In view of the increasing number of small, scout airplanes and the evident necessity for more accurate aërial navigation, it seems opportune to explain the problems confronting the naval aviator and his efforts to navigate this type successfully. Unless one has had the experience in actual flight overseas, it is difficult to comprehend the real inconveniences of the navigator of the two-seater open-cockpit plane. This state of inconvenience—a condition that impairs efficient navigation in any type of craft—will be difficult to remedy.
The designer of the scout or observation plane, absorbed in the placing of bombing, gunnery, and radio appliances, can give but little thought and less space to the requirements of navigation. Moreover, since the performance of aircraft is so intimately linked with weight, some useful navigational instruments are dispensed with due to the extra weight involved. Furthermore much equipment that has contributed so materially to successful transoceanic flights cannot withstand the heavy shocks incident to service operation; hence their installation is quite impractical. Very few of the aforementioned handicaps are placed upon the commercial plane of a similar size. As a consequence, it is not uncommon to note extreme accuracy in present-day long-distance over-sea flights. Without wishing to detract one iota from the credit due the pioneers of ocean flights, this accuracy can in a large measure be attributed to far superior instrument installations together with a high degree of convenience for the navigator.
Only recently has it been recognized that dead reckoning is the proper method for successful navigation of the small scout and observation type of aircraft. Celestial navigation is most impractical, considering the vibration, restricted arc of vision, cramped position of the observer, exposure to wind blast, and endurance of the plane. Of course, the radio homing loops have been and will be of inestimable value in guiding lost planes back to their parent vessels in peace time.
Of the many errors in dead reckoning, probably the largest can be attributed to the effect of wind drift. This effect is similar to ocean currents in surface navigation. However, the force of the wind aloft is usually vastly greater than the strength of ocean currents. Also the direction of the wind at altitude does not follow any rule of thumb from what it may be at the surface. To add to the difficulties in the air, the force and direction of the wind varies with change in altitude and at indeterminable times. The determination and continuous checking of the actual force and direction of the wind at altitude over the sea is the most important problem not yet solved in small scout planes. At present, there are two methods generally in use, namely the “seaman’s-eye” method and secondly the float light system. The “seaman’s eye” consists essentially of judging wind velocities as indicated by the surface of the sea, i.e., the wind streaks, waves or ripples. This is sometimes difficult in light breezes. The direction is obtained by heading the plane into the estimated wind and reading the compass.
The aforementioned system is a rapid way of obtaining wind force and direction. It has a distinct disadvantage, though, in that the plane must be flown close to the surface of the sea. Otherwise, flying at the most favorable scouting altitude, the wind may double its strength and change its direction. No rule can be followed to estimate this change sufficiently accurately for navigational purposes. The “seaman’s eye” method has at times been referred to as getting the drift “by guess and by God.” This, in my opinion, is quite incorrect. Accuracy can be attained. It is the direct result of a close study of wind ripples on the surface of the sea and plotting the results over familiar territory during a long period of training. Experienced navigators in using this system have obtained results consistently equal to or better than other ways now used in small scout planes overseas (except possibly the radio homing loops). It might be mentioned that the seaman’s eye” was used by one of the recent transatlantic fliers, who made a preliminary training flight to Bermuda. This pilot attributed much of his success in reaching Bermuda under adverse visibility conditions to his experience with the “seaman’s-eye” method.
The float light system is the one in general use to obtain the wind drift at altitudes much above the surface. The plane is flown on a steady course at a constant speed and altitude by the first pilot. The second pilot simultaneously observes the angle of drift through a telescopic sight focused on a float light dropped from the plane. The latter reads off the angle of drift from a base plate mounted at the side of the rear cockpit. Observations are usually taken on two headings separated by ninety degrees. From the drift angles thus obtained many methods are in use to compute or lay off the plane’s track and ground speed. There is the mark IV drift computer, an instrument that is hardly adaptable for use in small scouting planes. The aircraft plotting sheet accurately describes and clearly illustrates several methods of plotting. There are tables from which the track and ground speed can be directly read. Countless devices of squadron invention are in use for determining the required data. Practically all of these methods use the drift angles as the basic argument. Any system that requires the use of drift angles as obtained at present, regardless of improved methods for converting the drift angles into ground speed and track will not materially reduce the large dead-reckoning error. An entirely new instrument is needed. It is understood that a simple device of proved accuracy has recently become available.
The remaining errors in dead reckoning are mainly due to the inability of the pilot to hold the plane exactly on the course (magnetic compass) under average air conditions, the general lack of convenience for the navigator, and instrument errors. There is a wide divergence of opinion as to just how close a small scout plane can be held on its course under average air conditions. A conservative average seems to be three degrees on either side of the proper course with the magnetic compass. It is estimated that the actual error in the course steered approximates two degrees; in rough air the error is greater. A directional gyro would reduce this error, if one were developed that would be suitable for installation in the subject type of aircraft.
The general lack of convenience for the navigator will be difficult to overcome. However, the continued improvement of the instrument board, the installation of a convenient map case and provision for chart board with instruments and charts suitable for working thereon; all will assist the navigator.
While there has been a steady improvement in the navigational instruments, a dead-reckoning error can be attributed to the faults of the present magnetic compass and the air-speed meter. It is not generally understood that an appreciable correction should be applied to the air-speed meter in order to obtain the true air speed, when operating at a temperature widely different from the temperature and altitude of instrument calibration. The mark VI magnetic compass appears to be a real improvement. Under present conditions it will be difficult to reduce the dead-reckoning error below eight miles on a scouting flight of 250 miles, conducted entirely overseas with a mobile ship as the destination. Since it is not uncommon for the visibility to be less than eight miles at sea, the importance of reducing this error is apparent. Decreasing the error materially will be largely dependent upon: the adoption by the service of an improved wind drift instrument of proved accuracy and dependability; a more extensive training period devoted to actual over-sea flights; a closer study of aërial navigation by all naval aviators; the installation of improved navigational instruments; a better understanding of and providing for the needs of a navigator of a scout airplane.
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Our country has the first demand for our services, and private convenience, or happiness, must give way to public good.
I have invariably laid down, and followed close, a plan of what ought to be uppermost in the breast of an officer: that it is much better to serve an ungrateful country than to give up his own fame. Posterity will do him justice; a uniform conduct of honour and integrity seldom fails of bringing a man to the goal of fame at last.
I have not a thought on any subject separated from the immediate object of my command nor a wish to be employed on any other service.
Their high state of discipline is well known to you, and with the judgment of the captains, together with their valour and that of the officers and men of every description, it was absolutely irresistible.
My mind is fixed not to fight them, unless with a westerly wind outside the Hieres, and with an easterly wind to the westward of Side.
Do not imagine I am one of those hot-brained people who fight at an immense disadvantage without an adequate object.
We won't part without a battle. I think they will be glad to leave me alone if I will let them alone; which I will do either till we approach the shores of Europe, or they give me an advantage too tempting to be resisted.
Small measures produce only small results.
I knew when I decided . . . that perhaps my life, certainly my commission, was at stake, but being firmly of opinion that the honour of my kind and country was involved ... I determined at all risks to support the honour of my gracious sovereign and country, and not to shelter myself under the letter of the law.—Nelson.