M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)

Журнал Flight

Flight, December 10, 1910.

IS THE HELICOPTER POSSIBLE?

[940] Although from time to time, both in FLIGHT and the public Press, the question of the helicopter or self-raising machine is discussed or referred to, it is significant that there is no actual example of this type of machine that has ever flown or even risen from the ground by its own power, although we read of "propellers" or "lifters" having been constructed showing a high duty in thrust in lbs. per sq. ft.
   From consideration of the matter it seems to me that the true explanation of the failure of the helicopter to materialise is that it is a mechanical impossibility to construct one owing to the mechanical and structural difficulties which arise from the inevitable concentration of weights in a helicopter machine, for the following reasons. As the helicopter propeller or lifter has to lift the total weight of the whole machine from the ground from a state of rest, it is evident that the "lifter" or "propeller" must be of a sufficient size and strength to move a volume, and therefore weight of air at a sufficient velocity to not only balance the total weight to be lifted, but also provide an excess of power, and therefore weight to cause the translation of the machine after being lifted. And it will be seen that this necessitates the whole load, due to the total weight of the machine, and that excess required for the translation of the machine through the air, being borne at a point over the end of the axle of the propeller or lifter ; and the strength of the framework of the machine to take this concentrated load requires a structural weight which at once precludes any chance of its being lifted, as there is no known material which could be used and would give the required strength and necessary lightness, even if no factor of safety were provided for.
   Admitting that probably anyone attempting to construct a helicopter would use two or more propellers instead of one, that will not make the case any better but rather worse, for although the total weight to be borne would be divided between the propellers, still the share of the weight of each propeller is still concentrated above it, and it will be found that the combined weights of the structures and each propeller will be actually heavier than if one propeller only were used. Further, in a helicopter, it is necessary that the propellers or lifters are unobstructed both above and below to allow of free entry and egress of air to and from the propeller. This necessitates a cantilever type of construction by which the strains set up in the structure are, of course, enormously increased.
   Take the case of a propeller of 25 ft. diameter, and suppose it to be revolved at a sufficient rate to lift 3 tons (that is to say, it would just balance 3 tons, and no extra power is available for progress), one half of its diameter would be 12 ft. 6 ins., and allowing 1 ft. for clearance, the length of the cantilever from its junction with the body of the machine to the centre of the propeller-shaft would be 13 ft. 6 ins., and assuming that the depth of the supporting-arm at its junction with the body of the machine is 2 ft. 6 ins., the strain in the top and bottom members of the arm at this junction will be 16 tons 4 cwt. to tear it away at the bottom and the same to crush the members at the top, from which it will be seen that nothing but an iron plate girder could carry the weight, and this is allowing for no factor of safety. In such a construction a factor of safety of 2 at the lowest would be required; this would at once double the strains the structure is to be capable of bearing, which would then be 32 tons 8 cwt. at bottom and top respectively, and there is still to be added the extra thrust of the propellers required to propel the machine. No wonder the helicopter has never materialised, for it is an impossible machine, in my opinion.
Maidenhead. CHARLES JAMES REYNOLDS.


Flight, December 24, 1910.

IS THE HELICOPTER POSSIBLE?

[978] With regard to your correspondent's remarks re helicopter flying machines, these are, at any rate at present, not a practicable type of machine as helicopters pure and simple, but given a suitable plane surface as a weight-carrying medium, it appears to me that helical screws could be used to very great advantage in assisting when rising or descending, and for other manoeuvres, as providing a more positive and quicker means of handling an aeroplane.
   If it were not possible to actually elevate and sustain the necessary load by means of the screws alone, it should be possible by their aid to get up with a much shorter run than at present, and also to sustain oneself in the air at a very much lower flight speed than is now required with the thrust of large diameter screws, of small pitch ratio, helping to maintain and equilibrate the machine if suitably arranged.
   This would greatly facilitate the handling of a flying machine, especially for scouting and other observation purposes, and would probably enable the machine to practically hover in the air, or at any rate to descend very slowly, under the sustaining influence of its screws.
   I cannot agree with Mr. Reynolds' figuring of the probable necessary weight of such a machine, in fact if, say, two large diameter screws were arranged to pull the machine up from the ground, which would probably be found more convenient for constructional purposes, the weight could hang suspended from the axis of each screw, on a light framework similar to the method used on dirigibles.
   A smaller propelling screw could be used to acquire velocity to raise the machine from the ground, if assisted by plane surfaces, and powerful vertical screws, and should result in a very quickly rising machine. As a purely direct lift machine, I am of opinion that the ornithopter is the probable type, although I seem to recollect a French helicopter, by one M. Cornu, I believe it was, getting off the ground, but very few particulars were published, and as the experiments were carried out some four years ago nothing very striking can have resulted, or more would have been heard of the machine.
   From experiments with my ornithoplanes I have found that a very positive lifting effect can be obtained by flapping wings properly arranged, and I have no doubt that a successful machine of this type will be evolved which will rise straight from the ground. He will be a bold man who can say that anything is impossible in these days of scientific advancement, and every new development in light yet strong metals, improved motive powers, &c., only places more material to the hand of the worker wherewith to attain his end, and render possible the conquest of that elusive element the air.
   My ornithoplane No. 2, equipped with a new type of 40-50-h.p. aerial engine, and embodying several of my ideas in this direction, will be out again shortly, and in the meantime I shall be pleased to give particulars of my experiments and the results obtained to anyone who is interested in the above types of flying machines, as I believe that the exchange of ideas on such a subject may often save time and money which would otherwise be wasted in following out useless experiments, and which could be used in advancing along the paths pointed out by the many failures of the past, which have at least resulted in a partial solution of the problem of mechanical flight.
Coventry. WILLIAM A. WEAVER.


