Rotorcraft Efficient and Safe ProcEdures for Critical Trajectories (RESPECT)

Air Transport

Rotorcraft Efficient and Safe ProcEdures for Critical Trajectories (RESPECT) C. SERR,G. POI7, J. HAMM, J. HUGHES, M. SIMONI, A. RAGAZZI, A. DESOPPER, A. TAGHIZAD, H.J. LANGER, C. YOUNG, A. RUSSO,A. VOZFLLA, J. STEVENS One aim of the RESPECTproject was to critically analyse current helicopter operations and propose validated guidelines for improved methods of operation, The method developed during the study and proposed as 'Improved Methodology for take-off and landing procedures" will be described. The code and some very specific simulator cues will be presented, helicopters studied in RESPECT (Rotorcraft Efficient and Safe ProcEdures for Critical Trajectories) cover a wide technical range of solutions for tail rotor, landing gears, fin, main rotor hub and a large weight envelope for cMl transportation. The RESPECT consortium brings together all of the major helicopter manufacturers and most of the aerospace research organisations in Europe. In addition some contacts were initiated with operators and airworthiness auflx~rities to inform them about the progress of RESPECT and finally to show the complete results. he

step validation phase. The general method proposed was: * to develop and validate off-line performance simulation software; • to optimise take-off and landing procedures; • to demonstrate their feasibility by piloted simulations and flight tests.

improvement. To improve the efficient\ of the consortium it was chosen to work with a common off-line code. As sucln a code did not exist, the project partners decided to develop that tool. A big effort was made on the x alidation phase. This code was used to analyse flight malmal operations to find safety criteria and fields of improvement (fit#re' 1). Using this code for parametric studie~, or for coupling with numerical optimiser was not a very difficult task and the optimisation process for existing operations or for future uses of helicopter, was performed.

Methodology description The first stage was to look at the current operational procedures and techniques and to find anv possible ways of C IJFFelIt oper .-3tinFi81

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Respect objectives The objectives of RESPECT were: • to determine how and bv how much terminal manoeuvres can be modified to improve mission effectiveness witln tlne same level of safety; • to demonstrate the feasibility of these manoeuvres taking into account all the practical difficulties. The manoeuvres dealt with are take-off and landing manoeuvres, taking into account that an engine failure may

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The project was not limited to the improvement of existing procedures or trajectories but allowed also research to demonstrate the safety issues of new trajectories or new type of operations. To reach these objectives with the best chance of success, a complete methodology has been proposed, with a step-by-

Operational Aircraft

EUROPA Manoeuvre OptJm isation

Figure I. RESPECT Methodology

Piloted Simulation

Flight Test 1 Future Operation

,Air Transport

AIR TRAFFIC MANAGEMENT

~,ome improved or new techniques were selected and were assessed through piloted simulations. This step gave the ;,pportunity to have 'a pilot in the loop' ta evaluate new trajectories, including ,,ome important points like repeatabilily, visibility, pilots' workload with and , vithout engine failure and without any danger for the crew or people on the ground. It was the first time that simulators were ~sed for emergency situations and the pilots were really enthusiastic about it. h e n , after having checked the pilotability of manoeuvres, some flight tests 'vere performed to validate, in actual light, the behaviour of helicopter. km~e guidelines and recommendations vere issued for improved or innovative roced u res.

Performance software Overview

the code developed is called EUROPA or European Rotorcraft Performance \nalvsis. The code is capable of finding :he performance limits of a helicopter at ~ach point in its operating envelope for ~oth steady-state and dynamic perfor'nance.

Manoeuvres can be complex (catego O A operation) and can be evaluated with engine failure, different atmospheric conditions etc... One additional use of the code is to simulate flight manual procedures to help defining safety criteria. Some optimisation techniques were coupled to easily iterate and find the appropriate manoeuvres (TDP, LDP). This code was de\eloped in Fortran and can be run on any kind of platform

{figure 2). Thanks to the very efficient cooperation between the partners and after 18 months of activity, the challenge proposed at the beginning of the project is on a good way to be reached. A ~lew code was developed in common under precise spec!fications for the code architecture and accurac> together with rules for the FortraJI development. The contribution of the partners to the development and the modularity of the code gave, as a result, a rather efficient code for steady amt lmsteady pelltbrmancc a~lalysis. A really big effort was also made on the code documentatioll with the production

• D e v e l o p e d in F O R T R A N • C a n be run on P C o r w o r k s t a t i o n Simulation models • Vehicle • Helicopter pilot • Environment (atmosphere, terrain) • C o n t r o l l o g i c (for m a n o e u v r e o p t i m i s a t i o n etc.)

Helicopter models

~ Choice of rotor models S t a n d a r d tail r o t o r o r Fenestron • Choice of engine models • etc...

