Tехнические науки/ Авиация и космонавтика

Nickolay Zosimovych, Achhaibar Singh

Sharda University (Greater Noida, India, UP)

CONSTRUCTION OF AN ALGORITHM DETERMINING THE OPTIMAL TOLERANCE FOR THE DESIGN OF UAV

As a result of perfection of forms modern and perspective Unmanned Aerial Vehicle (UAV) of typical geometrical parameters of a surface have been made the technique of appointment of admissions and criteria for tolerances external surfaces on external surfaces is offered. That allowed us to build the algorithm and applied computer program for solving the task to choosing optimal tolerance for the UAV external surfaces.

Key words: Unmanned Aerial Vehicle (UAV), surface, aerodynamic quality, sinuosity, technological roughness’s, ledge, constructive and technological actions, fuselage, fuel consumption, specifications, performance, manufacturing, maintenance, cost, lifecycle, technical requirements (TR), design and technology implementations.

Introduction. Increase of efficiency of UAV is caused, on the one side, by a problem of fuel resources, and with another side a tendency of change of structure of expenses for life cycle aside reduction of a share of initial UAV cost. Aircraft engineering practice marks following basic ways of increase of UAV efficiency [1]:

1. Application of essentially new constructive decisions and materials (10-20%).

2. Perfection of engines (20-30 %).

3. Aerodynamics perfection (0-40 %).

The importance and urgency of improving the aerodynamic efficiency by improving the forms of modern and advanced UAV, including by improving the quality of exterior surfaces, confirmed by the entire history of aviation. Detailed consideration of dependence of resistance on quality of performance of external surfaces by manufacturing shows that additional resistance can reach 2-10% at zero upward force [2]. The greatest share is brought by the deviations increasing a lateral section, details for example acting in a stream (approximately 5 %). Nearly 1.2-1.5 % is necessary on rivets and bolts connections; 0.5 % on joints of sheets; 1.0-1.5 % leaky position of shutters and hatches gives; rough coloring (over 20 microns) – up to At speed above М=1.5, the size of all components increases approximately twice and resistance from a sinuosity - more than 5 times. For the reasons specified above, the resistance increase through technological roughness is for subsonic UAV makes approximately 5-6 %, and for supersonic (М=2-3) – 10-16% [2].

Perfection of quality of external surfaces, due to constructive and technological actions, can lead to additional expenses. Therefore, an important question at definition of quality of external surfaces, quantitative estimations of similar actions. As such criterion for a quantitative estimation of losses from additional resistance it is possible to accept the expense or fuel cost. The expediency of an estimation of such kind is obvious, as fuel consumption is unique precisely measured parameter at the given design stage UAV, directly reflecting infringement of aerodynamics of a surface, both in manufacture, and in operation [3].

Problem statement. In development of designs UAV and, accordingly, technologies of their manufacture always crucial importance had constant increase in speeds of flight [1]. Growth of speeds of flight not only causes of application of new, more and more heat-resistant materials, but also is accompanied still nearby important for development of the production technology of tendencies [4].

Deviation of elements of a surface from a theoretical contour, a raising of heads of bolts, rivets, screws in a stream, steps, a roughness etc. on everyone concrete FV or group of planes are appointed in specifications developers.

Results of researches. By working out of constructive and technological decisions it is necessary to define the requirements shown to quality of object of manufacture and technological processes, in particular to appoint maximum deviations of aerodynamic surfaces. Admissions on a relative positioning of global surfaces of separate units and units among themselves in this case are not considered.

1. Technique of appointment of admissions on external contours of flying vehicles. For the purpose of definition of a generality of the constructive and technological decisions accepted in specifications, revealing of the reasons defining size of the admission have been analyzed specifications for more 30 FV various types and appointment [5].

2. Criteria for choosing tolerances for contours of the UAV. Qualitative performance indicator, as noted in [1], is a ratio impact on target impact cost to the whole lifecycle is As for since the cost of surface quality of a targeted output are generally, does not change the improvement in the efficiency is possible by changing the value of the life cycle. Hence the condition for as a selection criterion of tolerance is assumed as [6]:

(1)

where manufacturing cost; maintenance costs for the entire lifecycle, equal to staff salaries; the cost of ground handling and support of UAV flights; the cost of UAV repairing; fuel costs.

Surface quality a direct impact on UAV fuel costs, because deviations from ideal surface in majority cases helps to increase the resistance at zero lift, i.e. Whereas where range (field) error.

3. The factors determining value for admission to contours of the UAV. The magnitude of external outline tolerance influences range of factors which determine the value derived from operating costs which depend on the quality the external surface is defined as the cost of an additional fuel [3]:

(2)

where hours fuel consumption; increment value of resistance due to surface defects.

