Flight, September 1921

THE D.H.32 COMMERCIAL BIPLANE
360 H.P. Rolls-Royce Engine

   CONSTRUCTION is just about to be commenced at the Stag Lane Works of the De Havilland Aircraft Co., Ltd., on a new machine designed for commercial work. As may be gathered from an inspection of the accompanying general arrangement drawings, the D.H.32 is a biplane following somewhat on the lines of the famous 18 which has now been in use for some three years on the London-Paris lines, where it has given excellent results. This machine was described in FLIGHT of March 24, 1921, to which issue we would refer readers wishing to trace the differences and similarities of it and of the new 32 biplane.
   In spite of the excellent service given by the D.H.18, there are bound to be certain matters in which improvements can be effected. Three years of hard service will find weak spots (we do not mean this to be applied literally to the structure) in any machine, and bring to light features which could be improved upon, or simplified. This is actually what has happened in the case of the 32, with the result that the new machine will be very much cheaper in first cost with a consequent reduction in insurance, maintenance, and depreciation charges.
   The engine to be fitted in the new machine will be a Rolls-Royce "Eagle" (Commercial) of 360 h.p., so that the fuel consumption should also be smaller than that of the D.H.18. We are not at present in a position to quote the price at which the 32 will be sold, but it will be a very material reduction on that of the 18. At the same time, performance will not be allowed to suffer to the extent of lessening the suitability of the machine for use on the "Airways."
   In general construction the D.H. 32 will follow more or less usual de Havilland practice. That is to say, the fuselage will be covered with ply-wood so as to avoid cross bracing, which requires attention and interferes with cabin arrangements. Also the plywood covered body has considerable flotational capacity in case of a forced descent in the sea.
   The cabin will be spacious in proportion to the size of the machine. Its length will be 12 ft., and the height and width 7 ft. and 4 ft. respectively. There will thus be ample headroom, while the fuselage construction is such as to leave no unsightly projections anywhere in the cabin. The seats will be arranged in two parallel rows along the sides, with a passage between them. The entrance door will be on the starboard side near the aft end, and in front there will be a door communicating with the pilot's cockpit so that the navigator, wireless operator or engineer - whichever is carried in the seat next to the pilot's - can, if desired, come down into the cabin and give passengers any information that might be required, such as the decision to land at some aerodrome other than that intended, owing to weather conditions, etc. Aft of the cabin there will be a lavatory, while still farther aft a separate luggage compartment will carry some 200 lbs. of luggage. This compartment will have a separate door, so that it will not be necessary to pass the luggage through the cabin.
   Large windows in both sides will give the passengers a good view, and the question of heating and ventilation has received careful attention. It is probable that the system will take the form of pressure, feed air pipes running the whole length of the cabin at floor level. These pipes will have small holes in them through which the air is diffused into the cabin, while the foul air will be sucked out by special ventilators in the roof. It is well known that air sickness is mainly caused by bad lighting and ventilation, and in this respect the new D.H.32 should go a long way towards avoiding this the only unpleasant feature of air travel in rough weather.
   As in all de Havilland commercial machines, there will be emergency exits in the roof. The exact form which these will take is still a matter for experiment. It is possible, however, that they will be in the form of light frames, covered with thin white fabric. Such a window would admit sufficient light, and at the same time would not be in danger of being broken or cracked. If doped on to the roof by a narrow strip it would be easily detached in emergency.
   As regards the equipment of the cabin itself, the seats will be of the light wicker work type, well upholstered, and a thick carpet will cover the floor. This carpet will be in three separate units so as to be easily removed for cleaning purposes. Should it be desired to carry cargo in place of passengers, the seats can be readily removed, when the cargo space available is 288 cubic ft. The load that can be carried will be just over 1,500 lbs. as a cargo machine, or eight passengers in the cabin and, if desired, an extra passenger next to the pilot. If we take the passenger capacity as eight only, the number for which there is accommodation in the cabin, and assume a maximum power of the engine of 360 h.p., the power expended per passenger is 45 h.p., which, it will be seen, is a very good commercial proposition. Moreover, once flying at the desired level, the engine will be throttled down to about three-quarter power, when the cruising speed is estimated to be 98 m.p.h. The power per passenger is then less than 34 h.p., which would give very good economy in running. At the same time, over most routes a cruising speed of nearly 100 m.p.h. should be ample, especially as the maximum speed will be about 110 m.p.h.
