如何为你的无人机选择合格的一个降落伞回收系统外文文献翻译、中英文翻译、外文翻译
如何为你的无人机选择合格的一个降落伞回收系统外文文献翻译、中英文翻译、外文翻译,如何,无人机,选择,合格,一个,降落伞,回收,系统,外文,文献,翻译,中英文
附录一：
如何为你的无人机选择合格的一个降落伞回收系统
德拉·c·巴特勒,Jr 总统
巴特勒降落伞系统集团公司
罗伯特·Montanez 副总裁
巴特勒降落伞系统集团公司
文摘
本文提出实质性的和详细的信息关于影响设计的常见问题,测试和资格降落伞回收系统的所有类别无人机的侦察、空中目标、武器等)。假设我们的主要受众将无人机制造商和运营商。因此,为了熟悉读者设计的基本过程和排位赛复苏无人机系统,我们提供了一个简单而详细在回收系统设计和锻炼,回顾项目管理。
背景
自 1976 年以来,巴特勒降落伞系统集团、Inc.2,它前任和它的各种设计和子公司生产范围广泛的降落伞和恢复系统。1979 年,我们收到我们的第一个联邦航空局技术标准的授权(TSO)利用和秩序容器组件用于人员进入紧急状态(救助)背包降落伞;在1991 年,我们收到了TSO3 一个圆形树冠设计用于在我们的紧急降落伞系统;在 1992 年,我们开始旋转和深失速回收系统飞行测试飞机从一个系统 SJ-30 名叫史瓦金;在 1994 年,我们开始制作无人机降落伞回收系统开始复苏系统设计和建造捕食者 SBIR 第一篇文章
介绍
作者假设您和客户已经进行了基本的成本/收益分析决定你的无人机必须有一个降落伞回收系统的一个或多个通常的原因。我们将讨论回收系统)与根本的影响因素目标是帮助你成为一个“聪明的买家”整个设计和智能决策资格无人机的回收系统的过程。
1 在本文档中“我们”指的是作者和/或管家无人降落伞系统,LLC(bup);“你” 指的是读者,假定在项目经理的角色工程技术人员的无人机制造商我们电话通用无人机 Associates(GENUAVASS)时,我们需要有一个名字的故事;“客户”的最终用户无人机,就是我们所说的大秘密机构(BSA)当我们需要有个名字的故
事;“回收系统”包括降落伞回收系统和所有相关的组件工作;和“无人机”将适用于任何类型的无人机或目标。
（bup Qualification.doc——回收系统）
2 2002 年,巴特勒降落伞系统,公司重组是管家降落伞系统集团公司与子公司除以产品区域。特定的兴趣这是子公司巴特勒无人降落伞系统,LLC(bup)。
3 过程设计、测试和符合条件的人员降落伞树冠与我们自己的资金,使我们强烈意识到变化莫测的降落伞测试。这些问题寻找灵感方法来消除这些失败的根源, 最终导致的发明蝙蝠草帽滑块(项全球专利)。在引用您可以找到大量信息的链接设备,但在这里,我只想说,蝙蝠草帽滑块传统降落伞由几个订单增加的可靠性级的。我们已经从每一个项目都学到一些东西在技术经验,但特别是在程序管理领域。因此,我们觉得优秀的呈现这些信息;尤其是在希望它将允许有人避免一些我们遇到的陷阱。
项目管理
航空工业中的每个人都知道一些组件的任何飞机都或多或少的“标准”。所以, 项目经理,你可能会偶尔发现你可以买东西像一个交流发电机和“现成的”螺栓上,走了。然而,一个降落伞回收系统很少在这一类。因此,作为该项目经理,你必须方法的过程的设计、测试和资质的回收系统类似于无人机其他复杂的飞机子系统,即。,一个人必须不断考虑形式的“6-pack”,健康,功能,性能、时间表和一如既往地成本。虽然这是半开玩笑的提到 6-pack——这个特殊的 6-pack 绝对可以导致头痛,如果不是宿醉适当的管理,它肯定会帮助传播工作负载在那些最能胜任的每个部分项目。
