- Email: [email protected]
Think again
THE LAST WORD Plane thinking What is the lowest speed a full-size fixed-wing aircraft can fly without stalling? (Continued)
n A competent answer would have been 40 kilometres per hour. There is a class of light aircraft known as microlights that stall at speeds slower than 43 kpm. Some specialist aircraft can fly slower, but at the expense of a poor top speed. This is because the main limit to minimum speed is the weight per unit area of wing surface; called the wing loading. Trailing edge flaps, leading edge slats and slots can assist a little, but the complexity and weight of such devices may degrade top speed while only reducing stall speed by around 10 per cent and
“Microlight aircraft will stall when flying at speeds slower than 43 kilometres per hour” increasing costs considerably. An extreme example would be the aircraft that won the Kremer prize for crewed flight after being pedalled across the English Channel at a cruise speed of less than 30 kilometres per hour. John MacDonald London, UK While we were thinking mainly of commercial or military aircraft, we take John MacDonald’s point that our question was – because of reasons of space – ambiguous. As John says, on 12 June 1979, the
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
Last words past and present, plus questions, at last-word.com
Kremer prizewinning Gossamer Albatross completed the 35.8-kilometre crossing of the English Channel in 2 hours 49 minutes, achieving a top speed of 29 kpm and an average altitude of 1.5 metres. It was piloted by amateur cyclist Bryan Allen, whose leg power drove its large twobladed propellor. Fantastic – Ed n The lowest stalling speed I
know for a powered light aircraft is 50 kilometres per hour for the Fieseler Fi 156 Storch, a German liaison aircraft from the second world war. The Storch has a low wing loading and is fitted with full-span leading-edge slats, Fowler flaps and ailerons that droop with the flaps. These all combine to improve airflow over the aircraft’s wing and prevent airflow separation over the rear part of the wing. This contributes to its low stalling speed and allows the aircraft to take off from a runway only 45 metres long and land in just 18 metres. Thanks to these high-lift devices, at full throttle a Storch can be flown at less than its normal stalling speed. Its nose is well up, so the engine thrust is helping to support the aircraft. I’ve read that it could stay airborne at 35 kph when flown in this fashion. Martin Gregorie Harlow, Essex, UK n The lowest speed at which a plane can remain airborne is stationary, as in Harrier jump jets
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
during vertical take-off. Here, the lift is provided by Newtonian reactive force, but this is achievable only when planes are not fully laden. In conventional flight, where a wing’s lower surface encounters the air ahead of it obliquely and the airflow leaves the wing’s rear obliquely, the thrust required to provide sufficient downforce far exceeds engine capabilities. At the other extreme, the lowest reported airspeed a Boeing 747 can achieve without dropping as dead weight is 154 kph – if minimally laden on approach for landing. If approaching into a headwind, for every kph the headwind increases, the plan’s airspeed can drop by an equivalent amount and still stay airborne. Len Winokur Leeds, UK
Squeaky cheese Why does halloumi cheese squeak against your teeth as you eat it?
