2007: Centennial of the Helicopter?

[Graviman]

Dave, old boy, not having a go at you - this is a good piece of analysis. I'm just applying critique honed from years of looking at this sort of problem. Part of my job is to determine whether my own analysis is in error.

What is mean by "flat aerofoil" is that the Cornu design was fabric stretched over structure. I do not know whether 8-H-12 profile captures the flat, but cambered, section accurately - lets assume that it does. What the Ray Prouty model will not catch is the local turbulence caused by structure exposed to the airflow.

Also there is the Reynolds number factor. Most pioneers of this era (including the Wright brothers) did wind tunnel testing on small models, but found that it did not scale up to a large structure. This is because flow transitions from laminar to turbulence the same distance along a surface, so does not scale with the model to actual.

What i am basically saying is that the Cd vs AOA will likely be higher than the data suggests...

[Dave_Jackson]

Mart, please.

Part of my job is to determine whether my own analysis is in error.

Is this unique to you?

flat, but cambered

And your dictionary is....?

What the Ray Prouty model will not catch is the local turbulence caused by structure exposed to the airflow.

Have you read your Prouty, page 7?

Most pioneers of this era (including the Wright brothers) did wind tunnel testing on small models, but found that it did not scale up to a large structure.

Are you saying that Cornu did not fly his model?
Are you saying that he was ignorant of scaling?

than the data suggests..

And that data is?


Momentum Theory,
which Leishman used to evaluated Cornu's helicopter, considers a rotor disk that has; ideal twist, constant chord, no cutout, and a consistent induced velocity across the surface of the disk. As you can see from the pictures, Corn's rotors are about as far as one can get from the momentum theory actuator disk.

IMHO, perhaps a better means of evaluating Cornu's rotor would be to consider the lift and drag etc. of four small trike wings at a mean 'forward' velocity.

Leishman may be correct or he might be incorrect, however, opposing technical critiques are better than hasty conjecture.

Dave

[Graviman]

Dave, the 8H12 aerofoil does not look like the one that Cornu used, whatever the terminology:




From this thread:

http://rotaryforum.com/forum/showthread.php?p=66738

Originally Posted by Dave Jackson

Momentum Theory,
which Leishman used to evaluated Cornu's helicopter, considers a rotor disk that has; ideal twist, constant chord, no cutout, and a consistent induced velocity across the surface of the disk. As you can see from the pictures, Corn's rotors are about as far as one can get from the momentum theory actuator disk.

Which would be why he chose a sensible Figure of Merit of 0.5. He also justifies this choice with typical FM values throughout the century.

In 1907 hardly anyone knew about either Reynold Number scaling or about Prandtl aerofoil theory. In fact few understood how to build a flying machine. Cornu's accomplishment was impressive regardless or not of whether it hovered long enough to be photographed.

Several potentially useful applets:
http://www.geocities.com/CapeCanaver.../nvfoilen.html
http://www.mh-aerotools.de/airfoils/javafoil.htm

[Dave_Jackson]

Graviman

The 8-H-12 was use because it is one of the few airfoils that have been coded into my database.


Telling you that the use of FM is only practical when comparing similar rotors would be boring, because you have probably read it written by so many other rotor aerodynamicists.

However, let Leishman tell you in his own words: "Because the FM is a function of many interdependent parameters, it is only useful as a comparative quantity when using rotors of the same equivalent solidity and operating at the same disk loading; it cannot be used to compare efficiencies of substantially different types of rotors, a common error in its application."


Now that I have answered your questions, please answer mine above!

Dave

[Graviman]

Dave, Leishman has stated that he believes the Cornu Helicopter required 30HP to hover. So it could not have hovered using the 1907 Antoinette V8 engine quoted at 24CV. My only disagreement is whether the 24CV quoted is actually 24HP.

The 1908 Antoinette V8 is quoted at 50CV, so even if Cornu did not actually hover in 1907 he came damn near close.

[slowrotor]

Dave,
Cornu was probably operating at a much lower tip speed. I notice todays aero guys (Prouty) assume the usual high tip speeds. As you know low tip speed requires less power. Did Leishman account for tip speed?

[Dave_Jackson]

Graviman,

My only disagreement is whether the 24CV quoted is actually 24HP.

cheval-vapeur (550 ft.lb/s)[GB] 745,6999 watt (W)
cheval-vapeur (métrique) 735,499 watt (W)

The above came from a friend in France, who coincidently co-wrote a small book on helicopters for children. This book was commissioned by Eurocopter for the celebration of 100 years of the helicopter.
________________

You spoke of scaling therefore the following may be of interest.

Additional Information on the Ability of the Cornu Helicopter to Hover in Ground Effect:

• 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 282 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 +/-. To hover out of ground effect.
  • 16 lbs per hp * 1.39 = 22.24 lbs per hp. To hover out of ground effect.

• 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?

I have answered your questions. Would you please answer mine on a previous posting.

_________________________

slowrotor,

Cornu was probably operating at a much lower tip speed.

This is very true. Leishman used the Momentum Theory, which does not consider RRPM, plus other relevant criteria.

IMHO, Leishman, appears to be very knowledgeable when it comes to conventional rotor and blade aerodynamics. However his knowledge of configurations, other than the single rotor (and tilt-rotor) appears to be minimal, at best.

Stepniewski was probably the most knowledgeable person on the pros and cons of the various rotorcraft configurations.

____________

The latest issue of Vertiflite, Winter 2007, has another article by Leishman entitled 'Paul Cornu and His 1907 Helicopter: A Postscript'.


Dave

[Graviman]

Dave, for a moment of peace:


Is this unique to you?

No, i believe Martians analyse themselves very carefully too.


And your dictionary is....?

Somewhere under the pile of helicopter books.


Have you read your Prouty, page 7?

