FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1952
1952 - 0967.PDF
11 April 1952 433 sometimes be observed in practice in the premature failure of one component; and, although such failures are useful to the engineer in indicating the accuracy of fatigue calculations, they may well constitute nothing less than a disaster to others with less scientific inclinations. But no such lack of accuracy was envisaged by Holmes. He foresaw clearly a standard of design not even attained to this day, in which all the components had exactly the same fatigue life, and this figure was to be the conveniently round value of a hundred years. As the fatigue life of a component becomes slowly used up, the designer naturally looks for the first signs of failure. But in this respect at least the one-hoss shay was singularly uncommunica tive :— Eighteen Hundred—it came and found The Deacon's Masterpiece strong and sound. Eighteen Hundred increased by ten-— "Hahnsum kerridge" they called it then. Eighteen Hundred and Twenty came— Running as usual, much the same Thirty and forty at last arrive. And then come fifty and fifty-five ... First of November-—the Earthquake-day— There are traces of age in the one-hoss shay, A general flavor of mild decay, But nothing local, as one may say. There couldn't be—for the Deacon's art Had made it so like in every part That there wasn't a chance for one to start. All fatigue failures tend to become a source of danger. Some are not serious in their consequences, whereas others may involve loss of life. Although the actual failure may in itself not be striking, it is almost certain that the immediate results will be spectacular. The direct consequences of fatigue failure of a driving axle of a diesel-electric locomotive at high speed come readily to the mind. Nor was the consequence of the simultaneous and final failure of the shay less spectacular than would satisfy the best tradition in this sphere, as the next extract shows. the stainless-steel firewall. The exhaust is collected in a four-piece manifold and ejected from four short tailpipes. These are sur rounded by muffs which, as the only outlet from the cowling, induce the heated cooling air from the cylinders to eject at increased velocity. The system, similar to that on the Convair Liner, reduces power-plant drag to a minimum. The installation was tested for many hours on a full-size mock-up to investigate cooling problems and arrive at the best outlet sizes. There is no gill or other outlet control. The three-bladed airscrew is actually a stan dard DC-3 type with 3m cropped off each blade. From a distance, when the engine is idling, this large, slow-turning airscrew pro duces a curious aural effect, for it causes a beating noise not unlike that of a helicopter. I saw several take-offs at full load: when the engine is opened up and the brakes released the tail comes Up, acceleration is rapid and then the Otter lifts off and climbs very steeply. Coming in to land, the approach is made with the nose right down, in an attitude akin to that of a steep dive, but at what looks like a walking pace. Once, when flying alongside in a Chipmunk, I saw that it was impossible to keep down to the Otter's speed when flying level with full flap—about 46 m.p.h. I.A.S. When flying with George Neal, chief test pilot, I was able to amplify these general impressions. The tests being made when I was aboard were measurements of gliding angle at various speeds with full load. The unfurnished cabin contained ballast, automatic observer, a multiple manometer for flap pressure-plotting and two flight-test observers. A partly frozen runway, well out of wind, was not the best venue for demonstrating a slow-flying aircraft; but, even so, the Otter nipped very smartly into the air at about 55 m.p.h. I.A.S. There after we climbed (at 75 m.p.h. I.A.S., 2,000 r.p.m., 30m Hg and 75oft/min) at an angle so steep that a head-rest would have been an added comfort! Take-off and initial climb are made with about 30 deg of front flap and about 50 deg on the rear one. When the flaps (operated by a hydraulic hand pump between the seats with a jack in the roof connected by push-pull rod to bell-cranks in the wing) are raised there is a marked nose-up change of trim, but it is quite easily held on the stick until the tailplane incidence has been adjusted by handwheel. It is scarcely fair to comment on the amenities of an unfurnished prototype, but a few words may be of interest. Cockpit layout is very like that of the Beaver, with a neat T-shaped instrument