射 器每次弹射最大输出能量可达到95兆焦耳（95兆瓦秒，若弹 射在3秒内完成，则功率为32000千瓦，此数值与前面3的估 算结果接近），弹射器最短工作周期为45秒，平均每次弹射 耗用近700公斤蒸汽。 6，弹射气缸蒸汽压力估算： 设弹射力为98 吨，弹射气缸活塞直径为21 英寸（美国C—13 —2弹射器情况），换算为公制，活塞直径为21 X 2.54 = 53.3 厘米，活塞面积为2231 厘米2，使用双气缸，活塞面积加倍， 弹射蒸汽压强应当是22 公斤/ 厘米2，按照过去习惯的单位 就是22 大气压。工程上，22 大气压的参数，对于航母弹射装 置所需要的锅炉以及气缸，从技术层面来看是能够实现的。 下面是弹射器剖面示意图和实际结构照片。
即将登场的航母电磁飞机弹射系统 院系： 班级： 学号： 学生姓名：
火炮、火箭等发射装置大多属于化学发射器,它们在军事领域占有重要的地位。随着科学技术的发展, 产生了电磁发射技术EML ( Elect romagneticLaunch) 。电磁推进技术的原理早在19 世纪初就已有人提出,后经过几十年的探索与研究,人们相继研制出了各种电磁感应原理的直线发射装置或模型,但由于受相关研究领域技术的影响,上述模型的性能距工程实用尚存在着较大的差距。70 年代以后,超大功率脉冲技术和电子技术的飞速发展使电磁发射技术有了重大突破。1978 年澳大利亚的马歇尔等人用550MJ单极发电机作为电源和采用等离子体电枢在5m长的导轨炮上把3 g重的聚碳酸脂弹丸加速到了5. 9km/ s 的初速度。这个具有划时代意义的研究成果证明了用电磁力可以把较重的弹丸推进到高速的可能性,使世界各地的科学家受到极大的鼓舞和启发,由此也将电磁发射技术的研究推向了一个新阶段。 直线电磁发射器(又叫电炮) 按照其工作原理或工作方式可分为导轨型、线圈型和重接型。在线圈型原理的基础上,又发展出了电磁弹射技术。 一弹射器的原理和发展前景 1 线圈型电磁发射器的原理和特点 线圈型电磁发射器早期又称“同轴加速器”,一般是指用序列脉冲或交流电流产生运动磁场从而驱动带有线圈的弹丸或磁性材料弹丸的发射装置。由于工作的机理是利用驱动线圈和被加速物体之间的耦合磁场,因此线圈型电磁发射器的本质可以理解成直线电动机。 一个简单结构的线圈型电磁发射器的模型如图
1a 所示。一单匝的驱动线圈和一发射线圈同轴排列。发射线圈上以永磁或电励磁方式建立一恒定磁场,两个线圈之间的互感M 如图1b 所示。当驱动线圈中通以图1c 规律的电流时,发射线圈上始终要受到一个轴向力F ,从而使其加速,沿着X 轴的正方向前进。 一般地,为了减少加速力F 的波动和延长其加速行程,上述的驱动线圈和发射线圈都做成多匝结构,一个多匝线圈型电磁发射器的原理结构示意图如图2 所示。根据发射线圈上磁场的形成机理和驱动线圈的结构与控制方式,线圈型电磁发射器可分为多种类型,相应的特点如下表所示. 美国海军航母目前使用的飞机蒸汽弹射器不仅体积笨重、噪音大，而且能量效率