Flight, January 7, 1911.

IS THE HELICOPTER POSSIBLE?

[1005] In Mr. Reynolds' letter, No. 940, appearing in your issue of the 10th ult., he states "that there is no actual example" of a helicopter type of machine having flown or even risen from the ground by its own power.
   It is evident that he is not conversant with the very careful experiments carried out by M. Cornu in France. M. Cornu in 1907 constructed a helicopter consisting of two 20 ft. diameter screws, one behind the other, the blades of which were adjustable to any angle; provision was made for the horizontal progress of the machine by means of two inclined planes, so placed that a small portion of the downward current of air produced by the screws was changed in direction so as to obtain a horizontal thrust. The power of the Antoinette engine at the speed at which it ran (about 900 revolutions per minute) was estimated by the maker at not more than 14-b.h.p.
   The machine rose from the ground carrying two men and travelled forward at a speed of 10 ft. per second, the weight lifted being about 704 lbs. The flight was of very short duration, under a minute, somewhat less than the first aeroplane flight of the Wright Brothers.
   There is no doubt that M. Cornu's machine was very unstable. The most interesting point in the experiment from a scientific point of view is, if we calculate the possible lift from the screws with the power applied (assuming the machine to be stationary), we could not expect a greater lift than about 450 lbs. This goes to prove that the forward motion tended to augment the lifting power; after all, that is what we should expect, because by the forward motion each screw is enabled to act upon and set in motion air over a greater area in a second of time. If we substitute this value for the area acted upon in place of the disc area of the two screws, we at once see there is no reason why the screws should not lift the above weight.
   Experiments at the Koutchino Institute have since proved that the lifting power of a screw was increased nearly three times when subject to a considerable horizontal blast. The reason is obvious in either of the above cases. With the forward motion of the machine, or the horizontal blast of air, the screws are unable to force the air downwards with the same velocity as when stationary; this causes a greater resistance, resulting in a greater lift.
   We are therefore forced to the conclusion that to obtain great lifting power from a helicopter the forward speed must be considerable.
   M. Cornu, I believe, experimented further with this object, but his results seem to prove that the question of stability altogether outweighs the question of lift, principally for the reason that with a forward motion the reaction from one blade is not counterbalanced by the reaction from the blade opposite (one blade is acting against a horizontal air current and the other is travelling with the current during a period of each revolution).
   From the above I am forced to agree with Mr. Reynolds that the helicopter is not a practical machine, although my reasons for doing so, it will be noticed, are very different to his.
Gray's Inn Square. J. R. PORTER, A.M.Inst.C.E.


