Flight, June 1939

DIRECT TAKE-OFF MAKES GOOD
The C.40 Autogyro Now Ready for Production : Service Order for Five : Some Flying Impressions

   LOOKING ahead is a very good thing in all walks of life, and nowhere is foresight more necessary than in flying. This applies in civil no less than in military aviation, and that nation which succeeds in designing ahead of its time may well establish at least a temporary lead, although in the process it may make mistakes which have to be paid for in some way or other. And one must always bear in mind the fact that there may be considerable risk in attempting too much, technically speaking. An aircraft with too many new and untried features represents a combination which may prove too ambitious in that if it fails to fulfil the expectations of the designer it is difficult to assign the cause.
   In the field of rotating-wing aircraft great energy is being concentrated on the development of the helicopter, and quite rightly so. The somewhat crude attempts made in recent years, although they do not in themselves represent practical solutions, have shown the way to improvement and have indicated that there is every reason to believe that a really practical helicopter can be produced. But it is to be expected that before this desirable object is achieved there may come to light several snags anticipated at the moment, and it may well be three years or more before the direct-lift aircraft has got over its teething troubles.
   In the meantime it does seem a pity not to make use of the intermediate step which is available in the form of the gyroplane. This type of aircraft may not be as efficient as, theoretically, is the helicopter, due to, among other things, the fact that an airscrew has te be used for propulsion and thus introduces a second source of efficiency loss. This comparative inefficiency may be the source of lack of performance, in the aeroplane sense, but one can easily visualise conditions in which a relatively low speed is no great disadvantage.
   For work with the Army, for example, the ability to start from and alight on almost any small field, no matter how rough its surface, must obviously confer advantages which the aeroplane does not possess. And the fact that nearly vertical descent is possible makes the gyroplane a very useful observation platform, from which movement on the ground can be much more readily detected than from a fast-moving aeroplane.
   When applied gyroplane would many uses and range submarine mind at once, and it is even conceivable that a gyroplane could not merely locate the submarine but could carry a depth charge and drop it with great accuracy, owing to the gyroplane’s ability to sink slowly along an almost vertical flight path. Add to this the ability of the type to take off and land without forward run, and the possibilities of operation from the deck of apparent.
   In the latest type of Autogiro, the C.40, we have an aircraft which seems to go a long way towards doing what the helicopter is expected to do ultimately. For certain specialised work the relatively low forward speed is no great drawback; in fact, it might, in some cases, be an advantage. And the jumping start and no-run landing of this machine makes possible operation from very restricted spaces indeed. In fact, it is possible to argue that in practice it does everything which the helicopter could do. Take, for example, the case of landing. In a perfectly flat calm the helicopter could descend vertically into any space wide enough to accommodate the diameter of the rotor. But on how many days of the year do we get a flat calm? If there is any wind, and particularly if that wind is unsteady, as it usually is, and always near the ground because of obstacles, then the vertical descent becomes a very delicate operation calling for great piloting ability.
   The Autogiro C.40, on the other hand, can descend very nearly vertically (in a wind the flight path is virtually vertical), although for the last few feet of the descent some forward speed is necessary if a light landing is to be made. The extra space required is, however, so small as to be unimportant, on land at any rate. On board ship there may be some slight difficulty, although this could probably be got over by a comparatively simple platform arrangement.
   Similarly, the take-off is now simplified by the use of jump-starting. The height reached in the jump is not very great - some 10ft. or so - and has been kept down deliberately in order to get better forward acceleration at the top of the jump. It is sufficient to get the machine out of quite ridiculously small fields, and, of course, the absence of take-off run means that rough grass land or even a ploughed field can be used. On shipboard the superstructure might present some obstruction, but even there it would probably be relatively easy to arrange for the jump start to be made obliquely to the ship's centre line.
   The Cierva Autogiro Co., Ltd., have given many demonstrations at Hanworth and elsewhere, using a roped-off enclosure to represent the "field." Impressive as such demonstrations are, they cannot convey the shut-in impression because of the large surrounding space. To overcome this disability the company looked around for a suitable small field, and one was found but ten minutes’ run by car from Hanworth aerodrome. This field is not only very small indeed, but it is surrounded bv trees, and the approach from one side at least is obstructed by high-tension cables. Furthermore, the ground is extremely rough and at present covered in very tall grass.
   The photographs which illustrate these notes were taken last week while Mr. Reginald Brie was giving us a demonstration of the C.40. They give a sufficiently convincing idea of the sort of terrain which the C.40 uses and likes. No aeroplane could possibly land there, let alone getting off again. The C.40 did so repeatedly with no trouble at all.
   One very noticeable feature of the new C.40 is the absence of "sink" from the top of the jump. The machine appears to accelerate horizontally with remarkable celerity, in spite of its fixed-pitch airscrew, and in spite of the fact that the Salmson engine, rated at 200 b.h.p., is only developing about 170 b.h.p. as installed in the C.40. This absence of sink is due partly to the new rotor head (differing in detail from the “autodynamic” head of the experimental machine) and partly to the technique of Mr. Brie in letting the nose drop slightly in the jump, so that the lift of the rotor is inclined forward and assists the airscrew in pulling the machine along. This, of course, must not be overdone, or the machine would lose height.
   The new rotor head is a great improvement on the “autodynamic” in several ways. For one thing, it is very much lighter. Weight has been saved by a rearrangement of the major component parts. The pitch hinges are now placed inboard of the flapping hinges, and their angle has been changed, so that now the pitch of the blades is reduced when they are being driven and increases when they overrun the drive. Also, the slope of the hinges is such that the angular increase in pitch is smaller for a given angle of change in the plane of the rotor. This results in a smoother jump, although the maximum height reached in the jump is not quite so great. However, in practice there is usually no great advantage in jumping very high. So long as the wheels are clear of long grass, for example, that is really all that matters, provided there is no "sink" from the top of the jump.
   The flapping hinges are now outside the pitch hinges, an arrangement which enables one pile of friction dampers to do the work for all three blades. Previously it was necessary to adjust the friction in individual dampers very carefully. Now that the one central damper serves all three blades (via crank arms) this is taken care of automatically.
   It will be appreciated that in an aircraft like a gyroplane the throttle becomes a very important control member during take-off, and, particularly, landing. So important is this fact that in the new C.40 the pilot is able to keep his hand on the throttle all the time, except for the brief moment it takes to set the vacuum-operated control incorporated in this machine. This takes the form of a small control panel on which is a three-way cock. With the pointer in the central position the wheel brakes and the rotor brakes are "on." For revving-up the rotor the small control lever is turned to the right. This takes off the rotor brake and lets in the rotor clutch. When the rotor has reached sufficient speed (265 r.p.m. in the present rotor) the pilot turns the small control lever to the left and moves his hand immediately to the throttle lever, which is pushed forward. Owing to the very slight delay in building up the vacuum there is just comfortable time to change from rotor control lever to throttle. The vacuum system automatically declutches the rotor drive, and as soon as the rotor overruns it changes into coarse pitch automatically and the machine jumps. From the handling point of view the new arrangement is obviously a great improvement, and no "third hand" is needed.

