C. Stepanenko ONE METHOD TO DROP THE AVIATION OUTBOARD BLOCK WITH VARIABLE GEOMETRY

One method to drop the aviation outboard block with variable geometry is proposed. For grounding of this method the calculation and exploration of aerodynamic characteristics of the outboard block, which consists of the outward cylindrical body and inside a sharp body of rotation with a tail plumage, is performed. Estimation of the implementation possibility of a method to drop such block is carried out also.


I. INTRODUCTION
At application some types of aviation outboard blocks during the flight it's necessary to provide for their forced separation from the aircraft [1] - [3].The most common methods of the aviation outboard block (AOB) separation from aircraft: shooting with the help of pyrocartridge or separation through the use of the pusher, which is located on aircraft [1], [2].
It is obvious that the discharge of AOB only with a help of weight force admissible in case of the aerodynamic forces, which are acting on the AOB considerably less than a value of weight.Otherwise, it's necessary to apply, for example, methods as described below.
In this article the ground of method for the AOB dropping is offered due to aerodynamic forces operating the aviation outboard block with changeable geometry.
Clearly that on the stage of planning of such aviation outboard block with changeable geometry the preliminary analysis of their aerodynamic and dynamic characteristics is needed.Such analysis will allow reasonably to choose needed mass-overall parameters of block construction and conditions of their safe application.

II. PROBLEM STATEMENT
It is necessary to conduct a calculation and analysis of the basic aerodynamic characteristics of the AOB, made from a cylindrical outward body 1 and (central) inside being a sharp body of rotation with a tail plumage 2. Schematically the block is shown in the Fig. 1, thus movable part of the block is connected with the immobile flexible cowling 3, eliminating the transmission of the aerodynamic loading from one part to other and flowing of a stream in the inside of the block.The AOB is hanged to an aircraft with a help of castles mount 4.
The task is to calculate and explore of aerodynamic characteristics of the AOB without a displacement of the moving part of a block (MPB) and with a displacement of the MPB.It also follows to estimate values of forces and moments, which is acting on the configuration of the AOB with displacement of the MPB.

III. THE TASK SOLUTION
In our case, the use of the known methods of calculation of aerodynamic characteristics [4], [5] for the isolated movable part can give incorrect results in connection with absence of flowing around of its central component of a body.
At calculation of aerodynamic characteristics, we will consider movable part of a block, as a combination of head part and tail unit [4].
Thus, coefficient of lift force , where , According to the linearized theory [4] : where  is the an angle of attack in rad., and coefficient of lift force for tail unit (stabilizer, consisting of angular wing and rectangular wings, connecting it with a body) where D, d are diameters of stabilizer and body.
Coefficient of pitch moment of the MPB   1) -( 4) and the experimental data shows the satisfactory accuracy of the calculation results.
Experimental data for subsonic airflow, namely at Mach number M ≤ 0.8, are given.In this case, flow without separation around the tail moving part of a block is achieved by the smooth transition from the nose part to the outer cylinder and to the rear.
The method of calculating the value С хst is set out in the work [5] .Coefficient of profile resistance , where xc C is a coefficient of cone resistance; С хfr is a coefficient of resistance of friction of the lateral block's surface, referred to the area of mid-section: where sp  is the aspect ratio of spout.
As it follows from analysis of expressions ( 5) -(7), at turning MPB through an angle  relatively to the external cylindrical body (Fig. 4), its aerodynamic characteristics can be calculated separately.

