question about V1

[PorcoRosso]

I'm a bit confused about V1
I've done my perf A few months ago, and if I remember my course, V1 is depending of many factors, including the runway length.
Went to do my MCC;there an instructor gave the example of an aircraft accepting a Tak-off clearance from an intersection therefore reducing runway available. He told us that V1 was unchanged as it mainly depends on the weight of the A/C ?????
I think I missed something, what is the truth or the logical explanation ?

------------------
Flying is not dangerous, crashing is

[quid]

The instructor is correct. Most airlines use a "balanced field" concept to determine t/o data. The V speeds (with a few minor adjustments for wind and slope) will remain the same no matter what the runway length is. The gross weight for t/o will be limited on the shorter runways.

There have been a few very complete discussions here on that subject here on PPrune over the last few months. You may want to go back and review them.

------------------

[m&v]

V1 is the accelerate/stop distance.Speed to decide which on"limiting" runways(always assumed).With Heavier weights, V1 higher(engine out go=stopping distance)once the failure is recognized after Vef.Runway annalysis charts predicated on set runway distance,should a runway be changed the crew are required to confirm sufficient runway exists!!!!Remember"flex/reduced"thrust utilizes all the runway as stipulated on the Chart.The higher the weights the higher the V1's to meet the stop or go.

[mutt]

Vspeeds are based on WEIGHT, weight is based on runway length, climb limit, obstacles, brake limits.

If you use an insection for takeoff, the length gets shorter, the obstacles get nearer and the weight changes.

M&V VEF is 1 second prior to V1, if you havent recognized the engine failure at this point and started to react you are going off the end of the runway!

How many of you use a line up distance at the start of the runway?

Mutt

[m&v]

Vef is generally about one second prior to V1,in some three engine cases it could be as high as 3.5seconds to fail the centre engine/recognition(B727/dc10/l1011
Cheers..

[PorcoRosso]

Thank you for your explanation guys.
I accept the balanced field one, and I also understand that the range of V1 you can get in some situations, allow you to accept an intersection T.off.
But I understand better Mutt's word. it seems obvious to me that if you change one factor (weight or distance available) you screw up your nice calculations.
I guess am also gonna ask to alex whittingam what is his point about that.

Thank you all

------------------
Flying is not dangerous, crashing is

[Fat Boy Sim]

Porco, A lot of the above is true. However, from a practical point of view, if you do not have the figures for the intersection, then you cannot schedule the take off.In my company that would result in lots of tea and bikkies with the boss.

[quid]

PorcoRosso-

It's not the *range* of V1 that allows the t/o, it's the t/o *weight* that allows the takeoff. Unless your carrier allows a range of V speeds from which to choose (a few do, but that's the subject for another thread), then the V1 for a given weight will be the same for a 6000' runway as a 12,000' runway.

------------------

[Roadtrip]

V1 is not necessarily balanced field length when operating reduced takeoff thrust. Operators and manufacturers often limit reduced thrust to a maximum of 25% reduction resulting a different V1 than that of a pure balanced field.

[SKYYACHT]

V1 may also be increased or decreased (within certain parameters) in order to enable clearance of either close-in or further out obstacles. This is normally calculated by performance engineers before the figures are published in the "balanced Field" tables used in many Perf Manuals.

Tailwinds