According to Wikipedia, the Pratt & Whitney JT3D engine inlet doors purpose is to provide additional air. Is the thrust higher on more air intake? Why don't modern engines have it anymore? -
![Pratt and Whitney TF33-P-9 (JT3D-7) as removed from a VC-137C, retired presidential aircraft in the test cell. Note the sky blue translating cowl and the polished thrust reverser. : r/aircraftengines Pratt and Whitney TF33-P-9 (JT3D-7) as removed from a VC-137C, retired presidential aircraft in the test cell. Note the sky blue translating cowl and the polished thrust reverser. : r/aircraftengines](https://i.redd.it/jtkzuq7x7sa71.jpg)
Pratt and Whitney TF33-P-9 (JT3D-7) as removed from a VC-137C, retired presidential aircraft in the test cell. Note the sky blue translating cowl and the polished thrust reverser. : r/aircraftengines
![Pratt & Whitney JT3D turbojet engines attached to the wing of Boeing VC-137 Stratoliner (Boeing 707) Freedom One Stock Photo - Alamy Pratt & Whitney JT3D turbojet engines attached to the wing of Boeing VC-137 Stratoliner (Boeing 707) Freedom One Stock Photo - Alamy](https://c8.alamy.com/comp/W89WK7/pratt-whitney-jt3d-turbojet-engines-attached-to-the-wing-of-boeing-vc-137-stratoliner-boeing-707-freedom-one-W89WK7.jpg)