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

[flying dog]

I get it that I don't fly those and the "rules" have existed for a long time and the "work".  

But do they?

There are 3 important speeds needed when taking off:  V1, VR and V2.

Before I continue with this I'll digress slightly to when I was doing/trying to do the BAK.

You are flying a plane at an airport and are going to take off.   You need to know these things:
1 - QNH
2 - Temperature
3 - Wind speed and strength
4 - TODA
5 - TODR
6 - TOW

Ok, so QNH and Temperature, fair enough.

TOW - Take Off WEIGHT.   Again:  Fair enough.

TODA - Take Off Distance AVAILABLE

TODR - Take Off Distance REQUIRED

The QNH, wind, temperature and TOW go through a table to give you your TODR.

That has to be less than the TODA, or you will run out of runway.   Kinda obvious.

You can't take off on a 1,000 foot runway if you need more than 1,000 feet to take off.

So, that is fairly self explanatory.

But now things get interesting for me....   V1, VR and V2.

V1 - Above this speed you MUST take off.   (Confusing for reasons to which I shall address soon)

VR - This is the speed at which you "rotate" the plane.  That is:  You take off.

V2 - Minimum climb out speed needed.   If you are slower than this: you are not going to continue flying.

So, let's break this down a bit more:

Your plane weighs... 500Kg.

The wind is still.  (Just to keep things simple)

Your TODR is.... 800M  (Arbitrary/random number)

The runway is 1000M long.

You get to the start of the runway and start your take off roll.

And this is where it all falls apart for me.

Let's say your V1 = 80 and VR = 100.
You set off down the runway and the entire runway is ahead of you - good.
You continue down the runway getting faster and faster... and faster.
You get 800M down the runway but haven't got to VR speed (let alone V1 speed) and slam on the brakes.
Where is your stopping distance required calculated?

You are in a plane doing - say 70 kts - 800M down a 1,000M runway and decide to abort the take off.

The STOPPING DISTANCE REQUIRED (I just made that term up now) is.... 300M.
Guess what is going to happen.

Problem as I see it:
V1 is misleading.

V1 should be replaced by a P1 - Point1 which indicates:  YOU MUST BE FLYING BY NOW OR YOU WILL NOT STOP BY THE END OF THE RUNWAY!

Also the fact that VR > V1 is also weird/strange/confusing.

You have a "gap" between when you can take off and when you must take off.

Surley VR should be LESS THAN V1, or more correctly:   P1
And P1 is a point on the runway where if you reach it and are not flying, you MUST ABORT AND STOP.

So the take off would be more like, you start (at the start) and accelerate down the runway.
If you get to P1 before you get to VR, you abort the take off.  The remaining runway distance is enough for you to stop.

All things being good:  You get to VR well before P1 and you are flying before you get to P1 on the runway.

And - of course - P1 will vary from plane to plane and with different conditions.  Temperature, wind, etc.

Yes, it is more complicated to work out and "way back then" it may have been too difficult to calculate.
But now, with computers coming out of every hole in "everything"....  that isn't too difficult to do.

So really looking back at the V1, VR and V2 speeds, and their association that:
V1 < VR < V2 is really problematic.

VR < V1 for starters.

V2 and VR.... well....  I'm not sure.

Thoughts?

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

 

[Thruster88]

V1 only applies to aircraft with 2 or more engines. Below V1 the aircraft can stop on the remaining runway, above V1 the good engine will get the aircraft airborne on the remaining runway. 

[flying dog]

Ok, 2 or more engines....

 

Still doesn't really address the remaining runway distance remaining (with 2 engines) and not getting to V1.

 

You could be rolling down the runway slowly accelerating towards V1 and not getting there and only when you are about to run out of runway do you realise you need to abort.

 

There was an example of this happening in NZ (I think) in a twin engine prop plane and the brakes were not fully released.

They took off (JUST), retraced the wheels and then the wing caught fire.

 

Plane crashed.

