News 1998 Army Science and Technology Master Plan



3. Air Vehicles

Rotorcraft are of particular interest to the Army. They are, and will remain, essential for a variety of critical scout, transport, and combat missions. The operational flexibility afforded by vertical takeoff and landing (VTOL) capabilities has created growing civil and military markets, particularly in third world nations. As a result, the helicopter industry has become highly internationalized and interdependent. In addition to the capabilities in the U.S.–Canadian industrial base, Germany, France, the United Kingdom, Russia, and Italy are all capable of designing and producing state–of–the–art military rotorcraft. Japan, Malaysia, India, and South Africa all have substantial capabilities for rotorcraft production. India and South Africa have indigenous military helicopter development programs. Other countries, notably Malaysia and China, have acquired modest capabilities (principally through licensing arrangements with other countries) in rotorcraft manufacturing to meet local market needs. These countries are not currently at a level that would contribute to significant advances in technology, but could develop niche capabilities in the future.

Competition for international military sales is intense and marketing rights and export prospects have affected a number of development decisions, particularly in international programs. Such market forces continue to push worldwide developments. Foreign capabilities may offer opportunities to reduce the cost of improving each of the key technology subareas: aeromechanics, flight control, structures (including survivability and as a major consideration signature reduction), and subsystems. Table E–6 and the following paragraphs summarize potential prospects.

Table E–6.  International Research Capabilities—Air Vehicles

Technology

United Kingdom

France

Germany

Japan

Asia/Pacific Rim

FSU

Other Countries

Aeromechanics 1s.gif (931 bytes) Rotorcraft design 1s.gif (931 bytes) Rotorcraft; CFD 1s.gif (931 bytes) Rotorcraft 5s.gif (958 bytes) CFD; hypervelocity   Russia

3s.gif (977 bytes) Wind tunnel test facilities

Italy, Israel, Sweden

5s.gif (958 bytes) Aeromechanical design

Flight Control 2s.gif (968 bytes)Active harmonic control 1s.gif (931 bytes) Adaptive controls; fly–by–light 1s.gif (931 bytes) Control theory       Sweden

5s.gif (958 bytes) Adaptive controls

Structures 1s.gif (931 bytes)Composites

2s.gif (968 bytes) Smart structures

1s.gif (931 bytes) Crash survivability; C–C matrix ceramic

2s.gif (968 bytes) Smart structures

1s.gif (931 bytes) Smart structures; fatigue 1s.gif (931 bytes) Ceramics; composite materials & structures Malaysia, China

5s.gif (958 bytes) Rotorcraft

Russia

2s.gif (968 bytes) Rotorcraft structures; Ti & steel alloy structures

Canada

4s.gif (949 bytes) Fracture/
fatigue analysis

Italy

5s.gif (958 bytes) Rotorcraft structures

Subsystems 1s.gif (931 bytes) FADEC; rotor systems 2s.gif (968 bytes) 2s.gif (968 bytes) Advanced cockpit systems 5s.gif (958 bytes) Avionics cockpit system 5s.gif (958 bytes) 5s.gif (958 bytes) Israel

5s.gif (958 bytes) Advanced cockpit systems

Note: See Annex E, Section A.6 for explanation of key numerals.

 

a. Aeromechanics

Aeromechanics technology includes multidisciplinary efforts in acoustics, aerodynamics, rotor loads, vibration, maneuverability, and aeroelastic stability. The goal is to improve the performance of rotorcraft while reducing noise, vibration, and stress loads inherent in helicopter operation. Major efforts involve refining analytical prediction methods and testing capabilities, and improving the versatility and efficiency of modeling advanced concepts. Another area of interest is attaining a smoother and quieter ride, which will improve performance and also enhance public acceptance. Technical challenges include the inability to accurately predict and control a number of factors:

Stall and compressibility characteristics of airfoils
Viscous and interactive aerodynamics and separated flow forces
Rotor blade forces and loading limits
Effects of rotor wake and blade response
Aeroelastic rotor couplings to increase damping.

The proliferation of low–cost, high–performance computing (HPC) systems has lead to a growing worldwide interest in computational fluid dynamics (CFD) to address many of these issues.

Use of CFD for design of rotors and blades can enhance helicopter speed, maneuverability, and lift capabilities, while reducing acoustic signatures and structural vibration. While the United States is the world leader in CFD and related techniques, France, Germany, and Israel have complementary world–leading efforts to improve and develop analytical techniques and generate experimental databases that may contribute to ASTMP goals in this area. The U.K. has strong capabilities in rotor and overall rotorcraft design, and Italy and Sweden have noteworthy capabilities in aeromechanical design. In addition, Japan has special skills in CFD especially related to hypervelocity vehicles, and finally, Russia has special strengths in wind tunnel test facilities. Russia has also fielded some of the most capable military rotorcraft in terms of aerodynamic performance (speed and lift capability).

b. Flight Control

Flight control technology defines the aircraft’s flying qualities and the pilot interface. Helicopters are inherently unstable, nonlinear, and highly cross–coupled. Advances in smaller, more powerful computers hold tremendous promise in this field, to allow realization of the full potential of the rotorcraft’s performance envelope and maintenance of performance even in poor weather and at night. Integrating flight control with weapons control is of great interest, to permit improved pointing accuracy and the use of lower–cost unguided rockets as precision munitions. Other goals include improved external load handling at night, and increased exploitable agility and maneuverability. Technical challenges in flight control include:

Knowledge of rotorcraft response and interactions with load suspension dynamics
Sensing the onset of limits and cuing the pilot to fly safely at or near the envelope limits
Air vehicle mathematical modeling for control system design, optimization, and validation
Knowledge of optimum functional integration of flight controls, engine fuel control, weapons systems, and the pilot interface.