   As in the D.H.18, the engine will be mounted as a complete unit with its radiator, water and oil tanks. To remove it from the machine all that is necessary is to undo four bolts at the corners of the fuselage, disconnect the engine controls and petrol leads, and the whole engine unit can be removed for adjustments or repairs. One imagines that in actual use a good plan would be to have a complete spare engine unit which could be substituted in a very short time, thus preventing loss of earning capacity through being laid up for engine repairs.
   The radiator will be of the "saddle" type, fitted in the nose of the machine. The oil tank will be fitted inside the engine housing and removable with it. The placing of the petrol tanks is interesting. There will be two streamline tanks placed immediately under the top plane, some little distance out from the body. By this arrangement the risk of fire in a crash is thought to be greatly reduced, while the petrol system is very simple. A fireproof bulkhead will be fitted aft of the engine. Blaisdell "Petro Flex" will be used where sharp bends or relative motion occur, so that there should be no possibility of a fractured petrol pipe.
   The wings will be of the biplane form, with two pairs of inter-plane struts on each side. They will attach direct to the fuselage corners, as the latter is of sufficient depth to give the required gap. The pilot will be seated just in front of the leading edge of the top plane, where his view should be exceptionally good, a feature which is not always given the attention it demands in machines intended for commercial use.
   In view of the success which the D.H.18 undercarriage has had, it is not surprising to learn that a very similar, although in certain respects improved, undercarriage will be fitted on the 32. The feature of this type is the very long travel, giving good shock-absorbing qualities, and the absence of "bouncing" attained by the use of oleo damping gear. The undercarriage will be so proportioned that when the tail skid is on the ground the planes are at a large angle of incidence. The result is that the machine pulls up very quickly. This is a feature which has been amply tested out on the 18's. Another desirable feature of this undercarriage is the ease with which it can be removed by undoing four bolts.
   The question of control has received very careful attention. Ball-bearing controls will be fitted throughout, as this has been found in the D.H. 29 monoplane to give exceptional ease, and thus relieves the pilot of hard work, which is of great importance in flights of long duration. Another feature which will be incorporated after trial in the monoplane is a new method of balancing the ailerons. A form of differential movement is obtained so that the upward movement of one aileron is greater than the downward movement of the opposite one. In this way not only are the ailerons very easy to work, but, what is perhaps of even greater importance, when near the stalling angle the ailerons do not have the same tendency to precipitate a spin as is the case when the lower aileron is pulled down to a large angle.
   The following will be the main characteristics of the new D.H.32 biplane :- Engine 360 h.p. Rolls-Royce "Eagle" (Commercial). Span about 50 ft. Chord, 6 ft. 6 ins. Area, 618 sq. ft. Overall length, 39 ft. Overall height, 12 ft. Capacity, 8 passengers, or 1,536 lbs. of freight in a space of 288 cubic ft. Weight empty, but with water, 3,412 lbs. Crew, 180 lbs. Useful load, 1,536 lbs. Petrol (68 gallons), 490 lbs. Oil, 60 lbs. Lavatory, etc., 60 lbs. Total weight, fully loaded, 5,738 lbs. Speed at ground level, 110 m.p.h Cruising speed, 98 m.p.h. Speed all out at 5,000 ft., 107 m.p.h. Climb to 10,000 ft. in 27 1/2 mins. Ceiling, 14,000 ft. Range, 4 hours at cruising speed of 98 m.p.h.

Flight, January 1922

THE D.H. TYPE 34 COMMERCIAL BIPLANE
Napier "Lion" Engine

   As will be seen from the accompanying general arrangement drawings, the D.H.34 is a good deal like the famous D.H.18 in its general lines. It has, however, been improved in several respects, as a result of the extensive experience gained with the 18's, and will represent a real step forward in the development of the truly commercial aeroplane.
   Apart from improvements in aerodynamic design, the D.H.34 incorporates constructional simplification which makes for cheapness of manufacture. Its performance is also better than that of the 18, while the useful load is greater. The quick get-off and rapid pulling up after landing which characterise the 18 have been retained in the new type, so that altogether the machine has much to recommend it for commercial flying in the true sense of the word.
   In the construction of the fuselage considerable simplification has been effected. This structure is now entirely covered with three-ply, so that there will be no trueing-up to attend to during use. Also, in case of a forced descent on the sea, this form of construction gives great flotation, as the cabin doors will be provided with means for watertight closing. The cabin occupies a large amount of the fuselage space, the main cabin being 12 ft. long by 4 ft. wide, by 7 ft. high. It is thus possible for the passengers to stand upright, and as there are numerous windows in the sides as well as roof lights, the cabin should be both light and airy, especially as ventilators are provided by means of which the used air is constantly sucked out through the roof, fresh air - either cold or hot as required - entering through pipes near the floor. Eight seats are arranged in the main cabin, a ninth being placed opposite the lavatory, and if desired the seat next to the pilot can be occupied by a passenger, thus bringing the total capacity up to 10. This gives a power expenditure of 45 h.p. per passenger carried, which is very good, especially as the cruising speed is 105 m.p.h. The pilot's cockpit is in front of the wings, thus giving an excellent view.