Yes, i have dutifully read the entire book. My memory occasionally needs refreshing, and has been so for pages 69-72.


Are you saying that Cornu did not fly his model?

As i wasn't there i can't say. All of the evidence seems to indicate that he was very close to success, but was a little ahead of his time.


Are you saying that he was ignorant of scaling?

The Wright brothers did not initially know about Reynolds number scaling for turbulent flow, nor did many pioneers of the era. I doubt Cornu realised initially either. Aerodynamics has come a long way since.


And that data is?

As stolen from C. Beaty on the linked thread for 8H12 aerofoil.


What i am saying is that you have come to the conclusion about Cornu's machine having a rotor FM of 0.7 by using a modern aerofoil. Since the actual aerofoil would not have given the same lift/drag performance then this conclusion is wrong. I am more inclined to believe Leishman's estimate of an FM of 0.5. If you allow the pulley system to work without slippage this still means the helicopter was slightly underpowered.

The final proof of how close Cornu got is that photo of the rear of the machine in the air, but there are no photos of sustained hover. There were likely moments of occasional wheels off hover from gusts of wind, but it appears it would not quite sustain a hover.

Still an achievement for 1907.

[Dave_Jackson]

Another version of the paper 'Engineering Analysis of the 1907 Cornu Helicopter' by Gordon Leishman and Bradley Johnson has been published in the July 2009 issue of the 'Journal of the America Helicopter Society.' It attempts to strengthen the 'engineering' side of their argument.

However, the paper's claim that "the engineering analysis described in this article is unequivocal." is a little over the top, particularly when they make a number of assumptions. My questioning relates to their assumptions of; a Figure of Merit of 0.5, and a Transmission Efficiency of 0.75.

This figure of merit is based on the craft having flat blades, whereas pictures show that the blades are undercambered. Secondly, calculations show that wide-chord, slow turning rotors improve efficiency. Thirdly, Cornu used the side-by-side configuration, which is the most efficient arraignment for hover. IMHO, a meaningfully higher FM is more reasonable.

The power transmission from motor to rotors was by flat-belt. Flat-belt were a well-known and much-used means of transmitting power in machine shops, including Cornu's shop. Today's flat-belts are capable of efficiencies up to 0.98, therefore it could be assumed that the one-minute long eliminations of the belt slippage would have temporarily increased the power at the rotors.

There is nothing to indicate that Paul Cornu did not achieve short-term vertical flight.

Perhaps, his disappointment regarding the Deutsch Archdeacon Grand Prix, and disenchantment with the future potential for his current design caused him to refrain from further promotion, and return to engineering and patenting improvments, such as a continuously variable swashplate system.

Could this be-
_ 'French fries' _ _ 'Freedom fries'

[Graviman]

Dave,

I think this is an example of an idea being of its time...

To work the helicopter needs more than just enough power to enter hover in ground effect. It needs a surplus of power for control, since there are no ailerons to suck manouvreing power from flying speed. It also needs to have an element of stability (often supplied by the pilot) but this is as much for confidence in the machine as for performance. Finally the aerodynamics for helicopters are just much more complicated than for seized wing aircraft.

Like i say, whatever the exact calculations Cornu came close enough to warrant the credit for the first flyable helicopter - even if this was only a gusty hop. From the power point of of view he was only seperated by 1 year from achieving sustained hover.

It would be a shame to think that he was discouraged from further development, but like i say helicopters are complicated. He may just have realised that there were many more issues than just having hover power on tap from the engine. It's quite likely that he continued to think about future developments from what he learned - it would be interesting to find out what he documented (including the patent on continously variable swashplate) although his home was destroyed in 1944 so little probably survived.

Paul Cornu - Wikipedia, the free encyclopedia

[Dave_Jackson]

Hi Mart,

Here is Cornu's swashplate.



French Patent No. 398,545, June 7, 1909.

Dave

[Graviman]

Clever chap - control system pioneer too.

It's a pity there was no internet to publicise his innovations...

[Dave_Jackson]

Cornu vs. Revisionist History

Leishman has produced another paper (2012), which is; Performance Measurements of a 1/6-Scale Model of the 1907 Cornu Rotor.

In it Dr. Gordon Leishman says; ”Engineering challenges to the claims of a successful piloted first flight of the Cornu helicopter in 1907 have been made, first by Boulet (Ref. 8) and then by Leishman (Refs. 9–12). Based on engineering arguments, it has been shown that the power required for Cornu’s machine to have flown successfully would have significantly exceeded the rated power of the 24-hp Antoinette engine that Cornu had installed in his machine.”



Counter Argument:

Boulet provided specifications on the craft but no engineering. In addition, his information on Cornu came from Cornu’s article in L’Aerophile of 15 April 1908. Therfore Leishman is the sole source of “engineering challenges”.

Leishman used Boulet's (Cornu's) specifications, which have little information on the airfoil, to build a 1/6th scale approximation of one rotor. This rotor was then placed on a test stand and data was acquired.

The data was then used to give a Power Correction Factor of 2.208. This remarkably high value is in stark contrast with “For preliminary design, most helicopter manufacturers use their own measurements and experience to estimated values of the Induced Power Correction Factor, a typical value being about 1.15.” Airplane wings and bird wings are also slightly above 1.0.

In contrast to this, Cornu built a complete model helicopter that was 2-1/2 times the size of Leishman's, and then flew it. He then built his full-size craft based on the success of his model. Cornu’s model will obviously be significantly more indicative of the full-size craft then Leishman’s model.


Cornu’s helicopter may, or may not, have lifted a man out of ground effect. However IMO, Leishman’s critique, using questionable data and algorithms that are inappropriate for Cornu's type of rotor, will not revise history.


Leishman's Argument.
A Counter Argument.


Dave