The HP-13 (HP stands for high performance) was a developmental milestone aircraft between the HP-11 and the later HP-14. The HP-13 was designed by taking the fuselage of the HP-11 and wings similar to the HP-12, featuring the same Wortmann FX 61-163 airfoil but extended from the HP-12's 49.20NaN0 FAI Standard Class span to 54feet for the open class. Eight HP-13s were completed.
The HP-13 was later developed into the HP-14 by designing a new fuselage for the wings. The HP-14 was later type certified in the United Kingdom, while the HP-13s were all amateur-built.
In April 2011 there were still five HP-13s registered with the Federal Aviation Administration, all in the Experimental - Amateur-built category.[3]