团队领导人 GENUAVASS(这里假定工程和项目经理)必须设置优先级每个因素的6-pack 最早可能的点程序。他们还将指定工作区域,并确定团队成员之间的相互作用,在他们的工作监督。团队领导人 bup 将做同样的事情。当然,通过设置现实
的所有这些参数因素,你应该能够避免常见的处罚等不必要的重量、体积和成本和/或时间表对程序的影响。
几乎任何规模的组织工作的过程
本文中概述,当然我们必须首先开球“团队会议”的所有球员,于是每个人必须承认:
• 团队的目标是完成回收系统时间,在预算和内部所需的性能参数;
• 这支队伍的你(买方,GENUAVASS)和我们(卖方,bup)和客户(BSA)员工,在合作工作环境;
• 没有人可以让任何单方面改变;
• 形式、合适,功能和性能不可避免互相联系;
• 时间表和成本彼此密不可分;
• 这两个子组也密不可分,但在一个不同的方式;
• 所有这些因素可以在一定程度上操纵只有知识和赞同的球员;
• 任何变化的因素将波及过程中,必须小心走近。
请注意,尽管我们坚持一个“开始”会议,以及一个“毕业”当我们见面完成后, 我们通常必须强烈觉得会议尽量减少或避免如果可能的话。
事实上,考虑到团队中的每个人都可以或多或少不断的沟通,通过电子邮件,某种形式的协议宇宙(CC)实际上应该建立在团队成员的电子邮件通信。的团队成员应该决定看看——谁需要点不隐藏任何东西,以避免增加了“垃圾”邮件。
记住,如果一个特定的团队成员看到十无用为每一个相关的一个消息,他们很快就会开始忽略所有的人。
成本和进度
这个问题可能要花上几周所有本身只是短暂的,请记住最重要的方面实现的完成按时并在预算之内的计划目标是:
在开始设置现实的参数!
例如,如果您设置总重量为主因素在性能参数(同时还持有公司下降速度),你可能无意中要求使用的材料,如。、碳纤维与 ABS;或者一些的高档聚酯薄膜代替尼龙降落伞布,等等。你可以打破银行(和时间表)减少恢复系统的重量也许 10 - 15%。这可能是一个非常昂贵的饮食只是为了保存一个或两磅更有可能会更容易保存。
当然,
成本成反比!
从这个意义上说,一个回收系统的发展无人机没有不同于其他无人机项目的一部分。和更远的到期日期之前你给必要的信息恢复系统建设者,越少项目的总成本的一部分。一个特别重要的问题各方要牢记是,团队必须避免“镀金”的倾向程序通过签署合同后要求蠕变和展开。
设计过程中一些常见的设计问题包括:常规或应急使用;总重量范围(特别是预期体重增长),飞行包线,打开负载限制,必需的下降速度;积载的形状和体积,部署启动和手段;地面释放和安全问题。但是在深入研究回收系统的细节设计审查的项目,让我们开始使用的变量确定树冠大小和流动的相关因素从这一点。这以后, 我们将做一个设计运动,这样我们就可以说明整个过程从头到尾。基本方程组件的定义的基本性能方程中使用降落伞设计:
• ft.2 表达的树冠表面积(S)或科幻小说。
• 阻力系数(Cd)是一种经验,无量纲数用来量化的性能降落伞的树冠。我们的遮篷考虑这里 Cd 的范围可以从约 0.7 至 1.3。为我们的案例研究中,我们将使用 Cd =
1.0 简化数学。
• 拖动领域,树冠的表面积(年代)次(Cd)和表达平方英尺(Cd ~ ft.2)或科幻小说;
• 空气密度(ρ)“ρ”;在海平面ρ是常见的参考价值(ρsl ~ 0.002378 磅/发生变化);
