  A Barak-Erd\H{o}s graph is a directed acyclic version of the
Erd\H{o}s-R\'enyi random graph. It is obtained by performing independent bond
percolation with parameter $p$ on the complete graph with vertices
$\{1,...,n\}$, in which the edge between two vertices $i<j$ is directed from
$i$ to $j$. The length of the longest path in this graph grows linearly with
the number of vertices, at rate $C(p)$. In this article, we use a coupling
between Barak-Erd\H{o}s graphs and infinite-bin models to provide explicit
estimates on $C(p)$. More precisely, we prove that the front of an infinite-bin
model grows at linear speed, and that this speed can be obtained as the sum of
a series. Using these results, we prove the analyticity of $C$ for $p >1/2$,
and compute its power series expansion. We also obtain the first two terms of
the asymptotic expansion of $C$ as $p \to 0$, using a coupling with branching
random walks.