 

[facthunter]

V1 is decision speed  (GO or NO GO) but is really a point on the runway. Vr is not far from V1 and then you rotate to lift off attitude which may be limited to  a comfort figure ( Like 18 degrees nose up.)

  The amount of weight you can be at is (a) Length limited or an obstacle limited (climb performance) situation.. Accelerate stop length may include an over run area...

   For a worse than expected acceleration like a  binding brake, which is hard to quantify (unless you had an accelerometer) you have double jeopardy. Poor acceleration and a hot brake and a fire risk with it, IF you retract it and it's too hot. Nev

Edited October 27, 2021 by facthunter

[flying dog]

Yeah, I kinda get it.

 

It just seems wrong how V1 is determined.

Really VR < V1 by how I think.

 

No good saying you have to take off (reason still not understood) before you reach VR.

 

[facthunter]

V1 is a variable point on the runway defined by a speed achieved at certain weights and conditions in the absence of anything else being available. On any runway YOU can decide your own decision point for any plane. If it's a steep down hill runway, the decision point may be the beginning of the runway. You are then committed to the take off.

   Rotating a large plane may/should take say four seconds and lift off should soon follow and you should be at V2 minimum to be at 35 ft by runways end..  THAT condition is called a "balanced field length". Nev

[APenNameAndThatA]

13 hours ago, flying dog said:

V1 - Above this speed you MUST take off.   (Confusing for reasons to which I shall address soon)

VR - This is the speed at which you "rotate" the plane.  That is:  You take off.

V2 - Minimum climb out speed needed.   If you are slower than this: you are not going to continue flying.

 

V1 should be replaced by a P1 - Point1 which indicates:  YOU MUST BE FLYING BY NOW OR YOU WILL NOT STOP BY THE END OF THE RUNWAY!

Also the fact that VR > V1 is also weird/strange/confusing.

You have a "gap" between when you can take off and when you must take off.

 

I am far from an expert on this (RPL, 150 hrs) but I note the following

1. People do replace V1 with something like your P1. There is a rule of thumb that by the time that you are a certain distance down a runway you should be at a certain percentage of VR. Big aircraft, the ones people use V1 and V2, operate on paved strips with known winds and gradients, so the pilot will know where they they should be on the strip by the time they get to VR. They will be able to work out V1 from that. Also, it is hard for people to know where they are on an airstrip, so V is a way of working out P. 

     Just because there is such a thing as V1 does not mean that you can safely stop or take off in time if an engine stops.

     V1 only applies to twin engined aircraft, because in a single engine aircraft, if the engine keeps going, there is no decision to make and if the engine stops there is no decision to make.  

2. V1 has to be less than VR because once you get to VR you will have taken off already! There is no point having a decision speed that by the time you get to the speed you will have already decided. 

 

Others know more about V1 and V2 than me and can correct me. 

[APenNameAndThatA]

P.S.

1. I would have thought that if it is too late to stop it will be too late to take off on one engine. Shows what I know. 

2. Light twins are stupid and dangerous and should be replaced by single-engined turboprops! 

 

[facthunter]

I think for U/L's you can ignore the" rotate" is it's more marked and significant with twin Jets in particular as they are quite overpowered on BOTH engines unless reduced thrust is used for take off and initial climb. You can only use reduced thrust if the conditions permit it and it's approved and in the manual. Full throttle is necessary on nearly all GA pistons to get into the RICHER  range that protects the engine from detonation,

  After you advance the throttles to take off position. (full throttle for most U'L's) you should note the engine is delivering normal power early in the take off roll and that it's accelerating normally. (Power and performance check). IF you are not happy, abort the take off and check things. You would also do this if any control felt "wrong" like a brake not fully released or there was say smoke from somewhere. Don't take known faults into the air..

       Your point on the runway would relate to where you would have expected to be able to get airborne, but for some reason it's not happening. What do you do? You have 2 options. Abort, brake hard and slow down and hopefully stop before the fence OR reef it into the air and hit either the fence or the trees at a faster speed or worse lose control..

