For a power-propeller, it is important that the volume of ullage be kept away from the input that leads to the engines, because the liquid must enter the engines. Powered gas turbopumps will protrude and may fail when they absorb large amounts of gas during operation; When the gas is inert, the pressurized engines lose their stable combustion. are integrated into a delivery contract, varies from supplier to supplier. In some cases, the orlage in the hold of a ship may be relevant to stability; Liquid or dry bulk goods in a partially filled hold may move asymmetrically on one side, while the vessel retreats to one side and the other, reducing the stability margin compared to a full hold. Excessive ullage in a tank can contribute to the free surface effect. If we refer to the free surface effect, the condition of a tank that is not full is described as a “slack tank” while a full tank is “depressed”.  Question: But I still don`t quite understand what is ullage or not in the context of missile science. Is it just a name, or does it have a form of verb? In this context, does Ullage always refer to a force that pushes liquid fuel to the end of a tank in which the exit is present? Can gas pressure in a tank that also contains liquid provide ullage, or is the ullage limited to acceleration (for example. B by using an ulcer motor just before the engine is switched on) or a membrane or gas pocket? The membrane/balloon solution for the ulcer problem (typically found in tanks of small thrusters such as Apollo RCS nozzles) is a terminology incident.
Is it Ullage or not? It`s ullage, if you look at both sides of the diaphragm, I guess, but if you look at both sides of the diaphragm as separate tanks, one is a gas tank without liquid, and the other is a liquid tank without gas, so there is no ullage in sight. In weightlessness in the engine without thrust, the vacuum is created in partially filled tanks, and the liquid moves away from the engine entrance, which is undesirable for a stable operation of the engine. Small rocket thrusters are sometimes used to provide sufficient acceleration to place fuel at the bottom of tanks before the main engine or engines are ignited. Engines dedicated to this purpose are called ulcerative motors; sometimes jet beam oars.