OTHER: Helicopter - Outside - Side-by-Side - Cornu, Paul, 1907 - First flight

• History of the Helicopter ~ Jean Boulet (translated) Pages 21-24
• Cornu_1.jpg, Cornu_2.jpg, Cornu_3.jpg, Cornu_4.jpg
• Cornu's Helicopter ~ First in Flight? Article by Dr. Gordon Leishman in the 2001 Fall-Winter edition of of American Helicopter Society's publication Vertiflite.
• The two pages; Page 54 & Page 55. ~ Clicking on the pages will double their size. ~
• AHA:, 2007: Centennial of the Helicopter? From the AHS's Web site.
• Engineering Analysis of the 1907 Cornu Helicopter by Dr. Gordon Leishman and graduate research assistant Bradley Johnson
• The Helicopters ~ Paul Cornu
• Paul Cornu and His 1907 Helicopter: A postscript. Article by Dr. Gordon Leishman in the 2007 Winter edition of of American Helicopter Society's publication Vertiflite.
• A Revised Version the above 'Engineering Analysis of the 1907 Cornu Helicopter ' ~ In the Journal of the American Helicopter Society (July 2009). ~ by Dr. Gordon Leishman and graduate research assistant Bradley Johnson
• A section on Cornu section was added to Leishman's revised book 'Principals of Helicopter Aerodynamics'

• Specifications:
• Rotor radius; = 3 M = 9.842 ft
• Cutout: = 0.4 R
• Airfoil selected. NACA 0012. The Cornu airfoils were undercambered
• Twist: None
• Taper: None
• Chord = 2.34 ft.
• Gross weight; 260 kg. = 575 lbs.
• Pitch = 14.8º
• If the belts had not slipped, at 170 RRPM it should have flown, out of ground effect for under 20 hp.
• However, the pitch would have been 14.8º and this might have produced a leading edge stall .
• Momentum Theory, which is what Leishman used, shows 30 hp required. No tail rotor; 8-10% [Western], 10-12% [Kamov] = 10%. This would reduce the required power to 27 hp.
• DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed leads me to believe that the wide chord (Rotor solidity 0.151) and large cutout has an advantage.

• No tail rotor; 8-10% [Western], 10-12% [Kamov] = 10%

• Gyrobee Gyrocopter, 500 lbs GW, 38-40 hp
• For the Cornu weight of 575 lb the power would have to be 575/500 * 39 = 45 hp.
• Mechanical vs. aerodynamic power transmission losses; (82% [Prop] * 82% [Rotor Figure of Merit]) - 5% [Mechanical ] = 72%. Therefore 72% of 45 hp = 32 hp
• In vs. out of Ground Effect; 15% - 20% [Leishman] = 17%. Therefore 32 Hp * .83 = 27 hp,

• The conventional Momentum Theory and Blade Element Theory should probably be reduced by 10% to account for the lack of tail rotor. See: http://www.unicopter.com/B329.html#Tail_Rotor
• Then the value should probably be reduced due to the very large cutout of 0.3R. 27 sq-ft / 304 sq-ft = -.9% off of the above value.
• Then the value should probably be reduced again due to the very wide chord and the slow rotor rpm. See: tables on DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed

• "The Antoinette engine was designed and built in France by Léon Levavasseur. Named after the designer's daughter, it was Europe's most widely used engine until 1909-1910. The first Antoinette engine dated from about 1901 and was used in a speedboat. By 1905, Levavasseur had produced a water-cooled engine with eight-cylinders arranged in a 90-degree "V" and with direct fuel injection. It was safe, strong, and fairly powerful, generating 50 horsepower (37 kilowatts) and weighing about 110 pounds (50 kilograms). Its power-to-weight ratio was not surpassed for 25 years."

