Development and Validation of an On-Deck

Helicopter Manoeuvring Simulation

Dr. Robert G. Langlois, Assistant Professor, rlangloi@mae.carleton.caAmanda R. Feldman, Graduate Student, mandyfeldman@rogers.com

Darren R. Linn, Graduate Student, dlinn82@hotmail.comMechanical & Aerospace Engineering, Carleton University, Ottawa ON Canada

Dr. Atef R. Tadros, Director of ASIST Engineering, atef tadros@indaltech.comIndal Technologies Inc., Mississauga ON Canada

Abstract

This paper describes an ongoing multi-phase project to develop and validate the capability for performingdetailed analysis of shipboard helicopter manoeurvring and traversing operations. The first phase of theproject involves developing a four-degree-of-freedom interactive transient-dynamic simulation of shipboardhelicopter handling. In the simulation, aircraft motions result from commanded force inputs provided by theIndal Technologies Inc. (ITI) Aircraft/Ship Integrated Secure and Traverse (ASIST) shipboard helicopterhandling system. A detailed tire model is used to accurately represent complex tire-deck interactions. Thesecond phase involves designing and commissioning a single-degree-of-freedom scale-model experimentalmotion platform, a scale-model ASIST system with two degrees of aircraft actuation, and a scale-modelreconfigurable dead load test vehicle representative of a variety of maritime helicopters. The third phaseinvolves comprehensive qualitative and quantitative validation of the simulation using both full-scale datawithout ship motion and scale-model data including the effect of ship motion. This paper describes thederivation and implementation of the mathematical simulation model, the design of the experimental motionplatform, validation activity, and an overview of immediate and long-term applications of this technology.

Introduction

The proposed paper focuses on the safety and easeof shipboard helicopter on-deck handling opera-tions. Shipboard aircraft handling equipment suchas the Indal Technologies Inc. (ITI) Aircraft/ShipIntegrated Secure and Traverse (ASIST) shipboardhelicopter recovery and on-deck handling system,shown in Figure 1, provides the capability to secure,straighten, and traverse helicopters on small shipsin severe sea conditions. The usual process is to re-motely align the aircraft with a deck-mounted track,then to traverse it forward to the ship’s hangar. Thesame process is reversed prior to launch.

The helicopter/ship dynamic interface simulationprogram Dynaface Rg[1] has been developed by ITIover the past 15 years to support the analysis and de-

1Presented at the American Helicopter Society 59th An-nual Forum, Phoenix, Arizona, May 6-8, 2003. Copy-right c© 2003 by the American Helicopter Society Interna-tional Inc. All rights reserved.

sign of helicopter handling systems and the safety ofembarked helicopter operations. While Dynaface Rgis effective for analyzing the touchdown transient andon-deck securing phases of shipboard operation, itdoes not currently address the transient motions dur-ing aircraft straightening and traversing along theship deck and into the hangar. This aspect of dy-namic interface analysis is now being investigated indetail as part of a project sponsored jointly by ITI,Materials and Manufacturing Ontario (MMO), andCarleton University (CU).

This research project includes three phases: thedevelopment of a two-dimensional planar manoeu-vring simulation, the development of a dynamic in-terface analysis experimental motion facility, andcomprehensive validation of the results of the pre-vious two phases. Once completed, the newly de-veloped capability will be used to perform detailedanalysis of embarked helicopter manoeuvring andtraversing operations. The first phase involves de-veloping an accurate planar model of shipboard he-

1

Figure 1: Indal Technologies Inc. ASIST system

licopter handling using the ASIST system with at-tention primarily focussed on tire/deck interactionand the ASIST manoeuvring control system. Thevalidated simulation will then be used to analyze on-deck handling and to develop efficient manoeuvringsequences. In the second phase of the project, an ex-perimental facility is being developed such that theeffect of motion on the manoeuvring sequences canbe investigated using a scale-model dynamic inter-face analysis motion platform and a scaled dead loadtest vehicle. The motion platform will be used forvalidating the planar simulation, assessing its perfor-mance in the presence of motion, and for validatingan extension to Dynaface Rgto include the manoeu-vring capability developed with the planar simula-tion model. In addition, the motion platform mustbe flexible so that it can be used to explore a vari-ety of dynamic interface issues beyond validating thesimulation models.

In general, the interactive planar simulation mustmodel the force profiles applied by the operator tothe helicopter-mounted ASIST securing probe by theASIST rapid securing device (RSD); complex low-speed tire behaviour; and planar helicopter dynam-ics including the possibility of a castoring or steer-able nose or tail wheel. Modelling a slow movingtire, as in this application, requires accurate methodsfor modelling relaxation length and cornering forcegeneration. This means using non-steady-state prop-erties to predict the behaviour of the tires, therebymaking the tire model the most complex part of thesimulation.

