Why do planes take off down the centre line?

Why do planes take off down the centre line?

Author
Discussion

bitchstewie

Original Poster:

55,089 posts

217 months

Saturday 20th January
quotequote all
I feel I'm setting myself up to look stupid here but having watched a lot of cockpit videos on YouTube something that's always puzzled me is why takeoff seems to be exactly down the centre line so it looks from the cockpit vids like the airplane is getting quite a shaking from the front gear going over all the centre lights.

Seems a bit like deliberately driving down a row of cats eyes at high speed and the accompanying bumps unless the videos are exaggerating the effect?

normalbloke

7,703 posts

226 months

Saturday 20th January
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The pilots like to monitor the rate the cats eyes pass under the front wheel, as an additional positive indicator of rate of acceleration….

Jimbo.

4,039 posts

196 months

Saturday 20th January
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A good visual indicator of how far left or right the aircraft may be drifting?

Boozy

2,389 posts

226 months

Saturday 20th January
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Because it’s the middle and planes are quite big?

Bill

54,200 posts

262 months

Saturday 20th January
quotequote all
It's just a habit from the old paper licence where it says tear along the dotted line.






Sorry...getmecoat

greygoose

8,636 posts

202 months

Saturday 20th January
quotequote all
Bill said:
It's just a habit from the old paper licence where it says tear along the dotted line.


Sorry...getmecoat
hehe



mike_e

588 posts

270 months

Saturday 20th January
quotequote all
Because the wheels under the wings are closer to the edge of the runway than the nosewheel, and crosswinds can make the plane veer to one side.


Prawo Jazdy

4,974 posts

221 months

Saturday 20th January
quotequote all
If your directional control is impacted by (as said above) wind, “contamination” on the runway, or an engine failure on a twin (or other thrust asymmetry), you’ll benefit from having as much room as possible to sort it out before running off the edge.

Some airports like Mykonos have narrower runways than the fairly standard 45 metres, so flying there requires extra training to be completed.

Motorman74

432 posts

28 months

Saturday 20th January
quotequote all
Surely because it's good practice to be in the centre of the runway, so if something unexpected happens, you have the maximum available space on both sides to keep it on the tarmac

surveyor

18,138 posts

191 months

Saturday 20th January
quotequote all
They should not be exactly in the centre...

https://aviation.stackexchange.com/questions/95794...

Leon R

3,331 posts

103 months

Saturday 20th January
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Surely if you were right on the centre line the nose wheels would be either side of the lights.

In most aircraft anyway.

Countdown

41,978 posts

203 months

Saturday 20th January
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For those suggesting the planes are quite big , surely 6 inches either side of the centreline still leaves a fair amount of safety gap to either side ?

Terminator X

16,289 posts

211 months

Saturday 20th January
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2 wheels isn't it so if exactly mid point the wheels would be either side?



TX.

Mr_J

425 posts

54 months

Saturday 20th January
quotequote all
surveyor said:
They should not be exactly in the centre...

https://aviation.stackexchange.com/questions/95794...
We put them in the centre.

IanH755

1,998 posts

127 months

Saturday 20th January
quotequote all
The centreline lights are actually used as a form of braille for the few blind pilots on a diversity hire, so when the "bumps" get closer together the pilot knows to lift the nose and take-off. Landing was a whole lot trickier until they allowed guide dogs to be used, now the pilot can just feel when the lead goes slack to know they're close to the ground.

True story.

smile

texaxile

3,386 posts

157 months

Sunday 21st January
quotequote all
IanH755 said:
The centreline lights are actually used as a form of braille for the few blind pilots on a diversity hire, so when the "bumps" get closer together the pilot knows to lift the nose and take-off. Landing was a whole lot trickier until they allowed guide dogs to be used, now the pilot can just feel when the lead goes slack to know they're close to the ground.

True story.

smile
Have a biglaughbiglaughbiglaughbiglaugh

Reminds me of that old joke about the blind parachutist...

Cl4rkyPH

272 posts

54 months

Sunday 21st January
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Going over the lights doesn’t cause them or the plane any harm, nor any discomfort to passengers (other than an already abrupt/loud part of the journey). So it makes perfect sense to train pilots to position the aircraft right down the middle.

If pilots were taught to align the aircraft “just to the side of the centreline” it would then create a grey area e.g “how far can I stray from the middle?” As other posters have said above, straying from the middle is not ideal for many reasons.

As such, the centreline serves the best point for pilots to align with.

bitchstewie

Original Poster:

55,089 posts

217 months

Sunday 21st January
quotequote all
Thanks all.

Honestly when you watch some of the videos the sound of the bumps seems very audible to the point where if it was a car you'd try not to go over them.

If it's as simple as other than sounding a bit noisy they don't do any damage that's fair enough and perhaps I was overthinking it smile

normalbloke

7,703 posts

226 months

Sunday 21st January
quotequote all
You want to see the efforts a B52 goes to, trying to avoid them…

Eric Mc

122,854 posts

272 months

Sunday 21st January
quotequote all
The Trident airliner's nose wheel was offset so keeping to the middle of the runway ensured that the nose wheel didn't hit the lights. That wasn't the reason the nose wheel was offset but it was a consequence of the design.