Flight, April 1930
A School Machine with Very Low Landing Speed
A LITTLE over a year ago a small party of aviation enthusiasts happened to gather one evening at a certain hostelry in Yeovil. On the morrow the Westland Aircraft Works were to celebrate
the completion of the first "Wapiti" built for the Royal Australian Air Force, by a christening ceremony performed by Lady Ryrie, and many had wended their way Yeovilwards in order to be present. The talk, during the evening before, turned to the subject of machines for the private owner and for school work. Capt. Neville Stack threw a bit of a bombshell into the party by stating as his considered opinion that what was wanted was a machine capable of flying very slowly indeed, at something like 25 m.p.h., if possible, the top speed being of no importance whatever.
As frequently happens on such occasions, the discussion which followed this remark grew quite heated, and although Capt Stack found a few supporters, his opponents were in a very considerable majority. Briefly, the argument advanced by Capt. Stack was that, for sheer pleasure of flying, the average person who goes up for a short flight in the vicinity of an aerodrome, or even for a short cross-country flight such as from London to one of the South Coast towns, does not want high speed. He does want to fly in comfort, troubled with as little noise and draught as possible, but speed does not interest him. He also wants to be able to fly fairly low so as to see the countryside over which he is passing, and he wants to feel that he is on a machine having so low a landing speed that it can be "put down anywhere" without risk of damage. To get these things he is quite prepared to sacrifice a good deal of top speed if necessary.
For school work, the slow-flying machine is an advantage, especially where raw beginners are concerned. Not only is risk of accident reduced by virtue of a low landing speed, but the chances of any mishap occurring at all are reduced because the slow-flying machine gives the beginner time to think and to correct mistakes.
Thus, approximately, did Capt. Stack formulate his arguments. His opponents, reluctantly agreeing that "there might be something in it," maintained, however, that the slow-flying machine must, of necessity, be one with very low wing loading, and that a lightly-loaded machine would be very uncomfortable in a gusty wind, and would "go kiting along" when being landed.
At the time of the Yeovil discussion there was, we believe, very little likelihood of friend Stack's slow-flying machine materialising, and the subject was regarded by most of those present as being largely of academic interest. None of those present expected to see such a machine built in the near future. Whether Capt. Stack has continued his arguments elsewhere, or whether it is another case of "great minds thinking alike," we do not know. The fact remains that Mr. Dudley Watt, owner of the D.W. Aircraft Co., of Brooklands Aerodrome, has produced a machine which answers in almost every respect to that visualised by Stack a year or so ago.
The D.W.2, as the new machine is called, was designed for Mr. Dudley Watt by Capt. Pearson, the inventor of the "rotary aileron" and designer of, among other machines, the Glenny-Henderson "Gadfly." It was constructed in a few weeks in a very small shed at Brooklands, and Mr. Watt has been testing the machine out before sending it to Martlesham for its type tests. Pending the Martlesham report, it is not possible to give exact performance figures and so forth, but already it has been established beyond a doubt that the D.W.2 does definitely fly very slowly indeed, still remaining under control.
At round about 30 m.p.h. the machine does not exhibit any tendency to "fall out of the pilot's hands," and the actual landing seems to take place at something like 25 m.p.h. In a slight breeze the machine lands at a quite surprisingly low speed, and the run is almost nil. As for the "kiting," which many had expected from such a lightly loaded machine, there is very little. The D.W.2 seems to "sit down" very nicely, and to stay down.
The expression "light 'plane" conveys an idea of smallness rather than lightness, and the casual observer would not recognise in the D.W.2 a machine of the light 'plane class. In point of fact, it is roughly of the same size as a Hawker "Hart," but the weight is, approximately, that of a "Moth" or "Avian." The considerable size is, of course, due to the need for a large wing area to give the low wing loading. The tare weight is in the neighbourhood of 950 lb., and the C. of A. gross weight is 1,500 lb. As the wing area is 350 sq. ft., the wing loading is only about 4 1/4 lb./sq. ft.
