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无人机能做到多小?

译自:陆军技术网
作者: Richard B Gasparre, Consultant,
编译:全球防务(知远/朝阳门)

        当一项新技术刚刚得到应用,与之相关的名词和术语也会流行起来,而且通常会一直流传下去。在无人机的世界里,技术的进步会使得当前的技术变得十分不完善,如果没有到完全淘汰的地步的话。
对于当前来说,这也许是个语义上的问题,但是外表尺寸和机械特性的变化会引发重要的整体功能上的变化。

美国空军的黄蜂无人机
假设无人机属于飞机的定义范畴,让我们使用美国空军无人机分类方法作为基线。美国空军系统分为四层,高度最低的一层是建议名称为N/A层,小型无人机的独特性质正是该层区别于第一层的主要标志。
目前N/A层的飞机原型是由Aerovironmen公司建造的战场空中战术微型航空器(Wasp block 3型)系统。像大多数小飞机一样,黄蜂无人机通过固定的翅膀获得上升力,并通过螺旋桨获得推动力,螺旋桨的动力来自一个10w的电动马达。
        三种黄蜂模型的最快速度都是大约40mph,最大高度范围大约三英里,续航能力大约1个小时。但是看一看黄蜂尺寸大小的发展:
        Block 1: 长5英寸,宽13英寸,0.4磅
        Block 2:长6英寸,宽16英寸,0.6磅
        Block 3:长15英寸,宽29英寸,0.9磅
        尺寸与重量成正比,但是黄蜂无人机最有用的特性是单兵可以用手发射它。相比之下,第一层的小飞机重量为500磅,因此在目前1磅的黄蜂无人机与上一层的发射上限之间还有很大的空间。毕竟,奥运会铅球比赛的铅球重量才16磅。

美国陆军的乌鸦无人机
        陆军定义的最低飞行高度层是第一层,这正是是备受赞誉的RQ-11乌鸦无人机的飞行高度,它也是由Aerovironment公司建造。和蜂鸟无人机一样,乌鸦无人机也有标准的固定机翼,一个螺旋桨和一个电动马达。
        “乌鸦无人机的附加功能确实需要比蜂鸟无人机更大的尺寸”
        然而,与蜂鸟无人机不同的是,乌鸦无人机的最快速度比蜂鸟快50%,大约60mph,高度范围是蜂鸟的2倍,大约6英里(具备翻越山地的能力),并且具有接近两倍于蜂鸟的续航时间90分钟,并且通过可控制的高度可以获得更长的续航时间。这么大的差异并不存在于任何其他的标准航空部队中,例如战斗机和运输机。
        乌鸦无人机的这些附加功能确实需要比蜂鸟无人机更大的尺寸。乌鸦无人机B模型的长度为3.5英尺,翼展4.25英尺,重量为4.21磅。相对而言,翼展在这三位中是最小的,但是即便如此,乌鸦无人机的翼展几乎是蜂鸟无人机的两倍。
       
