Streamlining or fairing is defined as ways and means of reducing parasite resistance of parts exposed to the flow of air. This reduction will naturally be affected by having the molecules of the air passing the object without their relative positions, without creating turbulency. This smooth flow of air may be

accomplished by shaping the whole unit for minimum resistance, by adding material to form the best shape, by adding guide vanes, by reducing interference between parts, by concealing or retracting the unit

within the structure without lowering the safety factor of

the airplane. For the sake of simplicity, the air flow is assumed to be twodimensional, though it is always three - dimensional. It may be undisturbed (laminary) or disturbed (turbulent) depending on the object and speed. Fig. 1 shows the air passing a sphere, a streamline body and an airfoil. By closer investigation it is noticed that for a certain distance (Fig. 2) the air clings to the surface of the airfoil; this layer of still air, about 1/1000 of

an inch thick

at average

speed, is called the boundary

layer; at a point (the transition point) it breaks away from the surface and becomes turbulent. Both airflows, the laminary and the turbulent, are a function of size and speed. The surface texture will affect the resistance only if the grain of the finish is larger than the thickness of the boundary layer. The diagram in Fig. 3 shows that at low speed the resistance is the same, but that at high speed the difference is so great that only a high polished surface will give satisfactory results. From this may be deducted that all entering sections (nose)

8

of an aerodynamic unit shall be made as smooth as possible so as to have the turbulency delayed as far as practical, for the closer the transition point is to the trailing edge, the lower

will be the drag. Turbulency may be decreased or increased by placing two objects close to each other by the effect called "interference". Two wires or cables placed one after

another reduce the total resistance; filling the space (Fig. 4) with a wood strip, the resistance

is reduced to one-third of the resistance of a single wire. The

wing-fuselage interference may be explained by the interference of the effective air flows; a small fillet will reduce the created turbulency. The interference of the lift strut is kept low by hav-

tubing. Fig. 7 shows a theoretical double fairing and a practical, single fairing with an outline formed by circular arcs. Fig. 8 shows the streamlining of a strut at the point of attachment and the correct slope of a windshield of a cabin. Fig. 9 shows the streamlining of the carburetor air intake especially important on high speed airplanes. Streamlining of large

engines is not such a grave problem when the thickness of the wing is nearly the same (Fig. 9) as the diameter of the engine. Another method to reduce the resistance is to conceal the unit within the structure; placing the landing lights (Fig. 10) inside the wing; confining the loop antenna within the fuselage; designing "pancake" engines to

ing the width of the strut smaller than the distance to the surface of the wing; very often a braced narrow strut, a jury strut

fit inside the wing; and eliminating all outside supporting ele-

must be used to conform to this design; the same basic idea is

Retracting is necessary with the landing gear, tail skid control surfaces or part of the wing in order to eliminate such resistances. The retraction of a

employed in the construction of a cantilever landing gear shown in Fig. 5.

Fig. 6 shows the general outlines of a streamline body, of a strut and of an airfoil. The airfoil is of interest, for the distance over the upper surface is nearly the same as past the lower surface. Thus both airstreams will meet at the same instant causing a minimum of turbulency. Different drag values are obtained for open air tests and wind tunnel tests having the same relative air speed. This phenomenon is explained by the different drag values of the laminary and of the turbulent flow, for the wind tunnel has always a certain turbulent flow. The difference will be nearly 30% if the medium is water. Streamline struts are not always obtainable. In that case, fairing a round tube with balsa wood (or sheet metal) will be an effective substitute. Good streamlining reduces the resistance to 1/20 of the unfaired

ments by making the airplane

a cantilever construction.

will be parallel with the body; the area of the frontal and rear opening of a size to give an airflow equal to the outside airflow and sufficiently large to cool the engne. The three main designs are indicated in Fig. 12.

The minimum drag of a submerged radiator will be about five percent of power output, which is low compared with the 25% of a radial engine.

