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A QUESTION OF STABILITY

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    Posted: 22 Jun 2009 at 09:00

A QUESTION OF STABILITY 

EARLY RESEARCH INTO AIRCRAFT CONTROL BY SEBASTIAN DE FERRANTI

 

Introduction

Aviation is a very young science. There are people still alive today who were born before  the Wright Brothers first flew and started to draw their old age pensions around the time that Neil Armstrong set foot on the Moon. However, because the advances in aviation science have been so rapid it is easy to forget a recent time when the now accepted fundamentals of flight were matters for speculation and argument.

 

Gliders and Chauffeurs

Experimenters tended to adopt one of two approaches to achieving practical powered aviation. The 'gliders' believed that a thorough knowledge of how to control an aeroplane should be gained through gliding before powered flight was attempted. The 'chauffeurs' believed that the priority was to get airborne and the issue of controllability could be dealt with empirically. The latter became increasingly interested in the idea of inherent stability, i.e. an aeroplane capable of resisting forces which tend to disturb its equilibrium and which automatically returns to equilibrium in flight if disturbed. Inherent stability, particularly longitudinal, is necessary for model flying  and many of the European experimenters began with making models. The problems of imposing control and manoeuvrability on an aeroplane which had been designed to fly in a level straight line had not been appreciated and this hindered further developments. Foremost among the 'gliders' were the Wright Brothers while European experimenters tended to be 'chauffeurs'.

 


The Wright Flyer at Le Mans

This geographical separation of the two 'schools' is in itself important. Prior to the arrival of Wilbur Wright at Le Mans in 1908 France had assumed the role of world leader in the sphere of aviation. The performance of the Wright Flyer demonstrated just how far behind the European experimenters were. However when it became generally accepted that the Wrights had developed a fully controllable aeroplane the initial euphoria was soon replaced by doubts as to how this had been achieved.

 

The doubtful practicality of the Wright Flyer


The Europeans did not perceive the achievements of the Wrights as being a consequence of their different approach to achieving practical powered flight. Instead it was commonly believed that the Wright aeroplanes were flown in a manner akin to performing some sort of acrobatic feat and success was the result of several years of intense training. (J W Dunne stated "It is no good having a machine which cannot go up on a windy day, or a machine which takes four years to steer with even approximate safety, like the Wrights." Letter to Colonel Baden-Powell, May 9, 1904, quoted in P B Walker Early Aviation at Farnborough Volume II : The First Aeroplanes, Macdonald and Janes, 1974.) This notion endured and may well be the foundation for the theory that an ability to ride was a prerequisite for any would be aviator.) This perceived need for protracted training would seriously hamper expansion plans for any nation's air force. The 'chaffeurs' maintained that their approach was still the most appropriate for practical aviation. An analogy was drawn from ships : stable ships were easier to control in bad weather so would it not be reasonable to assume that stable aeroplanes would be very easy to fly, even in  high winds, and could be used by pilots with the minimum of training ? F W Lanchester believed "that the future of flight as a useful and practical means of navigation will depend upon the abolition of hand-maintained equilibrium and the substitution of automatic stability." ('The Wright and Voisin Types of Flying Machine : a comparison', F W Lanchester, The Aeronautical Journal, January 1909)

 

Stability for safety ?

The Editor of The Engineer (June 6, 1913) identified the need for stability as being associated primarily with safety : "....we are entitled to expect machines which will not only fly, but fly safely. Towards the attainment of this the elimination of the human element from the control of the stability must help very materially. " The Editor identified two ways of attaining stability : "according to those who argue in favour of (inherent stability) the machine should be so designed that its own form without further addition ensures stability  under all circumstances. The adherents of automatic stability hold that the machine need not be inherently stable to a greater degree than it is at present, but that mechanism should be fitted to it which will automatically operate the controls in the required manner when occasion arises.... To attain complete inherent stability is...  the dream of the mathematician : to achieve automatic stability that of the engineer."

 

Early work on stability

The Royal Aircraft Factory at Farnborough took particular interest is the notion of inherent stability as something which could be designed into aeroplanes. The work of J W Dunne produced a tailless design with swept back wings imitating the inherently stable winged seed of the zanonia plant and later the work of E T Busk  facilitated the development of the BE 2c.

