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24 WORLD AIRNEWS, MAY 2014.

Des Barker flies the

DIAMOND GUARDIAN DA42MULTI-PURPOSE PLATFORM

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There is no doubt that the technology gap that has traditionallyexisted between the classic military/civil purpose-built platforms

and the generic, smaller commercial airframes, is rapidlydiminishing. A “first” in South Africa as a surveillance

platform for CK Aerial Surveys, the Diamond DA42 MPP waspresented for evaluation in the LIDAR surveillance mission.

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WALKING OUT to pre-flight theDiamond DA42 Multi-PurposePlatform (MPP) for a flight test

from Lanseria International Airport, nearJohannesburg, recently, made for someintriguing viewing and even more interestingcomments.

It was clear that this was not your averagelight general aviation aircraft; a number ofunique design features have been included tooptimise the performance of the aircraft in thesurveillance role.

Hunched over the under-slung LIDAR Podand letting his imagination run for a while, anobserver’s comment was heard: “With thebubble canopy and the proboscis nose, itreminds me of a mosquito, no possibly adragon fly.”

Irrespective of the comments, it certainlylooked “operational”.

LIDAR, a combination of the words “light”and “radar”, is essentially remote sensingtechnology measuring distance by illuminatinga target with laser energy and then analysingthe reflected energy returns, much the sameas radar; basically using laser energy instead ofelectromagnetic waves as is the case in radar;laser, of course, being more accurate thanradio waves.

Raising further interest, a label on the topof the wing adjacent to the refuelling pointposted the following: “WARNING: APPROVEDFUEL JET A-1”, this while staring at thepropeller and engines of a non-turboprop?

The two Thielert 2,0-litre Centurion 135 hpengines are gas turbine engines that can befuelled with either JET A-1 or diesel.Considering the ever decreasing availability ofAvgas, this design attribute was an enhancingfeature essential for remote operations inwhich either of the two fuels would, in alllikelihood, be available.

THE AIRCRAFT At a maximum takeoff weight of 1 785 kgs, theDiamond DA42 MPP is categorised as a lighttwin-engine aircraft designed as a multi-purpose platform to carry a range of sensors,thereby providing a multi-role surveillancecapability.

It is clear that the designers strove toimprove performance through the use ofcomposites, in which the fuselage “wettedsurface area” was visibly decreased to reducedrag, winglets on the wingtips and the

tailplane to improve the aerodynamics andstability and control, a sharpened, multi-purpose “universal nose” and a bubble canopyto provide improved field of view for thesurveillance mission.

From a design philosophy of cost effectivesensor capability, the team of DiamondAirborne Sensing (subsidiary of DiamondAircraft) has integrated several different sensortypes on the DA42 MPP including RIEGL’s state-of-the-art airborne laser scanner LMS-Q680i.

The semi-monocoque fuselage is made of

Getting into and out of the DA42MPP poses no problems as can be seen above.The systemsoperator sits behind the pilot with his computer nicely positioned for easy access.

ultra-light, high-strength composite materialswhile the low wing cantilever design integratesoutboard aerofoils, an inboard split flap and anoutboard plain flap, while the tail sectionincorporates a T-tail, elevators and rudder.

In an effort to provide docile handlingqualities, the Wortmann FX 63-137/20 - W4aerofoil, the first aerofoil designed to operateat low Reynolds numbers of <1 000 000, wasused since it has become the benchmark forthis category of aircraft. With a large pitchingmoment and a relatively thin trailing edge anda maximum thickness of 13,7 % at 29,7 %chord, it generates high lift-to-drag ratios.

The composite wing structure is smoothand seamless in which the structural engineershave used a reliable aerofoil section togenerate the lift efficiencies evident in theperformance and also the handling of theDiamond. Washout towards the wingtipsterminates in a winglet to reduce liftdependent drag and provide symmetrical andrelatively docile stall characteristics.

Another enhancing feature is the bubblecanopy providing a very wide field of view ofapproximately 290o – 145o each side in thehorizontal and 125o in the vertical whichprovides for a relatively wide field of view that isideal for the visual surveillance role and pro-vides a feel of head space and unrestricted view.

To enable operations from remote stripsoften associated with the surveillance mission,

the DA42 aircraft is equipped with a robusthydraulically retractable, single bogeyundercarriage.

The DA42 MPP is fitted with a duplicatedanti-icing system which protects wings, tail andwindshield using anti-icing liquid TKS.

