DERA's new Eurofighter aircrew suit. Diamond missile domes. DERA's micro air vehicle power solution scaled against a British 50-pence coin.

Anti-g suits have been common in fast jets for many years, but DERA says the suit it has designed for Eurofighter aircrew helps push out the parameters at which they can operate. The suit developed by DERA is unique to Eurofighter and, together with its associated life support system, provides crew functionality at altitudes up to 60,000 ft and acceleration up to +9g. Above 40,000 ft, aircrew receive pressurized oxygen to their mask. This reduces the risk of hypoxia, but may lead to distension and damage to the lung. DERA's Eurofighter flight jacket contains air-filled bladders surrounding the chest wall that are filled with a gas at the same pressure as gas in the mask. This is said to prevent lung distension. As with other aircrew clothing and anti-g systems, the trousers also contain bladders. These are similar to those in the jacket pressurized at increasing levels with increasing g's. DERA is understood also to be developing boots which contain small bladders to further reduce g-force effects.

A new fighter pilot helmet has also been developed by DERA, offering a weight reduction of 25-30% compared to conventional in-service types. It uses what DERA describes as "a novel composite sandwich structure" giving it equal impact protection at reduced weight — or advances in impact protection at the same weight — as current helmets. A clamshell design, it is said to allow the pilot to remove the helmet more easily and safely. The helmet integrates the breathing system, biochemical protection, active noise reduction, and communications equipment.

Composite research is a particular focus at DERA and the Agency has revealed that it has developed a novel method of joining lightweight sandwich panels. A problem when using sandwich construction may be the loss of load-bearing strength at a joint, which can lead to failure in a structure. Traditional joining techniques may use either a cut and fold method, or a cleated joint, often with bolts for extra strengthening, but that increases structure mass.

However, DERA claims that its new technique is four times stronger than traditional methods. It is a development of a comb joint, commonly used in carpentry. DERA explains that this corrugated joint comprises two ridged sections that are easily mated. These sections are incorporated in the end of the sandwich panels during the manufacturing process and replace the core material near the joint. When bonded together, the joint is virtually invisible. The corrugated joint provides a structurally efficient technique for any type of sandwich panel. It is very adaptive and can be used for joining panels at any angle. The technique is also successful for joints on a curved surface, linear panels, or T-joints. It is easy to manufacture, lightweight, and places the adhesive in shear. DERA sees applications including fuselages, engine cowlings, and flooring.

A very different area of materials research at DERA involves the development of a protective dome for hyper-velocity missiles. To find a solution, the Agency has been working with DeBeers Industrial Diamonds (DEBID); it decided that a diamond dome would meet all requirements. An infrared (IR) seeking missile dome needs to combine necessary optical properties with the ability to withstand rapid heating at launch and in the cruise, and to resist long-term sand and rain erosion during aircraft flight carriage. A long-term goal has been to find a material that could be used as a dome to enhance performance and help achieve lower ownership costs. Diamond was found to combine "unsurpassed" mechanical performance with excellent optical properties across the visible near-IR and far-IR spectrum.

DEBID developed a chemical vapor deposition (CVD) technique to manufacture the domes. This is a meta-stable process in which the diamond is formed from excited carbon atoms in a gaseous state. Diamond crystals thousandths of a millimeter in diameter form on a substrate and evolve into a continuous sheet of polycrystalline diamond. A low-pressure process, it enables conformal substrates to be used to produce three-dimensional diamonds. DERA explains that the domes are "grown" and configured by DEBID using proprietary CVD diamond synthesis and processing technology. The growth process has been developed to enable uniformity and morphology to be tightly controlled to tailor the properties of high-quality diamond specifically for IR dome applications. After growth, the domes have to be configured into optical components, accurately processing the inner and outer faces to be parallel with highly polished surfaces. The finished components exhibit low loss, negligible scatter at IR wavelengths, and are suitable for a wide range of imaging applications.

A 13-mm-long hydrogen peroxide-fueled engine has been developed as a powerplant for micro air vehicles (MAV) by DERA. Not entirely surprisingly, it is called Microjet. It could power an air vehicle having a wingspan of up to 152 mm, which could be used for very short-range tactical reconnaissance or for civil surveillance operations. Until now, no suitable form of propulsion system had been identified to power these tiny craft, according to DERA. Model aircraft engines and electrically driven propellers have been tried, but often problems relate to packaging or flight duration. For its solution to the requirement, DERA's system mixes hydrogen peroxide with kerosene or a similar fuel to give a duration of up to an hour. Starting (or stopping) the engine is achieved via a simple on/off valve. It can be used as a pure jet or in conjunction with a ducted fan. The development is not the result of a big-budget project, but came out of an internal DERA competition in which a small level of funding was made available to scientists to experiment with new innovations.

Stuart Birch

Aerospace Engineering October 2000