Mission and Concept Evaluation for a Multirole

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Aircraft Design 2 (1999) 65}80

Mission and concept evaluation for a multirole,mission-adaptable air vehicle

V.L. Wells*, J.W. Rutherford, A.M. Corgiat

Department of Mechanical and Aerospace Engineering, Arizona State University, Box 876 106, Tempe,

AZ 85287-6106, USA

US Army Aviation and Troop Command, Huntsville, AL, USA

Received 8 January 1999

Abstract

The paper describes the results from a concept exploration study to assess the feasibility of a modu-

lar/recon"gurable rotorcraft designated the `multirole, mission-adaptable air vehicle (MRMAAV)a. The

initial phase of the study consisted of developing mission and operational requirements for the vehicle. This

phase resulted in the assessment that the aircraft should be considered primarily an attack vehicle but with

the capability, through recon"guration, for performing several alternate missions. Evaluation of several

high-speed rotorcraft concepts led to the selection of two platform con"gurations for further study. Theseincluded the variable-diameter compound helicopter (VDCH) and the joined-wing tilt rotor (JWTR).

Detailed sizing e!orts focused on the VDCH as the more feasible of the two concepts. Innovative aspects of

the air vehicle include variable-diameter main rotor, turboshaft/turbofan convertible engine, virtual-canopy

cockpit, and recon"gurable payload bay. The mission-equipment package is highlighted by an autonomous

remote sensor platform. The study identi"es areas which best lend themselves to a modular or recon"gurable

design approach and describes in detail a candidate vehicle meeting the MRMAAV objectives. 1999

Published by Elsevier Science Ltd. All rights reserved.

1. Introduction

For decades, visionary US leaders have provided for the strategic development of superior

military equipment, training and doctrine that have enabled the optimization of the soldier intoday's battle"eld environment. However, because of the rapidly changing global situation, a newdirection is forseen for the soldier and the Army of the future. Imminent challenges include resource

*Corresponding author.

E-mail address: [email protected] (V.L. Wells)

1369-8869/99/$ - see front matter 1999 Published by Elsevier Science Ltd. All rights reserved.PII: S 1 3 6 9 - 8 8 6 9 ( 9 9 ) 0 0 0 0 3 - 8


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constraints and the proliferation of technology, and yet the next-generation Army must possess the

ability to operate as a quick reaction, globally self-deployable force incorporating new operationalconcepts such as fully integrated operations of US Military Services. Such projects as Joint Vision

2010, Force XXI and Army After Next (AAN) provide a conceptual framework from which the USArmed Forces can formulate a blueprint for the upcoming decades. Emerging from these e!orts are

the attributes that will characterize the military beyond the year 2010 } strategically mobile, covert,force projecting and sustaining, and expandable.

To meet the emerging challenges set forth in Joint Vision 2010 and AAN, the Aviation ResearchDevelopment and Engineering Center (AVRDEC) of the Army Aviation and Troop Command

(ATCOM) has conceptualized a future air vehicle, termed the multirole mission-adaptable airvehicle (MRMAAV). In principle, this vehicle will be mission-recon"gurable for use in a variety of

joint-venture aviation roles. A high degree of subsystem modularity is envisioned for this aircraft.Flight controls, structures, avionics, propulsion, weapons and the con"guration itself all present

opportunities for modular design. The mission #exibility available through the use of a single

platform of this type represents the greatest advantage of the MRMAAV approach. Such versatilityenhances the vehicle utility and reduces the need for multiple platforms with their respective costlyinfrastructures. For example, training, maintenance, supply, and manpower requirements diminish

in complexity and cost if one vehicle can replace up to three others in the #eet, and large life-cyclecost savings would result from the "elding of such a multi-use aircraft. Commanders in the "eld

would inherently possess assets capable of performing a multiplicity of missions, simplifying theforce structure, allowing increased #exibility in tailoring the force and reducing dependency on the

availability of external assets.The concept of modular, recon"gurable systems has been successfully employed with other

Army systems. The HUMMV probably represents the best recent example of this approach. This

vehicle is available in many con"gurations ranging from weapons carrier to communicationscenter to "eld ambulance. The current challenge is to apply this philosophy to an aircraft which ismore sensitive than a ground vehicle to large excursions in design parameter values. While this

appears formidable, emerging technologies, coupled with a design e!ort speci"cally orientedtoward achieving this goal may prove the practicality of such a system.

