Diego From Italy, joined Apr 2001, 135 posts, RR: 0 Posted (14 years 1 day 13 hours ago) and read 1066 times:
Hi folks I know that the questions I am about to ask is a kind of tricky but it is a matter that really bugs me.
As far as I have been told the decision speed represents the speed at which the takeoff procedure can be either aborted or carried on if a major failure occurs. Considering an airplane operating on a very long runway and experiencing an engine failure right before V1, the distance required to bring the airplane to a complete halt, measured from the beginning of the takeoff roll, is referred to as acceleration stop distance. If the engine failure occurs upon reaching the V1 and the pilot is committed to continue the takeoff procedure, the distance required to reach a safety altitude of 35ft agl is referred to as the acceleration go distance. The greater the V1 is, the longer is the acceleration stop distance since the airplane has achieved a greater speed and the time, and thus the runway length required to dissipate that kinetic energy, is longer, and the shorter is the acceleration go distance since the airplane has travelled a significant amount of time with all engines running. Considering that the V1 has to give the pilot an option, the runway length required has to be the greater between the acceleration stop distance and the acceration go distance. There is a V1 though that meets both the requirements corrisponding to the speed at which the curves of the two distances meet and it is called basic V1 . If the runway available is longer than the one required for the V1 basic, the pilot can elect to go for a gtreater V1 called runway V1, faster than the basic one. Generally speaking the basic V1 is preferred rather than the runway V1 since it is considere to be more dangerous aborting a high speed takeoff rather than continueing the procedure and therefore picking up a slower V1 reduces the chances that the failure occurs at a point where the take off has to be called out.
Now here are the questions: how are the basic V1 and the runway one realeted to the weight of the aircraft and to the power output? What is the preferred flap setting considering that a greater flap deflection results into a smaller V1 but in a lower climb gradient, taking into account the limits set by the second segment of the takeoff procedure requiring a minimum climb gradient of 2.4%, while a bigger flap setting increases the vertical speed but increases the V1 too?
AAR90 From United States of America, joined Jan 2000, 3531 posts, RR: 44
Reply 2, posted (14 years 1 day 9 hours ago) and read 1020 times:
>how are the basic V1 and the runway one realeted to
>the weight of the aircraft and to the power output?
As weight increases, rate of accelleration decreases... i.e. takes longer and uses more runway to get to accellerate therefore causing V1 to decrease. As power output is decreases, same thing happens with same resultant decrease in V1.
>What is the preferred flap setting considering that a greater flap
>deflection results into a smaller V1 but in a lower climb gradient,
Airplane specific. Need to consult performance figures for the aircraft you are contemplating.
>...taking into account the limits set by the second segment of the
>takeoff procedure requiring a minimum climb gradient of 2.4%, while a
>bigger flap setting increases the vertical speed but increases the V1 too?
Even more aircraft specific. Most aircraft with a large takeoff or landing gross weight range also have a relatively large flap setting range they are certified for.
The basics are obvious, if looking for specifics, you need to consult operating manuals in detail.
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