如何為你的無人機(jī)選擇合格的一個降落傘回收系統(tǒng)外文文獻(xiàn)翻譯、中英文翻譯、外文翻譯
如何為你的無人機(jī)選擇合格的一個降落傘回收系統(tǒng)外文文獻(xiàn)翻譯、中英文翻譯、外文翻譯,如何,無人機(jī),選擇,合格,一個,降落傘,回收,系統(tǒng),外文,文獻(xiàn),翻譯,中英文
附錄一：
如何為你的無人機(jī)選擇合格的一個降落傘回收系統(tǒng)
德拉·c·巴特勒,Jr 總統(tǒng)
巴特勒降落傘系統(tǒng)集團(tuán)公司
羅伯特·Montanez 副總裁
巴特勒降落傘系統(tǒng)集團(tuán)公司
文摘
本文提出實(shí)質(zhì)性的和詳細(xì)的信息關(guān)于影響設(shè)計(jì)的常見問題,測試和資格降落傘回收系統(tǒng)的所有類別無人機(jī)的偵察、空中目標(biāo)、武器等)。假設(shè)我們的主要受眾將無人機(jī)制造商和運(yùn)營商。因此,為了熟悉讀者設(shè)計(jì)的基本過程和排位賽復(fù)蘇無人機(jī)系統(tǒng),我們提供了一個簡單而詳細(xì)在回收系統(tǒng)設(shè)計(jì)和鍛煉,回顧項(xiàng)目管理。
背景
自 1976 年以來,巴特勒降落傘系統(tǒng)集團(tuán)、Inc.2,它前任和它的各種設(shè)計(jì)和子公司生產(chǎn)范圍廣泛的降落傘和恢復(fù)系統(tǒng)。1979 年,我們收到我們的第一個聯(lián)邦航空局技術(shù)標(biāo)準(zhǔn)的授權(quán)(TSO)利用和秩序容器組件用于人員進(jìn)入緊急狀態(tài)(救助)背包降落傘;在1991 年,我們收到了TSO3 一個圓形樹冠設(shè)計(jì)用于在我們的緊急降落傘系統(tǒng);在 1992 年,我們開始旋轉(zhuǎn)和深失速回收系統(tǒng)飛行測試飛機(jī)從一個系統(tǒng) SJ-30 名叫史瓦金;在 1994 年,我們開始制作無人機(jī)降落傘回收系統(tǒng)開始復(fù)蘇系統(tǒng)設(shè)計(jì)和建造捕食者 SBIR 第一篇文章
介紹
作者假設(shè)您和客戶已經(jīng)進(jìn)行了基本的成本/收益分析決定你的無人機(jī)必須有一個降落傘回收系統(tǒng)的一個或多個通常的原因。我們將討論回收系統(tǒng))與根本的影響因素目標(biāo)是幫助你成為一個“聰明的買家”整個設(shè)計(jì)和智能決策資格無人機(jī)的回收系統(tǒng)的過程。
1 在本文檔中“我們”指的是作者和/或管家無人降落傘系統(tǒng),LLC(bup);“你” 指的是讀者,假定在項(xiàng)目經(jīng)理的角色工程技術(shù)人員的無人機(jī)制造商我們電話通用無人機(jī) Associates(GENUAVASS)時,我們需要有一個名字的故事;“客戶”的最終用戶無人機(jī),就是我們所說的大秘密機(jī)構(gòu)(BSA)當(dāng)我們需要有個名字的故
事;“回收系統(tǒng)”包括降落傘回收系統(tǒng)和所有相關(guān)的組件工作;和“無人機(jī)”將適用于任何類型的無人機(jī)或目標(biāo)。
（bup Qualification.doc——回收系統(tǒng)）
2 2002 年,巴特勒降落傘系統(tǒng),公司重組是管家降落傘系統(tǒng)集團(tuán)公司與子公司除以產(chǎn)品區(qū)域。特定的興趣這是子公司巴特勒無人降落傘系統(tǒng),LLC(bup)。
