AEROSPACE

Specialist Polyimide Polymers

Solutions for Critical and Demanding Applications

Combining thermal oxidative stability with exceptional low wear and low friction and an excellent strength to weight ratio to provide long operational life of aerospace precision components.

Auxiliary Power Unit

Spline couplings can be used in a wide variety of locations within aerospace. Here, we are looking at the connection between the Auxiliary Power Unit (APU) and the auxiliary power generator. In this application, the spline coupling is used to accommodate potential misalignment between the APU and the generator. The spline coupling must transmit torque between these two devices over a long service life, generally without lubrication.

A spline coupling in service experiences a huge number of small displacements under the load caused by torque transmission. To fulfil this need, the coupling must be extremely wear-resistant, have low friction to avoid power losses and heat generation, as well as being creep resistant. Lastly, the coupling cannot, under any circumstances, be allowed to damage the metallic splines on the adjacent shafts.

Ducoya spline couplings can be manufactured to demanding tolerances and enable long life at high rotational speeds under high torque loads. Ducoya does not gall adjacent shafts or corrode. It is light and high strength to transmit rotational force.

Under these arduous conditions, Ducoya exhibits minimal wear in unlubricated conditions.

The function of a Constant Speed Drive (CSD) is to ensure consistent rotational speeds at the electrical generator. The CSD may be driven by a range of different input shaft speeds (2000-9000 rpm) and needs to accommodate continuous variations between these extremes. Failure to do so would result in AC power generation at an inappropriate frequency.

As a complex mix of hydraulic and mechanical systems, the CSD poses many material challenges. These include: low wear to give long component life, low friction to minimise mechanical losses and effective sealing whilst sliding to minimise hydraulic losses. The Pressure-Velocity (PV) values in the hydraulic system can be high and any dynamic sealing elements need to be compatible with this, as well as the chosen oil.

Temperatures in the CSD can range from -90°C (-130°F) to +100°C (212°F) or more. Chosen components must be compatible with this temperature range.

Ducoya precision aerospace components deliver low friction, low wear and effective sealing in almost all oils. Ducoya is also capable of operating over a wide temperature range. Components can be made to tight tolerances and small axial dimensions to minimise packaging requirements.

The high strength of Ducoya allows minimisation of component dimensions, as well as compatibility with high pressures.

Ducoya can also be used in mechanical Continuously Variable Transmissions (CVT).

If you would like to learn more about the unique characteristics of Ducoya and its uses in the aerospace industry, please see our applications guide.

Clamps and Fasteners

Fasteners are a small but vital precision aerospace component, binding sometimes critical structures together. Fasteners located close to the engines or Auxiliary Power Unit (APU) can see extended periods of high temperature. Creep or deformation can cause failure of the fastener. It must also be possible to disassemble fasteners such as lock nuts without galling that could damage the threaded countersurface. Ideally, lock nuts can be re-used multiple times but retain sufficient friction to not become undone.

Fasteners must be strong enough to survive design loads. Ducoya is creep resistant at high temperatures and has stable friction over a wide range of conditions and over time. Ducoya locking elements do not require complex and dirt-attracting features such as castellations. The high strength of Ducoya allows application in many areas of the airframe, including engines and APUs.

Being polymeric, Ducoya does not corrode, nor does it induce galvanic corrosion in adjacent components. It is also tolerant of high levels of vibration without impairing performance. Ducoya fasteners can be re-used multiple times and do not gall with metallic countersurfaces.

These small components perform a vital function in keeping fuel, oil and hydraulic pipework secure and protected from vibrational stresses that could induce a fatigue failure. They should also be high strength and high stiffness to protect against off-design loads. Clamps must be creep resistant at engine temperatures to ensure optimal performance over a long life. Lastly, clamps should add a minimum of weight to the engine or Auxiliary Power Unit (APU).

Clamps in novel fuel systems may be exposed to cryogenic temperatures for example, liquid hydrogen at -253°C (-423°F) in addition to normal high-altitude temperatures, perhaps -90°C (-130°F). Under these conditions, clamps must not become embrittled or allow dissimilar coefficients of thermal expansion to damage the service line being clamped.

