redcordes
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V1 Vs Vr

Thu Jun 29, 2006 9:02 pm

I realize that on runways of typical length V1 is reached before Vr, but on long runways can Vr be reached before V1? Also, would V1 be lower for a 7000 ft. runway vs. an 8000 ft. runway? Assume identical conditions for these questions. Thanks.
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wing
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RE: V1 Vs Vr

Thu Jun 29, 2006 9:18 pm

Lets define the meaning of V1 first to explain this question.
V1 is the last point where you can start your abort maneouver,I repeat its not where you decide to abort,its the last point where your action shoud have started,your decision was already made.

VR is the calculated number, of the airplane's assumed rotation should begin.Can be differed depending on many variables.

A pilot can abort the take off roll when because for some reason he believes that he will not get safely airborn,or stay airborn.A V1 point is calculated to let him know at which point he should he should rather continue of discontinue the take off.The main idea behind all these is not to brake up the airplane and ofcourse yoursef in it.

As a result, if you think that you can reached to a speed that you can take and remain in the air you GO,if not STOP.
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David L
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RE: V1 Vs Vr

Thu Jun 29, 2006 9:23 pm

Quoting Wing (Reply 1):

So having V1 higher than Vr makes no sense - you wouldn't abort the take off after you'd started rotating?
 
miamiair
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RE: V1 Vs Vr

Thu Jun 29, 2006 9:52 pm

Quoting Redcordes (Thread starter):

On the 727 V1 and Vr are the same iunder certain conditions.
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redcordes
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RE: V1 Vs Vr

Thu Jun 29, 2006 9:55 pm

Quoting David L (Reply 2):

So having V1 higher than Vr makes no sense - you wouldn't abort the take off after you'd started rotating?

You might if the situation warranted, depending possibly on how much runway was left. Also could V1 and Vr be almost the same value on a very long runway? And again, would V1 vary on different length runways, given identical conditions?
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
CosmicCruiser
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RE: V1 Vs Vr

Thu Jun 29, 2006 10:22 pm

Quoting Miamiair (Reply 3):
On the 727 V1 and Vr are the same iunder certain conditions.

In a light weight MD-11 they are most often the same. I've seen V1 & Vr 138kts a lot and it happens fast.

Quoting Redcordes (Reply 4):
would V1 vary on different length runways, given identical conditions?

Of course all the way up to Vr. There's really no reason to have V1 higher than Vr. I can't imagine an existing runway (ok we're not counting Edwards) where you could do it nor why. Keep in mind V1 also changes with runway conditions and wx conditions.
 
vikkyvik
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RE: V1 Vs Vr

Thu Jun 29, 2006 10:24 pm

Quoting Redcordes (Reply 4):
You might if the situation warranted, depending possibly on how much runway was left. Also could V1 and Vr be almost the same value on a very long runway? And again, would V1 vary on different length runways, given identical conditions?

Every discussion I've read on this forum about this topic (there have been a bunch) has basically stated the following:

1. V1 can and does vary depending on all the variables that go into takeoff calculations (weight, temp, altitude, runway length, etc etc etc)
2. ditto for Vr
3. V1 and Vr can be the same speed in certain conditions.
4. Vr will always be greater than or equal to V1.
5. V2 will always be greater than Vr.

Feel free to correct me if I'm wrong.

~Vik

EDIT: Thinking through it again, I assume that runway length would actually have no effect on Vr. The airplane doesn't really care how much runway you have left; it'll still want to start flying at the same speed.

[Edited 2006-06-29 15:27:27]
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Jetlagged
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RE: V1 Vs Vr

Thu Jun 29, 2006 10:25 pm

As has been pointed out more eloquently than I can elsewhere on this forum, V1 is not affected by runway length. If you look at charts for computing V1 you will not find runway length as an input. If the runway is short, takeoff weight is limited so that the aircraft can stop from an abort at V1.
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vikkyvik
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RE: V1 Vs Vr

Thu Jun 29, 2006 10:40 pm

Quoting Jetlagged (Reply 7):
As has been pointed out more eloquently than I can elsewhere on this forum, V1 is not affected by runway length.

Looks like you're correct. Found this thread that has some info in it:
Takeoff Speeds (by Cmckeithen Jan 24 2004 in Tech Ops)

Replies 12 and beyond are particularly good, by SlamClick et al.

~Vik
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redcordes
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RE: V1 Vs Vr

Fri Jun 30, 2006 2:26 am

Quoting Vikkyvik (Reply 8):
Quoting Jetlagged (Reply 7):
As has been pointed out more eloquently than I can elsewhere on this forum, V1 is not affected by runway length.



Quoting Jetlagged (Reply 7):

Takeoff Speeds (by Cmckeithen Jan 24 2004 in Tech Ops)

Replies 12 and beyond are particularly good, by SlamClick et al.

