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Aviation History
1948
1948 - 1233.PDF
AUGUST 5TH, 1948 FLIGHT 165 CORRESPONDENCE The Editor does not hold himself responsible tor the views expressed by correspondents. The names and addresses of the witters, not necessarily for publication, must in all cases accompany letters. I THE PLANET SATELLITE Stalling Speeds Too High ? WAS most interested in the article on the Planet Satellite which appeared in your issue of July 15th. It is most stimulating to read of such a complete breakaway from the usual stereotyped design in this field, and confirmation of the estimated performance will be awaited with interest. How- ever, I should like to make a few remarks on the estimated take-off and landing characteristics. The wing loading of 191b/sq ft at the gross weight, and the resultant stalling speeds of 68 m.p.h. flaps-up and 62 m.p.h. flaps-down, must be con- sidered high for a single-engined personal aircraft and, in i_ct, * the writer has been unable to find those values exceeded by a similar machine. Incidentally, the Armstrong-Whitworth Ensign four-engined air liner, and the fairly early Hawker Hurricanes, had stalling speeds of a very similar value to this. In this connection, a common enough reason given by de- signers for a relatively high stalling speed is that it is better to have a good-natured stall at a moderate speed than to drop a wing at a lower speed. Few will disagree with this dictum, but in point of fact, the Miles Messenger and Gemini manage to retain innocuous stalling characteristics at 25 m.p.h. and 35 m.p.h. respectively. ., Since a primary aim in tne design of the Satellite has been to keep the selling price to a low figure and thereby to find a large market, this point would seem to warrant some con- sideration. Again, the ranges of 1,000 miles with full payload or 2,450 miles with the pilot only, should not be of very great interest to the private owner, when a four-engined aircraft would give considerably greater safety. L. H. W. HARRIS. Yeovil, Somerset. I GREATER AIR SAFETY High Flash-point Fuels and Crash-proof Tanks HAVE read with considerable interest the editorial comments and correspondence following the publication of my article —"Towards Greater Air Safety"—(May 20th), and I would like to make a few further comments on the subject. Many of your correspondents have argued the pros and cons of the use of " safety " or high flash point fuels. I think most people will agree, however, that the use of diesel oil is not a practicable proposition with aircraft engines, and the day when all aircraft will use jets is some years ahead, particularly for small and medium sired aircraft not designed to fly at great altitudes. There appear to be two features common to. the arguments propounded: 1. That the provision of more and better emergency exits is considered the most suitable means of reducing the number of deaths through burning, by reducing the likelihood of being trapped in the aircraft. 2. That the use of high flash point fuels is considered to be a better safeguard than the use of crash-proof tanks. The first conclusion assumes that passengers are able to reach the emergency exits ifnder their own power, but in many cases they are likeiy to be injured and unable to move. The first requirement, therefore, is a crash resistant protective seat, which will give uniform support to the body during decelerations up to 25g. This can only be done by fitting rearward facing seats, as forward facing seats and safety belts cannot provide anything like the same amount of protection. I do not think anyone could strongly object to rearward facing seats; after all, half the seats in a railway train face aft, and the sense of relative motion is much greater in a train than in an aircraft unless it is flying very low indeed. The present trend in "executive" and "V.I.P." aircraft furnishing styles is to place the seats facing each other, with a table between them. This arrangement, however, favours the rearward facing passenger, who is well protected in the event of a crash, while the forward facing passenger will be thrown violently against the table. Emergency exits should be placed on both sides of theaircraft in case one side is obstructed through the fuselage lying °n its side, or through the exit being jammed against a largeobstruction. Regarding the second conclusion, the argument for safety fuels must assume that diesel engines are to be used, for although paraffin admittedly does not ignite so easily as petrol, under certain conditions, such as a large accumulation of vapour inside the wing, it can detonate with extreme violence, and the explosion might do as much damage as a petrol fire. The objections to crash-proof tanks seem to be based on the ideas that they are very heavy and that they involve a con- siderable reduction in fuel carrying capacity. This argument can only be applied to rigid metal tanks fitted with a crash- resistant covering, a type which is not very effective. The reasons for the bursting of metal tanks are (a.) the hydraulic shock wave which is built up inside the tank and which bursts it outwards, and (b), the distortion of the surrounding structure which produces similar distortion and rupture of the rigid tank inside it. An adequate covering to protect a rigid tank against these forces calls for the application of numerous layers of high rip-strength fabric which build up the wall thickness and add a lot of weight, much of which is due to the amount of cement required to stick the layers together. The only tanks which are really effective are flexible bag tanks, and these are not only lighter than metal tanks but provide considerably more fuel capacity in an equivalent tank bay. Their wall thickness is less than a sixteenth of an inch and they are made to fit the compartment exactly, with no waste space. Obviously they must do, for they are not self- supporting and are only held in shape by the aircraft structure, hence when the structure distorts, the tank goes with it and suffers no damage. By far the most important consideration, however, is the hydraulic shock wave caused by a sudden deceleration of high magnitude, such as, for instance, if an aircraft crashed and the wings came into violent contact with some solid obstruc- tions. Usually in these cases the wing skins are burst outward by the movement of the fuel which distorts the forward end of the tank, and the forces generated inside the tank are expended on the aircraft structure, the tank remaining undamaged. Whilst agreeing with your correspondents who have pointed out that pipe lines, etc., can be broken in a crash, I would point out that the amount of fuel which can get out of a fuel pipe which is quite probably crushed, thus reducing its effective bore, is nothing like as much as will pour out of a tank which is ripped open. If one can reduce the quantity of fuel feeding the fire, then either it can be got under control and prevented from spreading, or more time can be gained to extricate the occupants of the aircraft. Even a few minutes' breathing space gained can make all the difference between none saved and all saved. First, rescuers who reach the aircraft can get more people out, secondly by preventing the fire from reaching the fuselage a panic can be averted and the occupants can do more to help themselves. Fire creates panic more than anything else, and since panic destroys reasoning powers, the resultant struggles to get away from the flames become futile and aimless. Fear of fire is a deep rooted instinct in all living creatures, and the fact that it can so easily cause panic is shown by the great attention paid, for instance, to fire precautions and emergency exits in theatres and cinemas, where large numbers of people congregate in a confined space. Thirdly, anyone experiencing a deceleration of anything over log is going to be considerably shaken up and may require some time to recover. If only a few seconds elapse between the shock of impact and the envelopment of the cabin by fire, then most people will not have pulled themselves together in time to think about getting out. If the interval can be increased to a few minutes, those able to move are given a chance to recover and help those not so fortunate, and the crash-proof tank can, by remaining fuel-tight, prevent the spread of fire for those essential few minutes. Alternatively, if fire fighting equipment is quickly on the scene, the fire may be put out before it has got too great a hold. In either case the tank will have served its purpose from the crash protection point of view, while the fact that a bag tank installation has fuch a highly efficient capacity/weight ratio means a greater range for the aircraft, and therefore a better fuel reserve factor when flying in bad weather conditions. Wolverhampton. Staffs. W. A. HANNAM.
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