The following describes results from a concept exploration study to oversee the feasibility of

a modular/recon"gurable rotorcraft. The study identi"es candidate areas that best lend themselvesto a modular design approach and speci"es high risk technology areas that, if developed, couldenable the development of otherwise marginally feasible modular concepts.

1.1. Mission requirements

The initial phase of the project consisted of developing mission and design objectives. Recogniz-

ing that no requirement for a multi-mission vehicle currently exists, the "rst step in the designprocess consisted of developing notional missions and goals. Though the Army has no speci"c

mission capabilities de"ned for the MRMAAV, some initial guidelines for development of therequirements were provided. These include:

1. The vehicle should have tri-service applicability with emphasis on Army and Marine Corpsneeds.

66 V.L. Wells et al. / Aircraft Design 2 (1999) 65}80


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Table 1

Extended-attack sizing mission

Segment Condition Distance Speed Time

Take o! HOGE 5 min

Cruise to forward assembly area 4000, 953F 150 Nmi 350 kt

Forward assembly to holding area NOE 20 Nmi 40 kt

Holding area to battle position NOE 10 Nmi 40 kt

Battle position HOGE 40 min

Battle position to air control point NOE 5 Nmi 40 kt

Cruise to rear assembly area 4000, 953F 150 Nmi 350 kt

Reserve 350 kt 20 min

Land HOGE 5 min

2. The vehicle should perform in attack, utility, scout, and search and rescue roles.3. The vehicle should require a maximum of one pilot. Autonomous capability for some roles

should be considered.4. The vehicle should carry four troops or two stretchers.

5. The vehicle should have the capability for escorting V-22.6. The vehicle must have VTOL capability with a vertical rate of climb of 400 ft/min.

7. The vehicle should be self-deployable up to a range of 2100 Nmi.

The requirement for tri-service applicability immediately speci"es the maximum dash speedwhich the vehicle must attain. To function as an escort for the V-22 Tilt Rotor, it must have the

capability to #y faster than the V-22. This requirement indicates the need for a high-speedrotorcraft and rules out a conventional helicopter. However, the bulk of the missions other thanV-22 escort do not require high speed; in fact, helicopter-like attributes dominate. Table 1 outlinesthe extended-attack mission used to size the vehicle. The entire mission is #own with 2860 lb of

weapons and ammunition.

2. Selection of modular components

`MRMAAVa implies that the vehicle perform a variety of missions through the use of a singleairframe. Aviation history is replete with attempts to accomplish multiple missions with a single

aircraft only to compromise their capabilities so much that they could reach only a mediocre levelof performance in any one capacity. Designers of these vehicles attempted to include the multi-mission capability completely within the weapons system so that performance of each mission waspenalized for the capability of performing some other mission. It is the philosophy of the

MRMAAV concept to tailor the air vehicle to the particular mission through modularity andrecon"gurability so that it becomes optimized for the speci"c mission to be accomplished. Whilethis seems to be a very di$cult goal to achieve, again history rescues the designer, particularly in

rotorcraft development, with examples. During the Vietnam War, UH-1s (Hueys) equipped withguns and rockets became the "rst armed helicopters with the added capability to carry troops or

V.L. Wells et al. / Aircraft Design 2 (1999) 65}80 67


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Fig. 1. Mission/design characteristics QFD matrix.

payload. The CH-54, Tarhe included a `people poda to transport troops although its design was

intended primarily to carry large external loads. Tilt wings and tilt rotors represent concepts thatrecon"gure from hovering vehicles to high-speed capable vehicles in #ight.

