MountainFlyer
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What Are These Doors?

Fri Apr 13, 2012 9:28 pm

Does anyone know what the doors are on the front of the JT-3Ds on the 707-320B? In these pictures, they appear to be open during takeoff, and closed during decent. What is their function?

My shot in the dark guess is something having to do with diverting bypass air into the engine core during high power settings.


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Fabo
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RE: What Are These Doors?

Fri Apr 13, 2012 9:36 pm

they allow additional air into the engine, bypassing the inlet, when air demand is high (at high power setting)
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larshjort
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RE: What Are These Doors?

Fri Apr 13, 2012 9:38 pm

They provide extra air to the engine at high power settings. They are actuated by the low presserue in the inlet, when it is low enough they will open.
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KELPkid
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RE: What Are These Doors?

Fri Apr 13, 2012 11:57 pm

They are called "Blow-in doors", and they make the engines scream when they blow in   Boeing had them on early 737's and 747's, too...
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Viscount724
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RE: What Are These Doors?

Fri Apr 13, 2012 11:57 pm

JT9Ds on early-model 747-100s also had them. You can see them open in the following photos. The engines were later modified and the blow-in doors removed.


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akiss20
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RE: What Are These Doors?

Sat Apr 14, 2012 1:23 am

Did they do this because the flow went sonic at the face of the inlet but they didn't want to increase the inlet area because they didn't need the diameter in the fan?
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Accidentally
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RE: What Are These Doors?

Sat Apr 14, 2012 1:45 am

Why were they ultimately deemed unnecessary and removed?
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tdscanuck
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RE: What Are These Doors?

Sat Apr 14, 2012 4:26 am

Quoting akiss20 (Reply 5):
Did they do this because the flow went sonic at the face of the inlet but they didn't want to increase the inlet area because they didn't need the diameter in the fan?

The flow can never get sonic at the fan face (aerodynamics won't allow it). The problem was getting enough air into the inlet at high power and low speed without separation around the inlet leading edges and acceptable pressure loss.

Tom.
 
Fabo
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RE: What Are These Doors?

Sat Apr 14, 2012 4:48 pm

Quoting Accidentally (Reply 6):
Why were they ultimately deemed unnecessary and removed?

They made the engines too noisy. Inlet diameter and shape was tweaked instead.
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HAWK21M
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RE: What Are These Doors?

Sat Apr 14, 2012 7:44 pm

The Inlet cowl Blow in doors were common on the early JT8D-7s too.....
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DL_Mech
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RE: What Are These Doors?

Sat Apr 14, 2012 9:39 pm

Here's a good video of the "sucker doors" in operation:

http://www.youtube.com/watch?v=Sf3mo3QROC8
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Viscount724
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RE: What Are These Doors?

Sun Apr 15, 2012 12:31 am

Quoting HAWK21M (Reply 9):
The Inlet cowl Blow in doors were common on the early JT8D-7s too.....

Some early 737-200s with the blow-in doors visible. I don't think they existed on the 727.


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Why did those doors only seem to be used on Boeing types? I can't recall a similar feature on other types that used the same engines (e.g. JT3D on DC-8, JT8D on DC-9)?
 
AirframeAS
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RE: What Are These Doors?

Sun Apr 15, 2012 1:49 am

Quoting DL_Mech (Reply 10):
Here's a good video of the "sucker doors" in operation:

http://www.youtube.com/watch?v=Sf3mo3QROC8

I take it that video was filmed at KIWA!!! Awesome video!
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HAWK21M
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RE: What Are These Doors?

Sun Apr 15, 2012 8:39 am

Quoting Viscount724 (Reply 11):

Why did those doors only seem to be used on Boeing type

The later JT8Ds beyond the -7 did not utilize the blow in doors on the Inlet cowl on the B732.
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strfyr51
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RE: What Are These Doors?

Wed Apr 18, 2012 9:19 pm

fan inlet doors for supplimental air to be available for the turbofan at takeoff thrust, later found not to be needed as better inlet cowls were built

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