The second phase of the research project involvesthe design and construction of a scaled one-degreeof freedom motion platform with two degrees of air-craft manoeuvring actuation. The experimental mo-tion platform must be capable of simulating variousmagnitudes of ship motion to study the effects ofmotion on the manoeuvring of a helicopter using aphysical model of a helicopter and a physical modelof the ITI ASIST system. Ship motion in general is

fully three-dimensional thereby having six degrees offreedom. A challenge in this project is to use a sin-gle degree of ship actuation to capture ship motionsin multiple directions to the extent possible. Theassociated helicopter model must be capable of rep-resenting a 1/10th-scale model of a typical maritimehelicopter, which contains a full suspension systemand an adjustable frame to represent different heli-copter configurations, as well as both nose and tailsteerable or castorable wheel designs.

Comprehensive validation of the planar simulationwill occur in four stages: qualitative testing; scale-model experimentation on the experimental motionplatform without motion; full-scale experimentationusing the ITI integrated test facility, a functioningASIST system, and a dead load test vehicle repre-sentative of an in-service shipboard helicopter; andscale model experimentation on the motion platformwith motion. For qualitative testing by an experi-enced ASIST operator, a joystick and virtual realityinterface is being implemented.

This paper describes the development of theproject, including the design, quantitative and quali-tative analysis, and validation activity for each of theproject phases. The paper is structured such thatthe derivation and implementation of the planar he-licopter simulation is described first; followed by themotion platform design and associated analysis. Theremaining three sections describe validation activity,intended short- and long-term applications for theresearch, and concluding remarks respectively.

Planar Manoeuvring Simulation

Essential elements of the planar manoeuvring simu-lation are described in this section. Attention is fo-cussed on the core governing equations that are care-fully structured to allow the extraction of joint reac-tion forces at the castoring point required by a jointfriction model, and such that only ordinary differ-ential equations result, thereby permitting efficientcomputer implementation without requiring the so-lution of complex differential-algebraic equations.

Dynamic Helicopter Model

The generic helicopter on which the model is basedis shown in Figure 2. It consists of two bodies rep-resenting the fuselage and the rotatable wheel as-sembly interconnected by a revolute joint; and threesuspension stations each having either single or dualwheels. The geometry of the system is completelyarbitrary with no implied assumptions of symmetry.

Figure 2 illustrates the four degrees of freedom in-cluded in the helicopter model, where the generalizedcoordinates qi are: the linear x position of the heli-copter centre of mass (CM) (q1); the linear y positionof the helicopter CM (q2); the orientation of the he-licopter (q3); and the orientation of the optionallycastorable wheel assembly relative to the helicopterbody (q4).

Kinematic analysis of the system allows the iner-tial frame accelerations of the helicopter body andcastor assembly to be related to the generalized co-ordinates and their first and second time derivatives

AHx

AHy

αH

ACx

ACy

αC

=

1 0 0 00 1 0 00 0 1 01 0 B43 B44

0 1 B53 B54

0 0 1 1

q1

q2

q3

q4

(1)

+

000b4

b5

0

where,

B43 = rcB/Cy

C(q3 + q4) + rcB/Cx

S(q3 + q4)−rh

B/HyCq3 − rh

B/HxSq3

B44 = rcB/Cy

C(q3 + q4) + rcB/Cx

S(q3 + q4)

B53 = rcB/Cy

S(q3 + q4)− rcB/Cx

C(q3 + q4)−rh

B/HySq3 + rh

B/HxCq3

B54 = rcB/Cy

S(q3 + q4)− rcB/Cx

C(q3 + q4)

b4 = −rhB/Hx

Cq3q23 + rh

B/HySq3q

23

+rcB/Cx

C(q3 + q4)(q3 + q4)2

−rcB/Cy

S(q3 + q4)(q3 + q4)2

b5 = −rhB/Hx

Sq3q23 − rh

B/HyCq3q

23

+rcB/Cx

S(q3 + q4)(q3 + q4)2

+rcB/Cy

C(q3 + q4)(q3 + q4)2

and C and S represent the cosine and sine functionsrespectively. For subsequent analysis, Equation 1can be written more compactly as{

a}

=[

B] {

q}

+{

b}

(2)

where individual terms are identified by comparisonwith Equation 1.

The applicable forces were next considered and theNewton-Euler method was used to derive the equa-tions of motion using the full set of accelerations.

