Assuming constant acceleration, of course. That works pretty well on wheels, but for floats, the part before you get on step is a lower rate of acceleration than once on step. At least it is for boats unless you have a lot of power to jump out of the hole quickly.
the acceleration on wheels is relatively constant. Not so on floats. The variation in acceleration rates is minimal enough for me to discount in a cub that flys at about 40 MPH.
to put this in numbers and I hope more simply and practically:
On wheels a cub will fly at about 40 MPH.
it starts at 0. Since acceleration is relatively constant the average speed of the ground run is 20 MPH 40/2=20
We know that 60 MPH is 88 feet per second. If we don’t know it we should. Flying over a landing area in both directions at 60 MPH and timing it will give you the approximate length. If we round the 88 feet per second to 90 feet per second it is easier to do the math mentally. If it takes us 10 seconds to fly over a potential landing area at 90 feet per second it is approximately 900 feet long. More time in one direction than the other gives us an indication of wind speed, and direction, the average will give us a better idea of length.
since we’re going 90 feet per second at 60 MPH at 1/3 the speed we’re going 30 miles an hour.
if we take the 1/3 of our velocity and apply it to our take off speed average of 20 MPH we are taking off at, the distance we travel on a takeoff roll is approximately 30 feet per second.
a ten second takeoff is approximately a 300 foot take off. A three second takeoff is approximately a 90 foot take off.
it is my understanding and outside my experience that big aircraft like jets don’t have constant rates of acceleration.
this is an approximation only. It’s pretty accurate but you can’t beat good judgement.
with floats I would estimated my distance along the shore then come back over and time the distance at 60 MPH which gives me an estimate. After I have that down for a particular aircraft I can then fly over a landing area at 60 MPH and get an estimate of It’s length.