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Boeing 720 - What's On The Engines?  
User currently offlineTimePilot From Switzerland, joined Sep 2005, 296 posts, RR: 0
Posted (3 years 4 months 2 weeks 6 days 6 hours ago) and read 4616 times:

I've been watching this utterly fantastic video of a 720 doing a touch & go: http://www.youtube.com/watch?v=Sf3mo3QROC8 (turn the volume down if you're at work)

At 0:50 as the engines spool up, these little ports? vents? open on the engines. What are they? What's going on?

9 replies: All unread, jump to last
 
User currently offlineAKiss20 From United States of America, joined Sep 2007, 603 posts, RR: 5
Reply 1, posted (3 years 4 months 2 weeks 6 days 6 hours ago) and read 4611 times:

My guess is the first gen of thrust reversers?


Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlineChamonix From France, joined Mar 2011, 316 posts, RR: 1
Reply 2, posted (3 years 4 months 2 weeks 6 days 6 hours ago) and read 4611 times:
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Lip inlets on the turbojets
Bleedless Engines On KC-135/707? (by LockstockNL777 Apr 16 2008 in Tech Ops)


User currently offlinearluna From United States of America, joined Jun 2006, 88 posts, RR: 1
Reply 3, posted (3 years 4 months 2 weeks 6 days 5 hours ago) and read 4553 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.

User currently offlineN707PA From United States of America, joined Apr 2000, 279 posts, RR: 0
Reply 4, posted (3 years 4 months 2 weeks 6 days 5 hours ago) and read 4543 times:

Quoting Chamonix (Reply 2):
Lip inlets on the turbojets

AKA "Sucker Doors"


User currently offlineNorthwest727 From United States of America, joined Jul 2005, 491 posts, RR: 1
Reply 5, posted (3 years 4 months 2 weeks 6 days 5 hours ago) and read 4531 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):



User currently offlineJT8DJET From United States of America, joined Jul 2000, 214 posts, RR: 0
Reply 6, posted (3 years 4 months 2 weeks 6 days 5 hours ago) and read 4524 times:

arluna   

The technical name is Secondary Inlet Doors.

Here is a previous thread.


Holes On The Cowlings Of The 747? (by CalAir Apr 16 2006 in Tech Ops)


User currently offlineViscount724 From Switzerland, joined Oct 2006, 24868 posts, RR: 22
Reply 7, posted (3 years 4 months 2 weeks 6 days 4 hours ago) and read 4502 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:



User currently offlineTimePilot From Switzerland, joined Sep 2005, 296 posts, RR: 0
Reply 8, posted (3 years 4 months 2 weeks 5 days 7 hours ago) and read 4233 times:

As always, thanks everyone  

User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (3 years 4 months 2 weeks 4 days 6 hours ago) and read 4035 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:

Known as 'advanced cowl'.


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