Figure 2: Schematic of the dynamic helicopter model

This formulation was selected so that the reactionforces at the castor joint would naturally result andcould be used to drive a joint resistance model. Theresulting matrix equation is

mH 0 0 0 0 00 mH 0 0 0 00 0 IH 0 0 00 0 0 mC 0 00 0 0 0 mC 00 0 0 0 0 IC

AHx

AHy

αH

ACx

ACy

αC

(3)

=

F1

F2

F3

−FBx+ Fttx1 + Fttx2

−FBy + Ftty1 + Ftty2

F6

where,

F1 = FPx+ FBx

+ Fmltx1 + Fmltx2

+Fmrtx1 + Fmrtx2

F2 = FPy+ FBy

+ Fmlty1 + Fmlty2

+Fmrty1 + Fmrty2

F3 = ~rP/H × ~FP + ~rB/H × ~FB + ~rmlt/H1 × ~Fmlt1

+~rmlt/H2 × ~Fmlt2 + ~rmrt/H1 × ~Fmrt1

+~rmrt/H2 × ~Fmrt2 + MB

F6 = ~rB/C ×−~FB + ~rtt/C1 × ~Ftt1

+~rtt/C2 × ~Ftt2 −MB

and where mH and IH are the helicopter mass andmass moment of inertia respectively. Subscript Prefers to the probe, mlt refers to the main left wheels,mrt the main right wheels, and tt the steerable or

castorable wheels. Subscripts 1 and 2 refer to the leftand right tires in dual-tire applications. Moment MB

is the bearing resistance at the castor joint. Equa-tion 3 can be expressed more compactly as[

M] {

a}

={

F}

(4)

To develop the final dynamic model, Equation 2 issubstituted into Equation 4 resulting in[

M] ( [

B] {

q}

+{

b} )

={

F}

(5)

Next, Equation 5 is manipulated to get all of the un-knowns onto one side. The generalized accelerationsare kept on the left and everything else is moved tothe right hand side[

M] [

B] {

q}

={

F}−

[M

] {b

}(6)

At this point there are six equations with six un-knowns. The four generalized accelerations are un-known, along with the x and y reaction forces onthe castor joint. The {F} vector is then decomposedinto the known forces {Fk} and the unknown forces{Fu} {

F}

={

Fk

}+

{Fu

}(7)

Equation 7 is substituted back into Equation 6 andthe unknown forces are moved to the left hand side[

M] [

B] {

q}−

{Fu

}=

{Fk

}−

[M

] {b}

(8)

The forces must then be separated from the positionvectors by creating a position matrix [C]

{Fu

}=

[C

]{FBx

FBy

}(9)

where,

[C

]=

1 00 1

−rhB/Hy

rhB/Hx

−1 00 −1

rcB/Cy

−rcB/Cx

(10)

[C] is then merged with the matrix product [M ][B]to put all six unknowns into one vector on the left-hand side

[ [M

] [B

]−

[C

] ]

q1

q2

q3

q4

FBx

FBy

(11)

={

Fk

}−

[M

] {b

}Matrix Equation 11 contains six independent equa-tions with six unknowns that are solved in the simu-lation using a numerical equation solver. An analyt-ical solution was found, but proved to be impracticalfor implementation based on the anticipated solutionefficiency using the complex analytical expressions.

The forces that drive the equations of motion canbe broken down into two categories, operator appliedforces and tire reaction forces. The operator appliedforces are generated by the RSD model and are ap-plied to the helicopter through the probe attachedto the helicopter body.

RSD Model

The RSD model interprets input from the ASISTcontrol system joystick and generates the force pro-file that should be applied to the helicopter probe.The deflection in the probe is used to generate theforce and the physical limitations of the real RSDsystem are considered. These limitations restrict thevelocities and forces that the RSD is able to applyto the probe.

The simulation has also been configured to runwithout the RSD model being used, by applyingforce profiles specified in an input file directly to theprobe. This feature is useful during validation andfor analysis where repeating inputs exactly, whichwould be very difficult with a joystick, is necessary.

Tire Model

During manoeuvring, the helicopter tires roll at rela-tively low speed compared with conventional vehicleapplications. The low speed effectively complicatesthe tire model. When modelling a slow-moving tire,as in this application, accurate methods of modellingrelaxation length and cornering force generation areneeded. This means using non-steady-state proper-ties to predict the behaviour of the tires, therebymaking the tire model the most complex part of thesimulation. Smiley and Horne [2] present accuratemethods for modelling the non-steady-state proper-ties of a rolling aircraft tire.

