Hey Mr. Smith:
I guess I should explain myself a bit better, sorry. Of course, I recognize that specific numbers are calculated – what I meant was that you can’t calculate anything until you have defined what it is you are calculating. And after you have calculated the appropriate numbers, you select the number you are going to use for a certain value.
What I placed in my post was the definition of the terms, in an attempt to help interested parties understand how these terms relate to one another. Take “V1” for example.
Yes, you gather the information you need, and “calculate” V1 for the particular takeoff. But what is V1? I know it can’t be less than the speed at which the pilot recognizes that an engine failure has occurred and continue the takeoff, achieve the required height above the takeoff surface, and do it within the takeoff distance. I also see that, by definition, I can’t use a V1 that is less than Vmcg. So, now I have to understand what that number is so that I don’t use a V1 less than that. And, I also have to know what the required height above the takeoff surface is.
Reading the definition of Vr, I see that this is a height of 35 feet above the takeoff surface. But I also see that I have to begin to rotate the airplane (at a particular rotation rate) so that I”ll arrive at that 35-foot height after reaching a speed called V2. OK, what is V2 speed?
After further definition reading, I find that V2 is a takeoff safety speed – but it, too, has to meet some definitions; i.e., it may not be less than V2min and may not be less than Vr plus the speed gained prior to reaching the 35-foot height. And the effort continues…. (as we know).
But, even after running around to understand and get these values to determine the smallest V1 I can use, I still have to come back to the original definition of V1 and recognize that V1 also may not be any greater than the speed at which a decision to stop can be made; and that stop has to be able to be made within something called the accelerate-stop distance. And, as I’m sure anyone here would recognize, if I carry this on we would have to know how to obtain Vmcg and Vmca and Vmu and on and on – and then we would have to relate all these numbers to each other.
And then, after all this, we would still have two numbers – and we’d have to pick the one we wanted to be V1 – unless all the factors just fell into place and they happened to be the same number (balanced field).
My point is (and was) that V speeds are as much “defined” and “selected” as they are “calculated;” and I should have made that point more clear initially.
AirRabbit