[1006] In reference to the remarks of your correspondent, Mr. William A. Weaver (letter 978, in your issue of December 24th), concerning my letter under the above title (940, in your issue of December 10th), your correspondent does not seem to realise that, whether for a flying machine, a bridge, or any other mechanical structure, the same mechanical laws and limitations govern all, and that any structure or machine in which the load is concentrated will and must be heavier to sustain the load than one in which the load is more distributed or less concentrated, and that the larger the machine or structure is, and therefore the greater the total weight or load borne, the lighter per unit of weight will be the machine to bear the load; and therefore it follows that if, as stated in my letter, supposing the machine to be of such a size that the weight to be lifted amounts to 3 tons for each propeller, it is impossible to obtain a structure strong enough to bear the load and at the same time be light enough to fly or be air-borne; it will be still more impossible to do it with a smaller machine as then the unit weight in respect to unit strength will be increased, and the smaller machine will be found relatively heavier than the larger, and Mr. Weaver's suggested combination of supporting planes and propelling screws with lifting screws as well, will be heavier than either, for the more the total power required is divided up the heavier will the machinery and necessary supporting structure be to transmit that power. The same remarks apply to flapping wings or reciprocating paddles; these must be very strong, as they bear the whole weight of the structure at the hinge to which they are articulated, and the weight of the machinery per horsepower (that is the useful horse-power exerted by the wings or paddles) is very heavy indeed, as owing to their reciprocating action the inertia stresses, due to their reversals in direction are very heavy, and absorb so large a proportion of the engine-power that so large an engine has to be provided that its weight becomes prohibitive. Mr. Weaver talks about suspending the structure from the screws in a helicopter, instead of resting it on the top of the axles. This will be an actually heavier form of construction than the one I mentioned; the friction will be greatly enhanced, and therefore the necessary horse-power (and weight) of the engine will also be greatly increased, while the concentrated weights on the structure still remain as I have said in my former letter. If Mr. Weaver cares to write to me, I shall be pleased to hear how far he has got. But, all said and done, a certain weight has to be lifted in a certain way. This requires a certain horsepower (and, therefore, weight) to be exerted at a certain place or places; this requires a certain structural strength, which can easily be calculated and its weight known, when the question, to fly or not to fly, can at once be answered, without any waste of time or money in experiment. No structural conception that does not agree with the laws of mechanics can ever be brought to a successful issue.
Maidenhead. CHARLES J. REYNOLDS.


Flight, April 15, 1911.

Is the Helicopter Possible.

[1140] After reading the letter which appeared in your issue of January 7th (letter 1006, from Mr. Reynolds), I have taken the trouble to go more fully into the question of designing a helicopter on the lines I suggested in my letter of December 24th, and I am now in a position to state, positively, that a machine of the type I proposed would be a mechanical possibility at a weight not exceeding 15 cwts.
   Mr. Reynolds cannot have much practical knowledge of flying machines, or he would not compare their structural laws with those governing the design of bridges and other mechanical structures.
   If Mr. Reynolds takes as his guide the data available to the ordinary engineer-designer and applies it to the construction of a flying machine, he will be very much astonished at the weight of the resulting machine. It will be found in all machines which can fly, that the question of the safe load margin, so beloved by English designers of machinery, has to be almost entirely disregarded, and a machine produced which will stand up to its work with the lightest possible margin of strength, and (as is borne out only too sadly by most of the fatal accidents to aviators) with practically no margin for extraordinary strains which may arise in the course of flight.
   In the machine I have sketched out planes are provided of sufficient size to assist the helical screws in supporting the machine in flight, and to counterbalance any fluctuations of horse-power which might momentarily reduce the efficiency of the supporting screws, and cause the machine to drop and to parachute the machine, or enable it to execute a vol plane in case of total stoppage of the screws. A helicopter without planes would be a death-trap, if it ever got any height up, to my mind.
   In the machine I propose a 100-h.p. engine would drive a 10-ft. pair of helical screws, revolving in opposite directions (the gyroscopic effect of these screws would greatly enhance the stability of the machine), and a 50-h.p. engine would drive a 7-ft. tractor and propeller.
   As nearly as I can estimate from what little data there is on the subject the planes would be 25 ft. by 8 ft., and steering would be effected by ailerons on the extremities of the planes.
   Although it would possibly not attain high flight speeds, a machine on these lines would have great controllability, and would hover and descend in an almost vertical path, consequently less area would be required for stopping and starting places, and it would be much handier for general observation purposes.
   Now that the question of human flight is having the attention of all thinking men in engineering circles, no doubt great strides will be made, but not on present aeroplane lines I feel sure.
   The possibilities of aeroplanes are, after all, very limited, and I am convinced that before long the practical bird machine will make its appearance, and it will then give an impetus to a growing industry, and concentrate the lines of thought in a direction which will lead to the evolution of machines thoroughly practical and commercial in their uses, and more in accordance with natural principles.
   There is a great deal more in the action of a bird's wings than most people, I venture to say, think; and when it is copied mechanically it will be simple but very different to the preconceived notions of bird flight, and very much less power will be required ; in fact, I believe that man has sufficient power to fly if he can learn to apply it properly.
Coventry, WILLIAM A. WEAVER.


Flight, May 6, 1911.

"Is the Helicopter Possible?"