Ducoya clamps have higher stiffness than aluminium or titanium clamps while offering a density 30% lower than aluminium. Ducoya resists creep, even at high temperatures and can help protect critical service lines from fatigue failure. An important characteristic of Ducoya polyimide precision aerospace components is there wide temperature range without embrittlement at temperatures as low as -273°C (-459°F). Ducoya clamps can be well matched to aluminium and steel service lines in terms of coefficient of thermal expansion (12×10-6 m/m/°C to 25×10-6 m/m/°C).

Ducoya clamps are compatible with the vast majority of aerospace fuels, lubricants and hydraulic fluids, as well as environmental contaminants such as de-icing fluid, water etc.

If you would like to learn more about the unique characteristics of Ducoya and its uses in the aerospace industry, please see our applications guide.

Engine

Variable stator vanes are integral to good compressor performance in advanced gas turbines. Operational characteristics include frequent changes of position under load, especially on short haul flights, high levels of vibration, a desire to minimise weight, large temperature variations from -90°C (190°F) to +370°C (700°F) and the related requirement for high precision aerospace components to accommodate thermal expansion. This is all coupled with the need to keep maintenance costs low while having the engine remain on-wing and flying profitably and at maximum efficiency for as long as safely possible.

Ducoya polyimides deliver low wear and low friction in extremes of temperature, minimising unison ring actuation force while extending maintenance intervals. Good stability in hot, oxidising conditions allow extended use of high-power settings without shortening part life time. Ducoya’s moderate modulus helps effectively dampen vibrations, extending part life and reducing stress elsewhere in the engine. Ducoya polyimide grades can be chosen with different levels of thermal expansion in order to best integrate with adjacent, metallic components, they can also be manufactured to demanding tolerances. This combination of properties combined with a good strength to weight ratio, means your engines can deliver maximum efficiency for the longest periods of safe operation.

One of the challenges of modern jet engine design is minimising losses of compressed air. Reducing leakage increases engine efficiency, leading to lower cost per passenger mile. Shrouds can help reduce compressed air losses, but also need to exhibit low friction and low wear, as well as being stable at high operating temperatures.

Ducoya’s “soft but strong” character allows good sealing of compressed air while also exhibiting low friction, which minimises actuation forces and low wear maximising part life.

Unison rings are a critical aerospace component in the actuation of variable stator vanes and inlet guide vanes. They are exposed to a wide range of temperatures, vibration and frequent motion under load. To reduce the size of the unison ring actuator, wear pads should have minimal friction. They also need to be durable, but lightweight to aid weight targets. Low maintenance and long life are critical factors to allow maximal safe operation of the engine on wing.

Ducoya delivers a coefficient of dynamic friction which can be as low as 0.09 and a coefficient of static friction of 0.27 against hardened stainless steel, unlubricated in air. These low coefficients of friction can improve responsiveness and keep the size and weight of the actuator to a minimum. Low wear rates mean long component life and extended operating periods on the aircraft. Ducoya also possesses good thermal oxidative stability, thus retaining its properties over a wide temperature range while not having the complications of a phase transition such as Tg. This means behaviour is consistent with good strength over this wide temperature range.

Air management doors and their actuation are a critical part of jet engine operation, especially during start up and shutdown procedures, as well as responding to off-design conditions in flight. These aerospace components ideally are maintenance-free, giving long life and low friction without lubrication to minimise the size of the actuator. They must endure the same large range of temperatures as other engine compressor components without degradation. Tight tolerances can be needed to ensure reliable operation over this wide temperature range.

Ducoya precision aerospace components deliver dynamic friction, which can be as low as 0.09 and a coefficient of static friction of 0.27 against hardened stainless steel, unlubricated in air. These low values minimise the size of the actuation system. Low wear of Ducoya components means long part life. Ducoya components can be manufactured by a range of techniques to achieve tight tolerances.

Fuel proportional valves and cut-off valves are safety critical precision aerospace components. They must be compatible with the fuel being used, for example Jet A-1, JP-8, Avgas etc, without excessive swelling. A key performance requirement is reliable and effective sealing to control flow of fuel into the engine, especially in a cut off situation. It is important that proportional valves give a precise, predictable and consistent flow rate for a given command input. Stiction in proportional valves is highly undesirable tribological phenomenon as it conflicts with the above. Valves are also exposed to a wide range of temperatures.