A weeping wing system, also known as a TKS(Tecalemit-Kilfrost-Sheepbridge Stokes) systemuses a liquid based on ethylene glycol to coatthe wing surface and prevent ice fromaccumulating. The leading edges of the wings,horizontal and vertical stabiliser are made ofporous, laser-drilled titanium panels, throughwhich the fluid is pumped during flight in icingconditions. A “slinger ring” is used to distributefluid on the propellers, and a spray bar is usedto apply fluid to the windshield.

ENGINEAn enhancing feature is the engine powermanagement controls. The two Thielert 2.0 ltrCenturion 135 hp turbocharged, common-railinjected diesel engines drive two MT three-blade constant speed propellers, generating arelatively low 270 hp.

Engine management is essentially via theengine control electronic unit (ECU) whichfacilitates automatic engine control so thatpilots no longer have to manage six levers tocontrol and feather an engine manually andsynchronise rpm; in fact, the two engines ofDA42 MPP are controlled fully by a single lever

for each engine.Pitch and mixture are automatically

controlled allowing the pilot to focus on flyingthe aircraft. Engine feathering is equally easy.To restart after a simulated engine failure, it isenough to turn the switch on and restart it.

The engines are capable of operating atmaximum power without time limit, which,with the ability to climb on single engine atmaximum weight, provides a degree ofresilience and reassurance for the mission,both during day and night time.

It must be emphasized that this is a lighttwin, yet single engine performance wasdemonstrated at 1 700 kgs/7 500 ft pressurealtitude/ISA +18oC at Vyse = 82 KIAS whichresulted in an absolute ceiling density altitudeof 9 530 ft. The manufacturer’s single engineoperational flight ceiling for a DA42 withoutthe Lidar Pod is reported to be 10 000 feet.

The DA42 is claimed by Diamond to beenvironmentally friendly, burning far less fuelthan any other aircraft while using jet fuel in aturbo-charged diesel engine which results inlow carbon emissions. Most otherconventional general aviation aircraft usingpetrol-based engines burn high leaded fuels atapproximately three times the rate that a DA42burns fuel!

Diamond claims that passenger carbon taxmeasured in a passenger mile context is thelowest of any aircraft.

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AVIONICS, FLIGHT SYSTEMSThe DA42 MPP is provided with the GarminG1000 integrated avionics system, a fullyintegrated flight, engine, communication,navigation and surveillance instrumentationsystem.

The system consists of a primary flightdisplay (PFD), multi-function display (MFD),audio panel, engine sensors and processingunit, and integrated avionics containing VHFcommunications, VHF navigation, and GPS.

The aircraft is also equipped with GarminGDC74 integrated digital air data computer,Garmin integrated Mode S transponder, solid-state attitude and heading reference system(AHRS), and dual flight controls to provide thepilot with the capability required to accuratelyfly the surveillance mission.

The primary function of the PFD is toprovide attitude, heading, air data, navigation,and alerting information to the pilot. Theprimary function of the MFD is to provideengine information, mapping and terraininformation and, in conjunction with autopilotGFC700 and Garmin ChartView system,displaying aero navigation maps on a flightdata indicator provides the pilot automatednavigation capability.

The system is also installed with Garmin SVT(synthetic view technology) incorporated asstandard equipment. Throw in TCAS, GPWS,GPS, VOR and DME, the multitude of flight,engine and navigation information available tothe pilot is equal to that possessed by the mostsophisticated aircraft crossing world airways.

Remembering that the aircraft is designedfor single pilot operation, the danger of pilotcognitive saturation exists, but this has beencleverly negated by displaying all requiredflight and navigation data such as TAS, densityaltitude, OAT, fuel flow, etc, via digital tapelinesand digital displays making it possible for thepilot, in a single glance, to determine aircraftstatus, thus reducing pilot workload andthereby enhancing safety.

The synthetic vision overlay of the primaryflight instruments provides the pilot with a“bird’s eye view” for spatial orientation whichwith a coupled autopilot, TCAS and groundproximity warning, additionally makesavailable a protective bubble to allow the pilotthe luxury of being the system’s manager.

AIRBORNE LASER SCANNINGAirborne laser scanning is a rapid, highlyaccurate and efficient method of capturing 3D1 Pilotdata of large areas for variousapplications, for example: city modelling,power line monitoring, large area and flood-plain mapping and even precise digital terrainmodelling.

