V1

[globaltrainer]

Hi,

Some books are saying V1 is always equal to Vr on dry runway. However, with a reduced TODA, wouldn’t V1 be affected and reduced as well since an earlier decision must be made? As for Vr, it should stay the same since Vr is only driven by weights, pressure altitude, etc.

Thanks

[AmarokGTI]

V1 is not always equal to Vr on a dry runway. Absolute nonsense. Yes it might OFTEN be, but certainly not always.
I took off with a 5kt tailwind today. V1 112 Vr118 V2 118
I took off from a different port yesterday with nil wind. At the weight I was at we had V1 120 Vr 121 V2 121

Turboprop RPT operator.

[RAT 5]

GT: fundamentally Yes.

[galaxy flyer]

If you are on the Global, the type-specific answer is V1 = Vr on dry runways 99.9% of the time. I’ve never seen an exception, but there might be IF you are using an optimized runway analysis where there is a clearway, so TORA < TODA.

The B727 was similar, but this is very type specific.

[Skyjob]

V1 = Vr is applicable on any balanced field (limited) runway, which many are in aviation.

Once obstacles are introduced, head/tailwinds, stowaway, clearway, then the V1 changes.
However the Vr should remain the same for the same weight in all these cases.

[mustangsally]

V1 is a decision speed, or simply go/no go. And stop in the remaining runway.
VR is a speed where rotation occurs to reach V2 as the aircraft lifts off the runway. On larger aircraft it is usually something close to three seconds from VR to V2.


With straight wing aircraft VR and V2 are usually very close or identical. The greater the wing sweep will usually produce a greater difference between VR and V2.


Just mudding the water.....

[galaxy flyer]

A lot of muddying here. If the original poster is who I think; my post stands. Corporate planes rarely optimize the runway performance like airlines. They just assume it’s a balanced field and take the numbers. If the BFL on a middle weight G6000 is 4,000’ and TORA is 8,000’, they take the BFL case, V1=Vr and go. There’s no need to optimize payloads vs. runway available and, with exceptions, obstacles are rarely limiting. Limiting runways are uncommon, but happen.

[john_tullamarine]

The speeds will fall out of whatever AFM analysis is figured for the runway. Generally, there will be a range of speed choices unless the runway is quite limiting.

VR is linked mainly with V2 such that V2 is achieved OEI with rotation commenced at VR.

Where V1 fits in the equation will depend on the match of aeroplane and runway lengths (especially ASDR/ASDA) and what you choose to do with V1/VR ratios.

If ASDA is not limiting, there should be no reason, generally, why one couldn't push V1 up to VR if that's what floats your ops engineering boat. The AFM data will take care of the backroom certification requirements.

[globaltrainer]

Start introducing improved climb V2 etc that also throws a spanner in the works on that.

Runways (dry) where I've seen a split from memory were runways with obstacle issues.

Me too, hence my question.

[galaxy flyer]

Agreed, JT, but in the simplified performance world of biz aviation; they just show BFL in tabular data. To increase the V1 to equal Vr would unbalance the distances. I’m not sure how they selected V1 in the Globals to always equal Vr on dry runways. An APG runway analysis will sometimes show a change in ?V1.

[H Peacock]

It's definitely type specific. As others have stated, in the Global (dry) V1 =Vr. Wet and you have a lower V1, but you could then use a higher than actual weight to go into the TOLD card and prove you could take V1 back up to Vr. A nonesense on 15,000ft of tarmac to be using an 'incorrect' lower V1!

In the Phenom V1 is invariably less than Vr. I guess the Phenom doesn't have quite such good brakes and certainly no TR!

[boofhead]

V1 is related to runway performance (length, condition, wind etc) for a given weight while Vr and V2 are related to the airplane weight alone.

The relationship between V1 and V2 is usually expressed as a ratio. If a turbo prop it might be a ratio of 1.0 thus V1 = Vr, or it might be .85 in a jet thus V1 would be 85% of the Vr speed.

[john_tullamarine]

they just show BFL in tabular data

BFL's fine .. easy operation but, in general, sub-optimal numbers. Sometimes you don't get to choose, eg DC9.

I’m not sure how they selected V1 in the Globals to always equal Vr on dry runways

Not had a play with the Global AFM. However, that suggests that you have a good ASD performance and the V1/VR has been chosen to be 1.0 to give you the best obstacle clearance weights.

