Disregard of this summand leads to existence of internal gravity wave (§13) whose nature is unclear. When the first summand equals zero, which is the condition for incompressibility of the medium, the second summand remains, equaling isobaric change of its density. The generalized mass conservation equation is obtained in work, in the right part of which an additional summand is entered determining the change of density of constant mass, under isobaric change of its volume as a result of temperature variations conditioned by entropy oscillations in inhomogeneous (nonisentropic) medium. It appeared that the equation in its current form is fair only for homogeneous medium and as any medium in gravity field is more or less inhomogeneous, it needs to be generalized. These results led to necessity of changing the mass conservation equation. Strongly inhomogeneous medium, which is largely influenced by external force filed, is always incompressible and sound speed in it is isobaric. Homogeneous medium, which is free from the influence of external force field, is always compressible and sound speed in it is adiabatic. Upon correct determination of sound speed, according to which its true (real) value in the medium is determined by combination of adiabatic and isobaric sound speeds, it became evident that compressibility and incompressibility have thermodynamic rather than mechanic meaning and they are directly related to homogeneity or inhomogeneity of the medium. Irrelevance of condition of incompressibility to liquids was shown in work. If the medium is incompressible within the above sense, then any perturbation will be propagated with infinite velocity and thus, generation of wave is impossible. The first assumption apparently contradicts the concept of mechanical wave in medium itself, since it is known that a wave is propagated only when, under disturbance of density of medium in any point, the elastic forces originate, spreading these perturbations to other points. The vast majority of these works rely on two assumptions: (a) liquids are incompressible (i.e., their densities are constant) and (b) liquid motions are potential, that is, noncircuital. A great number of scientific publications have been dedicated to the study of this problem, which stemmed from the second half of the 18th century. Such waves arise in consequence of disturbance of these surfaces and depending on the volume of disturbance, they may be either linear (when disturbances of parameters of liquids are much less than their equilibrium value) or nonlinear (when disturbances of parameters of liquids are bigger or of the order of their equilibrium value). Surface gravity waves are generated and propagated on the interface of two liquids therefore, while studying them, the methods of theory of hydrodynamic tangential gap are applied. None of them will go remotely as fast at low level.The paper considers the applied problems of hydrodynamics and based on the new results, published by the author in recent years, shows that main assumptions used in the course of their solution, namely, incompressibility of liquids and potentiality of their movement, are not applicable to liquids in the gravitational field of the Earth. The World outright low-level airspeed record was held for years by a Tornado F2 on flight-test out of Warton, which achieved 800kts (920 mph) with no pylons and a very 'clean' airframe.Īll the M2.0+ fighter aeroplanes need to be up in the stratosphere to reach those Mach nos. Jet engines are also much more efficient at high altitude and airspeed.Ī lot of 'supersonic' military aeroplanes struggle to go faster than M1.0 at low-level, especially if they are carrying external stores. At altitude, lower air density = less drag, more speed and higher Mach No. So the 350 kts IAS becomes less limiting, as at 37000' the jet may have an IAS of 180 kts, a TAS of 580 kts, and a Mach no. At higher altitudes for a given actual 'speed' (TAS, True Airspeed), IAS decreases and Mach No. Now 350 kts doesn't sound very fast, and at low-level if the power levers were left all the way forward our Boeing would quite quickly exceed its design max speed, although it would only be doing Mach 0.6 or something. Most Boeing airliners are around 350 kts IIRC. Aeroplanes have a maximum, limiting Indicated Airspeed (IAS) which they can achieve.
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