Plane stopped by a parachute
QUESTION Is it true that the Air France Caravelle jet airliner of the Sixties did not use reverse thrust to slow down on landing? If so, how did it come to a safe stop?
THE Sud Aviation Caravelle was a French short/medium-range jet airliner. Early versions of the Caravelle, the mark III and VI-N, did not have thrust reversers.
They had a parachute that pilots would deploy on landing to slow the aircraft so the brakes could then be used to stop the aircraft. Later models did have thrust reversers. Their Rolls-Royce Avon engines were the same as employed in the De Havilland Comet.
I remember one wet night at Manchester Airport in the Sixties when a Caravelle of Sabena (the now defunct Belgian carrier) had a parachute failure and went off the end of the runway, shutting the airport for a few hours until it was retrieved from the grass at the end of the runway.
Mike Howell, Folkestone, Kent. WHEN the Sud Aviation Caravelle was introduced in 1958, it did not have reverse thrust, but neither did the De Havilland Comet, first flown in 1949, or any propellerdriven airliner prior to this.
Airliners such as these came to a stop perfectly safely using their wheel brakes alone. Reverse thrust was introduced later as a means of shortening the landing run and reducing wear and tear on the brakes and tyres.
When tyres go from zero to over 100 mph, as they hit the runway to slow down a hundred tons of aircraft, they get very hot.
Another advantage of reverse thrust is that it is not affected by water on the runway. As with a car on a wet road, a wet runway will increase the distance needed to stop.
Thrust reversers on jet aircraft work by having moveable vanes or doors at the rear of the engine that block off the normal exhaust and divert it forwards to produce streams of jet exhaust at 45 degrees to the direction of travel. The most effective time to use the thrust reversers is just after the airliner has touched down.
As the airliner slows, reverse thrust is turned off because there is a danger that the exhaust from the engine or debris blown off the runway by the exhaust could be ingested by the air intake.
This is why you hear the engine noise increase just after you touch down and then decrease in the landing run.
Denis Sharp, Hailsham, E. Sussex.
QUESTION Why are French horns configured so the valves are played left-handed?
WHEN playing the French horn — a valved brass instrument with a funnelshaped mouthpiece and a tube of conical bore coiled into a spiral — the weight is supported with the right hand inside the bell, balanced by the left hand, allowing the left-hand fingers to remain relaxed as they play the keys.
The instrument is almost entirely lefthanded because of its origins as a natural horn, which does not have valves.
In its 17th- and 18th-century form, it was a circular horn made from a single tube with a mouthpiece and flared bell.
During the mid-18th century, German horn player Anton Joseph Hampel developed the hand-stopping technique, which involved inserting a pad of cotton into the bell to change the pitch.
When horn players used their hands to partially or fully close the bell, the pitch was altered in such a way that scales could be produced over a wider range. Since most people were right-handed, this hand was kept in the bell. However, changing notes in this way does not give an even tone.
After developments in engineering and manufacturing produced a rapid and air-tight means of switching extra lengths of tubing into all horns and trumpets, the first horn with valves was invented in 1814 by Heinrich Stolzel, a German baroque composer. Valve designs changed over time and gave birth to the modern French horn (a misleading adjective, though the French may have been the first to introduce hunting horns to the orchestra).
However, some composers still call for ‘stopped horn’, an effect used to create a nasal timbre.
Modern horns are a quarter-tone sharp so that when the hand is inserted into the bell, the pitch is corrected.
Emilie Lamplough, Trowbridge, Wilts.
QUESTION Did the U.S lumber industry use giant log flumes to transport wood to sawmills?
FURTHER to the earlier answer, my wife and I travelled from Kamloops in British Columbia to Vancouver on the Rocky Mountaineer train.
For much of the second day, the train ran alongside the Fraser River, which, as it approaches the Pacific north of Vancouver, becomes ever wider due to being swelled by three merging rivers — the Bridge, Seton and Thomson.
This natural watercourse is used as a giant log flume to transport thousands of tons of lumber down to the coastal sawmills and timber product factories, and for export from the port of Vancouver.
The huge tree trunks are chained together to form large floating rafts that make their way down to the sea without any man-made power being required.
Some logs become detached and end up in the ocean. A thriving sub-industry has developed whereby locals with a boat and entrepreneurial spirit capture these rogue logs and tow them into harbour to claim salvage.
These logs can be so large that a house could be built out of just one.
Lyn Pask, Blackwood, Gwent.
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