bjornhall, that's all absolutely fine if you have a POH or Flight Manual to work from but many (if not most) operations from short strips do not.
As I understand
OC619's original question, he is looking for a rule-of-thumb which is separate from any performance calculations (if indeed there are any!), in order to assess likely take-off performance by comparing %-age take-off speed against %-age runway used, for use on-the-day and in the
general case.
Obviously, if there are performance figures available in a POH or FM, these should be used before any attempt to take-off. Clearly they could then be translated by proportioning and measuring achieved against calculated distances. However, I don't believe that is what
OC619 was asking. He wants a general-case check of speed-v-distance as he hurtles along the runway in an attempt to (hopefully) leap into the air, and in a form that can be used on-the-day, as-it-happens, quite independently of any specific performance calculation.
That's how I read it, anyway ...
JD
