Block bundles are PL analogs of vector bundles, see e.g. Rourke-Sanderson's 
 [article](http://projecteuclid.org/euclid.bams/1183528512)
in Bulletin of AMS, 1966. There is a classifying space $B\widetilde{PL}\_q$ for rank $q\ $ block bundles, which is a PL analog of $BO\_q$, and there are similar classifying spaces $B\widetilde{SPL}\_q$, $BSO\_q$ for oriented bundles.


**Question.**  *Is the rational homotopy type of 
$B\widetilde{SPL}\_q$ recorded in the literature?*


Long time ago Colin Rourke explained to me how to compute the rational homotopy type of $B\widetilde{SPL}\_q$, but I cannot find the correspondence. If memory serves, the result
was as follows. 


1. If $q\ge 3$ is even, then $H^\*(B\widetilde{SPL}\_q;\mathbb Q)$ is a polynomial algebra on the Pontryagin classes and the Euler class. The Euler class occurs in degree $q$, while the Pontryagin classes occur in all degrees divisible by $4$ (which is different from $BSO\_q$ where there is no Pontryagin classes in degrees $\ge 2q$).
2. If $q\ge 3$ is odd, then $H^\*(B\widetilde{SPL}\_q;\mathbb Q)$ a polynomial algebra on the Pontryagin classes, which occur in all degrees divisible by $4$, and a new class
in degree $2q-2$ which arises from works of Haefliger and Hirsch.
3. If $q\le 2$, then $BSO\_q\to B\widetilde{SPL}\_q$ is a rational homotopy equivalence.


As usual, the Pontryagin classes are stable, i.e. they survive in $B\widetilde{SPL}\approx BPL$, while the Euler class and the Haefliger-Hirsch classes die in $B\widetilde{SPL}\_{q+1}$. I recall that the proof of 1-2 was not too hard, and I can probably reconstruct it, but it would be much nicer if it were written somehwere. 



Characteristic classes for block bundles
I don't know where the results are written down in one place (perhaps in the book of Madsen and Milgram?), but see the the end of this post for a list of references.


In any case, here is a proof of the result for $q \ge 3$.


By a result of Haefliger, there is a homotopy cartesian square
$$
B\widetilde{PL}\_q \quad \to \quad BG\_q 
$$
$$
\downarrow \qquad \qquad \quad \downarrow 
$$
$$
B\widetilde{PL} \quad \to \quad BG
$$
where $BG\_q$ classifies oriented $(q-1)$-spherical fibrations, $BG$ classifies stable oriented spherical fibrations and $B\widetilde{PL}$ classifies stable block bundles. Rationally, $BG$ is trivial (since its homotopy groups are the shifted stable homotopy groups of spheres), and $B\widetilde{PL}\simeq BPL$ is rationally weak equivalent to $BO$.


Consequently, there is a rational equivalence
$$
B\widetilde{PL}\_q \simeq BO \times BG\_q .
$$
It suffices to identify the rational homotopy type of $BG\_q$.


Note that $G\_q$ is the topological monoid self-equivalences of $S^{q-1}$.
Let $SG\_q \subset G\_q$ be the submonoid of degree one self maps. Then $BSG\_q \to BG\_q$
is a rational equivalences as well (they have the same rational homotopy groups).
It therefore suffices to identify $BSG\_q$ rationally (note: the advantage of $SG\_q$ over $G\_q$
 is that the former is connected).


**Case 1, $q$ is even:**
If $q$ is even, then $S^{q-1}$ is rationally 
equivalent to an Eilenberg-Mac Lane space $K(\Bbb Q,q-1)$.
Using the fiber sequence $SF\_{q-1} \to SG\_q \to S^{q-1}$ (where $SF\_{q-1}$ is the topological monoid of degree one pointed self maps of $S^{q-1}$) and the fact just noted,
we see that $SF\_{q-1}$ is rationally trivial, so $SG\_{q}$ is rationally $K(\Bbb Q,q-1)$.


Consequently, $BSG\_q$ is rationally $K(\Bbb Q,q)$ when $q$ is even, so we get 
a rational equivalence
$$
B\widetilde{PL}\_q \simeq BO \times K(\Bbb Q,q)
$$
when $q \ge 3$ is even.


**Case 2, $q$ is odd:** In this instance $S^{q-1}$ is not rationally an Eilbenberg-Mac Lane space. But there is a rational fiber sequence
$$
S^{q-1} \to K(\Bbb Q,q-1) \to K(\Bbb Q,2q-2) .
$$
Arguing similarly to case 1, we see that $SG\_{q-1}$ is rationally $K(\Bbb Q,2q-3)$. 
Hence $BSG\_q$ is rationally $K(\Bbb Q,2q-2)$ and we obtain
a rational equivalence
$$
B\widetilde{PL}\_q \simeq BO \times K(\Bbb Q,2q-2) .
$$


**Addendum**


(1). Haefliger's theorem can be found in 


Haefliger, André : Differential embeddings of $S^n$ in $S^{n+q}$ for $q>2$. 
*Ann. of Math.* **83** (1966), 402–436.


The proof uses embedded framed surgery.


(2). In Wall's book, he says that the case $q=2$ follows from


Wall, C.T.C.: Locally flat PL submanifolds with codimension two. *Proc. Cambridge Philos. Soc.* **63** (1967) 5–8.


(3) The proof that $B\widetilde{PL}\simeq BPL$ is a consequence of Rourke and Sanderson's paper on block bundles:


Rourke, C. P.; Sanderson, B. J.:
Block bundles. *Bull. Amer. Math. Soc.* **72** (1966) 1036–1039. 


(4). The proof that $BO \to B\widetilde{PL}$ is rational requivalence is a consequence of Kervaire and Milnor's work (which amounts to the Browder-Novikov sequence for a sphere), since $\pi\_n(\widetilde{PL}/O)$ is the group of exotic homotopy
$n$-spheres (at least if $n \ge 5$), and this is a finite group.


