The Su-57 is planned to be the first operational aircraft in Russian Air Force service to use stealth technology. Similar to other stealth fighters such as the F-22, the airframe incorporates planform edge alignment to reduce its radar cross-section (RCS); the leading and trailing edges of the wings and control surfaces and the serrated edges of skin panels are carefully angled to reduce the number of directions the radar waves can be reflected. Weapons are carried internally in weapons bays within the airframe and antennas are recessed from the surface of the skin to preserve the aircraft's stealthy shape. The infrared search-and-track sensor housing is turned backwards when not in use and its rear is treated with radar-absorbent material (RAM) to reduce its radar return. To mask the significant RCS contribution of the engine face, the walls of the inlet ducts are coated with RAM and the partial serpentine ducts obscure most of the engines’ fan and inlet guide-vanes (IGV); the remaining exposed engine face is masked by a radar blocker similar in principle to that used on the F/A-18E/F. According to Sukhoi's radar blocker patent, the slanted blocker grid is placed in front of the IGV at a distance of 0.7—1.2 times the diameter of the duct. The fuselage of the aircraft is coated with RAM to absorb radar emissions and reduce the reflection back to the source.