07a82104-helicopterengineering1h

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Code No: 07A82104 R07 Set No. 2

IV B.Tech II Semester Examinations,AUGUST 2011

HELICOPTER ENGINEERING

Aeronautical Engineering

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

1. (a) Describe with sketches and plots the difference between a conventional airplaneand Helicopter. Emphasize on the generation of lift in both cases.

(b) Explain with sketches and plots the requirement of tail rotor in a conventional

single rotor helicopter. Describe the rotor transmission mechanism. [8+8]

2. (a) Discuss the aerodynamics of an airplane propeller and a ducted fan/rotor usedfor forward motion of a Hovercraft.

(b) Provide the principal details of a Hovercraft in as far as its forward and hov-ering motion is concerned. [8+8]

3. A helicopter weighs 30,000N and has a single rotor of 16m diameter. Using mo-mentum theory estimate the power required for level flight at a speed of 20m/secat sea level. Take CD = 0.0065 based on rotor disc area. [16]

4. A rotor in a given flight condition has the following flapping motion with respectto the control axis (control plane): () = 60 40 cos 40 sin.

(a) Sketch a side view and rear view of the rotor.

(b) How much is the TPP inclined in the fore and aft direction? Forward orbackward?

(c) How much is the TPP inclined laterally? Is the advancing or retreating bladehigh?

(d) What angle does the blade make with the control plane at = 00, 900,1800,

270

0

,(e) At what azimuth angle is the flapping angle greatest?

(f) What is the flapping angle at this point? [16]

5. A helicopter is operating in level forward flight at 63.6ms1 under the followingconditions: shaft power supplied = 488.4kw, w = 2722 Kg, = 1.038 Kg/m3. Therotor parameters are R = 5.75m. = 0.08, R=212.12ms1, K = 1.15, Cdo = 0.01.

(a) How much power is required to overcome induced losses?

(b) How much power is required to overcome profile losses?

(c) What is the equivalent flat-plate area, f?(d) If the installed power is 596.56kw, estimate the maximum rate of climb possible

at this airspeed. [16]

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6. Derive the power calculations for plenum chamber and peripheral jet machines.[16]

7. The drag on an airfoil (at low angles of attack) can be estimated by measuring thestream wise velocity in the wake behind the airfoil in a plane normal to the chord.The resulting distribution of velocity can be approximated by the equation:

(y)V

=

1 12

cosy

2W

,

where 2W is the total width of the wake normal to the airfoil chord. Using themomentum deficiency approach (application of momentum conservation equationin integral form to a control volume surrounding the airfoil and its wake), find anexpression for the drag coefficient Cd in terms of the measured wake width W. [16]

8. (a) Given a helicopter of weight, W = 2,727.3 kg, calculate the power requiredin hover and up to 10,976.4 m/s axial rate-of-climb. The radius of the mainrotor is 6.0 m and the rotor has a figure of merit of 0.75. Assume sea levelconditions.

(b) Plot your result in the form of power required versus climb velocity. Discussthe factors that will determine the maximum vertical climb rate of a helicopter.

[8+8]

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1. (a) Explain blade element theory in case of vertical flight.

(b) Define figure of merit for a helicopter rotor. [8+8]

2. Based on the modified momentum theory, show that the operating thrust coefficientCT, to give the lowest power in hover (best power loading) is CT for best

PL = 12

Cd0

2/3Also, show that this condition corresponds to a figure of merit

of 2/3. [16]

3. (a) Illustrate performance curves of a helicopter rotor with the effect of attitude.

(b) Explain induced, profile and parasite power in forward flight. [8+8]

4. By means of the blade element theory in forward flight show that by including theeffects of reverse flow on the drag, the profile power coefficient can be written as

CP0 =Cd08

1 + 3

2

+38

4. Neglect the radial component of velocity. Compare

this result to the predicted power obtained without reverse flow. [16]

5. (a) Consider a single rotor, conventional helicopter. Explain the generation of lift.How does the helicopter obtain its forward motion?

(b) Write the difference between compound helicopter and single rotor helicopter.[8+8]

6. (a) For a hovering rotor, momentum theory gives a result for the ideal contractionratio of the wake. In practice, experimental observations show that the wakecontraction is not as much as the ideal value. Why?

(b) Show by means of simple momentum theory that a wake contraction that isless than the ideal will result in a higher induced power for the same totalthrust.

(c) Find an expression for the induced power ratio (actual power relative to idealat a constant thrust) in terms of a measured wake radial contraction ratio of0.78. [5+5+6]

7. (a) Explain the principle of the ground cushion vehicle known as hovercraft,make use so detailed sketches to explain its forward motion over water andsolid surface. How do you incorporate various controls in it?

