ARMORED SHELLS WITH STRAIGHT AIR JET ENGINE
Authors: Kovalchuk O. , Skorohvatov O. , Galkin A. , Gordishevski L. , Liskovchuk V. 
Published: August 2022

The article analyzes the problems of sub-caliber feathered projectile, offers a variant of equipping such a projectile with an air-jet engine, graphs of air resistance, calculations of the required thrust of the air-jet engine. Features of armor-piercing projectiles with a direct-flow air-jet engine are considered, the main calculations are performed using high-level Python programming language.
Currently, as armor-piercing ammunition are widely used armor-piercing sub-caliber feathered shells (BPOS) with high penetrating ability
This is achieved due to the high initial velocity of ammunition (1650-1840 m / s) and small cross section (d = 20-30 mm). To compensate for the force of air resistance, the provision of jet propulsion ammunition is used.
But the main disadvantage of such shells is the dependence of the ability to pierce armor from a distance to the target. That is, due to the resistance of the air, the speed of the projectile is lost, namely its energy. What they are inferior to cumulative projectiles, for which the ability to pierce armor does not depend on the distance to the target. Modern armored vehicles have significant armor and BPOS lose their importance in the range of cumulative projectiles and anti-RPG. This situation can be corrected if the BPOS is equipped with direct-flow jet engines (PPD).
Direct-flow air jet engine (PPD), simple in design, has a high efficiency at large Mach numbers, compact, because it does not require the presence of an oxidant in the fuel, as it uses oxygen from the environment. Compressed air entering the combustion chamber from the inlet device is heated by oxidation of the fuel supplied to it. Created from a mixture of air with combustion products gas mixture – the working fluid in the nozzle reaches the speed of sound, and at its output expanding to supersonic.
The working fluid flows at a speed greater than the speed of the oncoming air flow, which creates a jet thrust.
When the flight speed is much less than the speed of the jet, the thrust increases. As the speed of flight approaches the speed of the jet, the thrust decreases, passing some maximum corresponding to the optimal speed of flight.
With the development of mixed solid fuel technology, it began to be used in PPRD. A fuel checker with a longitudinal Central channel is placed in the combustion chamber. The working fluid passing through the combustion chamber oxidizes the fuel from its surface and heats up.
The use of solid fuel further simplifies the design of the PPRD as it does not require a combustion chamber.
The main part of the filler of mixed fuel PPRD is a fine powder of aluminum, magnesium or beryllium, the heat of combustion, which is much higher than the heat of combustion of hydrocarbon fuels.
With the development of mixed solid fuel technology, it began to be used in PPRD. A fuel checker with a longitudinal Central channel is placed in the combustion chamber. The working fluid passing through the combustion chamber oxidizes the fuel from its surface and heats up.
The use of solid fuel further simplifies the design of the PPRD as it does not require a combustion chamber.
The main part of the filler of mixed fuel PPRD is a fine powder of aluminum, magnesium or beryllium, the heat of combustion, which is much higher than the heat of combustion of hydrocarbon fuels.
An example of a solid propellant PPRD can be the propulsion engine of the anti-ship missile P-270 Mosquito.
Depending on the speed of flight PPRD are divided into subsonic, supersonic and hypersonic. This division is due to the design features of each of these groups.
In the supersonic range PPRD is much more effective than in the subsonic. For example, at a speed of M = 3, the degree of pressure increase in the PPRD is 37, which can be compared with the most high-pressure compressors of turbojet engines.
Keywords: armor-piercing sub-caliber feathered projectile, air-jet engine, external ballistics.