• Vt 终端速度(Vt ~英尺/秒。)的任何设备自由落体,如一个 200 磅的圆柱形测试车辆(CTV)由 14 个“直径钢管(14“dia = 1 ft.2 &使用 Cd = 1.0)在自由落体加速将达到一个终端大约 410 英尺/秒速度约 240 年起亚。
• VT-ROD 稳态,终端沉降率(杆)期望(VT-ROD ~英尺/秒)。在地面的影响
• 六世时的初始速度打开降落伞(六世~英尺/秒)。
• 阻力(D ~磅)是气流所产生的力量特定的速度
• 车辆的毛重(W)。请注意,W = D 任何稳态条件;在我们的讨论最常被 VT-ROD。降落伞的重量,Wp 指的树冠本身。
• 开放力减少因子(X1)5 是一个实证派生,无因次系数量化的影响在打开负载的减速的过程。(这反映了最大阻力区域因此树冠发生的最大力量)比初始速度明显降低。X1 的因素以非常低的树冠范围从约 0.05 加载(< 0.5PSF)的最大值 1.0 在树冠加载的高于 80 PSF;实际用途对应于一个速度> 250 英尺/秒。在这个设计练习我们将使用 0.05 和 0.10,对应的负载 200 和 400 英镑。
• 开放力系数在无限质量的条件(Cx)是一个经验,无量纲因子量化的影响在风打开降落伞隧道(实际上,无限质量)于是负载并不在开幕式和降落伞减速将充气充过头瞬间,否则因此造成过度——的负载率过度的稳定状态负载是残雪。这些讨论等降落伞(也就是在这里。下,最后降落杆 30 FPS)无限的质量情况,实际上,几乎相反的现实世界条件 X1 所反映的因素上面所描述的。我们将使用 1.8 的设计运动。
• 礁百分比(R ~ %)显示(如果多少任何)降落伞已经被传统的珊瑚礁烟火或其他device6 手段。R 表示剩下的阻力区域,如。在这些方程,25%意味着阻力面积减少75%。
• 最大开放力(F)计算基于初始速度、重量和设计因素。
• 问的动态压力来源于½ρV2 和嵌入一种形式或所有下列方程另一个地方。事实上,“q”这个词经常用于设计讨论降落伞(以及其他所有的空气设备)。
记住,这不是一个教程的设计降落伞,我们将利用所有的最简单的形式后计算。
在把这些组件通常的形式,让我们开始我们的设计计算如下:
A——动态压力
动态压力“q”来源于½ρV2 和用磅/英国《金融时报》表示。2 或 PSF。q =½ρV2
B -稳态拖稳态阻力(等于重量)来源于:D =½ρVt2 cd
C -稳态下降速度终端杆(Vt)来源于基本阻力公式用 D WVt =[(2 W)/(ρCdS)]½
D -需要拖动区域稳态速度为了找到所需的阻力区域达到所需的稳态速度在一个已知重量,我们使用:cd =(2 W)/(ρV2)
E -最大力量
开幕式力在规定速度计算(Vi)使用 F =½ρVi2 X1 残雪 cd R 派生的价值观:有几十种的组合输入值(W、V、Cd 等)和基本的结果上面列出的方程。最有用的跟进在下面。
F -树冠加载
最有用的一个参考数字使用的降落伞设计师是所谓的树冠加载(CL)表示每平方英尺磅的毛重(W)(PSF)的树冠阻力面积:CL = W / cd。这提供了一种快速瞥了一眼情况没有回到计算器或电脑的一个最有用的花边新闻,树冠加载 1.0 PSF 导致沉降率(杆)29 英尺/秒的海平面。注意,树冠加载对应动态压力,即。问在 29 英尺/秒 1.0 PSF。由于所有这些关系 V2 那么你是相关的可以快速估算杖一旦你知道这伞吗加载;例如,如果你减少树冠加载一半,新的下降速度将:V2 = V1 *(½)½= V1 * 0.707 相反,如果你是双树冠加载,杆将:V2 = V1 *(2)½= V1 * 1.414 简单的规则要记住树冠加载:
树冠加载（psf）
繁殖 29.0 次