A three-degree-of-freedom tire model has beenconstructed using the properties outlined by Smileyand Horne. No motion in the vertical direction isconsidered in the planar simulation, but the verti-cal tire deflections are automatically calculated suchthat they are consistent with the helicopter weightdistribution. In the longitudinal direction, a rollingresistance model is applied. The lateral directionis much more complex and involves calculating the

relaxation lengths and cornering power generation.This unyawed relaxation length is defined as the dis-tance the tire must roll in order for the lateral defor-mation to drop to a fraction 1/e of its initial value.The relaxation length LS is calculated using Equa-tion 12.

LS = (2.8− 0.8P/Pr)(1.0− 4.5δ0/d)W (12)

where,

P is the instantaneous tire pressure;Pr is the rated tire pressure;δ0 is the vertical tire deflection for the pure;

vertical loading condition;d is the outside diameter of the free tire; andW is the width of undeflected tire

The lateral deformation is what creates the corner-ing force in the tire and can be generated (corner-ing power generation) by giving the tire a velocityin the lateral direction. This is done by calculatingthe yawed relaxation length in a similar manner asthe unyawed relaxation length. The transient peri-ods are so short in many other simpler applicationsthat relaxation lengths are often ignored in the tiremodel.

Computer Implementation

The simulation model combines the three parts de-scribed above: the dynamic helicopter model, theRSD model, and the tire model, and numerically in-tegrates the resulting equations. Figure 3 illustratesthe simulation process. All of the physical helicopterproperties are input, along with the simulation pa-rameters, which include the simulation time, initialposition, force profiles (if the joystick is not beingused), etc. Next, the initial forces and displacementsare calculated based on the initial conditions. Thenthe numerical integrator moves the solution forwardin time. Currently a fourth-order Runge-Kutta nu-merical integrator is implemented to propogate thesolution. The numerical integrator needs to be ac-curate as well as fast enough to drive the simulationin real time. As the simulation runs, information isgathered and output to a file for subsequent postpro-cessing and analysis.

Experimental Motion Platform

The scaled one-degree-of-freedom motion platformwith two degrees of aircraft manoeuvring actuationis capable of simulating various magnitudes of ship

Figure 3: Flow chart of simulation

motion to study the effects of motion on the ma-noeuvring of a helicopter using a physical model of ahelicopter and a physical model of ITI’s ASIST sys-tem. The experimental motion platform has severaluses regarding the on-deck helicopter manoeuvringsimulation study: the qualitative and quantitativetesting of the two-dimensional planar manoeuvringsimulation with and without motion; comprehensivevalidation of securing simulation software; develop-ment of manoeuvring algorithms; and experimentalinvestigation of other helicopter dynamic interfaceissues.

Motion Requirements

The experimental motion platform was designed torepresent the motions of a 1

10 -scale model of a typicalfrigate where the motions must be scaled using thefollowing scaling laws:

(θr,p,y) 110

= (θr,p,y)1 (13)

(θr,p,y) 110

=

√1R

(θr,p,y)1 (14)

(θr,p,y) 110

=1R

(θr,p,y)1 (15)

(rx,y,z) 110

= R(rx,y,z)1 (16)

(rx,y,z) 110

=√

R(rx,y,z)1 (17)

(rx,y,z) 110

= (rx,y,z)1 (18)

where R is the scaling ratio, R = 110 .

The most intense motions that will be simulatedduring the manoeuvring of the model helicopter cor-respond to an upper sea state 5 condition. Thedesired scaled motions for the motion platform areshown in Table 1.

Table 1: Scaled motions of a 110 -scale model of a

typical frigate operating in an upper sea state 5 con-dition.

Motions Displacement Velocity Acceleration

Roll 20.4 deg 40.1 deg/s 84.2 deg/s2

Pitch 5.4 deg 19.2 deg/s 74.1 deg/s2

Yaw 13.0 deg 2.4 deg/s 20.6 deg/s2

Surge 285.8 in 69.3 in/s 265.8 in/s2

Sway 85.4 in 42.5 in/s 132.2 in/s2

Heave 44.5 in 60.2 in/s 211.0 in/s2

Due to technical design and budgetary considera-tions, attention was focussed on the motions of great-est importance. These are roll and pitch motions andwill be scaled appropriately, as shown in Table 1.Surge, sway, and heave are less important and willbe produced along with the angular motions, whichwill be discussed subsequently. However, these sec-ondary motion components will not reach the fullmagnitudes of the motions shown in Table 1.

Ultimately, during component selection, it was de-cided that it would be desirable to allow the motionplatform to have a greater angular displacement forpotential subsequent studies in more extreme condi-tions. Therefore, the motion platform was designedwith the ability to produce angular displacements ofup to 45 degrees with little incremental cost associ-ated with this capability.

