What's happening: Shares of AeroVironment (NASDAQ:AVAV) were up 10.5% as of 2:30 p.m. Wednesday after the drone maker announced stronger-than-expected fiscal-fourth-quarter 2015 results on Tuesday.

Quarterly revenue rose 18% year over year to $86 million, driven by a 31% increase in Unmanned Aerial Systems (UAS) sales to $78.7 million, and held back by a 42% decline in sales from AeroVironment's smaller Efficient Energy Systems (EES) segment to $7.8 million. That translated to a 12% decrease in net income to $7.1 million, or $0.31 per diluted share, including a $0.01-per-share negative adjustment due to losses on its equity investment. For perspective, last year's fourth quarter included a positive $0.08-per-share adjustment due to the increase in fair value of Aerovironment's convertible bond investment.

Either way, these results were good enough for AeroVironment to easily outpace expectations. Analysts were anticipating revenue of $85.7 million to result in significantly lower earnings of $0.18 per share.

As of April 30, 2015, AeroVironment's funded backlog was $64.7 million, compared to $65.9 million at the same point in 2014. As a result, for the current fiscal year AeroVironment expects revenue of $260 million to $280 million. By contrast, Wall Street's models anticipated revenue near the high end of that range at $277.3 million.

Why it's happening: "During the quarter," elaborated AeroVironment CEO Tim Conver, "we strengthened our market positions, moved key programs forward to generate value, and focused on innovation. ... In our core business, our team delivered revenue in-line with our expectations and exceeded targeted profitability."

Conver went on to note AeroVironment enters fiscal 2016 "with strong momentum," as last year's strategic investments have served to expand the company's growth portfolio and position it for new markets.

As it stands, it's mildly concerning to see AeroVironment's backlog decline while revenue guidance for the coming year came in light. But with shares still down around 13% over the past year, it's hardly surprising that investors are willing to overlook these concerns in favor of AeroVironment's big earnings beat. With the UAS market effectively still in its infancy, AeroVironment should still be poised to benefit over the long term as a leader in the field.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends AeroVironment. The Motley Fool owns shares of AeroVironment. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.