(a) from whatever starting point where we have a given weight from the sums ..
if the TO is ASD-limited, then there is no option to increase V1 without reducing weight .. which is not the aim of the game. (It is presumed that the TO has been optimised to the extent that the figures are near limiting for the TOD case - if not, why not ?).
If the figures are not AT the limiting TOD case then it is possible to reduce V1 until the TOD limit is reached. This will make the ASD limited weight equal to the TOD limited weight will it not?
One Maximum TOW limited by the intersection of the go and stop lines. With the appropriate and singular V1.
However, if we get a bit more TODA by introducing or extending clearway, then we can look at reducing V1 a little which MAY allow us to juggle a resulting small increase in ASD-limited TOW provided that one of TORR and TODR doesn't then immediately become limiting.
So as I said earlier clearway will result in a reduced V1 and increased MTOW.
if the TO is TOD limiting, then the increase in TOD should give an increase in TOW due to the extra TOD or MAY allow us to increase V1 a little and get a bit more TOW providing that neither of ASD/TOR immediately becomes limiting.
How can an increase in TOD lead to an increase V1 unless the V1 was not optimised before hand? If it was then an improvement in the accel go case will reduce V1 rather than increase it.
(d) if the TO is TOR limiting, then we can only look at increasing V1 to improve TORR, providing that ASDR doesn't immediately become limiting.
However, one would expect that this option had been exploited fully first time around so, in reality, TOR-limited cases ought not to respond to an increase in clearway.
Agree.
if nothing were limiting first time around, then we could have increased/decreased V1 as appropriate until one case became limiting in such a way that we ended up with an optimised (ie maximised) TOW. If then we can get some more clearway, we could revert to (b) or (c) and maybe tweak a bit more weight out of the calculations.
If nothing was limiting then an increase in TOD is irrelevant.
For any runway analysis it is very much a case of juggling things a bit this way or that to end up with something becoming limiting but in the way which gives us the maximum RTOW for the chart. Sometimes one can spend quite a lot of time on this iteration process .. hence the reason we all loved the advent of microprocessors to do the slave labour numerically intensive bits of the exercise.
If the above is confusing, either OS or I can run up some pictures to help clarify the words.
one graph with v1 along the x axis and TOW on the y with two lines one plotting accel go and the other accel stop for a fixed TOD and ASD is all you need.
How can a take off be accel stop limited in isolation?
Quite easily.
Find a runway with a given set of ASDA/TODA/TORA .. when you do the sums for a given set of ambient conditions, you will find that each results in a particular maximum TOW. Once ALL the various sums have been done, the lowest resulting TOW becomes the limiting TOW for that particular set of ambient conditions.
I dissagree that each will result in a particular MTOW. I would say that if a predetermined V1 is used then this is true but if V1 is optimised then ASDR and TODR can be equalised.
This set of weights will have a predictable relationship depending on the particular Type and that predictable relationship may well be very different for another Type.
If the ASDR ends up being the limiting factor (ie results in the lowest TOW) then the TO becomes ASD limited.
Or you use a lower V1 until VMCG or TOD limits equal ASD limit.
I can always stop below v1 so by reducing v1 i can declare a higher stop limited weight.
Very true .. but the down side is that the TODR/TORR increases and that might prove to be less than useful.
So ASD in isolation is not limiting.
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or the go case as weight increases for a fixed TODA v1min must increase.
True - due to increasing Vs unless I am missing your point ? Alternatively, once TODR (or, if you prefer, in this case, TODA) becomes limiting, we can only increase that limiting weight by increasing V1 with the caveat that ASDR may soon become the limiting problem.
If I plot the go line and the stop line where they cross must be the OEI runway limited weight.
If we are only considering ASD/TOD.
adding clearway moves the go line such that i can have my failure at a lower speed and still go. Now where the go and stop lines cross is at a lower speed (v1) and a higher weight.
However, as soon as you start going down this path we also need to be looking at ASDR, TORR as well as TODR - one will become the limiting case. Much easier to present this discussion with some graphs to illustrate the considerations.
And why wouldn’t we?
Clearway has no effect on V1 max but will reduce V1 min so long as it isn't limited by something else. (VMCG)
But note that increasing clearway may permit an increasing V1 until either TODR or TORR becomes limiting. It can be rather confusing to folk if we ignore the TOR consideration ..
For a given takeoff weight, any increase in V1 leads to a reduction in both TODN-1 and TORN-1. The reason is that the all engine acceleration phase is longer with a higher V1 speed, and, consequently, in case of an engine failure occurring at VEF, the same V2 speed can be achieved at 35 feet at a shorter distance.
I think I would be emphasising things a little bit differently. Yes, the AEO distances up to the failure point will increase somewhat. However, the main consideration is that the OEI distances between a lower V1 and the nominated Vr will be SIGNIFICANTLY greater than between a higher V1 and the same nominated Vr. (Note, also, that Airbus are including both TOD and TOR in their discussion).
Airbus words not mine.
But it's saying the same thing. Increase V1 leads to reduction in TOD n-1 is the same as increase TOD n-1 leads to reduced V1.
.. but not a useful observation when considering what a varying clearway might be doing to the calculations .. except to the extent that the comment has relevance to juggling V1 in the presence of clearway to get a better ASDR/ASDA margin at the same weight. I think that you might be missing the underlying point that the aim is to increase TOW in general.
Point not missed at all. What I’m trying to say is exactly that. But the only way adding Clearway to an already runway limited TO can increase the MTOW is if it comes with a reduction in V1.
The driving point in the discussion needs to be that, in the presence of whatever I have in the way of runway etc. lengths, the aim is to juggle V1 to maximise TOW.
And having done that if someone gives me clearway I previously didn’t have I may be able to juggle my V1 LOWER to give a HIGHER TOW.
So what effect will stopway have on V1 and MTOW?