Haya Gyro Horizon.
Interior of a cockpit with the Haya Gyro Horizon in the centre.
Instrument panel of the “Cuatro Vientos” with the engine and fuel gauges: compasses, flight integrometer, altimeter, variometer, speedometer as well as the radiator and fuel transfer controls.
Lieutenant Colonel Herrera inspects the Haya Gyro Horizon in the company of a German technician and the engineer Sr. Escribano.
An article on the Artificial Horizon published by the daily newspaper AS on the 18th October 1932. Page One. Photograph of the Artificial Horizon and photo of a plane flying with hood.
An article on the Artificial Horizon published by the daily newspaper AS on 18th October 1932. Page Two. Photographs of the presentation of the Artificial Horizon with Herrera and details of the cockpit with hood.
Carlos de Haya and his pupils from the second year of Exterior Visibility Flights. Photo signed by the participants.
Short story by Muntadas on how Carlos de Haya’s artificial horizon helped him.
Front cover of the patent for the Gyro Horizon “Haya Patent” 1933.
Plans for the patent application of the Gyroscopic Integral.
Notes made by Captain Haya on multiple aspects of instrumental, visual and night flight and on personal experiments.
Front page of the notebook used for imparting courses in non-visibility flight with annotated thoughts of Captain Haya.
Letter from an Aviation student in California in 1933. In that year the Gyro Horizon was already known in the United States.
Click on photo to see image enlarged.



The inventor himself used to say that his invention was a quite a simple affair, like the story of “Columbus’ egg”, bring together two simple things and round off a simple and extremely useful idea. Obviously, from the first version to the last, the Gyroscopic Artificial Horizon, as he liked to call it, underwent a few slight modifications and evolved in physical appearance, gradually improving its design and adaptability to the instrumental panels into which it was to be fitted.

The best description of the Artificial Horizon comes in an article appearing, as could be expected, in the March 1933 issue of the Aeronautical Gazette, alas anonymously, although there is no doubt that the information was provided by someone well versed in instrumental flight. The article clearly explains the need for instruments and indicators for flying under all weather conditions, with a simplicity that could not be bettered nowadays, in this age of Glass Cockpits with their EFIS (Electronic Flight Instrument System), ECAMS, FADEC and other instruments displayed through CRTs.

“Flight without visibility, being based on the need to substitute the visual sensations that allow the pilot to establish the position of his plane in relation to the horizon for the reading of the indications provided by instruments that show this same position, and the variations affecting it in relation to different axes, has been evolving slowly due to the need to invent and upgrade delicate and sensitive devices that provide clear and accurate indications; and still today this problem cannot be taken as finally solved. Nowadays, piloting a plane without external visibility requires attention to be paid to the following instruments:

Route Stability . . . . . . . . . . . . . . . . . . . . . Compass Turn Indicator

Lateral Stability . . . . . . . . . . . . . . . . . . . . . Transverse level signal

Longitudinal Stability . . . . . . . . . . . . . . . . . . . . . Variometer
Pitching level

Numerous long-distance night flights, the most notable of which are the record breaking international flights over distances of 2,000 and 5,000 km (the latter still unbroken) and that of Seville to Bata (Guinea), made it necessary to find a solution to the problem of flight without visibility, and he had the chance to practise using the instruments that made such flight possible on repeated occasions, succeeding in devising a more complete and perfect one, which led to the making of the gyroscopic artificial horizon that bears his name.”.

“Inside the sphere of this instrument is a small aeroplane set against a background of showing the sky and the earth, separated by a bar which serves as an artificial horizon. The figure of the plane moves from one side to the other, rising and falling and leaning to one side or the other in the same way as the aeroplane on which it is fitted does in relation to the natural horizon. Thus, by merely observing this instrument, the pilot can operate the controls in the same manner as if he were looking at the horizon itself.”.

“The Gyroscopic Artificial Horizon described here is made up of the following elements:

1. A gyroscopic artificial horizon, by means of which the longitudinal and lateral bank of the plane can be determined.
2. A gyroscope with a two degree margin of freedom (turn indicator), which responds to the lateral movements of the plane.
3. A signal level, held in liquid, enabling the pilot to check whether the turn is correct or not.

