Fig. 1: Above, a slight push by Dad duringa test run sends the air car slowly alongthe driveway. Close up photo at rightshows air car tilted to direct it to the right

GO-CATDo-lt-YourselfAir Car

By GERALD W. CRISMAN

FOR $20 and an old lawn mower engine youcan build this pint-size air car and makeyour youngster the happiest kid in the

block. And, he'll think you, Dad, are thebestest do-it-yourselfer what is."What's more, both you and your youngster

DECEMBER, 1962

will benefit from the knowledge gained in thedesign and theory of operation of this promis-ing new mode of transportation.

When selecting the lawn mower engine besure you get one of the vertical shaft, light-weight aluminum jobs used on a rotary-typelawn mower. Cast-iron engines are too heavyfor air car use. It should have a rating of atleast 2-1/2 hp and a 3-1/2 hp engine will give you

43

even better performance.Start Construction With the Box Frame

(Fig. 2A). After cutting the 4 x 4 ft. top piecefrom 1/4-in. plywood, locate the exact centerby drawing diagonal lines from corner tocorner and scribe a 19-1/4-in. circle. If you donot have a portable electric jigsaw to cut outthe circle, a keyhole saw will do the job. Thenfasten the 3/4 x 1-in. cleats to what will be theunderside of the top with glue and #6 x 1-in.

fh screws. Note that the cleats are set back1/4 in. from the edges of the plywood top sothat the 1/4-in. plywood sides will be flush withthe top. When cutting the side pieces, maketwo of them 48-in. long and two of them 47-1/2-in long. Since the 1/4-in. plywood is very diffi-cult to fasten securely at the corners, rip sawsome 1-in. triangular cleats 3-in. long and in-stall at each corner of the box frame with glue

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DECEMBER, 1962 45

44 SCIENCE and MECHANICS

Go Cat • • • • (Continued from page 45)

and 3/4-in. nails.The Pilot's Seat and seat frame was made of

1/8 x 1 x 1-in. aluminum as detailed in Fig.2D, to keep the overall weight of the air caras light as possible. If aluminum angle is notavailable in your town, 3/4 x 1-3/4-in. clearlumber glue and bolted together could beused instead. Before making the seat frame,check the 15-in. height of the seat to makecertain it will clear the engine you will beusing.

Make the seat of 1/4-in. plywood as shownin Fig. 3C, and fasten to the uprights of theseat frames so that it is held securely in placeyet easily removable to work on the engine.

Make the Prop Guard (Fig. 3D) next. Yourlocal sheetmetal shop will have the sheetsteel for this. Bend the 2 x 61-in. strip aroundthe 19-1/4-in. hole in the frame top and markthe overlapped ends for riveting together. Theclips for anchoring the prop guard to the topcan be made from scrap pieces of 16 ga. sheet-metal.

The Fan or Prop is made of .090-in. thick2024 aluminum plate tempered to T3 specifi-cations. You can make it yourself as detailedin Fig. 3B or, you can purchase a completedprop balanced and tempered to T3 specs, for$10 (see Materials List). The method ofmounting the prop on the engine shaft willvary depending upon the type, make and sizeof engine you use.

If you intend to make the prop yourself,first draw a full-size pattern of the prop onheavy paper and use as a template for mark-ing and cutting the hubs and blades. The51-1/20 on the segment end of the blades isslightly oversize. After sawing the hubs andblades to size, file and fit the segment ends ofeach blade so that the seven blades fit to-gether snugly. Then layout the 3/16-in. drilledhole locations and assemble and clamp thehubs and blades together. A bolt with largewashers through the hub shaft holes andseveral C-clamps will hold the assembly to-gether. Drill the 3/16-in. holes through thethree thicknesses of aluminum at one time.Insert the 10-32 machine screws, which willmake a snug fit with the 3/16-in. holes as theyshould. Also, be sure to number or mark thelocation of each blade in respect to its posi-tion on the hubs so that the prop can be takenapart to bend the pitch angle in the blades andthen reassembled exactly as originally fitted.

When bending the pitch in the blades, gripthe segment end of the blade in a vise as inFig. 3A and clamp boards on each side of theblade portion. This will put the 26° twist rightat the narrow or "necked" part of the blade.When reassembling the prop, be sure to useslotted nuts and drill the machine screws forcotterpins so there is no chance of the nuts

vibrating loose.The Engine Mount consists of two lengths

of 1/8 x 1 x 1-in. angle irons bolted to theunderside of the circular engine flange. Usetwo of the original engine mounting holes foreach angle iron. The exact height of the 1-1/8thick wooden blocks (Fig. 3C) will have to bedetermined from the engine you are using.Position the engine so that the prop is cen-tered in the 19-1/4-in. hole in the box frameand temporarily block up the angle iron en-gine mounts until the prop is centered verti-cally in the 2-in. height of the prop guard(Fig. 3C). Then measure the height of thel-1/8-in. wooden blocks needed and cut blocksto size. Two wooden blocks, one on each sideof the 19-1/4 in. hole, will be required. Use%-in. bolts to fasten angle irons and blocksto top of box frame.

The Anti-Torque Vanes (Fig. 2B) tend toprevent the blast of air from whirling in thedirection of the prop rotation and thus stabil-ize the air car. Make the vanes as in Fig3A from 1/16-in, thick aluminum or 1/4-in. ply-wood and fasten to the underside of the boxframe top as in Fig. 3A.

The Flexible Skirt around the bottom of thebox frame (Fig. 3) is an optional attachment.Its purpose is to increase the altitude or liftof the air car and provide flexible box sidesthat will deflect and thus allow the car toclear low obstacles in the path of travel.

Make the skirt 16-1/2-ft. long from strips ofcanvas, 6-in. wide. Double sew a 1-in. hemcontaining a length of plastic clotheslinealong the bottom edge, and fasten the otheredge to the inside bottom edge of the boxframe with glue and staples as in Fig. 3B.Hand sew the ends of the skirt where theyjoin, to prevent air from leaking out. Thentighten the clothesline until the canvas puck-ers from the inward pull.

As a safety measure, to prevent youngstersfrom putting their feet near the engine orprop, surround the seat frame with 1/2-in. wirehardware cloth screening as in Fig. 3C. Bendthe screening where it meets the box top andfasten with 1/8-in. bolts with large washers.Bring the screening up as high as possiblewithout interfering with use of the rope en-gine starter.

For a test run, place the air car on a pavedsurface such as a driveway or large parkinglot. Have your youngster on the seat with hislegs crossed under one another and handsgripping opposite sides of the seat. Start theengine and set the throttle to maintain analtitude of about 1/2-in. above the bottom ofthe skirt. Then gently push the car forward asin Fig. 1. Your youngster will soon learn tocontrol the direction of travel by simply lean-ing his body to tilt the car in the direction inwhich he wishes to go.

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