Ducoya demonstrates minimal swell in a wide range of aviation fuels. Excessive swelling can result in high actuation forces or in extreme cases, operational failure of the valve. Its low friction and low stiction characteristics allow precise and reliable operation of valves. Ducoya’s combination of high strength and low modulus allow for excellent sealing in a wide range of conditions.

Shaft bumpers must allow safe engine operation to continue in off-design conditions, where the bumper’s role is to prevent the main shaft(s) deflecting excessively. In extreme cases, this condition may continue for an extended period of time to allow the aircraft to land safely. These periods of contact between the high rotation speed of the shaft, potentially under high load, can generate extreme PV (pressure-velocity) conditions which in many materials can lead to very rapid wear of the component. Bumpers must also endure temperatures of normal engine operation as well as higher temperatures caused by frictional heating.

Ducoya polyimide components can survive both extremes of temperature and PV conditions that other materials cannot endure. A low coefficient of dynamic friction minimises heat generated due to sliding contact while a high level of thermal oxidative stability reduces the rate of part erosion. Additionally, a low wear rate, even under extreme PV conditions, may allow for a sufficiently long part life for the duration of off-design operation.

If you would like to learn more about the unique characteristics of Ducoya and its uses in the aerospace industry, please see our applications guide.

Landing Gear

The undercarriage system, particularly the nosewheel, must provide robust directional control without shimmy or vibration at take off and landing speeds. It must also survive shock loads at landing including hard landings and retain mechanical integrity. The undercarriage must operate over a wide range of temperatures and is exposed to the elements and aerospace fluids. Long service life without lubricants or excessive maintenance is also required.

Ducoya has high strength and wear resistance, even without lubricants under high load. Grades with high modulus help maintain good alignment of components. Ducoya can be made into precision aerospace components with closely controlled small tolerances which can be integral to successful performance.

Ducoya can be used over an extremely wide temperature range, more than covering landing gear requirements.

Successful landing gear design must provide for vibration and shimmy-free taxiing and take off runs. Landing gear must also be able to absorb the shock loads of a hard landing without damage to allow a subsequent taxi run to the parking stand. Damper sealing is a vital part of undercarriage design in achieving the above.

Damper seals are precision aerospace components, carefully controlling the movement of hydraulic fluid through the system to reach consistent and optimum behaviour. It is self-evident that such seals must be compatible with the chosen hydraulic fluids and other aerospace fluids that they may come into contact with, for example, de-icing fluid etc.

Ducoya polyimide components can be made to extremely tight tolerances for controlled damping rates. Ducoya’s low wear rate ensures long life and consistent performance. Ducoya is also compatible with a wide range of hydraulic and other aerospace fluids, including de-icing solution.

Ducoya has high strength and high elastic elongation enabling it to survive shock loads and return to the intended dimensions without damage. An additional feature is low density, minimising weight.

If you would like to learn more about the unique characteristics of Ducoya and its uses in the aerospace industry, please see our applications guide.

Flight Control Surfaces

Flaps and slats are an important part of aircraft operation during take off and landing. Flaps and slats can be deployed against high aerodynamic forces in flight. Actuation of these surfaces needs to endure these high loads, have minimal friction and have sufficient wear resistance to be capable of reaching the design life of the aircraft without maintenance.

The flaps and slats actuation system can be exposed to rainwater, de-icing fluid, Skydrol® hydraulic fluid and jet fuel. The wear and friction surfaces of the actuation system cannot have their lifetime shortened by exposure to these fluids. Lastly, the actuation system, as well as being extremely durable, must be lightweight and have low friction. While lightweight is always a requirement in aerospace, low friction is desirable to keep the actuator itself as small as possible, consistent with the high loads that are possible.

Ducoya can be very valuable in aerospace actuation systems because its high strength allows it to carry high pressure loads, as can be found when deploying flaps and slats in flight. Ducoya G021’s low density of 1.51 helps keep the weight of the actuation system compatible with the composite materials found on the latest generations of civil and military aircraft.

The coefficient of friction contributes to the size of electric or hydraulic actuation of the control surfaces. Ducoya helps minimise this with a coefficient of friction as low as 0.12 (depending on tribological conditions).

For the critical requirement of being maintenance-free for the life of the aircraft, Ducoya excels, offering extremely low wear rates under a wide range of conditions.