杆（米/秒）
0.25
0.50
14.5
0.50
0.71
20.5
1.00
1.00
29.0
2.00
1.41
41.0
4.00
2.00
58.0
8.00
2.83
82.0
G -树冠拖效率
另一个方便的数量是拖动树冠的效率本身表示为每磅平方英尺的阻力区域(CdS) 树冠(Wp):Ceff = cd / Wp 表达 ft2 /磅。这反映了许多的因素,进入设计和构建的树冠,即。、形状、材料、施工等细节出来。值的范围可以从低 40(古董设计如 USN /美国空军 28 平圆)低 80 年的技术发展水平降落伞非常专业应用程序(也很少与结构性储备)。为了简化的数学我们将使用价值 Ceff = 50 ft2 /磅。在下面的设计练习。
H -树冠重量
一旦我们知道所需的阻力区,可以估计拖动效率(通常是基于之前的工作相似我们可以通过简单的确定权重的设计)乘法。例如使用一个 600 英尺的树冠拖效率, 我们发现:cd / Ceff = 600 ft.2 /(60 ft.2 /磅)= 10 磅。
I -充填密度
所谓的充填密度用磅/立方英尺(磅/发生变化或 PCF)使用的派生(或实际重量) 树冠,以确定需要装载量树冠降落伞(至少)。包装方法包括传统的限制大约 25 PCF;真空袋和烤 8 约 40 的限制 PCF;压力 packing9 约 50 PCF 的限制。你应该小心使用这些包密度值因为有很多不同的包装方法许多其他因素如包几何影响可以实现的实际密度。
设计决策的层次结构
现在我们已经正确地分析的工具我们几乎已经准备好开始我们的性能需求设计运动。然而,在我们开始之前回收系统项目,以下问题必须回答。请注意,我们已安排这些大致的项目的重要性和影响。
1. 这将用于常规恢复或紧急吗只有吗?
2. 最小和最大容许 rate-ofdescent 是什么(杆)和最大总空的条件?
3. 所需的杆是什么?(通常在 1724 英尺/秒)
4. 飞机重量是多少在部署——最小和最大的预期,特别是免税额体重增长?
5. 什么是飞机速度部署;最低和最大预期?
6. 什么是你想要打开负载限制;表达吗磅力吗?或者你可以指定一个最大值负荷系数通常在 5 到 10 g 最大的部署速度。
7. 最大结构界面的限制是什么?
8. 什么结构界面是必需的——通常 1 到 4 附件点?
9. 什么是所需的态度——即着陆。,右侧;颠倒,鼻子和鼻子或 ?
10. 你设想充填回收系统在哪里?为的例子中,这可能是内部模具行或以下在外部皮肤外部某处。
11. 什么卷可以在装载舱设想?
12. 降落伞会重用吗?如果是这样的话,哪些组件将回收?
13. 你在水面上(多目标)或污垢(大多数无人机)?
14. 飞机飞在雨中吗?
15. 你希望我们提供装载容器(我们可以吗根据需要提供真空成型或复合壳)?
16. 你希望有多少用于序列我们处理吗?
17. 你需要一个“智能”系统部署吗对高度敏感或速度?
河海大学文天学院本科毕业设计（论文）
18. 你需要一个地面(或水)发布系统?如果是这样,你要我们提供吗?
19. 如果要重用会改装领域或者发送回到制造商?
20. 这是飞机“stow-able”滑翔机的形式——或者是什么它完全永久组装-什么影响,如果有的话这对回收系统吗?
21. 很多无人机传感器包底部一侧因此,净成本(机体损伤和传感器损害)在降落伞着陆着陆颠倒时显著降低。这是否适用于您的程序吗?
22. 请提供 3-view CG 的飞机明显。
23. 请提供详细的飞机布局和推进:即。推杆式或拖拉机,飞机,道具,单旋翼带尾桨或 ?