In order to reduce the amount of calculations for comparing various design and technological solutions, the concept of costs per unit of surface area ($/m²) is introduced [7]:

Taking into account the additional resistance for irregularities such as wave, step, slit, etc., can be described by the following equation:

(3)

where drag coefficient of isolated irregularities; functions reflecting the influence of speed and altitude; maximum height of the surface that is equal to scale of error; the coordinate characteristic parameter roughness (in m, for example, maximum amplitude of wave, a step, etc.); relative area occupied by roughness of investigated; the exponents.

According to the equations (2) and (3):

(4)

where

Thus the additional cycle costs are defined by basic parameters of UAV and conditions of its exploitation. Expenses of manufacturing, in general, depend on pre-production method adopted; level of the cost of one hour defined by accepted methods and means. In general, this set of determines the technological solutions which used to implement the some set design solutions.

Establishment of functional relation between cost of production and size of the construction errors are self-task. The present paper considers only the final results to principal design solutions. Proceeding from the results of statistical analysis, manufacturing costs may be given as:

(5)

These equations (1), (4) and (5) allow establishing a quantitative correlation between the described forms factors, i.e. to present the process of choice of tolerances as mathematical models.

Presented equations (1), (4) and (5) enable us to establish the quantitative relationship between the described form factors and define the process of selecting tolerances as a mathematical model (Fig. 1) [8].

Fig. 1. The structure of the mathematical models of choice the tolerance on the external contours

In general this MM should be supplemented by description of effects of external factors on the goal function, represented in the form of fuel prices, the unit cost of labor, etc. [9]. The optimal value of tolerance according to accepted criteria given by the equation [10]:

(6)

using which one can find an estimate of each factor relative to the base value, i.e.

(7)

The equation (7) allows recalculating the tolerance when you change the flight modes, design and technology implementations and external conditions. For example, the service life changes is determined by the ratio [7,9]. Then for a close tolerance as is needed. Influence of the speed estimated by the flight ratio [1]:

(9)

In the case of monotonic change incoming parameters required for the tolerance with toughening of the rising of For the solution problems of choosing the tolerance (especially in the case of iterate options), for example, more than 30 and the various flight conditions we can use the algorithm and program of calculation developed by the authors based on the proposed mathematical model.

4. Construction of an algorithm determining the optimal tolerance for the design of UAV. The procedure of determination the optimal tolerance by for a particular design solution must be performed in solving tasks enumerated in the previous section.

In order to prepare the information and as a basis for the calculation must be taken of (2) and (3) that characterize the influence of various factors on the operating costs, and the equations describing the effect of structural and technological factors (STF) (5). The final result of the calculation should be formed as an array of data elements of optimal tolerances for different STF as a result of the solution of (6) [7].

The sequence of calculations

1. Determine the typical design solutions, the area of their placement on UAV coordinates

2. Find the possible technological implementations and parameters and depending from expenses for manufacturing tolerances.

3. Find the specific geometrical parameters of roughness or in the case waviness – the allowable wavelength [1].

4. Determine normative data depending on the type of UAV and flight mode: and compute

5. For the researched define species roughness coefficient which takes into account the probabilistic nature of value

6. Calculate parameters and For obtain the waviness For the remaining unevenness

7. Compute the

8. Check the possibility of realization

9. Compute the quantities of losses or effect compared with the analogue as the difference between the above costs, i.e.

Conclusion. The analysis of appointment of admissions on external surfaces of units UAV, practice of their appointment and realization in manufacture allow drawing following conclusions:

1. Practically UAV in one interval of numbers admissions on performance of geometrical elements of an external surface are identical to all and decrease with growth The highest requirements to quality of an external surface are shown to a wing, as to the unit creating carrying force.

2. Experimental researches of the isolated roughness are put in a basis of calculation of resistance from roughness’s taking into account its site in the boundary layer. The roughness height is defined by admissible size of additional resistance. Practical technique to an establishment of dependences and functional communications between values of admissions and expenses by the generalized criterion and consequently, and to a choice of economically optimum admissions, still it is not defined unequivocally. Therefore for the generalized criterion accept additional fuel consumption because of resistance of roughnesses, as influence of additional resistance on speed almost slightly.

3. Thus, the additional life-cycle costs are determined by the basic parameters of UAV and conditions of its exploitation. Production costs in general depend from method adopted pre-production, the level of cost per hour, determined by conventional methods and means.

4. These dependences allow presenting the process of choosing the tolerances as a mathematical model and build the algorithm and applied computer program.

References

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