(b) What are the principle details of an Hovercraft. How does it obtain forwardmotion? [8+8]

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8. (a) What types of rotor-airframe interaction problems might be involved in theflight of an autogyro? Consider both winged and wingless autogyros, as wellas tip-jet driven rotor machines such as the Rotodyne.

(b) Derive a set of governing equations to solve numerically for the locations ofthe cutting interactions of the tail rotor with the main rotor wake vortices.Explore the pattern of interactions for different values of the ratio TR/MR.In each case, examine the effect of changing the direction of rotation of thetail rotor. [16]

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1. In the design of a swept tip rotor blade, it is desired to introduce only as muchsweep angle as necessary to keep the Mach number incident to the leading-edge ofthe blade equal to a constant, say Mc, over the tip region. Because of unsteady

flow effects, critical azimuth angle for the design is taken to be at =1000

find anexpression for the sweep angle as a function of r, the hover tip Mach number MR,the design Mach number Mc and the advance ratio, . IfMR = 0.65 and Mc=0.8,plot the sweep angle required as a function of radial blade station for a series ofadvance ratios. [16]

2. Make use of ideal actuator disc theory to show that in hovering flight the powersupplied to the rotor varies as T3/2, where T is that thrust developed by it. Whatis the total power required if we account for other parts of the helicopter? [16]

3. A helicopter weighs 46,000N and has a single rotor of 12.3m diameter. Estimate

the power required to fly forward at a speed of 16m/sec at sea level. Take CD(based on rotor disc area) as 0.006. [16]

4. For the helicopter gross weight 1,363kg, main rotor radius 4.0m and rotor tip speed207.3m, power delivered to the rotor 205kW, the tail rotor radius is 0.701m andthe tail rotor is located 4.66 m from the main rotor shaft. Calculate the thrust andpower required by the tail rotor for hovering conditions at sea level. Assume thatthe Figure of Merit of the tail rotors is 0.70. [16]

5. The downstream wake from the rotor hub can often affect the unsteady loads onthe tail rotor and empennage, to the extent that adverse lateral airframe forces can

be produced. Suggest at least two techniques that could be adopted to alleviatethis problem. [16]

6. The 1/4-chord line of the horizontal tail of a particular helicopter is located ap-proximately 0.2R below and 1.1R aft of the rotor hub. Using a simple rigid wakeanalysis to determine the approximate flight conditions (forward speed, climb, andor descent) where the tail would be immersed inside the boundaries of the rotorwake. Choose several representative rotor operating conditions (thrust, disk angleof attack, climb/descent, etc.). [16]

7. Using the rotor performance theory, calculate the power required for flight for an

autogyro and compare your results to an equivalent helicopter of the same grossweight. Make any realistic assumptions that you find necessary, but be sure tojustify them. [16]

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8. (a) Describe the basic parts of Hovercraft in defining:

i. The vertical lifting action, andii. Forward motion action.

What are the limitations in design and operation of such hovering ma-chines with limited capacity? What are its established uses?

(b) Explain the different types of hovercrafts with suitable diagrams. [8+8]

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1. (a) What is a rotorcraft what are the different types of rotorcrafts?

(b) Configure helicopters based up on torque reaction. [8+8]

2. A helicopter weighs 34,000N and has a single rotor of 11.3m diameter. Estimate

the power required to fly forward at a speed of 16m/sec at sea level. Take CD(based on rotor disc area) as 0.0065. [16]

3. In a hypothetical helicopter rotor design, the use of blade taper has been shownto increase the figure of merit of the main rotor by 1%. Estimate the percentageincrease in vertical lifting and payload capability of the helicopter with all otherfactors being assumed constant. [16]

4. (a) Explain the different types of hovercrafts with suitable diagrams.

(b) Describe the types of jet machines used in hovercraft, explain briefly withdiagrams. [8+8]

5. The inflow distribution over a rotor operating in hover with no tip losses is assumedto be linear, that is = tipr where tip is the value of the inflow at the tip. Byconsidering a momentum balance on successive annuli of the rotor disk, show thatthe induced power factor for such a rotor is 4

2/5. [16]

6. Consider the possible types of aerodynamic interactions that might be found on atilt-rotor when it is operating in hovering flight. You should consider the possibilityof both steady and unsteady flow effects. Discuss design options that could usedto alleviate any adverse effects. [16]

7. Discuss the factors that limit the low speed flight characteristics of an autogyro. Isthere any truth in the claim that the autogyro is essentially a stall-proof aircraft?

[16]

8. (a) Find the effective drag coefficient, CD, acting on a rotor that is in verticalautorotation at Vc/vh -1.85. Compare your result to the published dragcoefficients of standard bluff-body shapes, e.g. a flat plate, and comment.

(b) Calculate and plot the values of the slipstream velocities in the fully contactedwake of a hovering rotor at sealevel as a function of disk loading T/A. Assum-ing a figure of merit of 0.75, compute and plot the power loading versus disk

loading. [8+8]

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