V speeds in planes.... (The big ones)

[aro]

Rejecting a takeoff after rotation would be considered a different kind of emergency... it gets significantly more difficult.

[Roundsounds]

33 minutes ago, APenNameAndThatA said:

Why can’t V1 be greater than Vr? 

 

V1 is “V1 is the maximum speed at which the rejected takeoff maneuver can be initiated and the airplane stopped within the remaining field length under the conditions and procedures defined” said the doc linked to. 

 

My aircraft at Archerfield could probs get to Vx before V1. Would you like me to check for you? 

The stopping distance is predicated on the application of wheel brakes, this can’t be done with the wheels off the ground. 
V1 does not apply to single engine light aircraft. 
 

have a read of this document to understand the application of V1.
CAO 20.7.1B

Edited November 7, 2021 by Roundsounds

[flying dog]

19 hours ago, Ryanm said:

V1 isn't just about an engine out situation. It's a decison speed. If I have ANY issue prior to V1, I'll have enough runway to stop the aircraft on the remaining runway. If an issue presents itself after passing V1, I no longer have the stopping distance required and if I decide to stop, I'm probably going to go off the end of the runway.

 

V1 is calculated prior to EVERY departure and includes many variables. It's factored for weight, weather, aircraft performance and config etc. The calculations are quite complicated behind the scenes. Luckily most of the hard work is done by the manufacturer and the Performance department. Aircraft acceleration is taken into account, that in turn depends on the weather, flap setting, thrust reduction (if any) etc. So they know what the airspeed should be at each point down the runway. At some point, we've used enough of the runway that a decision to stop will mean an overrun. That's all it is.

 

VR is the rotate speed. This is also a complicated calculation behind the scenes. Basically it is the safest speed to begin rotation. Yes, we could try to rotate earlier, but I'll have to explain why the tail hit the deck. On my fleet, V1 is usually about 5-15kts less than VR, but on a long runway it's often the same speed.

 

V2 is the speed to fly if we lose an engine once were airbourne.

The first paragraph:

 

I still beg to differ.  Be it "engine out" or what ever.  I think there is confusion there, but I'll leave that alone.

 

So you are going down the runway taking off - or attempting to.

 

V1 < VR

 

You get to V1, but don't seem to get to VR.  You are "stuck" between these two numbers.

 

What are you supposed to do?

 

You have exceeded V1 and are "supposedly" obliged to take off, but can't get to VR speed.

 

VR should be less than V1 so there is a margin where if you can't/don't get to VR: you are below V1 - allowed to abort the take off.

 

I'll now read the other posts.

[Flightrite]

On 27/10/2021 at 10:34 AM, flying dog said:

 

..............Who can help me get my head around why these are called what they are called and why.
 

we’ve tried, several times! You are way over thinking this!

 

 

[flying dog]

> My aircraft at Archerfield could probs get to Vx before V1. Would you like me to check for you? 

 

I think I know what you mean, but....

 

If V1 is lower than VR and any/all other Vx...   You can't.   Sorry.

[flying dog]

Flightrite:   Yes, I over think a lot of things.

 

And I am asking not specifically for GA/Light planes.

 

I am asking in the bigger picture.

Edited November 7, 2021 by flying dog

[flying dog]

Just to clarify - as it seems there is confusion:   (yeah and probably on my side)

 

V1 is your "GO/NO GO" speed for taking off.

VR is the speed at which you rotate/take off.

 

V1 is more a position on the runway, but.....

 

If you are taking off you need to get to VR to take off.

 

But this is greater than V1.

 

Given rejected takeoffs are because of a problem happening and not because of some other reason.

 

You get to V1 and exceed it.   So you are committed to taking off, but for reasons unknown:  you can't get to VR speed.

 

You are not going to "obey" the fact that V1 is the "you are committed to takeoff" speed.

 

Therefore I put it that VR should be less than V1 so if anything does happen you would be below V1.

In my example you would get to VR before V1 so at VR, you take off and all is good.

And you remain below V1 so you are complying with the less than V1 aborted take off speed.

[facthunter]

You can abort a take off at any speed below V1 safely. (IF the plane has accelerated normally).  IF you had dragging brakes or a partial engine failure the V1 speed has become meaningless as being somewhere you can safely stop from.  V1 and "rotate" can be the same point., on some occasions . Anytime you are too far down the runway to stop in the remaining runway, you are going into the fence if you try to stop, at some speed or other. It will be slower than If you have managed to stagger into  the air but have a problem with maintaining flight. In that situation you do the least worse thing. (Stay on the ground and slow down as much as possible.)

   The REALITY of what is going on is what matters not adherence to speeds on the ASI that may have ceased to have relevance. Nev

[Roundsounds]

4 hours ago, flying dog said:

Flightrite:   Yes, I over think a lot of things.