panel; flight instruments are on the left, engine instruments and controls centrally and radio on the right. The rudder pedals swing instead of being hinged from the floor, but there is the same swing-over stick with a ram's horn wheel. The all-round view is First of November, 'Fifty-five ! This morning the parson takes a drive. Now, small boys, get out of the way ! Here comes the wonderful one-hoss shay, Drawn by a rat-tailed, ewe-necked bay. "Huddup !" said the parson—Off went they. The parson was working his Sunday's text, Had got to fifthly, and stopped perplexed At what the—Moses—was coming next. All at once the horse stood still, Close by the meet'ri'-house on the hill. First a shiver, and then a thrill, Then something decidedly like a spill— And the parson was sitting upon a rock, At half-past nine by the meet'ri-house clock— Just the hour of the Earthquake shock ! What do you think the parson found, When he got up and stared around ? The poor old chaise in a heap or mound, As if it had been to the mill and ground ! You see, of course, if you're not a dunce, How it went to pieces all at once— All at once, and nothing first— Just as bubbles do when they burst. End of the Wonderful one-hoss shay. Logic is logic. That's all J say. The story of the final failure of the one-hoss shay appeared in a number of" publications. One which appeared in England in 1891 contains an introduction by Holmes in which he explains the concept on which his poem was constructed:— "The Wonderful One-Hoss Shay is a perfectly intelligible conception whatever material defects it presents. It is conceivable that a being of an order superior to humanity should so understand the conditions of matter that he could construct a machine which should go to pieces at a given moment of the future. The mind may take a certain pleasure in this picture of the impossible." The poet's simultaneous failure of all components is still for tunately only a theory—and, even now, not a very attractive one to a design engineer. excellent, although rooflights, as on the U.S.A.F. Beaver, would make it even better. The noise level was not high, but the sound had a rather harsh note, which will probably go when sound proofing is complete—although one remembers the hollow bark of the Convair Liner. We did not cover the full speed range, but I noted that we were making 145 I.A.S. at 6,000ft with 33m Hg and 2,200 r.p.m. The nose was well below the horizon under these conditions and the view was like that from a balcony. Still at 6,000ft, and using a little flap, height could be maintained with only 2oin Hg and 1,780 r.p.m. at 50 m.p.h. I.A.S. Returning to the circuit, the nose-down attitude gave one the Qirious feeling of being in a balloon. For one thing, the circuit was started at about 1,000ft right over the middle of the aerodrome, from which we made one long, slow, stately descending turn to touch down almost exactly under the spot from which we started. Despite the great change in attitude from the glide to the three- pointer, the round-out was smooth. The landing run was just a short trundle of less than a hundred yards. Bearing in mind the generous size of the fin, the absence of any appreciable weather- cocking tendency was surprising in the strong crosswind that still prevailed. Altogether an outstanding aircraft; the all-round performance is excellent for 600 h.p. and to be able to carry a ton payload at over 160 m.p.h. and at only 50 m.p.h. is good by any standard. DHC-3 OTTER: PROVISIONAL DATA (P. and W. Wasp R-1340 Series H (600 h.p. for take-off) Span 58ft Length 42f Height (tail down) 10ft 6in Wing area 375 sq ft Wing loading 18.9 Ib/sq ft Span loading 2.1 Ib/sq ft Power loading 11.9 Ib/h.p. Cabin dimensions o.a S3.2in/62.5in wide x 58in high x 197in long Max. cabin volume 260 cu ft Grossweight 7,200 (7,200) • lb Basic tare weight (inc. 36lb radio) 4,165 (4,550) lb Payload, 300 miles 2,290 (1,890) lb 500 miles 2,040 (1,640) lb 800 miles 1,690 (1,265) lb Max. range (190 Imp. gal) 1,190 (1,000) milei Max. speed (s.l.) 163 (156) m.p.h. Cruising, 66 per cent M.E.T.O., 5,000ft 151 (144) m.p.h. 55 per cent M.E.T.O., 5,000ft 139 (133) m.p.h. Stalling, power off, full flap ... : 52 (52) m.p.h. Service ceiling 18,700 (18.000) ft Absolute ceiling 20,000 (19,300) ft •Figures in brackets are estimates for the seaplane version with standard Edo 7170 floats, for a gross weight of 7,540lb. The structure is stressed for 7,500 lb. D.H. CANADA OTTER (Continued from page 429)
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
