Aircraft hydraulics

Polyalphaolefin Hydraulic Fluids. No human studies for polyalphaolefin hydraulic fluids were located. Polyalphaolefin hydraulic fluids are used in U.S. military aircraft hydraulic systems thus, there is a potential for occupational exposure. Animal studies were insufficient for determining the primary targets of toxicity. Epidemiology studies examining a number of end points would be useful for identifying targets of toxicity. 

Uses Plasticizer for lacquers, plastics, cellulose esters, and vinyl resins heat-exchange liquid carbonless copy paper systems in aircraft hydraulic fluids solvent extraction of metal ions from solution of reactor products uranium extraction and nuclear fuel reprocessing pigment grinding assistant antifoaming agent solvent for nitrocellulose and cellulose acetate. 

Aircraft hydraulic power unit fuel tank (containing a mixture of anhydrous hydrazine and monomethyl hydrazine ) (M86 fuel) 3165... 

Skydrol I Solatia], TM for a series of fire-resistant aircraft hydraulic fluids. 

A Used for hydraulic systems in turbo jet and turbo prop aircraft, which must operate at -54C. 7000 Used in aircraft cabin superchargers, expansion turbines for air-conditioning systems and the aircraft hydraulic system itself. 

Phosphate esters have been produced commercially since the 1920s and now have important applications as plasticisers, lubricant additives and synthetic-based fluids for hydraulic and compressor oils. Their first use in lubrication was as anti-wear additives. Later developments in aircraft hydraulic control systems, particularly during the Second World War, introduced phosphate esters as less flammable hydraulic fluids. As esters of orthophosphoric acid they have the general formula OP(OR)3, where R represents an aryl or an alkyl group or, very often, a mixture of alkyl and/or aryl components. The physical and chemical properties of phosphate esters can be varied considerably depending on the choice of substituents [59, 60], selected to give optimum performance for a given application. Phosphate esters are particularly used in applications that benefit from their excellent fire-resistant properties, but compared to other base fluids they are fairly expensive. 

The first aircraft hydraulic fluid was castor oil based. Modern aircraft now use one of two broad classifications of hydraulic fluid, hydrocarbon based or phosphate ester based. 

One of the major advantages of these fluids is that they are all compatible with each other in all proportions and with all the aircraft hydraulic systems and hydraulic system materials designed to use any of these three hydraulic fluids. That has enabled transition from one to the other by attrition, i.e. just convert by topping off with the new hydraulic fluid. This saves considerable fluid and maintenance time compared to repeatedly flushing and filling to obtain a high percentage of the new fluid in the aircraft. 

Another mechanism for the formation of acids is through thermal degradation. There is no easy solution to this problem, so the operational temperatures of the commercial aircraft hydraulic systems must be maintained well below the thermal degradation temperatures of the phosphate ester hydraulic fluids, reported as being above 200°C [26]. 

Fuel cells are electrochemical devices in which fuels (e.g., hydrogen, carbon monoxide, hydrocarbons, and alkali metals), oxidants, and reaction products move into and out of a system of electrodes separated by an electrolyte. The reduction-oxidation reactions that take place generate a direct current while the materials are supplied to the cell. A number of transportation and other applications for this technology are being explored, partly because of the environmental benefits the reaction products have over those of fossil fuels. M86 fuel, a mixture of anhydrous and methyl hydrazines, is used in fuel cells including those used to generate electricity for some aircraft hydraulics systems. These fuel tanks are leak-tight, double-walled aluminium pressure vessels that contain up to 42 litres of M86. 

Bonds made with acrylics typically resist immersion in isooctane, motor oil, aircraft hydraulic fluid, 10% sodium chloride solution, distilled water, ethyl alcohol, and dilute mineral acids and alkalies. However, they are not resistant to concentrated acids and alkaline solutions or acetone. Weathering resistance, including salt spray environments, is also excellent. 

Triaryl phosphates are used in aircraft hydraulic fluids where low flammability and low-temperature operation are required. They are also used in place of petroleum oils as lubricants and coolants where fire hazards have to be reduced (Figure 12.19). 

No apparent reaction occurs on ZA 27 after 2 weeks at 49°C in a static test of three fluids Shell Tallus T-15, Shell Decol T-23, and Shell Aircraft Hydraulic Fluid 4. 

In the consideration of seals or O rings for the aircraft industry, it is worth knowing the basic fluid flow mechanism in the hydraulic system, since the purpose of seals in aircraft is to preserve the pressure in such a system. Every aircraft hydraulic system has two major parts, the power section and the actuating section. The power section provides fluid flow, regulates and limits pressure. 

A second test which is even more discriminating is the so-called "contamination test, in which the rubber is soaked in the fluid for several hours at room temperature and is then subjected to hot air ageing at high temperature. This test simulates the environment of many engine components (e.g. seals, gaskets, hoses, etc.). The main rubbers commonly used in such applications are nitrile rubbers which are not appreciably swelled by hydrocarbon oils and ethylene-propylene (EP) and their ter-polymers (EPDM) which are resistant to the phosphate ester fluids (e.g. Skydrol) used in aircraft hydraulic systems. The following discussion is concerned with the performance of antioxidants under these veiry aggressive conditions. 

Acetone, aivd solutions 1090 26 Aircraft Hydraulic Power Unit Fuel Tank 3165 28... 

This alloy finds application as aircraft hydraulic lines, heat-exchanger tubes, pollution-control equipment, and particle-accelerator tubes. 

Skydrol 500B aircraft hydraulic fluid 23 30 9 Stable 0.5 102 " "... 

Other refractory semiconductors will continue to be developed and compete for niches. A suitable high-temperature semiconductor technology could allow bulky aircraft hydraulics and mechanical control systems to be replaced with heat-tolerant in situ control electronics. Onsite electronics, actuators, and sensors would reduce complexity and increase reliability. Hydraulic system, a fire hazard in aircraft, and heat radiators in satellites could then be greatly reduced in size and number, yielding a considerable weight reduction (4). In addition, many wide-gap semiconductors are anticipated to find applications in thermoelectric, electro-optic, piezoelectric, and acousto-optic devices and heat sinks. 

Aircraft Oiis aircraft hydraulic acid 20 6 Slight attack some absorption depends on end use conditions ... 

Skydroi 500B aircraft hydraulic fluid 23 180 9 100 Celanex... 

Skydrol 500B aircraft hydraulic fluid 22 14 8 No cracking for duration of test Flexural stress Ultem 1000 GE Plastics... 

---