 

And I am asking not specifically for GA/Light planes.

 

I am asking in the bigger picture.

Read the material behind the links I’ve shared if you are genuine about understanding these speeds. 
I teach this stuff in my day job. 

[flying dog]

Yes, thanks.

 

I'm just saying.

[APenNameAndThatA]

On 7/11/21 at 7:42 PM, aro said:

Rejecting a takeoff after rotation would be considered a different kind of emergency... it gets significantly more difficult.

You don’t have to rotate at Vr. You don’t have to take off even at Vx (not that I would try to prove that). And, you can take off without rotating. 

[APenNameAndThatA]

On 7/11/21 at 7:43 PM, Roundsounds said:

The stopping distance is predicated on the application of wheel brakes, this can’t be done with the wheels off the ground. 
V1 does not apply to single engine light aircraft. 
 

have a read of this document to understand the application of V1.
CAO 20.7.1B

a) You can have the wheels on the ground above Vr. b) You can still calculate a stopping distance for wheels of the ground until decelerated a certain amount if you want to. 

[APenNameAndThatA]

On 8/11/21 at 6:12 AM, flying dog said:

> My aircraft at Archerfield could probs get to Vx before V1. Would you like me to check for you? 

 

I think I know what you mean, but....

 

If V1 is lower than VR and any/all other Vx...   You can't.   Sorry.

If I go along the runway, speed past Vr and still manage to stop before the end of the runway, when how have I not PROVED that V1>Vr? 

[aro]

If you don't rotate at Vr, it's not Vr??

 

V1 is only applicable to multi engine aircraft. It's the point after which you can't reject the takeoff, either because there is not enough runway to stop or you have already begun to rotate.

 

Performance calculations ensure that at V1 you have enough power to continue the takeoff even if you lose an engine. If you don't, you have to adjust performance e.g. reduce the aircraft weight.

 

The ability to continue the takeoff or stop on the runway after engine failure is only a requirement for larger aircraft. For smaller twins on shorter runways it may not be possible. I'm not sure where the cutoff is but it definitely applies to the jets operated by the airlines.

 

(Not a multi engine pilot myself, happy to be corrected...)

[aro]

On 08/11/2021 at 7:40 AM, flying dog said:

You get to V1 and exceed it.   So you are committed to taking off, but for reasons unknown:  you can't get to VR speed.

That's never supposed to happen. The theory is you detect the problem before V1. At V1, you should be able to reach Vr and fly away even if you lose an engine. This is factored into the aircraft design.

 

If you need to be able to stop from Vr you potentially need a much longer runway or much more restrictive limits on weight.

[Flightrite]

Oh brother!😂

[APenNameAndThatA]

2 hours ago, aro said:

If you don't rotate at Vr, it's not Vr??

 

V1 is only applicable to multi engine aircraft. It's the point after which you can't reject the takeoff, either because there is not enough runway to stop or you have already begun to rotate.

 

Performance calculations ensure that at V1 you have enough power to continue the takeoff even if you lose an engine. If you don't, you have to adjust performance e.g. reduce the aircraft weight.

 

The ability to continue the takeoff or stop on the runway after engine failure is only a requirement for larger aircraft. For smaller twins on shorter runways it may not be possible. I'm not sure where the cutoff is but it definitely applies to the jets operated by the airlines.

 

(Not a multi engine pilot myself, happy to be corrected...)

according to something I just copied from a link in this thread: V1 = maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. I can’t see why that wouldn’t apply to a light single. Singles gave accelerate-stop distances. And Vr is still Vr if you ignore it. 

Edited November 9, 2021 by APenNameAndThatA

[APenNameAndThatA]

3 hours ago, APenNameAndThatA said:

You don’t have to rotate at Vr. You don’t have to take off even at Vx (not that I would try to prove that). And, you can take off without rotating. 

And, for soft field takeoffs, you rotate before Vr. In a Foxbat, you can rotate at the start of the takeoff roll. I discovered that by accident. 

Edited November 9, 2021 by APenNameAndThatA

[aro]

The point of V1 is that it is a pre-made decision about when you will continue the takeoff instead of stopping in the event of an emergency e.g. engine failure. It is there so you don't use up runway and options while you wonder should I stay or should I go?

 

We don't use V1 in smaller aircraft For the case of an engine failure in a single, V1 doesn't exist. Jets etc. are required to be able to stop on the runway from V1, because running off the end of the runway after an engine failure is considered a bad thing. For smaller aircraft, people don't really care e.g. your takeoff charts for runway required do not include an allowance for stopping distance after a rejected takeoff.

 

9 hours ago, APenNameAndThatA said:

for soft field takeoffs, you rotate before Vr

If it's a planned speed for rotation, aren't you using a lower Vr?