Up and Off
   When watching the C.40 jump-start, one forms the impression that the acceleration must be quite unpleasant for the occupants. Actually, as the writer can testify from personal experience, this is not the case. The rate of pitch change in the new hub is such that, although the jump only lasts about two seconds, there is no unpleasant sensation. One feels as if a gigantic hand lifted one rapidly but quite tenderly some ten feet into the air. And the absence of "sink" at the end of the jump gives a feeling of great security.
   In the air the C.40 appears to behave pretty much like the C.30. The rotor seems to be very smooth, and the way it "irons out'' the bumps is quite remarkable.
   The landing is, of course, quite incredible, with no run at all. When the machine is handled by Mr. Brie there is no trace of a jar, although if the machine were allowed to sink on to the ground straight from the approach, it would probably strain things somewhat.
   The results obtained in service with the Army and Navy C.40’s will be awaited with interest.

Flight, September 1939

To-day's Light Aeroplanes

AUTOGIRO

   AT the moment the C40 Autogiro is not available to the public and, as the type is of special interest to the Air Ministry and Admiralty, no figures can be given. The C.40 is the production version of the experimental "jump start" models, and carries two people, side by side, in a semi-enclosed cabin. The machine both leaves the ground and lands without forward run, but, in the air, behaves like and is controlled in the same manner as the older C.30 type, with direct control.
   Makers : The Cierva Autogiro Co., Ltd.. London Air Park, Feltham, Mddx.