The initial task, given the array of missions for MRMAAV, was to determine which vehicle

attributes lend themselves to the modular approach. A Qualify Function Deployment (QFD)exercise provides a systematic means for assessing the importance of each subsystem to a given

mission. Through weighting of the missions, those characteristics scoring highest re#ect those

needed most across the mission spectrum. Those scoring low (those not needed often or thoseneeded only for a particular mission) represent opportunities for introducing modular componentswhich con"gure the system speci"cally for a certain role while maintaining the generality of the

platform itself. Fig. 1 shows this relation. A high value (3) in the matrix represents a strongdependence of the mission on the characteristic, while a low number (1) represents little depend-

ence. Results obtained using the QFD procedure indicate that the attack mission has the highestrelative importance factor by a considerable amount signifying that the design process shouldultimately focus on this mission.

The relative importance among the design characteristics, tabulated along the bottom row, is

determined by multiplying the abovementioned relative importance factor by the characteristic'sdependence strength and adding down the columns. The totals show that there are several

characteristics important to all of the missions: crash survivability, high ballistic tolerance,environmental hardening, su$cient pilot "eld of vision, and deployability.

In a similar manner, engineering attributes are related to the mission characteristics in Fig. 2.

3. Air vehicle description

The terms `modulara and `recon"gurablea evoke visions of removing and replacing parts of theaircraft depending on the mission. Candidates for this may include wings, fuselage parts and



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Fig. 2. Design characteristics/attribute QFD matrix.

auxiliary engines. Examples of aircraft intended to have recon"gurable options exist throughout

the history of aviation though most were never "elded. Considering logistical aspects of deployingthe aircraft and the support equipment and pieces required to recon"gure quickly returns thedesigner to the advantages of working with a single vehicle incorporating the necessary attributes

to accomplish all required missions. Unfortunately, this approach requires compromises whichresult in a non-optimum platform for any one mission. Once again, history has demonstrated thepitfalls with this approach.

The high-speed dash, e$cient hover, and vertical take o!and landing (VTOL) requirements ledto consideration of the class of vehicles known as `high-speed rotorcrafta which have the ability totake o!and land vertically but also convert to a forward-#ight mode for achieving cruise speed and

performance similar to that of a "xed-wing aircraft. A modular approach to the airframe was notentertained because of the previously stated concerns. However, a recon "guration serves as the

basis of the design approach. Most high-speed rotorcraft con"gurations recon"gure from helicop-ter to "xed-wing modes through transferring of lift from rotating blades to "xed wings. At the sametime, propulsion may be shifted from one source to another. In each case, the air vehiclerecon"gures in #ight enabling it to achieve the performance of either a helicopter or a "xed-wing

airplane. In selecting a con"guration, emphasis was placed on maximizing the e$ciency of the airvehicle in both #ight modes. This approach called for relatively low disk loading in helicopter modeand aerodynamic cleanliness in "xed-wing mode.

Previous studies have demonstrated the advantages of incorporating an integrated propulsionsystem that is used in both #ight modes since, in general, empty weight and fuel weight increase



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when an auxiliary independent propulsion system is employed [1,2]. Folding- and stowing-rotor

concepts fall into this category of aircraft requiring auxiliary engines and were eliminated fromfurther consideration. Maneuverability requirements during hover and conversion and the

necessary capability to attack targets in all #ight modes forced the tilt-wing concept out ofcontention as well. The fan-in-wing was considered too ine$cient to e!ectively operate in vertical-

#ight mode. It was therefore determined to commit to study further a variation of the tilt-rotorcon"guration and the variable-diameter compound helicopter.

3.1. The joined-wing tilt rotor(JWTR)

Because the `conventionala tilt rotor, as exempli"ed by the XV-15 and V-22 aircraft, requiresa very thick wing, and because the location of the rotors with respect to the wing results in a largedownloading penalty, the joined-wing tilt rotor was considered as an alternative which could

alleviate the di$culties associated with the conventional design. The joined wing, proposed byWolkovitch [3], is comprised of two sets of wings arranged to form a diamond shape in both front

and plan views. The primary bene"ts of this con"guration are reduced weight and greater wingsti!ness for a given wing area.

Fig. 3 shows a conceptual drawing of a candidate JWTR. Because of the increased wing sti!ness,the wing thickness can be reduced as compared with conventional designs, increasing the wing

critical Mach number and, thus, the high-speed e$ciency of the aircraft. The planform of the wingresults in a lower download drag, increasing the hover and VTOL e$ciency. Because of the 350 kt

Fig. 3. Conceptual joined-wing tilt rotor with variable-diameter prop-rotors.



