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Bill Sherwood
Forums Junkie

Location:
Brisbane / Gold Coast
Registered:
May 2002

Re: jumbo jet 1/4 mile

Thu, 02 December 2004 04:12

river wrote on Thu, 02 December 2004 11:19

Hi,

It's not an easy question to answer 'cos there are many variables.

What model Jumbo are you talking about? The "Classic", which is the 747-100 or 747-200 models? Or are you referring to the 747-300 or 747-400 model? Or perhaps the stubby ultra-long range 747SP?

Is the aircraft loaded or empty? Also, temperature plays an important part 'cos the hotter the temp the longer it will take to accelerate. Furthermore, altitutde has a lot to do with it 'cos the higher the altitude (ie Mexico City) the thinner the air and the longer it will take. What engines... Rolls Royce, Pratt & Whitney or General Electric?

For example, I've taken off at as low as ~205 tonnes, right up to 377.8 tonnes. That's a big difference.
The most powerful engines I've flown were the Pratt & Whitney JT9D-7R4G2's at about 53,850 lbs of thrust.
The wussiest where the P&W JT9D-7A's, at about 43,000lbs .... Pathetic!

Quote:

Asking the speed time of a Jumbo is sorta like asking for the speed time of a Corolla. Which Corolla? Which engine, etc?

Bill would be the best to answer this. But I don't think it would be a very good time 'cos a Jumbo needs quite a few thousand feet of runway to get to take-off speed. Assuming take off speed is around 200-230kmh and its taken you 5,000 feet to get to that speed (ie about a mile) then at 1/4 mile you're not going to be going very fast.

If we're light we can get up to about 135kts or ~250km/h in around 1500 metres or so. (just guessing here)
If we're heavy, we run full power for about 45 seconds to get up to about 165kts or ~305k/h to lift-off, and we use over three kilometres of runway to do that. A four kilometre runway starts looking pretty short just before lift-off .... !

I'll try to get some numbers soem time with the G-Tec I have. It's not easy to do though, I have to steer the bloody thing with my left hand, my right hand is on the four throttles, etc ...

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