Edited November 9, 2021 by aro

[APenNameAndThatA]

13 hours ago, aro said:

The point of V1 is that it is a pre-made decision about when you will continue the takeoff instead of stopping in the event of an emergency e.g. engine failure. It is there so you don't use up runway and options while you wonder should I stay or should I go?

 

We don't use V1 in smaller aircraft For the case of an engine failure in a single, V1 doesn't exist. Jets etc. are required to be able to stop on the runway from V1, because running off the end of the runway after an engine failure is considered a bad thing. For smaller aircraft, people don't really care e.g. your takeoff charts for runway required do not include an allowance for stopping distance after a rejected takeoff.

 

If it's a planned speed for rotation, aren't you using a lower Vr?

The confusion here is that you are confusing what a thing is for with what it is. Specifically, what V1 is for (decisions) does not alter the definition of V1 (accelerate-stop distance and runway length). Stated differently, if V1 is useless for light singles, it is still V1. 

 

Also, there is no reason V1 can’t be greater than Vr for a twin. In fact, if it was then that would be important info. I would mean the pilot did not have to think about it. 

 

As for the planned speed of rotation, that sounds true to me. 

[aro]

10 hours ago, APenNameAndThatA said:

Also, there is no reason V1 can’t be greater than Vr for a twin.

Before V1 you need to be able to abort the takeoff and stop safely in the remaining runway. After rotation the task is fundamentally different, so V1 cannot be higher than Vr. If you don't plan to rotate at "Vr" it is not Vr.

 

10 hours ago, APenNameAndThatA said:

Stated differently, if V1 is useless for light singles, it is still V1.

I was thinking about when V1 might apply in a single. There are problems where the correct thing to do is continue the takeoff so you could say V1 does apply. For example, if a door pops open in the takeoff roll.

 

Early in the takeoff roll, if a door pops open, cut the power and come to a stop, no problem.

 

If the door pops open as you rotate, cutting the power and trying to stop on the runway is a recipe for a broken aeroplane. Better to continue the takeoff, and do a normal circuit and landing. Or if the runway is really long, maybe you can stabilize the aircraft, reduce power and land straight ahead. But again that is different to an aborted takeoff before rotation.

 

If the runway is short, e.g. you have a 500m runway and calculated a 400m takeoff distance, at some point before rotation you are committed - you probably can't stop in the remaining runway. At that point, if the door pops open you need to continue the takeoff. That is your V1 - even if no-one ever calculates it.

 

10 hours ago, APenNameAndThatA said:

The confusion here is that you are confusing what a thing is for with what it is.

There is no reason for V1 to exist except "what it is for". If the definition doesn't quite capture it there is a problem with the definition. "What it is for" and how it is used are the whole basis of V1.

 

V1 is most critical when the runway length is limited. Yes. on longer runways V1 can be equal to Vr and you can abort the takeoff any time before rotation.

[APenNameAndThatA]

Re: Before V1 you need to be able to abort the takeoff and stop safely in the remaining runway. After rotation the task is fundamentally different, so V1 cannot be higher than Vr. If you don't plan to rotate at "Vr" it is not Vr.

 

You are making the same mistake as before: confusing characteristics of something with its definition. Stated differently: nobody cares that if you don’t intend to rotate at Vr its not Vr anymore. 

[RossK]

My simple understanding of V1 is;

The PIC has done the calcs and has an abort point (ie a distance on the runway).

If he hears the co-pilot call V1 before that point, he knows there is sufficient runway and thrust available (even with an engine failure before Vr) to reach Vr before the end of the runway.

If he doesn't hear V1 at the abort point, he aborts.

 

[facthunter]

There's limited interest here about what "Heavies" do but the question was asked. (I always try to keep my answers simple and talk to the principle of what is happening.)

  A Rotation on an RPT  is a practiced timed action when lift off should occur when a fairly significant up Pitch attitude is reached. Usually in the order of 18 degrees. MORE if you are light and not using reduced thrust. 18 degrees is often company practice for Passenger comfort OR possible tail strike in some planes.

   There's NO equivalence of this in flying ultra light aircraft. IF the runway is soft a bit of back stick is the go. IF there's a decent crosswind you might hold it on a bit longer to get a clean and positive break with the runway and no chance of a second contact.  

  With RPT,   A FULL cockpit briefing is done before every take off by the person doing the take off. That's Standard Operating Procedure(s). SOPs. Nev

Edited November 11, 2021 by facthunter
more content.

[Roundsounds]

As Nev says, V1, VR and V2 as defined have zero relevance to Single Engine GA aeroplanes. 
this discussion is more about threat and error management considerations during takeoff. 
a very worthwhile discussion. 

Edited November 11, 2021 by Roundsounds