“The artificial horizon is made up of a gyroscope with a three degree margin of freedom, which acts over a bar that represents the natural horizon. The rotation of this gyroscope is achieved by the depression produced inside the casing by two Venturi suction tubes which force the air to penetrate in the form of a violent jet, beating against the cogs of the duct, which causes its rapid rotation. The construction of this artificial horizon means that it can respond to high altitudes and dives of up to 60 degrees and lateral banks of 100 degrees from one side and the other of the horizontal.

The gyroscopic turn indicator consists of a gyroscopic duct that turns in a longitudinal case assembled on ball bearings, which tends to lean to the right and left when the plane moves to the left or the right. By means of a connecting rod the case moves the figure of the plane visible in the centre of the instrument in the same direction as the plane and which by means of a spring returns to the centre when the plane moves back into a straight line. The rotation of the duct is achieved in the same way by a depression inside the case that joins the two gyroscopes and by means of an injector mechanism it receives a violent jet of air that beats the peripheral springs of the duct causing its rapid rotation.

“The bank gyroscopic level, which is only useful in the turns as a way of knowing the degree of bank of the aeroplane in relation to the level it should correctly maintain, is made up of a glass tube curved towards the base, filled with a shock absorbent fluid, inside which a steel ball moves in the same way as a pendulum in response to the simultaneous defining effects of gravity and the centrifugal forces of the turns. It is commonly known that this key can be used in order to activate separately the gyroscopes, thus quickly rendering the device ready for use.

“The suction device has two Venturi suction tubes joined together with independent channels from the instrument casing through which a depression is produced and the air current that moves the two gyroscopes penetrates from two separate inlets. Only one of these tubes is sufficient during the flight to maintain the two gyroscopes active.”

The extraordinary simplifying effect that this genuine Artificial Horizon –cum- Turn Indicator had in that period, as indeed in our own, is made clear in the following commentaries on its advantages:

- By consulting a single indicator the pilot is informed of all the movements carried out by the plane in such a way that a single reading reveals the flight position.
- Having an artificial horizon similar to the natural one means that this instrument can be used by any pilot, without the necessity of attending a course, etc.
- Not only can use of the instrument be learnt quickly thereby making it highly economical, but also the great similarity between this artificial horizon gyroscope and the natural horizon increases the pilot’s level of confidence making a flight without visibility as highly agreeable an experience for the pilot as if he were looking at the natural horizon.
- It measures the pitching gyroscopically. By means of a small pointer it changes the position of the casing and consequently of the small aeroplane in relation to the artificial horizon, these changes being measured from degree to degree up to a maximum bank of ascent or descent. In this way during flight the pilot levels the wings of the plane in line with the artificial horizon and in order to ascend or descend to specific bank degree all he has to do is to move the pointer placing it in the indexing corresponding to the number of degrees of ascent or descent he wishes to effect opposite the index marked on the casing. Once this is done all he will to do is to maintain the figure of the small aeroplane lined up with the artificial horizon to ensure that the flight is carried out with the number of bank degrees set by the pilot.
- It reduces fatigue and eliminates the dizziness caused by constant attention to the flight instruments when there is no similarity between them and the natural horizon, which means that the false sensation of equilibrium received by the pilot which is often contradictory to what the various instruments indicate, produce a confusion in the brain, the centre of our system of equilibrium, thus causing dizziness and loss of confidence in the manoeuvres that need to be effected.
- This instrument is doubly accurate compared with any other normal gyroscope as it is sufficient for only one of the gyroscopes to be functioning so that with the other one the flight can be maintained as normal in combination with the other indicators. Thus, if for any reason the artificial horizon should not be functioning, the small plane figure would be used as a turn indicator, and in combination would serve as a turn indicator, and in combination with the ball transverse level and other instruments it could enable flight without visibility; and if the turn indicator broke down the flight could be maintained using the artificial horizon and the compass. This safety aspect, which should be the requirement of flight without visibility gyroscopic instruments, is of the utmost importance because if the pilot flying under these conditions should suffer a failure to any of these instruments, he would go into an open spin as has been shown both in theory and practice. Flight without visibility has already been marked by several accidents caused by this, and in this instrument the safety element has been carefully studied such that, today it could be said to be the safest indicator for non-visibility flight.



This instrument is extremely easy to use. The pilot, by making the necessary movement of the controls must try to ensure that the small model of the plane on the indicator maintains the correct position in relation to the line representing the horizon in order to carry out the desired manoeuvres, as shown in the figure illustrating these pages, in which we can see the different indications provided by the device when the plane was in its main development stage. The movements to be carried out with the controls are the same as if the pilot were observing the natural horizon.

