ACCORDING TO THE RULES. Twenty years ago there was an extensive debate: to allow or deny self-made cars? The idea of their buildings were resistant opponents. The latter believed that “homebrew” is driven by the mere desire to get the lowest cost vehicle. Argued that such transport is made in the handicraft way, appearance is far from perfect and will not decorate the streets. But, more importantly, it can even be dangerous, as an Amateur production does not meet the requirements of industrial technology. In addition, skeptics have suggested that the need to use scarce parts can push fans to bypass the distribution network and other abuse.
As you know, the discussion was won by the Pro-Amateur autostructure. The state automobile Inspectorate of MIA of the USSR approved the “Technical requirements for improvised small-displacement cars and sidecars”. As stated in the preamble of the claims of GAI, they “are intended to regulate and stimulate independent creativity in the design of cars, especially among young people, direct them to create original, useful and competent structures.”
Since the construction of many hundreds, and maybe thousands of home-made cars, which have fully confirmed its right to exist. Neither one of them did not happen any serious accident, is not registered and abuse. The form and the purity of execution other “handmade” compete with many factory models, pictures of them bypassed the world press. It is interesting to note that among the designers-lovers and the owners of production cars. This once again confirms the creative, not the “consumer” nature of the Amateur autostructure.
However, not all designs will be called “a useful and literate.” Too often builders operate according to the method of trial and error, instead use the accumulated other enthusiasts, automotive industry experience to apply proven methods and techniques taking into account design theory and calculation of car.
Of course, lover, it is difficult to compete with a professional designer working in a large team, with modern equipment, in the atmosphere saturated with information on automotive engineering. But why not try to bring, where possible, the method of working the Amateur to the professional level? This is of particular interest.
The goal of such “approximations” and now confronts us.
So, we will design and build the car according to the rules, deviate from them only to the extent which is unavoidable in the activities of autoconstructor-lover.
First of all the question arises: what kind of machine to build? And immediately come into effect three factors: practical need in the future, car, creative ideas for the designer, its “production” capabilities.
Sometimes passion for creative ideas leads away from proper consideration of the practical needs. Many enthusiasts, for example, my dream is to build a floating car (see the “MK” No. 6 and No. 10 in 1974).
Why the amphibian lover! How often he will use all of its features? After all, working amphibious vehicle is a complex, relatively slow moving machine on land, with a sealed body, adjustment of tire pressure for driving on the coastal viscous soil and so on. Amphibian and professionals really mastered half a century later than the land vehicle.
And fans are just beginning! Hundreds of times in a year they will be on the ground to speak ill of the lack of doors on the body or slow-moving machine only a few times and sailed on her fishing. Isn’t it easier to change seats in the boat?
The car must be conceived to meet the basic conditions. However, if the main goal of the design process, then you can make a flying car though! In short, the designer, whether Amateur or professional, first and foremost, must be clear, specific aim, purpose designed machine.
For example, they are clear. You can go to work. Most often, the designer wants to make the machine certainly not similar to any other, or, conversely, certainly reminiscent of some kind of any existing model. Any of them will be right only if his intention, on the one hand, corresponds to the previously identified destination machine, and with another — the third factor — production opportunities.
Usually start with determining the number of seats in the back and set maximum speed (in our case it is limited by the requirements of GAI — 70 km/h).
The number of seats in accordance with the requirements of GAI a maximum of four. Many motorists, that number somehow seems insufficient. Meanwhile, from the statistics it is known that the average vehicle load for individual use does not exceed two persons. So, you can make the car double or triple or build according to the scheme “2 + 2”, that is, with two seats for adults and two for children. This will allow to minimize the length (it should not exceed 3200 mm) and the weight of the car, give the body beautiful proportions to simplify its structure. That is why the Builder needs to carefully weigh what do the load without the extra reserve “just in case”, you must calculate future vehicle.
The choice of the number of seats associated with the determination of the necessary brand of engine as its power per ton of complete (loaded) vehicle weight must be again in accordance with the requirements of GAI in the range of 20-25 HP In the current environment, when the traffic became more intense and allows installation on a homemade car engine with a working volume up to 1000 cm3, the values should be increased to 30-40 HP/ton So specific power does not give the car excessive “playfulness” (if not very technologically advanced performance cars could be unsafe), but provides with proper selection of gear ratios in the transmission are satisfactory acceleration, the ability to overcome the climbs and bad roads, to develop enough speed.
Table 1 roughly shows which engine power is necessary in these conditions for different cars.
If you mean the engine of one of the manufactured motorcycles (except the so-called heavy — Irbit and Kiev factories), it would be a mistake to build a 4-seater car, relatively big and heavy. It is known that engine power is not enough, it will work perenapryazhenie and wear out quickly.
Reasonable based on the destination of the vehicle and the wishes of its owner may facilitate the work of the designer. If machine will be used only in the summer, it is possible to dispense with heating of the body, to carry it open. If the owner and passengers — young people, athletes, you do not have to worry about the special amenities of the entrance to the car and make it a body as the racing cars, open, with no doors or with small cutouts in the sides. If driving a car is always one and the same person, it can be adapted to his body type, the controls and the seat without applying the adjustment mechanism the last, etc.
THE FRONT OR THE BACK!
The choice of the car resembles a math problem with several unknowns. Its solution usually takes place in three steps. First, the designer, guided by the analysis of the advantages and disadvantages of different schemes and your own ideas, stop at one of them. However, he often relies on the power unit of a certain type. Then made a preliminary layout of the future car, the approximate calculation of its performance and the distribution of masses along the axes. On the basis of these works clarifies the selected scheme.
However, car designers believe that in any scheme you can make a good and a bad car. It’s all in the ability to identify the advantages and weaken the disadvantages of the scheme and to bring it into line the class of the machine.
Let’s start with the latter, Every homemade car belongs in accordance with the requirements of GAI to the class of very small, since the working volume of its engine should not exceed 1000 cm3. What is the circuit layout is most suitable for this class? Why do the small cars of the Soviet production — “Zaporozhets” and Serpukhov С3Д have rear engine unlike the rest of our machines, built according to the so-called classical scheme (front engine, drive wheels — rear)?
The story of the formation of the classical scheme, the analysis of all its pros and cons is not included in our plans. It is important to note that the spread in 30-50-ies of very small cars revealed the unsuitability for them of the classical scheme. Passing under the floor of the body of the driveshaft does not allow to lower the floor. As a result of deteriorating the resistance, increases the frontal area of the car. In order to fix the position of the seat was made very low, and this has led to the increase of longitudinal distances between them, lengthening and weighting machines, the deterioration of its maneuverability, high fuel consumption. Can I ask you a question: is all of this is only relevant for a small machine? The fact that a big car, because of its “spaciousness”, the shortcomings of the classical scheme impact weaker. That’s why it fell out of use it on small cars, replaced schemes with the location of the engine directly around the drive axle — front or rear, no propeller shaft beneath the floor of the body. On these diagrams and you should expect an Amateur designer, if he wants to make a compact and fairly comfortable car.
What is the location of the power unit is more profitable — front or rear? Both have advantages and disadvantages.
BRIEF CHARACTERISTICS OF DIFFERENT SCHEMES OF THE LOCATION OF MECHANISMS FOR CARS
It is believed that the front (i.e. front-wheel-drive scheme) is particularly suitable for high-speed vehicles, as it provides the stability on turns and slippery road. Drive wheels at the same time serve as guides. In addition, this scheme goes well with body type “universal”, as far as the door in the back of the body can be made flat floor. The disadvantage of front — wheel drive- the presence of a complex, expensive and relatively fragile joints on the front axles, and also the fact that the clutch wheel with the road is weakened just when it is most needed — during acceleration and movement uphill. In these conditions there is a redistribution of load from the front to the rear wheels. To improve the work of joints, restrict their angle of rotation, and suffers a maneuverability of the car. Despite the flaws, the front-wheel scheme was recently a big spread in connection with the increase in speed.
“Rear-engined” car reverse picture. The design of the drive axle is simple; its wheels are always well loaded, maneuverability is ensured.
Because the speed of home-made cars is limited, they should keep RR scheme. It is easier to perform, are suitable ready-made units that are easy to acquire.
Of the many possible combinations of location of the units select eight of the most common, simple and real. They are summarized in table 2.
The scheme A corresponds to the car “Zaporozhets”, scheme B, his predecessor, experienced domestic vehicle “Belka”, the scheme as deposed by car for the disabled. Scheme G built a., buses and some experimental cars. Scheme D is inherent in a British car “mini” and his numerous followers in Western Europe, the scheme of E — LUAZ Lutsk-970 (with the power unit “plows”), the scheme W is a number of French cars, the scheme 3 — American “Toronado” and “Cadillac Eldorado”.
On what grounds to assess the scheme? First, the use of space — more precisely, the length of the car. In this respect it is most advantageous transverse-engine outside the wheelbase, is the space between the front and rear axles and, if necessary, one of the “eaves” of the body, and the “overhang” in the field of engine — short. The length of the latter increases with the longitudinal position of the engine outside the base (G, A, B, E), that is, the usable space is the same as in the first case, but the length of the car is greater then the ratio of effective length to total (ratio using the length) is less. In order to further assess the complex of heterogeneous symptoms, apply a five point system. Give the listed options assessment — respectively 5, 4 and 3 points on the basis of use of space.
Equally important is the distribution of weight on the wheels. It is desirable that the load on the driving wheels was more or less constant, regardless of the number of passengers in the back, and was 50-60% of the total mass of the vehicle. On this basis it is beneficial to any engine outside the wheelbase (4), but the ideal distribution (5) is not achieved.
On signs of use of space and mass distribution of the special position occupied by the rear-engined cars of the so-called wagon-type forward of the driver seat. Usually, their body length is used very efficiently, and so the machine can be shorter povorotnie and easier than at any circuit with the speakers in front of the hood. And the weight of the engine, near the rear wheels, constantly balanced by the weight of the driver near the front. It also provides a good view of the road from the driver’s seat. No wonder wagon scheme widely used on buses and trucks. It attracts artists and designers (see “M-K” No. 2, 1975). But to create a good passenger car wagon type harder than a bus or a truck. This will be discussed in one of our subsequent articles.
But back to the comprehensive assessment of different schemes.
The third significant feature — the use in the construction of finished units. Avtostroitel — power units, motorcycles, cars “Zaporozhets”, С3Д and LUAZ, transmission of the listed machines, and if necessary, drive axles and gear boxes of cars VAZ and Moskvich. Preferred (5) to use the entire power unit and drive axle “Zaporozhets” or (for double car) С3Д, Somewhat difficult (4) all other schemes with a longitudinal engine layout and some with a cross, when you have to combine individual components from different machines. Even more difficult (3) is the case if this combination is connected with the front-wheel drive; only, as we have said already, a suitable drive axle — car LUAZ — is available in limited quantities. Finally, the most difficult (in Amateur terms) is the creation of a special powertrain, mounted in the crankcase (2).
Engine cooling is best accomplished when the front location; access to the units is most useful when the transverse (front or rear). The simplest system of control mechanisms is obtained, if the transmission and the clutch is not separated from the driver motor (5 in the front location, 4 at the back; in other cases, the rating drops to 3). These three signs are much less significant than the first. Therefore, when a comprehensive assessment it is advisable to reduce their importance (“weight”) by about half.
We reduce estimates in table 2, we summarize them and get a picture. First pop up the layout (but suitable only for double cars, as this refers to the use of comparatively weak power unit С3Д), next-link A, G, D, then B, and 3, and to close the table scheme J. it is Obvious that the designer who should focus primarily on the scheme of the vehicle with the power unit “Zaporozhets”. The schemes A, G, D gives also a good result, but is aware of the difficulties.
WHICH IS NOT RECOMMENDED
The requirements of the traffic police allow the construction vehicles of a variety of schemes, including tricycle.
Urgent advice to the Builder is to make a four — wheeled vehicle. It is more stable, topples under the action of relatively large lateral forces, has good permeability, compared with the three-Wheeler because the rear wheel will follow the trail laid front.
It should be said that the use of three-wheeled vehicle with one front wheel and not allowed by the police. This ban is prompted by the bitter experience of sidecars С1Д, previously serpuhovskiy the plant.
The construction of a three-wheeled vehicle can be justified except for the double machine, and for reasons some simplification of work of the Builder. While it is unlikely that a suitable front-wheel drive. Thus, at the disposal of the designer remains virtually three-wheel scheme to drive a motorcycle type rear wheel — chain or torque.
An intermediate position between the four – and three-wheeled cars is the cars with two very closely spaced rear wheels; a narrow rear track allows you to do without a differential and use a simple drive system of a motorcycle type, but acquires four track!
Not to mention the so-called “mid-engine” cars, that is, with the engine ahead of the rear axle. Despite the fact that when this scheme is achieved an even distribution of weight on the wheels, it is unsuitable for General-purpose vehicles, since the useful space of the body is severely limited, deteriorating access to engine cooling. If the driver’s seat forward to make, it disappear the main advantage of the car scheme, the front wheels are overloaded. If we include this scheme to our table, she would have received the lowest rating. Therefore, it can be recommended — or rather allow only for two-seat sports car, open body which gives satisfactory access to the engine and ensures its cooling.
Looking back at the work done, satisfied that we were doing it all the time with caution, albeit preliminary, written in the beginning of the article three determining factors — operational requirements (purpose of the machine, the number of seats), creative ideas (“I’m attracted to so-and-so scheme”) and manufacturing capabilities (the use of ready-made units). We observe this principle further.
(To be continued)