One of the problems with a stealth aircraft is that the face of the turbofan engine is a huge radar reflector. The only real solution is to bury the engine deep into the airframe and have the air duct that feeds it turn in an S-shape. The problem is that air traveling at a few hundred miles an hour really doesn't like making such sharp corners and tends to cause turbulent air at lower pressure reaching the engine, which reduces its efficiency. The Lockheed Martin Skunk Works is trying to solve this problem with a new design. Sensors detect the state of the air flow (which changes as the aircraft maneuvers, with altitude, and as speed changes) and feed the data to a computer, which injects bursts of high pressure air into the engine inlet at strategic points to keep the airflow in line.Stephen V Cole