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Aviation History
1945
1945 - 0457.PDF
MARCH 8TH, 1945 FLIGHT the " Bol/ins " as he appears to be with the latest military aircraft, he would rtalise that landing in zero-zero conditions is a possibility now. Furthermore, so safe is it that aircraft have been successfully landed although they had no special equipment aboard, and the pilot was unaware that the particu- lar system even existed. Equally so the problem of icing will be overcome, although icing conditions may call for a reduced pay load; petrol in- jection to ensuie that our engines give full power to enable a rapid climb through icing layer would appear to be of con- siderable help in these circumstances. At the moment all transport—air, rail, sea or road—is delayed by conditions of poor visibility, with the possible exception of the local Underground rail system. It does not seem to be appreciated that air travel has the opportunity of Incoming more reliable than any other form of transport, since only in the air is no strain involved while proceeding at full speed in zero visibility (given an automatic pilot), and there- fore the schedule can be maintained irrespective of weather conditions. Two things remain; accurate control of aircraft to avoid collision, and a safe system to bring them to ground again. The first is easier than with any other form of trans- port, since variations in height are possible, and the second has already been discussed. For goodness sake let us show more vision and determination in our planning for the future; this glamourising of flying must give way to providing air service for the public. Admittedly f some little while to come we are calling for a high degree skill from our crews, but there is an abundance of material available, and I would suggest to operators that they aim to employ more crews to ensure full rest periods, as the majority of accidents are due to carelessness often caused by overstrain. Very few accidents to transport aircraft in the last five years have been attributed to ice or landing conditions. By far the majority still seem to he due to flying into high ground while off track, and with modrrn equipment there would seem to be no excuse for this. To change the subject, I would like to express my thanks for the article by W. S. Shackleton on "Cargo Aircraft," but I still do not like that non-retractable undercarriage of the Bristol Freighter. Perhaps you will ease my mind by stating (with the nelp of Horace if ntcesKary) the gain in speed at 160 m.p.h. if it were fully retractable. COLIN C. RICHARDSON. IMPLICATIONS OF V2 The -' R " Formula and Critical Speed /CALCULATIONS about rockets -seem to have a way of pro- V> ducing results in excess of the work equivalent of the fuel. The mass ratio or "R" formula (V = v logc R — gt) apjK'ars to have a limitation which is outstripped by the V2. The thrust multiplied by the distance traversed is a measure of the work done. In the early stages of the flight it is not equal to the power of the fuel to do work. This accounts for the inefficiency of the rocket as an engine at low speeds. But there comes a time when T x S = E. That is to say, when the thrust multiplied by the distance covered is equal to the work equivalent of the fuel expended in the same time. At this critical point the rocket engine has reached 100 per !ent efficiency. If the acceleration continues to increase in accordance with the formula, then TxS becomes greater than E, and the engine is doing more work than the power of the fuel can provide. It exceeds 100 per cent, efficiency, and, by the end of the flight, will reach 200 per cent., or even higher, with a mass ratio higher than that of the V2. That is to say, beyond the critical point the formula is producing a result that the fuel cannot. In any example it is found that the critical speed is wnen the velocity (V) is equal to half the velocity v) of the exhaust. It is easy to see why this occurs. If " m " is the mass of the fuel expended in one second, then T = mv and E = \mv2. Then, when T x S = E : — 1 mv During the same second, S = the mean V, so V = \v. Let us see how this applies to the example about which there has been some correspondence. The time of flight is 46J sec. The final velocity-is 3,010 metre/sec. All the 8£ tons of fuel is considered as effective. It has an efficiency of 50 per cent., and v — 2,820 metre/sec. The work equivalent of all the fuel is 3,440,000 metre/tons, "r 74,000 metre/tons per sec. The thrust T) = mv = 52.4 tons. E 74,000 " , . , f= yTT^ 1"*I° metre/sec- = fr- it can be lound from the "R" tormula lh;it the velocity of 1,410 metre sec. is reached m a fraction under 30 sec. In the next second it will be more, and the work done "will exceed the power ration of 74,000 metre/tons per sec. Hy the end ot the flight the work done will reach 1 =50,000 tin tic ton-; in a second, or double the work equivalent ol the iuel ration in lh».t second. What, then, really happens after the critical point has been reached ? No doubt .some mathematician will be able to evolve a formula that provides for the work done to equal the wink equivalent of the fuel expended (74,000 metre/tons pti set.). But it is not difficult to work out the further performance in a less mathematical way. It is found that the acceleration remains almost coiistanl with a consequent reduction in the thrust, rind the final velocity is 2,550 metre/sec, ami not 3,010 as given by the loriiiula. (Actually, the acceleration falls oil slightly alter passing the critical speed until the 37th second, then it picks u|> again with the crescendo of the mass ratio towards the end ol the flight.) There is no quest inn about the correctness ol the iormiil.i up to the critical speed. The problem begins there. It begins with a velocity of 1,410 metre/sec. There are 3 tons ol luel in the tanks with 1OJ sec. to complete the course. It is clear that the final velocity of 3,010 metre/sec, as given by the "K" formula means that the rocket is doing work far in excess of the capacity of its fuel. My suggestion is that the 3 tons of fuel, rationed at a work equivalent ol 74,000 metre, tons per sec, is onlycapahle of giving an art clem tion up to 2,550 metre/sec. If the above is correct, it would seem that the lonnul.i dues not apply beyond the critical speed (where V = Ji>). It would seem also that the possibilities of the pick-a back rocket need further consideration, since it starts lite at a velocity highet than its critical speed. However, I am not a mathematician and know nothingabout rockets, so am open to correction. E. FARBUKY. ASYMMETRY /.GAIN An Idea Well Worth Trying? I?LIGHT of January 25th has only just reached this cottxi of Holland, but despite the delay I would like to add a few words or the criticism of my ideas on asymmetry. I made no pretence of presenting a complete and detailed design, nor specified any particular engines, so the question of whether the artist has shown all the air intakes or exits is surely rather superfluous. The same applies to undercarriage details. The weight on the main wheels is evenly distributed, and the thrust lines are symmetrical. Any tendency to swing at take-off would be much less than that of the Bv. 141 with its offset thrust line. The wing loading and aspect ratio are high, but they can be reduced only at the expense of speed and range. My specification for a long-range fighter may be all wrong; the only point I wanted to make wa3 that an asymmetrical design would fulfil that, or any other, specification for a twin-engined lighter more efficiently than any other shape. I believe, foi instance, that if one were to take the Mosquito specification, an asymmetrical design could be made faster and lighter. If it is more economical to run with two engines ticking over than with one at normal cruising output, then a lot ot motor boat and truck designers have been making a mistake for a long time, as well as several aircraft designers. The idea of towing a flying fuel tank may be all wrong, too. but I think the idea is worth trying out. Experiments have been made in America with towing gliders to assist take-off. The principle is just the same as that of the composite aircraft. With normal towing arrangements, the lift from the glider has too great a movement arm, and lends to prevent the pilot of the tug lrom getting his tail down to climb. A tow-line rigged to transfer the pull to a point above the centre of gravity of the tug might be the answer. Tailless gliders have been towed without pilots, and this form of glider is probably the best because of its great inherent stability. If your two indignant readers think that because one aircraft is cleaner than another it will necessarily glide faster, their ignorance of aerodynamics is even greater than mine. In any case there would never be any question of landing with the glider still in place. If the glider-tank did no more than support its own weight, it is still greatly reducing the take-ofl distance as compared with a tank slung under the airciaft itself in the usual manner. ROGER TENNANT.
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