• The Cornu Model: Leishman, in his latest article, has stated that "a model weighing up to 18 kg (40 lb) lifted by a 2 hp engine driving two contra-rotating rotors - was to make several sustained flights, in both hover and forward flight, and with many witnesses to the event." This is 20 lb/hp.
• The Flettner 282 Intermeshing: "It was capable of lifting 16 lbs. per horsepower - a figure not attained to this day by any of the modern helicopters." ["this date" - unknown]
• The Flettner had a GW of 2202 lbs and a 160 hp engine.
• The 282 had an Intermeshing configuration and this configuration has a Thrust/Power efficiency that is meaningfully below the Side-by-side configuration.
• The twin Rotor Factor for my SynchroLites and UniCopters in the Access database is 1.39 +/-. This seems to be too close to the Coaxial's 1.41. However, for the fun of it 16 hp * 1.39 = 22.24 hp.
• The Cornu Full size:
• 573.3 lb / 24 hp = 23.89 lb/hp Was this the GW weigh of his 13 November 1907 attempt when the craft was carrying a 121 lb sandbag?

• A/ Momentum theory ~ Leishman in 'Aerodynamic Optimization of Coaxial Proprotor' mentions that momentum theory cannot be used to compare dissimilar configurations. Cornu's low aspect ratio, reverse tapered rotors are also very dissimilar to today's rotors. Why then does his evaluation use Momentum Theory?
• B/ Leishman's writes; "At first, the assumption of an aerodynamic efficiency of only 50% may seem low, but we must remember that even the best helicopter rotors that were to follow in the 1940s and 1950s had efficiencies of only 60% (i.e., figures of merit, FM, of 0.6), and this was using low solidity rotors with high aspect ratio blades...".
• Ba/ This is an interesting statement considering that in the early 1940s Flettner's FL282 had a FM of 0.72 (out of ground effect). It should be noted that Flettner's helicopter and Cornu's helicopter are not subjected to the tail-rotor power consumption.
• Bb/ In addition, an increased solidity ratio and decreased rotor rpm has been shown to significantly reduce the required power. Rotor - Disk - Large Chord & Low Tip Speed. From note (3) below, it appears that Cornu's rotors had a solidity ratio of 0.113, if the large root cutout of 0.40 is deducted from the disk area.
• C/ Where did the flat-belt efficiency of only 0.75 come from? Flat-belts are very efficient [up to a maximum of 98%]. In addition, could not Cornu have had instances where his modifications briefly eliminated the belt slippage? He certainly tried to, plus he was knowledgeable about belt drives since his bicycle manufacturing facility used them.
• D/ The article says; "The blades were also flat (no proper airfoil section) and untwisted, both chordwise and along their span." However, in this photo and in others it is shown that the blades were not flat but had a camber.

0. Speed at 85% of blade span. 85% is used due to very large cutout and reverse taper.
1. These wings (blades) have a partial elliptical shape and this might reduce the induced drag.
2. The article states; "The blade length was 1.8 m and had a chord of 0.9 m at their maximum point near mid-span. This means that the total rotor radius was 0.9 m (radius of inner spoked hub) plus 1.8 m (blade length) to give 2.7 m (8.86 feet). ~ [By some accounts, however, the rotor radius was reported to be as much 3.0 m.]". The views of the rotors show that that the root edge of the blades are 10% of the span beyond the radius of the spoked hub and this gives a rotor radius of 3m ( 9.84 feet). In addition. The maximum chord appears to be near mid span of the blade and this is near 70% of rotor radius.
3. Prouty's Momentum theory (assuming that my coding in the Access database for this was correct many years ago) says that the power to hover must be increased by 52% to give a rate of climb of 500 fpm,
4. I have no idea what the Coefficient of Lift is for Cornu's rotor-wing or the trike's wing is, however, the above suggests that Cornu's craft MIGHT have been able to produce sufficient lift to hover.

