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Can a 747 go supersonic when there is a very heavy tail wind?
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No way, I don't even think it can break the sound barrier.
"The Director also sets the record straight on what would happen if oxygen masks were to drop from the ceiling: The passengers freak out with abandon, instead of continuing to chat amiably, as though lunch were being served, like they do on those in-flight safety videos."
-- The LA Times, in a review of 'Flightplan' -
Here is some information as I have read it in other forums and sites in the internet:
Firstly, supersonic is relative to the airspeed. A tail wind will increase it's speed relative to the ground, but it won't increase it's Mach speed.
Assuming that you could add enough power to propell a 747 to supersonic speeds (and it would require a tremendous amount of power), controllability would become a big issue. Wing design has a lot to do with it. The airflow over and around a 747's wings would loose their (relatively) smooth flow characteristics and lift would be distupted. Also the turbulence created near other parts of the aircraft would seriously restrict manoverability.
There have been some reported cases of non-SST airliners exceeding the speed of sound, none of them in level flight:
-a Chinese 744-SP spiralling downward over the Pacific ocean, then somehow regaining control and landing safely
-727 spiralling out of control, over the Great Lakes, only to regain control and landing safely
-a brand new DC-8 on a deliberate steep decent with full power during testing (this aircraft apparently still had acceptable handling characteristics while supersonic). The aircraft was subsequently delivered to CP as a brand new aircraft. Perhaps the world's first supersonic aircraft (in the early 60's)
That's about all I can think of right now.Comment
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Oh and I should add that there was some minor damage to the 747 and 727, flaps and gear doors, if I recall correctly.Comment
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A 747 can't exeed Mach 0.92 or so. If the wind is from behind, airspeed decreases, as it is measured looking at the (moving) outside air. If there is really a lot of wind, she could exceed 620 mph measured from the ground, but not in airspeed, so she won't break the sound barrier.
Grtz,
NickiComment
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I'm not quite clear about what is meant by going supersonic. does it mean the indicated airspeed exceeds the speed of sound? not the ground speed?
Is there a limit speed set for every aircrafts? Also, Is Mach 1 equals the speed of sound? what is the speed of sound in km/h?
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Mach 1 is the speed of sound. It equals 620 kts, 620 mph or 1220 kmh. This speed is obviously airspeed. If there is a 100 kts (= 100 mph) tailwind, and your airspeed is 600 kts, your groundspeed will be 700 kts, but you will not be flying supersonic, as it's the airspeed that counts for the Mach-calculation. Ground speed has absolotely nothing to do with Mach-speed.
Grtz,
NickiComment
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Any kind of plane can go supersonic if it falls far enough.
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I have been on UAL 772ER from ORD to FRA in summer 2001. They went 700MPH over the Atlantic Ocean.Comment
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Groundspeed yes, but not airspeed (and thus not more than Mach 1), or I wouldn't be talking to you...
Grtz,
NickiComment
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The 747 design will not tolerate supersonic flight. Aircraft designed for supersonic speeds have a characteristic pinched waist design to prevent the shock wave from separating the airflow away from the fuselage before it reaches the tail. Without this feature a normally designed plane transiting to supersonic will experience shock wave separation that will in effect prevent the airflow from reaching the tail and resulting in a loss of elevator control. This is sometimes referred to as "Mach Tuck." Some planes that operate just below Mach such as the Learjet have speed alarms so that as they gain speed during sustained cruise flight the pilot is warned before Mach Tuck occurs.
On the 747 a similar shock wave separation would occur along the wings somewhere between the root and wingtips. This is because the relatively long span wings have insufficient sweep for such speeds. The airflow separation would result in loss of aileron control in that case. The only way to overcome this would be to hinge the wings and change their sweep angle as the speed increased the same way it is done on the F-14 and FB-111. Boeing toyed with that idea on their proposed SST during the late 60's and early 70's but dropped the idea as impractical on such a large aircraft and altered the design for a fixed delta similar to the Concorde wing.
Tailwinds have no effect on an aircraft in cruise flight other than on groundspeed and track. The aircraft is moving along with the wind so a steady tailwind will not increase the aircraft's airspeed to exceed Mach. However, if a plane is cruising close to Mach and has a strong tailwind it is possible to have a groundspeed that exceeds Mach. In fact for aircraft cruising at Jet Stream altitudes this is not uncommon.Comment
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I flew a LH747 from FRA to China...1100km/hComment
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