Flight, November 1921

THE SUPERMARINE "SEAL," MARK II
An Interesting Deck-Landing Amphibian Fleet-Spotter.

   NOT only on account of its higher engine power, but also due to detail improvements of various kinds, the new Supermarine amphibian fleet-spotter "Seal," Mark II, is a very great step forward as compared with the machine of last year, which did so well in the Martlesham and Felixstowe tests. The older machine had a fairly high power loading, and as a result of this its performance was not spectacular although it was certainly by no means bad for the weight and power. The new machine, with its Napier "Lion" engine, naturally has a much greater reserve of power, with the result that the get-off and climb are much improved. The fitting of a higher-powered engine is not, however, the only alteration which is responsible for the general improvement. The Martlesham machine, it should be remembered, was designed and built in a few weeks, and as no risk could be run of anything failing it was, generally speaking, a good deal heavier than was really necessary, in the "Seal," especially the Mark II, which forms the subject of this description, there has been more time for refinements, and, consequently, it comes much nearer a reasonable and uniform factor of safety than did the older machine. In the amphibian gear itself so many improvements have been effected that it cannot, in fact, be compared at all with, that of the Martlesham machine. Unfortunately, as the "Seal" is built for the Air Ministry, it is not permissible to give a technical description of the amphibian gear, beyond mentioning the fact that it is a great improvement on the older one, and has proved very satisfactory during tests.
   In attempting to form an opinion of any Supermarine flying boat, it should always be borne in mind that this firm has always aimed at seaworthiness. This quality is regarded by Mr. Hubert Scott-Paine and Commander James Bird as of the very first importance. The result has been that Supermarines are always of substantial construction, a proper boat-built job, a boat that will fly rather than an aeroplane that will float. There is all the difference in the world between these two types, and if at times one may be apt to compare, perhaps unconsciously, the performance with that of a lighter machine, it should be realised that such comparison is scarcely fair to the builders of the boat, who have had quite different objects in view. Broadly speaking, there are two different ways of evolving a flying boat, and even then the final result will be two different types, according to the evolution followed. One is to start with a hull which one knows to be seaworthy, and then to put on to that hull wings and engines to give the best performance possible. The second method is to start with an aeroplane having the lightest possible flotation gear, and then, as necessity arises, strengthen the structure and improve the seaworthiness of the flotation gear according to requirements.
   It will easily be seen that the final results of the two methods will still present fundamental differences, so much so that the two types, instead of being rivals, supplement one another, the one type being the more suitable where seaworthiness and robustness of construction are the main desiderata, the other where performance is the most important feature.
   As already mentioned, in the Supermarine boats it has always been strength and seaworthiness which have been first considerations. That is not to say that their performance is inferior. For instance, although few figures relating to the "Seal," Mark II, may be published, it is permissible to state that the maximum speed is in the neighbourhood of 93 knots, while the landing speed is as low as 39 knots, a very good speed range indeed for a flying boat.
   From the accompanying general arrangement drawings (which, although somewhat sketchy, are approximately to scale) and photographs it will be seen that, as regards general outlines, the main innovation in the "Seal" is that the machine is a tractor. This change was somewhat of an experiment, as it changes the weight distribution very materially. However, the experiment has proved a success, with the result that the Supermarine Works can now provide boats of either type, according to whether the main load is required to be in the front or aft of the main planes, knowing that either type behaves satisfactorily on the sea and in the air. Incidentally this machine is, we believe, the first British flying boat to be designed as a tractor. As regards appearance the change is, we think, an improvement. The pusher always looks somewhat short and tubby, while the new tractor machine conforms more to usual designs and, therefore, looks more pleasing to the eye.
   Structurally, the "Seal" follows usual Supermarine practice, having a hull of approximately circular section, boat-built of planking over a light skeleton of timbers and stringers, and covered with fabric on the outside. As in previous Supermarine boats, the steps are separate units, built on to the main hull. They form a double bottom, and are subdivided into numerous watertight compartments, so that in case of the hull striking some object floating in the sea there is no fear of sinking. Also, in case of damage, a step can be repaired or renewed without interfering with the main hull. In the Martlesham machine, it may be remembered, the combined tail skid and water rudder was mounted some distance forward of the stern. In the "Seal" it has been shifted aft to the sternpost, where it is much easier to provide the necessary strength and water tightness than it is with a rudder working in a trunk in the hull. Also the tail loads, which are very considerable, are lessened by placing the skid aft. An easily detachable shoe is fitted to the heel of the rudder, so that, as wear takes place, the shoe can be easily renewed.
   For reasons already mentioned, it is not permissible to refer in detail to the amphibian gear, beyond what can be gathered from the illustrations. It can be seen that the wheels and their strutting form a structure independent of that of the main hull. Thus, when alighting on the deck of a seaplane carrier or on an aerodrome, the hull is not subjected to landing shocks. The track is wide, and the wheels, as may be seen from some of the photographs, lift sufficiently clear of the water not to hinder the getting off from the sea.
   It should be observed that the upper and lower centre-sections form a complete unit, detachable from the hull, so that replacements can be made without interfering with the boat proper. The Napier "Lion" is very accessibly mounted on a system of struts resting on the lower plane centre-section, and the radiator is so mounted that it is not affected in the slightest by engine vibration.
   The monoplane tail plane is of the semi-cantilever type, giving a good field of fire for the rear gunner. As in previous boats, it is of the negatively cambered type, and is carried high, well clear of the water, which is a great advantage in a rough sea.
   The wing tip floats are of a type somewhat different from that previously used. Instead of the covered-in space between the lower plane and the wing tip floats, this space has been left open on the "Seal," it having been found better to leave the water free to get through the space thus formed.
   As distinct from previous Supermarine flying boats, in which the wings have folded forward, the wings of the "Seal" fold back as in the majority of other machines. This has been necessitated by the new arrangement of the machine as a tractor, so as to enable it to be stowed in the smallest possible space. If the wings had been folded forward, they would have projected a considerable distance forward of the bows of the hull. Personally we prefer, for several reasons, the forward folding of the wings where practicable. Not only is the load on the tail skid greatly reduced thereby, but with wings folding forward the hinges are on the front spars. Thus, should one of the locking pins come adrift or break, the wings would still be held in their place by the horizontal component of the air resistance. However, this is probably mainly a theoretical objection, and we must admit that we have never heard of any trouble arising out of having the wings folding back.
   As regards the accommodation, the "Seal" is designed to carry three people. The pilot, as distinct from the older model, occupies the front seat, whence he has an exceptionally fine view. A machine-gun mounting is provided in his cockpit, the gun being withdrawn when not in use, and the opening through which it projects being provided with a cover which prevents water getting into the cockpit when the machine is taking off the sea or alighting. The other two occupants are placed aft of the wings, the wireless operator's cockpit being about level with the trailing edge, and that of the aft gunner slightly farther aft. Owing to the mounting and strutting of the tail plane, the aft gunner has quite a good field of fire.
   As already mentioned, few performance figures may be published, but it is permissible to state that the total military load carried, including fuel, is 1,790 lb., with a cruising radius of five hours. We understand that, in addition to the "Seals" being delivered to the Air Ministry, the Supermarine works have received an order from Japan.