The instrument’s sensitivity can be adjusted by means of the valve regulating the inlet of air to the gyroscopes, thus ensuring that the indications are not disproportionate to the plane’s movements.

The rest of the indicators on board are used in the same way with the gyroscopic artificial horizon as in normal flight.

The ‘Haya’ artificial horizon has undergone numerous tests in flight demonstrating the qualities described above and proving that it is a perfectly operational device capable of providing an excellent aid to exterior non-visibility navigation.

As early as 5th June 1929, our intrepid pilot had already recorded a flight from Cuatro Vientos to Seville and thence on to Los Alcazares in which we find noted down the following information: “Flights using experimental devices. Shortly afterwards, at the end of 1930 and beginning of 1931, we see him already experimenting with the most basic model of artificial horizon on board a twin-seater reconnaissance Loring R-III adapted for instrumental flight in continuous “hooded cockpit” flights and in cloud.



In the first year course of Flight without visibility, in November 1931, for the teaching staff of the Alcala de Henares Flying School, as Instructor of Non-Visibility flight, Haya continued to use and perfect the artificial horizon assembled in two Loring R-III and two De Havilland DH-9 Hispano planes. “Without prejudicing the service” he made the Raid-Seville flight on the 24th December of that year, but in April 1932 we find him yet again running the 2nd year course of NVF in Cuatro Vientos and Alcala de Henares for pupils of those schools. In May and June he continued to make hooded cockpit and cloud flights, personally experimenting with escape manoeuvres to irregular positions and spins using the artificial horizon, a technique that he himself describes in another text to be quoted later on, and which he helped to design and perfect.

His investigations also extended to the technique employed for hooded take-off, dedicating numerous flights to “entering a spin and then levelling off” on board an HD-9. 9.166, and taking with him as observers and monitor pilots Commander Jordana and, on many occasions, Ferreiro, Llorente, Azcárraga, Muñoz, Pazo and Vela.

Las pruebas finales con el Integral Giroscópico se llevaron a cabo del 10 de noviembre del 32 al 22 del mismo mes, utilizando el Loring R-III.88 y a partir del 9 de diciembre con Pazó para presentar el Integral ante la Comisión Examinadora nombrada al efecto. Ese mismo día vuela 25 minutos más en el R-III.88 con el Teniente Ponte y durante el resto del mes 32 vuelos más en Sevilla con los Capitanes Gudín, Ordiales, De Arce y Con el Comandante Barrón.

Once the Gyroscopic Artificial Horizon had been “certified” and was in the process of obtaining the relevant patent, the application and concession being made through the company Telmar of Madrid (which would later belong to Marconi) its installation began in different aeroplanes and it started to arouse the interest of people both inside outside the field.

At the end of February 1933, the war Navy expressed interest in installing the artificial horizon in the sea-planes of the Martynside Squadron and the possible inclusion of the instrument in the submarine control panel for submersion was considered.



As a result of these considerations, in December 1933 an item appeared in the General Naval Review on the “Haya” Artificial Horizon, detailing the indicator that in the words of the Spanish aviator was for flying “blind” and which provided the aeroplane pilot with indications that enable him to keep a constant check on the position of his plane in relation to the true vertical and, consequently, to correct any irregularities which he would otherwise be unable to do. He goes on to give a brief but precise description of the instrument.

It is clear that the interest shown by the Navy for the Artificial Horizon was not superficial , as is demonstrated by the tests carried out in person by the Naval airman Lieutenant Antonio Alvarez-Osorio along with Carlos de Haya, and whose interesting report, highly detailed and explicit, appeared in the General Naval Review in April 1934.

The text opens with a transcription of specific paragraphs taken from a report submitted to the Naval Aeronautics Administration at the San Javier Naval air base in which the need is clearly expressed for what was then known as a Flight Controller, which would assemble all the indications which at that time were available to the pilot in panels containing 6 to 8 or more instruments, fully marked with numbered scales, circular or linear scales, dispersed or different scales. The reading and rapid frequent interpretation of all these indicators was a superhuman task that often resulted in the pilot quickly tiring and making mistakes which in some cases, when the plane was flying through a thick and uninterrupted bank of cloud, could lead to irresolvable situations.

