Flight, June 1935

STANDARDISED EQUIPMENT
New Monospar S.T.25 - the Jubilee Model - to be Sold Only with Standard Accessories

   WHAT may be described as an attempt by a British aircraft manufacturer to deal in aeroplanes on motor car lines was inaugurated by General Aircraft, Ltd., at Hanworth Air Park, on Wednesday of last week.
   There really seems little reason for treating the purchasers of what are commonly called private aeroplanes any differently from the purchasers of cars. Both want the price cut as low as possible, and this can only be done by standardising the article and its equipment, the degree to which the price can be lowered thereafter resting on the numbers which are produced.
   Cars are turned out in hundreds of thousands, but aeroplanes - that is, a production batch of one type - are still only laid down at the most in a few hundreds. Hitherto, purchasers of aeroplanes have usually been sold a stripped article for which they have had to buy, as extras, many of the essential instruments and fittings, and, naturally, there has been a great deal of grumbling, because they felt that they ought to be given these extras as standard fittings. It was, however, impossible to do this while the purchaser was allowed to have all his own fads and foibles incorporated.
   The new plan of General Aircraft looks like putting this phase of the business on a sounder and more rational footing.
   The S.T.25, or "Jubilee Model," is being built as a standard article, with standard equipment, and the price has been fixed so low that the machine offers excellent value. Presumably, purchasers will be able to have the equipment varied, but in that case they will have to pay what those alterations cost - a far greater sum than any of them will believe possible, but which is undoubtedly justified when one considers the disorganisation of production which such special work involves.
   This standardisation of equipment does not mean that anything has been skimped; in fact, the equipment is in some respects more complete than that normally provided. For example, among the features listed are: cabin engine-starting gear (which we know from personal test to be thoroughly satisfactory); swing-over control wheel with two-level adjustment on each side and full dual controls; navigation, instrument and cabin lighting; Vickers' landing headlamp; Radio Transmission Equipment radio receiving set, with visible homing device; choice of two colour schemes; fire extinguisher; sunblinds; Palmer hydraulic wheel brakes on Palmer wheels with medium-pressure tyres; Smith's turn indicator, and pitch indicator; Husun compass; time-of-trip clock; Air Log; and the usual very full range of instruments.
   On the top of all this, the new Pobjoy "Niagara II" engines are supplied with the makers' full guarantee, which specifies the cost of overhaul and maintenance for a period of 860 hours or two years, whichever is the shorter, in the case of a private owner, or 2,000 hours or two years in the case of a commercial user.
   So much for the equipment, which really speaks for itself. The machine does not differ radically from the S.T.10, except that the cabin has been arranged to accommodate five persons. The fifth seat has been built in behind the divided rear seat in such a manner that the back of it can be folded down, when not in use, to form additional luggage space. This seat is comfortable - even for the writer, who is probably somewhat more bulky than the average; it does not perhaps provide a superabundance of leg room, but it should be adequate for anything except very long journeys. The upholstery, the work of Rumbold's, is pleasing, and the results of the soundproofing are entirely satisfactory. The undercarriage is the fixed Monospar type with a Dowty compression leg. The two alternative colour schemes of black and primrose or red and grey are pleasingly carried out, and the finish is good.
   A short trial in the air showed that the S.T.as handles even better than previous machines. She is beautifully light and the controls are admirably balanced, and, what is equally important, the surfaces are well proportioned, so that side-slipping or turns with ailerons alone are straightforward and can be well controlled. The leading edge of the wings now has sheet metal under the fabric, back to the spar; the smoothness of entry secured by this means has naturally resulted in a cleaner machine aerodynamically and a flatter glide. The angle is, however, steep enough for comfortable approaches without necessitating undue use of the excellent side-slipping qualities. As can be seen from the table of performance figures, the take-off is very good - surprisingly so when one flies the machine for the first time - and the air speed indicator, at any rate, fully substantiated the cruising speed.
   The new Radio Transmission Equipment (or R.T.E., as it is more commonly called) receiver and homing device is most interesting. At the present time the production model is not quite ready, but a short trial of the preliminary installation clearly proved - we have been convinced for a long time that some form of homing device would sooner or later have to be used for all serious flying, even by private owners - that a simple apparatus like this can be of the greatest value navigationally. It really has three functions: the reception of weather broadcasts, assistance directionally, and entertainment; and we imagine that now the ice has been broken, so to speak, it will soon become standard on most machines.

