makes distinguishable differences. we ll show you examples. first what a standard black hawk helicopter sounds like. this has a rhythmic, whoosh, whoosh sound. now we ll show you what a stealth helicopter sounds like from an earlier test program. experts say this sounds a lot more vague. you may not be able to tell whether this is another vehicle entirely or a helicopter. you may not be able to tell whether the helicopter is moving toward you or moving away. experts say the small wings, called stabilizers, are also unique to this chopper. they re usually at a hard right angle, but these are angled off, analysts say, to avoid radar detection. the chinese have a huge interest in this technology. they re developing a stealth fighter jet called the j-20, which they ve already test flown. contacted by cnn, a chinese official in washington said he had no information on whether his government has tried to get access to the tail section of that helicopter. u.s. officials are not