       This should have already been considered in the assessment and mental briefing you have given yourself BEFORE you started to roll. . Proper Planning Prevents Piss Poor Performance.

  As for light twins the "later" ones WILL fly on one engine if you do everything correctly. They don't make certification if they don't.

   Flying is very unforgiving of errors and mistakes. That's the way it IS  and ever will be. Most of the remedy is in YOUR hands. Nev

Edited October 27, 2021 by facthunter
more content.

[Roundsounds]

Have a read of these definitions. 
 

there lots of other resources online explaining V speeds related to takeoff performance. 
 

https://www.faasafety.gov/files/notices/2015/Nov/V_Speed_Review.pdf

[Flightrite]

I think you are over thinking this. For SE machines it’s irrelevant. The POH in small GA machines is all you need, it’s been like that since Noah built his first float place!😉

Edited November 2, 2021 by Flightrite

[flying dog]

Sorry:  POH?

[biggles]

Pilots Operating Handbook I guess …. Bob 

[flying dog]

Thanks.

 

I maybe should have worked that out...   But.....

[facthunter]

Pilot Operating Handbook.

  I forgot to send this before...Nev

[Ryanm]

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.

[Cosmick]

On 27/10/2021 at 6:34 AM, flying dog said:

 

V1 should be replaced by a P1 - Point1 which indicates:  YOU MUST BE FLYING BY NOW OR YOU WILL NOT STOP BY THE END OF THE RUNWAY!

Also the fact that VR > V1 is also weird/strange/confusing.

You have a "gap" between when you can take off and when you must take off.

Surley VR should be LESS THAN V1, or more correctly:   P1

 

I don't know what i'm talking about but looking from the outside in - VR and V2 are airspeed. V1 is Groundspeed Vs remaining runway. The longer the runway V1 moves further down the runway so VR could be less than V1.

[Flightrite]

V1 is a decision speed only for ref to being able to stop on the remaining Rwy, (balanced field length) Vr is never calculated as less than V1. All the speeds are related to what the speedo shows, GS etc is irrelevant. Most of this stuff doesn’t apply to SE light A/C anyway.

Edited November 7, 2021 by Flightrite

[Ryanm]

9 minutes ago, Cosmick said:

I don't know what i'm talking about but looking from the outside in - VR and V2 are airspeed. V1 is Groundspeed Vs remaining runway. The longer the runway V1 moves further down the runway so VR could be less than V1.

They're all airspeeds. V1 is factored for wind.

2 minutes ago, Flightrite said:

V1 is a decision speed only for ref to being able to stop on the remaining Rwy, (balanced field length) Vr is never calculated as less than V1. Most of this stuff doesn’t apply to SE light A/C anyway.

It really does apply. Rejecting a take-off too late will end the same irregardless of what you're strapped to. You should have a Go/No-go point figured out BEFORE you commence the take-off. In a SE Light, an engine failure will obviously take some of the decision making away.

[facthunter]

V1 IS a POINT on the runway, but you determine it using an increasing speed which considers the conditions including your actual TO weight at the time. . When you attain the desired "DECISION" speed you have reached the POINT where you stop or go. The distance may include an over run that is NOT part of the normal runway, as a stop way.. It's not for you to invent one though. It's either there or it isn't. Nev

[Roundsounds]

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

I get it that I don't fly those and the "rules" have existed for a long time and the "work".  

But do they?

There are 3 important speeds needed when taking off:  V1, VR and V2.

Before I continue with this I'll digress slightly to when I was doing/trying to do the BAK.

You are flying a plane at an airport and are going to take off.   You need to know these things:
1 - QNH
2 - Temperature
3 - Wind speed and strength
4 - TODA
5 - TODR
6 - TOW

Ok, so QNH and Temperature, fair enough.

TOW - Take Off WEIGHT.   Again:  Fair enough.