Using the Homing Device

   There would seem to be little doubt that inexperienced pilots will only get the best out of the apparatus directionally after they have had a reasonable amount of instruction in its use and a fair amount of experience, but this could be arranged as part of the service provided, just as some agents are giving flying instruction to those who purchase aeroplanes, but with the difference that even the inexperienced man will get fair results out of the homing device, and very short instruction will enable him to get the best out of it.
   On the occasion of the first presentation to the public of the S.T.25 at the company's works at Han worth, Mrs. Shelmerdine (Lt.-Col. Shelmerdine, the Director-General of Civil Aviation, was unfortunately unable to be present as well) performed what may be termed the unveiling ceremony, and Sir Maurice Bonham-Carter, chairman of the company, made her a presentation in commemoration of the occasion.

Flight, April 1936

FIVE MONOSPARS
Specialised Standard Equipment on the Latest Versions of the S.T.25: Trimming Tabs for New Models: The De Luxe Monospar in the Air

   ON more than one occasion it has been said that when aeroplanes are sold complete in every necessary detail then flying can be considered to have become a properly recognised means of transport. Last year the General Aircraft Company introduced a five-seater, twin-engined Monospar, which, in its standard form, carried full night-flying equipment, including a landing head light in the nose, blind-flying instruments, and a radio homing and receiving set, in addition to a number of other refinements which have been part of the equipment of cars for a decade.
   This year the scheme has been carried a stage farther. The Jubilee model, as it was known, has become, so to speak, a foundation on which five new types have been erected. Based on the very same standard equipment, the new models have additional equipment specially suited to the needs of operators as well as of private owners. The corner-stone is the Standard, with the De Luxe model for the more particular private owner, and the Transport for the small air line or taxi operator, while the Freighter and Ambulance are similar, respectively, to the De Luxe and Transport models, save that the internal fittings have been designed specifically for the duties which the names indicate.
   Needless to say, the private owner who holds a radio licence, or who has his own professional pilot, may prefer the Transport model if he is to use his machine for very serious touring. This machine has, in place of the normal homing equipment, an R.T.E. receiver and transmitter as well as a Sperry artificial horizon and directional gyro panel, special instrument lighting, and, of course, slightly modified cabin equipment.
   Generally speaking, however, the De Luxe model may be taken as representing the 1936 type of S.T.25. To the casual observer three new features are immediately noticeable. A tab on the elevators is used for longitudinal trim in place of the adjustable tail plane; directional trimming is now possible since an adjustable tab is fitted also to the rudder; and directional stability has been attended to by the use of increased fin area. The engines are Pobjoy Niagara IIIs, with Rotax electric starters. However simple the "pull" cabin starter gear of the previous model may have appeared to the normally brawny owner, button starting will certainly be an improvement thereon.
   Inside the cabin, too, the changes are marked. A completely redesigned dashboard carries the latest version of the R.T.E. homing receiver, and there is a special switchbox immediately in front of the pilot for the electrical controls, including the starter buttons, and for the rudder bias lever. With the elevator tab now fitted, the trimming control consists of a very small and conveniently placed lever, on the port side of the cabin, moving through 180 degrees. The landing headlamp switch and its angle adjustment control are mounted beside this trimming lever and in their usual place. Apart from the normal flight instruments, which include a Smith turn and bank indicator and the homing indicator, the equipment, as before, includes Ki-gas engine priming installation, an Essex fire extinguisher and a dial-type fuel gauge which is mounted between the front seats. The screen is now in three pieces with a safety-glass centre panel, and special attention has been paid by Rumbolds to the upholstery and to the soundproofing arrangements.
   The dashboard position for the R.T.E. homing receiver brings it within easier reach of the pilot, who is now a to read the tuning dial with accuracy and, consequently, to make greater use of the equipment when flying alone or with passengers who do not understand its operation.
   Although the majority of broadcasting stations in this country are situated at distances of ten to thirty miles from the nearest aerodrome, the examination of a ten-mile aviation map suggests that quite good use could be made of them on the majority of long flights, and during the summer months the weather broadcasts from Borough Hill, Daventry (on 1,181 m.), will be virtually continuous throughout the day and part of the night. The importance of up-to-date knowledge of developing weather conditions cannot be overestimated.
   On the Continent there are, according to a list worked out by the Automobile Association, no fewer than forty stations which are less than ten miles from an aerodrome, and, of these, seventeen are three miles or less from the appropriate landing ground. For Continental work, therefore, the homing equipment can form much more than a mere check on the direction of one's peregrinations.