• (1) The first number is the total area of both disks. The second number is with the large root cutout ratio of 0.40 deducted from the area of both disks
• (2) The two values are based on the two disk areas directly above
• (3) An increased solidity ratio and decreased rotor rpm has been shown to significantly reduce the required power. Rotor - Disk - Large Chord & Low Tip Speed.
• (4) A tail rotor consumes 8-12% of the available power and Cornu helicopter does not use a tail rotor.
• (5) Gross weight c/w pilot ~ from Leishman
• (6) The last given rotor speed by Leishman was 85 rpm. I have arbitrarily taken it up to 170. This will also reduce the torque and hence the belt slippage.
• (7) It looks like Cornu's helicopter, with its 24 hp engine, MAY have produced sufficient lift to hover.

• Rebuttal to Leishman/Johnson Figure of Merit argument;
• The paper states; "The blades were also flat (i.e., they had no proper Airfoil section) ..." and ".. the Cornu rotor system was further analyzed by using the blade element momentum theory ... the blades were modeled as thin flat plates."
• Response; Pictures clearly show that the rotor blades, and even the control surfaces, were not flat. They were undercambered.
• Outside quote; "The early aviation experimenters began with flat plate wings but soon realized that curvature [undercamber] improved efficiency; influenced most likely by the observation of birds' wings."
• Response; The bottom line in this table above is calculated from Prouty's blade element momentum theory.
• Response; Also, the side-by-side configuration, as used by Cornu, is the optimal one for high Figure of Merit.
• Rebuttal to Leishman/Johnson Transmission Efficiency argument;
• The paper states; "... a transmission efficiency of η=0.75 (note that a canvas belt can never be as efficient as a efficient as a geared transmission ...".
• Response; η=0.75 is far less than what flat-belt transmissions are capable of. Flat-belt transmissions can have up to 98% efficiency. This is one reason why they were used in Cornu's bicycle manufacturing facility and thousands of other plant at that time.
• The paper states; "One issue was that the belt was twisted several times from the engine to the rotors."
• Response; This is another of the flat-belt's attributes.

• Reynolds Number of Cornu's Blade;
• Mean chord length = 14.4 sq.ft. / 5.9 ft.[span] = 2.44 ft.
• Speed at 0.85 R = 74 fps at 85 rpm ~or~ = 148 fps and 170 RPM
• = chord (ft) x speed (fps) x 6378; at sea level. = 2.44 x 85 x 6378 = 1,322,800 ~or~ 2.44 x 170 x 6378 = 2,645,600

 Summation:

• Leishman/Johnson infer an inability to fly, due to a need for-;
• 1/ "a larger rotor disk with a lower disk loading"
• 2/ "a higher aerodynamic efficiency"
• 3/ "a better method then a canvas belt drive"
• 4/ "a much more powerful engine"
• 5/ "Paul Cornu's claim to successful piloted flight with a helicopter, free of the ground and under positive control, is extremely dubious."

• Counter-argument to Leishman/Johnson arguments;
• 1/ The rotor disk was extremely large and the disk loading was very small. See 'Cornu's Disk', above.
• 2/ See 'Rebuttal to Leishman/Johnson Figure of Merit Argument'', above;
• 3/ See 'Rebuttal to Leishman/Johnson Transmission Efficiency Argument', above;
• 4/ No so if the Figure of Merit and the Transmission Efficiency are corrected. See Power comparisons, above.
• 5/ The control system probably was inadequate for meaningful flight. However, the above statement is an assumption lacking solid technical support.

• Conclusion: The above 'Counter-argument' certainly does not claim that Cornu's craft did or could have successfully flown. However, it significantly weakens the Leishman & Johnson claim of an 'Engineering Analysis'. Their papers come across as a prejudicial belief, supported by a litany of self-admitted assumptions.

_ 'French fries' _ _ 'Freedom fries'

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Flat ~ undercambered The spar is located The spar on Sikorsky's flat .. is located at 30% of chord

Cornu's description says "skidding of the belts prevented us from sustaining the lift for more than one minute.".... This may imply that the belts would start skidding after a minute of use. Get original French of this sentence translated by Pascal

BUT, see: OTHER: Aerodynamics - General - Angle of Attack and Rotor RPM ~ August 6, 2011