Ground Speed
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Ground Speed
Returning from LAS on Sunday/Monday, on V044, was interested to see indicated ground speed of 650mph on IFE seat-back screen display. Is this close to maximum possible? Aircraft was 747-400.
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Taking a cruising speed of M0.84 and OAT of -55 celsius gives a true airspeed of 559 statute miles per hour. Hence being in a jetstream with a tailwind component of only 90 mph would give you a groundspeed of 650. Perfectly feasible.
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This one is for Greaser....just a query...however i bow to your superior knowledge due to the fact that I only have a PPL(A). Isn't an OAT of -55 impossible due to the fact that the temp becomes constant at -36.5 or something....or am i digging a big big hole
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Thanks guys, glad it didn't get too technical! I forgot to say that the altitude was 37K, but I didn't record the outside temperature!
Does anyone have any idea of the greatest groundspeed ever registered for a commercial aircraft?
Does anyone have any idea of the greatest groundspeed ever registered for a commercial aircraft?
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Flying low is correct, -56.5 is the ISA temp minimum at the tropopause, however it is feasible that the temperature could be below this. The fastest true airspeed though for a given Mach number will be at higher air temperatures where the speed of sound is greater than in cooler temperatures.
Why do it if it's not fun?
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newswatcher,
Don't know the numbers, but I'd expect the greatest groundspeed for a commercial aircraft would have to have been achieved by Concorde..... Certainly more than 650mph!
FFF
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Don't know the numbers, but I'd expect the greatest groundspeed for a commercial aircraft would have to have been achieved by Concorde..... Certainly more than 650mph!
FFF
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newswatcher
INS/IRS read-outs on the flight deck are generally displayed in knots, and personally speaking, I wouldn’t place too much reliance on the accuracy of the mph/kph conversions displayed on the cabin IFE screens.
Concorde cruise-climbs at M2.0, so at typical altitudes of say around FL580, and assuming ISA temperatures, this would broadly equate to a ground speed of 1,150 kts (1,320 mph) in still air.
At these altitudes, the winds tend to be light - as the strong jet streams that subsonic aircraft sometimes experience tend to die off above about FL450 - so we don’t often see indicated ground speeds above 1,200 kts (1,380 mph).
I’ve seen a ground speed of 1,218 kts (1,400 mph) a few times, but never, as yet, 1,260 kts (1,450 mph).
We suspect that the TU 144, which was originally aiming for M2.35 (1,550 mph), actually cruised nearer to M2.05, which would have given it a ground speed of roughly 1,350 mph in still air, probably still fast enough, just, to take the title of fastest commercial? aircraft.
INS/IRS read-outs on the flight deck are generally displayed in knots, and personally speaking, I wouldn’t place too much reliance on the accuracy of the mph/kph conversions displayed on the cabin IFE screens.
Concorde cruise-climbs at M2.0, so at typical altitudes of say around FL580, and assuming ISA temperatures, this would broadly equate to a ground speed of 1,150 kts (1,320 mph) in still air.
At these altitudes, the winds tend to be light - as the strong jet streams that subsonic aircraft sometimes experience tend to die off above about FL450 - so we don’t often see indicated ground speeds above 1,200 kts (1,380 mph).
I’ve seen a ground speed of 1,218 kts (1,400 mph) a few times, but never, as yet, 1,260 kts (1,450 mph).
We suspect that the TU 144, which was originally aiming for M2.35 (1,550 mph), actually cruised nearer to M2.05, which would have given it a ground speed of roughly 1,350 mph in still air, probably still fast enough, just, to take the title of fastest commercial? aircraft.
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" I wouldn’t place too much reliance on the accuracy of the mph/kph conversions displayed on the cabin IFE screens."
Any particular reason why not? I'm sure your average pocket calculator wouldn't have any problems at all with this conversion.... and the IFE map systems get their speed data directly from the INS's, IRS's or FMC's (on later versions), so the source itself is unlikely to be inaccurate.
The Airshow will hold a value for a particular (short) time, rather than constantly updating it. This would produce the greatest source of error (with the aircraft rapidly decelerating/accelerating).
Rgds.
Q.
Any particular reason why not? I'm sure your average pocket calculator wouldn't have any problems at all with this conversion.... and the IFE map systems get their speed data directly from the INS's, IRS's or FMC's (on later versions), so the source itself is unlikely to be inaccurate.
The Airshow will hold a value for a particular (short) time, rather than constantly updating it. This would produce the greatest source of error (with the aircraft rapidly decelerating/accelerating).
Rgds.
Q.