   The engine installation is similar to that of the 18 already described in this journal. By undoing four bolts and the petrol and engine connections the whole engine unit can be removed. An underslung radiator is fitted which can be removed without disturbing the propeller. The petrol tanks are placed some distance out, under the top plane, and there are two independent low-pressure systems to a common filter and junction box. A fireproof bulkhead separates the engine from the rest of the machine. Danger from fire is further guarded against by the use of Blaisdell "Petro-Flex" at all points where relative movement occurs, and all rubber joints will be avoided.
   In other respects, such as wings, tail, undercarriage, etc., the 34 is similar to the 18. The control system incorporates the differential aileron movement first experimented with in the type 29 cantilever monoplane. This has been found to give very good results. Ball-bearing controls are fitted throughout, and all cables passing over pulleys or through guides have been avoided. It is thought that this is a feature which will be appreciated by those responsible for running the machines, as control cables are a constant source of trouble.
   The undercarriage is similar to that which has proved so successful on the 18's, its main feature being long shock absorber extension (12 ins.) and oleo damping gear. The whole undercarriage can be removed from the machine by undoing four bolts.
   The main characteristics of the D.H.34 are as follows: Length o.a., 39 ft.; span, 51 ft.; height, 12 ft.; wing area, about 590 sq. ft.; weight of machine empty, but with water, 3,365 lbs.; pilot, 180 lbs.; useful load, 10 passengers with luggage, or about 2,000 lbs. of freight; 80 gals, of petrol, 575 lbs.; oil, 78 lbs.; wireless and electric lighting, 120 lbs.; total loaded weight, 6,218 lbs. approximately; wing loading, 10-5 lbs./sq.ft.; power loading, 13-8 lbs./h.p.; cruising speed, 105 m.p.h.; duration, 3 1/2 hours at cruising speed.
   Economical as was the D.H. 18, the 34 promises to be considerably more so, and the figure for ton-miles per gallon should work out very well as compared with other rapid means of transport, especially when it is remembered that this machine does its travel at the rate of over 100 m.p.h., while older means rarely average half of that speed. As there is a considerable reserve of power which can be used in case of head winds, etc., the machine should be able to maintain its average of 100 m.p.h. with good regularity, even under unfavourable conditions. Later on, when construction has progressed a little further, we hope to be able to publish sketches of some constructional details.

Flight, March 1922

THE D.H. TYPE 34 COMMERCIAL BIPLANE
First Machines Ready

   IN our issue of January 5, 1922, we published general arrangement drawings and a brief preliminary description of the D.H.34 biplane, Napier "Lion" engine, then in course of construction at the Stag Lane Works, Edgware, of the de Havilland Aircraft Co., and promised to give further particulars and illustrations when the machines were completed. This week we are able to fulfil our promise, and some of the more interesting and novel details of the 34 are illustrated in the accompanying sketches. For the use of the photographs we are indebted to the Daimler Airway, for whom the first of the machines to be finished are intended. Quite a number of 34's are coming through the works, and on our visit last week we inspected several in the new buildings recently erected at Stag Lane. Some of these machines are painted all over in "pillar-box" red, this being the colour chosen by Daimler Airway for their machines. Others are painted the particular blue which one associates with the Instone Air Line, and it was learned that these were, as a matter of fact, being built for that firm. With such up-to-date flying stock, the air lines should do good business during the coming season, and already there are indications of considerable competition, which, we are always being told, is good for trade.
   The D.H.34 resembles, as regards outward appearances, the famous "18's," which have done such good work on the London-Paris services for a couple of years now, and we understand that, as a matter of fact, it has been the aim of the designers to retain the aerodynamical features of the 18, which were found excellent, while at the same time introducing such improvements in construction and fitting-out as have been shown in practice to be desirable, or which have been asked for by the operational firms who are to use the machines. There is every appearance in these machines of the closest co-operation between constructor and user, and the result cannot fail to be a considerable improvement. In the past the constructor has been handicapped by not knowing exactly what the user wants, while the user, on the other hand, has found fault with certain features of machines, which were due to the lack of realisation of his requirements on the part of the constructor. It is quite evident that only by close co-operation can we hope to attain success, and, as already stated, the D.H.34 bears traces of such co-operation. This is highly gratifying, and is decidedly a step in the right direction.