   In practice it is probably easier to use the indicator, the earphones and the compass together during a long period of homing. A short test between Hanworth and the Brookmans Park transmitter showed that no difficulty was experienced either in holding a course both towards and away from the station or in stopping a steepish turn accurately on the correct course. The air was a trifle bumpy even at 2,500 ft., and it was impossible to keep the needle absolutely steady, yet the machine returned to Hanworth on "back bearings" quite accurately when allowance was made for the natural drift on a course which was slightly off-wind.
   So far as the flying qualities of the new model are concerned there is little change, though the effect of the increased fin area would probably be noticeable in really bad weather. When flying light, at least, the De Luxe S.T.25 can be trimmed to fly both hands and feet off so far as the directional and fore and aft axes are concerned. With the tab balances on the ailerons these are so light that lateral corrections are made quite effortlessly and the lack of inherent stability in this axis is no hardship.
   The new tab trimmers, however, are a considerable boon, from the pilot's point of view. Never a very arduous business with the standard trimming wheel, fore and aft adjustments are now carried out with the little lever which moves only through a half-circle with a radius of perhaps three inches. Another small lever, also within easy reach, operates the rudder tab, and this can be set to take all the load off a rudder control which, in any case, is very light. This directional bias will not take all the effects of a dead engine, but it reduces the amount of necessary rudder pressure to a minimum. Turns, incidentally, can be made against a throttled motor quite easily.
   As a flying machine the S.T.25 is decidedly interesting, since all the controls are light and very effective. The human animal's pedal extremities being the least controllable, it is as well, perhaps, that the rudder is the softest. This, however, is powerful enough to hold the nose properly up in a sideslip. The controls, in fact, are sufficiently exciting to tempt the enterprising owner to fly in a manner which might not please his less youthful passengers. Tight turns, for instance, are so effortless and natural in their development that they tend to become a stock-in-trade manoeuvre.
   The majority of machines have to be known to be understood - the Monospar, perhaps, more than some, though the characteristics of the low-wing monoplane are becoming sufficiently well known to require no comment. With little previous experience of the machine, only two of some half-dozen approaches made into Hanworth required more than a shade of engine or slipping adjustment, yet this aerodrome is by no means large, and the buildings on the perimeter are always liable to cause one to misjudge an approach even with a familiar aeroplane.
   The S.T.25 is gliding under full control at 60 m.p.h., and at this speed height can be lost quite usefully so long as the nose is put down a little in order to have a reserve of momentum for the hold-off. A normal approach is best made at 70 m.p.h., since at higher speeds the actual approach angle is much flatter. Deceleration is fairly rapid at lower speeds, so that, if care is exercised during the last phase of the approach, the amount of aerodrome used is disproportionately smaller than one would expect.
   Of six landings by one who had never previously made any on this machine, the first had to be washed out, the second was bad, the third was good but shaky, and the final three were firm and clean. Obviously, therefore, there is nothing really difficult about the S.T.25 from that point of view. The newcomer might be misled by the efficiency of the elevator control at low air speeds and be surprised into making a series of paraboloid motions. Once the machine is held off, in fact, no progressive backward movement of the control is necessary as the speed drops.
   While on the subject of landings it is worth remembering that, once the S.T.25 is firmly down, it is safe to apply the Palmer brakes with full force. This was done more than once during the trial, and the pull-up on dry turf is extraordinarily smooth and rapid. A pressure gauge on the dash gives the pilot an indication of the braking power in use and is particularly valuable while taxying.
   With the throttles back the machine stalls at a little more than 50 m.p.h (indicated), and one wing usually drops quite gently at the final moment of full stall. Control remains until the last and is recovered quickly enough to prevent the wing from falling too far, since the nose drops and the speed rises again immediately. On full throttle it is possible to hold the machine up at speeds as low as 45 m.p h. without loss of height, and in this case, of course, the rudder becomes the dominant controlling factor.

MONOSPAR S.T.25 DE LUXE.
Two Pobjoy Niagara III 90/95 h.p. Engines.

   Tare weight with all equipment 1,758 lb.
   Disposable load 1,117 lb.
   Span (folded) 14ft. 10in.
   Length 26ft. 4in.
   Height 7ft. 10in.
   Cruising speed at 3,200 r.p.m. (77% power) 123 m.p.h.
   Duration at this speed 3.81 hr.
   Rate of climb at sea level 700 ft./min.
   Service ceiling 12,000 ft.
   Take-off in still air 195 yds.
   Landing run with partial braking 120 yds.
   Landing speed 54 m.p.h.

