V1
 

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

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.

GT: fundamentally Yes.

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.

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.

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.....

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.

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.

Me too, hence my question.

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.

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!

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.

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 ..

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.

The numbers I gave came straight from the Gulfstream book.

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.

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

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?

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.

Who said Vr was below V1?