 


Consideration was also given to the development of a control system, the benefits of which were later outlined in a manufacturer's booklet :

 

"The full value of such an apparatus can be appreciated only by those who have experienced the difficulties of flying under unfavourable atmospheric conditions. The pilot is not only relieved of the nervous and physical fatigue of maintaining equilibrium of his machine but, his hands being free, is enabled to draw maps, drop bombs etc. for which an observer has heretofore been required. The increased ability for carrying fuel and war munitions, due to the elimination of the passenger, will at once be recognised as the most important factor." (1)

 

Hiram Maxim, designer of the Maxim machine gun, investigated the matter and concluded "some have suggested shifting weights, flowing mercury, and swinging pendulums; but none of these is of the least value, on account of the swaying action which always has to be encountered. A pendulum could not be depended upon for working machinery on board a ship, and the same laws apply to an airship. We have but one means at our disposal, and that is the gyroscope."(2)

 

It seems that the idea for using the gyroscope probably came from Bolton-born Robert Whitehead who had set up a factory in Milan to manufacture torpedoes. Whitehead is credited as being the first to use gyroscopes to "set a body on a desired path" (3). Maxim is noted as commenting on the use of gyroscopes : "It will certainly not be more difficult to manoeuvre and steer such machines (i.e. aeroplanes) than it is to control completely submerged torpedoes." (4)

 


Maxim built a large biplane model in 1892 using a control system which he had patented the previous year encompassing an electro-hydraulic gyroscope (5). Maxim recognised that "a flying machine must be steered in two directions - right or left, and up or down" but decided that he "should first experiment with the more difficult one - namely, the up and down or vertical direction." However "he had no conception of the need for lateral control - the need to be able to bank the aircraft and control its movements in the rolling plane." (6) Thus the gyroscopes gave Maxim  a control centre but his design lacked adequate control surfaces to represent a practical control system.

 

In 1903 Louis Brennan, inventor of the Brennan Torpedo,  registered a patent for "two sets of gyrostats to maintain the stability of an aircraft, the precession being accelerated either automatically or by hand, and a third set for steering."

 

Ferranti's idea

SEBASTIAN De Ferranti visited the Rhiems aviation meeting in 1909 and his observation of the flying aircraft led him to speculate about possible means of automatically controlling aircraft. Despite a general lack of knowledge of aviation theory, developments and practice Ferranti produced a scheme to use gyroscopes as the basis for an automatic stability system which he patented. Correspondence now held by the Library and Record Centre of the Museum of Science and Industry in Manchester indicates the difficulties Ferranti faced in gaining support for his system, the pressure of other work and  personal problems. Not least of the latter was the fact that Ferranti had been a boy genius who was not used to having the validity of his ideas questioned.

 


Although the patent was registered in 1909 it was some time before Ferranti actively pursued the matter and one gains the impression that it may have been the result of a mere passing fancy. On June  24, 1911 Ferranti wrote to A A Campbell Swinton regarding his system : "In my opinion the importance of the apparatus lies in the fact that it would deal with very sudden disturbances: that is to say it would offer a positive resistance to the motion following on a very sudden disturbance. I believe that it is this sort of thing which causes disaster at present. The slower acting disturbances can be, so far as I know, dealt with by the movement of the elevator or the wings and this under my system is provided for automatically as the precession of the gyros in neutralising an upsetting force also operates on the wings and elevator so that they do what is necessary to right the machine and so make the disturbance of extremely short duration... I believe that without increasing the weight of the apparatus one could so construct it that it gave a very much greater stabilising force... I am inclined to think that the apparatus as now designed would be satisfactory for making a first trial and would show more quickly than would be possible in any other way how far the idea was right and on what lines it would have to be pursued."

