INDIAN INSTITUTE OF TECHNOLOGY KANPUR

Transcription

1 INDIAN INSTITUTE OF TECHNOLOGY KANPUR

2 INDIAN INSTITUTE OF TECHNOLOGY KANPUR Removable, Low Noise, High Speed Tip Shape Tractor Configuration, Cant angle, Low Maintainence Hingelesss, Good Manoeuverability, Maintainence Free, Foldable Composite Hub Low Vibratoin, Smooth Ride Vibration Isolation System Advanced Airfoils Efficient Lift Variable Incidence Stabilator, Improved longitudanal stability, Easy to trim Efficient at forward speeds, Reduced Rotor Wake Interaction, Removable Easily configurable interiors Twin Engines with Full Authority Digital Electronic Control Multifunction Displays, AFCS, Less pilot work load Cabin Door Easy Access, Sliding Cargo Tracks Extensive use of Composites Long Life, Corrosion Resistance Safety, Modular Self Sealing Fuel Tanks Tapered, Swept Back, 25% chord Flaps, Reduced Hover Download Optimised Lift in Forward Flight, Removable

3 BASELINE HELICOPTERS Kaman UH-2A Turbojet-single 2,500 lb static thrust General Electric YJ85 Trials carried out using a modified UH-2A Seasprite. Modifications were made to graft a pair of wings from a Beech Queen Air light executive transport aircraft onto the sides of the lower fuselage, giving the aircraft a wingspan of ft Reached speeds up to 225 mph. Pilots reported that the wings did not hinder autorotation Lockheed XH-51 A Turbojet-2,500 lb static thrust Pratt & Whitney J60-P-2 A set of wings spanning 16.9 ft in was fitted to the aircraft The auxiliary turbojet and stub wings partially unloaded the main rotor in forward flight, reducing the critical blade tip speed and blade angle The wings were each equipped with spoilers to assist entry into autorotation at high speed in an emergency. In addition, the horizontal and vertical tail surfaces were enlarged On June,1967, the XH-51A Compound set an record for rotorcraft by attaining a speed of mph. Sikorsky X-2 Propeller-LHTEC T800 Turbo shaft Engine. Incorporated the research findings from Sikorsky S-69 coaxial helicopter developed as a part of the Advancing Blade Concept (ABC) program. Maximum Speed 250knots. The demonstrator also reached a speed of 260 knots in a shallow 2 to 3 dive. Poor Payload / Gross Weight ratio

4 MISSIONS Wing Insertion : i) Best range speed of 120 knots. ii) Carries a heavy payload of 4000 lbs. iii) Does not require thrust and lift compounding and hence wings and propeller are removed. iv) TOGW: lbs Return Flight : lbs Main Rotor Auxiliary Thrust Main Rotor Main Rotor Rescue Mission : i) Speed of 192 knots achievable ii) Reaches destination within the golden hour. iii) Both thrust and lift compounded. iv) TOGW: lbs Return Flight : lbs Resupply : i) Best Range speed of 120 knots. ii) Lower payload and hence has lowest gross weight among the three missions. iii) This mission also doesn t require thrust and lift compounding. iv) TOGW :12900 lbs Return Flight : lbs

5 MAIN ROTOR ITEM DETAIL Radius ft Chord 1.97 ft Tip Speed 644 ft/s Solidity Twist -2 o Lock Number 12 Mass 920lbs Hinge Offset 15%R Tip Speed The tip speed is limited to 644 ft/s because of compressibility, noise and retreating blade stall effects Solidity Twist Aspect Ratio The solidity is high because it has lower vibration, noise, and delayed retreating blade stall It has low twist to prevent blade stress during fast forward flight Small aspect ratio to ensure natural frequency of 2 nd flapping mode is below 3/rev BERP Tip This blade tip shape reduces compressibility and has high stall angle.

6 WING DESIGN Variable incidence wing It provides the ability to optimize the wing lift ratio. It adds to structural complexity of the design, adding to the weight of the aircraft and the inability to build in components such as undercarriage and fuel storage into the wing. Since wings are used only in search and rescue mission requiring a large volume of fuel, this concept was not incorporated. Flaps A trade off which allows the wing lift to be controlled to a greater degree is the use of flaps which allows controlled the wing lift to a greater degree while not impairing the structural simplicity. A plain flap of 25 per cent of the wing chord length and with a deflection less than 90 o, to a void flow separation, could reduce the download of a wing by the order of 30 per cent. Spoilers and Brakes Previous experiences with compound helicopters have indicated that the auto rotative capabilities are not enhanced substantially with spoilers hence they have not been incorporated into our design. Wing Plan form and Geometry A majority of past compound helicopter designs have utilized a compromise wing aspect ratio of around 6 to create a balance between low induced drag in cruising flight and hover download minimization. Sweep has been used to a moderate degree on a majority of the past compound aircraft, mainly as a means of correctly positioning the wing aerodynamic centre. Aerofoil The general thought on the choice of aerofoil section for compound helicopters has been to use a section of fairly large thickness, with low drag in cruising flight, a high maximum lift coefficient and gentle stall.