The text goes on to describe the manoeuvres and the indications observable during such manoeuvres, as well as the perturbations that are normal when flying with instruments, such as wing slips etc. Such array of different indicators, which required almost simultaneous attention, called for a simple integrated device, that would contain most of the indicators in a single panel. It then explains the advantages and disadvantages of the “Pioneer” Controller, of the “Speery” Artificial Horizon and lastly, of the “Haya” Integrated Artificial Horizon.

This last device enables the pilot to:

“1. Calculate the angle of dive or upturn from 0º to 30º .
2. Determine the bank up to 100º, by setting the amount in the upper grading of the sphere.
3. Register the turn taken by the plane; the slope around the three spatial axes and also by means of the ball inclinometer, if the turn is correct. Also, by adjusting the calibrated knob, it enables the pilot to effect glides or ascents using only the artificial horizon, from 0º to 12º, with the possibility of broadening these limits easily.”


In the words of Alvarez-Ossorio “The great advantage of this controller is that it brings together all the indicators into one single instrument thus unifying the data that has to be interpreted (tiring mental work); but the greatest asset is the simple format of this single indicator, as it is as if you were looking at the hood of the plane. It therefore does away with the need for a long training in blind flight and must undoubtedly inspire greater confidence for its simplicity even avoiding a possible demoralisation of the pilot due to overtiredness on a long and difficult flight.

The comments made by ship’s lieutenant Alvarez-Ossorio in his report on the tests carried out in flight using the artificial horizon are the best and fullest account of an instrumental flight with that device which, however, made the pilot’s job substantially easier, setting a direct and inspired precedent for later and present day standard IFR instrument panels.

The proposed programme consisted of the following:

First test.- In a closed cockpit, Sr. Haya, with no other blind flight controls than the Haya tachometer (with me in the dual cockpit ). Acoustic communication. The flight had to be made following acoustic orders. Direct flight. Ascending flight. Gliding flight. Turns on a horizontal plane. Turns in gliding and ascending flight. Spiral in gliding flight. Try out a number of position acrobatics.

Second test.- Captain Haya in the open dual cockpit. Myself in the closed cockpit (if possible until the previous programme has been effected).

Having got ready a plane for flight on 31st January (the year in question is 1934) in the Cuatro Vientos aerodrome, I agreed that before closing the hood in flight Captain Haya should make the adjustment to the longitudinal and lateral instrument settings. Once done, the hood was closed and all the programmed tests were carried out, including five “false looping” manoeuvres from one side to the other. All of which were completed to my entire satisfaction.

The was no need to alter the sensitivity adjustments of the gyroscopic indicator or of the springs that ensure the plane model returns to its central position.

On take-off the controller was functioning (the Venturis were placed in the flow of the propellers), making take-off feasible in thick fog or night without external reference markers in properly adjusted planes. On a number of different occasions I ordered tight turns, checking that the lateral tilt had passed 45º; the object of this was to find out if the accelerations or centrifugal force affected any of the gyroscopes, at which point there would be no reference provided and the manoeuvre would be disturbed. The turns were at all times correctly carried out, which I was able to verify not only by virtue of the external visibility I had but also by the Air controller in my cockpit. After flying for approximately an hour I landed.

In the afternoon the second test took place. I should put on record that the conditions under which it was carried out were not ideal, as I was totally unfamiliar with that plane and, therefore, had no knowledge of its handling or, rather, its peculiar characteristics, and consequently all the movements had to be governed by the controller, even the slightest one. It also needs to be said that this plane had certain peculiarities about the way it manoeuvred which were to affect its piloting, such as the great importance attached to the gyroscopic torque of the moving parts of the engine (mainly crankshafts, etc.) and which had a great effect on the turns (diving and upturning when turns are made to right and left, respectively); and secondly, the tendency of that plane to drift to the left, the correction of which involves constantly pressing down on the right hand pedal.

I took the front cockpit control, taking off, flying and landing with independence.

After briefly checking the performance of the plane in flight, I closed the hood, initiating non-visibility flight. The first few minutes were of total disorientation, not through fault of the indicator, but through my own for not being accustomed to the required correction manoeuvres to rectify any irregularity detected by the controller. Later I assumed control of the plane until I was able to correct the deviations sufficiently. I found the handling of the controls easy and pleasant. Finally, over the plane intercom Sr. Haya suggested we carry out a test and I agreed as it seemed interesting. This test consisted of instructing me to close my eyes while at the same time handing the controls over to him, who would effect several continuous irregular manoeuvres in order to nullify my reflexes and possible sense of orientation; then, to leave the plane flying in a notably incorrect position and then instructing me to take over the controls again. My interest in the result was guarantee enough of my obeying his instructions. The test was repeated four times for different positions and on each of the four occasions a quick glance at the controller was enough to give me an idea of the position of the aeroplane, enabling a rapid correction.

