STREAMLINING

Evening Post, Volume CXVII, Issue 76, 31 March 1934, Page 20

STREAMLINING

NATURE EXPLAINED

AIR, ROAD, AND RAIL

The following article, with the illustrating block,' is -..fronr a recent number of "Science and Invention".—

Today all -vehicles oi tianspoitation aie changing m appeaiance Aeioplanes, divested of external biacing, look like flj ing wings, fast trains, take on the appearance of airships on -wheels, and motor ears show tho first signs of true streamline' form.

Aast lcsults will accrue fiom these changes m Iho economy and. bpeed tianspoitation, and in some ic«pects in the comfort of travel. The reasons for these jmpio\ements aic not peihips a--clciily undcistood as they might be The an which all lehicles pass tlnough is all rervadmg, but it is. mjs terious because, invisible. Its lawa of ilow and iesistan.ee aic difficult to gii^p, although leseiich into sucli Itwdites back to tho fifteenth centiH> ■\\hen Leoniido da, Vinci tned to build i holicoptei and to explain the flight of birds on mechanical pniuiples Ihc greatest impetus to the study of aciodvnamic^ gi\en bj man's attempts to build the aeroplane. Theie lnis been d uipid de\elopmcnt ot e\pennient«il aerodynamics, Avith .the- employment of laige -wind tunnels In such wind tun nelh a huge piopcllei fan chau^, au rapidly, through: a'channel or waistlikc Mi ipe, while delicate balances mea->uie the foiees experienced bj vauous bodies, and indicate how thej uia\ be stieamlinecl.

The maiii effect of this intensive study of streamlining has been on the acioplane itself The eailj nncliines

had many exposed stints and wiies and wings and bodies of poor shape. Today we have transport machines with speeds of 2QO miles an hour or more, with ictracted landing gears, beautitullyshaped wings, and| streamline fuselages, or, bodies.

Perhaps the best,way to grasp tho significance, of stieamlining is by leferenee to the two sketches of a flat plate and of an aiiship form placed in the path of the- wind. Bound these bodies have been tiaeed tho lines of flow. The air objects to all violent deviations, of'its path. In the case of the flat plate, the air refuses to tuin tl.o sharp corncis, and fails to close up smoothly behind the obstruction. A-> n lcsult, -violent eddies oi whiils,l"miniature'cyclones,-" are formed behind the plate. '

If, instead ot ha-ving a wind flow aiound motionless bodies-.—as in the wind tunnel tests—we visualise thu bodies as being in motion thiough tho -air, these eddies become most significant. For they represent vacua, and these vacua set up a suction which pulls the body back while its -power seeks to .drive it forward. A great loss in motive power results.

With the streamlined or airship form, with,nicely lounded bow and long, delicately tapering stern, the flow is perfectly smooth, and tho air, free from all violent.' deviations; follows the contour closely.

It is not an accident that we have drawn the stieamlincd form so that its cross-section is sixteen times tho area of the plate. It is because the tiny plate has the same lesistaneo as> the relatively huge streamlined" form.' If we consider a conventional motorcar, we may determine that it is subject to the same violent eddies and whirls, and hence offeis a leaistancc but little less in pioportion to projected aieti than a flat plate. In tho history ot"invention and engineering- it is a well-known fact that progress comes most rapidly when thoic is an intermingling of vaiious blanches of engineering. The stupendous effects of streamlining on the speed of the aeroplane did not fail to strike engineers and inventors in other fields and notably those concerned with the motorcm. Why did they fail to take ad\antagc of such effects?

The leasons aie not f.ir to seek. The tractive or rolling resistance of' the motoi-car is practically independent of the speed, and the hor^o-poHt'i i-, fhcic foie piopoitional to the bpecd. On the other liand, the ail lcsistanec vauos as the square of the speed and ilie lioisepower as the cube of the speed. At slow speeds it is tho tiacthe 01 1 oiling 'horse-power that is impoitant, tho \\oik done in overcoming air resistance is negligible. But as speeds! iin.ie.i-,0 the s,toi> chfinges. Perhaps the following figures will illustiate the state ot aftsiiis best. At twenty miles an houi, the hoiso-powoi of the conventional motor-c.Tr needed to ovcicomc ah icsistance repicsents only 25 per cent, of the total .hoiso-power expended; at 40 miles it has mounted to 61 per cent; at 60 miles it amounts to 77 per cent of the total.

At 60 miles an hour, stiange as it may seem, much more of iho.fuel is being used to overcome the ccidies and whirls of the air than to meet gnVml friction. Thus, air resistance makes motoring more expensive on the one haml, ancl impedes the attainment of high speeds, on the other, while vibration and discomfort result from a car being, buffeted by winds.