Wright propellers (rev3)

Wilbur Wright develops the Aircraft propeller

In Dec 1902, Wilbur and Orville wright returned from Kitty Hawk after as season of
successful flight tests of their new glider. They had both learned to fly and demonstrated that
complete control of a “flying machine” was possible through movement of the control
surfaces alone without any shifting of body weight. Aircraft of any weight and size could be
controlled in flight. Through the use of a wind tunnel of their own design they established the
criteria needed to design an efficient aircraft wing. they then verified their findings through
these flight tests.

The time had come to develop the gasoline motor and propeller required to turn their
successful glider into the worlds first airplane. Orville Wright with the help of their machinist
Charlie Taylor built the four cylinder inline motor, though crude by modern standards, had as
high a power to weight ratio as the best auto racing engines of the day. This motor was first
operated in February 1903, only six weeks after development began.

Wilbur Wright took on the task of designing their first propellers. In December 1902, no
design 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 be
tested on the Wright’s new motor. The story of Wilbur Wright’s amazing achievement is the
subject of this presentation.

P A1

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 = 5.4

The Wrights Estimated that the thrust required to ﬂy the 925 pound 1903 Flyer at 24MPH was 90 Pounds. The
speed at 330 Rpm at the center of pressure of the 8.5 foot wright props would be about 80 mph. The dynamic
pressure on the blade would be 11 times that of the wings. The thrust required was estimated at 9.7% of the
aircraft weight. The required blade area of both props would then be 0.88% of the wing area or 4.5 sq. ft. The 1903
Wright Propellers were 8 inches wide and had a total blade area of 5.4 sq. ft. The 12HP 1903 Wright Motor turned
the Propellers at 350 rpm and produced 120 pounds of thrust.
PA2

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 his
first 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 at
the 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 dynamic
pressure 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 at
that 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 over
12:1 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 to
keep the dynamic forces on these thin wooden propellers from twisting the blades at high thrust levels. The last two entries in table 1 show
that 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 measured
values. 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 from
6 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

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-2009

On March 6, 1903 only weeks after the successful performance of his test propeller, Wilbur Wright designed the propeller
which would be used on the historic flight of December 17, 1903. He designed the new propeller to produce 90 lbs. of thrust at
an airspeed of 24 mph with a propeller speed of 330 rpm. Wilbur calculated the torque force at 40 lbs. resulting in the need for
a 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 7
degree 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 4
and 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 power
required to 12 hp at 24 mph. The same twist was assumed at the estimated fight speed of 30 mph where the propeller
efficiency 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 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

Table 3
The Performance of 102 inch Diameter Propeller @ 405 rpm, 1904


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-2009

The Wrights spent a large part of 1904 attempting to take off and fly successfully with the inconsistent and usually light winds
experienced at Huffman Prairie as well as to remain in its limited confines when airborne. They developed a winch type launch
mechanism which allowed them to lake off in light winds. Their motor was continuously improved, the 1903 motor would sag
from 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 4
minutes. 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 thrust
at 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 2
through 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 to
185 pounds at 24 mph. The same twist was assumed from 30 mph down to zero forward speed. Our analysis also shows that
this 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 2 Wilbur Wrightʼs notebook H 1902=1905 Pages 9,10
reference 3 Wilbur Wrightʼs estimate of performance March 6,1903

Table 4
The Performance of 102 inch Diameter Propeller @ 473 RPM, 1905

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-2009

The year 1905 saw the Wrights develop the worlds first practical flying machine. Two accidents, both with Orville at the controls led to
solutions which had previously eluded them. The first accident occurred on July 14th when Orville lost control in pitch shortly after take off and
completely destroyed the machine. He was unhurt although being thrown through the upper wing. The flyers had always been sensitive in
pitch 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 wing
leading 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 on
August 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 to
make 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 intending
to 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 50
flights 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 low
altitudes 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 weeks
had 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 “bent
end“ prop” produced 210 pounds thrust @ 450 RPM. We calculated the performance of this propeller at 473 rpm using modern propeller
theory with the the results shown in Table 4. This analysis shows that at 473 RPM this propeller could reach a maximum efficiency of 82% at
39 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

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, lbs

Uprights 6.0 4.0 2.46 9.8

Wires 0.8 0.4 2.46 1

Engine 2.0 2 2.46 4.9

Chains 0.3 0.3 2.46 0.7

Misc 2.3 2.3 2.46 5.7

Pilot 1 1.0 2.46. 2.5

Total 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 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29 P A7

wright flyer performance 1905
Table 6A
Drag 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 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29
P A8

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 -23.0

Tables 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 2 Wilbur & Orville notebook O 1902=1905 Pages 10,11,& 29

Wright propellers (rev3)

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