 

The problem was that Ferranti was simply theorising. As Professor G H Bryan had pointed out in 1903, as part of a lecture to the Aeronautical Society, "I do not wish for a moment to undervalue the experimental side of the investigation of aeroplane stability. What I do wish to call attention to is the futility of random experiment." As this point "random experiment" is exactly what Ferranti was advocating but he soon realised that he needed some practical experience on which to develop his theories for on  July 1, 1911 he stated his intention to "see one or two flying men so as to get their views as far as possible regarding the question of natural stability owing to the position of the centre of gravity in relation to the centre of support."

 


Seeking support in France


It is unclear whether Ferranti made contacts among British pilots but he did speak to the French designer Robert Morane. The latter suggested that Ferranti should seek an introduction to Messieurs Seguin, the French designers and manufacturers of the Gnome rotary engine. it seems unlikely that he made much progress as on December 4, 1911 he wrote to Messieurs Seguin, "My object in writing to you is to ask if you are sufficiently interested in the gyroscopic steadying of aeroplanes to look into the matter with a view to taking up this business." Ferranti had already taken the precaution of applying for a French patent for the apparatus, No. 421530, and enclosed with his letter "a photograph of a small turbine driven model which I have made for experimental purposes." Ferranti continued : "My reason for putting this matter before you is first because your rotary motor is I believe very suitable for use as the steadying element in connection with my apparatus, and secondly because you are largely interested in aeroplane work at present. I believe that great development in aeroplane work will only take place as soon as means have been found for making the aeroplane automatically stable under all conditions, that is to say when starting from the ground or alighting on the ground and when travelling in eddying currents of air. The object of my invention is to bring this about by means of two gyroscopes mounted upon the machine which give stability in all directions but will not affect the steering and which can be so controlled that the machine may be steered up and down for the purpose of rising and falling and can also be banked to turn as at present. I believe that in the first instance the most easily made experiment would be by installing two suitably mounted gyroscopic wheels driven by small air turbines. This apparatus would of course add to the dead weight to be carried by the aeroplane. If this system was found to be successful I think that the ultimate development would be in two motors of your rotary type in which the motors themselves were so hung and connected through gearing that they would give the desired gyroscopic effect. According to this system very little weight would be added to the ordinary mechanism of the machine." Clearly Ferranti had previously discussed the matter with Seguin turned down the proposal on the basis that the was "excessivement occupes dans la fabrication des moteurs." (December 7, 1911).

 

On March 11, 1912 Ferranti asked Castelnau for introductions to pilots, particularly citing Lieutenant Conneau who had won the 1911 Daily Mail Circuit of Britain. Castelnau provided the names of two "Engineers in the French Army who were interested in the question of aeroplanes" but on May 12, 1913 Ferranti wrote again asking Castlenau to contact one of them and discuss the apparatus due to pressure of other work. Ferranti enclosed the following paper :

 

Aeroplane Steadying & Controlling

 

The idea consists in obtaining forced stability and control in an aeroplane by means of a system of gyroscopes so coupled that they give stability in all directions in which disturbance can occur.

 

The gyroscopes would either consist of wheels driven by small low pressure air turbines fed from the main engine or would be formed by a pair of rotating engines so coupled as to act as gyroscopes.

 


The idea underlying the gyroscopic action is that the gyro apparatus should oppose a considerable force to counteract any sudden disturbing force put upon the aeroplane. In doing this the gyroscopes precess against a certain definite friction and in precessing move the ailerons and the elevator so as to counteract the disturbing force which has been put upon the machine. In this way any sudden force acting on the machine would be forcibly resisted and to counter-balance the continuance of this force - which would eventually overcome gyroscopic stability - the directing mechanism would be set so as to counteract the disturbance. There are of course many more details involved but the above is broadly the principle of the idea.

 

I believe that no gyroscope arrangement alone which gives forced stability would be sufficient and I do not think that any gyroscope which simply sets the controlling mechanism would be sufficient as it would not deal with the sudden disturbances. I however think that the combination of an apparatus which would give a momentary forced stability so giving time for the correction of the control apparatus to take effect is the true solution towards making the aeroplane safer and more manageable."

