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Aviation History
1946
1946 - 0273.PDF
FEBRUARY 7TH, 1946 FLIGHT CORRESPONDENCE The Editor does not hold himself responsible for the. views expressed by correspondents. The names and addresses of Ihe writers, not necessarily for publication, must in all cases accompany letters. R.A.F. SLANG " Strip-tearing " Began at Cardington ANENT "strip tearing," balloons were rapidly deflated atCardington in 1939-40 by pulling off a strip 6in. wide by6ft. long, and it was the practice to threaten bombasts with the same procedure. \V. G. HICKS. LONG-DISTANCE RECORD Potentialities of the Wimpey I READ with interest Mr. A. Sansom's letter in Flight,lauuary 10th, 1946, concerning the long-distance record.He suggests that the Lancaster is a suitable aircraft tor regain- ing the above-mentioned record, but, good as the Lancaster is,I think that the Wellington Mkl is capable of a greater range. Below are some comparative figures which I have workedbut with regard to the range qualities o£ the two aircraft. . LANXASTEK I WELLINGTON' 1 (Four 1,200 li.p. (Two 1,f)iH> h.p. Merlin XX) I'iiGASUS X\ Ulj Ut. empty 34,000 1b. 18.00(1 Ib. Crew 5 1.0CO 1,000 (»il 1,500 7.">0 Fuel (4,900 gall.) 3fi,5f0 (2,7.'iO gal.) 10,9JI> Wt. loaded 73,(KH) 1b. :i!i,700 lb. Wing loading 56.1 lb./sq. ft. 47.2 Power loading 14.6 lb./h.p, 3 0.S K-.mae cruising 8,000 miles 10.000 miles (at. 1!K) ra.p.h.) (at 17."> m.p.h.) Duration ' 42 hr. .r>7 lir. Consumption per engine ... ... 29 gall./hr. iMgal.'hr. JOHN LAWSON COVERDALE. BLEND APPROACH Met. Pilots versus the BirdsH AVING had the privilege of being for two years a memberof that small but happy band of Met. Flight pilots, I have heard in my time many lines about bad-weather flying,but the one that I remember best is that '' shot'' by a col- league as he climbed out after having landed in a really good"pea-souper." Pointing skywards, he said, "A couple of birds up there asked if they might formate on me on the wayin. They reckoned that it was too thick for them to make it down to the deck on their own." As a matter of serious interest, can any of your readers tellme if birds do fly above areas of thick and unbroken fog and make descents through it to earth? We frequently met thoseintrepid seagulls off the Norfolk coast at altitudes of io ft. or so in fairly thick fog, and frequently carried the necessaryproof back to base in the radiator, but, to my knowledge, none of us ever saw a bird of any kind flying over the topof a thick, unbroken, and extensive fog layer. May we .members (past and present) of this happy breed offlying weather men thus claim to have beaten the bird, or can some reader claim equality for our feathered friends on thequestion of proficiency on blind approach? EX-MET. FLIGHT PILOT. HEATHROW Loading and Momentum THINK that the average pilot of large aircraft will tendto agree with the statements, however loose, which have peared about the difficulty of making cross-wind landingswith large aircraft, and not so much with " Puzzled." Though your correspondent may be quite right in saying that aheavily loaded aircraft can be more easily landed across wind than one that is lightly loaded, so much depends on variousother considerations. All is well, thanks to the additional momentum of a. heavy aircraft, so long as ample control isavailable at final approach speeds, and so long as the pilot 1 s not make a mistake—but it is surely not fair so to place • the responsibility on him and demand the execution of aLTuss-wind landing on nearly every arrival at any: particular ^viield. After all, the pilot might fail to complete the drift utralisation and landing action at the right coincident'<>ment, so that the aircraft would start to drift off the run- u'»y just before touching, and he would then need to make up his mind immediately whether to complete the landing or togo round again. With a hundred-tonner the drift and neces- sary ground correction after landing might be more than thetyres would stand, while "overshoot" procedure might, in bad weather, involve the crew in yet another quarter of anhour of S.B.A. routine. We are surely asking too much of the captains of really large aircraft in expecting them to coperegularly with cross-wind arrivals. Incidentally, the speed of drift will be the same for anyaircraft, whether landing at 50 or 100 m.p.h.—it is merely that the relative angle of drift is smaller with the faster landing. . J- B. COMPACT POWER The "Magic" Figure of 100 b.h.p./litre IN the issue of Flight, dated January 17th, under the heading"Compact Power," the b.h.p. per litre of seveial engines is compared, and you ask who will be the first to achieve100 b.h.p. per litre. As a point of fact this figure has been practically achieved on the Merlin engine. From the engineer's point of view, however, the method ofassessing an engine's performance by the power developed per litre capacity is not entirely sound since it tends to favour theengine with a very short stroke. For mechanical and other reasons, all engines are found todevelop their maximum power at approximately the same piston speed. Since piston speed is a function of the lengthof stroke multiplied by r.p.m., a long-stroke engine will have to be run at lower r.p.m. than a shprt-stroke engine to givethe same piston speed. Tiie horsepower developed by an engine is given by theformula: — , , PLAN b.h.p. — — r 33,000 where P = mean effective pressureL = length of stroke A = piston areaN = r.p.m. 4- 2 (For 4-stroke cycle engines). As already stated the product of L and N is approximate! 'constant for all engine sizes which means that the horsepower formula could be rewritten as:— - *b.h.p. = K (P X A) where K is some constant.From this rewritten formula it is at once evident that the power of an engine is proportional to the mean effective pres-sure multiplied by the piston area. Since the mean effective pressure is a function of the degreeof supercharge employed, from practical considerations piston area becomes the controlling term in comparing the perform-ance of engines of different types. Expressing the figure of 60.5 b.h.p./litre for the Griffon 65in terms of piston area we find that the figure becomes 6 53 b.h.p./sq. in. The published rating of Griffon 130 incident-ally gives the higher figure of 7.15 b.h.p./sq. in. of piston area.On the new basis of comparison the figure of 83.5 b.h.p./ litre for the Sabre VII becomes 6.50 b.h.p./sq. in. of pistonarea. In conclusion, your article on the Merlin 130 series in Flight,January 21st, stages that powers in excess of 2,000 b.h.p. have been recorded on the test beds at Derby. This is equivalentto 96.3 b.h.p./litre. The development proceeding at the time resulted in a type test rating giving 8.0 b.h.p./sq. in. Thehighest sustained b.h.p. figure recorded on the test bed was 2,640 which gives the remarkable figure of g.6 .b.h.p./sq. in.,and but for the cessation of hostilities this figure would no doubt eventually have been cleared for combat use. As amatter of interest, this figure is equivalent to 98 b.h.p./litre. From the foregoing it will be seen that a target figure of10 b.h.p./sq. in. of piston area might mean more to the engi- neer than the layman's magic figure of 100 b.h.p./litre.This letter is not in any way meant to decry the very fine achievement of the 3,000 h.p. Sabre engine, but is anattempt to show that there is possibly a better method of comparing the performance of engines of widely differentdesign. : G. MORRIS, Rolls-Royce, Ltd.
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