7 AUXILIARY THRUST Mainly used for improvements in the fuel consumption over the turbojet and the resultant gross weight reductions enabling it to be used for long high-speed missions. Used in Bell-533 compound Helicopter. Turbofan The efficiency of the propeller offers improved acceleration and extended range for a set fuel load, particularly if a majority of the flight time is to be spent in cruising flight. The first is that by using reverse pitch it acts as an extremely effective braking device to slow the aircraft. Propeller The ducted fan is in a way a compromise between the propeller and the turbofan, attempting to maintain the efficiency of a propeller while using less disc area. The shroud incurs a weight penalty for the aircraft and, particularly if wing mounted, may induce significant blockage effects in hovering flight. Ducted fan For the given mission profile, and taking into account the nature of various missions and reconfigurations, propeller complied with most of the mission requirements and provided a lighter, less noisy and a reliable source of auxiliary thrust. Ease of Installation and removal during reconfiguration. It has greater fuel efficiency as compared to turbofan and turbojet engines. It reduces mechanical complexity and separation losses as compared to the fan-in-fin ducted fan concept. When auxiliary thrust is not required in Insertion and Resupply missions, ducted fan concept poses problems in reconfiguring the helicopter. The transmission system selected is the simple mechanical transmission as 2 engines were installed. According to Trade studies, Variable Cycle- Single Powered Shaft gives the best efficiency for a single engine compound helicopter with propeller. Has the benefit of being a proven and mature technology. Its drawback is that to ensure an adequate fatigue life it generally results in a system of significant weight. Mechanical Single power shaft connected to a variable pitch fan, the fan pitch determining how much shaft power is available for the rotor shaft. Benefit of leaving the engine core essentially unchanged, apart from optimizing the geometry. Variable cycle Single Power Shaft Separate turbine for driving the rotor and the propeller, allowing their speeds to be independently controlled. Efficiency will depend on that of fixed geometry system at its design point. Variable Cycle- Separate free Turbines By reducing the nozzle area a backpressure is formed, which transfers energy from the shaft to the jet thrust. A fixed nozzle was used on the world speed record Lynx aircraft to produce this effect. Variable Cycle- Variable Nozzle Area

8 WEIGHTS GROUP WEIGHT(lbs) Main Rotor and Hub 920 Tail Rotor and Hub 127 Body 2445 Engine 1226 Horizontal Stabilizer 60 Vertical Fin 88 Wing 484 Propeller Unit 100 Transmission 1280 Fuel Tanks 3000 Nacelles 296 Crew 730 Cockpit Controls 30 Landing Gear 398 Mission Search and Rescue Location (ft) Resupply Insertion (outboard) Insertion (inboard)

9 TRIM Pitch Moment Equation (gives an estimate of Β 1c ) Horizontal Force Equation (calculation of α,c at ) Vertical Force Equation (calculation of C t ) Roll Moment Equation (gives Β 1s ) Calculation of inflow ratio λ Calculation of Tail Rotor Thrust coefficient C at Calculation of Roll Angle φ Estimation of θ 0,θ 1c,θ 1s

10 TRIM CURVES Inflow Curve Control Input (θ) Flap Angle (β) Roll Angle(φ)

11 Search & Rescue PERFORMANCE Insertion Resupply

12 REVERSE FLOW AND RETREATING STALL Retreating Side Retreating Side Stalled Region To prevent retreating blade stall, the airfoil is designed in such a way that it has a high stall angle limit. The airfoil als has a high Mach drag divergence number. Advancing Side Reverse Flow Region Advancing Side Stalled Region

13 RECONFIGURATION Addition of wings and propeller for compounding lift and thrust Cant angle is zero. Horizontal stabilizer incidence angle is varied for outbound leg and inbound leg since both are at different speeds and wing setting angle is fixed. BERP airfoil is used for the tips. Rescue Wings and Propeller are removed. Cant angle and horizontal stabilizer angle is given to adjust for the change in C.G and is the highest for all missions during the inbound leg. Swept tips are incorporated in the rotor. Insertion Wings and propeller are removed. Cant angle and horizontal stabilizer angle is given to adjust for the change in C.G. Swept tips are incorporated in the rotor. Resupply

14 SEARCH AND RESCUE CONFIGURATION

15 POSSIBLE INTERIOR ARRANGEMENTS IATA Container Type 8 IATA Container Type 8D 6 Passengers Cargo Container Transport

16 IMPORTANT COMPONENTS Hub Tail Wing Flaps Engine Auxiliary Propulsion

17 Calculated using Harris and Scully relation. It is found that price increases with disk loading. Engine power is also a key factor influencing the price Pr=$5.1 million By factoring in advanced research and development technologies Pr=$ 6 million. Relative Price of Unit Depreciation Charges Dpr= Pr/10000 Direct Operating Cost DOC h =2.25*Dpr/ *Q where Q is the fuel consumption in kg/hr. Direct Operating Cost COST ANALYSIS Time of Mission ~ 3 hrs Fuel Consumed ~ 1360 kg Q= kg/hr Dpr=600 DOC h =$ /hr Time of Mission ~4 hrs Fuel Consumed~1040 kg Q=260 kg/hr Dpr=600 DOC h =$ /hr Time of Mission ~4 hrs Fuel consumed ~900 kg Q=225 kg/hr Dpr=600 DOC h =$ /hr Search & Rescue Insertion Resupply