Takeoff speeds and field length

[QNH1013]

Hello all,
I believe that if runway field length is limiting then as aircraft weight increases, then the V1 Reduces. This can be seen from company takeoff performance charts.

This means this is for a balance field length correct?

I thought QRH speeds assume balanced field length so how come as weight increases when looking at the QRH, the V1 Increases?

Finally, if a balanced field is say 13000ft and charts take TODA and ASDA/EMDA to equal 13000ft then this would mean the V1 is the lowest V1 correct?

So if we were not a field length limited weight, then V1 could be increased so if we increase takeoff weight isn't this the opposite of the first paragraph?

I'm getting a bit confused
For a 737 on a long international airport runway you could feel a bit more confident of stopping on the runway after an abort at V1 but at another airfield with a shorter runway this is not the case even though both performance charts for the airfields are assuming balanced field lengths. How do we know how much margin of V1 do we have?

Thanks and sorry for the confusing post! I'm on study overload right now

[john_tullamarine]

Perhaps a thought or two to start the discussion off ..

if runway field length is limiting then as aircraft weight increases .. the V1 Reduces

Keep in mind that there are several field length limits, any one of which can be the critical case .. takeoff distance AEO/OEI, takeoff run AEO/OEI, ASD .. one could even see BEL coming into your consideration. In general, though, increasing weight leading to reducing V1 suggests an ASD limitation. The downside is that the continued takeoff numbers rapidly get interesting ..

This means this is for a balance field length correct?

.. probably not

I thought QRH speeds assume balanced field length

.. usually the case

.. so how come as weight increases when looking at the QRH, the V1 Increases?

... because that's what normally happens .. but one needs to look at the whole picture, not just the typical QRH table where the data probably relates to distance in proportion to that needed to accommodate the weight.

Finally, if a balanced field is say 13000ft and charts take TODA and ASDA/EMDA to equal 13000ft then this would mean the V1 is the lowest V1 correct?[

.. or the highest .. one can't say without the full story. For a 737 one probably could take one's choice according to one's preferred philosophy .. providing that the continued takeoff obstacle profile were not to be unduly limiting

So if we were not a field length limited weight, then V1 could be increased so if we increase takeoff weight isn't this the opposite of the first paragraph?

.. not totally sure that I understand your point .. but this probably would be the normal case for an obstacle limiting situation where an overspeed takeoff schedule might buy you a bit more payload

For a 737 on a long international airport runway you could feel a bit more confident of stopping on the runway after an abort at V1 but at another airfield with a shorter runway this is not the case even though both performance charts for the airfields are assuming balanced field lengths.

.. all BFL indicates is that TODR=ASDR .. until one matches the required lengths to the available, it is not possible to draw any useful conclusions

How do we know how much margin of V1 do we have?

.. (I presume that your interest is in spare runway rather than V1) .. only by comparing required to available distances

[mutt]

I believe that if runway field length is limiting then as aircraft weight increases, then the V1 Reduces. This can be seen from company takeoff performance charts.
This means this is for a balance field length correct?

Nope its not balanced.

I thought QRH speeds assume balanced field length so how come as weight increases when looking at the QRH, the V1 Increases?

QRH charts are balanced. Higher weight requires greater runway length and higher V1.

Finally, if a balanced field is say 13000ft and charts take TODA and ASDA/EMDA to equal 13000ft then this would mean the V1 is the lowest V1 correct?

On a 13000 ft runway, i doubt that its the lowest V1.

So if we were not a field length limited weight, then V1 could be increased so if we increase takeoff weight isn't this the opposite of the first paragraph?

Boeing call this IMPROVED CLIMB....

How do we know how much margin of V1 do we have?

Quite frankly.... you dont!

Mutt

[privateer]

V1 is a factor of stall speed and minimum unstick speed, so as weight increases then V1 also increases.

If the runway is limiting then then take-off weight is capped at that limit.

[john_tullamarine]

... would you like to expand on your comments ?

[QNH1013]

Thanks for the comments. john and mutt especially, your pearls of wisdom are always appreciated!