n This is an example of the stickslip phenomenon. The cheese is rubbery and as your teeth begin to squeeze it, the halloumi deforms with increasing resistance until it loses its grip and snaps back to something like its original shape. At the point where the slipping stops it regains its grip and the process repeats, commonly at a frequency near 1000 hertz, give or take an octave or two. The vibration produces a squeal of corresponding frequencies that may vary with the
circumstances; such as whether the cheese has oil on it. Squeaky halloumi is enough to make some people’s toes curl, like fingernails dragged down a blackboard. This is because such sounds often warn of injury – a broken bone grating – or an unpleasant sensation, such as sand in your teeth, or stone abrading fingernails. Probably long before our ancestors evolved into apes, they developed an inherited distaste for such noises and the associated sensations. It was likely an evolutionary adaptation to their way of life; those who did not respond to the signals tended to have shorter and less productive lifespans. Jon Richfield Somerset West, South Africa
This week’s questions Think again
My 14-year-old daughter asked me what language people who are deaf from birth think in? Does anybody know how this cognitive feature develops in deaf people? Mike Dunn Sherborne, Dorset, UK Heated debate
High blood pressure can be reduced by taking a hot bath, but why does one’s pulse quicken when relaxing this way? And is high blood pressure related to a faster pulse in any way? R. Hazelwood Guildford, Surrey, UK
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans
n A competent answer would have been 40 kilometres per hour. There is a class of light aircraft known as microlights that stall at speeds slower than 43 kpm. Some specialist aircraft can fly slower, but at the expense of a poor top speed. This is because the main limit to minimum speed is the weight per unit area of wing surface; called the wing loading. Trailing edge flaps, leading edge slats and slots can assist a little, but the complexity and weight of such devices may degrade top speed while only reducing stall speed by around 10 per cent and
“Microlight aircraft will stall when flying at speeds slower than 43 kilometres per hour” increasing costs considerably. An extreme example would be the aircraft that won the Kremer prize for crewed flight after being pedalled across the English Channel at a cruise speed of less than 30 kilometres per hour. John MacDonald London, UK While we were thinking mainly of commercial or military aircraft, we take John MacDonald’s point that our question was – because of reasons of space – ambiguous. As John says, on 12 June 1979, the
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
Last words past and present, plus questions, at last-word.com
Kremer prizewinning Gossamer Albatross completed the 35.8-kilometre crossing of the English Channel in 2 hours 49 minutes, achieving a top speed of 29 kpm and an average altitude of 1.5 metres. It was piloted by amateur cyclist Bryan Allen, whose leg power drove its large twobladed propellor. Fantastic – Ed n The lowest stalling speed I
know for a powered light aircraft is 50 kilometres per hour for the Fieseler Fi 156 Storch, a German liaison aircraft from the second world war. The Storch has a low wing loading and is fitted with full-span leading-edge slats, Fowler flaps and ailerons that droop with the flaps. These all combine to improve airflow over the aircraft’s wing and prevent airflow separation over the rear part of the wing. This contributes to its low stalling speed and allows the aircraft to take off from a runway only 45 metres long and land in just 18 metres. Thanks to these high-lift devices, at full throttle a Storch can be flown at less than its normal stalling speed. Its nose is well up, so the engine thrust is helping to support the aircraft. I’ve read that it could stay airborne at 35 kph when flown in this fashion. Martin Gregorie Harlow, Essex, UK n The lowest speed at which a plane can remain airborne is stationary, as in Harrier jump jets
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
during vertical take-off. Here, the lift is provided by Newtonian reactive force, but this is achievable only when planes are not fully laden. In conventional flight, where a wing’s lower surface encounters the air ahead of it obliquely and the airflow leaves the wing’s rear obliquely, the thrust required to provide sufficient downforce far exceeds engine capabilities. At the other extreme, the lowest reported airspeed a Boeing 747 can achieve without dropping as dead weight is 154 kph – if minimally laden on approach for landing. If approaching into a headwind, for every kph the headwind increases, the plan’s airspeed can drop by an equivalent amount and still stay airborne. Len Winokur Leeds, UK
Squeaky cheese Why does halloumi cheese squeak against your teeth as you eat it?
n This is an example of the stickslip phenomenon. The cheese is rubbery and as your teeth begin to squeeze it, the halloumi deforms with increasing resistance until it loses its grip and snaps back to something like its original shape. At the point where the slipping stops it regains its grip and the process repeats, commonly at a frequency near 1000 hertz, give or take an octave or two. The vibration produces a squeal of corresponding frequencies that may vary with the
circumstances; such as whether the cheese has oil on it. Squeaky halloumi is enough to make some people’s toes curl, like fingernails dragged down a blackboard. This is because such sounds often warn of injury – a broken bone grating – or an unpleasant sensation, such as sand in your teeth, or stone abrading fingernails. Probably long before our ancestors evolved into apes, they developed an inherited distaste for such noises and the associated sensations. It was likely an evolutionary adaptation to their way of life; those who did not respond to the signals tended to have shorter and less productive lifespans. Jon Richfield Somerset West, South Africa
This week’s questions Think again
My 14-year-old daughter asked me what language people who are deaf from birth think in? Does anybody know how this cognitive feature develops in deaf people? Mike Dunn Sherborne, Dorset, UK Heated debate
High blood pressure can be reduced by taking a hot bath, but why does one’s pulse quicken when relaxing this way? And is high blood pressure related to a faster pulse in any way? R. Hazelwood Guildford, Surrey, UK
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans