Originally posted by niklas
that formula does indeed mean what i tried to say. I only have a problem with the term Ps because it looks like a power.
That's because it is a power, P sub s (Ps) is the term used for specific excess power, that's the quantity we are discussing.
W in a level flight for a given speed is not W in a climb at the same speed, so while the formula is correct you still canīt determine from a level fight acceleration your exact climbrate.
Of course you can, if you are in level flight, regardless of acceleration, your climbrate will be exactly zero! I do see your point though, if you enter a climb, things will change, and of course so will the thrust and drag values in that equation. So the fact remains that you can always determine your instantaneous climbrate and acceleration from that equation. Naturally, it will be different for every flight condition, and even when you are established in a climb, the climbrate given by the Ps equation will only be correct for the instant at which the values were taken, that's why it isn't very helpful to consider isolated values. To be useful you really need a map of the Ps contours over the entire envelope. That way you can get a true impression of the behavior of the aircraft. In the same way that with a little experience, it is possible to obtain a 3 dimensional image of a hill by looking at contours on a map, it is also possible to obtain a similar perspective from an aircraft's Ps contours, or curves. Some of the work I'm doing involves a three dimensional approach to aircraft performance comparison, so instead of looking at the Ps curves or contours, I compare three dimensional surfaces, a bit like looking at a hilly terrain. It's exciting stuff
Badboy