 


Ferranti wrote next to the Directeur General of Clement-Bayard, using a letter  of introduction provided to him by Henry du Cros of Dunlop. Ferrant explained, "I would propose to run the gyroscopes with small air turbines similar to those I am using for other purposes, the power being obtained from a compression cylinder on the engine. Later if this apparatus was successful I think it is quite likely that the rotary engines supplying power to the machine could be so connected and swung that they would form the gyroscopic effects themselves." (Letter to Clement-Bayard, December 19, 1911). Ferranti suggested that Clement-Bayard should conduct  trials with Ferranti's system and left a model apparatus with Clement-Bayard in January 1912. Clement-Bayard were unwilling to commit themselvesas they were carrying out their own research, "Nous examinons comparativement les divers modes de stabilisation aerodynamique et gyroscopique entre autres." (Letter to Ferranti March 4, 1912). By January 1913 Clement-Bayard had still not come to a decision and on May 10, 1913 returned Ferranti's model.

    

Also in 1912 Ferranti was corresponding with Colonel Bouttiaux, Director of the Aeronautical Laboratory at Chalais Meudon, about the possible use of Ferranti's apparatus for stabilisation of aircraft. This seems to have come to nothing either.

 

Correspondence with Lanchester


Ferranti had been discussing the matter with Lanchester for some time. Copies of the earlier correspondence do not seem to have survived but on December 17, 1912 Ferranti wrote : "You will remember that some considerable time ago I tried to persuade you that the right way to make aeroplanes safe was to fit them with a controlling gyroscope system either separate from the engines or using the engines themselves (employing the gyroscopic effect of rotary engines). You then told me that the only real way to get safety was to travel at very high speeds... I see from a recently published patent that you have covered an arrangement of engine so as to take advantage of gyroscopic action. As you were so positive before upon this subject and that any gyroscope arrangement was unnecessary, may I ask whether you now believe in the desirability if it can be properly applied of gyroscopic stabilising ?" Lanchester replied "I think that your recollection of our conversation must be grievously at fault... I have always looked upon gyroscopic control as being one of the possibilities of the future. I would point out in this connection that in my second volume of my aerial flight (published by Constable 1908) I have devoted over fifty pages to the discussion of the gyroscope... I confess that my faith in the gyroscope as a means of obtaining stability is comparatively limited. I scarcely think I have met with a single individual who had "ideas" on the flight question, but he expresses some vague sort of belief in the gyroscope as a means of securing stability. The difficulty is really to find an effective way to utilise gyroscopic action... the gyroscope as illustrated in my patent does not seriously diminish in any way the need for high flight speed and does not altogether do away with the danger that might overtake an aeronaut in landing, but I think it would result in a machine being much steadier than anything that hitherto has been flown and I think it would leave the aeronaut free to devote his attention to the legitimate business of flight instead of spending his time balancing "a billiard board on te top of a cue" so to speak. I confess that I am rather amused at the wording of your letter, you almost suggest that the virtue of using a gyroscope for stability was a particular pet idea of your own of which I expressed disapproval and that now I have suddenly changed my mind and have taken out a patent ! I do not think you realise that the gyroscopic stabilising is in the abstract an old idea that has been discussed 'ad nauseum' in fact one can hardly call it an "idea" at all, if there is any virtue in the idea it will be found in some specific application or applications if it is to be found at all. The greatest danger to day in flight apart from failure of structure or mechanism is the effect of a gust of wind when the machine is only a hundred or so feet off the earth's surface, if for example a flying machine be operating against a wind blowing at something near its own flight velocity and either alighting or in flying low it happens to get in the shelter of some terrestrial obstacle  it virtually falls like a stone having little or no motion relatively to the air, under these conditions no gyroscope or any other known appliance will save the situation and I think this is the factor that will (for a long time at least) prevent flight from being a popular pastime. P.S. Hiram Maxim fitted a gyroscope as an auxiliary for stability last century."

 

Ferranti replied on January  3, 1913, : "I quite agree with a great deal of what you say in your letter. I do  not for a moment think that there is any merit in the abstract idea of using a gyroscope to steady an aeroplane : lots of people have thought of this. I am of course aware of what Maxim advocated in this direction." Ferranti went on to dispute Lanchester's recollection of their meeting and suggests that Lanchester's patent can be improved upon.