The fidelity and capabilities of airborne

sensors has increased exponentially over thelast ten years and the ability to generate 3Dproducts is now within easy reach of even thesmaller airborne surveillance companies.

The REIGL airborne laser scanning systemprovides a rapid, highly accurate and efficientmethod of capturing 3-D data of large areas forvarious applications.

Up to now airborne service providers had toput a lot of time and work into systemintegration and data acquisition; a major costfactor of the whole surveying mission – today,it has become “plug and play”.

A laser-scanner captures the terraintopography by firing a laser and measuring thetime it takes for the laser to be reflected backfrom a point. The result of the collectedmeasurements is a digital terrain model in theform what is known as a “point cloud”.

By merging an ortho-photo with the “pointcloud”, a precise, realistic 3D model of theobject is generated. So what is the principle ofoperation?

SURVEILLANCE MISSION PROFILECritical mission requirements for surveillanceaircraft have, and will continue to be, costeffective operations with maximum enduranceutilising high technology sensors.

In this specific LIDAR mission, the pilot isusually “hands-on”, following the instructionsof the backseat operator, monitoring andcontrolling the aircraft flight path along adesignated route, manually making changes tokeep the platform level; so, no banked turns,only “flat turns”.

This obviously requires harmonised controlinputs from aileron and rudder, the amountbeing a direct function of the directionalstability of the aircraft.

A typical surveillance mission using airborneLIDAR could require the aircraft to operate at100 KIAS and normally at a height between1 000 to 5 000 ft agl. Under such conditions,the DA42 MPP is flown at relatively low powersettings of 45% to 65% which provides

endurance from six hours to nine hours. Once the aircraft is trimmed out, the

positive stability enables the precisionrequired to maintain tracks hours on end, thatis until, according to the mission pilot, you areforced to land due to a “weak bladder or a sorebutt”.

FLIGHT TEST PROGRAMMEA “snapshot” of aircraft performance andhandling testing was conducted specificallywith reference to the surveillance mission andwhich included takeoff performance, specificexcess power tests at 5 500 ft pressure altitudeand climb performance testing from 5 500 ftpressure altitude to 7 500 ft pressure altitude.

Stability and control testing included stalltesting in cruise, approach and landingconfigurations;. longitudinal and lateraldirectional static and dynamic stability testingincluding Phugoid damping, short perioddamping, steady heading sideslips, spiralstability and Dutch Roll damping wasevaluated. In addition, single engine climbperformance was evaluated.

IN-FLIGHT HANDLINGWith brake release against full power onLanseria’s runway 07 (26oC/density altitude =6730 ft/ISA +20oC) and a seven knot crosswind,rotation at 72 KIAS occurred after 24 seconds,lift off at 76 KIAS at 26 seconds which resultedin a ground roll of 540 metres and a totaldistance of 600 m to cross the 50 ft agl screenheight.

To assess the effect of the under-slung podon the specific excess power of the DA42 MPP,a level acceleration at full power wasconducted at 5 500 ft (ISA+20oC) densityaltitude 7 100ft from 80 KIAS (90 KTAS) to 140KIAS (156 KTAS). Despite the increased dragfrom the LIDAR Pod and a relatively low power-to-weight ratio of only 0,15 hp/kg, the aircraftaccelerated at an average rate of approxi-mately one knot per second demonstratingadequate excess power at the higher densityaltitudes typically found in African conditions.

Level cruise performance tests wereconducted in an effort to determine typicalrange performance. An economy of 29,1nm/gallon at 65%/2 050 rpm/135 KTAS wasmeasured at 7 500 ft pressure altitude (ISA+18oC) which would enable a range ofapproximately 1 300 nm plus 45 minutesreserve or 10 hours of flight. Pilot fatiguewould be the singly most constraining factor tomaximising this specific capability.

At 75% power, the performance was equallyimpressive; a 142 KTAS at fuel flow of 5,3 gphprovided a SAR of 26,7 nm/gal. To givesubstance to this platform/sensor combinationperformance, the DA42 MPP is able to

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BASIC CHARACTERISTICSDiamond DA42 MPP

Capacity:..............................1 Pilot + 3 PaxLength:............................................8,56 mWingspan: ....................................13,42 mHeight: ............................................2,49 mWing area: ..................................16,29 m2

Empty weight: ..............................1 520 kgGross weight:................................1 785 kgMaximum speed: ............................192 ktRange:............................................914 nmService ceiling: ............................18 000 ftRate of climb: ......................1 280 (ft/min)

complete an impressive 10-hour survey flightwith a range of up to 1 042 nm at an altitudeof 10 000 feet and can collect data from areasof 3 400 km² during a single flight.