Upon reading the thread referred to above, V1 is definitely related to runway length. Isn't it common sense that on a runway 7000 ft long the decision to continue (V1) must be made earlier than on a 10,000 ft runway given identical conditions? Forget about balanced/unbalanced, let's keep it simple. Also, if runways are of sufficient length, V1=Vr. So, how then is V1 independent of runway length if V1 varies from being significantly below Vr to a point of equaling Vr (given that all variables except runway length are equal)? Nonsense!
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
SlamClick
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RE: V1 Vs Vr

Fri Jun 30, 2006 3:12 am

Quoting Redcordes (Reply 9):
Also, if runways are of sufficient length, V1=Vr.

This statement is only true in regards to a couple of specific types, such as the obsolete B-727 where they are equal. On almost all other jetliners V1 will be lower than VR. FAR Part 25.107 specifies that VR may not be lower than V1.

The only relationship between V1 and runway length is this: The V1 selected must permit acceleration, engine failure, rejected takeoff and a safe stop on the remaining runway OR engine failure after V1 and continuing the takeoff with an engine inoperative and meeting the liftoff and initial climb criteria under the prescribed conditions of Part 25 and Part 121. The important distinction is that if there is a problem with the runway length you adjust the airplane weight at brake release and not the speeds bugged.

Again, when calculating a V1 speed for a given takeoff there is no input for runway length other than the maximum allowable takeoff weight from the charts or the computer that guarantee that this accelerate/stop can be met. This calculation normally gives us only the most restricted weight (climb limited) and the most restricted weight (runway limited) and does not inform us as to what the particular restriction is. It could be:

Structural
Accelerate - stop.
Accelerate - go
Initial climb.
Second segment climb
Final climb.

Nowhere in there is there an adjustment to V1 for the length of the concrete. That factor boils down to a YES/NO decision.
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n8076u
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RE: V1 Vs Vr

Fri Jun 30, 2006 3:31 am

I checked a couple of the flight manuals I have on hand, and only temperature, altitude, and gross weight are used in calculating V1, Vr and V2.

The max. gross weight for the conditions (including any runway limitations due to length or obstacles in the flight path) would have already been established.

Some of the people who have replied to this topic are real airline pilots, and do this every day, so arguing with them is silly.

Chris
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redcordes
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RE: V1 Vs Vr

Fri Jun 30, 2006 3:36 am

Slam, wouldn't an accelerate-stop restriction be dependent on runway length, given all other variables are the same? Therefore, given all other variables the same, V1 very well could be dependent on runway length. Or can you somehow eloquently describe how an accelerate-stop distance is NOT dependent on runway length? Again I ask the simple question:

Isn't it common sense that on a runway 7000 ft long the decision to continue (V1) must be made earlier than on a 10,000 ft runway given identical conditions?

Forget about restrictions on this, that and the other thing. Everything is identical. Your saying that V1 will be the same?

Also, below is a link to takeoff Vspeeds for the B737 200-500. You'll note that the V1 and Vr speeds are equal at all but the lowest takeoff weights for the 500 with the 18.5k engines (a fairly common aircraft I would guess).

www.b737.org.uk/vspeeds.htm

[Edited 2006-06-29 20:53:37]
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
GE90110B1
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RE: V1 Vs Vr

Fri Jun 30, 2006 4:11 am

Speaking of V speeds I watch a lot of the cockpit videos. It seems like the US procedure is "V1, Vr, V2, positive rate of climb gear up" Many of the non-US pilots seem to say "V1, Rotate" and they do not seem to call out V2. And actually on the Airbus aircraft these V speeds are announced through the speakers by the computer. I also hear some pilots call out "80 knots" then the other pilot says "takeoff thrust set" "check." Also I was watching a 777-200 and the F/O placed his hand behind the throttles as the Captain pulled back on the throttles to slow the engines, it seemed as if the F/O was making sure the captain did not pull back too far on the throttles as he could not look down.
 
CosmicCruiser
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RE: V1 Vs Vr

Fri Jun 30, 2006 4:52 am

Quoting GE90110B1 (Reply 13):
It seems like the US procedure is "V1, Vr, V2, positive rate of climb gear up" Many of the non-US pilots seem to say "V1, Rotate" and they do not seem to call out V2

Not totally true, at my airline we call 80kts (to confirm airspeed on both sides) V1, rotate, positive rate. No V2. Depending on the jet the F/O may have his hand there to "fine tune" t/o pwr and prevent movement but in the MD-11 the F/O doesn't touch the throttles during the t/o roll.



Quoting SlamClick (Reply 10):
On almost all other jetliners V1 will be lower than VR

As I posted earlier I've seen V1=Vr on the MD-11 at low weights a number of times.