3 過程設(shè)計(jì)、測試和符合條件的人員降落傘樹冠與我們自己的資金,使我們強(qiáng)烈意識到變化莫測的降落傘測試。這些問題尋找靈感方法來消除這些失敗的根源, 最終導(dǎo)致的發(fā)明蝙蝠草帽滑塊(項(xiàng)全球?qū)＠?。在引用您可以找到大量信息的鏈接設(shè)備,但在這里,我只想說,蝙蝠草帽滑塊傳統(tǒng)降落傘由幾個訂單增加的可靠性級的。我們已經(jīng)從每一個項(xiàng)目都學(xué)到一些東西在技術(shù)經(jīng)驗(yàn),但特別是在程序管理領(lǐng)域。因此,我們覺得優(yōu)秀的呈現(xiàn)這些信息;尤其是在希望它將允許有人避免一些我們遇到的陷阱。
項(xiàng)目管理
航空工業(yè)中的每個人都知道一些組件的任何飛機(jī)都或多或少的“標(biāo)準(zhǔn)”。所以, 項(xiàng)目經(jīng)理,你可能會偶爾發(fā)現(xiàn)你可以買東西像一個交流發(fā)電機(jī)和“現(xiàn)成的”螺栓上,走了。然而,一個降落傘回收系統(tǒng)很少在這一類。因此,作為該項(xiàng)目經(jīng)理,你必須方法的過程的設(shè)計(jì)、測試和資質(zhì)的回收系統(tǒng)類似于無人機(jī)其他復(fù)雜的飛機(jī)子系統(tǒng),即。,一個人必須不斷考慮形式的“6-pack”,健康,功能,性能、時間表和一如既往地成本。雖然這是半開玩笑的提到 6-pack——這個特殊的 6-pack 絕對可以導(dǎo)致頭痛,如果不是宿醉適當(dāng)?shù)墓芾?它肯定會幫助傳播工作負(fù)載在那些最能勝任的每個部分項(xiàng)目。
團(tuán)隊(duì)領(lǐng)導(dǎo)人 GENUAVASS(這里假定工程和項(xiàng)目經(jīng)理)必須設(shè)置優(yōu)先級每個因素的6-pack 最早可能的點(diǎn)程序。他們還將指定工作區(qū)域,并確定團(tuán)隊(duì)成員之間的相互作用,在他們的工作監(jiān)督。團(tuán)隊(duì)領(lǐng)導(dǎo)人 bup 將做同樣的事情。當(dāng)然,通過設(shè)置現(xiàn)實(shí)
的所有這些參數(shù)因素,你應(yīng)該能夠避免常見的處罰等不必要的重量、體積和成本和/或時間表對程序的影響。
幾乎任何規(guī)模的組織工作的過程
本文中概述,當(dāng)然我們必須首先開球“團(tuán)隊(duì)會議”的所有球員,于是每個人必須承認(rèn):
? 團(tuán)隊(duì)的目標(biāo)是完成回收系統(tǒng)時間,在預(yù)算和內(nèi)部所需的性能參數(shù);
? 這支隊(duì)伍的你(買方,GENUAVASS)和我們(賣方,bup)和客戶(BSA)員工,在合作工作環(huán)境;
? 沒有人可以讓任何單方面改變;
? 形式、合適,功能和性能不可避免互相聯(lián)系;
? 時間表和成本彼此密不可分;
? 這兩個子組也密不可分,但在一個不同的方式;
? 所有這些因素可以在一定程度上操縱只有知識和贊同的球員;
? 任何變化的因素將波及過程中,必須小心走近。
請注意,盡管我們堅(jiān)持一個“開始”會議,以及一個“畢業(yè)”當(dāng)我們見面完成后, 我們通常必須強(qiáng)烈覺得會議盡量減少或避免如果可能的話。
事實(shí)上,考慮到團(tuán)隊(duì)中的每個人都可以或多或少不斷的溝通,通過電子郵件,某種形式的協(xié)議宇宙(CC)實(shí)際上應(yīng)該建立在團(tuán)隊(duì)成員的電子郵件通信。的團(tuán)隊(duì)成員應(yīng)該決定看看——誰需要點(diǎn)不隱藏任何東西,以避免增加了“垃圾”郵件。
記住,如果一個特定的團(tuán)隊(duì)成員看到十無用為每一個相關(guān)的一個消息,他們很快就會開始忽略所有的人。
成本和進(jìn)度
這個問題可能要花上幾周所有本身只是短暫的,請記住最重要的方面實(shí)現(xiàn)的完成按時并在預(yù)算之內(nèi)的計(jì)劃目標(biāo)是:
在開始設(shè)置現(xiàn)實(shí)的參數(shù)!
