ONCE AGAIN, THE “PISTONE”

The main parameters that affect the launch model rockets with gas-dynamic unit (GDU) are the starting mass of the model, engine type and its characteristics, the aerodynamic resistance model and the pipe where the diameter of the piston GDU, elementary zadannyi (recovery) displacement, length acceleration phase, the mass of the pipe where the friction force and the degree of obturation in the system “the piston — pipe” GDU.

 

Nekotorye of these parameters can be “frozen” within the boundaries of the real nominal values, which can significantly reduce the multiple listing of options for the numerical solution of problems of dynamics mnogoparametricheskikh start. Among the “frozen” parameters, we consider the mass of the movable part of the GDU (50 g), the friction force between the piston and the tube DGG (0.5 N) and the degree of obturation between the piston and the tube GDU (96%).

The calculated structure CDB is shown in figure 1. When you select it was assumed that the friction force in a pair of “motor — hub pipe” is close to zero (loose fit), and the holes in the bottom of the tube provide free drainage of air, eliminating the increase in the pressure in the buffer cavity and the occurrence of the relevant drag forces. The calculation is performed with the following initial data: initial mass of the model 230, 260 and 290 g, aerodynamic resistance model is equivalent to the feathered body of rotation with a length of 800 mm and a diameter of 80 mm, the engine — MRD-or MRD 20-40 at a nominal supply characteristics and a temperature of 20 degrees C, the piston diameter DL = 23.5 mm, the length of the acceleration path Lmax = 700 mm, initial zadannyi (recovery volume) WO = 7.0 noob.cm. On Rianne 2 shows the estimated curve for different values of the starting mass of the model.

 

Fig. 1. Calculation scheme of the structure of CDB.

 

 

 

Fig. 5.The dependence of total force from the current start time for different values of piston diameter and reviriego volume.

 

 

Fig. 6. Scheme GDU with pipe reseveral camera.

 

 

Fig. 7. The dependence of the maximum force in planting the “engine hub” of the diameter of the piston and resiverov volume.

 

 

Fig. 9. The dependence of the optimal amount recovernow camera WP from the piston diameter for models with a mass of 260 g at the length of the upper area of 700 mm.

 

The determining parameter for the thickness Stanny pipe is the magnitude of the internal excess pressure of gases flowing from the engine raketnogo in the cavity. The calculated dependence of the inner excess pressure in the tube in the process of acceleration in relation to the model weight of 260 g is shown in figure 3.

 

With regard to manufacturing technology, to improve the durability of the starting ustanoveni and reduce the number of replacement tubes can be recommended to do strengthening stekloplastikovyh pipe retrieves an additional one or two layers sanatani thickness of 0.06 — 0.1 mm. the Cycle of operation of such products increases in neskolno times with a slight decrease in the rate of descent of the model with GDU. For record-breaking flights and the responsible competition it is better to make the shell of pipe with a variable cross section Stanny in accordance with risunkom 4.

Among the problems determining the operational reliability of the GDU, select the required landing force between the engine and the barrel of the pipe. The solution of this problem allows to exclude premature “jumping” Raney of the sleeve when the engine is started. At the start of the model, this effort should slightly exceed the largest modulus, the maximum force generated in the pair “model — pipe GDU”. The current in the landing zone of the engine and the bushing force can be determined by dependencies:

Figure 5 graphically shows the results of calculating R for different diameters of piston GDU and sachalinobiini volumes by time of dispersal. Note that when the piston diameter is 23.5 mm and the initial receivername volume Wo = 7 CC maximum force acting on the system “model — pipe GDU” does not exceed 10 N, and so the force of the landing engine in the sleeve pipe may be small, for example 15-20 N.