Quoting SlamClick (Reply 10):
Again, when calculating a V1 speed for a given takeoff there is no input for runway length other than the maximum allowable takeoff weight from the charts or the computer that guarantee that this accelerate/stop can be met

It still looks like length has to be considered as I remember my old S/O days in the 727 where we did it manually from the books and you did the performance data for a PARTICULAR runway so the dist is already a factor! If you arrive at "balanced field" then all that can change is weight. In that scenerio I agree. Just as clutter affects V1 because of stop dist so would length in general.
 
SlamClick
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RE: V1 Vs Vr

Fri Jun 30, 2006 5:32 am

Quoting Redcordes (Reply 12):
wouldn't an accelerate-stop restriction be dependent on runway length, given all other variables are the same?

Well, I usually like to give generalized answers that are not specific to one particular 'type' airplane. We are getting to a point now where we almost have to pick a make and model and if we do that we must pick a runway and set weights and temperatures and so on for the answer.

Quoting Redcordes (Reply 12):
Isn't it common sense that on a runway 7000 ft long the decision to continue (V1) must be made earlier than on a 10,000 ft runway given identical conditions?

Common sense does indeed say that under otherwise identical conditions we could accelerate to a higher speed and still reject the takeoff on the longer of these two runways than on the shorter. I would hazard a guess though, placing these two runways at sea level, standard day, most two-engine jet airliners could accelerate to V1 for their maximum certificated takeoff gross weight (structural limit) and then reject the takeoff on the 7000' runway. Therefore neither of these runway limits is a factor in V1.

That is, unless we are going to do an 'improved climb' takeoff where we use a V1 speed higher than that dictated by the charts for the purpose of gaining second segment climb performance improvement. This is a special case and worthy of its own thread, especially since saying much more about it is only likely to muddy the waters on this one.

I'd say that you'd have to shorten up pretty much on runway length, like maybe down around 5000' before accelerate-stop begins to lower your V1 speed. When that does happen, then the runway length did indeed affect V1, but it affected it by placing a cap on the speed we can use, and not by changing the number we should use.

Damn! I've even confused myself.
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redcordes
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RE: V1 Vs Vr

Fri Jun 30, 2006 10:25 am

Thanks Cosmic and Slam. I appreciate your inputs because I am interested in this stuff, it can be complicated and I have a hard time saying I understand something when I don't. I suppose one problem has to do with regulations and operator requirements. I guess I'm thinking more in theoretical terms and considering part 91 operations not just airline ops. Like a near MGW G5 sitting on the end of a 4000 ft runway--is it safe to depart and would V1 be lower than on a 5000 ft runway?
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flymatt2bermud
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RE: V1 Vs Vr

Fri Jun 30, 2006 11:11 am

On many transport category aircraft V1 is reduced with a wet runway factor. Here is a specific example using a Global Express. With a 75,000 Takeoff Weight
DRY WET
V1 110 101
VR 110 110
TOFL 4,069 4,128
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flymatt2bermud
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RE: V1 Vs Vr

Fri Jun 30, 2006 11:31 am

Quoting Redcordes (Reply 16):
Like a near MGW G5 sitting on the end of a 4000 ft runway--is it safe to depart and would V1 be lower than on a 5000 ft runway?

A Gulfstream 550 or Gulfstream V at close to MTOW had better not be intending to use that 4,000 foot runway for takeoff. It won't have the performance. Note the performance on the Global Express, at 75,000 lbs is 23,000 lbs or so under max weight. At MTOW same scenerio the numbers would be V1 = 122, VR = 127, TOFL 5,960.

Runway Limiting performance comparisions on a wet runway are:
5000 4000
V1 119 109
VR 119 109

Note V1 is not reduced at the field length of the runway is the limiting factor.
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redcordes
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RE: V1 Vs Vr

Fri Jun 30, 2006 8:00 pm

The more I know, the more I realize I don't know!

Are V1 and Vr both reduced for runway-limiting factors like wetness/contamination? Reducing V1 makes sense due to an increased accelerate-stop distance (assuming it was the primary factor) , but why reduce Vr. Here's a link and quote therefrom:

www.espania.com/aspa/bibliot/gen-10.htm

On wet and slippery runways without rolling resistance our acceptance and use of reduced V1 is also an acceptance of a lower margin, down to 15 foot clearance over the runways end. (Engine fail-ure at reduced V1.) In order to further reduce recurring overrun incidents and accidents, perhaps the time has arrived to recognized that a small trade in clearance at the runway end is also acceptable under other conditions on the remote occasions when a critical go/no-go decision has to be made.
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Starlionblue
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RE: V1 Vs Vr

Fri Jun 30, 2006 8:48 pm

Apparently at Courchevel (CVF) V1 is 0 knots. The Dash-7 in the last pic has just passed V1.