After about thirty five minutes of flying time I opened the hood, and started back to the aerodrome, thus concluding the day’s tests.


The third test, a flight through clouds, was carried out the following day, 1st February (1934).

We reached an altitude of 2,000 metres finding a vast expanse of cloud which we entered in horizontal flight and with the hood open. The clouds were cumulus and cumulo-stratus at times covering a large area. The controller was in perfect working order. The flight seemed as simple as if the horizon were visible and even more so for the extreme sensitivity of the gyroscopic controllers. Later, we did ascents, glides and the odd turn. The flight did not seem tiring as no we had no need to perform any mental calculations only to observe the position of the model aeroplane on the index and horizon simulating a flight with visible horizons.

I am, therefore, fully satisfied with the functioning of the Haya controller, especially as it requires no instructions for use and because of how easily it gives an idea of the aeroplane’s position, enabling a correction manoeuvre to be quickly carried out; a feature of great importance in seaplanes and heavy aircraft, in which a delay in determining a normal position could have fatal consequences. After flying for fifteen minutes in cloud the test was concluded.

Having agreed upon a fourth experiment aimed at evaluating in absolutely real terms the performance of the Haya device in flight and the degree of tiredness that might result from its prolonged use, on the 3rd of February (of the same year), after receiving the weather report, which predicted a flight in average conditions, we took off from the Cuatro Vientos aerodrome at seventeen minutes past ten, en route for Albacete.

Shortly after take-off I closed the hood, and initiated Flight without visibility. After about twenty minutes flying Sr. Haya, who was navigating, corrected a drift caused by a strong cross wind, giving me a new course which I kept to continuously in blind flight until reaching Albacete. We arrived at this destination at five past twelve, and not feeling any tiredness after one hour forty eight minutes flying without visibility and taking as sufficiently tested the controller in a navigational flight, I opened the hood, continuing the flight in this way until landing at the San Javier Naval air base at nineteen minutes past one.

In spite of the bad weather that prevailed during most of the flight, with a intense cold and atmospheric conditions that caused “shaking and shuddering”, and despite the obvious discomfort of flying under a hood for such a long time, I found the piloting easy, safe and, as I mentioned before, not at all tiring. I am certain that if I had been piloting with another controller and been obliged to handle the controls on the basis of indications drawn from various sources, it would have been less pleasant and particularly tiring.


With all the precision and meticulousness of a perfect naval officer, Alvarez-Ossorio, summing up his experiences, could find no basic or inherent flaw in the Artificial Horizon, nor did he detect any fault in its application, in spite of the fact that he made a practical suggestion to Sr. Haya, and they talked about the possibility of adding a curve to improve the presentation in certain positions. Haya had foreseen that possibility and for the time being had preferred the solution of reducing the sensitivity of the gyro-director. He also perceived its great usefulness in seaplanes and heavy aircraft, with its capacity to rapidly indicate any irregularity in the position of the “flying device”, as well as to maintain stability by using a bombsight. In addition to this, the fact that all its indicators are sufficiently luminous makes it enormously useful for night flight. Lastly, the brief instruction required for its use seemed to him to be a admirable asset whilst at the same time there appeared to be no need for the retraining that was essential for the other controllers to avoid losing the habit of using them.

Thus ended the curious and detailed report of Ship’s Lieutenant Antonio Alvarez Ossorio, a sea-man who a short time afterwards was to gain notoriety for his contribution to the written polemic appearing in the pages of the Aeronautical Gazette on Independent Aviation, and which found response in the General Naval Review and other press corps of the period, and in which illustrious aviators participated.

The first leaflet publicising the “Haya” Gyro Horizon was edited in 1933 by Telmar and contains a photograph of the first version of the device along with a concise general technical description, a diagram of the most common indications in 25 positions of a plane fitted with the Artificial Horizon and a reference to the above-mentioned advantages of the device.