Prices (with full equipment)

   Standard model ?1,750
   De Luxe ?1 985
   Ambulance ?2,550
   Freighter ?1,700
   Transport ?2,250

Flight, April 1936

MODERN LIGHT AIRCRAFT REVIEWED

MONOSPAR

   LAST year's S.T.25 was produced in its standard form with full day- and night-flying equipment well as a radio homing and receiving set. This year the same principle has been expanded to provide five separate types for different purposes, in each of which the equipment has been standardised to suit these five purposes.
   The new De Luxe model may be taken as typical of the range, since it incorporates most of the features which are found on the 1936 machines, such as trimming tabs, electric engine starters and a redesigned dashboard layout in which the R.T.E. homing receiver is within easy reach of the pilot, and all the electrical switchgear is mounted on a single panel or box. Structurally, the S.T. 25 remains unaltered, and it will be remembered that this is all metal and involves the well-known Monospar system of construction, by which the structure weight can be kept down to a minimum.
   The trimming tabs on the elevator and rudder are operated by small and convenient levers which require no effort, and the whole business of flying the new Monospar is reduced to one of mere flying judgment. Its characteristics are interesting and soon mastered, and the pilot, in particular, has a very excellent, and consequently safe, field of view. In common with most low-wing machines, it is possible to adjust the approach by increasing or decreasing the gliding speed, and really short approaches can be made by a pilot who is thoroughly accustomed to the machine. Once it is firmly on the ground the Palmer brakes can be applied to their fullest extent without risk of nosing over, and full control is retained right down to the stall, which is harmless enough if the rudder is not maltreated.
   In Europe, paricularly, the radio homing equipment would be very useful and, even if this cannot be used in this country on every flight, there is always the regular and valuable Air Ministry meteorological broadcast from Borough Hill to be received. The electrical equipment of the Monospar, incidentally, includes landing and navigation lights, instrument and cabin lighting, as well as electric starters on certain models, as already mentioned.
   The General Aircraft Company have specialised in the production of carefully worked-out running-cost schedules for the benefit of air-line operators and others who are interested in the Monospar as a dividend-earning machine. A series of these have been published in booklet form. Incidentally, the company has evolved an economical hire scheme which includes the services of a "B" licence pilot.
   The specification of the De Luxe Monospar is as follows: Weight empty, 1,758 lb.; disposable load, 1,117 lb.; span folded, 14ft. 10in.; length, 26ft. 4in.; cruising speed at 3,200 r.p.m., 123 m.p.h.; duration at cruising speed, 3.81 hr.; initial rate of climb, 700 ft./min.; price, ?1,085. Makers: General Aircraft, Ltd., London Air Park, Feltham, Mddx.

Flight, June 1936

MONOSPAR MODIFICATIONS
Twin Rudders and Increased Dihedral for All ST.25 Machines: Improved Stability in All Axes

   FOR some time it has been known that General Aircraft were experimenting with a new form of tail for the S.T.25, and the machine in its latest form made its first public appearance at the R.Ae.S. Garden Party a little less than a month ago. To the ordinary ground spectator it was obvious only that the appearance had been considerably improved by a "strengthening” of the rear of the machine and that turns against a throttled engine could be carried out with greater ease.
   In addition to the use of twin fins and rudders and of an elevator which is a complete unit, S.T.25S will, in future, have an increased dihedral. Lightly loaded, the Monospar has always been easy to fly even in very bad weather, and the modifications have been carried out largely with the idea of improving the stability in all axes when the machine is flying with an absolutely full load in the "blind" and bumpy conditions which are so often experienced in modern all-weather flying.

Single-engine Flying

   The improvement is noticeable immediately the engines are opened out for the take-off. Full rudder control is available as soon as the tail has lifted, and any tendency to swing can be checked at once and without the necessity of big movements - which always tend to be persisted in after they are necessary. On the day of our trial there was a fairly high wind blowing, and the air was so very rough at lower levels that it was impossible for the newcomer to obtain any real idea of the improvements, though violent directional movements were effortlessly checked.
   Once out of the very disturbed layer, however, it was possible to fly the machine quite accurately on the rudder alone, and, when correctly trimmed by means of the easily operated elevator tab, there was no further need for attention, and all minor movements were self-corrected. For some good reason that is not immediately apparent, accurate steep turns required less conscious attention, and the machine was even more noticeably stable in the glide, both when flying straight and in turns. However, unless one, so to speak, has a chance of flying the new type immediately after the old, it is impossible to speak of anything more concrete than impressions.
   It is a fact, however, that turns can now be made against a throttled engine with the greatest of ease, and both the amount of rudder movement and the pressure required are surprisingly small. When flying straight on one engine, no conscious aileron correction is necessary. In production models the elevator will be heavier, so that the landing movement will require less delicate attention, and the trimming lever will be a trifle less sensitive in action.
   The use of twin rudders in a bi-motor machine has a number of useful aerodynamic effects, apart from the more obvious ones resulting from the fact that the rudders are directly in the slipstreams. It may be remembered that the original Lockheed Electra had a single rudder, and experiments with twin rudders produced some interesting results.
   Structurally, the changes in the new Monospar are comparatively small. Additional steadying struts have been introduced between the leading edge and the primary structure. The original finpost has been cut short above, and the ends of the tailplane are now stayed back to the tailplane spar.

