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Wright propellers (rev3)

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  • 1. Wilbur Wright develops the Aircraft propellerIn Dec 1902, Wilbur and Orville wright returned from Kitty Hawk after as season ofsuccessful flight tests of their new glider. They had both learned to fly and demonstrated thatcomplete control of a “flying machine” was possible through movement of the controlsurfaces alone without any shifting of body weight. Aircraft of any weight and size could becontrolled in flight. Through the use of a wind tunnel of their own design they established thecriteria needed to design an efficient aircraft wing. they then verified their findings throughthese flight tests.The time had come to develop the gasoline motor and propeller required to turn theirsuccessful glider into the worlds first airplane. Orville Wright with the help of their machinistCharlie Taylor built the four cylinder inline motor, though crude by modern standards, had ashigh a power to weight ratio as the best auto racing engines of the day. This motor was firstoperated in February 1903, only six weeks after development began.Wilbur Wright took on the task of designing their first propellers. In December 1902, nodesign theory existed to guide Wilbur Wright in the development of the aircraft propeller.Nevertheless six weeks after he began development, Wilbur’s first propeller was ready to betested on the Wright’s new motor. The story of Wilbur Wright’s amazing achievement is thesubject of this presentation. P A1
  • 2. 1902 Wilbur Develops the first Aircraft propeller Prop Diameter = 28 inches Blade Width at tip = 7 inches Fan Speed = 1600 Rpm Fan Thrust = 12 pounds Drive Power = 0.8 HP The thrust was found to vary as the square of the Rpm Wind Speed = 25 mph Prop Diameter = 8.5 feet Blade width at tip = 6 inches Blade Area = 2 sq. ft. Prop speed = 245 Rpm Speed at C.P. = 61 mph Normal pressure = 12.4 lb./sq. ft. Thrust = 18.75 lbs. CL = 18.76/24.8 = 0.756 Angle for airfoil #31 = 7.25 deg Measured torque = 3.5 lbs Measured power = 0.58 HP L/D of propeller airfoil = 5.4The Wrights Estimated that the thrust required to fly the 925 pound 1903 Flyer at 24MPH was 90 Pounds. Thespeed at 330 Rpm at the center of pressure of the 8.5 foot wright props would be about 80 mph. The dynamicpressure on the blade would be 11 times that of the wings. The thrust required was estimated at 9.7% of theaircraft weight. The required blade area of both props would then be 0.88% of the wing area or 4.5 sq. ft. The 1903Wright Propellers were 8 inches wide and had a total blade area of 5.4 sq. ft. The 12HP 1903 Wright Motor turnedthe Propellers at 350 rpm and produced 120 pounds of thrust. PA2
  • 3. wright test propeller performance 1903 Table 1 The Performance of 102 in Diameter Test Propeller @ 245 rpm, February 1903 Method Airspeed, mph Power, hp Thrust, lbs Incidence. deg Twist. deg Measured 0 0.58 18.75 7.25* NA Calculated 0 0.45 15.97 9.4 0.000 Calculated 0 0.58 18.38 11.5 3.20** Calculated 16 0.32 2.79 1.73 3,20**In February of 1903 six weeks after he began the task of designing the worlds first scientifically designed air propeller Wilbur Wright tested hisfirst full scale Propeller.This prop had long thin blades which tapered from about 2 inches at the hub to a full six inches at the tip. The pitch angle was 15 degrees atthe center of pressure 42 inches from the center. Wilbur calculated the speed at the center of pressure to be 89.83 ft per sec. with a dynamicpressure of 12.4 lbs per sq ft. Using the 18.75 lbs. measured value of thrust and assuming that the full 2 square feet of blade area acted atthat point, he estimated the coefficient of lift to be 0.756 and the angle of incidence to be 7.25 degrees.Table 1 shows the calculated performance of the test propeller using modern propeller theory as well as the values measured by the wrights.The discrepancy can be explained by errors in the pitch of the prop under load. This propeller was very narrow with an aspect ratio of over12:1 and would have twisted so as to increase pitch angle under load. The Wrights were later to sweep back the prop tips in an attempt tokeep the dynamic forces on these thin wooden propellers from twisting the blades at high thrust levels. The last two entries in table 1 showthat introducing a linear twist from zero at the root to 3.2 degrees at the tip brings our analysis in almost perfect agreement with the measuredvalues. The last entry shows that the pitch of the test prop was far too low to support the expected airspeed of the 1903 Wright Flyer.In the next few weeks Wilbur Wright would design the 102 inch diameter propellers for the 1903 Flyer. He would increase the blade width from6 to 8 inches and the pitch from 15 to 27 degrees and would include the effect of down wash (throw down) in his calculations. Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 601, 606 Reference 2 Wilbur Wrightʼs notebook H 1902=1905 Pages 8,9,10 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The propeller Note 1* Wilbur estimated the incidence based on using 100% of the propeller blade area acting at C.P. Note 2** we assumed a linear twist to the blade due to loading adjusted to yield the correct power level P A3
