News 1998 Army Science and Technology Master Plan



D. Air Vehicles

1. Scope

DoD has assigned the Army as the lead for rotary wing science and technology in aeromechanics, flight control, structures, and subsystems supporting development of military rotary–wing air vehicles. The aviation community is aligning all planning documents to coincide with the DoD Director, Defense Research and Engineering (DDR&E) requirement to establish technological objectives, identify technical barriers, and establish milestones for achievement. Programs will be tracked by Office of the Secretary of Defense (OSD) to these detailed plans. The rotary–wing vehicle subarea is divided into four technology efforts: aeromechanics, flight control, subsystems, and structures. The objectives for each technology effort and the timeframes have been set in accordance with the DDR&E document, Rotary Wing Vehicle (RWV) Technology Development Approach (TDA), and are summarized below.

2. Rationale

Rotorcraft have become critically important members of the combined arms team, bringing a degree of deployability, mobility, lethality, and sustainability to the battlefield commander not available with other systems. With the continuing decrease in fiscal resources, affordability and dual use have become increasingly important in shaping Army Aviation’s S&T strategy. Technology must support solutions to real world problems, avoiding work that does not provide leap–ahead improvements in system capabilities. This is important to sustaining current systems because fielding new systems is being pushed further to the "outyears." From a dual–use perspective, civilian and military rotorcraft communities have a mutual stake in all but very few areas of rotorcraft technological research, such as reducing the vulnerability of rotorcraft in battlefield environments. Improvements in handling qualities, vibration, and sound level reductions are equally important to civil and military rotorcraft operators. It is estimated that 95 percent of the DoD investment in rotary–wing technology has civil application.

3. Technology Subareas

The air vehicle technology subareas are quantified at milestones of 2000, 2005, and 2010 and they support the systemic improvements articulated by the Defense Technology Area Plan (DTAP). These include:

Reduction in RWV empty weight fraction—7, 15, and 22 percent.
Increase in cruise efficiency—4, 11, and 20 percent.
Increase in maneuverability and agility—48, 66, and 112 percent.
Reduction in RWV maintenance cost—18, 35, and 50 percent.
Reduction in signature—35, 50, and 60 percent.
Reduction in development time (2005, 2010 milestones) 15 and 25 percent.
Reduction in RWV flyaway cost (2005, 2010 milestones) 35 and 50 percent.

a. Aeromechanics

Goals and Timeframes

Work in aeromechanics technology addresses efforts in multidisciplinary phenomena including acoustics, aerodynamic performance, rotor loads, vibration, maneuverability, and aeroelastic stability. Aeromechanics S&T seeks to improve the performance of rotorcraft while reducing the noise, vibrations, and loads inherent to helicopter operation. Efforts are focused on refining analytical prediction methods and testing capabilities, on improving the versatility and efficiency of modeling advanced rotorcraft, and on achieving dramatic advances through concept applications. Attaining the goal of a "jet–smooth ride" in helicopters will greatly enhance public acceptance, along with providing quieter rotorcraft. The goals are set at the component level and the associated milestones are provided in Table IV–4.

Table IV–4.  Aeromechanics Objectives

Aeromechanics

Improvement (%)

 

By 2000

By 2005

By 2010

Reduce vibratory loads

20.0

40.0

60.0

Reduce vehicle adverse aerodynamic forces

5.0

12.0

20.0

Increase maximum blade loading

8.0

16.0

24.0

Increase helo/rotor aerodynamic efficiency

3.0

6.0

10.0

Increase prop/rotor aerodynamic efficiency

1.5

3.0

4.5

Increase rotor inherent lag damping

33.0

66.0

100.0

Aeromechanics prediction effectiveness

65.0

75.0

85.0

Major Technical Challenges

Challenge—The inability to accurately predict and control stall and compressibility characteristics of current airfoils and their impact on unsteady loads and the resulting structural dynamic responses.

Approach—Investigate the influence of airfoil profile on development of dynamic stall in compressible flow, quantify influence of compressibility on flow control techniques, and develop innovative ways to use smart materials for flow control and structural response.

Challenge—The inability to accurately predict and control forces caused by viscous and interactional aerodynamics and separated flow.

Approach—Enhance flowfield visual techniques using Doppler global velocimetry; study various models’ rotor wake and fuselage pressure distributions using isolated rotor test system. Calculate adverse forces using validated computational fluid dynamics (CFD) and comprehensive analyses. Develop reliable, validated engineering computational codes based on full–potential, vortex embedding techniques to predict rotor performance and loads in all flight regimes.

