Investigation of the feasibility of using wing struts and non-retractable landing gear struts on a light multi-purpose aircraft

. In this paper, we consider a method for determining the feasibility of using a wing strut and non-retractable landing gear on a light multi-purpose aircraft. In a certain range of cruising speeds and flight ranges, it is advisable to use non-retractable landing gear and wing strut. With an increase in cruising speed and flight range, these engineering solutions must be abandoned to improve aerodynamic characteristics. The dependencies obtained in this work make it possible to make decisions on the use of a wing strut and non-retractable landing gear at the early design stages. To obtain aerodynamic characteristics in the Siemens NX program, a three-dimensional model of a light multi-purpose aircraft was created and an aerodynamic experiment was performed in the FloEFD program. Then the calculation of flight performance was carried out. As a result of the study, the dependence of the speed up to which it is advisable to use the undercarriage strut and fixed landing gear on the flight range for a light multi-purpose aircraft weighing 2000 kg was obtained. When designing an aircraft, it is necessary to make decisions about the use of one or another engineering solution, which, on the one hand, has a positive effect on aerodynamics and negatively on the weight of the aircraft, and vice versa. In this article, using the example of a wing strut and fixed landing gear in the first version of the aircraft, and a cantilever wing and retractable landing gear in the second version, a model for solving such a problem is shown.


Introduction
Sectors of the economy such as healthcare, forestry, weather service, geodesy, construction and industrial enterprises around the world use light aircraft. Currently, there is a need for simple, cheap and small competitive manned and unmanned aircrafts in our country [1][2][3][4]. According to statistics, the aircraft of local air lines are divided into the following categories according to the required target load:  1st category: 5-7 passengers, mail, cargo (total 500-700 kg)  2nd category: 10-12 passengers, mail, cargo (total 900-1100 kg)  3rd category: 15-18 passengers, mail, cargo (total 1500-1800 kg) In the sanitary version -two stretcher patients and two accompanying medical workers, medical equipment (about 400-500 kg in total). Forest patrol option -four parachutists, firefighters, equipment and cargo (in total about 400-500 kg).
Therefore, for patrolling forests, sanitary services, for the transportation of 5-7 passengers, for aerial surveys, as well as for transport and communication work, it is primarily advisable to have a light multi-purpose aircraft of the first weight category [5]. Such aircraft are commonly called multipurpose. They should allow for the rapid conversion of one option into another, the possibility of operation on skis, floats. The aircraft of this category will be considered in this article. Namely, the use of such design solutions as non-removable landing gear struts and wing struts on the aircraft.
Non-retractable landing gear has its pros and cons. The advantages include: lower weight, cheapness, ease of production and operation. More free space in the fuselage and other units, where the supports could potentially be removed. The disadvantage of nonretractable landing gear is harmful resistance. Retractable landing gear, in turn, have more weight, are more expensive in design and production, and are more difficult to operate, since dirt, dust, snow and water are clogged into the compartments and niches of the landing gear during movement along the unpaved airfield. The advantage of this solution is the best aerodynamic characteristics. The wing slope unloads the bending moment of the wing, reducing its maximum value. As a result, it allows you to reduce the weight of the wing. At the same time, by analogy with non-retractable landing gear creates additional harmful resistance.
The study should show in which range of cruising speeds and flight ranges it is advantageous to use non-retractable landing gear and wing struts, and in which retractable struts and free-bearing wing from the point of view of mass return [6,7], speed and range of flight. The obtained dependencies will help to make more effective decisions at the early stages of designing light multi-purpose aircraft.

Design and modelling
Initial data: Power: 2 engines of 200 hp, total 400 hp (294 kW); Number of passengers: 5 passengers, mail, cargo (total 500-700 kg) Flight range, cruising and maximum flight speeds are specified in the source data at the first stages of the life-cycle [8,9], since these characteristics are the main criteria.
As a result of the collection and analysis of statistics, the main parameters and appearance of the aircraft were determined (

Aerodynamic experiments
Based on the sketch of the base aircraft in the Siemens NX program, two three-dimensional models were built (Fig. 2, 3)   Fig.2. Three-dimensional model with retractable struts and a free-bearing wing.

Calculation of the mass of the chassis
The mass of the chassis is calculated using the Torenbik formula [10], in which the mass is determined by summing the masses of the main supports and the front support.
= + (1) Where the total weight of the main supports and the weight of the front support are determined by the formula (2). = * (А + 0 0,75 + 0 + 0 1.5 ) Where = 1.08 for a high-plane. The values of the remaining coefficients are given in Table 1.

Calculation of the wing mass
Weight of the strut wing is calculated by the formula (3). Weight of the free-bearing wing is calculated by the formula of Badyagin and Mukhamedov (4), using the weight model [11,12] (∆ ) 1 − (∆ ) 2 = 0 (5) In this formulation of the problem, it is assumed to reduce the thrust of the engines on aircraft No. 1 in a cruising flight at a given altitude, as a result of which fuel economy can be obtained (6). Neglecting the difference in due to throttling on aircraft No. 1, we get the formula (7): The power method was used to plot the required and available thrust (Fig. 7   The speed to which it is advisable to use a slope and non-retractable landing gear according to schedule No. 5 is determined as follows: Let us say, the flight range of the aircraft should be at least 800 km. This range corresponds to a critical speed of 200 km/h. That is, if the cruising speed of this aircraft is less than 200 km / h, then it is more expedient to derail and non-retractable landing gear, if more than 200 km / h, then retractable landing gear and a free-bearing wing.