Years ago, I looked after some Argosies .. generally I pushed V1/VR to, or near, 1.0 to minimise problems with an abysmal first segment .. but that was for the Queen of the Skies, you understand.

It's definitely type specific.

Not so much the plane but more the way the AFM is structured and how flexible the performance options might be.

V1 is related to runway performance (length, condition, wind etc) for a given weight while Vr and V2 are related to the airplane weight alone.

A few other things to consider but that's a reasonable start ..

[g450cpt]

Not sure about other types but the G650 can have a different V1 to Vr both for BFL or V1 min data. For example departing LFMN with the current conditions this morning (15 degrees, wind 080/18, dry runway). At 103,600# take off weight with BFL V1 136 kts, Vr 140 kts, V2 148 kts. Select V1 min numbers and we get V1 112 kts. Vr 140 kts, V2 148 kts.
Lower the take off weight to 80,000 BFL V1 113 kts, Vr 117 kts, V2 133 kts. For V1 min numbers V1 108kts, Vr 117kts, V2 133kts. Selecting V1 max numbers V1 and Vr will be equal.

[g450cpt]

The numbers I gave came straight from the Gulfstream book.

[galaxy flyer]

Interesting that GLF provides for a variable V1.

JT With a Vmcg of 86 knots, which was well below the V1 at an absolute minimum useable take-off weight and huge stopping power, ASD perf was great. Thanks for your insights.

[g450cpt]

Off the FMS. V1 is selectable for V1 Min, BFL, or V1 Max.

[H Peacock]

When would you ever want a V1 which is 'artificially' lower than the highest V1 that you could safely use? In effect it commits you to 'go' when you could actually comfortably stop. When is that ever going to be advantageous?

[Skyjob]

Increasing safety margins...
Especially maybe on non-dry runways when friction coefficients are not accurately determined...

Separately, some operators do not maybe want to operate on the limit of V1 for each departure, especially when a decision delay of a fraction of time could be the difference between stopping as per AFM and disaster in case of eg a cliff at end of threshold... To each operator the choice what to do.

IMHO, depending on the operator, their crew training and average/minimum crew experience levels it would be wise to have an artificially lowered V1 for these reasons. Increasing safety margins by reducing V1 would surely be on the forefront of my mind in certain types of operations.

[g450cpt]

Not true. V1 is the maximum speed at which it is safe to reject the takeoff. VR is the speed at which you take off.

If VR is below V1, then you have gone wrong somewhere there. I've seen it happen before!

Who said Vr was below V1?

[galaxy flyer]

Sky job,

I’d be careful about unduly limiting V1 on non-dry runways. While reducing V1 does half reduce the AD; one should account for the increased time on those non-dry surfaces controlling the OEI case. Contaminated surfaces significantly complicate control by increasing the actual Vmcg.

[AerocatS2A]

When would you ever want a V1 which is 'artificially' lower than the highest V1 that you could safely use? In effect it commits you to 'go' when you could actually comfortably stop. When is that ever going to be advantageous?

Who says you can "comfortably" stop from V1?

Some companies consider the risks of a limiting V1 stop to be higher than the risks of carrying a failure in to the air (I have not seen the stats to support this so make no comment on the validity), therefore they use the lowest V1 available.

[john_tullamarine]

Not true

Providing that the AFM data is observed and the sums done correctly with respect to the AFM, the background certification stuff will be taken care of transparent to the user.

If VR is below V1

The AFM will never let you do that. Ergo, a mistake along the way.

However (and we don't do this for the obvious Standards reasons) providing the brake energy is OK and the ASDA adequate, the physics will permit such a non-SOP action.

When would you ever want a V1 which is 'artificially' lower than the highest V1 that you could safely use? In effect it commits you to 'go' when you could actually comfortably stop. When is that ever going to be advantageous?

If the risk assessment is such that one is more concerned about stopping than going. It is essential to keep firmly in mind the fact that the AFM and certification, generally, is based on probabilities, not guarantees.

It is held, generally, that a high speed abort, even with a generous ASDA pad, is a high stress, high risk business ...

Sometimes, the flight standards assessment is that a lower V1 might be a better option .. in general, more risk of killing yourself stopping than going.

Increasing (stop - my addition) safety margins...

Who says you can "comfortably" stop from V1?

Precisely.

Contaminated surfaces significantly complicate control by increasing the actual Vmcg.