Challenge—The inability to accurately predict and control stall and compressibility characteristics of current airfoils along the span of the rotor blades and their impact on blade loading limits. The inability to markedly increase maximum outboard blade lift coefficients.

Approach—Develop high dynamic–lift stall–free airfoils with multi–element concepts such as slat, slots, variable leading edges, or boundary layer controls.

Challenge—The inability to predict and control the effect of the rotor wake and blade response on unsteady aeroacoustic loads. Controlling compressibility effects on advancing–blade acoustic sources and propagation phenomena is hampered by the interdependence of numerous parameters that influence noise radiation.

Approach—Develop verified CFD code to predict wake geometry, airloads, and performance for rotor blades, in particular blade–vortex interaction regimes and the resulting aeroacoustics.

Challenge—Identify successful combinations of aeroelastic rotor couplings to increase damping. The constraints include conflicting design requirements, rotary–wing operating regime diversity, and fail–safe reliability requirements.

Approach—Investigate kinematic and smart structures couplings that result in less dependency on separate damping devices. Utilize parametric rotor testing to substantiate prediction fidelity of marginally damped rotor configurations.

Challenge—The lack of solutions to the multidisciplinary rotorcraft system phenomena. Significant difficulty in acquiring high–quality correlation data for validation. Prediction–to–design interface inadequate for complex rotorcraft synthesis.

Approach—Prediction effectiveness attributes defined and composed against data to determine element accuracy. Metrics for improvement shall include quantifiable subelement effectiveness and system integration value, such as in a product and process development simulation.

b. Flight Control

Goals and Timeframes

Flight control technology defines the aircraft flying qualities and pilot interface to achieve desired handling qualities in critical mission tasks, synthesizes control laws that will facilitate a particular configuration’s achieving a desired set of flying qualities, and integrates advanced pilotage systems to the aircraft. Helicopters are inherently unstable, nonlinear, and highly cross coupled. As with many other technologies, the revolution in the power and miniaturization of computers holds tremendous promise in this field, permitting realization of the full potential of the rotorcraft’s performance envelope and maintenance of mission performance in poor weather and at night. The objectives are provided in Table IV–5.

Table IV–5.  Flight Control Objectives

Flight Control

Improvement (%)

 

By 2000

By 2005

By 2010

Improvement in platform flight path pointing and accuracy (attack only)

50

65

80

Improve external load handling qualities at night (cargo only)

75

185

225

Reduce the probability of encountering degraded handling qualities due to flight control system failures

40

65

90

Improved handling qualities at night with partial actuator authority CHPR 4* CHPR 3* CHPR 3*

Increase in precision maneuvering at extreme load factors

20

35

50

* CHPR = Cooper Harper Pilot’s Rating

Through the integration of the vehicle’s flight control system with weapons fire control, significant improvement in pointing accuracy will be achieved by the turn of the century and will permit increased use of low–cost, unguided rockets as precision munitions. Further, a significant development cost driver is being assessed. Objectives have been set to: improve external load handling qualities at night with partial actuator authority (from a Cooper Harper Pilot’s Rating (CHPR) of 4 to 3) reduce the probability of encountering degraded handling qualities due to flight control system failures 40 percent to 90 percent, and improve the flight path and accuracy by 50 percent to 80 percent. Reduction in flight control system flight test development time should be realized. Time span for accomplishment is from the present through year 2010, with an intermediate milestone at year 2005.

Major Technical Challenges

Challenge—Lack of knowledge of optimal rotorcraft response types (rate, attitude command/attitude hold, translational rate command) and their interactions with load suspension dynamics and load aerodynamics.

Approach—Use piloted simulation and flight test to investigate handling qualities requirements for external loads. Develop appropriate criteria for poor weather and darkness. Extend efforts to address high speed flight and loads with significant aerodynamic interactions.

Challenge—Lack of techniques for sensing the onset of limits, determining appropriate actions, and cueing the pilot or generating automatic interference to permit the pilot to safely, but aggressively, fly the rotorcraft out to the limits of the flight envelope.

Approach—Use analysis and piloted simulation to develop techniques for protecting the pilot from loss of control and avoiding catastrophic failures or reduced fatigue life. Validate critical concepts in–flight, using a variable stability helicopter.

Challenge—Inadequate air vehicle mathematical modeling and flight control system (FCS) design, optimization, and validation techniques. These deficiencies prevent achieving desired handling qualities for advanced configurations and critical mission tasks, without time consuming iteration during flight test.