Motion Platform Design

The motion platform, shown in Figure 4, was de-signed to be easily adjustable and expandable toachieve different motion combinations. It presentlyuses a single degree of actuation to produce combina-tions of roll, pitch, sway, surge, and heave motions,yet is expandable in the future to include a secondangular degree of freedom for separate pitch and rollactuation, if required.

The single linear actuator is positioned on the mo-tion platform to produce roll motion. However, thehelicopter model on the ship deck will experienceroll, sway, and heave motions as the result of kine-matic coupling between linear and angular motionsdepending on the location of the axis of rotation andthe position of the model on the motion platform.The platform also has the ability to be horizontallyrotated about the centre post (yaw angle) so themodel can experience a combination of roll, pitch,sway, surge, and heave motions with the single lin-ear actuator.

The motion platform consists of three components:

the deck, the frame, and the rotating plate. The mo-tion platform’s deck is the top surface on which thescaled helicopter model will manoeuvre. The deckhas been sized to allow the scale model helicopter toperform a full 360-degree rotation and to travel alongthe deck a distance of approximately four times thelength of the model. This will allow ample roomfor the model’s manoeuvring algorithms to be per-formed.

The deck is made of a lightweight foamboard, sincean aluminum frame is used to support the deck andto house the linear actuator used for the traversingcomponent of the ASIST model. The rotating plateallows the frame and deck to rotate about the centrepost to allow a combination of pitch and roll motions.The rotating plate yaw orientation remains constant,while the frame and deck rotate about a centre pinon the plate. Four clamps are used to secure theframe at the desired orientation.

The platform is attached to the centre post by auniversal joint to eliminate yaw but allow ±45 de-grees of roll and ±11 degrees of pitch. A supportpost is required to prevent the platform from rotatingabout the nonactuated horizontal axis. The locationof the axis of rotation is also adjustable to achievedifferent magnitudes of motions by placing the uni-versal joint at different locations along the centrepost. Additionally, the position of the posts and lin-ear actuator are interchangeable thereby producingdifferent combinations and magnitudes of motions.

Figure 4: Top and bottom views of the experimentalmotion platform

Analysis

As mentioned above, the helicopter model on theship deck will experience roll, pitch, surge, sway, andheave motions as the result of kinematic coupling be-tween linear and angular motions depending on themotion platform orientation, the location of the axisof rotation, and the position of the model on the mo-tion platform. Equations were derived to determinethe linear and angular displacements, velocities, and

accelerations at every point on the deck. Figures 5and 6 show the front and top views, respectively, ofthe key reference points and coordinate systems onthe motion platform, as well as the dimension vari-ables referred to in the upcoming equations.

Figure 5: Front view of the motion platform showingpoints and coordinate systems used for analysis

Figure 6: Top view of the motion platform showingpoints and coordinate systems used for analysis

By monitoring the global positions of the key refer-ence points, as well as the point P , which representsthe centre of gravity of the scale model helicopter,the required displacements, velocities, and accelera-tions of the linear actuator can then be determined.The global position of key points can be determinedfrom

rGE = rG

B + [Tijk→XY Z ] · rLE/B (19)

rGC = rG

E + [Tmno→XY Z ] · rLC/E (20)

rGD = rG

E + [Tmno→XY Z ] · rLD/E (21)

rGI = rG

E + [Tmno→XY Z ] · rLI/E (22)

rGJ = rG

E + [Tmno→XY Z ] · rLJ/E (23)

rGP = rG

E + [Tmno→XY Z ] · rLP/E (24)

where the superscripts L and G indicate a local co-ordinate system or global coordinate system with re-spect to point A, respectively, and

[Tmno→XY Z ] = R(x, θ) ·R(z, θ) (25)

[Tmno→XY Z ] = [Tijk→XY Z ] · [Tmno→ijk] (26)

[Tmno→XY Z ] =

1 0 00 cos θ − sin θ0 sin θ cos θ

·

cos λ − sinλ 0sinλ cos λ 0

0 0 1

(27)

where θ is the roll angle of the platform with respectto the horizontal, and λ is the yaw orientation of themotion platform with respect to a zero heading.