  • 4. wright propeller performance 1903 Table 2 The Performance of 102 inch Diameter Propeller @ 330/350/370 rpm,1903 Airspeed Efficiency Power Thrust incidence Date 24 66 8.7@330 90 7.0 Mar-1903 20-25 NA 12@350 132 NA Nov-1903 20-25 NA 12@350 120 NA Dec-1903 24 66 12@370 124 11.6 Jan-2009 30 75.0 10.6@370 99.8 8.6 Jan-2009On March 6, 1903 only weeks after the successful performance of his test propeller, Wilbur Wright designed the propellerwhich would be used on the historic flight of December 17, 1903. He designed the new propeller to produce 90 lbs. of thrust atan airspeed of 24 mph with a propeller speed of 330 rpm. Wilbur calculated the torque force at 40 lbs. resulting in the need fora 8.7 H.P. motor and estimated the downwash (throw down ) of 7.7 fps, resulting in a pitch angle of 27 degrees to yield a 7degree angle of incidence. He calculated the efficiency at 66 percent, These design elements are shown on lines 1 Table 2. Test on the 1903 flyer made in winds of 20 to 25 mph gave thrust at between 120 lbs and 132 lbs as shown on lines 2 and 3 This was much higher than expected. Success was assured !!.The performance of this propeller at 370 rpm was calculated using modern propeller theory. the results are shown on lines 4and 5 in Table 2. This analysis included a linear twist from zero at the root to 1,66 degrees at the tip added to bring the powerrequired to 12 hp at 24 mph. The same twist was assumed at the estimated fight speed of 30 mph where the propellerefficiency was calculated to be 75 percent. The development of this propeller was a magnificent achievement. It was far ahead of other experimenters and the design was completed in less than 3 month. Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 601, 606 Reference 2 Wilbur Wrightʼs notebook H 1902=1905 Pages 9,10 reference 3 Wilbur Wrightʼs estimate of performance March 6,1903 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller P A4
  • 5. wright propeller performance 1904 Table 3 The Performance of 102 inch Diameter Propeller @ 405 rpm, 1904 Airspeed Efficiency Power Thrust incidence Date 24 NA 20.0 185 NA Nov 1904 30 71.7 17.4 156 10.1 Jan-2009 24 62 19.1 185 12.6 Jan-2009 16 43.9 20.0 205 16.1 Jan-2009 0 0.0 20.4 202 22.6 Jan-2009The Wrights spent a large part of 1904 attempting to take off and fly successfully with the inconsistent and usually light windsexperienced at Huffman Prairie as well as to remain in its limited confines when airborne. They developed a winch type launchmechanism which allowed them to lake off in light winds. Their motor was continuously improved, the 1903 motor would sagfrom 16 hp to 12 hp in only a few minutes of operation. By June of 1904 their motor would sag no more than 25 rpm in 4minutes. In November 1904 the motor held a steady 395 rpm (at the props) for 12 minutes.The Wrights began operating their new 8.75 inch wide propellers in July of 1904 when Wilbur recorded obtaining 185 lbs thrustat 405 RPM as shown on line 1 of table 3.We calculated the performance of this propeller at 405 rpm using modern propeller theory. The the results are shown on lines 2through 5. This analysis included a linear twist from zero at the root to 1.23 degrees at the tip added to bring the thrust up to185 pounds at 24 mph. The same twist was assumed from 30 mph down to zero forward speed. Our analysis also shows thatthis propeller could reach a maximum efficiency of 78% at 38 mph. In the following year the Wrights would improve the stability and control of their of the flyer They would then be ready to take orders for the worlds first practical airplane. Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 601, 606 Reference 2 Wilbur Wrightʼs notebook H 1902=1905 Pages 9,10 reference 3 Wilbur Wrightʼs estimate of performance March 6,1903 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller P A5