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cruise requirement, the JWTR utilizes variable-diameter prop-rotors ("rst proposed by Sikorsky

[4]) in order to reduce the helical tip Mach number in high-speed forward #ight and to allowmissile launch from wing stores.

The JWTR has the advantage that the tilt-rotor concept is a proven one. The conversion processis relatively simple and the conversion corridor is wide. However, the maximum speed of the

joined-wing vehicle is limited by the whirl-#utter instability } an unstable coupling of the rotorin-plane forces with wing #apping and nacelle pitching modes. Analysis to date indicates that this

instability limits the JWTR to speeds lower than the required 350}400 kt. Nonconventional,optimized structural design of the joined wings may eliminate the whirl-#utter problem, but further

sizing of the JWTR was not attempted at this time.

3.2. The variable-diameter compound helicopter (VDCH)

Fig. 4 shows a three-view drawing of a conceptual variable-diameter compound helicopter. In

order to meet all performance constraints, the vehicle makes use of two convertible turbofanengines, able to provide shaft power to drive the main and tail rotors and jet thrust, eitherseparately or simultaneously. The wings allow for o!-loading of the main rotor so that rotor stall

and compressibility e!ects do not hinder the vehicle performance at high forward speed. Incontrast to other high-speed rotorcraft types, the VDCH has no true `conversiona. Instead, the

transition between helicopter and "xed-wing #ight occurs continuously throughout the #ightenvelope. At speeds above a critical cruise velocity (200 kt for this aircraft), the rotor has been

retracted to its smallest diameter and o!-loaded. At this speed, the engine acts mainly as a turbofanwith only a small amount of power diverted to maintain rotor rotation. A blown #ap incorporatedinto the wing trailing edge can perform as a conventional #ap, or it can use engine bleed air to

increase circulation. This device allows the aircraft to operate purely as a "xed-wing aircraft atrelatively low speed and also to take o! and land conventionally.

The VDCH has some signi"cant advantages over other high-speed rotorcraft. Conversion is

simple and fast relative to that of a tilt rotor or tilt wing, reducing vulnerability during the process.Rotor-wing or stowed-rotor aircraft require complex mechanisms to stop, lock and stow the rotor.The VDCH can operate as a "xed-wing aircraft even in take o! and landing, and, if necessary, it

can complete its mission with rotors inoperative.

3.2.1. VDCH design methodology

The fuselage designed for the VDCH features several innovative characteristics. (A fuselage forthe JWTR was also designed with minimal variation from that for the VDCH.) Sponsons hold the

forward, main landing gear for this tail-dragger con"guration. The pilot enters the canopy-lesscockpit through an opening formed by sliding forward the top portion of the fuselage surroundingand forward of the cockpit. The main gun is retractable to reduce drag at high speed. The payloadbay is designed to hold four seated passengers or two stretchers. Depending on the current mission,

this compartment can also carry weapons, fuel, cargo, or other equipment. The vehicle utilizesa tail-fan antitorque device embedded in the vertical "n.

For this particular vehicle, design rotor tip speed and maximum wing loading are related to each

other. Clearly, the wing must support the full weight of the aircraft at a speed corresponding to anadvance ratio of somewhat less than one. A wing loading can be determined for a typical hover



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Fig. 4. Conceptual variable-diameter compound helicopter.


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tip speed with the rotor in its fully extended con"guration (730 ft/s). As the vehicle increases

its speed, the rotor contracts to a minimum of 60% of its hover radius resulting in a reduced tipspeed (438 ft/s). Thus, 438 ft/s, or 260 kt, is the forward speed required for an advance ratio of 1.

Safety considerations require that the aircraft actually #y with the rotor completely o!-loaded at 30% lower speed than this, or 200 kt (337 ft/s). The wing loading is computed from

this minimum speed requirement along with a known maximum wing lift coe$cient and airdensity.