 

Lanchester further stated on January 7, 1913 : "I think that it would explain my views if I say, that from the point of view of the stability of an aeroplane I do not object to gyroscopic control with a high velocity (that is to say a substitute for some of the aeronaut's brains) but I have no faith in, and do not advocate, the gyroscope as a substitute for high velocity."

 

The Sperry System


Meanwhile development work was being undertaken elsewhere. In 1913 Lawrence Sperry (1893-1932), son of the founder of the Sperry Gyroscope Company, became a qualified seaplane pilot and later that year began to investigate the use of gyroscopes for controlling aircraft. The United States Army Aviation Corps conducted extensive trials at the Curtiss Camp at San Diego using Sperry's system (7). As has been noted, the idea of aircraft stability had become an issue of some concern to European aviators and in May 1914 the French War Department sponsored a competition for an 'aircraft stabiliser' and offered a prize of 50 000 FF. There were 54 entrants but Sperry's demonstration using a Curtiss Flying Boat was the most impressive. As the aircraft flew past the pilot could be seen with his hands on his head while a mechanic moved along the wing to upset the flying boat's stability. Despite this the aircraft continued to fly straight and level. Sperry's system consisted of four gyroscopes mounted in a frame to stabilise them in the vertical plane. The movement of the gyroscope frame actuated clutches which engaged servo motors to move the control surfaces. The servo motors were powered by a small propeller generator.

 

On June 7, 1913 Ferranti wrote to the editor of The Engineer about the Sperry article enclosing a copy of Patent 24112 of 1909 and stating "My object has been to avoid the use of relays and to get control of the aeroplane direct from the precession of the gyroscopes which give the stability..... If I were to tell you some of the people who have thought the idea of stabilising aeroplanes in this way no good you would I am sure be astonished... it may be that in this country one cannot readily find support for new ideas... P.S. I may say that two years ago when I met Mr Sperry in London I explained to him the importance of the use of two gyroscopes suitably coupled in any aeroplane stabilising. I came to discuss the question with him through having seen what he had done in the way of ship stabilising."

 


The Editor of The Engineer replied on June 9, 1913 : "I quite agree with you as to the importance of automatic control on aeroplanes, although I am not prepared to admit that the employment of gyroscopes is the only or best way to secure this. At present, however, they seem to be attracting the best share of attention. I have long thought that it might be possible to utilise the gyroscopic effect of the rotary propelling engine as a means in itself of attaining automatic stability. Lanchester is, I believe, working at this idea or was, a short time ago. Many other people in this country are trying to solve this problem and in as many ways as I feel certain that we are now within measurable distance of attaining practical success."

 

Correspondence with the Royal Aircraft Factory

On May 12, 1913 Ferranti wrote to Lieutenant Colonel R C Holden outlining his ideas and asking if Holden thought that they were of any value. Holden referred Ferranti to Mervyn O'Gorman, Superintendent of the Royal Aircraft Factory at Farnborough.

 

Ferranti wrote to O'Gorman at Farnborough on June 7, 1913 : "Some two years ago when I saw Sperry and discussed matters with him I explained to him the importance of using a pair of gyroscopes for the control of an aeroplane, and unless he had already devised this system no doubt the idea originated in this way."

 

Ferranti wrote gain to O'Gorman on June 29, 1913 : "I have also thought that for the purpose of observation and above all for the purpose of firing from an aeroplane this sort of rigidity in the air followed up by automatic control of the wings and elevator would be of the greatest possible advantage."

 

O'Gorman compiled a report on his meeting with Ferranti a copy of which he sent to Ferranti on July  9, 1913 :

 

"General Conclusions

The duplex principle of the apparatus is good, but the amount of "working out" to be done at present would appear to make it impracticable, unless very considerable sums of money are to be sunk in experiments on this line alone. It is more easy to make it practical in small form as a relay; additional and independent hand control would be easier, but I gather from conversation with Mr de Ferranti that it is contrary to the essence of his invention.

 

It should also be noted that at present it is rather early to consider the automatic controlling of both longitudinal and rolling motions before dealing with each one separately for a start.