例如,如果您設(shè)置總重量為主因素在性能參數(shù)(同時還持有公司下降速度),你可能無意中要求使用的材料,如。、碳纖維與 ABS;或者一些的高檔聚酯薄膜代替尼龍降落傘布,等等。你可以打破銀行(和時間表)減少恢復(fù)系統(tǒng)的重量也許 10 - 15%。這可能是一個非常昂貴的飲食只是為了保存一個或兩磅更有可能會更容易保存。
當(dāng)然,
成本成反比!
從這個意義上說,一個回收系統(tǒng)的發(fā)展無人機(jī)沒有不同于其他無人機(jī)項(xiàng)目的一部分。和更遠(yuǎn)的到期日期之前你給必要的信息恢復(fù)系統(tǒng)建設(shè)者,越少項(xiàng)目的總成本的一部分。一個特別重要的問題各方要牢記是,團(tuán)隊(duì)必須避免“鍍金”的傾向程序通過簽署合同后要求蠕變和展開。
設(shè)計(jì)過程中一些常見的設(shè)計(jì)問題包括:常規(guī)或應(yīng)急使用;總重量范圍(特別是預(yù)期體重增長),飛行包線,打開負(fù)載限制,必需的下降速度;積載的形狀和體積,部署啟動和手段;地面釋放和安全問題。但是在深入研究回收系統(tǒng)的細(xì)節(jié)設(shè)計(jì)審查的項(xiàng)目,讓我們開始使用的變量確定樹冠大小和流動的相關(guān)因素從這一點(diǎn)。這以后, 我們將做一個設(shè)計(jì)運(yùn)動,這樣我們就可以說明整個過程從頭到尾?；痉匠探M件的定義的基本性能方程中使用降落傘設(shè)計(jì):
? ft.2 表達(dá)的樹冠表面積(S)或科幻小說。
? 阻力系數(shù)(Cd)是一種經(jīng)驗(yàn),無量綱數(shù)用來量化的性能降落傘的樹冠。我們的遮篷考慮這里 Cd 的范圍可以從約 0.7 至 1.3。為我們的案例研究中,我們將使用 Cd =
1.0 簡化數(shù)學(xué)。
? 拖動領(lǐng)域,樹冠的表面積(年代)次(Cd)和表達(dá)平方英尺(Cd ~ ft.2)或科幻小說;
? 空氣密度(ρ)“ρ”;在海平面ρ是常見的參考價值(ρsl ~ 0.002378 磅/發(fā)生變化);
? Vt 終端速度(Vt ~英尺/秒。)的任何設(shè)備自由落體,如一個 200 磅的圓柱形測試車輛(CTV)由 14 個“直徑鋼管(14“dia = 1 ft.2 &使用 Cd = 1.0)在自由落體加速將達(dá)到一個終端大約 410 英尺/秒速度約 240 年起亞。
? VT-ROD 穩(wěn)態(tài),終端沉降率(桿)期望(VT-ROD ~英尺/秒)。在地面的影響
? 六世時的初始速度打開降落傘(六世~英尺/秒)。
? 阻力(D ~磅)是氣流所產(chǎn)生的力量特定的速度
? 車輛的毛重(W)。請注意,W = D 任何穩(wěn)態(tài)條件;在我們的討論最常被 VT-ROD。降落傘的重量,Wp 指的樹冠本身。
? 開放力減少因子(X1)5 是一個實(shí)證派生,無因次系數(shù)量化的影響在打開負(fù)載的減速的過程。(這反映了最大阻力區(qū)域因此樹冠發(fā)生的最大力量)比初始速度明顯降低。X1 的因素以非常低的樹冠范圍從約 0.05 加載(< 0.5PSF)的最大值 1.0 在樹冠加載的高于 80 PSF;實(shí)際用途對應(yīng)于一個速度> 250 英尺/秒。在這個設(shè)計(jì)練習(xí)我們將使用 0.05 和 0.10,對應(yīng)的負(fù)載 200 和 400 英鎊。
? 開放力系數(shù)在無限質(zhì)量的條件(Cx)是一個經(jīng)驗(yàn),無量綱因子量化的影響在風(fēng)打開降落傘隧道(實(shí)際上,無限質(zhì)量)于是負(fù)載并不在開幕式和降落傘減速將充氣充過頭瞬間,否則因此造成過度——的負(fù)載率過度的穩(wěn)定狀態(tài)負(fù)載是殘雪。這些討論等降落傘(也就是在這里。下,最后降落桿 30 FPS)無限的質(zhì)量情況,實(shí)際上,幾乎相反的現(xiàn)實(shí)世界條件 X1 所反映的因素上面所描述的。我們將使用 1.8 的設(shè)計(jì)運(yùn)動。
? 礁百分比(R ~ %)顯示(如果多少任何)降落傘已經(jīng)被傳統(tǒng)的珊瑚礁煙火或其他device6 手段。R 表示剩下的阻力區(qū)域,如。在這些方程,25%意味著阻力面積減少75%。
? 最大開放力(F)計(jì)算基于初始速度、重量和設(shè)計(jì)因素。