Approach—Improve mathematical modeling and simulation fidelity so that new aircraft actually fly as designed. Improve techniques for updating math models and control laws to minimize time required to diagnose and eliminate deficiencies. For advanced fly–by–wire flight control systems, develop simpler redundancy management and software verification and validation (V&V) techniques so that time for making changes can be reduced.

Challenge—Lack of knowledge of optimal functional integration of flight controls, engine fuel control, the weapon systems, and the pilot interface.

Approach—Develop a viable integrated fire and flight control (IFFC) system architecture, conduct manned full–mission simulation, ground demonstration of hardware and software for airborne vehicle application, and flight test demonstration of the IFFC concept.

c. Structures

Goals and Timeframes

Focusing on integrated product and process development (IPPD), rotary–wing structures S&T aims at improving aircraft structural performance while reducing both acquisition and operating costs of the existing fleet of aircraft and future systems. The technical feasibility of load synthesis methods (holometrics, et al.) and regime/flight condition recognition algorithms as means to predicting the actual loads experienced in–flight has been demonstrated; further improvements to the reliability of these methods will enhance the safety, performance, and cost effectiveness of rotorcraft. "Virtual prototyping" of systems to optimize the structural design for efficiency and performance will remove a large portion of the risk in exploring new concepts and rapidly move the most promising concepts to production. The objectives are provided in Table IV–6.

Table IV–6.  Structures Objectives

Structures

Improvement (%)

 

By 2000

By 2005

By 2010

Reduction in (structural component weight)/gross weight (GW)

5

15

25

Reduction in structures manufacturing, LH/lb

10

20

40

Reduction in structural component development time

25

40

Increased accuracy of structural load predictions

75

85

Increased accuracy of in–flight cumulative fatigue damage predictions

95

98

Increased displacement capability of smart materials actuator

300

500

Reduction in dynamically loaded structure stress prediction inaccuracy

30

50

Breakthroughs in these areas will effect improvements in maintenance and production costs, as well as reduce the empty weight fraction of the airframe, while increasing durability, performance, and ride comfort of rotorcraft. In FY97, progress was made in the definition of a structural configuration and its associated metrics for the Rotary Wing Structures Technology Demonstration (RWSTD). This included the determination of advanced structural concepts and appropriate exit criteria. Other accomplishments included the characterization and selection of low cost, embedded cure rheology sensors, and the development of fuzzy logic cure control algorithms. In FY98, the initiatives will include establishing an RWSTD system architecture to integrate distributed design disciplines, knowledge–based design tools and databases for the rapid development of novel structural concepts, demonstrating the use of adhesives to bond and co–cure primary structures in lieu of fasteners, developing analytical methods that will calculate the high impulse crash loads in landing gear fittings, and demonstrating the ability of closed–loop, fuzzy logic cure process control, using in–situ rheology measurements, to adapt to material and process variations.

Major Technical Challenges

Challenge—Lack of knowledge about and accurate methodologies for flight regime recognition algorithms for determining the rotorcraft flight conditions from state parameters in a dynamic environment. Lack of knowledge about and accurate methodologies for the synthesis of strains/loads from other measured parameters and loads in a dynamic environment. Limited fatigue life and durability of load/strain measuring sensors in a dynamic operational environment.

Approach—Develop and refine flight regime/flight condition recognition and load synthesis algorithms based on aircraft state parameters and other measured loads. Conduct bench and flight test evaluations on instrumented aircraft to validate accuracy. Collect operational data over a period of 1–3 years to validate the reliability of the flight data recorder and the algorithms.

Challenge—Lack of knowledge of accurate algorithms for determining the rotorcraft flight condition from state parameters in a dynamic environment.

Approach—Develop and refine regime/flight condition recognition algorithms based on aircraft state parameters. Conduct bench and flight test evaluations on instrumented aircraft to validate accuracy. Collect operational data over a period of 1–3 years to validate the reliability of the flight data recorder and regime/flight condition recognition algorithms.

Challenge—Inability to sense and measure rheological behavior of materials during cure, lack of optimization techniques to minimize scrap, insensitivity of embedded sensors for adaptive control of cure cycle, lack of defect characterization and impact on structural performance, lack of process simulation models, ineffective application of automated fiber placement/ply handling methods to lean manufacturing, and inability to measure bond integrity.

Approach—Design and fabricate representative components to demonstrate advanced manufacturing technologies and tooling techniques. Investigate manufacturing process simulation models through cure prediction, cure cycle optimization, and structural testing to validate cure cycle optimization and structural efficiency. Demonstrate the use of embedded sensors for adaptive control of the cure cycle through fabrication and test of representative rotorcraft components. Develop and demonstrate the use of nondestructive inspection techniques for determining the integrity of bonded structures.

