Why won't free-fall bombs detonate in H.A.W.X.?

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So I have been playing the H.A.W.X. demo and selected the free-fall bombs, but no matter how many different stratagies I try they won't detonate. they will lock onto a tank or an gunship, and I will fire but no boom, no KERPOW with fiery death and explosion, just a stupid blue triangle showing where it landed. What am I doing wrong!