Flight, November 1941

THE TAILLESS AGAIN
Jack Northrop's Latest Baby : Successful Test Flights by Scale Model : The Problem of Control

  THE late Professor Hugo Junkers is generally credited with being the first man to visualise an aircraft entirely without tail surfaces. He took out a patent somewhere around 1910, and he called the type a Nurflugel. The literal translation is wing-only, but many years ago Flight suggested "all-wing" aircraft as a better term, being descriptive in the way that "all-eyes" and "all-ears" are descriptive.
  What prevented the original Junkers design from being developed in the early days of flying was the fact that, to accommodate passengers, the wing chord had to be very great, some 30-35ft., and aircraft engineering had not then progressed so far that such a project could be made a reality.
  German glider designers continued to toy with the idea of the all-wing principle and several were built, as well as a few low-powered light planes. No great success was, however, achieved. In this country the champion of the tailless aircraft was Capt. Geoffrey Hill, now Professor Hill. He was originally concerned not so much with producing an all-wing aircraft for the sake of any reduction in drag which might be expected, but rather did he aim at a wing which would not spin. The first Hill tailless was named the Pterodactyl, and later Capt. Hill joined forces with Westland Aircraft. In addition to light planes, a military version was built, the Westland-Hill Pterodactyl V. With a Rolls-Royce Kestrel engine this machine did quite a lot of test flying, but it did not go into production, although its military merits were obvious, the most noteworthy being the amazing field of fire provided for the rear gunner, who had an uninterrupted hemisphere through which to swing his gun.
  Generally speaking, there are two main difficulties with a tailless design. The necessarily short wheelbase is likely to make the aircraft somewhat tricky on the ground. The second relates to controls. Instead of the elevator and rudder, used alone or in conjunction with the ailerons, control has to be exerted through the wing tip organs alone. It is possible to argue that if the Wright brothers had not thought of the separate rudders, tail and wing-warping (they did realise the possible source of trouble, and they interconnected the warp and the rudders), and if the Farman brothers had not adopted ailerons in place of the warping wing, we might have evolved a sensible form of control much earlier.

Two-Control Flying

  In the tailless design there does wem to be a chance of attaining the ideal of a two-control aircraft. In fact, the type almost seems to be impossible without it, since the wing tip surfaces must of necessity perform more than the single function of the aileron. They have to serve as elevators and rudders also. How that function is best achieved is a problem which is still a long way from being settled, but it may be that the American designer, John K. Northrop, has made yet one more step towards the solution in his new flying scale model.
  The Northrop tailless monoplane was patented some time ago and nothing more was heard of it until recently, when a small machine with two engines of about 120 h.p. each was test flown, apparently with a good deal of success. The machine seems to have two "flat" engines buried in the wing. They drive pusher airscrews, and thus to that extent the new Northrop is very modern. Another modern touch is a "four-wheeled tricycle" undercarriage.
  But the most intriguing puzzle about the new Northrop flying model is its aerodynamic controls. The plan view shows the pronounced sweep-back common to all tailless aircraft. But, in addition. Jack Northrop has tilted his wing tips down at an angle of roughly 45 deg. The thought which comes to mind immediately is that this has been done so that the control surfaces on the trailing edges of the tips can act both as rudders and elevators. That they are ailerons as well is obvious.
  Trailing edge flaps are fitted farther inboard. That was to be expected, but an unusual feature is that these flaps seem to be fitted with trimming tabs. That may merely mean that for the experimental flights it was desired to have some form of adjustment, apart from the wing tip control surfaces; or it may be an indication that the flaps are used also for elevator control or, perhaps more likely, for "tail trimming."
  That the new Northrop is merely a flying scale model of a much larger aircraft may be accepted. The practice of building such models is spreading. Instances from this country are the Short Scion, built to obtain data for the Empire boats, and a more recent small type, which was a flying scale model of the Stirling.
  The all-wing aircraft, owing to the absence of fuselage and tail, may be expected to have a much lower drag than the orthodox type, but from a military point of view there are other advantages. Not the least of these is the field of fire which can be provided for "Tail-end Charlie" (except for the pusher airscrews!). Some of the disadvantages have already been indicated. There are others. For instance, the short overall length of a tailless means that control surfaces act on short lever arms. The moment of inertia is low, of course, but the stowage of military load is likely to be somewhat exacting, and bombs could not be spread much in a fore and aft direction without causing a serious change of trim when they were dropped.
  By using two engines, several advantages are secured. The pilot obtains a very good view forward and laterally, although forward and downward the wing gets in the way (in the Northrop, windows in the leading edge help matters). But one problem arises as to what happens to a tailless when one engine stops. Although the airscrews can be placed close together, and consequently the offsetting of the thrust be reduced, one wonders if there is enough rudder power to hold the aircraft against the running engine.