Flight, March 1938

British light aircraft

MONOSPAR

   WHAT was previously known as the Monospar S.T.25 has, in slightly different forms, been on the market for a number of years. More recently this all-metal twin-engined machine has been available in three distinct versions, but for 1938 a single model, known as tire Universal, is being sold. This is normally a four-seater light transport, or luxury private-owner machine, but it may quickly be converted for either freight-carrying or ambulance use.
   From the point of view of the prospective owner who has previously done all his flying on single-engined machines, it may be said that the Monospar, particularly since it has had twin rudders, does not feel at all like a twin-engined machine. There is no need for careful throttle manipulation, for instance, dur­ing the take-off since the rudders are fully operative from the moment of opening up. In its standard form the Monospar is fitted with night-flying equipment which includes a headlight, and the machine was, in fact, probably the first British medium-sized machine to be sold in completely equipped form. Furthermore, the work of bonding and screening for radio involves the purchaser in no additional expense.
   The credit for much of the Monospar's extremely good performance must be given to the Pobjoy Niagara engines with which it is fitted. The high power­weight ratio of these engines has certainly given the designers plenty of opportunity.
   More recently, the company has been experimenting with a tricycle under­carriage adaptation for this machine, and it is to be supposed that this modification might possibly lie applied to the Universal in due course, though the experiments were made primarily to obtain data for the application of the principle to very much larger craft.
   SPECIFICATION: Span folded, 14ft 11in.; length, 25ft. 4in.; all-up weight, 2,875 lb.; weight empty, 1,805 lb.; maximum speed, 131 m.p.h.; cruising speed, 115 m.p.h.; landing speed, 50 m.p.h.; initial rate of climb, 710 ft. / min.; range 420 miles; price, £2.250. Makers: General Aircraft. Ltd.. London Air Park, Feltham, Middlesex.

Flight, October 1938

British Commercial Aircraft

GENERAL AIRCRAFT
  
   DESIGNED to meet the requirements of the charter operator, private owner or those air line companies which are experimenting with the traffic potentialities of new routes, the Monospar S.T.25 has been very little changed during the past few years. The type is now known as the Universal, and the cabin is specially designed for conversion for different purposes.
   The machine can be used either as a normal passenger-carrying craft for feeder work or for ambulance purposes and freight carrying, the necessary modifications being made in a comparatively short space of time. The type is probably best known in its ambulance form, and the special all-white demonstrator has been seen about in this country and in Europe a great deal. With the object of facilitating this work or, in the case of the freighter, for loading and un­loading bulky objects, the cabin has special large-aperture door on the starboard side, in addition to the standard folding roof and the door on the port side.
   The Universal is an all-metal fabric-covered low-wing monoplane with twin fins and rudders. It is powered with two Pobjoy Niagara III engines and carries, in passenger layout, four or, in special cases, five people. As in earlier years the Universal and its forerunners are notable specially for the Monospar type of wing construction in which pyramid bracing is used to take drag loads. The wings are arranged to fold outboard of the two engines. The fuselage is built in two sections, that in the front consisting of a shallow tray of steel tube, while that at the rear is built around a duralumin beam on Monospar principles. Dual rudders are arranged with a swing-over control column and the equipment in the standard machine includes navigation lights, a landing light, and the usual blind-flying instruments.
   Monospar Universal Data.- Span, 40ft. 2in.; length, 25ft. 4in.; all-up weight, 2,875 lb.; weight empty, 1,818 lb.; wing-loading, 13.21 Ib./sq. ft.; power loading, 17.08 lb./h.p.; maximum speed, 131 m.p.h.; cruising speed on 70 per cent power, 115 m.p.h.; stalling speed, 60 m.p.h.; rate of climb, 710 ft./min.; service ceiling, 13,000ft.; range at cruising speed, 420 miles; and price, £2,250.