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zeke
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RE: V1 Vs Vr

Sat Jul 01, 2006 1:30 am

Quoting N8076U (Reply 11):
I checked a couple of the flight manuals I have on hand, and only temperature, altitude, and gross weight are used in calculating V1, Vr and V2.

Runway condition, slope, width, CG location, flap setting, derate and/or assumed temp/flex, wind, FCOM limits (tire speed, brake energy, mass).

Quoting Redcordes (Reply 12):
Slam, wouldn't an accelerate-stop restriction be dependent on runway length, given all other variables are the same? Therefore, given all other variables the same, V1 very well could be dependent on runway length. Or can you somehow eloquently describe how an accelerate-stop distance is NOT dependent on runway length? Again I ask the simple question:

Isn't it common sense that on a runway 7000 ft long the decision to continue (V1) must be made earlier than on a 10,000 ft runway given identical conditions?

V1 must be
> Vmcg
< Vmbe
< Vr


If you had no terrain about, one would use a higher derate/assumed temp/flex. However the rules are not that simple. If you use a higher derate/assumed temp/flex you dont automatically get higher V speeds, you can actually end up with lower or the same V speeds, just the position on the runway you achieve this is further down the runway. If you use a higher derate, the amount of thrust on the wing is less, Vmcg decreases, which can reduce V1/Vr/V2.

Eight factors are normally considered for each takeoff mass, wind, flap setting, derate, assumed temp/flex, they are First segment, Second segment, Runway length, Obstacles, Tire Speed, Brake energy, MTOW, final takeoff, and Vmu.

Quoting SlamClick (Reply 15):
That is, unless we are going to do an 'improved climb' takeoff where we use a V1 speed higher than that dictated by the charts for the purpose of gaining second segment climb performance improvement. This is a special case and worthy of its own thread, especially since saying much more about it is only likely to muddy the waters on this one.

Yes agreed, V2 over-speed and V2 extended climb are not that easy to understand.

Quoting Redcordes (Reply 19):
Are V1 and Vr both reduced for runway-limiting factors like wetness/contamination? Reducing V1 makes sense due to an increased accelerate-stop distance (assuming it was the primary factor) , but why reduce Vr. Here's a link and quote therefrom:

Generally just V1 is reduced, however all three can be reduced.

On a wet runway V1 is less, and the screen height that the aircraft needs to achieve at the end of the runway is also reduced. This is to account for the lower V1 and the increased time to accelerate to Vr.
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CosmicCruiser
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RE: V1 Vs Vr

Sat Jul 01, 2006 2:50 am

Quoting FlyMatt2Bermud (Reply 18):
Note V1 is not reduced at the field length of the runway is the limiting factor.

Even our 727s don't use the old manuals anymore but I did find this regarding the inputs and calculations for t/o perf. data in the 727 computer. I used the 727 'cause I thought they might still have the manuals but regardless all our jets would use this same criteria.

V1MIN is provided whenever the Stop
Margin is less than 3000 feet. At 3000
feet Stop Margin, V1 is between V1MIN
and V1MAX, depending on input conditions
and runway length. At Stop Margin
greater than 3000 feet, V1MAX is provided.

note: RUNWAY LENGTH

For those possibly not familiar with STOP MARGIN it is the runway length remaining after a rejected t/o at V1 using all standard references (max brakes, no reverse, spoilers, etc.) Often in the MD-11 when the stop margin gets close to 1000' or less we will opt for max pwr.
 
redcordes
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RE: V1 Vs Vr

Sat Jul 01, 2006 4:35 am

Quoting CosmicCruiser (Reply 22):

V1MIN is provided whenever the Stop
Margin is less than 3000 feet. At 3000
feet Stop Margin, V1 is between V1MIN
and V1MAX, depending on input conditions
and runway length. At Stop Margin
greater than 3000 feet, V1MAX is provided.

Thanks Cosmic. This, although only one of the criteria for establishing V1, would seem to typically be the most important and result in the largest variations in computed V1. I'm guessing that any of the other factors would not vary V1 from min. to max. themselves. It also makes good old common sense.
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
WSOY
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RE: V1 Vs Vr

Sat Jul 01, 2006 6:03 am

Quoting CosmicCruiser (Reply 14):
Depending on the jet the F/O may have his hand there to "fine tune" t/o pwr and prevent movement but in the MD-11 the F/O doesn't touch the throttles during the t/o roll.

Yet they definitely do so in some parts: here's a Finnair MD-11 video:
http://video.google.com/videoplay?docid=258406597762808482
where both pilots not only touch the throttles, but also exchange the handgrip on the throttles between them, in between the calls!
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