TODA - Take Off Distance AVAILABLE

TODR - Take Off Distance REQUIRED

The QNH, wind, temperature and TOW go through a table to give you your TODR.

That has to be less than the TODA, or you will run out of runway.   Kinda obvious.

You can't take off on a 1,000 foot runway if you need more than 1,000 feet to take off.

So, that is fairly self explanatory.

But now things get interesting for me....   V1, VR and V2.

V1 - Above this speed you MUST take off.   (Confusing for reasons to which I shall address soon)

VR - This is the speed at which you "rotate" the plane.  That is:  You take off.

V2 - Minimum climb out speed needed.   If you are slower than this: you are not going to continue flying.

So, let's break this down a bit more:

Your plane weighs... 500Kg.

The wind is still.  (Just to keep things simple)

Your TODR is.... 800M  (Arbitrary/random number)

The runway is 1000M long.

You get to the start of the runway and start your take off roll.

And this is where it all falls apart for me.

Let's say your V1 = 80 and VR = 100.
You set off down the runway and the entire runway is ahead of you - good.
You continue down the runway getting faster and faster... and faster.
You get 800M down the runway but haven't got to VR speed (let alone V1 speed) and slam on the brakes.
Where is your stopping distance required calculated?

You are in a plane doing - say 70 kts - 800M down a 1,000M runway and decide to abort the take off.

The STOPPING DISTANCE REQUIRED (I just made that term up now) is.... 300M.
Guess what is going to happen.

Problem as I see it:
V1 is misleading.

V1 should be replaced by a P1 - Point1 which indicates:  YOU MUST BE FLYING BY NOW OR YOU WILL NOT STOP BY THE END OF THE RUNWAY!

Also the fact that VR > V1 is also weird/strange/confusing.

You have a "gap" between when you can take off and when you must take off.

Surley VR should be LESS THAN V1, or more correctly:   P1
And P1 is a point on the runway where if you reach it and are not flying, you MUST ABORT AND STOP.

So the take off would be more like, you start (at the start) and accelerate down the runway.
If you get to P1 before you get to VR, you abort the take off.  The remaining runway distance is enough for you to stop.

All things being good:  You get to VR well before P1 and you are flying before you get to P1 on the runway.

And - of course - P1 will vary from plane to plane and with different conditions.  Temperature, wind, etc.

Yes, it is more complicated to work out and "way back then" it may have been too difficult to calculate.
But now, with computers coming out of every hole in "everything"....  that isn't too difficult to do.

So really looking back at the V1, VR and V2 speeds, and their association that:
V1 < VR < V2 is really problematic.

VR < V1 for starters.

V2 and VR.... well....  I'm not sure.

Thoughts?

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

 

V1, VR and V2 have specific definitions and are speeds relating to performance criteria applicable to large transport category aeroplanes. You cannot apply theses speeds to small single engine aeroplanes. If you want to apply some TEM strategies to your operations that’s fine, but you’re never going to change the definitions of the above V speeds. 
 

This document explains these speeds. 
 

https://www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/takeoff_safety.pdf

[facthunter]

EVERY Take off has to conform to those FD, in RPT It DOES make the whole thing safer IF the crew perform to it. It works when it's pitch black outside or at minimum RVR  (Runway visual range)  You go entirely onto Instruments at Vr..  Nev

[Flightrite]

Those where scary days ‘Facty’, glad I only look out my bedroom window now when the RVR is that crook!😉

[facthunter]

Yes FLY only when you want to, is Bliss. Nev

[APenNameAndThatA]

6 hours ago, Flightrite said:

V1 is a decision speed only for ref to being able to stop on the remaining Rwy, (balanced field length) Vr is never calculated as less than V1. All the speeds are related to what the speedo shows, GS etc is irrelevant. Most of this stuff doesn’t apply to SE light A/C anyway.

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? 

Edited November 7, 2021 by APenNameAndThatA