Challenge—Lack of knowledge about and understanding regarding multidisciplinary design, control of rheological properties during curing, static and fatigue strain limits, fiber marcelling during braiding and weaving, and innovative configurations and concepts tailored to advanced materials applications.

Approach—Develop innovative structural design configurations using advanced materials tailorable for structural efficiency. Develop and demonstrate representative rotorcraft structures using IPPD to optimally meet multidisciplinary design requirements, which include cost, weight, performance, and reliability. Fabricate structural components in sufficient quantities to validate the quality, manufacturing repeatability, structural efficiency, and recurring cost. Develop and demonstrate advanced braiding and weaving equipment and methods to minimize fiber breakage and marcelling. Fabricate structural preforms and incorporate these preforms into tailored structural fittings and components to validate the structural efficiency and recurring costs.

Challenge—Limited displacement capability, limited force capability, limited high cycle fatigue life, and high power requirements of existing smart materials.

Approach—Investigate the force, displacement, and power requirements of new and emerging smart materials for advanced rotor actuation methods, conduct tradeoff analyses, and demonstrate smart materials applications to rotor actuators through laboratory testing in a dynamic environment.

Challenge—Inability to model and analytically predict the rotating and fixed system structural loads and the interaction of those loads with the vehicles’ aerodynamic environment. Inability to conduct detailed stress analyses of complex components under large deformations in a timely manner to support IPPD. Inability to accurately predict crushing loads and behavior of airframe structures in a dynamic crash environment.

Approach—Develop and validate enhanced comprehensive methods that incorporate multidisciplinary technology based on finite element techniques that include composite structures modeling, specifically concentrating on the rotor system loads and aeroelastic stability analysis. Develop and validate reliable finite element analysis modeling and simulation techniques that include large strain effects required to model the energy absorbing characteristics of crushable composite structures.

d. Subsystems

Goals and Timeframes

RWV subsystems encompass a broad range of S&T topics related to the support, sustainment, and survivability of increasingly complex aircraft systems and to the unique problems associated with the application of high performance weapons on rotorcraft. In addition to addressing affordability issues for operation and support (O&S) costs, this area also encompasses the extension of the useful life of weapon systems through upgrading armament and other mission equipment.

The objectives are provided in Table IV–7.

These key technological objectives have been established: reductions in radar cross sections (RCSs) and visual/electro–optical signatures, increased hardening against ballistic and NBC threats, and the autodetection of incipient critical

Table IV–7.  Subsystems Objectives

Subsystems

Improvement (%)

 

By 2000

By 2005

By 2010

Reduction in 0.4–0.7
micron (
mm) visual

35

50

60

Reduction in 3–5 mm IR signature

35

50

60

Reduction in 8–12 mm IR signature

35

50

60

Reduction in threat protection weight vs. gross weight

5

10

20

Reduction in total maintenance

15

30

45

Autodetection of critical component

40

60

75

mechanical component failures. Attainment of these objectives will translate into aircraft requiring fewer maintenance hours per flight hour, while still performing safely and effectively in a hostile environment.

Major Technical Challenges

Challenge—Modeling and analytical predictions for characterization of component materials and integration concepts performance in signature suppression are needed.

Approach—Conduct computer modeling from signature prediction to battlefield simulations. Conduct laboratory and flight testing of cost–effective attenuating materials and design concepts that will reduce IR, RCS, acoustic, visual, and EO emissions from rotorcraft.

Challenge—Modeling and analytical predictions for characterization of component materials and integration concepts performance in hardening are needed.

Approach—Conduct computer modeling of hardening concepts to provide reduced probability of kill across the full spectrum of known threats, as well as crash impacts. Conduct demonstrations of components and of the integration of lightweight armor, directed–energy weapons (DEWs), and nuclear, biological, and chemical (NBC) hardening that balance cost, weight, and effectiveness.

Challenge—Lack of reliable, rugged, cost–effective, nonintrusive monitoring techniques, sensors, algorithms, and methods.

Approach—Develop a quantified database of the performance of impending component failures. Conduct laboratory and field testing of advanced sensors and monitoring systems.

4. Roadmap of Technology Objectives

The roadmap of technology objectives for Air Vehicles is shown in Table IV–8.

5. Linkages to Future Operational Capabilities

The influence of this technology area on TRADOC FOCs is summarized in Table IV–9.