In designing the D.W.2, Capt. Pearson had to reconcile the conflicting requirements of simplicity and low cost with good view and the possibility of both occupants being able to make use of their parachutes. The former would indicate a vertical biplane arrangement, while the latter would call for a heavy stagger. Capt. Pearson's compromise shows a biplane with a lower wing of smaller chord and span than the upper, with the two trailing edges vertically above each other, and with the top plane rear spar placed relatively far forward so as to provide a centre-section cut-out of considerable depth from front to back, thereby bringing the occupant of the front seat fairly close to the cut-out and to the means of getting away by parachute in emergency.
The low weight, in connection with a large wing area, presented rather a problem in wing design. A single-bay biplane arrangement was obviously impracticable, and even an orthodox two-bay arrangement would have left rather long spars between supports. To keep wing weight down it was necessary to use very light main spars, and in long lengths these would have been somewhat flexible and "whippy," even if strong enough for their flying loads. Capt. Pearson in the end decided to adopt the Warren girder arrangement for his wing bracing, and by so doing he has been able to produce a wing which, although very light, is remarkably stiff. The fact that the Warren girder strut arrangement results in a somewhat considerable frontal area is of relatively small importance in a machine which is not designed to have a high speed. Weight in this instance is of greater importance than drag. And apart from the lighter wing structure which the Warren girder arrangement gives, the wing folding is slightly facilitated, as no jury struts are required. Also, as the lower front spar root is not braced when the wing is folded, the operation of spreading the wings after folding is made easier because the spar can flex slightly and is thus easier to get into place before pushing the locking bolt home.
As regards their structural details, the wings of the D.W.2 are of normal construction, with spindled spruce spars and ribs having three-ply webs and spruce flanges. The arrangement of the inter-plane struts in the form of a Warren girder has, however, necessitated the use of strut fittings of somewhat unusual form. One of these fittings is shown in a sketch on the next page, from which it will be seen that the steel plate forks the spar, while lugs running the opposite way form the supports for the struts. The spars, it should be pointed out, are not the full depth of the wing section, hence the strut plates are bent upwards so as to bring the plate ends above the level of the fabric covering. The interplane struts have fork ends for their attachment to the strut plates.
The fuselage is of the "box" type, with a framework covered with plywood. The covering, however, does not carry very much load, the internal framework being designed to be stable without the covering, i.e., the struts being attached to the longerons by plywood gussets. While the sides and bottom of the fuselage are planked with plywood, the top deck is formed of a light framework of stringers, with a laced-on fabric covering. This covering can be removed fairly readily, and the internal structure of the fuselage inspected.
The two cockpits are very roomy, and the instruments are so arranged that when the front occupant leans slightly to one side or other the rear occupant can see the instruments placed in the front cockpit. The machine is very quiet, and conversation can be carried out direct when flying at cruising speed.
The undercarriage is of very wide track, the telescopic legs being hinged to the top longerons, while the bent axles and the radius rods run to the centre-line of the fuselage bottom. The travel of the wheels is considerable, so that, what with the light loading and low landing speed, the machine can be "pancaked" down without doing any damage, another point in favour of the slow type of machine.
The "Cirrus III" engine is supplied with fuel from a tank housed in the top centre-section. This tank has a capacity of 20 gallons, but as it only occupies about one-half of the centre-section, another tank could easily be added, should the machine be required for flights of long duration. Incidentally, the D.W.2 might well be capable of establishing a world's duration record for light 'planes, as the power required to keep the machine in the air is very small indeed, and the fuel consumed per unit of time would be very small. The cruising speed would, however, be too low to make the machine suitable for long-distance records.
Some time ago we recorded the fact that the D.W. Aircraft Co. is moving to the old Ford aerodrome, near Bognor. There it is intended to establish a flying school and joy-ride concern, as well as works for the production of the D.W.2. We understand that at first the school work, etc., will be carried out with Avros, but that if the D.W.2 proves the success it promises to be, this type will gradually be introduced at the school.