   While thus retaining the good aerodynamical features of the 18, the D.H.34 is in reality, quite different as regards its construction and also, to a certain extent, in the manner in which component weights are disposed. The most notable departure in this respect is the placing of the pilot in front of the wings, instead of far aft in the fuselage, behind the cabin, as he was in the 18. There are, we believe, several reasons for this innovation. To begin with, the cabin is considerably larger than that of the 18, and even if shifted forward it would have brought the pilot very far back. Also, the forward position of the pilot will probably result in a better view, although this is, perhaps, open to discussion. In the 34 the pilot has an excellent view on one side, but the engine certainly appears to restrict the view forward, and to the other side. However, most pilots would probably prefer the forward placing of the seat, although after being used to the 18's, the change must appear somewhat bewildering at first. One advantage of the present arrangement is that the cabin is well separated from the engine, not only by two bulkheads but also by the space occupied by the pilot's cockpit. As very long exhaust pipes are fitted, there should be comparatively little noise in the cabin, and we understand that, as a matter of fact, it is quite easy to converse during the journey.
   As regards construction, the 34 differs from the 18 mainly in the manner of building up the fuselage, the whole of which in the 34 is built up of triangulated struts, the framework being covered throughout with three-ply wood. This form of construction has been found in practice to stand up well to wear and tear, and to require little or no attention beyond the usual cleaning of the cabin. With a wire braced structure there is always the possibility of wires stretching and necessitating trueing-up. In the construction of the wings there is less change, the general design of spars, ribs, and fittings being similar to that of the 18 wings, although the dimensions are somewhat different, the wing section not being the same as that of the 18.
   The undercarriage is similar to that of the 18, or rather to its later version as exemplified in the 29 monoplane. It consists of two simple Vees, of which the front legs are rigid while the rear are telescopic and provided with rubber shock absorbers and oleo damping gear. A feature of this undercarriage is its great resiliency, and its height which brings the machine down at a large angle of incedence when the tail skid is on the ground, thus enabling it (the machine, not the ground) to be pulled up very quickly on landing. While on the subject of undercarriages, it might be mentioned that the very substantial tail skid, the details of which are shown in some of our sketches, is provided with an easily renewable cast-iron shoe, so that replacements can be easily and quickly carried out. At the same time, a cast-iron shoe is cheap to manufacture, and its frequent renewal is not a large item in the expense sheet.
   As in the 18, and 29 monoplane, the Napier "Lion" engine is mounted as a separate unit, attached to the main fuselage structure by four bolts, and separated from the pilot's cockpit by a fireproof bulkhead. The underslung radiator is cowled-in, but swivelling slats in the front of the cowling allow of varying the amount of air admitted, the air escaping through an opening under the bottom of the fuselage. One advantage of this placing of the radiator, quite apart from any question of cooling, is that it can be removed without interfering with the propeller, whereas a nose radiator usually necessitates taking the propeller off in order to remove the radiator.
   The general appearance of the D.H.34 is well shown in the accompanying photographs. One of these shows the cabin, which has seating accommodation for nine passengers. The seats are of the wicker-work type, having their legs resting in sockets in the floor, and being secured by leather straps, which prevent the legs from coming out of the sockets. At the same time, all the chairs can be easily removed, should it be desired to use the machine for goods or other cargo. As a result of practical experience, it has been found that it is often desirable to be able to transport a spare engine from Paris to London, or vice versa, and consequently provision has been made for allowing this to be done. The cabin door, which is on the starboard side, is of a peculiar shape, and just allows of passing a Napier "Lion" through. Owing to the insufficient width of the cabin it is not, however, possible to turn the engine unless the two rear cylinders are removed first. In order to avoid the necessity for doing this, a circular opening has been cut in the port side of the cabin wall, through which the propeller boss and a small portion of the forward part of the crankcase can pass, thus allowing of swinging the engine round.
   The cabin itself is very roomy, there being about 7 ft. head room in the centre. Provision has been made for heating and ventilation. The former is effected by hot air from a muff around the exhaust pipe on the starboard side, led to perforated boards under the floor, via a diffuser box having a movable flap by means of which the amount of air can be regulated by the passengers themselves. Cold air is passed to this box from a trumpet projecting through the roof of the cabin just aft of the pilot's cockpit, and the regulator is so connected up that at the same time as the hot air is admitted the cold air is cut off, or vice versa. In this manner it is hoped that an agreeable temperature may always be maintained without giving a draught. The foul air is sucked out of the cabin by louvres in the roof.