[1163] In answer to Mr. Weaver's letter (1140 in your issue of April 15th), I would ask Mr. Weaver to re-read my letter (1006 in your issue of January 7th) and also the extremely interesting one (1005 in the same issue) from Mr. J. JR. Porter, when I think he will be led to modify his views.
   Mr. Weaver takes me to task for supposing that any factor or safety at all should be considered in the construction of a flying machine; but the necessity of some factor of safety is evident unless the machines are to be death-traps, and this is admitted by Mr. Weaver in his letter in spite of himself. For he there states that in a flying machine the factor of safety "has to be almost entirely disregarded," and then goes on to say that the fact that flying machines are thus constructed "is borne out, only too sadly, by most of the fatal accidents to aviators."
   As a matter of fact, the importance of a factor of safety in the construction of flying machines is now being recognised, and the advances that have lately been made in these machines are solely due to truer mechanical construction and the allowance of a more or less reasonable factor of safety.
   Mr. Weaver now proposes a helicopter type of machine of a total weight of 15 cwt., or 1,680 lbs. To be fitted with a 100-h.p. engine to drive a pair of helical (or lifting) screws 10 ft. in diameter, and also with a 50-h.p. engine to drive two screws 7 ft. in diameter (one as a tractor and the other as a propeller). The machine, in addition, to be provided with supporting planes (after the manner of an aeroplane) to have, as I take it, a total area of 25 ft. by 8 ft. = 200 sq. ft., and be provided with ailerons for steering purposes.
   If we take out the various weights of the above we shall find that it is impossible to construct the machine within the limits of the total of 15 cwt. The 100-h.p. engine, at the low weight of 4 lbs. per horse-power, will weigh, without the radiator and connections, 400 lbs., and the 50-h.p. engine, on the same basis, 200 lbs., a total of 600 lbs. for the two engines alone. The radiators with their connections and necessary water, at a modest estimate, will weigh 50 lbs. Then there is the fuel and oil, if enough is carried for only one hour's consumption we shall require, at the rate of 1/2 lb. per horse power per hour, 75 lbs. of petrol, which with its container will weigh say 85 lbs., and allowing 5 lbs. for the lubricating oil and its container, makes a total for engines, radiators, fuel, water, oil and tanks of 740 lbs. The two helical screws, 10 ft. diameter, which have to transmit 50 horse power each and support the whole weight of the machine, will weigh, at a moderate estimate, with their shafts and spindles, thrust-blocks and bearings, 200 lbs. each, or 400 lbs. for the two, and the transmission gear from the engine to these screws, with attachments, would weigh at least another 50 lbs., making a total for the helical screws and all attachments and gears of 450 lbs. ; each of the 7 ft. screws, with their shafting, gearing, bearings and attachments, would weigh at least 40 lbs., or a total of 80 lbs. for the two.
   The planes, at the low estimate of 1 lb. per square foot, will weigh 200 lbs., making a grand total up to now of 1,470 lbs., which deducted from 1,680 lbs. leaves a balance of 210 lbs. only out of which we have to construct the body of the machine capable of carrying all this and the weight of the driver as well, besides being strong enough to transmit the strains due to the exertion of 150-h.p. within it on a medium outside it; which, to my mind, is impossible.
   If Mr. Weaver can do this, both myself and others, I am sure, will be deeply interested to learn how it can be done, and to see the actual machine when it is made.
Maidenhead. CHARLES J. REYNOLDS.


Flight, May 20, 1911.

Is the Helicopter Possible.

[1178]. With reference to the above, and letter 1163 in your issue of May 6th, I do not wish to turn what has been, to me, an instructive correspondence into an argument, especially as I am able to prove what I said in my letter, having actually constructed a machine, on the lines I mentioned, some years ago.
   If Mr. Reynolds will call at my works here, I shall be happy to show him most of the parts which were used in this machine, and which, together with others which I have since used in the construction of my present machine, ornithoplane No. 2, weighed under 15 cwt. when complete.
   The reason I did not proceed further with the machine was owing to steering and other difficulties, which I could not see my way to surmount at that time.
   I had not embodied plane surfaces in the design, and this, as I pointed out in my other letter, appears to be necessary even with a helicopter machine.
Coventry. W. A. WEAVER.

[The accompanying sketch shows the arrangement of Mr. Weaver's proposed machine. This diagram and explanation should be read with his letter 1,140 on p. 344. A is the hull of aluminium and wood; B, 100-h.p. water-cooled engine ; C, 50-h.p. rotary engine ; D, pilot's seat and controls; C, C1, helical-screws, geardriven; F, F1, tractor and propeller; G, plane surfaces ; H, petrol, oil, and water tanks; I, shaft connecting tractor and propeller. All screws to be driven in opposite directions to each other, thus giving the machine gyroscopic stability.-ED.]