.. then let me use my annointed God-like mod powers to ferret about at the bottom of the peat bog and do a Lazarus on the original .. which I will combine with this reincarnation ..
Please, all, refrain from deleting threads ... sometimes it is incredibly frustrating to lose an interesting thread .. at least, with the current implementation of PPRuNe .. we can find deleted threads and undelete them ..
.. and, if you think that you have made a "dumb" post, don't worry about it .. just dig back through some of mine and I am sure that you will find that I have made a few dumber posts than you ever possibly could ... point is, in this forum, no-one (but no-one) is ever going to (be permitted to) make light of someone else's learning process .. so please don't ever have any fear of asking a question or putting a view ... as we say from time to time .. the only dumb question is the one which didn't get asked ...
by using the 10kt tailwind column, as opposed to the 0 wind column, this resulted in lower V-speeds (V1 and Vr. V2 seems to stay the same) for the same (or similar) weight
.. this sounds rather strange .. Vr and V2 should be sensibly tied together. Keep in mind, though, that, for the overspeed case, the V2 schedule is increased above the minimum V2 so there is no necessary problem with having a different degree of overspeed across an RTOW page.
when there is a tailwind there may be a reduced IAS (for a given TAS),
Probably not the case as the ASI doesn't have any way of knowing what the groundspeed and wind is doing ...
Might this not be more about ASDR
.. but if you reduce V1 for ASDR reasons, you still have to get from that (reduced) V1 to Vr .. so, what you gain here .. you lose there.
Maybe it's just that they automatically remove the safety margin whenever there is a tailwind, regardless of where you are.
No .. the general rules are the same ... in fact, there is a bit more fat in the tailwind case ... recall that the AFM uses only half of the headwind component, but one and one half times the tailwind component in the performance charts .. this is why you see a sharp discontinuity in all the wind component carpets at the nil wind line.
What was bothering me was the reduction in Vr
This can get messy .. as a principle, Vr will be linked to V2 so that, at the prescribed rotation rate, V2 (or thereabouts) will be achieved passing the screen height. If we are only talking a knot or two, that's fine and came out of the flight test confirmation of the aerodynamic model .. but a significant playing about with the Vr V2 split would raise the eyebrows .. the V1/Vr ratio might vary quite a bit, on the other hand. Keep in mind that a more detailed aerodynamic model might well split a few hairs along the way to determining the final numbers .. considerations such as vertical wind profile may be at play here ?
I fully accept the charts are right
.. usually .. but beware of presuming perfection on the part of the technocrats. One of the great values to be had in a pilot's general knowledge and appreciation of things is that it assists him/her in the role of being the last line of defence. Be aware that one sometimes sees significant errors in things like letdown plate obstacle data, RTOW charts and such like. All the QA processes in the world only result in a high system reliability ... but not perfection ... looking at Mutt's observation .. even Mr Boeing may not be immune to real world reality
Guess that this goes back to Mr Boeing
.. now, that might be a bit embarrassing ... you don't think someone along the way might have left a sign out of an expression, Mutt ?