Other values of interest are the linear actuatorstroke, velocity, and acceleration required to producethe desired ship motions. The linear actuator stroke∆ required for a specific roll angle is given by∣∣∣rG

G/F

∣∣∣ =∣∣rG

G − rGF

∣∣ (28)

∆ =∣∣∣rG

G/F

∣∣∣− original length (29)

The linear actuator velocity is determined by thefollowing equations:

vGG/F = θ ·

0 0 00 −sinθ −cosθ0 cosθ −sinθ

· rLG/B (30)

vactuator = vGG/F · (rG

G/F )UNIT (31)

The linear actuator acceleration is determined bythe following equations:

aGG/F = θ ·

0 0 00 − sin θ − cos θ0 cos θ − sin θ

+θ2 ·

0 0 00 − cos θ sin θ0 − sin θ − cos θ

· rLG/B (32)

aactuator = aGG/F · (rG

G/F )UNIT (33)

A Matlab program was used to implement thesehand-derived equations to determine the linear andangular motions of the model placed at any point on

the deck, the equilibrium forces acting on the motionplatform, and the linear actuator motion required toproduce the desired motions.

For any peak roll displacement, velocity, accelera-tion, and yaw orientation of the deck, the Matlabprogram also provides the ability to display two-dimensional images of the motion platform orienta-tion, shown in Figures 7 and 8, indicating the po-sition of the platform at the indicated peak motionand location of the scaled helicopter model.

Figure 7: Front view of the motion platform plottedby Matlab

Figure 8: Top view of the motion platform plottedby Matlab

A model of the motion platform was also createdusing ADAMS, which is multibody dynamic simula-tion software that can simulate the full-motion be-haviour of complex mechanical systems. This model,shown in Figure 9 was used to perform a dynamicanalysis of the motion platform and measure theforces and moments acting on the components of themotion platform during the most extreme conditions.This data, along with the Matlab results, were usedto size the components and compare alternative mo-tion platform designs.

Figure 9: View of ADAMS dynamic model scale-model dead load test vehicle on the experimentalmotion platform

DLTV

The associated helicopter model, as shown in Figure10, represents a 1

10 -scale model of a typical helicopterconfiguration, which contains a full suspension sys-tem and an adjustable frame to represent differ-ent helicopter configurations (nose or tail wheel andsteerable or castorable wheel designs). Values thatare measured on the DLTV during the manoeuvringsimulations include: probe securing forces, DLTVposition and orientation, and suspension deflection.

Figure 10: Top and bottom views of the DLTV

ASIST Model

The two degrees of on-deck aircraft actuation are:the longitudinal motion of the RSD and the lateralmotion of the RSD claw (the actual securing point),which grips the helicopter-mounted probe. Using thetranslational scaling laws stated above, the motionsof the model of the ASIST system were scaled to tra-verse the 1

10 -scale, approximately 20 pound, DLTVlongitudinally at 3.8 in/s and move the claw laterallyat 0.3 inches per second.

A leadscrew assembly, similar to the preliminarydesign shown in Figure 11, is used for both the RSDand claw actuation using an ACME thread screwshaft with a pitch of 3 threads per inch. Two steppermotors are used to actuate the physical model of theASIST system.

Figure 11: Model of the RSD for the ASIST system

Actuation Components

The motion system will contain three actuation axes:x, y, and z, as shown in Figure 12. The x- and y-axesdescribe the planar motion of the RSD, where the x-axis aligns with the longitudinal motion of the RSD(parallel to the ship’s longitudinal axis) and the y-axis represents the lateral motion of the claw. Bothaxes will use size 23 stepper motors to activate theleadscrews. The z-axis contains the vertical linearactuator that will be used to produce the ship mo-tions, which is a purchased leadscrew linear actuatorpowered by a brush motor. To reduce the cost ofthe system, all three initially-required actuators arecontrolled using a multi-axis controller. A four-axiscontroller was purchased to accommodate further ex-pansion to include pitch motion. All three axes willinterface with the operator through National Instru-ments (NI) Labview 6.1 software with additional NIMotion tools, which allow all instruments and con-trols to be virtual and displayed on the computermonitor.

There are three aspects of the project that deter-mine the controls required for the planar motion sys-tem. First, the controller must allow input from ajoystick to control the longitudinal and lateral mo-tions of the RSD. Second, pre-programmed algo-rithms from the computer should be able to controlthe RSD. Finally, through the measurement of theposition and orientation of the model, automationalgorithms will be developed to determine the mo-tions required for the RSD.

Validation

The validation of the simulation has been brokendown into experiments involving ship motion and notinvolving ship motion. The validation done withoutship motion will be broken down into three stages:qualitative testing; scale-model experimentation onthe experimental motion platform; and full-scale ex-

Figure 12: Schematic of the actuation components

perimentation on ITI’s integrated test facility (ITF).The validation done with ship motion will be doneon the experimental motion platform. A verificationplan is outlined first.