Primary flight control surfaces such as ailerons, elevators and rudder(s) are safety critical components. Actuation of these surfaces must be reliable and robust for obvious reasons. A wide range of different mechanical techniques can be used to actuate these surfaces. However, they are typically characterised by: potentially high mechanical or hydraulic loads, frequent actuation, possibly at high speed, as well as the need to minimise weight and friction, as well as any requirement for maintenance or inspection.

Ducoya’s low wear rate coupled with low density, low friction and high strength can be a useful solution for actuation of primary flight control surfaces. The ability to survive the high PV values generated by high speed and high load actuation while delivering reliability and long life is critical. Duvelco understands the nature of these critical controls and has exhaustive quality and traceability procedures in place for all aerospace-related materials.

Ducoya is compatible with a wide range of aerospace fluids, including Skydrol®. This can be useful in high pressure hydraulic cylinders.

Spoilers are important to safe and controlled landing. They are employed against high aerodynamic loads and must deploy reliably and quickly. The actuation system must reflect these requirements while minimising weight, friction and maintenance requirements.

Air brakes can provide manoeuvrability advantages to military aircraft. They can deploy under extreme aerodynamic loads with rapidity. They may also be employed repeatedly and frequently. In military aircraft, weight is at a particular premium and unnecessary friction must be eliminated to minimise the size and weight of the actuation system.

Ducoya’s low wear rate coupled with low density, low friction and high strength can be a useful solution for actuation of spoilers and air brakes. The ability to survive the high PV values generated by high speed, high load and frequent actuation is critical for air brakes. Reliable deployment of spoilers is important to all landings. Duvelco understands the difference materials can make to the performance of these systems. Duvelco invests in extensive research and development to enable Ducoya to be manufactured into the highest performance precision aerospace components.

Ducoya is compatible with a wide range of aerospace fluids, including Skydrol®. This can be useful in high pressure hydraulic cylinders.

Dynamic sealing elements in hydraulic pumps and motors can be exposed to high pressures and high sliding speeds, generating high Pressure-Velocity (PV) values. Providing reliable operation with minimal maintenance is a frequent design objective for both radial and axial hydraulic pumps and motors. Seal rings must be compatible with the chosen range of hydraulic fluids.

Low friction to maximise mechanical efficiency and minimum leakage to maximise hydraulic efficiency is generally desirable. Occasionally, low and controlled leakage is required to lubricate other areas of the pump or motor e.g. piston skirt, cam ring or swash plate etc.

To best control operating costs, a long wear life is very desirable, ideally maintenance-free for the life of the airframe.

Ducoya can excel in high PV conditions while delivering a long wear life, excellent sealing and low friction. Ducoya has high strength and low density, enabling operation at the very high pressures found in aerospace hydraulic systems.

Compared to metallic solutions, Ducoya is very simple to assemble, minimising manufacturing costs and potentially increasing First Pass Yield (FPY).

If you would like to learn more about the unique characteristics of Ducoya and its uses in the aerospace industry, please see our applications guide.

Engine Applications

Aerospace components for engines for commercial and military aircraft have a requirement for operating at high temperatures, minimising weight while exhibiting low wear in a harsh environment which often precludes use of lubricants. Minimisation of friction allows actuator sizes to be reduced, further saving weight. Parts must have long service lives to allow efficient operation with reduced maintenance costs.

Engine manufacturers are always seeking higher thrust-to-weight ratios and increased fuel efficiency. Increasing compression ratios and turbine temperature can help deliver this objective.

Ducoya® part properties allow high temperature operation with minimal oxidation, low friction, low wear and facilitates efficient air management in advanced compressor stage design.

Control Surfaces and Auxiliary Systems

Aerospace components for flight control systems can be characterised by the following requirements; frequent actuation, potentially high loads and the requirement to minimise weight and friction while ideally performing in service for the life of the airframe.

Parts also need to be compatible with a wide range of aviation fluids such as jet fuel, hydraulic oil, de-icing fluids, water and lubricants.

Ducoya polyimide parts can meet these challenges as well as being capable of being manufactured to tight tolerances. Ducoya exhibits low friction and low wear against a wide range of countersurfaces and is also not susceptible to corrosion. High compressive strength and a low density of 1.42 help keep component design weights within range. A limiting PV of 14.0 MPa.m/s unlubricated allows compact installation in a wide range of applications.