CLIMB, STALL PERFORMANCEClimb performance was evaluated at aconstant 85 KIAS as per manufacturer’spromulgated airspeed at a mid-weight of 1 750kgs. At an average ISA +20°C for the climb slicethrough 2 000 ft, the time to climb was 3,40seconds, providing an average rate of climb of550 ft/min which was considered acceptablefor the surveillance mission.

The stall characteristics were evaluated inthe cruise, approach and landing configurationat a mass of approximately 1 740 kg, 40 kgbelow MAUW. The aircraft was decelerated atapproximately one knot/second with stallwarning typically six knots higher than the stallspeed, buffet onset approximately two knotslater and then the uneventful stall.

There was no significant wing roll off, oruncommanded pitch; roll or yaw motion at thestall which was characterised by a wings level“parachute descent” at approximately 400ft/min. In the cruise configuration a stall speedof 67 KIAS was recorded; in the approachconfiguration, stall speed was 60 KIAS and inlanding configuration, 55 KIAS.

The average height required for recoverywas 300 ft. The POH figures for the 1 785 kgmass were: Cruise: 65 KIAS; Approach: 61 KIAS,and landing: 57 KIAS, which was within twoknots of the figures recorded on the flight.

STABILITY AND CONTROLA sample of stability and control tests wasconducted in the cruise configuration at atypical mission cruise power setting of 72% at

7 500 ft pressure altitude/115 KIAS (135 KTAS). In terms of longitudinal stability, the

Phugoid period was measured at 35 secondsand the motion damped within three cycles.

As in most conventional statically anddynamically stable aircraft, the short periodwas essentially deadbeat. This impliedsatisfactory control and “pointing” ability inpitch, so important in accurate height andpitch attitude control.

As could be expected from this class ofaircraft certificated to Part 23 requirements,the Phugoid period of 35 seconds waspositively damped while short period dampingwas nearly aperiodic, that is: approaching‘deadbeat’.

The implications of this in terms of handlingand flying qualities was that the aircraft, underthose conditions, would be easily controllablein pitch due to predictable response to pilot oratmospheric turbulence input.

The lateral/directional stability wasevaluated by means of steady headingsideslips and Dutch Roll damping. To the left,a roll/yaw ratio of 1:1 was measured, and tothe right, 1,5:1 was measured.

Dutch roll damping was measured at 2,5seconds with two cycles to damp. The roll/yawratio generated was approximately 1:1 whilespiral stability was neutral.

An enhancing feature of the handlingcharacteristics was the tactile feedback fromwell balanced controls, the control harmonyand the predictability of control inputs therebyallowing for predictable response to pilotinput.

Assessing the low speed handling qualitiesin the flapped configurations during approachand landing, the approach was flown atVref+10 with Vref = 71 KIAS.

The stability and control about all axes wassatisfactory and coupled to well harmonisedcontrols and positive speed stability, thelanding configuration was stable enablingprecise and smooth landings.

MILITARY UTILITYThe military utility of the DA42 has not goneunnoticed by several air forces worldwide. Theair forces of Ghana, Niger, Thailand, SwissArmy, Ukraine and the United Kingdomoperate DA-42MPPs in the training andsurveillance roles.

At least two of those operated by the RoyalAir Force were assigned to intelligence,surveillance, target acquisition andreconnaissance (ISTAR) missions by the BritishMoD. Civil operators operate the DA42 in flighttraining schools, aerial surveillance andmapping.

CONCLUSIONSThe integration of modern sensor systems onsmaller, cost effective general aviation aircrafthas changed the surveillance workplaceforever, allowing smaller players to enter thischallenging environment in which surveillance,monitoring, modelling and simulation areplaying a more significant role in modernsociety than ever before.

With over 500 delivered aircraft operatingworldwide, the DA42 is the best selling lighttwin engine piston aircraft, popular withprivate pilots and commercial flight trainingorganisations. With its all carbon airframe, icecertification, Garmin G1000 and single lever jetfuel powered turbo-diesel engines, the DA42is a technology leader in general aviation.

The message is there: the Diamond Austriaorder book is full until at least 2015. Q

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