TimePilot
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Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 12:21 am

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?
 
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akiss20
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 12:24 am

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
 
Chamonix
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 12:25 am

Lip inlets on the turbojets
Bleedless Engines On KC-135/707? (by LockstockNL777 Apr 16 2008 in Tech Ops)
 
arluna
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 1:40 am

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.
 
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N707PA
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 1:48 am

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

AKA "Sucker Doors"
 
Northwest727
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 2:02 am

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):

 
JT8DJET
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 2:12 am

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)
 
Viscount724
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 2:47 am

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:

 
TimePilot
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RE: Boeing 720 - What's On The Engines?

Sat Mar 12, 2011 11:41 pm

As always, thanks everyone  
 
411A
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RE: Boeing 720 - What's On The Engines?

Mon Mar 14, 2011 12:56 am

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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