Verification

The simulation is checked for programming errors.A set of inputs is run through the program and theresults at specific moments in time are then com-pared with hand calculations. This will be done fora wide range of inputs. The entire simulation is thenqualitatively scrutinized for a number of simple sit-uations. These situations include a constant probeforce inputs applied for different helicopter orienta-tions. Similar simple situations will also be used asdescribed subsequently in the context of the ITF-based validation process.

Qualitative Validation

An experienced ASIST operator will perform a num-ber of manoeuvres with the simulation interfaced toa joystick and a graphics package (ITI’s Dyna2D Rg).This will be done to get a general feel for the way thesimulation reacts, compared with the actual ASISTsystem.

Scale-model Experimentation on themotion Platform Without Motion

The simulation will be validated first with a phys-ical model of the helicopter and ASIST system onthe experimental motion platform. The helicoptertrajectory and orientation will be tested by runningthe helicopter through a few simple situations andmanoeuvres. These are described in greater detailbelow. The experimental results will then be com-pared with the simulation results.

Full-scale Experimentation on ITI’s In-tegrated Test Facility (ITF)

ITI’s ITF is currently equipped with a full-scale deadload test vehicle (DLTV) that can represent a num-ber of different helicopter configurations. Validationusing results generated by the ITF has been brokendown into three measurement phases. The complex-ity of the manoeuvres carried out increases with eachmeasurement phase.

The ASIST system joystick control input valueswill be recorded while each test is being carried outby a proficient ASIST operator. This allows for allof the phases to be recorded on the ITF at one timeand the validation results can be analyzed separately.The following data will be gathered from the ITF foreach test:

• claw velocities, to test the simulation joystickmodel;

• probe forces, to test the ASIST model;

• helicopter position, to map the trajectory;

• helicopter orientation, to map the orientationthrough the trajectory; and

• tire deflections, to further validate the tiremodel.

Simple Situations

The ITF will be run through some simple motionsfirst to catch any large discrepancies between thesimulation model and reality. These simple sit-uations will include, moving the helicopter: in astraight line; in a straight line along a curved track;and swinging the castor wheel laterally. These canalso be used to help determine if the instrumentationis set up correctly.

Manoeuvre Components

A number of standard manoeuvring situations willbe used for advanced testing. These manoeuvres canbe broken down into three different manoeuvre com-ponents. The next validation step is to run the ITFthrough these components that are:

• straightening where the helicopter is straight-ened from an askew angle;

• align probe where the probe is aligned with thetrack from an askew angle; and

• align castor where the castor wheel is realignedfrom 180 degrees and 90 degrees.

Standard Manoeuvres

Standard manoeuvres, which are groups of two orthree of the components defined above are used tostraighten the helicopter from an askew landing ori-entation. Three conditions, as defined by ITI, mustbe met for the helicopter to be considered straight-ened. The conditions are: the probe must be cen-tre on the track; the nose or tail wheel pivot axismust be on the track centreline; and the nose or tailwheels must be parallel to the centreline. These con-ditions must be met for a successful manoeuvre tohave taken place.

Effect of Motion on the ManoeuvringSimulation

The study of the effects of motion on the manoeu-vring of the helicopter uses the experimental motionplatform with a physical model of the helicopter andASIST system to simulate various magnitudes andtypes of ship motion during the manoeuvring of thescale-model helicopter. The resulting model trajec-tories under the influence ship motion will be com-pared to the model trajectories without motion. Theresults from the experimental motion platform canthen be compared to the planar manoeuvring simula-tion and simple alterations can be made to the simu-lation to represent the ship motion, such as changingthe direction of gravity. The alterations to the planarsimulation may not result in a completely accuratemodel of the manoeuvring of the helicopter with shipmotion, however it will be an approximation. Oncethe results of this project are incorporated into Dy-naface Rg[1], a comprehensive, accurate, and fully-three-dimensional simulation will result.

The cases that were used to validate the manoeu-vring simulation without ship motion will be re-peated with motion generated by the developed mo-tion platform. The data will be compared with thepreviously obtained data to determine the effect ofmotion. Six cases will be selected, based on roll an-gle and heading angle, for use during the study ofthe effect of motion on the manoeuvring of the heli-copter.

Application

This ongoing multi-phase project is comprised ofthree distinct parts. While the combination of thesethree parts is aimed at both resolving the immedi-ate need for analysis capability and demonstratingthe potential for a significant technological advancewith autonomous operation, each of the individual

parts is suitable for a variety of applications beyondthe immediate objective.

