HCH bond angle in cyclopropane and cyclobutane
Computational investigations of geometry, aromaticity and bond energies at HF/6-31G** theory level [1] revealed the following deformed  geometrical ($\alpha$) and interpath angles ($\beta$ -- the angle between two bond paths) for $\ce{H-C-H}$ bond, which are slightly deviating from the strain-free $109.5^\circ$ due to varying Baeyer strains:

\begin{array}{lr}
\hline
\text{molecule} &amp; \alpha,~^\circ &amp; \beta,~^\circ \\
\hline
\text{cyclopropane} &amp; 114.1 &amp; 117.0 \\
\text{planar cyclobutane} &amp; 107.9 &amp; 109.7 \\
\text{puckered cyclobutane} &amp; 108.3 &amp; 110.0 \\
\hline
\end{array}



P. S. Unfortunately, this data cannot be taken from single-crystal x-ray experiment as this method doesn't allow precise determination of H-positions, and I didn't find a neutron diffraction data on solid cycloalkanes mentioned.

Reference


Cremer, D.; Gauss, J. J. Am. Chem. Soc. 1986, 108 (24), 7467–7477 DOI: 10.1021/ja00284a004.