V1 also has 2 meaning- max speed at which an abort has to be initiated to stop on ry and (b) minimum speed at which you could lose an engine and continue takeoff and still meet all the performance and climb restrictions. Thats why it is not a good idea to mess with v1...I have heard about some pilots who have arbitrarily lowered v1 to give themselves a little cushion on stopping- however now if they decide to continue?
Let me agree with your main point & disagree with what you said...
"Dont' mess with V1." I agree. Being a test pilot without any engineering data to back you up amounts to "using the force," and that doesn't strike me as a very good idea for most of us. V1 gets determined using a LOT of factors (many of which have been touched on at some point in the discussions above), and arbitrarily mokeying with it is setting yourself up for some very uncomfortable questions from an FAA type. Or worse!
OTOH, V1
might be the max speed at which you can safely initiate an abort, and it
might be the min speed at which you can lose an engine & safely continue the takeoff, and it
might be both (i.e. exactly balanced field in front of you), but it
might be neither.
Take a lightly loaded small jet of your choice on a 15,000' dry runway with a good headwind on a cold day. Great performance, and, as you (BigSky) pointed out, V1 isn't much of a player -- you will get to rotation speed LONG before the point you need to put on the brakes to safely stop at the end of the runway, and you'd be able to continue the takeoff on one engine long before you reach Vr. In that case, V1 is
neither of the above.
In a "stop-oriented" airplane, say the C-130, you always made V1 (though we called it something else in the Air Force) as high as we could. It was either rotation speed, or refusal speed (i.e. accelerate on 4, lose one, and stop on the last brick). As long as you could fly on 3 at that speed (and you pretty much always could), you went with it. (and if you couldn't, all you could do would be reduce weight or increase thrust by going bleeds off) Unlike in fast jets, we never reduced V1 in deference to brake cooling or such things. Heck, we had lots of reverse & beefy brakes! (insert manly Tim Allen grunts here)
In a "go-oriented" airplane, say the T--38, you virtually ALWAYS had a significant gap between V1 and VR, just because the jet flew pretty well on one engine (afterburners are wonderful things), and regardless of how much runway you hed in front of you, absorbing the energy of a T-38 at it rotation speed was awfully rough on the brakes (and consequently, dangerous) if you didn't have a really stiff headwind.
Other airplanes are somewhere in the middle -- like the 737. Frequently, V1 = Vr; sometimes it is slightly lower, other times (contaminated runway) it's a LOT lower. And it can be driven lower by things other than just accel-stop distance. Anymore, there are enough factors going into the number-crunching computers that you can't always say for sure what the controlling factor is.
Usually, there is a range of speeds below refusal (accel-stop) and above decision speed (accel-go) where you -- or really, the engineers who write your takeoff data tables -- can set the V1, and you'll be able to stop at or below V1, and also be able to fly at or after V1. (And, live with the brake temperature if you stop.) For instance, if Vr is 130, you may be able to fly anytime after 110, and you can stop up until 125. Where's V1? In a Herk, we'd say 125; in a T-38 probably closer to 110 or 115. Where you put V1 in that range for a particular aircraft is a choice. Sometimes that choice is based on factors such as the knowledge that, on the one day in 1000 when you actually face to go/stop situation, you may not exactly duplicate the test pilots' performance. As one performance engineer put it, if you lose one and then cross the departure end at 34' instead of 35', nobody will care. But if you're a little slow getting on the brakes and you stop with the nose tire at 7001 down a 7000' runway, your day just got a lot worse!
So, in simple pilot terms, V1 is the speed by which you make your decision. Until V1 I can decide to stop, after V1 I need to go. At Vr I rotate. After that, if I'm flying with a problem, I want V2 at least. V2 may be predicated on Vyse, or Vmca, or other things. (for instance: Herk V2 went UP with increased thrust -- worse asymmetric thrust if you lost an outboard; 737 V2 goes DOWN with more thrust -- more thrust to balnce the greater induced drag at low speed) Prior to V1 you MAY be able to fly away safely, but it's a better decision to stop. After V1 you MAY be able to stop safely, but it's a better decision to go (if you can. If not... "hit the fence fast, or hit the fence slow" applies). In any event, as you're rolling down the runway, you need a simple decision point, not lots of factors to think about. And V1 is that easy simple decision for you. All the hard thinking has already been done by the engineers.
So I'll repeat my agreement with your main point: don't go "adjusting" V1 arbitrarily!
