In this paper, we propose transmit antenna selection based on receiver feedback of channel information obtained via link-layer probing. Furthermore, we report the performance gain of the proposed antenna selection scheme in an experimental multi-antenna 802.11 network. We built a low-altitude Unmanned Aerial Vehicle (UAV) testbed using commodity dual-antenna 802.11 hardware and performed field experiments to collect traces of link performance using antennas of various types and orientations. Based on the collected traces, we demonstrate that transmit antenna selection can achieve a significant amount of gain using a link-layer channel probing protocol at a relatively low probing rate. The largest improvement we observed with joint transmit/receive antenna selection in 2x2 systems was 32%, about twice as much as that of receive-only antenna selection in 1x2 systems, which achieved 17%. Moreover, a similar improvement is obtained with probing intervals up to about 200 milliseconds, which is infrequently enough to consume only a small fraction of the available 802.11 channel capacity. Since these results require only a low implementation and operational cost, we conclude that transmit antenna selection is a worthwhile technique to use with the kind of multi-antenna mobile ad-hoc networks we examined.