IV. THE IMPLEMENTATION POSSIBILITY OF THE PROPOSED METHOD
For implementation possibility of the proposed method, we shall calculate the lift and drag forces and then compare these values with the AOB weight.Besides, we'll estimate a dynamic of the AOB rotary motion after its separation from the aircraft.
The system of differential equations, which describes the movement of AOB in a vertical plane after its dropping from the aircraft, has the form [3] where , , z m Q J is the mass, weight and an inertia moment of AOB; , , z X Y M is the drag, lift forces and pitch moment of the AOB;  is the angle of velocity vector inclination to the horizon plane.
It is necessary to find a solution of (8) for the specified initial conditions.
We find an approximate solution of (8) under the following assumptions: -the speed of the AOB is not greatly reduced in the considered interval [ 1 2 , t t ], i.e. can accept const; V V    -coefficients of the pitch moment and lift force can write in the form: ; At these assumptions (8) takes the form: m    l = 2m; s = 0.52m 2 .So, the value A 3 = -9.729s - and the value A changes approximately from 157.513s -2 to -157.513s -2 at changing of the AOB angle  from 0 to 30 deg (-0.34 ≤ z m  ≤ 0.34).Numerical calculations (10) in Matlab 7.8.0 for different initial data of the AOB dropping prove a stable trajectory of its motion after separation from the aircraft (Fig. 6).The time of passing of the static instability plot depends on initial data and changes from 0.15s (Fig. 6c) to 0.6 s (Fig. 6a).From an analysis of these calculations follows that the AOB distance covered is equal-order digits with the size of the AOB.
Therefore the aircraft should not execute maneuvering a preset time after the AOB dropping.

V. CONCLUSION
The research shows the expediency of application method to drop the suspended block with variable geometry Obtained results may be used at calculations of the forced separation of aviation outboard block, and also in the determination of nominal conditions of its applying and during the experiments with it.

Fig. 1 .
Fig. 1.The form of aviation outboard block coefficients of lift force for a head part and tail unit.
is the coordinate of body center mass, measured from the toe of MPB; 1mp z m is a coefficient of pitch moment with respect to the toe of MPB.The coefficient of pitch moment of pressure center of (p.c.) MPB; st p x is the coordinate of pressure center of the tail unit.Dependence of the lift force coefficient from the angle of attack is shown in a Fig. 2 (continuous line), and the experimentally-received points are symbols "+" there.

Fig. 2 .
Fig. 2. Dependence of the coefficient C y from the angle  Dependence of the pitch moment coefficient of the MPB from an angle of attack is shown in Fig. 3 (continuous line), and the experimentally-received points are symbols "+" there.Comparison of the calculated dependencies of coefficients st y C and mp z m from angle  , calculated according to the equations (1) -(4) and the experimental data shows the satisfactory accuracy of the calculation results.

Fig. 3 .C
Fig. 3. Dependence of the coefficient m z of the MPB from an angle  In calculating the aerodynamic characteristics of the whole outboard block, the coefficient of lift force represented in the form , st c y y y C C C  (5) the dynamic coefficient of viscosity[5] ; V  is the speed of incident flow.Coefficient of base drag at subsonic speeds is debot d is the diameter of the block in finite part; c d is the cylinder diameter.The coefficient of inductive resistance , is the coefficient of suction force;  is the coefficient which depends on the shape of the nose part, particularly for the conical nose there is empirical dependence shown as:

Fig. 4 .Fig. 5 .
Fig. 4. The form of aviation outboard block with shifting of the MPB on an angle b  Dependencies of aerodynamic forces coefficients С у , С х and of aerodynamic moment coefficient z m of outboard block from angle of attack b  without displacement MPB and with a fixed displacement MPB relatively to axis of external body on 0.14 rad.(8 deg) are shown in Fig. 5.As can be seen of the

2 A
Fig. 5, then 0    and at (0) 0   a value    .In this case from (9), we have differential equation second order

Fig. 6 .
Fig. 6.Dependencies of the angle  and angular velocity z  of the AOB from time t at an initial data: (a) (0) 0   , rad deg (0) 0.0873 5 s z

Fig. 7 .
Fig. 7. Dependencies of AOB distance covered and its vertical velocity from time: d 1 , V 1 is the AOB distance covered and its vertical velocity at an action of maximal lift force; d 2 , V 2 is the AOB distance covered and its vertical velocity at an action of minimal lift force