The design of the wing circulation-control system determines the maximum C*

at any givenspeed and momentum coe$cient. Previous study of such a system indicates that an un#apped

C*

of 1.5 is easily achieved at a speed of 200 kt with a slot height of 0.02 in and a slot Machnumber of 0.65. Using this value for C

*and the density at 4000 pressure altitude at 953F gives

a maximum wing loading of 163 lb/ft. The circulation-control system requires 5% bleed aircorresponding to a speci"c thrust loss of 8%. Hence, at higher speed, the wing should support the

aircraft weight without the use of blowing so that full engine thrust may be utilized in attaining the

350 kt cruise velocity.For the sizing study, the wing loading was set at 130 lb/ft in order to conservatively estimate the

aircraft performance. The aircraft can maintain steady, level #ight at 270 kt with the 130 lb/ftdesign wing loading at a conventional (no blowing) wing lift coe$cient of 0.66. The #apped stallspeed with full blowing for this wing loading is approximately 125 kt so that the aircraft can

operate from conventional runways if desired.Using the hover tip speed of 730 ft/s and the maximum wing loading of 130 lb/ft, a version the

industry-standard sizing code HESCOMP II, modi"ed for use with a convertible engine, was usedto determine the aircraft characteristics. The vehicle gross weight for the design mission wascomputed to be 29,700 lb with an empty weight of 21,750 lb. Total weapons payload, excluding

"xed weight, was equal to 2960 lb. Fuel required to complete the extended-attack mission was4540 lb.

3.2.2. VDCH performance

Because it is designed for a high cruise speed, the VDCH equivalent #at-plate drag area is

26.4 ft, somewhat less than a typical attack helicopter. The 400 ft/min vertical-rate-of-climbrequirement dictates the engine size of approximately 4845 static hp per engine at sea level. Thehover ceiling is approximately 8500 ft density altitude. In "xed-wing mode, the aircraft ceiling is

about 39,000 ft at a speed of 185 kt, but a detailed analysis of thrust reduction as a function ofcirculation-control bleed percentage must be carried out to determine the exact ceiling since this

velocity is below the stall speed for the unblown wing. The aircraft reaches a maximum speed of415kt at approximately 33,000 ft.

The ferry mission is completed autonomously and with fuel tanks loaded in the payload bay.This con"guration increases the fuel capacity by approximately 9500 lb and the takeo! gross

weight by 6500 lb. For this mission, the aircraft uses a CTOL takeo! "eld. The circulation-controlsystem can provide a low-speed maximum lift coe$cient in takeo! con"guration (high-, plain#aps) estimated at over 4.0, giving a takeo!distance of roughly 4500 ft. The rotor can be used to o!

load the wing for STOL capability. The ferry range at 35,000 ft is computed to be 1950 Nmi, justshy of the desired 2100 Nmi.



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3.2.3. Modular and reconxgurable design

The cockpit, weapons systems, payload bay, engine, rotor and high-lift system are the primarymodular/recon"gurable components of the aircraft. The following sections will discuss crewstation

and mission-equipment packages in detail.The payload bay is 6.17 (1.88 m) high;8 (2.44 m) long;5 (1.52 m) wide. Four folding seats,

two against each side wall, hold the passengers. Alternatively, two stretchers "t in the compart-ment, one above the other. Troops and stretchers can be loaded through a sliding side door.

A two-panel, sliding #oor opening allows use of standard palettes for carrying alternate payloadssuch as ordnance, communications equipment, surveillance equipment, or fuel.

The variable-diameter rotor design is based on the Sikorsky TRAC rotor which can extend andretract in #ight using a jackscrew. A system of clutches in the rotor hub controls the exten-

sion/retraction. Fig. 5 shows a schematic of the TRAC-rotor design. The convertible engine can beused in turboshaft mode where gases are directed to the power turbine which drives the main-rotor

and tail-rotor shafts. In turbofan mode, variable-inlet guide vanes direct inlet air through the fan

and the shaft is de-clutched to provide jet thrust from the engine.The wing is out"tted with a trailing-edge #ap which can operate conventionally or with the

circulation-control system to produce high lift coe$cients. Engine bleed air is used to pressurize the

wing plenums. Slots located near the #ap hinge provided tangential blowing when the system is inuse. A crossover duct provides pressurization to both wing plenums in the event of engine failure.