Table IV–8.  Technical Objectives for Air Vehicles

Technology Subarea

Near Term FY98–99

Mid Term FY00–04

Far Term FY05–13

Aeromechanics Aeroacoustic and aeroelastic prediction codes verified and incorporated in comprehensive analysis

Rotor/fuselage interaction CFD–unique experiments

High–lift rotor concepts evaluated

Low–cost, high–efficiency rotor design methodology initiated

CFD/inflow analysis verified

Reduce critical unsteady loads by 50%

Reduce vehicle parasite drag by 15%

Increase in maximum blade loading by 15%

Increase in rotor lift/drag by 8%

Increase in rotor figure of merit by 7%

Reduce critical unsteady loads by 70%

Reduce vehicle parasite drag by 30%

Increase in maximum blade loading by 25%

Increase in rotor lift/drag by 15%

Increase in rotor figure of merit by 12%

Flight Control Establish cargo/slung load flight test maneuvers; conduct simulations to develop criteria for hover and low speed

Complete terrain correlated turbulence model

Develop and transition advanced control law synthesis techniques

Complete comprehensive identification from frequency responses (CIFER) UNIX upgrade and train industry

Complete IFFC piloted ground simulations

Develop techniques for pilot–envelope cueing and limiting

Improve slung load handling qualities to a CHPR of 4

70% increase in bandwidth while maintaining gust rejection capability

60% improvement in weapon–platform pointing accuracy techniques

66% reduction in envelope maneuvering margins

Improve slung load handling qualities to a CHPR of 3

80% increase in bandwidth while maintaining gust rejection capability

80% improvement in weapon–platform pointing accuracy techniques

75% reduction in envelope maneuvering margins

Structures Define RWST structured configuration and requirements

Select critical components for development, testing, and demonstration in RWST

Complete fabrication and testing of resin transfer molding (RTM) trial beam for RAH–66, thermoplastic (TP) horizontal stabilizer for OH–58D, and TP tailboom section for the RAH–66 baseline

TP horizontal stabilizer and TP tailboom section for the RAH–66

Develop system architecture for manufacturing and tooling expert system (MATES) and preliminary design concept for damage tolerant hub fixture for RAH–66 baseline

Initiate the harmonization of civil and military design requirements, specifications, standards, and the application and refinement of IPPD principle to reduce life–cycle costs

95% accuracy for loads synthesis

30% reduction in recurring production labor hours per pound for composite structures

200% increase in displacement capability of smart materials actuators

98% accuracy with flight regimes recognition algorithms

98% accuracy for loads synthesis

50% reduction in recurring production labor hours per pound for composite structures

400% increase in displacement capability of smart materials actuators

35% increase in structural efficiency

Subsystems 100% probability of detection of impending failures of structural components

20% increased operational durability and repairability of reduced signature materials

15% reduction in infrared and visual electro–optic vehicle signatures

10% increase in ballistic and NBC hardening technique

30% reduction in signatures

25% improvement in ballistic and NBC hardening techniques and concepts

95% probability of detection of impending component failures

35% reduction in signatures

30% improvement in ballistic and NBC hardening techniques and concepts

98% probability of detection of impending component failures

 

Table IV–9.  Air Vehicles Linkages to Future Operational Capabilities

Technology Subarea

Integrated and Branch/Functional Unique Future Operational Capabilities

Aeromechanics TR 97–022 Mobility—Combat Mounted
TR 97–023 Mobility—Combat Dismounted
TR 97–029 Sustainment
TR 97–037 Combat Vehicle Propulsion
TR 97–040 Firepower Lethality
TR 97–043 Survivability—Materiel
Flight Control TR 97–002 Situational Awareness
TR 97–016 Information Analysis
TR 97–017 Information Display
TR 97–022 Mobility—Combat Mounted
TR 97–037 Combat Vehicle Propulsion
TR 97–040 Firepower Lethality
EN 97–001 Develop Digital Terrain Data
Structures TR 97–022 Mobility—Combat Mounted
TR 97–024 Combat Support/Combat Service Support Mobility
TR 97–026 Deployability
TR 97–029 Sustainment
Subsystems TR 97–002 Situational Awareness
TR 97–022 Mobility—Combat Mounted
TR 97–024 Combat Support/Combat Service Support Mobility
TR 97–026 Deployability
TR 97–029 Sustainment
TR 97–035 Power Source and Accessories
TR 97–037 Combat Vehicle Propulsion
TR 97–040 Firepower Lethality
EN 97–001 Develop Digital Terrain Data

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