How so ? Vmcg is based on nil nosewheel steering input and the numbers consider friction characteristics.. it may be prudent to consider a reduction in crosswind limits for tyre force considerations .. However, a low speed go decision can provide an interesting piloting experience.

On that point, crosswind from the "wrong" side will increase the real world, on the day, Vmcg.

therefore they use the lowest V1 available.

Choosing the lowest V1 might introduce some exciting handling in the go case .. very much needing sim exposure and practice to reduce the startle factor. However, somewhere in the middle range makes more sense than routinely going at max V1.

I recall a period instructing on a 732 sim which had had the rudder mod incorporated ... very much a handful for the pilot at critically low speeds .. but trainable with exposure. Just how valid the observations might have been for transfer to the real aircraft I don't know .. but the stick and rudder exposure certainly upped the ante regarding instrument scan rate in the continued takeoff case.

[mustangsally]

A320 wrote, "Not true. V1 is the maximum speed at which it is safe to reject the takeoff. VR is the speed at which you take off"


Vr is a speed at which the rotation is commenced not the lift off speed. If one was to grab all the elevator available at Vr we would see a lot of sparks as it rolls down the runway. Now in a fairly straight wing aircraft not a problem, but with increase wing sweep and weight, save the tail skid and rotate reasonably and have V2 at left off.


I've seen it happen just to many times....

[galaxy flyer]

Contaminated surfaces significantly complicate control by increasing the actual Vmcg.

How so ? Vmcg is based on nil nosewheel steering input and the numbers consider friction characteristics.. it may be prudent to consider a reduction in crosswind limits for tyre force considerations .. However, a low speed go decision can provide an interesting piloting experience.

JT,

You got me doubting my fading (only a tiny bit) memory, so I dusted off the C-5 performance manual which is where I remembered Vmcg being corrected for contamination as well as crosswind. Calculating Vmcg was done as part of each take-off, run by the F/E and checked by the captain. Now, it’s on calculators, then paper spaghetti charts.

I ran a few samples and my memory was correct, there were corrections for each. With Zero crosswind, 0C, these are my results for three conditions: dry Vmcg (69 KIAS) to wet Vmcg (87 KIAS) to compacted snow (97 KIAS). Yes, the chart is titled Vmcg, 3-engine, no nosewheel steering. I can only guess the reason is that while on the ground the forces opposing the yaw are applied thru the tires. I’ve never looked elsewhere or seen Vmcg charts on civil types.

BTW, the beast increased Vmcg for crosswind component almost exactly 1kt for 1kt.

[john_tullamarine]

You got me doubting my fading (only a tiny bit) memory

Join the club, good sir.

I’ve never looked elsewhere or seen Vmcg charts on civil types.

It would, no doubt, be tied up with the C5's characteristics and certification .. both of which are outside my ken.

the beast increased Vmcg for crosswind component almost exactly 1kt for 1kt.

Thanks for that. My rule of thumb for 4-motor-jobs has been 1kt/kt or a bit more .. good to have more evidence.

[galaxy flyer]

If it matters, the contaminated correction was applied before the crosswind. No doubt, it’s specific to the Lockheed certification and test. It was flight test data. The only question I had and have is that the basic physics are the same—B737-200 or C-5 and everything in between; so it should only be the magnitude, not the direction, if I may say. A lot of the Lockheed and USAF procedure was very conservative.

Having that chart in mind at the time, I did a very wet runway, strong crosswind (20 knots, at least) take-off in a Challenger at Biggin Hill. Being Biggin Hill, it was downhill, too. After airborne for Geneva, I mentioned to the F/O that I’d love to have the Vmcg chart for that take-off. “Why?” “Well, let me explain.....”

[H Peacock]

I do buy the cliff-edge argument, but for any normal runway (talking about big airports) why does a crew choose to potentially require some

exciting handling in the go case .. very much needing sim exposure and practice to reduce the startle factor.

rather than: Idle, brakes, TR.

A 96,000lb Global at +45 deg, calm wind: Rolling t/o, rotate at VR, climb to 50ft, idle, land ahead, stop. All on a 15,000ft runway! Okay, in the sim, but why would I ever have used a V1 < VR?

[galaxy flyer]

Zhukovsky, perhaps? But, agree the Global is great!

[AerocatS2A]

I do buy the cliff-edge argument, but for any normal runway (talking about big airports) why does a crew choose to...