Manoeuvre Visualisation

• Helpful when developing manoeuvres • I m p o r t a n t to c h e c k p i l o t ' s v i s u a l c u e s • V a l u a b l e w h e n b r i e f i n g for flight tests • Useful for presentation of results

of detailed manuals for users and developers. The code includes simulation models for vehicle, pilot, environment and control logic. For some helicopter components, several options can be selected. For tile mai, rotor, a blade element integration, an analytical model and a flight test power identification can be selected according to the available aerodynamic data and the constraints on computation time. A conventional tail rotor or a 'fe,estron' can be used. El(~,@le models range from elementary time constant response to a thermodynamic description of engine components. A specific helicopter model is built by specifying appropriate modelling options as part of the input data files. Additionally a post processing visualisation software using the VRML language has been developed. This software provides animated visions of the helicopters and shows the manoeuvres studied. It is helpful for the first visual checking and also to brief pilots before simulation or flight tests. Code validation

Because some flight test parameters are not modelled (e.g. variations in vertical air mass motion and wind speed), validation tends not to be an exact science! It is normally necessary to model a number of similar flight test events and look for trends. The performance simulation is deemed to be valid if all of the predicted parameters sit close to the centre of the flight test 'scatter'. A sample of results for the steady state is given

{figure 3). Once the steady state performance of the simulation has been verified, the model is validated for the prediction of manoeuvres. The pilot model and the control logic allow the simulation of realistic mam~em,res according to the procedure under study. The effect of pilot abuse such as reaction times, overreaction or the repeatability qflma~zoemws can be parametrically investigated, making possible to assess accurately the saj¢'ty

mal~@~s. To validate the vehicle model, a 'flight test matching' subroutine was created.

Figure 2. The EUROPA Code, ~.6i

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The pitch and roll attitude time tlistorv from a measured flight test e\'ent is used as the 'target attitude' to make tile performance-simulation follow the measured aircraft attitude traces.

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Tile accuracx, of the performance simulation is checked by comparing the 'free' simulation parameters with flight test \ alues (figurc 4).

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Piloted simulation step After the off-line optimisation .~tep, fix' RESPECT methodology proposes a piloted simulation phase to present the procedures and ha\'e them evaluated b\ tile pilots. It is evident that those procedures are set tip in close cooperation with the test crews but the risks inherent in the flight testing for such procedures call for preliminary evaluation in tile ~imulator, which could also be used as a training platform. Tile simulation step gixes the possibility to simulate life-like nlanoetl\Tes, incltlding pilot reaction time, pilot abuse, repeatability, low \ isibilitv (clouds, fog, rain .... ). It was possible to train tile pilot to the malloeuvre and to anah'se the repeatability versus sara't)' marghls.

Studied cases The RESI~ECT project studied 4 different operational theatres: • Clear heliport - tile objecti\re was to reduce noise footprint and to rapid[\ clear the way; • Eh>vated he/iF,t - strong constraint with noise since many of these heliports arc, close to a city centre or hospital; • Helideck/q~#hon, olvrotioJl pel'formance and take-off weight are a major concern for such long range missions; • Cos!fiswd/smprepm'edlnc~?-thepilotdoes

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For clear heliport landing, steep approach is regarded a.,, a possibility, to reduce tile noise footprint on ground. Such procedures raise new safety issues. It is necessary to evaluate tile impact el such trajectories on fine helicopter to allow smooth landing or to keep the capacity to climb in engine faihlre situations at any point of the manoeuvre. RESPECT does not advise one slope or tile other, but shows tlx~ capacity to

,Air Transport

A I R TRAFFIC M A N A G E M E N T

Clear heliport landing i Steep approach

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:alculate the safe Decision Point versus dope. The TDP (Take-off Decision :%int) height is calculated versus slope ~r weight (fi,~lm' 5). n the simulator sessions, the pilot could :perform the manoeuvres with calculat:'d limitations. However, his visual sen~ation was quite impressive and he also Jetermined the natural limit with espect to his own visual feeling.

Helideck take-off. F:or the helideck take-off operation tfi,k'n'c 0), the limiting factor is the weight to get the edge clearance and the minihum height with respect to ground (or sea).

4 possible solution is a change in headng at the TDP. It was possible to calculate the maximum take-off weight (MTOW) with respect to platform elevation and to _temonstrate possible payload gains in changing the take-off technique. 'Some very interesting results were also demonstrated, showing the capa9ility of the method to evaluate ,twlarnic techniques for take-off and landing.

Conclusions In conclusion, the main usable results of the RESPECT project are:

• the common EUROPA pe(fivnlmlce tool. Tile large field of applicability' was demonstrated; • all the flight tests and the simulation data were dedicated to performance and emergency procedures. This large dab7 ba~lk is ready for further code development and validation; . it was demonstrated that the piloted simulations are not only useful for flight mechanics analysis but can also be used for procedures research and pilot training for emergency operations; • all this steplby-step acti\itv illustrates the nlethodohs,y proposed to help for helicopter development, certification and specific operations; • at the end of the project, ~widvlim's and rCCOtlllllOlldatiotls w e r e issued, which could help operators and authorities in setting up new or improved operational rules. Many further, possible benefits may emerge in the field of safety and performance, reduction of proceclures testing and, specifically, dangerous ones with engine failure near the ground. The results sho;x that the method can allow operators to study operations in specific conditions at an acceptable cost.

