Future design requirements and trends to overcome challenges of helicopter operations BY Wg Cdr (Retd) NS Krishna YSM
WHAT ARE THE DESIRED QUALITIES IN AN IDEAL AEROPLANE? Helicopters Ideal Aero plane Usually symmetrical.. Neither Aero foil design for high lift or high lift or high speed high speed NO.. In addition, various part of Wing adaptable for various rotor move at different speeds stages of flight NO Should be Trimmable Fuel efficiency per seat is over 5 Fuel Efficient times a A 320 HA HA HA Minimum noise Substantial losses by the time Minimal Loss of Power power is delivered to Rotors
Ideal Aeroplane Helicopter Minimum Drag Very draggy, primarily due to gearbox Sealed and capable of being Not designed to be pressurized pressurized Effect of Controls-Minimal Each movement cyclic, collective Cross couplings and rudder pedals has a primary, secondary and tertiary response Should be statically and Dynamic unstable.. Diverges Dynamically stable rapidly Range –should be large Very limited ranges Vertical/short Takeoff and Landing YES YES YES!!!!
• Helicopters are different from planes. • An airplane by it's nature wants to fly, and if not interfered with too strongly by unusual events or by a deliberately incompetent pilot, it will fly. • A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other • If there is any disturbance in this delicate balance the helicopter stops flying; immediately and disastrously. This is why • airplane pilots are open, clear-eyed, buoyant extroverts • helicopter pilots are brooding introspective anticipators of trouble.
So, why fly helicopters at all? Helicopters differ from Aeroplanes in that they :- • Can Hover • Can move sideways and backwards • Can fly very slow without stalling • Can fly very low to avoid radar detection • Can maneuver in small spaces
MAIN USAGE OF HELICOPTERS • Usage in civil is mainly for operations to/from places where big landing surfaces cannot be built • Mountains • Offshore oils rigs • Emergency Medical Services from unprepared accident sites to nearest Hospital ( roof top or nearby helipad) • Trump Towers to JFK Airport • Disaster relief
Exotic Civil Uses • Policing and Traffic management • Helitourism.. Such as ride to the Grand Canyon • Lifting heavy tree logs from Jungles or mountains to nearest processing plants • HT cables laying • Cattle rounding • Clearing water logging and snow from runways
MILITARY USAGES • Casualty Evacuation – Remember M*A*S*H? OF course you would not.. Even I was a kid then!! • Battlefield Air Support – Fighter Aircraft cannot fly low and slow as required • Anti Tank- Very effective as they can use a fire and forget missile, and duck after firing • Air Superiority– ie protect own troops and tanks from enemy helicopters and fighters using ATAMs • For direct attacks , as a Command post and for transporting troops during Anti Terrorist operations
“ The helicopter approaches closer than any other vehicle to the fulfillment of mankind’s ancient dreams of the flying horse and the magic carpet” – Igor Sikorsky • However, during all these roles, helicopters face certain operational limitations – Speed – Relatively costlier due to • Fuel Inefficiency in terms of seat per mile • Relatively lower payload capability • Lower cabin volumes for the same AUW – Maintenance intensive due to more rotating parts – Noisy- this is more noticeable as helicopters operate close to ground – Adverse weather operations in hills and to helipads carry great risks
FUTURE TRENDS OF HELICOPTER DESIGN SEEMS UGLY IS BEAUTIFUL!!