From February 1935 onwards a notice appeared monthly in the aeronautical Gazette about the Haya Gyro Horizon. This notice was accompanied by a photograph of the first version of the instrument and a diagram showing the possible indicated positions. Throughout the whole of 1935 the notice featured on a regular basis, even in December. January 1936 saw an advertisement in the same Gazette sponsored by Marconi Española, which had taken over the patent the inventor had granted to the company Telmar. In this advertisement we see a photo of a more modern version of the device, presented in an attractive and practical manner whilst retaining its overall simplicity and neat design. The last advertisement appeared in the July 1936 issue.



To sum up the very practical way of thinking shown by Haya regarding instrument flight that relies on his gyro horizon, we quote below some of the conclusions drawn observations made in the article he wrote on Flight without Visibility in May 1935.

After a brief run through of the first gyroscopic instruments used in flight from the earliest beginnings, he focuses on the first flights without visibility made in Spain after 1927. Despite referring to himself modestly in the first person plural, it is he who was perhaps the driving force of all the initiatives taken in that field. He goes on to consider the advantages for a Air Force implicit in the possibility of round-the-clock flight and lists the differences between flight without visibility and instrument flight but under real conditions of cloud, fog or moonless night. He describes the first American flights in bad weather, in particular the tough weather conditions experienced by pilots of the American Air Mail Service as well as the first demonstrations of hooded takeoff and landing, carried out by Lieutenant James H. Doolittle, and by Captain A.F. Hegenburg under the “hood”.



He praises the lay out of the American instrument panel, for the reliability attributed to its mixed system and tells of how an instrumental panel of similar characteristics was conceived in Spain in 1927, explaining the advantages and quoting its use in the Breguet 71 Seville-Guinea flight, noting that its easy handling “enabled us to fly all through the night with poor visibility and without succumbing to fatigue”.

Haya goes into detail when describing the altimeter instruments, the different panel fixtures and how it is protected from impact, the accuracy of the indicators and even one of the first Automatic Pilots of English design. He goes on to tells us about a number of accidents that had occurred as a result of a deficient understanding of instrument and cloud flight.

Regarding the flight panel and the invaluable instrument he had devised, when comparing it with other more sophisticated versions he observes:

““These panels displaying so many instruments, just looking at them gives one the shivers; they would scare off even the most daring of pilots. No wonder a French technician writing in “Les Ailes” calls this piloting system a “a one-man orchestra”. These panels, so carefully and studiously designed, lack one essential quality to be considered perfect: simplicity. Without this, non-visibility flight will always be complicated.

We must bring greater simplicity to flight without visibility, without sacrificing safety (obviously), so that it can be carried out by all pilots and cease to be the exclusive province of only a handful. The tendency nowadays is to incline towards this point of view and there are a great number of gyroscopic instruments named gyro horizons which aim to make flying without visibility the same as sighted flight.”

“We could say that with one of these (I refer to the gyro horizons) no other instruments are required for flight without visibility, and the other instruments, anemometers, altimeters, must be used as if in natural horizontal flight; consequently, we have done away with the need for that “constant battery” of glances at so many instruments simultaneously, which only a rigorous training and a “cool head” enabled the pilot to maintain a flight without visibility for any length of time. In fewer words, in order to fly without visibility we can design an instrument panel of great simplicity and which can be used in any type of large or small plane, since the problem of flight without visibility is the same for both, with a gyroscopic artificial horizon, a precision altimeter (which also does away with the need for the Variometer) and the other flight instruments, anemometers (protected from rain and ice) and engine indicators.”

The Haya Gyro Horizon was used in our air services until the outbreak of the Civil War, during which most of the planes used, both German and Italian, Russian or French, did not have anything even remotely similar to a Gyroscopic Artificial Horizon. According to sources unsubstantiated by documents, the patent was made over to the Government of the Spanish Republic by its creator on an unspecified date prior to the conflict, and the exploitation of this magnificent invention was, we believe, frustrated by the war that ravaged our Homeland from 1936 to 1939, in spite of the fact that it was patented and all its licences in order.

The American company Sperry, which had been producing different gyroscopic instruments for years, had never put on the market such a simple and brilliant indicator as the Gyro Horizon, shortly after its appearance began to produce more developed versions that were basically similar to the Haya Artificial Horizon.

All this information has been obtained from the following writings, books and encyclopaedias:
-Espasa-Calpe Encyclopaedia
- Aeronautical History Review (October 1989 issue nº 7/ November 1990 issue nº 8) R. de Madariaga.
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