让我们变得更小       
        很明显,陆军的第一类和空军的N/A层在结构设计上十分相似。考虑到螺旋桨驱动的固定机翼飞机是在一个世纪前的技术,这似乎是一个需要跨越的障碍。然而,喷气式飞机,如变几何压气机特性的F14和推力矢量控制的Harrier,对空气结构学设计的可行方案的启发要相比机场滑行道停的那些飞机所能提供的建议要更多。
        实际上,小型无人机技术是一个跨越工程领域的技术,从传统的航空工程到仿生工程。标准的航空技术,例如固定机翼和螺旋桨推进,并没有有效地将微型无人机变得比蜂鸟无人机更小。相反,研究人员正在使用自然生物学的设计,例如,在一个结构组件包中,利用拍动的翅膀提供上升力,推力,以及稳定性。
        实验室中更先进的微型无人机的尺寸真的和昆虫差不多了。在法国的国家航空实验室,Remanta项目有一项自定义的设计约束,15厘米的翼展,即接近6英尺。这么小的尺寸不仅是蜂鸟block 3无人机的五分之一,而且也比蝙蝠的最小翼展小1厘米。
        到底能小到什么程度?在哈佛大学微性机器人实验室,实验室的创建人、主管罗伯特.伍德正在开发一种飞行机器人,目前这种机器人的重量刚刚超过2盎司,翼展才1英寸多一些。重量和尺寸分别是蜂鸟无人机的七分之一和二十五分之一,但是,更重要的是,这样的尺寸就是你房间里飞舞的苍蝇的大小。
        “一种飞行机器人正在研发中,目前重量仅有2盎司多,翼展才刚刚一英寸多。”
        在这种体型尺寸下达到真正航空仿生学的目标预示着在许多方面有着可行的应用前景。特别需要指出的是,小型化也就是隐形,而隐形并不仅仅是小型化。能够像鸟,蝙蝠或者昆虫一样飞行使得无人机具备了自然的伪装能力,即使敌军看见了它,也可能误以为是一只动物。
        那么,军事机构应该怎样定义小型无人机呢?如果军事上的分类目标是抓住功能上的区别,那么单纯的第一类或者N/A层很明显是不够的。关键的问题是要分多少级,一些生物学的原则对这个问题可能有些帮助。然而,如果可见性是关键的因素,那么首要的是要区分传统的无人机和现在的新型仿生无人机家族。
        在后者中,由于设计的自然特征不一,简单的方法也许应该关注士兵是否能一眼识别出无人机。因此,从N/A层,也就是第0层,开始往后数,结果是:
        -1层:在飞行时能够被发现
        -2层:在飞行时无法察觉,但是静止在一个相对小的空间,例如起居室时,可以被发现,Remanta的产品应该属于此类。
        -3层:在静止时无法察觉,但是能够通过手臂的长度,或者通过触摸和仔细检查发现。伍德教授的机器人应该属于此类;
        -4层:只能通过类似犯罪现场鉴证科的机构进行的检查发现。
        如果没有什么别的,空军应该重新命名“小昆虫”,而陆军应该重新命名“小黄蜂”。比喻性的名字在十年前已经被接受了,但是现在微型无人机真的和小昆虫和黄蜂一样大小的时候,它们不再有意义了,而只是虚假广告。
HERE I STAND!