美国CVN 21航母与飞机弹射系统概 述转 原文地址：美国CVN--21航母与飞机弹射系统概述(转)作者：一见如故 美国CVN-21航母与飞机弹射系统概述 选自[全球军事快讯] 合众国际社报道，标准的美国"尼米兹"级航空母舰每艘的造价约为六十亿美元，美国的下一代航空母舰CVN-21的造价大约是这个数字的两僧。后面还有战机、舰员培训以及支援和保护航空母舰的其它水面舰只的费用。 从理论上说，中国可能对美国海军在太平洋的传统优势构成挑战。有人认为，建造航空母舰会使中国的预算无法承受，但是，这种观点不能完全令人信服。 报道认为，如果中国选择这样做，他们可能会得到美国海军的帮助。基廷上将访华时曾说，如果中国决定这样做，美国将愿意助一臂之力。 美国有一派的观点欢迎中国投巨资建造航空母舰，理由是中国人可能会需要长达二十年的时间才能造出这些舰只和飞机，培训舰上人员，学习操作航空母舰的战术，他们将很难赶上已经有八十年航空母舰经验的美国海军。 另一些人认为，引诱中国建设这样一支海军是一个聪明的财政陷阱，会在未来几十年里使中国的国防预算无法承受并使之扭曲，未来中国的航母对美国占优势的隐形攻击潜艇来说也是巨大的目标。 还有一种观点认为，在隐形潜艇以及快速鱼雷和精密制导武器的时代，大型航空母舰已经过时。 有人认为，建造航空母舰会使中国的预算无法承受，但是，这种观点不能完全令人信服。
基廷指出，美国在这方面的经验领先全球，但美国海军在设计、建造航空 母舰、配备飞机和训练航海船员及飞行人员，仍要花十年以上的时间。基廷说："如果中国要做这件事，将会是个非常艰难的工程。" 目前，蒸汽弹射器、阻拦索及大型升降机等关键技术，就算是海军强国也 很难掌握建造航母所有关键领域的技术，法国建造的"戴高乐"号核动力航母， 其蒸汽弹射器也是从美国进口的。 蒸汽弹射器实际就是一台往复式蒸汽机，只不过其动力冲程很长。蒸汽弹 射器由发射系统、蒸汽系统、拖索张紧系统、润滑及控制系统等部分组成。工 作时，由锅炉产生高压蒸汽，并把这种高压蒸汽储存在蒸汽室里，弹射前，用 拖索将舰载机钩在往复车上，一旦将高压蒸汽充入汽缸筒，蒸汽的巨大压力推 动活塞，活塞带动往复车，往复车带动舰载机飞速向前滑动，从而将飞机弹射 出去。如美国的C-13型蒸汽弹射器，可将36.3吨重的舰载机以185节(即339 公里/小时)的高速弹射出去。目前，美国海军的航空母舰弹射一架飞机仅需30 秒种。 为与发射系统配套，航空母舰的甲板上还设有喷气偏流板。(就是挡板)这 种安装在弹射台后方的偏流板又称为燃气导流板。飞机在起飞前，将支起这个 偏流板，用以挡住起飞时马力开得最大的喷气式舰载机向后喷射出的高温燃气流，以防对人员和甲板造成危害。每个弹射器后面有一组共3块偏流板。单发 动机的航母舰载机起飞时需支起3块偏流板。为防止高温燃气烧坏挡板，挡板 还装有供循环冷却水流动的格状水管。目前美国使用的这种水冷式喷气偏流板，当正在升起时能承受94.4千牛的喷气推力，若完全升起后，能承受400千牛的喷气推力。该板放下后与飞行甲板齐平，能承受31.572吨重的飞机在中等海况下从上面通过或静止不动地压在板上。在恶劣情况下，飞机一般不允许压在该 板上。 航母的蒸汽弹射器是一根70米长的钢管。当然是很多节接起来的。当它在工作的时候，蒸汽推动活塞在70米的距离上高速运行，把一架40吨质量的重 型舰载机在不到100米的距离上加速到足以升空的250千米每小时的速度，尽 管母舰航行的35节的速度和逆风获得的相速度可以减轻一些蒸汽弹射器的负担，但是毫无疑问，蒸汽弹射器就是一套高速高压长距离的气动活塞系统。