It is anticipated that a maximum of 8% thrust loss will occur when the circulation-control systemis in operation.

The gross weight of 29,700 lb is large compared with current attack helicopters. However, theLongbow Apache with full ordnance and fuel can reach nearly 20,000 lb while the Russian Hindand the prototype Sikorsky S-67 Blackhawk (both capable of carrying a squad of troops) weigh

over 22,000 and 24,000 lb, respectively. These do not #y at the speed required for MRMAAV,

Fig. 5. Schematic of Sikorsky TRAC-rotor system (from Ref. [5]).



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however. It is reasonable to expect that an aircraft developed to ful"ll the MRMAAV mission

would be of a size similar to the concept vehicle. All required technology for production of anair-vehicle prototype has been demonstrated, but development of MRMAAV would be considered

high risk, and the level of complexity is signi"cantly greater than a conventional aircraft orrotorcraft.

4. Crew station and avionics

The study did not include investigation into the single-pilot cockpit issues, which have con-sistently spawned a great deal of controversy particularly during the US Army LHX program.

Pilot workload remains the key issue for resolution. The approach taken with this study starts fromthe requirement that the vehicle capability include autonomous operation for some missions.

Given this capability, the crew can be viewed, for some missions, as the onboard decision maker

with a great many of the piloting tasks performed through the autonomous capability inherent inthe vehicle. The purely autonomous capability is used for missions which require little human, onthe spot, decision making, such as utility and self-deployment. Typically, these missions require

#ying from point to point with little deviation from the #ight plan, in contrast to an armed mission.Designing a crew station to maximize the advantage of the autonomous capability and yet

support a crew member represented a signi"cant challenge. A removable, modular crew station,while appearing at "rst to keep to the spirit of the MRMAAV concept, proved impractical after

considering the logistical impact of peculiar ground support equipment (PGSE) necessary to installthe crew station or the resources necessary to deploy the modular crew station while the vehicledeploys autonomously. The design of the aircraft would necessarily incorporate the crew support

systems, structure and space for the inhabited crew station even during missions allowing itsremoval. The removable cockpit seems to o!er few advantages and many disadvantages; hence it isnot included as a modular system.

Instead, a philosophy making maximum use of the aircraft's autonomous capability minimizesthe penalty associated with incorporating a permanent crew station into the vehicle. Speci"cally,extensive use of sensors for pilotage and target acquisition allow the display of actual imagery on

a virtual cockpit display in a manner similar to that found in modern simulators. The displayconsists of a wrap-around array of digital micromirror devices (DMD2+) which form the basis ofdigital light processing (DLP2+), pioneered by Texas Instruments. The display surface material is

a #exible plastic upon which are mounted semiconductor controlled micromirrors that serve asdisplay pixels. This type of display surface is extremely thin relative to current #at-panel displays

and exhibits sharp, high-resolution imagery. A grid layout supports a fail-operational system torevert imagery from failed panels to operational panels. Provisions for touch-screen technologycould be a future enhancement allowing the pilot to pinpoint areas for enhanced vision such as forIR, I2TV, and zooming. This approach minimizes the space, weight and power of the traditional

cockpit through lightweight displays, and improves structural e$ciency and ballistic protection forthe pilot.

Sensors located around the aircraft ensure adequate "eld of regard and "eld of view for the pilot.

Additional lower de"nition sensors are placed inboard on the fuselage to aid in close-in maneuver-ing. Fig. 6 shows exterior sensor locations. High-speed signal processors convert sensor images into



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Fig. 6. External sensor installation locations.

digital signals which can then be fused. A head tracker follows the pilots head, controlling theswitch from sensor to sensor providing for a seamless display of imagery with higher resolution in

the direction of pilot view. Lower resolution completes the peripheral view. Sight-line informationis also sent to the weapons processor for tactical engagement purposes.

Other highlights of the crew station design include a "ber optic bus and control system with builtin redundancy, multi-function displays for system monitoring and a recon"gurable missionprocessor array. The latter enables recon"guring the vehicle from piloted to autonomous operationthrough software changes only.

