Take off speeds

Sorry if this is in the wrong sections - Mods please move if so.

Why is it that I can be travelling the same route at the same time using the same equipment but sometimes I have been stuck to the back of the seat with the take off force whilst other times praying we don't run out of runway as the plane appears to be moving so slow???

Is the take off speed down to the Captian or ATC?

Thanks

[Decker]

I have no clue - so I'll guess cargo weight.

Oh good one ... the amount of lift a plane requires to take off is relevant to its weight. So Decker has a point, high cargo weight means more lift required, as does a long journey and therefore lots of fuel. Since lift is a factor of speed of and airflow over the wing, among other things and I'm not an expert at all, then I should think that the lift required for take off is a combination of the settings of the wing at take off (angle, use of flaps etc.) and the speed of the plane itself. 'Logic' leads me to concur that if the plane is heavy or the pilot wants to say because the runway is shorter, a faster speed is necessary or permissable [:p].

Coincidentally, I too have noticed this, especially of late when flying 343s the take off speed seems to be faster than I recall in the past ...

[mcmbenjamin]

There are a few factors: mass of aircraft, environment (air temperature, humidity, and elevation), runway surface condition (wet/dry, concrete/asphalt), aircraft configuration (flap settings, etc) and other things like climb out velocity, wind direction and velocity on the runway.

Thanks for all your replies.

I first noticed slow take off speeds flying A340 (3 and 6) with both VS and Swiss. In both instances, the flights were to Tokyo so I can imagine the extra fuel weight alone may have required a longer and slower take off. Also didn't know whether fuel conservation or noise abatement was a consideration (especially in Zurich).

Recent flights to Dubai have differed greatly. In May when departing DXB, we were literally stuck to our seats Ð fastest take off I can ever recall. More recently (same flight, similar pax loads) it was considerably slower.

[Scrooge]

Kind of depends on a lot of factors as Ben said...however to give you an idea roughly..

744 = 155 knts 180 mph
346 = 155 knts 180 mph

So as you can see the two main aircraft in VS's fleet have about the same speed, it is mostly just a case of how long it takes to get to that speed.

Of not the Concorde had a take off speed in excess of 220 mph.

Originally posted by slinky09
Oh good one ... the amount of lift a plane requires to take off is relevant to its weight. So Decker has a point, high cargo weight means more lift required, as does a long journey and therefore lots of fuel. Since lift is a factor of speed of and airflow over the wing, among other things and I'm not an expert at all, then I should think that the lift required for take off is a combination of the settings of the wing at take off (angle, use of flaps etc.) and the speed of the plane itself. 'Logic' leads me to concur that if the plane is heavy or the pilot wants to say because the runway is shorter, a faster speed is necessary or permissable [:p].

You may not be an expert, but you got most of it. The one major element missing is wind speed. My little plane takes off at 55 knots, but if I have a direct headwind of 10 knots, my ground speed only needs to be 45 knots to get in the air. Little wind and a full plane, be prepared to eat up that runway!

You may have seen this before, but here is a great link to a 747 taking off at Bournmouth.

I am not an expert either but I think I'm right in saying that the amount of take-off thrust set by the pilot varies(maybe due to noise abatement Etc). This will abviuosly have an effect on the take-off run.
All the other comments on high lift devices(flaps/slats Etc)wind speed and take-off weights are also significant factors.

Regards

NOC

One of the reasons is fuel, less thrust obviously less fuel. Depending on weight, runway length etc, the take-off thrust will vary. On the A340 you either have a 'flex' or 'TOGA' takeoff (TOGA being take-off, go around).

Could also depend on the status of the aircraft. Certain defered defects may also require use of TOGA (i.e a brake unit that is inoperative).

Air density is also a major issue, especially at this time of year. High density = less lift and lower engine performance. Anyone taking off from JFK this week would probably experience longer take-off rolls due to air density. My local airport is 99 feet above sea level, but the air density meant aircraft were operating at the equivalent of 1,900 feet.

Very interesting, thank you all for your comments

Interesting link here too...

http://uk.answers.yahoo.com/question/in ... 332AAMwjRC