? 問的動態(tài)壓力來源于?ρV2 和嵌入一種形式或所有下列方程另一個地方。事實(shí)上,“q”這個詞經(jīng)常用于設(shè)計(jì)討論降落傘(以及其他所有的空氣設(shè)備)。
記住,這不是一個教程的設(shè)計(jì)降落傘,我們將利用所有的最簡單的形式后計(jì)算。
在把這些組件通常的形式,讓我們開始我們的設(shè)計(jì)計(jì)算如下:
A——動態(tài)壓力
動態(tài)壓力“q”來源于?ρV2 和用磅/英國《金融時報(bào)》表示。2 或 PSF。q =?ρV2
B -穩(wěn)態(tài)拖穩(wěn)態(tài)阻力(等于重量)來源于:D =?ρVt2 cd
C -穩(wěn)態(tài)下降速度終端桿(Vt)來源于基本阻力公式用 D WVt =[(2 W)/(ρCdS)]?
D -需要拖動區(qū)域穩(wěn)態(tài)速度為了找到所需的阻力區(qū)域達(dá)到所需的穩(wěn)態(tài)速度在一個已知重量,我們使用:cd =(2 W)/(ρV2)
E -最大力量
開幕式力在規(guī)定速度計(jì)算(Vi)使用 F =?ρVi2 X1 殘雪 cd R 派生的價值觀:有幾十種的組合輸入值(W、V、Cd 等)和基本的結(jié)果上面列出的方程。最有用的跟進(jìn)在下面。
F -樹冠加載
最有用的一個參考數(shù)字使用的降落傘設(shè)計(jì)師是所謂的樹冠加載(CL)表示每平方英尺磅的毛重(W)(PSF)的樹冠阻力面積:CL = W / cd。這提供了一種快速瞥了一眼情況沒有回到計(jì)算器或電腦的一個最有用的花邊新聞,樹冠加載 1.0 PSF 導(dǎo)致沉降率(桿)29 英尺/秒的海平面。注意,樹冠加載對應(yīng)動態(tài)壓力,即。問在 29 英尺/秒 1.0 PSF。由于所有這些關(guān)系 V2 那么你是相關(guān)的可以快速估算杖一旦你知道這傘嗎加載;例如,如果你減少樹冠加載一半,新的下降速度將:V2 = V1 *(?)?= V1 * 0.707 相反,如果你是雙樹冠加載,桿將:V2 = V1 *(2)?= V1 * 1.414 簡單的規(guī)則要記住樹冠加載:
樹冠加載（psf）
繁殖 29.0 次
桿（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 -樹冠拖效率
另一個方便的數(shù)量是拖動樹冠的效率本身表示為每磅平方英尺的阻力區(qū)域(CdS) 樹冠(Wp):Ceff = cd / Wp 表達(dá) ft2 /磅。這反映了許多的因素,進(jìn)入設(shè)計(jì)和構(gòu)建的樹冠,即。、形狀、材料、施工等細(xì)節(jié)出來。值的范圍可以從低 40(古董設(shè)計(jì)如 USN /美國空軍 28 平圓)低 80 年的技術(shù)發(fā)展水平降落傘非常專業(yè)應(yīng)用程序(也很少與結(jié)構(gòu)性儲備)。為了簡化的數(shù)學(xué)我們將使用價值 Ceff = 50 ft2 /磅。在下面的設(shè)計(jì)練習(xí)。
H -樹冠重量
一旦我們知道所需的阻力區(qū),可以估計(jì)拖動效率(通常是基于之前的工作相似我們可以通過簡單的確定權(quán)重的設(shè)計(jì))乘法。例如使用一個 600 英尺的樹冠拖效率, 我們發(fā)現(xiàn):cd / Ceff = 600 ft.2 /(60 ft.2 /磅)= 10 磅。
I -充填密度
所謂的充填密度用磅/立方英尺(磅/發(fā)生變化或 PCF)使用的派生(或?qū)嶋H重量) 樹冠,以確定需要裝載量樹冠降落傘(至少)。包裝方法包括傳統(tǒng)的限制大約 25 PCF;真空袋和烤 8 約 40 的限制 PCF;壓力 packing9 約 50 PCF 的限制。你應(yīng)該小心使用這些包密度值因?yàn)橛泻芏嗖煌陌b方法許多其他因素如包幾何影響可以實(shí)現(xiàn)的實(shí)際密度。
設(shè)計(jì)決策的層次結(jié)構(gòu)
現(xiàn)在我們已經(jīng)正確地分析的工具我們幾乎已經(jīng)準(zhǔn)備好開始我們的性能需求設(shè)計(jì)運(yùn)動。然而,在我們開始之前回收系統(tǒng)項(xiàng)目,以下問題必須回答。請注意,我們已安排這些大致的項(xiàng)目的重要性和影響。
1. 這將用于常規(guī)恢復(fù)或緊急嗎只有嗎?