• All the future trends are towards :- – Overcoming Speed limitations – Reducing Noise – Improving Power to Weight ratio – Using Fly BY Wire and advanced Autopilots to artificially improve stability while retainingg maneuverability. – Improving fuel efficiency – All weather capability
VTOL X PLANE : A PROGRAM BY US DOD • VTOL X-Plane challenges industry and innovative engineers to create a single hybrid aircraft that would concurrently push the envelope in four areas: – Speed: Achieve a top sustained flight speed of 300-400 kt – Hover efficiency: Raise hover efficiency from 60 percent to at least 75 percent – Cruise efficiency: Present a more favorable cruise lift-to- drag ratio of at least 10, up from 5-6 – Useful load capacity: Maintain the ability to perform useful work by carrying a useful load of at least 40 percent of the vehicle’s projected gross weight of 10,000-12,000 pounds • Several companies have been funded for initial research, after which a short list will be made for competing for US Govt contract
EFFORTS TO INCREASE SPEED • Speed in helicopter is limited because :- – Dissymmetry of lift between advancing and retreating blade – Forward Control limits being reached as flap back is overcome – Retreating blade Stall – Compression effects on advancing tip ALL CURRENT PROJECTS ADDRESS THE ABOVE ISSUES
Trends in Speed Improvement Eurocopter X3 • Compound helicopters – – 253 KTs – Uses two puller propellers with differential pitch to provide antitorque – Stub wings offload rotors by 40-60 %, also preventing retreating blade stall – Rotors are slowed down to prevent drag from advancing blade tip
Trends in Speed Improvement Sikorsky X2 ( S (& Raider) • – 260 Kts – Rigid Contra-rotating rotors about 2 ft apart – Rear prop provides most of forward thrust requiring very little forward tilt of rotors – Resultant vibrations damped by active dampers – Instability countered by FBW and highly advanced AP
Trends in Speed Improvement Bell V280 Valor Designed for 280 Kts • Tilt Propellers at ends of a • straight wing Since control laws would be • very complicated, specially for transition f rom hover mode to forward flight, it has triple reduntant FBW system V tail for maneuverability • Range of 2600 nm – highest • of any new development of Future Vertical Lift ( FVL) aircraft
Boeing Concept :Phantom Swift • Employs a wide, blended body incorporating two large lifting fans, which are covered in forward flight. • It has ducted fans in swiveling nacelles at the end of the short wings. • Boeing has already built and flown scaled-down model of the Phantom Swift.
Avatar Planes? My Take? The Avatar helicopter/plane looks deadly, but cannot possibly be ideal for high speed! • Stub wings cannot give much lift • Rotors look too draggy for high speed • Rotors have very little tilt, and no propellor to give forward speed • DON’T SEE WHERE THE FORWARD THRUST IS COMING FROM
FUSELAGE SIZE • The space required for landing is determined by the rotor diameter and length • Requirement of an anti torque Tail Rotor and a supporting tail boom decreases available space for the cabin • Usable cabin space is steadily increasing with alternate solutions for anti-torque • These solutions could enable shuttles from heliport to heliport between city centres carrying 100 plus passengers
Trends in Rotor Blades • New thoughts in Rotor Design are required for – Optimising blade performance in advancing and retreating sides – Reduce vibrations – Reduce noise • “Smart” blades, which change shape Chordwise, or camber wise, are being developed • These use Local Mod of aerodynamic characteristics of a blade such as flaps, slots and boundary layer control to optimise performance across the full revolution in forward • Smart Blades use piezoelectric actuators–mechanical devices incorporating a material that changes shape when subjected to an electrical field
Trends in Rotor Blades GURNEY FLAPS- FOR INCREASING LIFT ON FLAPS- FOR MODIFYING LIFT REREATING SIDE AND REDUCING VIBRATIONS DROOP - FOR PREVENTING DYNAMIC STALL ON SLOTS FOR RE-ENERGISING RETREATING SIDE AND BOUNDARY LAYER REDUCING VIBRATIONS
Trends in Rotor Blades • NASA , in collaboration with Boeing and DARPA, has tested smart blades in a wind tunnel. • However, there is a long way to go as there are many challenges – Weight and Space constraints – Centrifugal loads – Reliability ( more than 10000 flight hours at failure rate < 10 -9 per hour) • Challenge greater for actuator which need to work more than once during a rotation cycle, for eg those used for active vibration control – Failures must not result in uncontrollability or adverse decrease in performance A SMART TEST PILOT WOULD BE VERY CAUTIOUS FLIGHT TESTING THESE!!
Efforts towards Reduction Of Noise Sources of Noise
DESIGN TRENDS FOR REDUCTION OF NOISE • Modulated Blade Spacing – Frequencies in equally spaced blades are related to spacing – Modulated blade spacing reduces noise by • Lower peak sounds • Distribution of acoustic energy over wider spectrum of frequencies • Reduced tip speed • Tip redesign mainly for reducing vortices and reducing noise impact of blade passing through vortices • Aerofoil tailoring as in smart blades
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