Foreign countries leading in flight control technology include the United Kingdom, France, and Germany. The U.K. has special capabilities in harmonic control for noise reduction. France has strong capabilities in adaptive controls and in fly–by–light technology. Germany has strengths in several areas that are of interest. One of the most important relates to ground–based and in–flight simulation studies on handling qualities. Specific areas of concern are the investigation of cross–coupling requirements, gust rejection for rate response systems, and the response time delay limits for high bandwidth response systems. Continuing work using Germany’s in–flight simulator and correlated U.S. ground–based simulators has produced a viable database to build on, which could not be accomplished using U.S. assets alone. In the area of stability and control analysis, the U.S. predominantly uses a frequency domain method, whereas the Germans predominantly use a time–domain approach. Each technique has inherent advantages and disadvantages. A coordinated approach combining the strengths of both techniques yields the most promising path to success in detailing complete and accurate portrayal of flight control system design and performance parameters. This technology provides a critical link bridging theoretical design, prediction, simulation, and test analysis. In addition, Sweden has some ongoing efforts in adaptive controls that are of interest.

c. Structures

Science and technology related to structures aims at improving aircraft structural performance while reducing both acquisition and operating costs. Virtual prototyping to optimize structural design for efficiency and performance is of particular interest to remove a large portion of the risk involved in exploring new concepts and moving rapidly from concept to production. An integrated product and process development approach will be used. The reduction in dynamically loaded structural stress prediction inaccuracy is another area of great interest, as is reducing the production labor hours per pound for composite structures. Breakthroughs in these and other areas will lead to improvements in maintenance and production costs, as well as reducing the empty weight fraction of the airframe, while increasing durability, performance, and ride comfort. Technical challenges in structures include:

Accurate methodologies for flight regime recognition algorithms
Accurate algorithms for determining rotorcraft flight condition from state parameters in a dynamic environment
Sensing and measuring rheological behavior of materials during cure
Multidisciplinary design and production techniques to meet cost, weight, reliability, and performance requirements
Advances in smart materials
Modeling and analysis of rotating and fixed system structural loads and their interactions with the vehicle’s aerodynamic environment.

Advanced composite structures and fly–by–wire/light are becoming common in international aircraft. Technologies for military systems reside primarily in the few countries that produce military helicopters. Predominant among these are France, Germany, the United Kingdom, and Italy. The United Kingdom has strong capabilities in composites and in smart structures. Crash survivability is an area of special interest. France has expertise and in general is on a par with the United States in this area. Survivability depends on a number of factors including equipment performance, which may be enhanced by more efficient design and testing of aircraft structures. Of particular interest is the testing of advanced structural concepts and manufacturing processes for composite and thermoplastic materials for primary helicopter airframe structures. In addition to the above countries, Canada has strong capabilities in fracture/fatigue analysis, and Russia in titanium and steel alloy structures. Finally, Japan has world–class expertise in ceramics and composite materials.

d. Subsystems

Rotary–wing vehicle subsystems encompass a broad range of S&T topics related to support, sustainment, and survivability of aircraft systems and their associated weaponry. Five key technology areas are of interest:

Reduction of radar cross section (RCS)
Reduction of infrared (IR) signature
Reduction of visual and electro–optic (EO) signature
Increased hardening to threats
Increased probability of detecting incipient mechanical component failures.

Technical challenges relate to modeling and analytical predictions for components and materials used in signature reduction and hardening against threat, and developing rugged, cost–effective, nonintrusive monitoring techniques, sensors, algorithms, and methods.

Several countries have capabilities of interest in subsystems for rotorcraft. Germany, Japan, and Israel all have strong capabilities in advanced cockpit systems, but the German work on cockpit integration is of special interest. Germany is a recognized world leader in cognitive decision–aiding, knowledge–based systems and in high–speed data fusion. It is actively pursuing integration of these capabilities in vehicle driving systems that could be of significant value. The United Kingdom is doing significant work on full authority digital engine control (FADEC). In addition, Japan has strong capabilities in avionics, based upon its world–class electronics capability.

AMC POC: Dr. Rodney Smith
Army Materiel Command
AMXIP–OB
5001 Eisenhower Blvd.
Alexandria, VA 22333–0001
e–mail: icpa@hqamc.army.mil

IPOC: Mr. Dennis Earley
U.S. Army AMCOM
St. Louis, MO 63120–1798
e–mail: earleyd@avrdec.army.mil

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