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How Does A Pilot Know When He's At V1?  
User currently offlinecvbcbcmv From United States of America, joined Jun 2011, 4 posts, RR: 0
Posted (3 years 3 months 1 day 5 hours ago) and read 4640 times:

So, a pilot is taking off. How does he know when v1 is? I know what v1 is, but how would the pilot know when it is? Also, for example, if your on a really long runway, and doing a lightweight takeoff, would it be possible to takeoff before hitting v1?

10 replies: All unread, jump to last
 
User currently offline9VSIO From United Kingdom, joined Dec 2006, 717 posts, RR: 2
Reply 1, posted (3 years 3 months 1 day 5 hours ago) and read 4636 times:
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It's calculated before take-off. A quick thread search will reveal many topics on the subject.


Me: (Lining up on final) I shall now select an aiming point. || Instructor: Well, I hope it's the runway...
User currently offlinelonghauler From Canada, joined Mar 2004, 4979 posts, RR: 42
Reply 2, posted (3 years 3 months 1 day 4 hours ago) and read 4598 times:

On older aircraft, a take-off chit is made up and displayed.
On newer aircraft, it is entered into the FMS and will be displayed on the digital airspeed indicator.

Depending on the airline's SOPs, the PNF will call V1 during the take-off roll.

Quoting cvbcbcmv (Thread starter):
Also, for example, if your on a really long runway, and doing a lightweight takeoff, would it be possible to takeoff before hitting v1?

No, when the runway length is not limiting, V1 will be the same as Vr. (this is entering into a grey area, as because V1 is the same as Vr for the take-off, theoretically the aircraft will still have room to stop after V1/Vr)



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlinecvbcbcmv From United States of America, joined Jun 2011, 4 posts, RR: 0
Reply 3, posted (3 years 3 months 1 day 4 hours ago) and read 4589 times:

Thanks for the answers guys. And sorry if I posted in the wrong place, I'm new here. Before I spent a long time typing out a long version of this question, when it told me I had to buy a premium membership. I figured I'd just buy a first class membership since I'll be spending a lot of time here. I wasn't used to having to pay, I'm a moderator over on a high powered laser forum and it's free lol. Lol high powered lasers and planes are my hobby, kind of weird. Don't worry, I don't point lasers at planes. You spend time on my forum and you will learn that very quickly.I will do so illegal things to people who point lasers at planes.

User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 4, posted (3 years 2 months 4 weeks 1 day 19 hours ago) and read 4191 times:

Quoting longhauler (Reply 2):
No, when the runway length is not limiting, V1 will be the same as Vr. (this is entering into a grey area, as because V1 is the same as Vr for the take-off, theoretically the aircraft will still have room to stop after V1/Vr)

I see that a lot with the CR7s and CR9s. V1 and VR is many times withing 1 or 2 knots of each other, if not the same. I don't know why that is though.



What gets measured gets done.
User currently onlinegolfradio From Canada, joined Jun 2009, 764 posts, RR: 2
Reply 5, posted (3 years 2 months 4 weeks 1 day 19 hours ago) and read 4181 times:

In the A380, the FMS has an automated V1 callout.

User currently offlinejetpilot From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 6, posted (3 years 2 months 4 weeks 1 day 18 hours ago) and read 4150 times:

In the 727 V1/VR are always the same speed.

User currently offlinetb727 From United States of America, joined Jun 2005, 1597 posts, RR: 9
Reply 7, posted (3 years 2 months 4 weeks 1 day 17 hours ago) and read 4120 times:

It's when the other guy says "V1" of course.

Quoting jetpilot (Reply 6):
In the 727 V1/VR are always the same speed.

I want to say I saw a split V1/VR only once on the 727 a few months back, I can not however remember why we did it, or really if we did it, I vaguely remember asking why because I had never seen it. Never mind, I can't remember lol.



Too lazy to work, too scared to steal!
User currently offlinejetpilot From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 8, posted (3 years 2 months 4 weeks 1 day 17 hours ago) and read 4114 times:

I think on the rare occasion of an unbalanced field V1 and VR can be different. But I have never experienced an unbalanced field TO in a 727.

User currently offlinelonghauler From Canada, joined Mar 2004, 4979 posts, RR: 42
Reply 9, posted (3 years 2 months 4 weeks 1 day 17 hours ago) and read 4107 times:

Quoting FlyASAGuy2005 (Reply 4):
I see that a lot with the CR7s and CR9s. V1 and VR is many times withing 1 or 2 knots of each other, if not the same. I don't know why that is though.

If you work it backward, start with V2 ... your safe climb out speed on one engine, under the conditions you are presently flying. Now, think about at what speed do you need to rotate so your initial climb speed is V2 ... that will be Vr. Clear enough so far. Vr and V2 are related to altitude/obstacle/ climb performance.

As you know though, V1 is a ground performance speed. Maximum speed at which a rejected take-off is possible, and (likely) stay within the confines of the runway.

But ... what is the airplane is very light, or the runway is very long? It is very possible that V1, could be higher than V2, and thus Vr. But that can never be, obviously, so V1 is set to the same as Vr. But as pilots we know that when V1 and Vr are the same, the aircraft could conceivably stop on the runway from a speed higher than V1.

Now, we would never do that. Mostly because we don't know how far above V1/Vr the aircraft could be stopped. But it gives one an "impression" the aircraft ground performance capability exceeds current conditions. Conversely, think about a contaminated short runway, in a heavy aircraft, and V1 is far lower than Vr. You then know that aircraft ground performance only equals current conditions.



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offline113312 From United States of America, joined Apr 2005, 572 posts, RR: 1
Reply 10, posted (3 years 2 months 4 weeks 1 day 17 hours ago) and read 4107 times:

Firstly, in many planes such as the 727, V1=VR in most but not all cases. An example of a V1 prior to VR will be contaminated runway.

V1 is a decision speed based upon indicated airspeed. There can be a V1 based upon rejecting a takeoff and stopping and a different V1 for electing to continue a takeoff after an engine failure and being able to achieve the minimum required climb gradient. While these two considerations might result in a different V1 for each, the most restrictive is used for the point where the decision must be made and action taken.


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