arluna From United States of America, joined Jun 2006, 81 posts, RR: 1 Reply 3, posted (2 years 2 months 2 weeks 18 hours ago) and read 3615 times:
Those little doors on the sides of the intakes are spring loaded and are designed to open when the engines are operating at high power settings and low airspeed. They allow more air to enter the intake to compensate for the lack of ram air at the intake mouth. As airspeed increases and the amount of ram air avilable at the intake increases the little doors will slowly close.
Northwest727 From United States of America, joined Jul 2005, 491 posts, RR: 1 Reply 5, posted (2 years 2 months 2 weeks 18 hours ago) and read 3593 times:
arluna is correct, those are the auxiliary intake doors, which are spring loaded and open when the engines are at high power settings and low airspeeds. I believe that due to "sharper" lips around the air intake, this robbed the early engines of ram air when they were operated at high power and at slow airspeeds. The early 737s and early 747s had them as well; in the mid 1970s when noise regulations were starting to come into play, engineers discovered that these doors allowed high amounts of noise to escape. A redesign of the nacelles created a "blunter" lip which eliminated the airflow problems, thus eliminated the need for these doors. That is why you don't see them today.
Here is one of such study, showing the 1960's era JT9D intake vs. the "quiet design" of the 1970s (that later became standard, and retrofits were offered for earlier 747s):
Viscount724 From Switzerland, joined Oct 2006, 21495 posts, RR: 24 Reply 7, posted (2 years 2 months 2 weeks 17 hours ago) and read 3564 times:
Quoting N707PA (Reply 4): Quoting Chamonix (Reply 2):
Lip inlets on the turbojets
AKA "Sucker Doors"
There were two different types on JT3Ds used on 707s. Early production aircraft had the thin narrow inlets as in the 720B video and in the 707 photo below:
On later production aircraft they were larger and further forward as in this photo:
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 9, posted (2 years 2 months 1 week 5 days 19 hours ago) and read 3097 times:
Quoting Viscount724 (Reply 7): There were two different types on JT3Ds used on 707s. Early production aircraft had the thin narrow inlets as in the 720B video and in the 707 photo below:
Known as 'old cowl'
Quoting Viscount724 (Reply 7): On later production aircraft they were larger and further forward as in this photo:
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