24. 基于飞机配置的细节积载舱,你必须选择一个部署方法。你能接受增加的可能性吗纠缠或其他失败为了使用更简单部署方法?
虽然这看起来像很多信息提供回收系统设计师,更应该发展的飞机设计,即毛重和期望的速度后裔,飞行包线和允许冲击荷载等。
5l
河海大学文天学院本科毕业设计（论文）
60
附录二：
ABSTRACT
How to Select and Qualify a
Parachute Recovery System for
Your UAV
Manley C. Butler, Jr.
President
Butler Parachute Systems Group, Inc.
Roberto Montanez VP, Operations
Butler Parachute Systems Group, Inc.
This paper presents substantial and detailed information regarding the common issues affecting the design, testing and qualification of a parachute recovery system for all categories of UAVs (reconnaissance, air target, weapon, etc). l We assume that our primary audience will be UAV manufacturers and operators. Therefore, in order to familiarize the reader with the basic process of designing and qualifying a recovery system for a UAV, we have provided a simple but detailed exercise in recovery system design and, a review of the program management thereof.
Introduction
The authors assume that you and the customer have already performed a rudimentary cost/benefit analysis and have decided that your UAV must have a parachute recovery system for one or more of the usual reasons. We will discuss the factors affecting the recovery system with the ultimate goal of helping you to become a "smart buyer" able to make informed and intelligent decisions throughout the design and qualification process of the recovery system for your UAV.
Background
Since l976 the Butler Parachute Systems Group, Inc.2, its predecessor and its various subsidiaries have designed and manufactured a wide range of parachutes and recovery systems. In l979, we received our first FAA Technical Standard Order Authorization (TSO) for the harness and container components used for a personnel emergency (bailout) backpack parachute; in l99l, we received a TSO3 on a round canopy designed for use in our emergency parachute systems; in l992, we began making spin and deep stall recovery systems for flight test aircraft starting with a system for the Swearingen SJ-30; and in l994, we began making UAV parachute recovery systems beginning with a recovery system designed and built for the Predator SBIR first article (see details in the reference section).
We have worked with over a dozen companies in the past l3 years and have developed parachute recovery systems for UAVs for weights from less than 50 pounds to over 6,000 pounds and recovery
speeds from under 30 knots to nearly 500 knots.
We have learned something from each of these programs both in technical experience but particularly in the program management arena.
Therefore, we feel well-qualified to present this information; particularly in hope that it will allow someone out there to avoid some of the pitfalls we have encountered.
Program Management
Everyone in the aviation industry knows that some components of any aircraft are more or less "standard". So, as the program manager, you might occasionally discover that you can buy something like an alternator "off the shelf" and just bolt it on and go. However, a parachute recovery system is very seldom in that category. Therefore, as the program manager, you must approach the process for the design, testing and qualification of a recovery system for a UAV as similar to that for any other complex aircraft sub-system; i.e., one must continuously consider the "6-pack" of form, fit, function, performance, schedule, and, as always, cost. Although this is a tongue-in-cheek reference to a 6-pack — this particular 6-pack can definitely cause headaches and a hangover if not managed appropriately; and it will certainly help to spread the workload around to those most qualified for each part of the project. The Organization of GENUAVASS
The team leaders at GENUAVASS (presumed herein to be the engineering and program managers) must set the precedence of each factor in the 6-pack at the earliest possible point in the program. They will also assign work areas to, and determine the interaction of, the team members working under their supervision. The team leaders at BUPS will do the same.
And, of course, by setting realistic parameters for all of these factors you should be able to avoid the common penalties such as unnecessary weight, volume, and cost and/or schedule impact to the program.