Communications systems allow transmitting and receiving digital voice, data, and imagerythrough encoded, compressed bursts. This provides high security with low susceptibility to jamming or interference. Vehicle diagnostics systems monitor the health and usage of major

subsystems, dynamic components and critical structure using algorithms designed to predictfailures and life usage.



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5. Mission equipment

5.1. Weapons

A variety of weapons were considered for implementation on the air vehicle. These ranged from

conventional weapons typical of attack/reconnaissance aircraft to non-lethal weapons used foroperations other than war. The latter included many weapons in the research and development

stage such as High Intensity Sound, Electromagnetic Pulse, Sonic Bullets, Lights, and Sticky Goo.The incorporation of non-lethal weapons increased the utility of the MRMAAV over current

attack/reconnaissance aircraft designed primarily for attacking armor.Brilliant weapons, those with the capability to detect, recognize, identify and lock on prior to or

after launch, were considered as critical enhancements to this kind of vehicle. Weapons of thisnature begin to reduce the need for a piloted presence even more than called for in the present

design. These signi"cantly increase the survivability of the vehicle allowing it to remain masked

while engaging targets. The hurdle to overcome with these weapons is cost and positive control.

5.2. Target acquisition

The weapons processors reside at the heart of the target acquisition system. For MRMAAV,

a redundant set of weapons processors process targeting data received from the sensors andcombine with aircraft state, and position information to compute "ring solutions. In addition to

second generation FLIR technology which promises increased range and reduced weight and size,RF technology in the form of a Smart Focal Plane Array will have the capability to cover a widerange of wavelengths. To ensure seamless coverage in all conditions, sensor fusion will be employed

to enhance target recognition capabilities and reduce possible pilot confusion when switchingbetween sensors. In general, sensors available at the time of development will be incorporated intothe MRMAAV concept. The ability to make the sensors modular will depend on the degree of

miniaturization that can be achieved in the future. Future R&D directions should address the tradeo! between size and capability of the sensors. Since not all missions require targeting sensors,a modular approach to implementation of these sensors is included in the following section.

Pilotage sensors are also linked to the weapons processors to provide limited target acquisitioncapability in the event that the primary targeting sensors are lost.

5.3. Remote sensor platform

Incorporation of target acquisition sensors on a remote sensor platform (RSP) o!ered a uniqueapplication of modularity for the air vehicle. Since these sensors are not required for a number ofmissions, the space weight and power allocated for them can be eliminated through such anapproach. Fig. 7 shows a notional RSP attached to the wing pylon of MRMAAV. The remote

sensor platform can be attached to MRMAAV for those missions requiring target acquisitionsensors, such as attack or reconnaissance. Initially, thought was given to attaching a sensor pod tothe vehicle when needed, but the added mission #exibility a!orded by the remote sensor platform

and the increased performance available to the `mothera ship after launch of the RSP provided allthe bene"ts of the pod, while enhancing its capabilities. The RSP is air launched from the vehicle



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Fig. 7. Variable-diameter compound helicopter (extented rotor) with RSP mounted on left wing.

and #ies autonomously along a predesignated #ight path. The controlling MRMAAV pilot is able

to change the #ight path by changing way points on a digital map. The new navigation informationis sent automatically to the RSP and it determines the control inputs to make changes to its #ight

path. In this way, the pilot can control the remote sensor platform but is not `#yinga it. In a similarmanner, the pilot can control the direction of the sensor view. Sensor information is relayed

back to the MRMAAV and provides targeting data to the weapons processor which can in turn berelayed to other aircraft for battle management. Target recognition algorithms are resident onboard the RSP, while systems on board MRMAAV provide fusion and the necessary processing

for positive identi"cation and targeting. Translation into "re control data requires using dataon the RSP position, sight-line and range to target translated into relative direction and rangedata from MRMAAV. The weapons processor then provides this information to the lock-on-

after-launch weapons for "ring. The RSP sensor view is digitally displayed to the pilot as a picture-in-picture on the crew station virtual cockpit display. Additionally, the weapons processorautomatically prioritizes targets, with a manual override capability. Finally, ordnance is "red by

the pilot.Upon completion of the mission, the RSP remains behind to assess battle damage, then #ies

autonomously to a preplanned landing zone for recovery.

