Very light weights, runway length required?

[911slf]

This is in the context of the Boeing Dreamlifter that landed at the wrong airport. As it's idle curiosity I did not want to post in the professionals' thread.

If I have got it right, a take off with full power at half maximum take off weight should require only a quarter the runway length of a maximum weight take off.

Based on a 30% reduction in take off speed, * a 30% reduction in time to accelerate if acceleration were the same, but acceleration is doubled (0.7*0.7*0.5). I think a heavy long range aircraft can probably take off at half weight if carrying no cargo and minimal fuel. Are my arithmetic assumptions justified? Would there be other considerations such as a need for reduced power to maintain lateral control in the event of an engine failure?

This would imply that if there were a need to get a 747 off a 3000 foot runway (perhaps a longer runway that had suffered damage in war or earthquake), it should not be impossible. So the TV people saying it was a dangerous takeoff were talking nonsense?

Not to understate the seriousness of getting into such a position in the first place.

[Wycombe]

Following the embarrassment of getting into the situation in the first place, I would be fairly sure that Atlas will have been very careful to ensure the take-off was (legally and operationally) possible and safe, what with the World's media watching.

They simply (you would like to think) would not have entertained a "dangerous takeoff".

[DaveReidUK]

So the TV people saying it was a dangerous takeoff were talking nonsense?

Unless the media has access to the 747 LCF's Flight Manual, anything they say about the aircraft's runway performance can be taken with a large pinch of salt.

[Trinity 09L]

Tug reverses aircraft to the start of runway, 10/15 degree flaps, light fuel load, stand on the brakes, power up, check tail skid plate is good, brakes off and go - & they would have taken bets on the take off run distance.
Did they do a overhead join & circuit to get in position for the right airfield this time. :rolleyes:

[Dont Hang Up]

If I have got it right, a take off with full power at half maximum take off weight should require only a quarter the runway length of a maximum weight take off.

Based on a 30% reduction in take off speed, * a 30% reduction in time to accelerate if acceleration were the same, but acceleration is doubled (0.7*0.7*0.5). I think a heavy long range aircraft can probably take off at half weight if carrying no cargo and minimal fuel. Are my arithmetic assumptions justified? Would there be other considerations such as a need for reduced power to maintain lateral control in the event of an engine failure?

This would imply that if there were a need to get a 747 off a 3000 foot runway (perhaps a longer runway that had suffered damage in war or earthquake), it should not be impossible. So the TV people saying it was a dangerous takeoff were talking nonsense?

911slf the important words in your post are "engine failure". The distance to stop after a high speed reject adds a substantial margin. Having said that (and acknowledging I am no expert), I find it hard to believe that 6100ft is that big a deal for an unladen 747 with minimum fuel.

[Airclues]

I have flown several 747-400's from Cambridge to Heathrow. From memory the TORA (Take-Off Run Available) is about 6200ft at Cambridge. On each occasion we were airborne in less than half the runway length.