It is well known, that the characterizing property of Clothoids is, that their curvature is proportional to length; that is also the reason, why they are used as design elements e.g. in road design.
Question:
Has the analogue to clothoids, where the slope and not the curvature is proportional to length, ever been described or investigated?
The associated differential equation $$y'(x) =\int_0^x \sqrt{1+y'(t)^2} dt $$ isn't hard to devise and the curve might also have practical applications also e.g. in road design.
I am specifically looking for articles on the solution of the associated differential equation, but other articles related to the curve are also welcome.