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THERESPECTPROJECT Further information about this work can be found in the following:

P. Roesch, G Samoni, Applications of Energy Concepts to the Determination of Helicopter Flight Paths, 5th European Rotorcraft Forum, Amsterdam, Sept 1979. Okuno Y., Kawachi K., Azuma A., Saito S., Analytical Prediction of HeightVelocity Diagram of a Helicopter Using Optimal Control Theory, Journal of Guidance, Vol. 14, No 2, 1991 (also published by AIAA in 1990). Vodegel H., Stevens J., A Computer Programme for the Certification of Helicopter Vertical Take-off and Landing Operations and an Application to the S-76B Helicopter, 47th Annual Forum of the American Helicopter Society, Phoenix (Arizona), May 1991. Tr/inapp N., Reichert G., Hepp H., Maneuverability Aspects for Helicopter TakeOff and Landing, Proceedings of the 18th European Rotorcraft Forum, Sept 1992. Hamm J., The Use of Pilot Models in Dynamic Performance and Rotor Load Prediction Studies, Proceedings of the 18th European Rotorcraft Forum, Sept 1992. Langer H.J., Tr~inapp N., BO105 Flight Test Data for a Wind Tunnel Test Program, DLR IBl11-93/58. Hamm J., The Development of Helicopter Pilot Models to Control Engineering Simulations, Proceedings of the RAes/AHS Symposium on Rotorcraft Simulation, May 1994. Morel F., Multivariate Optimization Applied to Conceptual Design of High Capacity Long Range Aircraft, 19th ICAS Congress, Ahaheim (California), Sept 1994. Gr/inhagen V. et al, A High Bandwidth Control System for Helicopter In-Flight Simulator, International Journal of Control, Vol. 59, Nol, 1994. Basset P.M., Heuz6 D., Taghizad A., Weinstock S., Desopper A., Etudes h61icopt6res en m6canique du vol et en qualit6s de vol ~ I'ONERA/DES, La Recherche Adrospatiale, 1995, N°3. Helicopter Performance Modelling, Final Report Action Group 07, 1996 (GARTEUR restricted distribution). Sharma V., Zhao Y., Chen R.T.N., Optimal Sideways Operation of a Category-A Helicopter from an Elevated Platform, 52nd Annual Forum of the American Helicopter Society, Washington DC, May 1996. Rollet P., La simulation pilot6e pour la conception et le d6veloppement des appareils ~ voilure tournante, AGARD FVP Symposium, May 1995 (published in CP-577). Steinke M.M. & al, Airport/ATM Capacity Increase Through Rotorcraft Operation, Final report of DG VII -Airport/4-Study, Sept 1995. G. Padfield, Flight mechanics. C. Serr, J. Hamm, E Toulmay, G. Polz, H.J. Langer, M. Simoni, M. Bonetti, A. Russo, A. Vozella, C. Young, J. Stevens, A. Desopper, D Papillier, Improved Methodology for Take-Off and Landing Operational Procedures - the RESPECT Programme - EKE Sept 1999 (Rome). Tile helicopter industry as a whole would profit from tile market growth triggered by improved flight procedures and by quieter heliport neighbourhoods, if it can be shown that flight safety is preserved or improved without degrading helicopter pa}doad performances. The exploitation of fine results of the time-to-market could, howexer, take

some years since it would be first necessary to convince the helicopter community (operators, airfield authorities, airworthiness authorities) of the advantages offered by the new approach. Two natural follow-on activities are foreseen: • one is collaboration with authorities and operators for procedure research

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and solving of specific prnhlen> to impro\e helicopter saM\ or to open new markets; • the other, issued from this truitful partnership, is the COMPLICES proposal. Tile aim is to apply fix, tool~ and tile methodology to the Tilt Rotor aircraft for stead~ and unsteady, performance calculations. It will give the opporttmity to provide performance charts and emergency procedures amended by piloted simulations. This first 'Computed' flight manual will reduce the development cost and increase the aircraft s~!ti'ty. Acknowledgements

The authors wish to thank the European Commission for tile partial founding ot the RESPECT project. Tile partnership in this programme led to a gathering of knowledge, competence and expertise, coming from Industry and Research, which allowed to succ~:ssfulh' carry out tile RESPECT project. •

About the author: C. Serr (EUROCOPTER), G. Polz (EURO COPTER Deutschland), J. Harem (GKNWestland), J. Hughes (GKN-Westland), M. Simon (Agusta), A. Ragazzi (Agusta),

A. Desopper(ONERA),A. Taghizad(ONERA), H.J.Langer(DLR),C. Young(DERA),A. Russo (CIRA), A. Vozella (CIRA),J. Stevens (NLR),

For further information: A web site was devePoped by the RESPECTteam for the information of interested organisations, http: / /www.nlr, nl/public /hosted-sites/r espec t /