Manoeuvring simulations have traditionally beendeveloped for four-wheel road vehicle applicationsat relatively high speed, with the force generatedthrough the wheels. The specific simulation thatis the subject of this work has addressed the moregeneral case where the system is driven by forcesgenerated externally and not necessarily coincidentwith the wheels. In the case of the ASIST system,the aircraft has three to six wheels and manoeu-vring forces are applied to a retractable helicopter-mounted structural probe that is located near thevehicle’s centre of mass. This technology could beapplied to a variety of material handling applicationswhere material is being towed on wheeled platformsor otherwise manipulated by external forces. For ex-ample, navies are looking for faster means to movecargo on deck to achieve faster replenishment at seaoperation. Analysis and simulation of the proposedequipment for such application would be necessaryfor the design process.

Development of a motion platform and associatedtest vehicle constitutes a fundamental research toolthat, in the current application, will be used for sim-ulation validation and to support development of au-tonomous manoeuvring and traversing algorithms inthe presence of ship motion. However, this generaltest facility could be used to investigate securing re-quirements in a variety of motion environments. Twoimmediate applications in Ontario include road andrail shipping of automobiles and rolls of processedsteel and cabling. A recent tractor-trailer fatality inOntario has been attributed to inadequate securingof such cargo.

Automation also has potential widespread appli-cability. The unique feature of the proposed work isthat a successful on-deck manoeuvring algorithm fora helicopter must combine conventional path plan-ning and error control strategies with a decision mak-ing approach as the optimal manoeuvring sequence iscomprised of multiple manoeuvres dependent uponthe initial position and orientation of the aircraft onthe flight deck. The considerations involved in thisaspect of the project have applications in other in-dustries including manufacturing, automotive, andtransportation.

In addition to the direct benefits to companiesthat become directly involved in the work, spin-offbenefits must also be considered. ITI is a systemintegration company, where improved market shareresulting from improved technology in its productswill lead to expanded sales and spin-off benefits forthe many Ontario manufacturing companies that are

subcontracted to provide the material and manufac-turing processes required for the production of ITI’sproducts. While the overall project is aimed at oneparticular technical challenge, the elements of theproposed project make the technology transferableto other industrial applications in Ontario and be-yond.

ITI markets its analytical services to navies andshipyards around the world. In the short termthis research program will add to ITI’s capabilitiesand opportunities to perform more extensive stud-ies and provide software licences to its customers.In the long term the research program will facili-tate the development of the TC-ASIST control sys-tem. TC-ASIST is being developed to target Euro-pean markets with a sales volume potential of over$30,000,000.

Development of the motion platform to replicateembarked helicopter securing and manoeuvring in acontrolled environment will set the foundation for fu-ture experimental research work relating to the dy-namic interface problem, and thereby offering long-term benefits in terms of securing equipment designas well as the safety of personnel during embarked he-licopter operations. Autonomous manoeuvring andtraversing has the potential for raising the state ofthe art for embarked helicopter handling systems andwill affect the direction of future developments.

Concluding Remarks

The vital role of helicopter/ship dynamic interfaceanalysis has been steadily increasing as shipboardhelicopters are required to operate in more extremeranges of sea conditions, as interoperability require-ments become more prevalent, and as the demandsplaced on the efficiency of on-deck operations - bothin terms of minimizing the number of deck person-nel and reducing the required time for on-deck op-erations increase. Simulation capability for investi-gating shipboard helicopter securing requirements isfairly mature with the availability of established he-licopter/ship dynamic interface simulation programssuch as Dynaface Rg[1]. The project described inthis paper addresses the increasingly important ship-board manoeuvring and traversing aspect of em-barked helicopter operation. It is expected that thehelicopter manoeuvring simulation and associateddynamic interface experimental motion platform willlead to significant improvements in analysis capabil-ity and will contribute to optimization of manoeu-vring algorithms, the possibility of autonomous ma-noeuvring and traversing, and refinements to heli-

copter securing methods that facilitate on-deck heli-copter handling.

Acknowledgment

This project has been sponsored jointly by IndalTechnologies Inc. (ITI), Materials and Manufactur-ing Ontario (MMO), and Carleton University (CU).

References

[1] R. G. Langlois and A. R. Tadros. User’s Man-ual for the Aircraft/Ship Dynamic Interface Sim-ulation Dynaface Release 5.0. Indal Technolo-gies Inc., Mississauga, Ontario, Canada, January1998. ITI Report No. 99/419 (dia5).

[2] R. F. Smiley and W. B. Horne. Mechanical prop-erties of pneumatic tires with special reference tomodern aircraft tires. Technical report, NationalAeronautics and Space Administration, LangleyResearch Center, Langley Field, Virginia, USA,1980. (dia24).

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