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Aviation History
1955
1955 - 0517.PDF
FLIGHT, 22 April 1955 MIXED POWER . . . highest rates of climb, and in such cases rocket fuel could beconserved for extended combat. A further advantage of the mixed-power intercepter was that,although the sum of the weight of mixed engines plus fuel was less than that for the pure-jet aircraft, the aircraft used morefuel in the climb. Thus the mixed-power aircraft arrived at altitude with a lower wing-loading, and this had an importantinfluence on manoeuvrability. The next diagram (Fig. 5) illustrated the break-even timeswhen the engine-and-fuel weight for given running times were equal; this approach was put forward by Prof. Baxter in his lectureon rocket propulsion [summarized in Flight of February 18th]. However, the interpretation of this diagram became rather difficultwhere a turbojet was already installed for take-off and climb purposes. It could be assumed that the existing turbojet was capable ofpropelling aircraft at M = 1.0 and that it was required to increase this flight speed to M = 2.0 at 60,000ft. Then, if the durationrequired at M = 2.0 was less than three minutes, it was best to use an additional rocket motor, since the weight of additional turbojetand fuel to provide the extra thrust was more than the weight of the corresponding rocket plus fuel. This was not the completestory, because the aircraft had to accelerate from M = 1 to M = 2 and it was in accelerated flight that the rocket was particularlysuperior. The weight of additional turbojet power would accelerate the aircraft to M = 2 in 10 min whereas the same weightof additional rocket thrust could do this in one minute or less. The necessity of accelerating to combat speed in the minimumtime was of the greatest importance in an interception. The shapes of the aircraft total-drag curves and turbojet thrust curveswere shown in the next illustration (Fig. 6); it could be observed how nearly parallel they were. Theoretically, a high Mach num-ber was possible on turbojet power alone, but the accelerating forces were small; the diagram showed that the aircraft shouldattain M=1.4 at about 45,000ft. Suppose that M = 2 had to be reached and that a turbojet or rocket was to be added to producethe required acceleration, the added weight of engine fuel being 1/5 of the take-off weight: the great differences in accelerationcould clearly be seen and the variation in time required to reach the required Mach number was important enough to warrant adifferent approach. The diagram in col. 2 (Fig. 9) showed the picture from a different point of view. Here, the sum of theadded engine-plus-fuel weight to accelerate the aircraft from M = 1 to M = 2 was plotted against the time taken. This showedimmediately that the rocket had to be employed if high accelera- tion was desired. At some time during the interception it was necessary to com-plete at least part of a turn before levelling up for the attack. The thrust requirements for the turn were not simply related to the O I 2 TIME TO ACCELERATE FROM M "I O MINS M -2O Fig. 9. Supersonic acceleration: illustrating the extra engine-plus-fuel weight required to accelerate an intercepter from Mach 1,0 to Mach 2.0 in specified times. acceleration; in most high-altitude turns the induced drag wasroughly five per cent of the aircraft weight and therefore the incremental thrust/weight ratio required for longitudinal accelera-tion would be 0.05 (n2 —1), where n was the normal acceleration. Thus, putting n = 3.0 (3g), AT/w became equal to 0.4. Returning to Fig. 6, it could be seen that, in order to obtainsuch performance, a turbojet would have to weigh considerably more than 1/5 of the aircraft weight; additional turbojet powerequivalent to 1/5 of the aircraft weight could give a normal acceleration of only 1.4g compared with a typical requirementof approximately 3g. In all the manoeuvrability cases considered in the paper it wasshown that the use of a rocket rather than additional turbojet power resulted in a lower total weight of engine-plus-fuel. Onthe other hand, it was still necessary to consider the take-off and steady cruising conditions, and the superiority of the turbojetat lower altitude and for continuous cruising for periods longer than 10 min made it an ideal choice in combination with a rocket. COUNTER ALTIMETER FOR U.S. NAVY AN American company, the Kollsman Instrument Corporation,has received an initial production order from the U.S. Navy for a new counter altimeter. The principle is not altogether new,but an instrument of this kind has long been sought after as a replacement for the present sensitive altimeter for jet aircraft.The new instrument indicates thousands of feet on a Veeder- type counter, there being also a single needle which travels onethousand feet per revolution. It is therefore no longer possible for the pilot to confuse the readings of three different needles. The great problem in adapting Veeder-type indications topressure altimeters is to eliminate sensitivity-limiting friction in the counter linkage. This Kollsman claim to have achieved.The original idea of a counter altimeter is stated to have originated from Dr. W. F. Grether of the U.S.A.F. Aero-medical Laboratory. Special balance-weight arrangements have been provided inthe new instrument to compensate for g effects during manoeuvre, and temperature compensation for from 160 deg F to —60 deg Fhas been incorporated. The cost of the instrument is said to be well within the range of present prices for such equipment. AIRSTOPS IN THE NEWSR EGULAR readers of Flight will recall that on a number ofoccasions we have referred, in leading articles and elsewhere, to the need for Britain's cities and towns to plan helicopter sites,or at least to reserve space for them. It may also be remembered that in our December 10th, 1954, issue we reported a speechby Mr. H. T. Hough, Liverpool's city engineer and surveyor, in which he described preparations made by his own city forestablishing airstops and also put forward some sound views on the question in general. That local authorities are showing a very real interest in thisquestion is shown by the number of enquiries for information that Flight receives. The Aerodrome Owners Association is experi-encing a similar reaction, especially following its decision to devote a day of its 1954 annual conference to demonstrations and discus-sions of helicopter landing facilities. At these demonstrations, it will be remembered, experimental landings were made by West-land and Bristol helicopters at a site within 1,000 yards of Northampton's Guildhall. Since that time, says the A.O.A., the volume of inquiriesreceived has been so large that it has been decided to inaugurate a new grade of associate membership at a reduced subscriptionof £10 per annum. The Association gives the following list of cities and towns "which have already signified their intention tobe prepared for the helicopter age by applying for A.O.A. mem- bership" : Barnsley, Barrow-in-Furness, Bath, Birkenhead, Black-burn, Bournemouth, Burnley, Folkestone, Glasgow, Halifax, Harrogate, Huddersfield, Kettering, Leicester, Macclesfield,Middlesbrough, Northampton, Oldham, Rotherham, Southamp- ton, Southport, Sunderland, Tynemouth, Wallasey. MR. N. F. NEWBERY WE regret to record the death on March 26th, after a shortillness—of Mr. Norman Francis Newbery, A.F.R.Ae.S., chief development engineer of B.O.A.C. Mr. Newbery, who was 38,began his aviation career as a ground engineer with the Cinque Ports Flying Club in 1936. After a short period with the deHavilland Airscrew Service Department he joined British Airways in 1939, subsequently holding a series of senior posts in connectionwith the maintenance of B.O.A.C.'s Boeing 3I4s, Liberators, Constellations, Super Constellations and Stratocruisers. Mr.Newberry assumed his last appointment in 1952.
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