  • 6. wright propeller performance 1905 Table 4 The Performance of 102 inch Diameter Propeller @ 473 RPM, 1905 Airspeed Efficiency Power Thrust incidence Date 40 82 12.0 92 3.4 Jan-2009 35 80.5 15.0 130 5.2 Jan-2009 30 75.9 17.4 166 6.9 Jan-2009 25 68.6 19.2 198 8.5 Jan-2009 0 0.0 20.7 247 22.6 Jan-2009The year 1905 saw the Wrights develop the worlds first practical flying machine. Two accidents, both with Orville at the controls led tosolutions which had previously eluded them. The first accident occurred on July 14th when Orville lost control in pitch shortly after take off andcompletely destroyed the machine. He was unhurt although being thrown through the upper wing. The flyers had always been sensitive inpitch with the problem increasing with increased power levels (the 1902 glider was much better behaved) After the crash the wrights rebuilt the flyer doubling the size of the front control surface (Canard) and moving it 12 feet ahead of the wingleading edge, In modern terms they increased the tail volume from 0.16 to 0.50 a value similar to today’s aircraft. The new flyer first flew onAugust 28, It was much more stable and a great success. Within a few week Orville flew in a figure 8 and both Wilbur and Orville began tomake longer and longer flights circling Huffman Prairie many times.The second accident occurred when Orville went into a spin in mid field and not wishing to crash into a thorn tree lowered the nose intendingto hit the ground first. To his surprise the spin stopped and he recovered control of the machine. Spins like this had occurred in one in 50flights even back to the earlier flights with gliders. Now that the wrights knew how to regain control they no longer had to fly at very lowaltitudes and at slow speeds to avoid the possibility serious injury in a crash. The very next day they flew for 20 minutes and within two weekshad flown as long as 39 minutes at speeds averaging 35 mph.In notebook “O” Wilbur estimated that the 1905 prop produced 210 lbs of thrust at 490 rpm at 35 mph. In notebook “L“ he states that the “bentend“ prop” produced 210 pounds thrust @ 450 RPM. We calculated the performance of this propeller at 473 rpm using modern propellertheory with the the results shown in Table 4. This analysis shows that at 473 RPM this propeller could reach a maximum efficiency of 82% at39 mph. This efficiency is better than that achieved by most modern propellers. Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 514, 521,&, 638 Reference 2 Wilbur & Orville Notebook “O” Pages 10,11,& 29 : Notebook “L “ Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller P A6
  • 7. wright flyer performance 1903 Table 5A Drag of structural elements and prone pilot for 1903 Flyer @ 30 mph Element frontal area drag area pressure Drag, lbsUprights 6.0 4.0 2.46 9.8Wires 0.8 0.4 2.46 1Engine 2.0 2 2.46 4.9Chains 0.3 0.3 2.46 0.7Misc 2.3 2.3 2.46 5.7Pilot 1 1.0 2.46. 2.5Total 124 10.0 NA 24.6 Table 5B Breakdown of Total drag for 1903 Flyer at 750 lbs at a number of airspeeds Airspeed Head Drag Airfoil Drag Induced drag Total Drag 20 10 40 86 135 22 12 33 71 116 24 15 29 60 104 26 17 28 51 96 28 20 28 44 92 30 23 29 38 90 32 26 31 34 91 34 30 35 30 94 36 33 38 27 98 Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 514, 521,&, 638 Reference 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29 P A7 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller
  • 8. wright flyer performance 1905 Table 6ADrag of structural elements and prone pilot for 1905 Flyer @ 30 mph Element Drag area Drag@ 30 mph Power Required Uprights 3 6.9 0.55 Engine 0.7 1.6 0.13 Chains 0.3 0.7 0.06 Wires & Tail 1.5 3.5 0.27 Uprights 3 1.2 0.04 Engine 0.7 2.3 0.08 Chains 0.3 2.3 0.08 Wires & Tail 1.5 18.4 1.47 Table 6B Airspeed, Head drag, Airfoil Drag, Induced Drag, and Total Drag Airspeed Head drag Airfoil Drag Induced Drag Total Drag 20 8 52 130 191 25 13 36 83 132 30 18 35 58 111 35 25 42 42 110 40 33 55 32 120 Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 514, 521,&, 638 Reference 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29 P A8 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller
  • 9. wright flyer performance 1903-1905 Table 7A 1903 flyer Airspeed, Prop Efficiency, Thrust, Aircraft Drag, and Thrust Margin Airspeed Efficiency Thrust, lbs Drag, Lbs Margin % 20 58.1 139 135 2.9 22 62.3 132 116 13.8 24 66.2 124 104 19.2 26 69.6 116 96 20.8 28 72.4 108 92 17.4 30 74.8 100 90 11.1 32 76.5 91 91 0.0 34 77.4 82 94 -12.7 36 77.4 73 98 -25.5 Table 7B 1905 Flyer Airspeed, Prop Efficiency, Thrust, Aircraft Drag, and Thrust Margin Airspeed Efficiency Thrust,lbs Drag,lbs Margin % 20 59.2 224 191 17 25 68.6 198 132 50 30 75.9 166 111 50 35 80.5 130 110 18 40 82 92 120 -23.0Tables 7A &7B show propeller efficiency, thrust, aircraft drag, and thrust margin as a function of Airspeed. The Cruise Speed for the Wright Flyer was about 32 mph in 1903 increasing to 37 mph in 1905 Reference 1 The papers of Wilbur and Orville Wright volume 1 pages 514, 521,&, 638 Reference 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29 Reference 3 Airplane Aerodynamics, Dommasch, Sherby, & Connolly Chapter 7, The Propeller P A9