It is not necessarily a crew decision. In some cases it may just be how the performance program spits out the data. Where I work we still use tabulated charts and have some limited visibility of the possible range of V1s. The V1 for our actual weight would be the lowest and the lower of Vr for actual weight or the V1 for the RTOW would be the highest available. Current procedure is to use the V1 for our actual weight, i.e. we are using the lowest available from the chart (we are "go minded"). In days past we would have used V1=Vr unless the RTOW V1 was lower (this equates to the highest V1 available - "stop minded").

[FE Hoppy]

When would you ever want a V1 which is 'artificially' lower than the highest V1 that you could safely use? In effect it commits you to 'go' when you could actually comfortably stop. When is that ever going to be advantageous?

Almost always.

It's statistically safer to go than to attempt a stop with little margin. Hence a bias which makes going more likely increases safety.

The exception is when the terrain is challenging.

[H Peacock]

It's statistically safer to go than to attempt a stop with little margin.

Wow, that does surprise me. Where are those stats coming from? Are we talking about many instances where crews are mishandling the idling of engines and application of brakes, or is there another factor?

[MarkerInbound]

Ah, Boeing?

Aero 11 - Rejected Takeoff Studies (http://www.boeing.com/commercial/aeromagazine/aero_11/takeoff_story.html)

And yes, usually there is some crew screw up involved. Think about it. Flight test crews head out to the airport knowing they are going to do rejected TOS. Crews headed for recurrent training know it's likely an engine will fail. Yet most high speed rejects aren't engine issues. On the line crews may repeat the standard mantra "I will reject for any master caution or master warning, an engine failure or ..." And yes, there's 2 seconds added for crew response time. History shows that may not be enough.

[john_tullamarine]

the basic physics are the same—B737-200 or C-5 and everything in between

Would love to hear anything further if you come across any detail ..

“Why?” “Well, let me explain.....”

Bit of a worry .. That's my main interest in Tech Log - we have an opportunity to discuss things which the minimalist training styles these days don't look at .. or, perhaps, don't have a clue.

Okay, in the sim, but why would I ever have used a V1 < VR?

Oftentimes, the numbers won't let you push V1 up to a comfortable value.

Consider the case of a min weight, min speed schedule with V1 down near Vmcg, decent crosswind .. and a critical failure. If the wind is from the wrong side, you're gone, no ifs, buts or maybes ... and it all happens super fast. In such a case, the pilot is faced with recognising that control has been lost and changing to an overspeed abort to salvage whatever might be salvageable.

The message we'd like to get across is this: if you are down near Vmcg with a strong crosswind, do have a think about pushing the V1 up (within the book range of figures) to give you a pad for the crosswind-driven increase in real world Vmcg. Alternatively, if you have the option, perhaps delay until the wind abates ?

The exception is when the terrain is challenging.

Even then, the gross/net fudge makes the continued takeoff preferable with typical terrain problems.

.. or the speed schedule is on minimum numbers and there is a stiff crosswind.

And yes, there's 2 seconds added for crew response time.

We need to keep in mind that the 2 second pad only applies to the more recent certifications. Older Types basically are raw data.

[mustangsally]

Muddy waters ahead.
Several have commented about V1 being a safe reject speed and what happen if during the reject. Some of this depends on certification. Not all agencies use reverse thrust in the calculation, just idle thrust and brakes. (Reverse thrust on a twin engine jet, with only one engine in maximum reverse and be a hand full and best. On a four engine maybe a little easier but not a lot of fun.)

Now if you happen to be at KMIA using a 3700 meter runway with an aircraft being rather light, no payload and maybe two hours of fuel, V1 could well exceed VR/V2. But, no pilot in his/her right mind would put V1 above VR/V2. So V1/VR are equal.

Many moons ago, at least several decades, a passenger aircraft departed San Juan, PR and aborted after V1 and at least after VR and maybe V2. The reject was not very successful, well into the grass and maybe a lagoon or two. So the lesson is reject at or below V1, if at V1 or above continue. It is generally recognized that it takes +/- three seconds to recognize, make a decision and react to the event. Thus, many experienced crew brief that approaching V1 we will continue.

It us usually better to get the airframe airborne, handle the problem, and return for an landing. Thus the airframe can be recycled to fly again than for scrap.

[galaxy flyer]

V1 is not refusal speed, aka accelerate-stop, the first action of stopping is to be actioned at V1. The USAF always calculates refusal speed and a V1, which is handled the same way as civilians do. Yes, refusal speed could be the same as tire limit in many take-offs.