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Bellorophan,
Are you flight crew on concorde ? If you are could you tell me when you bring the nose down for landing ? Is it on the approach checks or finals checks and below which speed does this happen at ? (from a mere pleb who flies the A320 !!)
Are you flight crew on concorde ? If you are could you tell me when you bring the nose down for landing ? Is it on the approach checks or finals checks and below which speed does this happen at ? (from a mere pleb who flies the A320 !!)
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-56.5 is the ISA temp minimum at the tropopause, however it is feasible that the temperature could be below this.
http://www.refdesk.com/102401fd.html
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This is not a fast groundspeed. On aircraft flying in jetstreams a ground speed over 700kts can easily occur. While not common it happens often.
Temperature often goes to -70deg. The isothermal nominal temp is akin to all land temps are 15deg and the lapse rate is-1.98.
Theory fellas, theory.
Aircraft often have to descend to warmer altitude to prevent the fuel freezing.
Temperature often goes to -70deg. The isothermal nominal temp is akin to all land temps are 15deg and the lapse rate is-1.98.
Theory fellas, theory.
Aircraft often have to descend to warmer altitude to prevent the fuel freezing.
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...the lowest recorded OAT was on an Antarctic Mountain (11,000ft), -90C. Athough I suspect that was due in part to horrendous windchill.
easondown
On Concorde, when reducing speed to 250 kts or less, the visor is selected down when decelerating through 270 kts, and, once locked down, the nose is then lowered to 5°, which is also the nose position for take-off. These actions are checked in the Approach Checklist.
The nose is further lowered to 12½°, the landing position, once the landing gear has locked down, and these actions are checked in the Landing Checklist.
The visor must be down, and the nose at 5° (or more), when flying below 250 kts.
In many photographs of Concorde at low altitude, gear down, the small but noticeable difference in the nose position is often the only way to tell whether she is taking-off or landing.
QAVION
I should have said I don't place too much reliance on the accuracy of any information on cabin IFE screens!
Partly because, as you say, the information updates periodically rather than continuously, partly because I regularly see discrepancies between the flight deck repeater of the cabin IFE information and what is actually happening, and partly because of some of the entertaining information I've seen displayed when flying as a passenger.
I would agree that the latest generation of cabin IFE displays are a marked improvement on earlier versions.
Regards
Bellerophon
On Concorde, when reducing speed to 250 kts or less, the visor is selected down when decelerating through 270 kts, and, once locked down, the nose is then lowered to 5°, which is also the nose position for take-off. These actions are checked in the Approach Checklist.
The nose is further lowered to 12½°, the landing position, once the landing gear has locked down, and these actions are checked in the Landing Checklist.
The visor must be down, and the nose at 5° (or more), when flying below 250 kts.
In many photographs of Concorde at low altitude, gear down, the small but noticeable difference in the nose position is often the only way to tell whether she is taking-off or landing.
QAVION
I should have said I don't place too much reliance on the accuracy of any information on cabin IFE screens!
Partly because, as you say, the information updates periodically rather than continuously, partly because I regularly see discrepancies between the flight deck repeater of the cabin IFE information and what is actually happening, and partly because of some of the entertaining information I've seen displayed when flying as a passenger.
I would agree that the latest generation of cabin IFE displays are a marked improvement on earlier versions.
Regards
Bellerophon
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maximum wind speed
FFF, guess I "forgot" about the Concorde!
Further research indicates that at that sort of altitude(37k), the jet stream seldom exceeds 175 knots, but I have yet to find the maximum recorded. Given that the typical cruising speed of the 747-400 is given as 492 knots(Boeing site), this would give a theoretical maximum ground speed of about 667 knots(767mph), so I guess I had a way to go!
FYI, the maximum recorded wind speed on a land-based recorder(Mount Washington) stands at just over 200 knots.
Further research indicates that at that sort of altitude(37k), the jet stream seldom exceeds 175 knots, but I have yet to find the maximum recorded. Given that the typical cruising speed of the 747-400 is given as 492 knots(Boeing site), this would give a theoretical maximum ground speed of about 667 knots(767mph), so I guess I had a way to go!
FYI, the maximum recorded wind speed on a land-based recorder(Mount Washington) stands at just over 200 knots.
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You realise windchill only affects heat loss not temperature?
Yes. None of the references to -90C stated how the figure was arrived at. Since this temperature is considerably lower than other 'records' I have doubts as to its accuracy, hence my conjecture that it might have been a windchill 'reading'.
Brass monkeys either way.
Yes. None of the references to -90C stated how the figure was arrived at. Since this temperature is considerably lower than other 'records' I have doubts as to its accuracy, hence my conjecture that it might have been a windchill 'reading'.
Brass monkeys either way.