2. 最小和最大容許 rate-ofdescent 是什么(桿)和最大總空的條件?
3. 所需的桿是什么?(通常在 1724 英尺/秒)
4. 飛機(jī)重量是多少在部署——最小和最大的預(yù)期,特別是免稅額體重增長?
5. 什么是飛機(jī)速度部署;最低和最大預(yù)期?
6. 什么是你想要打開負(fù)載限制;表達(dá)嗎磅力嗎?或者你可以指定一個最大值負(fù)荷系數(shù)通常在 5 到 10 g 最大的部署速度。
7. 最大結(jié)構(gòu)界面的限制是什么?
8. 什么結(jié)構(gòu)界面是必需的——通常 1 到 4 附件點(diǎn)?
9. 什么是所需的態(tài)度——即著陸。,右側(cè);顛倒,鼻子和鼻子或 ?
10. 你設(shè)想充填回收系統(tǒng)在哪里?為的例子中,這可能是內(nèi)部模具行或以下在外部皮膚外部某處。
11. 什么卷可以在裝載艙設(shè)想?
12. 降落傘會重用嗎?如果是這樣的話,哪些組件將回收?
13. 你在水面上(多目標(biāo))或污垢(大多數(shù)無人機(jī))?
14. 飛機(jī)飛在雨中嗎?
15. 你希望我們提供裝載容器(我們可以嗎根據(jù)需要提供真空成型或復(fù)合殼)?
16. 你希望有多少用于序列我們處理嗎?
17. 你需要一個“智能”系統(tǒng)部署嗎對高度敏感或速度?
河海大學(xué)文天學(xué)院本科畢業(yè)設(shè)計(jì)（論文）
18. 你需要一個地面(或水)發(fā)布系統(tǒng)?如果是這樣,你要我們提供嗎?
19. 如果要重用會改裝領(lǐng)域或者發(fā)送回到制造商?
20. 這是飛機(jī)“stow-able”滑翔機(jī)的形式——或者是什么它完全永久組裝-什么影響,如果有的話這對回收系統(tǒng)嗎?
21. 很多無人機(jī)傳感器包底部一側(cè)因此,凈成本(機(jī)體損傷和傳感器損害)在降落傘著陸著陸顛倒時顯著降低。這是否適用于您的程序嗎?
22. 請?zhí)峁?3-view CG 的飛機(jī)明顯。
23. 請?zhí)峁┰敿?xì)的飛機(jī)布局和推進(jìn):即。推桿式或拖拉機(jī),飛機(jī),道具,單旋翼帶尾槳或 ?
24. 基于飛機(jī)配置的細(xì)節(jié)積載艙,你必須選擇一個部署方法。你能接受增加的可能性嗎糾纏或其他失敗為了使用更簡單部署方法?
雖然這看起來像很多信息提供回收系統(tǒng)設(shè)計(jì)師,更應(yīng)該發(fā)展的飛機(jī)設(shè)計(jì),即毛重和期望的速度后裔,飛行包線和允許沖擊荷載等。
5l
河海大學(xué)文天學(xué)院本科畢業(yè)設(shè)計(jì)（論文）
60
附錄二：
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 ? 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 ? ρ V2 and is expressed in lb./ft.2 or PSF. q =? ρ V2 B -
Steady-State Drag
The steady-state drag (equal to the weight) is derived from: D = ? 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)] ? 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 = ? 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 * (?) ? = Vl * 0.707
Conversely, if you were to double the canopy loading, the ROD will be:
V2 = Vl * (2) ? = 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
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