Size Matters – Small is Sexy in the UAV Microcosm
BY:Richard B Gasparre, Consultant,
Richard B Gasparre discovers just how small a UAV can get.
When a new technology takes off, associated terms and names proliferate as well, usually with only a passing nod at overall consistency. In the UAV world, technological advances promise to make current categories seriously incomplete if not altogether obsolete.
"Like most small planes, the Wasp gets lift from fixed wings and thrust from a propeller."
This may be a semantic problem for now, but changes in physical scale and mechanical characteristics will have major functional consequences down the line.
THE USAF'S WASP
Given that UAVs are by definition flying vehicles, let's use as a baseline the UAV taxonomy of the US Air Force. The USAF system has four tiers, and the lowest-altitude layer is the suggestively named tier N/A, which was carved out of tier 1 in prospective recognition of the unique qualities of mini-UAVs.
The current archetype of the tier N/A vehicle is the BATMAV (Wasp block 3) system, built by Aerovironment. Like most small planes, the Wasp gets lift from fixed wings and thrust from a propeller, which is powered by a 10W electric motor.
All three Wasp models have top speeds of about 40mph, outright ranges of around three miles, and endurance of almost an hour. But look at the Wasp's size evolution:
•        Block 1: 5in long, 13in span, 0.4lb
•        Block 2: 6in long, 16in span, 0.6lb
•        Block 3: 15in long, 29in span, 0.9lb
Size is directly proportional to payload here, but one of the Wasp's most useful attributes is that individual soldiers can launch it by hand. In contrast, the tier 1 Gnat is 500lbs, which leaves a lot of room between the current 1lb Wasp and the upper limits of throw launching. After all, even Olympic shot-putters toss only 16lb weights.
THE ARMY'S RAVEN
The lowest-altitude layer in the Army's taxonomy is class 1, the home of the highly praised RQ-11 Raven UAV, which is also built by Aerovironment. Like the Wasp, the Raven has standard fixed wings, a propeller, and an electric motor.
"The extra capability of the Raven's does require some extra size compared to the Wasp."
Unlike the Wasp, however, the Raven has a top speed that is 50% faster at around 60mph, twice the range at just over six miles (including 'over-the-hill capability), and up to double the endurance at 90 minutes, not to mention an operational altitude and ceiling an order of magnitude greater. An intraclass disparity this large doesn't exist in any standard military aviation category, such as fighter or cargo aircraft.
The Raven's extra capability does require some extra size compared to the Wasp. The B model has a length of 3.5ft, a wingspan of 4.25ft, and weighs 4.2lb. Relatively speaking, wingspan is the smallest of these dimensions, but even so, the Raven is almost double the width of the Wasp.
LET'S GET SMALL
Clearly, the Army's class 1 and the Air Force's tier N/A are most similar in structural design. This may sound like a low hurdle to jump given that prop-driven fixed-wing airplanes are a century old. Nevertheless, jets such as the variable-geometry F-14 and the vectored-thrust Harrier suggest that structural aviation design possibilities are much broader than the line-up at your local airport taxiway would indicate.
In fact, miniature UAV technology has crossed the engineering threshold from traditional aeronautics to biomimicry. Standard aviation technology, such as fixed wings and rotorised propulsion, does not scale down effectively for micro-UAVs smaller than the Wasp. Instead, researchers are using natural biological designs, such as flapping wings, to provide lift, thrust, and stability in one structural package.
The more prominent micro-UAVs emerging from labs are indeed the size of insects. At Onera, France's national aerospace lab, the Remanta programme has a self-imposed design constraint of a 15cm wingspan, which is just under 6in. This is not only a fifth of the block 3 Wasp's wingspan, but 1cm less than the smallest wingspan in Chiroptera, the bat order.
How small can small get? At Harvard University's Microrobotics Laboratory, founder and director Robert Wood is developing a robotic fly that currently weighs just over 2oz and has a wingspan of just over 1in. These dimensions are one-seventh and one-twenty-fifth those of the Wasp, but more critically, they are the measurements of your average housefly.
"A robotic fly is in development that currently weighs just over 2oz and has a wingspan of just over 1in."
Achieving true aerial autonomy at this physical scale would have major implications for operational use in many respects. In particular, small is stealthy, but stealthy is more than just small. The ability to fly like a bird, bat, or insect gives a UAV a form of natural camouflage – even if hostile troops see it, they may well misinterpret it as an animal.
So how should the military services characterise small UAVs? If the goal of military taxonomy is to capture functional differences, a single class 1 or tier N/A is clearly inadequate. The key question is the number of levels to create, and several organising principles are possible for this purpose. If visibility is a critical consideration, however, the first distinction should separate traditional aeronautical UAVs from the new biomimetic family.
Within the latter, given the proliferation of design features in nature, a simple scheme might focus on the ability of soldiers to recognise a UAV as such at a glance. Therefore, counting backwards from tier N/A, which is really tier 0, would yield the following:
•        Tier -1: recognisable when in flight
•        Tier -2: indistinguishable in flight, but recognisable at rest in a relatively small space, such as a living room – the Remanta products would probably fall into this range
•        Tier -3: indistinguishable at rest, but recognisable at arm's length, or by touch and inspection – Professor Wood's fly would fall into this category
•        Tier -4: recognisable only through inspection by CSI teams or their equivalents
If nothing else, the Air Force should rename the Gnat and the Army should rename the Wasp. Metaphoric names might have been acceptable a decade ago, but they amount to no more than false advertising when micro-UAVs really are as small as genuine gnats and wasps.
HERE I STAND!

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谢谢你的帖子。

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http://www.proxdynamics.com/products/pd_100_prs/

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