Several advantages to this approach determined its selection. The modular approach this o!ersminimizes the penalty of added weight in missions not requiring that level of target acquisition. The

RSP provides the ability to acquire targets at longer range and around terrain features whileMRMAAV remains concealed. This capability provides an opportunity to focus less on the sensorrange, since the platform (RSP) extends the MRMAAV location without exposing the mainplatform. While deviating from current R&D directions, a more cost-e!ective approach to target

acquisition development could be taken rather than increasing sensor range. Survivability isenhanced since the MRMAAV can remain concealed or masked while the RSP searches for targetsor scouts the way ahead. From the perspective of the RSP, air launching it, as required, completely

under the control of the MRMAAV ensures positive control and it allows a reduction in weight ofthe RSP since mission fuel is not burned until the vehicle is launched.



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Despite this major modular feature, the MRMAAV would still have limited target acquisition

capability through its pilotage sensors in the event the RSP were lost. One RSP could providebattle"eld surveillance for more than one MRMAAV.

6. Conclusions

The study demonstrates the technical feasibility of a recon"gurable aircraft with multi-missioncapability. With continuing emphasis on automation, avionics miniaturization, and more powerful

processing, the practicality of such a vehicle increases annually. Several concepts outlined demon-strate approaches to this problem. Table 2 summarizes the major modular/recon"gurable conceptsas they apply to enabling missions.

During development of a modular vehicle, consideration must be given to the logistics impact

associated with transporting and assembling various modules. This severely limits the practicalityof a system with many large modular components. Avionics modularity may best be achieved

through common boxes recon"gured through software changes. Recon"gurable aircraft have been#ying for 40 years, but their capabilities improve with technology development. Automatic controlsand electronic control systems aid in smooth in-#ight recon"guring.

The greater emphasis applied to autonomous vehicles will help realize the goal of an aircraft that

can be both piloted or operated autonomously. In this case, the improvement in technology in onearea improves the capability in the other. This can be seen in the virtual cockpit of MRMAAV

where the ability to #y autonomously simply augments the pilot for a piloted mission. This level ofsophistication allows operation of a one-pilot vehicle and signi"cantly changes the nature of thecrew station. The idea of a remote-sensor platform builds on the increasing capability of auto-

nomous-vehicle technology and extends the range and #exibility of the target acquisition subsys-tem while improving survivablity of the weapon platform. An approach such as the RSP mayenable a change in sensor R&D direction.

The successful development and acquisition of any weapons system depends on cost. Despite itstechnical feasibility, which increases with time, the costs associated with placing advanced technology

Table 2

Summary of modular and recon"gurable components for multiple missions

Mission Modular components Recon"gurable components

Attack Weapons, RSP Piloted, Weapons Bay, VDR

Armed recon Weapons, RSP Piloted, Weapons Bay

Scout Weapons, RSP Piloted, Weapons Bay

Combat S & R RSP, Winch Piloted, Passenger Bay

Utility Cargo Hook Autonomous, Cargo Bay, Control Laws

Command and control Autonomous, Communications Console

Self-deploy Autonomous, Fuel Bay

Enhanced performance VDR, Convertible Engines, Control Laws

Variable Diameter Rotor.



16/16

and new operational concepts into a vehicle such as MRMAAV must be weighed against the costs

of separate dedicated platforms. A major motivation for MRMAAV is the life-cycle cost bene"t ofa single common platform for all missions and the associated reduced force structure. Life-cycle

costs reductions could then o!set the higher acquisition costs.

References

[1] Rutherford J et al. Technology needs for high-speed rotorcraft. Technical Report NASA CR-177578, April 1991.

[2] Rutherford J et al. A concept mission sensitivity study for several medium to high speed V/STOL aircraft.

AIAA-91-3096, September 1991.

[3] Wolkovitch J. The joined wing: an overview. AIAA-85-0274, 1985.

[4] Fradenburgh EA. Wind tunnel tests of variable diameter rotor. In: Proceedings of the 33rd Annual Forum,

American Helicopter Society, 1992.

[5] Scott MW. Technology needs for high-speed rotorcraft (2). Technical Report NASA CR-177 590, August 1991.


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Mission and Concept Evaluation for a Multirole

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