kdoner

Had a test today in class... ended up being a huge debate...

Q: What factors affect V1?
a. Density Altitude
b. Weight
c. Tailwind
d. All of the above
e. A and B only

Weight:
I understand that Weight affects V1... no clarification needed on that one...

Density Altitude:
I would like somebody to explain more on why Density altitude affects V1

My understanding is...
The higher the density altitude... the more your performance goes down. resulting in a longer ground roll.

So if V1 = Vr on a standard day, and your accelerate-stop distance = length of runway. Any increase in density altitude will lengthen the distance to acquire V1, resulting in over-running the runway while braking. so you must lower V1 to meet accelerate stop.

Tailwind:
This is the BIG ONE everybody was complaining about...

Same thing as density altitude, but instead of performance being the cause of the extended ground roll... it's the tailwind that causes the extended ground roll.

And on those same circumstances : V1=Vr and accelerate-stop = length of runway.

so the BIG question.. Does a tailwind affect V1. (5-10 kts prolly not that much, but nonetheless does it affect it at all???)

Cubdriver

I am not an expert on V speeds but I believe V1 is the airspeed at which the decision to fly or abort must be made due primarily to runway length, although it involves several important things. V1 is not an actual takeoff airspeed however it is used to allow pilots to decide whether or not to continue a take off. Since a takeoff can take vastly more runway if there is a tailwind, or vastly less if there is a headwind, it has an effect on V1 just as if the runway were shorter or longer.

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Ewfflyer

Basically, yes

It's Take-Off Decision Speed. If you have any engine failure before this point, you abort, any problem after, it's actually safer to continue the take-off. If you were hired by an operator, they'd give you plenty of V1 cuts in the sim to prepare you!

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Ewfflyer

It really depends on the operators V1 charts. I'll dig out my 727 manuals from college and see what, if any, reference it has to wind-component. In the 5-10kt range, I doubt it has any consequence, and most operators have a limitation of no more than 10kts tailwind component for T/o or landing.

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kdoner

I understand that nobody takes off with more than 10kts of tailwind....

BUT DOES IT AFFECT IT AT ALL???

10KTS 20KTS 30 KTS 40KTS??

Cubdriver

Of course it does. Most ops manuals would make the issue moot since tailwinds reduce takeoff performance to a point it is not a safe idea. And since a tailwind factor increases the amount of runway required to take off, V1 must tell the pilot early enough in his roll that hey, you are near the point of no return here under these wind- weight- density conditions. V1 is a rate-based dividing line established to warn the pilot at what point he or she can no longer safely stop the airplane on the remaining runway. Tailwind greatly reduces the speed used as V1 because the airplane is going to take up more of the field to get to a speed where it could actually takeoff. Pilot needs to decide whether to stop or continue much earlier than if there were an abundance of runway. Maybe your question in the class was intended to be a thought provoker, since tailwinds are not normally a big player due to ops manuals prohibiting takeoffs under tailwind conditions.

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HSLD

Does tailwind affect the speed - no. 140kts is 140kts.

However, the tailwind most certainly affects balanced field length which is why you calculate a V1 in the first place. With a tailwind, the jet will require more runway to reach V1, and depending on the velocity of the tailwind may not be able to meet the definition of V1.

If the question is asking about the speed V1, then I'd pick "a". If it's a practical performance problem and you want to determine balanced field, then "d" all of the above.

Disclaimer: It's been a long long time since I sat in a classroom.

Wheels up

Most civil airline takeoff data calculations are based upon balanced field length. In that case, weight must be subtracted from the assumed value to compensate for a tailwind, and yes, most companies restrict tailwind to 10 knots, while V1 remains the same.

Most of the time you do not have access to a true "V1" chart. In a FAA approved 747 "Takeoff Speed Table" chart (V1,Vr, V2) I have, it specifies that there is an adjustment to V1 of subtracting 2 knots per 5 knots of tailwind.

kdoner

So it does affect V1, because it increases your ground roll which will increase accelerate-stop, and accelerate go, and if directly proportional, the balanced field length??

blastoff

I think what everyone is trying to get at is your answer is yes, in most cases. Remember that take-off data is aircraft and company specific (ie, some companies may use differing criteria to determine V1), so there is no specific yes/no answer...but in most cases yes.