Nearly any size organization can work well with the process outlined in this paper so of course we must start with a kickoff "Team Meeting" with all of the players present, whereupon everyone involved must acknowledge that:
• the goal of the team is to complete the recovery system on time, within budget and within the desired
performance parameters;
• the team consists of you (the buyer, GENUAVASS) and us (the seller, BUPS) - and the customer (BSA), and all the employees thereof, working in a cooperative environment;
• no one can make any unilateral changes;
• form, fit, function and performance are inextricably linked with each other;
• schedule and cost are inextricably linked with each other;
• these two subgroups are also inextricably linked but in a somewhat different manner;
• all of these factors can be manipulated to some extent but only with the knowledge and concurrence of all the players;
• any changes in any of the factors will ripple through the process and must be approached with care. Please note that even though we insist upon a "kickoff" meeting, as well as a "graduation" meeting when we're finished, we do strongly feel that meetings in general must be minimized or avoided if at all possible.
In fact, given that everyone on the team can be in more-or-less constant communication, by email, some sort of protocol (other than CC to the universe) should actually be established for email communications amongst the team members. The team members should decide who needs to see what
— the point is not to hide anything, it is to avoid adding to the "junk" mail.
Remember that if a particular team member sees ten useless messages for every relevant one, they will soon begin to ignore all of them.
Cost & Schedule
This subject could take weeks all by itself but just briefly, keep in mind the most important aspect of achieving the program goal of finishing on time and within budget is:
Set Realistic Parameters in the Beginning!
For example, if you set total system weight as the primary factor within the performance parameters (while still holding firm on the rate of descent), you may inadvertently require the use of exotic materials; e.g., carbon fiber vs. ABS; or some sort of fancy Mylar film instead of Nylon parachute cloth, etc.
You can break the bank (and the schedule) to reduce the weight of the recovery system by perhaps l0-l5%. That could be a very expensive diet just to save one or two pounds that will more than likely be easier to save elsewhere.
And, of course,
Cost is Inversely Proportional to Time!
In this sense, the development of a recovery system for your UAV is no different than any other part of the UAV program.
And the farther ahead of the due date you give the necessary information to your recovery system builder, the less the overall cost of that part of the project.
One particularly important issue for all parties to keep in mind is that the team must avoid the tendency to "gold plate" the program via "requirement creep" once the contract is signed and underway.
The Design Process
A few of the common design issues include: routine or emergency use; gross weight range (specifically anticipated weight growth); flight envelope; opening load limits; required rate-of-descent; stowage shape and volume; deployment initiation and means; ground release; and safety issues.
But before delving into the details of a recovery system design project, let's start with a review of the variables used to determine the canopy size and the related factors that flow from that. After that, we'll do a design exercise so we can illustrate the entire process from beginning to end.
Basic Equations
The definitions of the components of the basic performance equations used in parachute design are:
• The canopy surface area (S) expressed in ft.2 or SF.
• The coefficient of drag (Cd ) is an empirically derived, dimensionless number used to quantify the performance of the parachute canopy. For the type of canopies we are considering here Cd can range from about 0.7 to l.3. For our case study, we will use Cd = l.0 to simplify the math.
• The drag area which is the surface area of the canopy (S) times (Cd) and is expressed in square feet (CdS ~ ft.2) or SF;
• The air density (ρ ) "rho"; p at sea level is the usual reference value (ρsl ~ 0.002378 lb/ft3);
• Vt is the terminal velocity (Vt ~ ft/sec.) of any device in freefall; e.g., a 200 pound cylindrical test vehicle (CTV) made from l4"-diameter steel pipe (l4" dia = l ft.2 & use Cd = l.0) left to accelerate in freefall will reach a terminal velocity of approximately 4l0 ft/sec or about 240 KIAS.
• VT-ROD is the steady-state, terminal rate-of-descent (ROD) desired (VT-ROD ~ ft/sec.) at ground impact
• Vi is the initial velocity when the parachute is opened (Vi ~ ft/sec.)
• Drag (D ~ pounds) is the force generated by airflow at a particular velocity
• The gross weight (W) of the vehicle. Note that W = D at any steady-state condition; which, in our
discussions will most often be VT-ROD.
• The weight of the parachute, Wp refers to the canopy by itself.