Radial aircooled engines are streamlined according to their number of cylinders. Engines having few cylinders may use individual cowls; for engines

with more than five cylinders a cowling ring will give lower resistance than any other design. For cutting down only resistance without improving the cooling of cylinders a narrow

cowl ring, a Townsend ring may be used. To reduce the drag of an engine to a minimum and to get the most efficient cooling, especially with twin-row engines, NACA cowling must be

used, designed to let the air pass only between the fins of the cylinders. Figs. 13, 14 and 15 show

landing gear must be complete,

sketches of cowlings.

for a 50% projected wheel (Fig. 11) at a certain point of the wing has a higher drsg than the whole cantilever landing gear for a low-wing airplane. A very interesting method of reducing resistance is the adding

shows a cowl with hammered

of vanes to guide the airflow, to confine the turbulent air within the structure and to conduct the air smoothly to the outside. The influence of vanes on the resistance of a body is shown in Fig. 11, giving the drag coefficient for each case. Streamlining radiators lately has become a very interesting problem, for liqu ; d cooled engines have shown good performances. Enclosing an open radiator into a streamline casing will reduce the drag by 50 % of its original value. Further improvement would be to place the radiator closa to a body and then

streamline it. A final improvement would be to submerge the radiator so that the outside cowl

Fig. 15

bulges for the rocker boxes and its diameter smaller than the diameter of the engine. It usually gives higher drag than a smooth cowl of larger diameter; sloping the protrusions into the slipstream of the propeller will improve the resistance. One streamline problem that stumped scientists and has been clearly e v a d e d is nature's streamlining. The well-known toroidal pocket left around a pole and the settling of snow on a car during a snowdrift does not conform to the expectations. There is a space between the snowbank and the unit that has snowflakes circulating in a whirl as shown in Fig. 16. This phenomenon was found on ice deposit on streamline wires. (Fig. 17) Therefore the ice formation on wings will show the circular gap or gaps as indicated in the sketches.

The first volume of our Amateur Builder's Manual has brought forth many compliments from the members. We think you'd enjoy hearing some of them, so here are a few: "I have just received my copy of the Amateur Builder's Manual and I think it's great! Many thanks to all of you at Headquarters for your fine work in preparing the manual. I sure am looking forward to the next one."

William J. Osniak, Everson, Pa.

"The 1957 Directory and the first volume of the Builder's Manual are really good. I think you will find many of those who just subscribe to the magazine now becoming members when the word gets around about these publications which come free to members."

George Sager, Williamsburg, Va., "Received the Manual and want to say it is great - terrific and what's more, it's a "cool jewel"!

Ed Huss,

Denver, Colo. "I just received my copy of the new ABM and I think it's sensational! A publication of this type really f i l l s the bill, and if it goes as planned, it should prove a real boon to anyone interested in build-

ing an airplane."

Tom Henebry,

Chula Vista, Calif. "Just a line to add my congratulations and sincerest thanks to those I know you and your staff will receive for having done so fine a job on the Amateur Builder's Manual. I might add that the same applies to your publication The EXPERIMENTER, which in my opinion improves each month." Robert Davenport, Middlesex, N. J. "I believe that the new Manual for homebuilders is one of the best things that the organization has come up with yet." Jim Eaton Rangner, Tex. "I just received the first volume of Amateur Builder's Manual and I went through it without stopping. My congratulations it is wonderful. or let me say 'It is wonder-useful '.!' The material and the artwork, the reproductions - everything is perfect." Ladislao Pazmany, San Diego, Calif. In addition the Canadian Owners and Pilots Association, Ottawa, Ontario, has advertised the Manual in their newsletter and has agreed to act as agent for sale of the manual in Canada to its members who are not in EAA. The second 1957 volume of the Manual is now in preparation and should be ready for mailing within about six weeks. Some of the items featured in this volume include several drawings of the new EAA biplane, a modernized version of the Gere Sport of 1930; part II of Guide to Airworthiness for the Homebuilder; specifications and drawings of the Franklin 50 and 90 hp engines; three-view skeleton drawings of a modern two-place aircraft; typical light plane engine mounts, and many other helpful and valuable items of use to the homebuilder. The Amateur Builder's Manual is published quarterly and is free to members as a part of their membership in EAA. Non-members may purchase copies for $1.25 each.

This scheme may be applied to the streamlining of struts or wheels as shown in Fig. 18 and may be called "controlled turbulency".

Nature's streamlining was used in 1927 by one pilot in imroving his racer. During a heavy downpour he flew his machine and noted where the rain water collected; there he placed balsa wood fillets and

niturally had the fastest machine of that make. All streamlining is done in

order ance often that

to improve the performof an airplane, and it is (but wrongly) mentioned the only improvements made during 20 years was streamlining the Wright brother's machine. With utmost streamlining the final outcome will be an allwing airplane consisting of one airfoil, landing gear retracted, engine concealed and every space within utilized for payload. 9