 

There is in the last part of the specification a reference to Hargreaves' Patent, most probably put in at the suggestion of the Examiner. From my memory this deals with gyros universally mounted, and probably has some bearing on this invention.

 

Mervyn O'Gorman

May 31, 1913"

 

On August 10, 1913 Ferranti wrote to O'Gorman : "I cannot help thinking that this matter is so important in view of the position that aeroplanes are likely to take up in warfare that it would be most certainly worthwhile spending money to make the necessary experiments to develop the idea... even if I am wrong in this experimenting upon the matter could not fail to add very valuable knowledge which could probably be turned to good account in other ways and so help on the desired object."

 

Interest from Austria


In June 1914 Ferranti was contacted by Ing. Rudolf Pauschmann of Austria who was interested in further developing Ferranti's apparatus. Ferranti believed "it is not likely that  very much will be done in a practical way until Aeroplane constructors or buyers insist upon some form of Stabiliser being embodied in the machine." (July 2, 1914). The outbreak of war probably prevented further correspondence. 

 

Conclusion

Ferranti's system can be regarded as having been unsuccessful for two main reasons.  The first is that it remained an idea which Ferranti was either unable or unprepared to develop into a practical system. Furthermore he failed to persuade established manufacturers to undertake the necessary development work. This had much to do with Ferranti's general lack of understanding of both aviation and the individuals and organisations involved in developing it. There are parallels here with ideas that Ferranti had for  the textile industry (8). The demonstration of Sperry's successful system in May 1914  made Ferranti's theoretical system irrelevant.

 

The second reason for failure was also inherent in Sperry's system. The latter was very heavy and so had an undue influence on contemporary low powered aircraft. Obtaining stability through airframe design appeared to be a more viable alternative and this is the approach adopted by the Royal Aircraft Factory (9).

 

It was not until the 1930 s that the idea of using gyroscopes in aircraft was resurrected as by then weight was no longer such a critical factor. The first civilian application being to Post and Gatty's Lockheed monoplane Winnie Mae in 1932. 

 

 

 

 

 

 

 

 

 

 

 


Footnotes ;

 

(1)       The Gyroscope Through the Ages, published by Sperry. 

 

(2)       Artificial and Natural Flight, Sir Hiram S Maxim, Whittaker & Co, 1908

The pendulum system Maxim was alluding to is probably  Matthew Boulton's 1868 patent  'to prevent a flying machine from rotating around the longitudinal axis' which could be operated 'by hand or by self-acting mechanism.' The latter was a pendulum weight employed on the mistaken assumption that it would hang vertically however much the wing was inclined.

 

(3)       The Gyroscope Through the Ages, published by Sperry.

 

(4)       Quoted in British Aviation : The Pioneer Years, Harald Penrose, Putnams.

 

(5)       The mechanics of this system as described in some detail in Artificial and Natural Flight, Sir Hiram S Maxim, Whittaker & Co, 1908.

 

(6)       'Approaches to Powered Flight', Philip Jarrett, Air Enthusiast No.60

 

(7)       These tests included investigation into the effect of "aerial disturbances created by gunfire" on aircraft controllability. This particular test consisted of Lieutenant Samuel McLeary flying a seaplane at 50 000 feet over the cruiser USS Maryland while the latter carried out target practice ! 'The Sperry Aeroplane Stabiliser', The Engineer, 6 June 1913.


(8)       'The Textile Inventions of Sebastian Zani de Ferranti' by K G Ponting, Textile History Volume 4.

 

(9)       Work at Farnborough by E T Busk led to the development of the BE 2c which was  put into wide scale contracted production. Discreditation followed because it was thought that the design of the aircraft made it very difficult for the aircrews to defend themselves against machine gun armed German scouts. Arguably this was not a function of the BE 2c but rather the function of British scouts which should have been deployed in such a way that the BE 2c crews were able to carry out their work unmolested. One can draw parallels between the BE 2c and the Junkers Ju 87 Stuka. Curiously there have also been claims (ref The Great War in the Air , by JH Morrow) that the standard of training of Royal Flying Corps pilots was such that it was not practical to expect them to be proficient in flying less stable aeroplanes. 

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