Aerodynamic trunk. Drawing, description

PERSONAL TRANSPORT: GROUND, WATER, AIR
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Aerodynamic trunk. Personal transport

Personal transport: land, water, air

Directory / Personal transport: land, water, air

To begin with, I suggest that readers-motorists conduct a small experiment. Once again leaving the city, stop on a high-speed section of the highway and watch the cars rush past you. However, here you need not to observe, but rather to listen. In a quarter of an hour you will learn to distinguish by ear the main brands of passenger cars: in the sound portrait, the main role is played by the characteristic noise of the stream flowing around the body. But then a car with a roof rack approaches - and the sound picture changes dramatically. It seems that the car literally squeezes through a dense, unyielding environment. By the way, this impression is also confirmed by experiments in wind tunnels. Purge models and full-size cars with roof racks have shown that the so-called Cx - drag coefficient increases dramatically. But it directly affects both the speed of movement and fuel consumption.

It is especially disappointing to install a lattice trunk - this kind of air brake - on such cars as the VAZ-2108, Tavria or the new Moskvich, which have a significantly lower Cx than the cars of the previous generation (for the VAZ-2108 it is 0,38 against 0,47 for the VAZ-2106), and resulting in reduced fuel consumption.

Meanwhile, a car with a closed trunk of a streamlined "aerodynamic" shape would not have much more fuel consumption than a car without a trunk. In addition, such a container will allow you to transport things in any weather.

Making such a trunk is not too difficult. First you need to mold the bottom of the container from fiberglass and epoxy resin, which is a cast from the roof of your car. To do this, a plastic film is stretched over the surface of the body. You just need to make sure that it does not have punctures or tears (otherwise you can ruin the paintwork). The film is seized with adhesive tape, and several layers of fiberglass impregnated with a binder - epoxy resin mixed with a hardener (ratio: 8 volume parts of resin per 1 part of hardener) are laid out on top of the polyethylene. Then everything is covered with another layer of film, which is pressed in one way or another over the entire surface of the pasting. The easiest way to do this is by placing plastic bags half-filled with river sand on the roof. After the binder has cured, the adhesive is cut off along the roof contour; its thickness should be 4 ... 5 mm.

Then, the frame of the future trunk is assembled from duralumin pipes Ø 22 mm. When bending pipes, it is recommended to use patterns made of cardboard or thin plywood that follow the corresponding contours of the roof - this will guarantee that the frame matches its contours. Pipes are joined using duralumin scarves and rivets or screws with nuts.

Rice. 1. "Aerodynamic" trunk and its main elements (in relation to the VAZ-2108) (click to enlarge): 1 - frame (duralumin pipes), 2 - deflector, 3 - deflector bracket, 4 - trunk shell, 5 - hatch

Aerodynamic roof rack
Rice. 2. Trunk frame: 1 - longitudinal lower elements, 2 - longitudinal upper elements, 3 - scarves, 4 - cross member, 5 - rear base cross member, 6 - base front cross member

Aerodynamic roof rack
Rice. 3. Preparing the frame for gluing the body shell: 1 - wire, 2 - frame, 3 - polyethylene film

After assembling the frame and making sure it fits the roof of your car, tightly wrap it with plastic wrap (you can also secure it with tape) from the outside of the frame. Then the frame is turned "upside down" and suspended from the ceiling of the workshop - preferably on a thin steel wire, as shown in our drawings. After that, glass mat impregnated with epoxy resin is laid out on polyethylene. The thickness of the gluing should be 3...4 mm. To obtain a smooth surface of double curvature, a polyethylene film is laid over the matting, on which a layer of river sand is poured. This must be done carefully, all the time observing the nature of the resulting surface. I must say that the curvature of the shape of the shell will depend on the thickness of the sand layer in a given place, therefore, in the process of curing the resin (it takes 2 ... 3 hours), you can make adjustments to the shape of the trunk body by adding or removing sand from one area or another. If a local, rather sharp bending of the surface is required, a long plastic bag filled with sand or an ordinary stocking is superimposed on the area of interest to you. After the resin has cured, the polyethylene is easily removed and the shell is glued on top with a layer of fiberglass.

Access to the trunk is through hatches in its side surfaces. Manhole covers are reinforced with foam plastic and two layers of fiberglass sidewalls of the shell. Please note that you should first glue the sidewalls from the inside with foam strips 10 ... 15 mm thick, then with two layers of fiberglass, and after the resin has cured, cut the hatches along the intended contour - this can be done with a fine-toothed circular saw or, better, with a hacksaw blade.

The covers can be hinged, but it is better to make them removable. It is best to fix them with furniture locks that have a cylindrical retractable tongue and an "English" key.

Docking of the trunk body with the bottom is made using strips of fiberglass and epoxy resin.

At the break of the roof of the trunk, it is desirable to install a deflector - a wing-shaped aerodynamic surface designed to improve the flow around the rear of the car. The deflector itself can be glued from epoxy resin and fiberglass or bent from 1,5 mm thick duralumin sheet.

The final surface finish includes sanding, puttying the surface with an epoxy and talc-based composition, finishing sanding and painting the trunk in several layers with intermediate surface grinding.

According to the magazine "Popular Mikenix" (USA)

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