• The opening force reduction factor (Xl) 5is an empirically derived, dimensionless factor that quantifies the effects of the deceleration of the payload during the opening process. This reflects that the maximum drag area (and thus maximum force) of the canopy occurs at a significantly lower velocity than initial. The Xl factor ranges from about 0.05 at very low canopy loading (<0.5 PSF) to its maximum value of l.0 at canopy loading of higher than 80 PSF; which for practical purposes correspond to a velocity > 250 ft/s. In this design exercise we will use 0.05 and 0.l0, corresponding to the loads of 200 and 400 pounds.
• The opening force coefficient at infinite mass conditions (Cx) is an empirically derived, dimensionless factor that quantifies the effects of opening a parachute in a wind tunnel (in effect, an infinite mass) whereupon the payload does not decelerate during the opening and the parachute will over-inflate momentarily, thus causing an overshoot in the load — the ratio of the overshoot to the steady state load is Cx. For parachutes such as those under discussion here (i.e., final descent with ROD under 30 FPS) the infinite mass condition is, in effect, nearly the opposite of the real world condition reflected by the Xl factor described above. We will use l.8 in the design exercise.
• The reefed percentage (R ~ %) indicates how much (if any) the parachute has been reefed by traditional pyrotechnic means or some other device6. R is expressed as the remaining drag area; e.g., 25% in these equations means that the drag area is reduced by 75%.
• The maximum opening force (F) which is calculated based on the initial velocity, weight and design factors.
• The dynamic pressure q is derived from ½ ρ V2 and is embedded in all the following equations in one form or another. In fact, the term "q" is used frequently in design discussions of parachutes (as well as all other airborne devices).
Keeping in mind that this not a tutorial on the design of parachutes, we will utilize the simplest form of all of the following calculations. Putting these components together in the usual forms, allows us to begin our design calculations as follows:
A - Dynamic Pressure
The dynamic pressure "q" is derived from ½ ρ V2 and is expressed in lb./ft.2 or PSF. q =½ ρ V2 B -
Steady-State Drag
The steady-state drag (equal to the weight) is derived from: D = ½ ρ Vt 2 CdS C - Steady-State Rate-of-Descent
The terminal ROD (Vt) is derived from the basic drag formula by substituting W for D Vt = [(2 W) /( ρ
CdS)] ½ D - Required Drag Area for Steady-State Velocity
In order to find the drag area required to reach a desired steady-state velocity at a known weight, we use: CdS = (2 W) / (ρ V2)
E - Maximum Opening Force
The opening force at the stated velocity (Vi) is calculated using
F = ½ ρ Vi
2 CdS Xl Cx R
Derived Values: There are dozens of combinations of the input values (W, V, Cd, etc) and the results of the basic equations listed above. The most useful of these follow
below.
F - Canopy Loading
One of the most useful reference numbers used by parachute designers is the so-called canopy loading (CL) expressed as pounds of gross weight (W) per square foot (PSF) of canopy drag area: CL= W/CdS. This provides a quick glimpse at the situation without going back to the calculator or computer — one of the most useful tidbits to remember is that a canopy loading of l.0 PSF results in a rate-of-descent (ROD) of 29 ft/sec at sea level. Note that the canopy loading corresponds to the dynamic pressure; i.e., q at 29 ft/sec is l.0 PSF.
And since all of these relationships are related by V2 then you can quickly estimate the ROD once you know the canopy loading; for example, if you reduce the canopy loading by half, the new rate of descent will be: V2 = Vl * (½) ½ = Vl * 0.707
Conversely, if you were to double the canopy loading, the ROD will be:
V2 = Vl * (2) ½ = Vl *l.4l4
Easy rules to remember on canopy loading:
Another handy number is the drag efficiency of the canopy itself expressed as square feet of drag area (CdS) per pound of canopy (Wp): Ceff = CdS/ Wp expressed in ft2/lb. This reflects many of the factors that go into designing and building the canopy; i.e., the shape, materials, construction details and so f
收藏