   In addition to the question of ventilation and heating, the problem of lighting has also received attention. The windows in the side give a fair amount of light, but in order to get the cabin as light as possible, additional fabric-covered, roof lights are provided. Some of these also serve as emergency exits. For night flying the machine is thoroughly equipped, not only as regards lighting the cabin itself, but also with the necessary navigation lights, Holt flares under the wings, etc. The power for the lighting is obtained from a dynamo driven by the engine, a special gear-box having been provided, with a short shaft running through the engine bulkhead to the dynamo placed on a shelf to the right of the pilot. The current for the wireless outfit is obtained from a wind-mill driven generator, mounted on a shelf on the port side of the machine.
   As regards instruments, etc., the 34 is very well equipped, and in fact it probably carries a more complete set than any machine at present in use. The pilot has a good deal to look after, and there is little fear of him getting bored on a trip, what with flying the machine, keeping his course, watching a number of dials, etc. In his cock-pit there is a seat for an engineer, navigator, or any passenger who prefers to travel “outside." Probably for the London-Paris service it will not be necessary to carry a navigator, and presumably the spare seat in this cockpit will usually be occupied by a passenger.
   A great deal of attention has been given to such items as affect the running of the machine in actual service. For instance, the doors in the engine housing have been so designed that they hinge so as to project horizontally, being supported when in this position by cables. They thus form platforms on which mechanics can stand while making adjustments to the engine. The value of this in the case of a forced landing will be apparent. Normally, without these platforms, it would be a matter of the greatest difficulty for the pilot or engineer to reach, for example, the sparking plugs, assuming that the machine had been forced down by sooted plugs. With the platforms it is an easy matter to get at any part of the engine, even when no steps or other appliances external to the machine are available.
   The Napier "Lion" is started by means of a starting handle on the port side, and a platform, which folds flat against the side of the fuselage when not in use, is provided for the engineer to stand on. Thus the antiquated method of swinging the propeller is to be done away with entirely. It is features such as these, which may seem but small items in themselves, which make for smooth working, and we think that this is really the first time we have seen such subjects seriously considered. In the past there has been too much tendency to let the mechanics scramble about on machines as best they might, providing, in the best of cases, a step on a strut or a foot plate on a wing. We therefore, welcome these improvements as a sign of that co-operation between constructor and user to which we have already referred.
   The petrol system comprises two tanks, mounted some distance out, under the top plane. Their height is not sufficient to give direct gravity feed, but a low-pressure pump, delivering petrol through Blaisdell "Petro-Flex," should not be a source of any trouble, even if one might have preferred to see direct gravity feed incorporated. On the front of each petrol tank is a level gauge, which can be easily read from the pilot's seat.
   The controls are of the usual type, except that several features from the D.H. monoplane have been incorporated. Thus all controls and control surfaces work in ball bearings, and the use of cables is reduced to a minimum. Wherever cables have to be guided, a short length of metal rod is incorporated, passing through a guide of large area, so that there should be no question of cables wearing out. The system of differential movement of ailerons, first tested in the monoplane, has been incorporated in the 34. Short crank arms, working in ball bearings, are housed in the top plane under the front spars. From these, tubes run to the upper aileron king posts, while struts connect upper and lower ailerons. In the aileron control system there should be no question of cable stretch and but little adjustment be required, although provision has been made for adjustment of the length of the aileron struts if necessary.
   We are informed that the first of the 34's was tested on Sunday, March 26, and was found to handle very well indeed, Mr. Cobham being, we believe, the pilot. Following are the main characteristics of the D.H.34 :- Length, 39 ft.; span, 51 ft.; height, 12 ft.; wing area, 590 sq. ft.; weight of machine empty, 3,365 lbs.; useful load, 10 passengers with luggage, or about 2,000 lbs.; total loaded weight, about 6,300 lbs.; power loading, 13.8 lbs./h.p.; wing loading, 10.5 lbs./sq. ft.; cruising speed about 105 m.p.h.; range, 3 1/2 hours at cruising speed.
   As already mentioned, the first of the 34's are to be put on the London-Paris service by Daimler Airway, while others are to be used by the Instone Air Line on the same route. The machines should prove a distinct improvement on the 18, although that machine has an excellent record, and we think that with the D.H.34, one more step has been made towards the ideal commercial aeroplane.